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Key design principles for successful deep drawing By Art Hedrick, Contributing Writer May 30, 2001 Successful deep drawing depends on many factors. Ignoring even one of them during die design and build can prove disastrous. Successful deep drawing depends on many factors. Ignoring even one of them during die design and build can prove disastrous. However, regardless of the many factors involved, the most important element to a successful deep drawing operation is initiating metal flow. flow. The following are key elements affecting metal flow, and each of them should be be considered when designing, building, or troubleshooting deep drawing stamping dies: 1. Mater ateria iall ttyype 2. Mate Materi rial al thi thick ckne ness ss 3. N an and R val values ues 4. Blan Blankk siz sizee and and sha shape pe 5. Part art geom geomet etry ry 6. Pres Presss spe speed ed (ra (ram m spee speed) d) 7. Draw ra radii 8. Draw ra ratio 9. Die Die sur surfa face ce fin finis ishh 10. Die temperature temperature 11. 11. Lubric Lubricant ant 12. Draw bead bead height height and shape shape 13. Binder pressure pressure 14. Binder deflection deflection 15. Standoff Standoff height Because thicker materials are stiffer, they hold together better during deep drawing. Thicker materials also have more volume, so they can stretch longer distances. The N value, also called the work hardening exponent, describes the ability of a steel to stretch. The R value—the plastic strain ratio—refers to the ability of a material to flow or draw. draw. Blank sizes and shapes that tha t are too large can restrict metal flow, and the geometry of parts affects the ability of metal to flow. Press speeds must allow time for materials to flow. Die surface finishes and lubricants are important because they the y can reduce the coefficient of friction, allowing materials to slide through tools more easily. easily. Die temperatures can affect the viscosity of lubricants.
SOCIETY4PAKSWISSIANS As a controller of metal flow, draw bead height and shape can cause materials to bend and unbend to create restrictive forces going into a tool. Increasing binder pressure exerts more force on a material, creating more restraint on material going into the tool. The remaining key elements affecting metal flow are examined in more detail in the remainder of this article. To illustrate the principles of metal flow, flow, this article examines two basic draw shapes, round and square. All deformation modes that occur in any given part shape are present in one of these common shapes.
Figure 1
In the illustration of incorrect draw ratio (L), the too-small post would cause metal to thin to the point of failure, while the correct draw ratio (R) will result in a successfully deep drawn part. The draw ratio is among the most important elements to be considered when attempting to deep draw a round cup. The draw ratio is the relationship between be tween the size of the draw post and the size of the blank. The draw ratio must fall within acceptable limits to allow metal to flow. During forming, a blank is forced into circumferential compression, which creates a resistance to flow. If the resistance resistance is too great, the cup fractures. If the post is too small or too far from the blank edge, the metal stretches and thins to the point of failure. If the post is the appropriate distance from the blank edge, and the die entry radius is acceptable, the metal can flow freely, freely, progressively thickening as it enters the die cavity (see Figure 1). When a very tall small-diameter part is being processed, draw reductions likely will be necessary (see Figure 2). A draw reduction is a process in which a part is first formed within acceptable draw ratio limits and then is progressively reduced or reshaped to a desired shape and profile.
SOCIETY4PAKSWISSIANS
Figure 2
Reduction percentages for various thicknesses of draw-quality steel.
The most important factor to remember when performing p erforming draw reductions is that all of the material necessary to make the final part pa rt shape must be present in the first draw. Figure 3 is a reduction chart for the first, second, and third draws with draw-quality steel. Reduction percentages are based on metal thickness and type. To determine the post diameter and height of the first draw, the total surface area of the finished part must be calculated. (If the part pa rt is to be trimmed, allow additional material during this calculation.) The calculated surface area is then converted into a flat blank diameter.
Figure 3
During draw reductions, the blank diameter should not change after the first draw. draw. The primary step in calculating the first draw post diameter is determining de termining the blank diameter. Multiplying the blank diameter by the percentage given in the chart, and then subtracting the result from the original blank diameter, yields the diameter of the first draw post. It is important to remember that all dimensions are taken through the
SOCIETY4PAKSWISSIANS centerline of the material. The height of the first draw is an area calculation directly related to the amount of material necessary to make the finished part.
Die Entry Radii Other important factors for successful deep drawing are the size, accuracy, accuracy, and surface finish of the die entry radius. Decisions regarding the die d ie entry radius should be based on material type and thickness. If a die entry radius is too small, material will not flow easily, resulting in stretching and, most likely, likely, fracturing of the cup. If a die entry radius is too large, particularly when deep drawing thin-gauge stock, material begins to wrinkle after it leaves the pinch point between the draw ring surface and an d the binder. If wrinkling is severe, it may restrict flow when the material is pulled through the die entry radius.
Figure 4
Minimum die entry radii are shown in this chart for round draws involving various thicknesses of draw-quality steel. Figure 4 provides general guidelines for die entry radii for round
draws of draw-quality
steel ranging in diameters from about 1.5 to 15 inches.
The die entry must be produced accurately in a fashion that makes it true and complete. It should be hook-free and polished in the direction of flow. High-wear tool steel should be used for die entry radii.
Binder Pressure
SOCIETY4PAKSWISSIANS Sufficient binder pressure must be present p resent to control metal flow. flow. If binder pressure p ressure is inadequate, the material wrinkles during compression. The wrinkles then cause the binder to further separate from the draw ring surface, and control of the material will be lost. Wrinkles will also be forced to unwrinkle when the material is squeezed between the post and the cavity walls. This can pull metal on the top of the cup and result in fracture. The problem of too much binder pressure can be overcome by using standoffs. Standoffs maintain a given space between b etween the draw ring surface and the binder, and they should be set at 110 percent of the metal thickness to allow for compressive thickening. If the standoff gap is too small, the material will be pinched tightly between the draw ring and the binder surface, reducing its ability to flow freely. If the standoff gap is too large, the material will wrinkle during circumferential compression. The recommended binder pressure p ressure for round draws of low-carbon draw-quality steel is 600 pounds per lineal inch around the post (draw post diameter x 3.141). For highstrength, low-alloy, low-alloy, and stainless steels, 1,800 pounds of pressure per lineal inch should be used. Other guidelines to remember when the processing draw reductions are: 1. Design Design open-ended open-ended draw cavities cavities for for draw draw depth depth adjustm adjustment. ent. 2. Once the proper draw ratio ratio is is achieved, achieved, metal metal will will flow and the part part can be drawn partially or completely off o ff the binder. 3. After the first first draw draw,, the blank blank diameter diameter should should not change. (See (See Figure 3).
Square Draws
Figure 5
Square draws are similar to round draws because they contain four 90-degree profile radii. Because of the radial corner profile, material flowing toward the corners is forced into compression. The straight sections of the square are simply being bent be nt and unbent.
SOCIETY4PAKSWISSIANS Considerably less flow restriction takes place in the straight walls of a square draw than in the corners (see Figure 5). Increasing the profile radius of the draw greatly increases the ability to draw deeper in a single operation (see Figure 6) because a larger-profile larger-profile radius reduces compression. c ompression. Too Too much compression in a corner restricts metal flow, resulting in fracture. Increasing the profile radius and reducing the blank size reduce forming severity. Mitering the corners of the blank also a lso can help to reduce compression. To help balance metal flow conditions during square draws involving heavy metals, it may be necessary to draw spot the corner areas of the binder or draw ring face with respect to the increasing material thickness. This process allows metal to thicken in corners without being pinched excessively between the draw ring and the binder.
Figure 6
If a proper draw spot is achieved, blank holding force is evenly distributed through the perimeter of the drawn shell. When thin metal is used, draw spotting the corners may cause undesirable wrinkling in the relieved areas. This results primarily from a lack of control of the metal flow and the inability of thin stock to resist wrinkling. If the square drawn shell is too tall to be drawn in a single operation, it must undergo a draw reduction. As with round draws, all material necessary to make the final part must be present in the first draw. Draw reductions for square shells are achieved by increasing the profile radius to acceptable compression limits and increasing the width and length to obtain the necessary surface area of the finished part. Other guidelines to follow when drawing square shells include: 1. Use the mini minimum mum blank size required required to to make make the the part. part. 2. Use standof standoffs fs to contro controll metal metal flow, flow, not binder binder press pressure. ure. 3. To redraw a square shell, shell, increase the width, length, and profile profile radius radius of the first draw to contain the necessary surface area of the final part geometry. geometry. Successful deep drawing is a combination of many important factors. This article highlights only the most frequently violated design and build principles. Although designing and building deep draw dies is fast becoming a science, the fundamental metal flow principles should never be ignored, for they are the foundations of a successful deep drawing operation.
SOCIETY4PAKSWISSIANS TPJ - The Tube & Pipe Journal®
Automatic or manual? Automation doesn’t solve process problems. People do. By Bob Want October 9, 2007
Whether it is as simple as a single CNC tube bender loaded by a robot or as complex as a fully automated line that turns raw coil into a finished and packaged bent tubular product, automated workcells have made their way into nearly every manufacturing theater. Once limited to the automotive industry with its ultrahigh production volumes, automated cells now are found in any industry in which the production rate is a "make or break" aspect of cost-effective manufacturing. As raw material costs and labor costs continue to rise and cutthroat competition forces prices down, automated cells ce lls are being used to produce more complex workpieces than ever before. Trials abound. The demand for higher production comes with an inherent requirement that the process runs nearly continuously. Automation in a tube bending cell must be well-planned and well-executed simply to bring the project to a successful launch. Once the workcell is up and running, the maintenance staff must keep it running for two or three shifts a day da y, six to seven days a week—and that's another challenge entirely. entirely.
Plan, Plan, Plan Successful tube bending is possible only after analyzing the application and matching the application to the proper techniques, machinery, and tooling. If the application is borderline—that is, just barely successful—when accomplished acc omplished manually, manually, no amount a mount of automation will make it more successful. In other words, automation doesn't reduce problems; it merely increases the output. If a manual process has a 10 percent scrap rate,
SOCIETY4PAKSWISSIANS under the best conditions a similar automated process has a 10 percent scrap rate. Debugging and simplifying the manufacturing process before automating it is critical. Taken as a stand-alone operation, o peration, tube bending is itself a juggle of changing variables. To simplify this facet of workcell planning, initial considerations must include: •
Raw material ductility. ductility. Does the tube bend to the desired radius without fracturing? If the material does not have enough e nough elongation, consider increasing the bend radius or using an alternate material, alloy, alloy, or temper. Also commonly overlooked is raw material consistency. It is absolutely essential that all the tube's properties—the chemical, mechanical, and an d physical characteristics—be consistent from lot to lot. Make certain from the start that the material selected is toleranced to optimize production, rather than a variable that makes steady, consistent production impossible.
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Bent part configuration. Does the application require more than one bender? Lefthanded, right-handed, or both? How many bends are in the part? Does the workpiece have a sufficient length of straight tube between bends, or does it require gripping a bent section to produce the next bend? If so, the application requires stacked tooling. How many stacked sets does it need? Bend severity and die tooling selection. Does the application need complete die sets, including internal ball mandrels and wiper dies? Adding one or both of these tools makes bending much more complicated. c omplicated. These tools are in constant friction with the workpiece, so they must be lubricated. They must be set and adjusted properly, properly, and maintained that way. They also must be changed chan ged quickly for maximum production efficiency. efficiency. Many tooling design techniques can help meet production demands, but the tooling must be as simple as possible, especially in a high-production-volume environment. Don't throw more technology (and complications) c omplications) at the application than necessary.
•
Bending machine selection. Simply stated, specify at least enough bender capacity to get the job done. If the workcell is expected to run close to 24/7, make accommodations for all manufacturers' preventive maintenance recommendations. reco mmendations. Don't simply follow them. Exceed them. Ignoring routine maintenance maintenan ce guarantees trouble when (that is when, not if) the cell goes down. With regard to maintenance, the degree of neglect and the mean time between failure are inversely proportional. In applications that require several die stacks, make certain that the machine is rigid enough to keep all the die sets in proper alignment. This often requires overhead tie bar supports for the bend die stack. While offering more strength and support, these tie bars also can interfere with some bent ben t tube configurations. Be
SOCIETY4PAKSWISSIANS certain that you and the machine manufacturer understand the requirements of the proposed bent part. With regard to several stacked wiper dies, remember that these fragile tools must be held in their proper positions securely. Otherwise they will not last or work effectively. effectively. It is often necessary to have a custom wiper bracket (holder) made to keep wiper dies secured and aligned properly and thus achieve acceptable die life and greater productivity. productivity. •
Acceptance criteria. Set a benchmark standard for tube acceptance before attempting to calculate the production rate of the automated cell. Criteria must include all aspects from processing raw strip to packaging finished parts. Because each operation hinges on the successful completion of the previous one, every operation must have a reasonable and repeatable go/no-go attribute or tolerance that can (and will) be monitored. Regardless Rega rdless of how this is done—visually, done—visually, with fixtures, or with sophisticated coordinate measuring equipment—the fact is that all aspects of the process must have some periodic inspection. Other-wise troubleshooting will be impossible. This also prevents manufacturing scrap. Empowering the operators op erators to verify part conformance frequently throughout the manufacturing process enables them to troubleshoot the process when they discover nonconforming nonco nforming parts. Doing so efficiently is a matter of checking parts randomly and frequently while they are being manufactured, not after they are finished.
•
Above all, keep it simple.
SOCIETY4PAKSWISSIANS A complete set of rotary draw bender tooling includes a bend die, clamp die, pressure die, wiper die, and mandrel. Understanding the role of each and how each interacts with the others is a crucial first step in troubleshooting bending problems.
Synchronize the Workcell's Operations Because tube bending generally is the nucleus of a workcell, the other processes must be synchronized to this process. Determine the optimal cycle time for bending, and adjust the loader speed accordingly. If the cell involves a shear that cuts the tube or, in an extreme case, a tube mill that produces the tube, these operations must be timed so the bender is neither over- nor underfed. Be aware that the overall speed of the automated cell or line must be based on the fastest tolerable cycle of the slowest operation of the cell. Also be aware that timing is nothing without debugging. Set up and troubleshoot every operation individually before attempting to integrate them in an automated process.
Launch the Cell Sophisticated animation software can facilitate placing and integrating every piece of equipment in the workcell. Most work flow problems and equipment collisions are caught in the programming stage. However, in the real world it can take some time and an d program tweaking to achieve the mechanized ballet we strive for in a workcell. When the optimal cycle times are dialed in and benchmarks set for speed and other acceptance parameters, the next critical phase of the start-up begins. Train the Operating and Maintenance Crews. Procedures for operations and maintenance training vary considerably from company to company. Some companies have three separate groups—one for tooling setup, a second for machine maintenance, and a third that operates the cell and monitors production. Considering the cell is likely intended to operate for two to three shifts per day da y, seven days a week, it is obvious that consistent output among all shifts requires consistent training among all personnel. pe rsonnel. Without maintenance training, equipment operators can do nothing more to solve bending problems than find the few knowledgeable troubleshooting personnel and inform them of the problem. Likewise, the tooling setup staff's responses to problems can be limited. "Let's replace the tooling!" is a fast, easy ea sy,, yet ineffective response if the trouble starts elsewhere. Ideally, Ideally, all personnel receive the same training and a set of written procedures so that everyone learns a single approach to troubleshooting. Keep Accurate, Thorough Records. Equally important—and harder to implement—is an accurate method of monitoring uptime and downtime, cycle speeds, scrap rates, maintenance procedures, tooling settings, and changeovers. This data is necessary for
SOCIETY4PAKSWISSIANS making informed decisions regarding equipment and tooling condition. Adjusting Adjusting procedures based on this information can help minimize downtime and anticipate catastrophic failure. Any steps for developing constantly updated (and consistently formatted) records are valuable. The records themselves are invaluable if they are frequently analyzed and used for planning preventive maintenance activities. If nothing else, good recordkeeping prevents running out of consumable tooling items (wiper dies and mandrels, for example). How many times do you need to run out of $50 wiper tips, causing the multimillion-dollar workcell to shut down and leaving your best customer stranded, before you realize that you should have a supply of all tooling and a steady flow of consumable items on recurring blanket orders? Proper documentation analysis and proactive process implementation are the only onl y ways to prevent consumable shortages.
Troubleshoot to the Source While it is just human nature to rush to get a high-speed workcell or production line up and running as quickly as possible after a problem arises, it is necessary to trace the cause of it all the way to its source. Follow the process back to the first step that did not meet the acceptance criteria. The principal reason for doing this, of course, is to solve the problem and not merely address the symptom. s ymptom. Allowing the problem to continue unchecked means it will compound later on. Resolving the problem now also prevents repeated and excessive downtime later la ter.. If the workcell is a completely automated line, it might involve a tube mill; straightening, punching, and forming machines; a weld seam detector; a bending machine; hydroforming press; laser cutting system; welding station; and, of course, a material handling system. The complexity and speed of such a system means that a small problem early in the process has the potential to get completely out of hand in the blink of an eye. Constant quality monitoring and proper and pragmatic problem-solving are not just advised. They are required.
Bob’s Troubleshooting Tips Troubleshooting a bending operation is like troubleshooting any other manufacturing manufac turing process—keep records, watch for changes, and keep symptoms and causes separate. Pay attention to consumable usage. For example, an increase in wiper tip reorder frequency is not a problem. More than likely, likely, it is a symptom of a problem. p roblem.
Consumables.
A wiper die's support comes from the tube groove of the bend b end die contour. Considering that the wiper is just 0.003 inch thick at the tip if machined correctly, correctly, it is easy to understand that this tip will conform to the bend be nd die regardless of its condition, new or
SOCIETY4PAKSWISSIANS worn. If the bend die's groove contour is worn, the wiper tip life will be a fraction of what it should be. How many tips did you discard last quarter after premature failure? How many replacement bend die bodies would have prevented this? Short wiper die life also can indicate that the tooling mounting surfaces are misaligned. This misalignment, in turn, can be caused c aused by excessive and uneven strain on the bender, which is a result of excessive bender bende r force. This doesn't just prematurely wear or ruin the tooling; it has the same effects on the bender bend er itself. ovality, the degree to Ovality. Bend ovality,
which the bent tube is out of round, also is a symptom and also can have one of several causes.
The most common (and generally gen erally wrong) step to reduce ovality loss is to replace the balls on the mandrel and leave it at that. The mandrel, like the wiper tip, is in constant contact with the workpiece. The bending process develops a tremendous amount of pressure and wears out the mandrel balls. While replacing the mandrel balls will improve bend ovality, ovality, this isn't necessarily the best course of action. If correctly made, a mandrel shank (the cylindrical section the articulated ball-and-link assembly attaches to) is generally 0.005 in. greater in diameter than the ball segments. The size difference and the proper placement of the leading corner of o f the shank (slightly ahead of the bend tangent) dictate that the shank does the initial forming and bears the greatest load in the forming process. Generally speaking, if the shank is worn and the new ball segments are the same diameter as (or larger than) the shank, all the load falls on the ball-and-link assembly, assembly, resulting in premature link failure and mandrel breakage. How many broken links could have been prevented, and how much downtime would have been uptime, if this condition were correctly diagnosed in the first place? These issues with wipers and mandrels are simply two common problems in high-speed automated workcells. Wipers and mandrels are consumable items, so their premature wear often is treated lightly. lightly. Although they are small, they shouldn't be regarded as insignificant. A little knowledge and some preventive actions a ctions would extend the service lives of these items and increase the workcell's uptime considerably.
Turning the corner on making doors: North Carolina company streamlines the process By Linda Baldwin, Contributing Writer Writer January 10, 2001
SOCIETY4PAKSWISSIANS A small fabricator North Carolina, familyowned company manufactures standard and custom electrical enclosures for the commercial construction industry and a growing number of OEMs. While some fabricators feel the pinch of today's tightening economy, a small fabricator in North Carolina has remained optimistic.
Figure 1: A safety door on
the forming "Production is our restriction. We have many mechanism protects operators using the machine. A foot foot pedal controls co ntrols the opportunities in the market. If we can produce more, the demand is there," said Jim machine, which will not work unless the door is shut completely. completely. Austin, president of The Austin Company, Company, Yadkinville, N.C. The family-owned company manufactures standard and custom electrical enclosures for the commercial construction industry and a growing number n umber of OEMs. The company has doubled its sales and size in the last 10 years. Although electrical enclosures are in high demand, the low unemployment rate in Yadkinville and the surrounding area has ha s followed the national downward trend, forcing Austin to rethink the company's production process. "With a short supply of qualified workers, we've investigated other ways to increase throughput. We came to a point where automation was necessary to keep up with demand," Austin said. "We've "We've been careful to invest inve st in equipment that will quickly reduce costs and increase production." Most enclosures made by the company include doors constructed similarly to a shoebox lid. When analyzing where the next investment would be made, Austin noted the laborintensive fabrication of these doors. "The metal for the lid is sheared, the corners are notched, and the four sides are bent. The next two steps, manually welding and sanding the seams, were time-consuming. Welding and grinding are an art; there are inconsistencies in these steps," Austin said. While corners were labor-intensive and results acceptable but inconsistent, Austin said he had not identified them as a production problem until he saw a routine sales presentation for a new product. "Once we saw it, we made a trip to New Jersey to see a corner-forming machine," he said. "We "We also sent samples of our own product so we could see how it would work for us."
SOCIETY4PAKSWISSIANS Austin said he had two criteria for bringing a corner former into his operation: It should reduce the labor involved in making and finishing corners, and it should produce a more uniform door flange. "I wasn't aware of anyone else who made a Figure 2: Austin's former can produce machine that would do this, so once it met my criteria, we brought it in," he said. He purchased corners with radii of up to 4 in. The thickness of the materials can range CIMID's ACF Multiflex automatic corner from 8 to 22 ga. Bend-up height former. depends on material thickness and bend radius. "It makes uniform corners in three steps instead of five," he said. "It was the next logical step in automating our production."
Forming Door Corners In the new process, operators form a part using standard press brake procedures, except for the bottom V die. They machine a relief on the bottom V die for the left side and the right side of the part. This relief produces a flare at the corner, instead of a 90-degree angle. They then take the part to the corner former and place it on top of a base block that has the same radius as the press brake and the expected corner. In its turn, the corner former pulls extra material below the edge of the panel pane l side. This material, which the machine shears off immediately after forming, is the difference between the maximum bend-up height and the minimum bend-up height. The machine then repeats this process for the remaining three corners. "The corner former has substantially reduced labor costs co sts associated with fabricating doors," Austin said. "The same operator does the bending and the corner forming in about one minute per part. Now we can shift employees to ease welding and grinding bottlenecks in other areas of the company." company." In addition, corner forming eliminates the need for stacking to weld and restacking to grind. The part does not need to be transported to the welding department and then again to the grinding department. Operators move the part once to the corner former. former. "The sheets for doors and tops of metal junction boxes can be very large. Material handling is a big issue," Austin said. "Increasing throughput and controlling labor costs co sts have resulted from moving parts as little as possible. Using a corner former has also reduced material costs since there are no abrasives or welding supplies needed." While the corner former increases production, it is also safer than the traditional welding and grinding processes. p rocesses. A safety door on the forming mechanism protects operators using the machine. A foot pedal controls the machine mach ine (see Figure 1), which will not work
SOCIETY4PAKSWISSIANS unless the door is shut completely. In addition, corner forming eliminates welding fumes, grinding dust, and the noise from grinding. Forming Options Austin's former can produce corners with radii of up u p to 4 in. The thickness of the materials can range from 8 to 22 ga. Bend-up heights depend on material thickness and bend radii (see Figure 2). His machine can handle corners with multiple bend heights, reverse or return flanges, and bull noses. Because enclosures are mostly of the familiar shoebox lid configuration, Austin's Austin's corner former gives him the option to consider con sider other markets in the future, such as trays, furniture, shelving, oven doors, food service equipment, traffic signs, all types of coversâ??anything that has sheet metal corners that are welded and ground. The corner former has no limitations on the size of the panels it can accept, because only the corner is placed into the machine. Using a corner former has given Austin flexibility in operating his production line. With one set of tooling, his operators can form four different thicknesses of material in all alloys and in all bend-up heights. Changing tooling to accommodate different radii takes them five minutes, according a ccording to Austin. "This technology has streamlined our door fabricating process," Austin said. "Growing our business undoubtedly means future investments in other automated equipment."
Pumping up productivity on older press brakes Increasing productivity with advanced tooling, clamping, crowning systems By David Bishop, Contributing Writer Writer June 8, 2004 In recent years faster, faster, more efficient cutting and an d blanking methods have emerged. However, these cutting efficiencies and corresponding increases in productivity have not always been met with similar increases in press brake productivity. productivity. Consequently Consequentl y, this has created a need to find new ways to improve press brake process productivity. productivity. Tall gooseneck punches can bend deep parts and parts with complicated bend sequences.
SOCIETY4PAKSWISSIANS Once a press brake has ha s been installed, methods to improve its functionality to increase bending capacity may be limited; therefore, you might consider purchasing more press brakes, but that will require more floor space and more operators. An alternative for improving press brake productivity and eliminating the bottleneck may be with more advanced tooling, antideflection (crowning) systems, and clamping systems. Tooling Systems In the past when bottom bending and coining were the only options, it was common for press brake owners to accumulate large inventories of press brake tooling. However, the advent of CNC press brakes, precision-ground p recision-ground segmented tooling, and precision air bending has made it possible to form more materials and part configurations with fewer tools. The two most versatile punch types for air bending applications are acute-angle punches and gooseneck punches (see introductory image ). Gooseneck punches allow you to form deep channels, boxes, and other parts with long return flanges. Gooseneck punches with a tip angle of 88 degrees or less can help you deal effectively with springback. Acute-angle punches allow you to bend almost any angle. They can be used to create the acute bend required for hemming applications. When produced from high-strength alloy steel and properly heat-treated, both punch styles are fairly strong and bend a range of material types and thicknesses. Generally, Generally, the taller a punch is, the more versatile it is. The flexibility these two punch styles provide normally results in fewer punch changes. Consequently, less time is needed for setup, and productivity will increase. Although the angle of the V opening on the die must match the angle of the punch tip in bottom bending and coining operations, this is not necessary with air bending, because the final bend angle is determined by the penetration of the punch into the die. For example, you can use acute-angle punches with a 28-degree tip and gooseneck punches with an 86-degree tip with dies with 30-degree V openings. This can reduce the total number of dies required to bend 0.036- to 0.135-inch (1.0- to 3.5-mm) mild steel, aluminum, and stainless steel. Be sure to use extra caution to avoid overpenetrating the die and possibly damaging it when using a die that has a V opening with an included angle that is less than that of the punch tip. When selecting a die, consider its overall ov erall working height. Tall Tall dies are flexible and allow you to bend parts with long down flanges (see Figure 1). Short dies normally are less expensive and consume less open height.
SOCIETY4PAKSWISSIANS Because single-V dies are narrower than the 2-V dies common with most European-style tooling systems, they are less likely to interfere with parts with a complicated bend sequence. In addition, single-V dies normally are designed with a common tang, so that a full range of dies can be used in a single die holder or antideflection device (crowning system). This reduces setup time because it eliminates the need to utilize multiple die holders to accommodate multiple die designs. Durability. Tooling durability is
an important consideration. Many tooling manufacturers now offer surface hardening on standard press brake tooling. These hardening processes include CNC deep hardening, laser hardening, induction hardening, and a nd coating. All processes provide good wear resistance compared to tools with unhardened wear surfaces. For example, research has shown that tools that have been CNC deephardened will last seven to nine times longer than tooling with unhardened surfaces. Finally, Finally, a good press brake tooling system should be portable. It should be supported by a series of holders for the upper and lower beam (ram and bed) that allow you to move it from one press brake to another.
Portability.
Clamping Systems The advent of high-precision, quick-change press brake tooling systems has resulted in huge productivity gains. Figure 1 However, it is quite common for precision-ground Tall dies can bend b end parts with punches to be used directly against the upper beam of the long down flanges. press brake and to be held in place by the manual ram clamps originally provided with the machine. On many press brakes, the load-bearing surfaces of the upper and lower beam are milled to finish rather than precision-ground. Inconsistencies in these surfaces directly alter the quality of the finished parts. This type of installation also does not speed up the loading and unloading of tooling. Advancements in clamping system technology in recent years have been driven by reduced lot sizes and an increase in the number of setups that press brake operators must perform. Fortunately, Fortunately, you have many clamping systems to select from, including manual clamping systems that simply open and close the clamps quickly and hydraulically driven systems that clamp, seat, center, and align all of the tooling with the push of a single button (see Figure 2). Precision clamping systems also provide a high-precision, load-bearing surface for punches, thereby reducing the problems with inconsistent bend angles caused by poorly
SOCIETY4PAKSWISSIANS machined surfaces or moderately damaged surfaces on the upper beam. They also act as an insulator against damage to the upper beam of the press brake. Finally, Finally, many advanced ad vanced clamping systems enable you to clamp punches either with the relief area facing toward the rear of the machine or facing toward you. This provides additional versatility because part extraction often is easier and less cumbersome when the punch is loaded with the relief area facing toward you. Antideflection (Crowning) Systems If your press brake is 8 feet long or longer, unless you bend nothing but thin materials or are fortunate enough to have a press brake with built-in deflection compensation, you probably have been shimming dies to overcome machine deflection. The time consumed and the subsequent costs of this tedious and productivityrobbing process are often overlooked.
Figure 2
This hydraulic clamping system for North Americanstyle press brakes is equipped with a crowning system that uses opposing wave tecnology to compensate for machine deflection.
Antideflection (crowning) systems are available that eliminate this problem. Basic systems are manually adjusted, and set screws clamp lower dies in place. Others are equipped with more advanced clamping bars that can be tightened against the die manually or with hydraulics for ultrafast die changes. Clamping bars make it possible for you to position small die segments anywhere along the full length of the unit to achieve equal clamping pressure. This prevents them from being moved or knocked over while handling the material. The deflection-compensating components in these systems can be a simple set of opposing wedges or a set of highly advanced opposing waves. Depending on the design, the motion of the wedges or opposing waves against each other cause the unit to deflect in an upward motion to compensate for the amount of deflection that is being generated in the press brake when it comes under load. You You can adjust these units un its with a basic lever, a hand crank at the end of the unit, or with an electronic motor driven by the CNC on the press brake. Some of the more advanced antideflection systems available also feature localized adjustments. This enables you to increase or decrease the amount of deflection compensation at frequent intervals along the full length of the unit. This makes it possible to fine-tune the deflection-compensating curve of the unit to overcome the nuances built into the machine, as well as compensate for wear that is specific to a particular area of the upper and lower beam or a specific punch or die.
SOCIETY4PAKSWISSIANS In the end, the choice of which crowning unit is best b est for you should rest solely on which features and benefits best suit your needs. Whichever system you choose can eliminate shimming with a process that requires only a matter of seconds secon ds to complete. Ironically, a press brake never comes into contact with the material that it bends; only the tooling and backgauge do that. When considering ways to improve press brake productivity, productivity, it is imperative that you examine exa mine all of the elements that affect overall productivity. productivity. This includes the machine, control, operating o perating software, and everything that goes between the upper upp er and lower beams—the tooling system, clamping system, and deflection-compensating device. Fortunately, Fortunately, when it comes to advanced tooling systems, clamping systems, and antideflection systems, the choices have never been better.
Using benchmarking for bend deductions By Steve D. Benson, Contributing Writer May 30, 2002 Benchmarking is a very good idea for your operation—just make sure your benchmarks are your own and not someone else's idea of perfect. Benchmarking is using measurement or evaluation to judge similar processes, parts, charts, and methods. The term benchmark is believed to come from medieval times—more specifically, specifically, form the stonemasons who built the great cathedrals of Europe. Before that time local craftsmen built every piece of furniture and cut every piece of stone to size by b y judging length, width, and height by eye. This meant there were no standards by which to judge components for length, width, and height relative to any other part. In other o ther words, everything was eyeballed. At some point someone came up with the idea of placing a mark or gouge into a workbench to indicate the length or width of a part. By comparing each leg of furniture or block of stone against aga inst the benchmark, the builder could be assured that each subsequent piece was pretty much the same size as the previous one. Modern Version—Bend Version—Bend Deduction Charts A benchmark, then, is a measurement that can be used as a reference for other measurements or data sets. In the modern sheet metal shop, bend deduction charts are a
SOCIETY4PAKSWISSIANS good example of benchmarking. be nchmarking. A bend deduction chart created in a shop where bending methods, bend types, and tooling are agreed upon by all becomes a valid benchmark. Ideally, Ideally, modern benchmarks benc hmarks would serve the same universal purpose as the notch in the bench did for our ancient brothers. A test run of the material being formed would validate the bend deduction values at any time. However, when inappropriate benchmarks are used, problems arise. For instance, benchmarks can be rendered invalid when they're used in a different shop where tooling or forming methods differ from the benchmarks' bench marks' source. Figures 1 and 2 show two different bend deduction (BD) charts for the same material
thickness and bend radii. Notice how different the bend deduction values are, even though both are correct for the shop in which they were created. One shows a bend deduction of 0.106 for a 1/32-in. inside radius for 16-gauge cold-rolled steel; the other chart shows it is 0.136. These are perfect pe rfect examples of how another shop's benchmark bench mark may or may not be correct for you. If you try to apply someone else's benchmark to your process, chances are it won't match the marks on your workbench, leaving you with one leg that is too long. Mathematics: Establishing a Common Benchmark As long as you use the same forming methods and tooling that were used u sed to create the original data set, validating the original numbers nu mbers should be easy. easy. If everyone used the following formulas and processes to create of their bend deduction charts, they could establish a common benchmark. To set a standard benchmark for your bend deduction charts, you must take an accurate measurement of the inside radius, either by meeting part specifications or by planning for what is going to be done. This radius measurement can be taken on the tip of the punch radius in bottom bending or coining. co ining. It also can be taken as a percentage of the V-die V-die opening in air forming using these percentages—20 percent for 304 stainless steel, 15 percent for cold-rolled steel, 15 percent for H32 5052 aluminum, and 12 percent for hotrolled pickled in oil. Simply multiply the V-die V-die opening by 0.20, 0.15, or 0.12 to find the value for the inside radius. Once a value for the inside radius is set, simply plug it into the following formulas to establish a proper benchmark in your bend b end deduction charts for a given material thickness and inside radius. Bend Allowance (BA)
SOCIETY4PAKSWISSIANS BA = [(.017453 x Rp) + (.0078 x Mt)] x ^ Outside Setback (OSSB)
OSSB = [tangent (^/2)] x (Mt + Rp) Bend Deduction (BD)
BD = (2 x OSSB) - BA Where: ^ = Complementary angle of bend Mt = Material thickness Rp = Radius of the punch (coining and bottom bending) bend ing) or inside radius (air forming) As long as the inside radius of the bend can be measured with a radius gauge, also a benchmark, the benchmark supplied by mathematics can be yours to apply ap ply in your shop and in any other shop that measures and calculates these values. The Key The key to valid benchmarking is understanding how the benchmark relates to the tasks, tools, and methods employed in your particular environment. Benchmarking the tasks that you generally perform rather than using a benchmark someone else has created will steer you in the right direction, unless they also are using mathematically derived benchmarks. Then you're OK.
Getting control of your cut-to-length line How to select the most suitable drive and controller By Martin Marincic, Contributing Writer July 11, 2002 There are many factors to consider when selecting a drive and control con trol system for a cut-tolength line. After choosing the line, you need to choose the drive, calculate the load inertia, calculate the feeder speed, and choose a motion controller. Many factors should be considered when selecting a drive and control system for a cutto-length (CTL) line.
SOCIETY4PAKSWISSIANS First, decide the type of CTL line best-suited for your application, specifications, and budget. Let’s assume you’ve chosen a loop roll feed. Where do you go from there? Drive Choices Figure 1 shows some typical
frequency response ranges for all types of drives available today. today. Performance varies widely among manufacturers. Figure 1:
In general, AC drives are Drive frequency response varies widely among preferred when power manufacturers, but ranges can be identified for all requirements are lower than 75 types of drives available today. HP,, when significant numbers of HP driven sections are likely to be braking continuously, for high-performance applications, and for large process lines using many driven sections. DC drives are most suitable when power requirements are higher than 75 HP; when power requirements are positive for all sections; when there is a large DC installed base; and when the application requires a wide, constant-horsepower speed range. For the roll feed CTL line, an AC vector drive probably would be the most suitable choice. Motion Profile Now that you've settled on an AC drive for your roll feed, you need to size the motor for the application by determining how much torque is required at what speed and what kind of performance you can expect. Because the line most likely will run materials of various lengths, you'll need to calculate for the entire product range. This application calls for you to move a strip of material a known distance. You can record and graph the velocity over a period of time, resulting in a motion profile chart from which you can determine distance, maximum speed, and acceleration rates. One of the most commonly used motion profiles is the 1/3-1/3-1/3 profile. The time allocated for strip movement is divided into three equal time segments: one-third for acceleration, one-third for traverse, and one-third for deceleration de celeration (see Figure 2). The distance and time requirements are known, so you can solve for maximum speed N(max): N(max) = 1.5 ¥ Total distance/ Total Total time (inches per second) This value for N(max) can be converted to RPM: Inches/second ¥ 60 seconds/minute ¥ 1 rotation/P inches
SOCIETY4PAKSWISSIANS where: P = inches per revolution Load Inertia Using the required application data information gathered for the machine, you can calculate the total connected load inertia. Two of the most common geometric shapes encountered in these applications are solid and hollow cylinders. To To calculate the inertia of each, use the following formulas:
In the 1/3-1/3-1/3 motion profile, the time allocated for strip movement is divided into three equal time segments: one-third for acceleration, one-third for traverse, and onethird for deceleration.
Solid cylinder for known weight and radius: J = (1/2) ¥ (W/g) ¥ r 2 Solid cylinder for known density, density, radius, and length: J = (1/2) ¥ [(Pi ¥ 1 ¥ p)/g] ¥ r 4 Hollow cylinder for known weight and radius: J = (1/2) ¥ (W/g) ¥ (or 2 + ir 2) Hollow cylinder for known density, density, radius, and length: J = (1/2) ¥ [(Pi ¥ 1 ¥ p)/g] ¥ (or4 - ir4) where: J = inertia (lb. in. sec.2) W = weight (lbs.) g = gravitational constant (386 in. per sec.2) l = length (in.) p = density (lbs./in.3) r = radius (in.) or 2 = outside radius (in.) ir 2= inside radius (in.)
Figure 2:
SOCIETY4PAKSWISSIANS To find the total connected load inertia, add together the inertia of each ea ch driven element. Feeder Speed Now that you know the load inertia and motion profile, you can select the correct motor and gearbox combination for load acceleration. First, look at the maximum required feeder load speed you calculated using the motion profile. If you know the base speed of the motor, you can calculate a reducer gear ratio. You now can calculate J(Re), the load inertia reflected through the gearbox gea rbox back to the motor shaft: J(Re) = J(1) / R2 (lb. in. sec. 2) where: J(Re) = reflected inertia J(1) = load inertia R = gearbox ratio If there is any load torque, the gearbox will reduce the amount at the motor shaft. You can calculate the load torque reflected back to the motor shaft as follows: T(Re) = T(1)/R where: T(Re) = reflected torque T(1) = load torque R = gearbox ratio Once the reflected inertia and reflected torque are known, you can solve for the required motor acceleration torque T(a) using the following formula: T(a) = {[(J(m) + J(Re)) ¥ N(max)]/(9.55 ¥ t)} + T(Re) where: T(a) = motor acceleration torque (in. lb.) J(Re) = reflected inertia (lb. in. sec.2) J(m) = motor inertia (lb. in. sec. 2) N(max) = motor maximum speed (RPM) t = acceleration time (sec.)
SOCIETY4PAKSWISSIANS T(Re) = reflected torque (lb. in.) The motor you select should be able to produce the amount of acceleration torque required. Because the load in this example is cyclical, you must check the average amount of torque the application requires to be certain that your motor can deliver that torque without overheating. Calculate the average required torque using the following equation: Trms = [(T12t1 + T22t2 + T32t3 + ***)/ (t1 + t2 + t3 + ***)]-2 where: T1 = acceleration torque (lb. in.) T2 = traverse torque (lb. in.) T3 = deceleration torque (lb. in.) t1 = acceleration time (sec.) t2 = traverse time (sec.) t3 = deceleration time (sec.) The continuous torque rating of the motor must be greater than the calculated average required torque. Once you've sized the motor for a particular cut length, you need to check the expected performance at all of the other possible cut lengths by rerunning all of the calculations for each cut length. Usually, a motor and gearbox sized to perform adequately at short lengths may have limited performance at other lengths. You You might have to give up performance in one area to gain it back in another. Constraints One of the constraints you will have to deal with is the type of shear and the maximum number of strokes per minute it can handle. This usually sets the maximum number of pieces per minute (PPM) that the line can handle. Another short-length constraint is the ability of the motor to accelerate fast enough to make the move. The motor must have enough torque to bring the connected inertia up to the maximum speed in the time allowed. Sometimes the acceleration constraint is not with the motor but with the machine mach ine itself. For example, the motor may have enough en ough torque to accelerate the load, but the feed rolls may slip on the material at that particular acceleration rate, causing inaccurate cut lengths. Or the acceleration rate may be too high for the mechanical portion of the machine to handle. Gearboxes, belts, and other driven equipment could become worn out quickly, quickly, chatter, or exhibit other unstable characteristics. Also, consider the control of the free loop. If the acceleration rate approaches or even exceeds the force of gravity, you will not have control over the loop, leading to an unstable condition.
SOCIETY4PAKSWISSIANS On longer lengths, a constraint con straint that may be encountered is that the maximum feeder speed is too slow. slow. You You could change chang e the selected gear ratio to allow for a faster maximum motor speed, but you would be giving up torque and losing some of the advantage of smaller reflected inertia. Another long-sheet constraint is the leveler gear in speed. The maximum line speed at the leveler divided by the cut length gives you the maximum PPM for longer lengths. Also, the amount of material stored in the loop must be considered for longer lengths. leng ths. These constraints must be observed for all cut lengths. You can do some things to overcome them. Sometimes it is a trade-off with other constraints, and sometimes a larger, faster faster motor will do the trick. But oftentimes o ftentimes you will find a situation of diminishing returns as you try to apply bigger motors. That is, the larger torques require larger frames that have larger inertias, and as you apply the formulas, you will find that the expected results begin to drop off even though you have a larger motor. motor. Motion Controllers A motion controller handles all of the computations to generate the motion profile used by the feeder drive. It usually is microprocessor-based and can be a stand-alone box or part of the programmable logic control con trol system. It can reside in a PC or industrial computer, or it can be part of the AC, DC, or servo drives. The motion controller calculates distances, velocities, accelerations, torque, and speed. It may have to accommodate several encoders and be capable of both analog and digital input and output. It has to be able to communicate to the real world to accept set points and other commands. And last, the motion controller must be fast enough enoug h to send its calculations to the drive in time for the drive to react. System Checks A few final checks remain: • Is the inertia of the motor equal equ al to or bigger than the total reflected load inertia divided by 3? This is necessary to ensure system stability. stability. • Is the continuous motor torque still greater than the required average torque? If you’ve made any changes, especially the gear ratio, you may have to recalculate. • Is the peak torque of the motor high enough to accelerate the load fast enough? enou gh? Again, changes can affect peak torque requirements. • Can the motor run at the top speed you've designed? In your efforts to reduce load torque and inertia, you might have hav e selected a gear ratio that requires the motor's top speed to be higher than the manufacturer recommends.
SOCIETY4PAKSWISSIANS • Is the acceleration rate acceptable? Is it high enough for good production but below a threshold for good control of the strip and acceptable wear on the machine? • Have the performance specifications been met? If not, you need to modify your design choices or modify your performance specifications. Martin Marincic is president of New Era Controls, P.O. P.O. Box 25630, 25630 , Garfield Heights, OH 44125, phone 216-901-1300, fax 216-901-1305, e-mail
[email protected] , Web site neweracontrols.com neweracontrols.com.. New Era Controls is a systems integrator that specializes in providing drives and controls for cut-to-length lines and other coil processing applications. This article is adapted from Martin Marincic's conference presented at Coil Cut-tolength Workshop, Workshop, Aug. 2 an d Oct. 18, 2001, ©2001 ©2 001 by the Fabricators & Manufacturers Association, Intl.
Material Handling on Squaring Shears Aiding productivity by making the operator's job easier By Rod Stouder, Contributing Writer Writer June 13, 2001 Proper material handling equipment in front of and in back of utmost importance to your operation. Its impact on operator comfort and safety should not be minimized. Often it is thought that to get more production from a shearing operation, another ano ther shift, or even a new shear must be added. However, because of a lack of funds, personnel, or floor space, a new shear is not always the answer. The basics of a productive shearing operation are often overlooked. What good is it to have a shear that will do 30 to 60 strokes per minute (SPM) if the material coming into and going out of the shear is not being properly handled? Typically Typically,, only 5 percent of a shearing operation is spent with the shear ram going up and down, cutting material. This means that the other 95 percent is spent handling the flow of material being sheared. Thirty percent of this handling is done on the front side, and 65 percent takes place on the back of the shear. Material handling involves labor. In the shearing operation, labor is the same whether the shear operator is feeding sheet, cutting, or picking up the mess at the back of the shear. Improving the flow of material into and out of the shear can increase shearing output. With the use of some basic material handling equipment, a shearing operation can be made more productive.
SOCIETY4PAKSWISSIANS Feeding the Shear The first place to consider material handling equipment e quipment for a squaring shear is at the front of the shear, especially if the shear is mounted flat on the floor. floor. Most shears have a 32-inch passline, p assline, which means that the shear table is 32 inches from the floor. It has been said that shear tables have been at the same height since the 1920s. 1 920s. If persons of average height are pushing steel at a 32-inch table, that means they are bending over, which is hard on their backs. Constantly bending over can cause c ause back strain. The more strain that takes place, the more the operator will stop shearing and straighten to relieve the pain. When there is less strain and pain, there should be more productive shearing taking place. Those with shearing operations should think about putting their shears on risers to at least a 36- to 38-in. working passline. Material flow into the shear can also be b e improved with infeed assist tables. By keeping the next piece to be sheared at table height or o r a little higher, the operator can let the material flow downward toward the shear. It is much easier to control a sheet sliding down than it is to lift and pull the same sheet up and onto the shear table. The operator can choose the most comfortable infeed height and maintain that controlled height at all times. Again, when the operator is working at a comfortable work height, shearing time can become more productive. Ball transfer and caster fields or even powered infeed rollers can also reduce strain on shear operators. When less force is used feeding the material into the shear, more finished material should come out the back. Removing Material from the Shear The time that passes between the cutting of material and removing it from the shear can account for as much as 65 percent of the shearing operation. This means that for the 15 or 20 minutes worth of shearing, twice this much time is spent sorting and stacking finished parts behind the shear.
Figure 1:
A material support system for a shear.
A material support system (see Figure 1) at the back of the shear can save wear and dulling on the lower blade because it holds the sheet up and keeps it from dragging across the knife. A support system also holds the sheet in place so that the operator can keep his hands away from the blade during shearing. In addition, a support system s ystem eliminates the
SOCIETY4PAKSWISSIANS need for personnel to be under or behind the shear, which means a safer work area. These systems also provide truer backgauging of the parts. When producing parts that are the same size, a stacker working behind the conveyor eliminates the need for a person to stack by hand. A stacker can place the sheets in a tight stack for banding and shipping. A stacker can also stack the sheets tightly front-to-back and loose from left to right. This makes the sheets easier to handle at the next workstation.
Figure 2:
A shear with conveyors can be fitted with built-in material supports and trim cut separators.
Some conveyors have material supports and trim cut separators built into them. While the shear is cutting parts, these devices separate the trim from the finished pieces going out the back of the shear housing. The finished parts then fall into a safe work wo rk area (see Figure 2). Working off of a shear table that has a 32-inch passline, a stacker can make a stack height of 16 to 20 inches. Putting the shear on risers would allow more stack height. As the shear table goes up from the floor, so does the useable stack height. In a production run, this means less time is spent stopping to remove sheared stacks. Safety Safety is a major concern. By adding material handling equipment, the risk of injury in the workplace can be reduced with the added benefit of increased production output. Employee Support Not every shearing operation will benefit from material handling equipment. However, managers who think it is worth considering should discuss equipment options with the shear operators. Without their input, material handling changes may not pay off in increased shear output.
8 ways to keep your shear in top shape By Robert Kotynski, Contributing Writer April 10, 2001
SOCIETY4PAKSWISSIANS Improving uptime and reducing maintentance when using shears for high production could mean following a few key steps. Shears are common pieces of fabricating equipment that can be found in many metal forming plants. From tube mills to small fabricators, the shear is one of the most critical and diverse tools used in metal fabricating. Varying in size from small hand-held metal shears and foot-operated trim shears to high production in-line flying cutoffs, the modern metal shear has replaced the saw as the machine of choice for high-production metal cutting. This article addresses improving uptime and reducing maintenance when using shears for high production. The following tips are from shear users and rebuilders who found success when they implemented them. Tip No. 1 — Understand Your Your Machine It is important to understand the function, design, and operation of your machine. The main cause of shear failure is overloading it beyond the OEM's parameters. Shears are designed to cut metal of an a n established thickness and width. When these limits are exceeded, damage occurs. In addition to following the OEM's load recommendations, normal adjustments should be made regularly, regularly, and maintenance schedules and service requirements should be followed carefully. Misusing lubricants and other fluids also causes damage. Lubricants and fluids must be used as specified by the OEM. Tip No. 2 — Perform and Document Regular Inspections A regimented inspection schedule should be posted and adhered ad hered to. Areas that should be inspected include the shear's ability to execute all functions of operation; on mechanical machines, all bearings should be checked for lost motion and wear; and all emergency and safety functions should be examined. Tip No. 3 — Review Documentation After regular inspections are performed and documented, the data should be reviewed systematically. systematically. This review can reveal wear patterns, the potential for accidents, and nonconformance so that repairs can be made.
SOCIETY4PAKSWISSIANS Documentation and analysis are the basis of preventive maintenance. With this information, a clearly laid out maintenance plan can be prepared, eliminating most emergency repairs. Tip No. 4 — Set the Blade Properly Setting the shear blade properly is key to extending e xtending blade and machine life. Setting the proper clearances for blade cutting affects the drive, ram, tooling, and cut quality. Additionally, Additionally, before setting the blade, the blade seat should be checked for flatness and to ensure that the tooling is seated properly p roperly to eliminate blade chipping caused by b y shifting during cutting. If the clearances are too tight, improper cutting action occurs because the metal jams between the blade and the machine. If the blades have no clearance, they will break. When clearances are too loose, the blade acts as a hammer h ammer that applies multiple forces to the machine's components, causing premature wear and failure. Tip No. 5 — Maintain Correct Gib Clearance Setting and maintaining proper gib clearances increase tooling life and machine uptime. The gibs maintain proper guiding action of the ram and attached tooling. If the clearances are not maintained, the same problems occur as those that take place when the blade clearances are ignored. Tip No. 6 — Isolate and Level the Machine Leveling a shear and isolating it from vibration are critical to proper operation. The proper selection and installation of isolation pads can increase tooling life and shearing speed, decrease vibration, improve foundation life, reduce noise, and eliminate shear frame distortion. Using today's isolators, machine leveling can be done in less than a half ha lf hour. Making sure that the shear is level eliminates the twisting action that can destroy a shear. Tip No. 7 — Follow a Basic Maintenance Plan The following parts of a shear require regularly scheduled maintenance: 1. The air system should be maintained properly to ensure e nsure that the air is clean. All regulators must be set so that they are operating correctly. Maintaining the regulators helps the pneumatically pneu matically actuated mechanisms to function func tion properly. properly. 2. The lubrication system must be cleaned, filled, and properly filtered. Broken, kinked, or twisted lines must be replaced. Each point must be disconnected and examined to determine if the lubrication is reaching its destination. Sumps and reservoirs should be routinely emptied, cleaned, and refilled.
SOCIETY4PAKSWISSIANS 3. The machine clutch and brakes must be examined for proper lining thickness, clearances, and signs of failure. Worn Worn linings must be replaced immediately. immediately. Overtravel beyond the machine builder's bu ilder's specifications must be adjusted and/or corrected upon inspection. 4. Counterbalance cylinders should be tested and reworked at the first sign of air leaks or failure. A counterbalance cylinder that has the proper action ensures the longevity of all working components of the shear and its tooling. Tip No. 8 — Make Repairs as Soon as Possible When damage, wear, or out-of-adjustment conditions are found, the shear should be immediately repaired or adjusted. Most catastrophic failure is caused by putting off simple repairs. Addressing repairs quickly is almost always less expensive than the cost of correcting the damage that can take place when repairs are ignored or put off. Additionally, Additionally, operator safety depends depe nds on timely repairs. Keeping the shear productive can be accomplished by b y performing these simple tasks. When a shear is maintained properly, replacement costs and catastrophic failure are avoided. Tip No. 4 — Set the Blade Properly Setting the shear blade properly is key to extending e xtending blade and machine life. Setting the proper clearances for blade cutting affects the drive, ram, tooling, and cut quality. Additionally, Additionally, before setting the blade, the blade seat should be checked for flatness and to ensure that the tooling is seated properly p roperly to eliminate blade chipping caused by b y shifting during cutting. If the clearances are too tight, improper cutting action occurs because the metal jams between the blade and the machine. If the blades have no clearance, they will break. When clearances are too loose, the blade acts as a hammer h ammer that applies multiple forces to the machine's components, causing premature wear and failure. Tip No. 5 — Maintain Correct Gib Clearance Setting and maintaining proper gib clearances increase tooling life and machine uptime. The gibs maintain proper guiding action of the ram and attached tooling. If the clearances are not maintained, the same problems occur as those that take place when the blade clearances are ignored. Tip No. 6 — Isolate and Level the Machine Leveling a shear and isolating it from vibration are critical to proper operation. The proper selection and installation of isolation pads can increase tooling life and shearing
SOCIETY4PAKSWISSIANS speed, decrease vibration, improve foundation life, reduce noise, and eliminate shear frame distortion. Using today's isolators, machine leveling can be done in less than a half ha lf hour. Making sure that the shear is level eliminates the twisting action that can destroy a shear. Tip No. 7 — Follow a Basic Maintenance Plan The following parts of a shear require regularly scheduled maintenance: 1. The air system should be maintained properly to ensure e nsure that the air is clean. All regulators must be set so that they are operating correctly. Maintaining the regulators helps the pneumatically pneu matically actuated mechanisms to function func tion properly. properly. 2. The lubrication system must be cleaned, filled, and properly filtered. Broken, kinked, or twisted lines must be replaced. Each point must be disconnected and examined to determine if the lubrication is reaching its destination. Sumps and reservoirs should be routinely emptied, cleaned, and refilled. 3. The machine clutch and brakes must be examined for proper lining thickness, clearances, and signs of failure. Worn Worn linings must be replaced immediately. immediately. Overtravel beyond the machine builder's bu ilder's specifications must be adjusted and/or corrected upon inspection. 4. Counterbalance cylinders should be tested and reworked at the first sign of air leaks or failure. A counterbalance cylinder that has the proper action ensures the longevity of all working components of the shear and its tooling. Tip No. 8 — Make Repairs as Soon as Possible When damage, wear, or out-of-adjustment conditions are found, the shear should be immediately repaired or adjusted. Most catastrophic failure is caused by putting off simple repairs. Addressing repairs quickly is almost always less expensive than the cost of correcting the damage that can take place when repairs are ignored or put off. Additionally, Additionally, operator safety depends depe nds on timely repairs. Keeping the shear productive can be accomplished by b y performing these simple tasks. When a shear is maintained properly, replacement costs and catastrophic failure are avoided.
Long loads, narrow aisles, easy access Side-loading lift truck handles cumbersome products in confined spaces
SOCIETY4PAKSWISSIANS By Eric Lundin, Senior Editor, The FABRICATOR® September 12, 2006 Since starting with just one warehouse in 1989, J G Kelly Supplies has grown along with Ireland’s Ireland’s booming construction industry. industry. Limiting factors such as the warehouse’s doorway width, narrow aisles, and 90-degree turns meant the company had to rely on manual labor to handle the long, cumbersome items in its inventory. inventory. A standard forklift was out of the question. The company compan y eventually purchased a multidirectional side-loading lift truck from Combilift for moving inventory in this challenging environment. Ireland is called the Emerald Isle, and for good reason. Regardless of the season, much of o f the island is covered with lush green vegetation. The mild winter weather is a product of the Gulf Stream, the Atlantic Ocean current that pushes moderate weather north from the Gulf of Mexico. The other factor, of course, is precipitation. It rains a lot in Ireland. And that's an understatement. According to the country's weather service, Met Éireann®, much of the island receives an average of 1,000 millimeters (40 inches) of rain annually, and the mountainous regions receive twice that amount. Seeing a lucrative and growing niche, Gerard Kelly founded J.G. Kelly Supplies, a service center that provides rainwater-carrying components to Ireland's construction industry. industry. Kelly's timing was good—the g ood—the construction industry has grown significantly over the past few years. According to data provided by the Central Statistics Office Ireland, completed dwellings increased from 30,575 in 1995 to 80,957 in 2005. Meanwhile the demand for gutters and downspouts has been as constant as the rains that keep the island green, and J.G. Kelly Supplies has grown right along with the construction industry. Since it started with a single warehouse in Monaghan in 1989, which supplied western Ireland, the company has added warehouses in Dublin and Limerick and now supplies goods to construction contractors in all of the island's 32 counties. Narrow Doorway Doorwa y, Narrow Aisles After opening for business, J.G. Kelly Supplies quickly filled its 1,200-square-meter (12,900-sq.-ft.) warehouse with inventory, inventory, which includes long, cumbersome cu mbersome gutters and downspouts. The warehouse's main door is just 3 m (9.8 ft.) wide, whereas the products typically measure up to 6 m (19.6 ft.) long. Using a standard forklift to take the products p roducts into the building was out of the question.
SOCIETY4PAKSWISSIANS Initially Kelly's suppliers left the deliveries on the sidewalk next to the warehouse. Getting the inventory into the warehouse was Kelly's problem. "We "We handled every piece separately from the road," Kelly said, recalling the days when his warehouse staff provided muscle power to move the inventory manually. The doorway wasn't the only challenge. cha llenge. The warehouse's narrow aisles and two 90degree turns prevented Kelly's staff from using a forklift inside the building. Kelly needed something like a forklift, but something much more versatile. Load It Sideways, Move It Anywhere Kelly eventually found a lift truck that matched his needs—a multidirectional sideloading lift truck manufactured by Combilift Inc. The truck, a model C3500, has a lift capacity of 3,500 kilograms (7,700 lbs.) and a lift height of 4,040 mm (13.25 ft). It is equipped with two small front wheels and one large rear wheel. All of the wheels can rotate up to 180 degrees, allowing the truck to move forward and backward and side to side. It also is versatile in the way it turns corners. Negotiating a tight, 90-degree turn is not a problem—because it has a single rear wheel, the truck can make zero-radius turns. The truck allows Kelly employees to move the products directly into the warehouse, eliminating manual handling of individual inventory items. It also allows them to move cumbersome products through the warehouse with ease. In addition, it also handles notn otso-cumbersome loads, such as the palletized aluminum a luminum coil that Kelly supplies for on-site roll forming. Move the Product, Not the Warehouse Warehouse The use of this specialized lift truck eased the burden on Kelly employees by b y eliminating the need for manual inventory transfer. The labor savings allowed Kelly to reduce his warehouse staff from 10 to six. More important, the lift truck allowed Kelly to use his warehouse space more efficiently. efficiently. As the construction market and demand for construction-related items in Ireland has grown, Kelly has been able to more effectively use the limited space in his Monaghan warehouse, allowing him to remain in the same location despite the growth in his business. "By now we would have had to move, if not for the Combilift," Kelly said
The importance of storage planning By Joe Harnest, Contributing Writer October 23, 2003
SOCIETY4PAKSWISSIANS Material and equipment storage can be a major concern for fabricators. Therefore, it is important to establish the purpose of a storage system and understand clearly what it needs to accomplish. In its most basic form, a fabricator’ fabricator ’s storage area must be a secure, dry place of sufficient size to house required items. Location and ambient conditions are the critical factors. Considering the Criteria In today’s fast-paced material handling world, fabricators must consider the workable criteria before the project can be implemented. They must consider the basic cubic-feet requirements, as well as the environment required for the materials to be inventoried. And of course, location is highly important. Failure to consider it would compromise operating efficiency. efficiency. A modern inventory manager, unlike inventory managers of the past, has complete control of all the factors associated with material storage. With advances in technology, the inventory manager can build bu ild higher than was possible in the past. Fabricators also have the ability to make their the ir buildings cold, warm, light, dark, dry, or moist with amazing precision. While these advances can improve operating efficiency and add value to the product, fabricators still may feel daunted sitting at the concept stage of a storage system. To To bring together all the variables and options op tions available requires input from many areas of expertise. Here is a quick rundown of what needs to be considered. First In, First Out New racking systems go far beyond simply stacking products. One of the objectives of these new racking system designs is to eliminate or reduce the aisles as much as possible. Flow-through systems are designed under the concept of o f turning over inventory by making sure the older materials are used first. These systems (carton flow and pallet flow) allow maximum floor density and permit the materials to be where fabricators want them when they want them, always ready for transfer to the shipping dock or production, however it may be required. First In, First Out (FIFO) is a form of flow-through system using a dynamic storage technique that allows the product to flow through the rack via gravity g ravity rollers, accumulating in an organized manner ready for the next step. These rollers are angled strategically at a pitch that permits the product to move forward. The speed is controlled
SOCIETY4PAKSWISSIANS by brakes acting on the rollers that prevent the loads from accelerating beyond be yond the design speed. Automated Handling Trucks Standard rack systems are complemented by a variety of material handling trucks that can be fully automated and attached to the racking. These are programmable logic-controlled and can be programmed to operate around the clock. Of course, the price tag and maintenance cost may scare a manager, but if the system has been properly applied, manufactured, and installed with the required precision and the proper scheduled maintenance, it can be a highly productive asset, depending on the fabricating system. Narrow-aisle Fork Trucks On the other hand, fork trucks exist that operate in narrow aisles only 54 inches inch es wide, producing an increase of usable u sable floor and air space that has a major impact in maximizing overall warehousing efficiency. efficiency. These trucks have a side-loading feature that eliminates the need for the vehicles ve hicles to turn to get the product out of its storage area. The conventional 12-foot aisle is fast becoming a convention of the past. Automated Storage and Retrieval Automated storage and retrieval systems (ASRSs) often are used to store smaller and frequently inventoried and retrieved parts. This type of system is self-contained and uses a series of traveling shelves or bins, usually traveling in a vertical configuration. When parts are required, the individual identifies the part to the programmable logic controller, which in turn looks for the piece at a specific location and presents the requested item at the location of input. In addition to high speed and enhanced storage density, density, security is increased because the machine forces the operator to sign on to the system, logging the operator’s op erator’s identity. identity. The system also tracks and identifies inventory items on its shelves. A similar storage storage system that rotates products in a horizontal configuration is commonly co mmonly known as a carousel system. s ystem. It uses more floor space but can be less expensive. expen sive. Conveyors Standard storage systems can be enhanced with the addition of a conveyor, which can be gravity operated or motorized. Personal computers can be used to direct products to the specific destination(s) as required. Like a modern highway highwa y with intersections, materials are diverted to predetermined areas.
SOCIETY4PAKSWISSIANS The conveyor even can be configured to become bec ome part of a truck trailer. The addition of special racks for multilevel storage allows full use of the cargo area inside the trailer. Loading and unloading become much less labor intensive. The logistics for this type t ype of setup require precision in terms of weight and size. Variables Variables must be reduced to make the system most effective. To To maximize space and reduce the overall handling requirements, fabricators need to load parts or materials into properly sized bins and containers. Planning the inventory system and proper product flow is necessary to ensure the best storage solution. Investment in the proper development of facilities and equipment using all modern advances will pay pa y back handsomely in terms of labor, time, and money.
Organizing your tooling To computerize or not to computerize—that is the question By Craig Padget August 8, 2007
Are you busy putting out fires? Is management by crisis preventing you from being proactive and establishing a preventive maintenance system for your tooling? Does your tooling gather more dust than uptime? Do you think you know your tooling needs, or do you collect data that shows your tooling needs? You could divide the fabrication world into two types of shop: those that have a preventive maintenance (PM) program, and those that don't. If you have worked in enough shops that practice PM, you likely know that establishing a good PM system is worth its weight in gold in the form of uptime. A good PM system starts with your inventory and is a matter of computerization co mputerization and discipline.
SOCIETY4PAKSWISSIANS The biggest step usually is getting started. Excuses for not getting started are just that, excuses, and it is better to move forward than to sit still. Wit Withh this in mind, understand that the system can be simple and stand-alone or it can be very v ery detailed and integrated.
Getting Started Computerized inventory is a must to support any an y fabrication plant. The first step in setting up a computerized tool inventory system is building an information database. The database must include critical information: • • • • • • • • •
Part number (the end user's part number) Die number Detail number (the number of the detail d etail of the tool listed with-in a die) Type Description (the tool's nomenclature) Order point quantity Order quantity Cost Delivery (estimated delivery time)
You might want to incorporate additional fields, but these are minimum requirements for the task.
Click to view image larger
Using a punch numbering system that describes and identifies each punch can be a good strategy in organizing your tooling. The key to setting up a successful system is including enough information to make the system useful but not so much detail that it becomes be comes overwhelming. Die Listing or Item Listing? Many tooling organization schemes exist. One common co mmon scheme organizes the tooling by each die tool. Another organizes the tooling by tool
SOCIETY4PAKSWISSIANS description. The most cost-effective plan uses the tool description because it prevents duplication of common tools, which happens when organizing tools by die system. Many fear the tool description system because they like to have backup tooling in other places. The problem is the backup tooling is generally unknown—that is, you're not really sure if you have it and where it is. Quite a bit of valuable time is spent, under urgent conditions, looking for tooling. In most cases, it's nonexistent. Not using the tool description system also can be an excuse exc use for not having better discipline. Organizing the tooling by die system can work, but usually such a system isn't detailed enough to cover all the bases and is much more expensive if it does. Keeping it simple will be rewarding too. Let's look at a plan organized by b y item description. The reason for the required data listed previously is to offer o ffer the filtered separation by die for reporting purposes. It also identifies common items utilized in several dies to support the required inventory levels, as well as obsolete inventory as dies are discontinued or transferred to other facilities. Dedicated tooling then can follow the same path. Identifying Individual Tools. Tools. The next step is identifying the individual tools. Once again, fabricators use many systems and descriptions. Dedicated descriptions that can be utilized regardless of the tooling brand provide clarity. Before creating a numbering scheme, you should familiarize yourself with your software's capabilities and limitations. Can it distinguish a hyphen from an underscore? If it cannot, c annot, the software will identify similar tool numbers (for example, Ball Lock Punch 500-S300 M2 P.258 and Ball Lock Punch500s300 M2 P.258) as two unique items, even though it's the same tool. It's a matter of devising a system and adhering to it—again, discipline is the key. key. Many Uses for Individual Tools. The final stage of computerization c omputerization is using the database. Through the catalog of built inventory you can offer the inventory to new die build groups in your company c ompany.. A specification specification can require that tooling currently inventoried be be preferred. You and your colleagues have the opportunity to build and use a library of tooling. This library can be used to drop CAD data directly into a drawing to reduce reduc e design time as well. You You will also gain a proper format for the nomenclature to be used as a description in the database function of inventory. This is the information that can then be shared with die builders. The result is fewer inventory items and larger purchase quantities of items that have volume discounts for further cost reduction opportunities.
How to select the right IRONWORKER for your application
SOCIETY4PAKSWISSIANS
Consider its capacity, versatility, versatility, safety features, and quality By Jim Hoag, Contributing Writer Writer January 16, 2003 An ironworker can be an a n important and versatile machine in a metal fabricating shop. Quite often ironworking is the first step in the manufacturing process, and one ironworker typically can provide enough fabricated material to keep up to seven welders or assemblers busy. Since its invention in the late 1800s, the ironworker's main strength has been its ability to perform a variety of operations. It can punch a range of materials with punches of various sizes and shapes. It also can shear rod, flat bar, angle, and channel. In addition, it can notch angle iron, pipe, channel, and flat bar. Many ironworkers are available with special tooling to bend, stamp, and form too. As versatile as the ironworker is, however, it is possible to purchase the wrong machine —or at least not the best machine—for your application. Important considerations for selecting a machine include its capacity, capacity, versatility, versatility, safety features, and quality. The material thickness you process will indicate whether to use an ironworker or a turret punch press. An ironworker punches plate up to 1 inch, and sometimes even thicker. Typically Typically,, turret punch presses are used on sheet material 1/4 in. and thinner. Ironworkers usually are used for shorter production runs and applications for which tolerances are not as critical. Determining Capacity Ironworkers typically are rated by b y tonnage at the punch station. A 40-ton ironworker should punch a 1-in. hole in 1/2-in. material; a 60-ton machine should punch a 1-in. hole in 3/4-in. material; and an 80-ton machine should punch a 1-in. hole in 1-in. material (see Figure 1). The first step, therefore, is to determine the maximum material thickness so you can Figure 1
SOCIETY4PAKSWISSIANS establish the tonnage range needed for your punching application. Examine the steel rack and the product that you are fabricating. Determine the maximum hole diameter to be punched; the maximum thickness of the material to be punched; and the maximum thickness and width of the channel, angle, and rod to be sheared or bent. The material or part width plays a part in your ironworker selection. The throat depth of an ironworker punch station should be b e greater than half of the part p art or material width. Material length, however, really is not an issue. An ironworker can process almost any material or part length. Because many different types of steel and ranges of hardness in mild steel exist, it is advisable to get a machine that is at least 20 percent larger than you think your everyday use requires to avoid getting a machine that is too small. Most machines are rated for material with tensile strengths between 60,000 and 65,000 pounds. Many mild steels have tensile strengths between 50,000 and 70,000 lbs. or higher, and your machine may not have the power to punch the material at the higher end of the hardness values. When punching hard steel, such as stainless steel, it is better to increase the estimated tonnage by 50 to 100 percent, depending on the grade of steel. Beware! Not all tons are created equal. e qual. A metric ton actually is heavier than a U.S. ton (2,200 lbs. versus 2,000 lbs.). A machine rated for metric tons should be able to punch a larger hole than a machine rated on the same number of U.S. tons. For example, 80 tons of pressure by U.S. standards can punch a 1-in. hole through 1-in. material; 80 metric tons should be able to punch a 13/32-in. hole through the same material thickness. Be sure to compare the rating of the machine not only on ly in tons, but also the diameter of the hole and thickness of material it can punch. Ironworker tonnage ratings can vary from ironworker to ironworker. ironworker. Assessing Versatility Needs All ironworkers are equipped with flat bar shears. The main differences between flat bar shear stations are the length and the approach of the blade to the metal. Some ironworkers use a guillotine, or fixed-rake-angle shear, and others use a scissors-type shear (see Figure 2).
SOCIETY4PAKSWISSIANS The advantage of the fixedrake-angle shear is that the angle of the blade as it approaches the work remains constant throughout the cut, sometimes offering larger capacity without increasing machine tonnage. The disadvantage is that without the ability to vary the rake angle, the distortion of the drop piece will remain the same throughout the cut.
Figure 2
The advantage of the fixed-rake-angle shear is that the blade angle remains constant throughout the cut, sometimes offering larger capacity without increasing The advantage of a scissorsmachine tonnage. The advantage of the scissors-type type shear is that it can vary shear is that it can vary the rake angle of the blade, the rake angle of the blade. thereby minimizing distortion. Thicker material is cut closer to the pivot point, and thinner material is cut farther from the pivot point, where the rake angle of the blade is flatter, thereby minimizing distortion. Scissors machines typically have a longer flat bar shear, some up to 24 in. long. On some ironworkers, the rake angle of the bar shear blade is adjusted by inserting and removing wedge-shaped shims above the shear blade. This may require substantial mechanical ability and substantial time. Also, if the shims are not adjusted each time material thickness changes, the machine could be damaged. Ironworkers are available with different designs to enhance versatility. versatility. For example, the stations on some machines are permanently built in. These machines mach ines offer punching stations, angle shears, rod shears, notchers, and short flat bar shears. If you are a structural steel fabricator, you may prefer these machines because the stations cover the majority of the materials you process and do not require tooling changes. If you are a general welding, fabrication, maintenance, and structural steel fabricator who does not know what a customer will bring in the door tomorrow, you may want an ironworker that offers the capability to adapt to all customer needs. Tabletop tooling concepts, which provide a wider variety of tooling, may suit your needs.
In addition to angle shears, rod shears, notchers, and flat bar shears, tabletop ironworkers offer options such as larger press brake bending attachments, tube shears, channel ch annel shears, pipe notchers, V notchers, picket tools, square tube shears, and a variety of special tooling. Although these machines can use a larger variety of tooling than those with builtin stations, time is required to switch from one operation to the next. Addressing Safety Issues
SOCIETY4PAKSWISSIANS Safety is an important factor when choosing an ironworker. ironworker. Be sure to choose an ironworker that meets ANSI B 11-5 standards. Examine the guarding. Be sure it can be adjusted down to within 1/4 in. from the top of the material to be punched, punche d, and to the bottom of the guard or stripper (this is an ANSI standard). This will prevent operators from placing any part of their bodies between b etween the material being punched and the stripping mechanism. All other stations should offer complete safeguarding as well. Beware of machines with automatic urethane hold-downs. Most operators realize the danger of the blade but do not expect to be hurt by safety guards and may not watch them. Automatic urethane hold-downs, if not adjusted properly, properly, also come down with many tons of force and can be dangerous pinch points. For productivity as well as safety, safety, the machine you choose ch oose should offer an infinitely adjustable stroke control to minimize machine movement, decrease the number of pinch points, and increase strokes per minute and production. This is especially important in bending applications and for special tooling for which the upstroke must be adjusted a djusted in addition to the downstroke. Electric stroke controls offer advantages over mechanical linkage controls. Electric stroke controls have quicker cycle times and more precise stopping because they use switches that send signals to the control valve almost instantly. instantly. Machines that use mechanical mechan ical linkage stroke controls must be in motion to cause the linkage to close the control valve. As the valve closes, the machine slows down and is more difficult to regulate. Safety instructions should include proper alignment of the punch and dies. Because punches are usually hardened to 58 Rockwell, the punch will not bend as it collides with a die. If it is out of alignment, it is more likely to flake or even explode, causing serious harm to the operator. operator. The preferred and most widely used method of aligning the punch and die is similar to the way punch presses have been aligned for many years. This is done by b y bringing the punch ram to the bottom of the stroke and installing the punch and dies with the stroke down. This way, the punch already has been entered into the die, the alignment can be checked, and guards may be replaced without machine movement. Assessing Quality In trying to determine quality, quality, consider the size of the pivot points and beam strength of the steel that is under pressure. Since your ironworker produces produ ces many tons of force, the force must be generated and transferred through the pivot points as well as the beam. b eam. Another good indicator of quality is how much shock is produced when the ironworker punches. Excess shock, which can be identified by a loud popping or banging noise as the punch goes through the material, could indicate the beam or o r side frame is stretching and
SOCIETY4PAKSWISSIANS snapping back into place. Continued shock can cause welds to break, as well as other failures. Higher-quality machines control this by increasing side frame, beam, and pin size. The number of grease points p oints also can be an indicator of o f quality. quality. Although all machines have grease points on pivot points and guide assemblies, some machines have an excessive number of grease points—as many as 20 or more. Usually these additional grease points have been added in an effort to correct galling problems. It is unrealistic to expect operators to grease more than five or 10 grease points, and machine failure or galling most likely will occur occu r. The hydraulic system also should be a consideration. c onsideration. You You are buying the machine for the tons of pressure it produces, not for the motor's horsepower rating. Some ironworkers are designed through mechanical advantages adv antages to produce more tonnage with less horsepower, thus making the machine more efficient. Machines with higher-horsepower motors usually operate at a higher hydraulic h ydraulic pressure, or pounds per square inch, and this increased pressure can produce more wear on hoses, pumps, and valves. Because an ironworker is an important part of most shops, when even one ironworker breaks down, the negative impact on production is significant, even paralyzing. Before purchasing an ironworker, take the time to analyze your needs nee ds and carefully assess the quality of the ironworker. It will be time well spent. Jim Hoag is marketing director for Scotchman® Industries, 180 E. Highway 14, Philip, SD 57567, phone 605-859-2542, fax 605-859-2499, e-mail
[email protected] [email protected] , Web site www.scotchman.com www.scotchman.com.. Scotchman Industries designs and manufactures ironworkers and saws for metal fabricators, machine shops, and technical schools.
Getting more punch life Alternate tooling alloy and coating reduce friction, heat buildup July 13, 2004 Augur Metal Products, a custom fabricator in Independence Ken., performs a variety of processes for manufacturers. While the company’s capabilities include shearing, cutting, forming, welding, and finishing, chief among them is sheet metal punching.
SOCIETY4PAKSWISSIANS One of its processes involves punching 750 75 0 small holes in 33-inch by 36-inch 10-gauge stainless steel sheet panels used in the manufacture of o f large commercial separators. Because stainless steel is hard and abrasive, it heats up and puts stress on both the tooling and the punch press. With With its previous tooling, the company was limited to punching pu nching just 10 to 15 panels before tool maintenance and sharpening were required. Stopping the line to sharpen punches often caused production bottlenecks. On a different operation for perforating compressor panels, two 0.750-in. round punches punch es were installed side by side in a turret so that when one tool became dull, the turret could be indexed to the next punch to continue punching without stopping the machine. When both the punches became dull, the machine had to be stopped and the punches removed for sharpening, at times disrupting part flow through the cell of five presses. “Our punch press operators do a great job of maintaining constant work flow through our press department,” said Joe Shotwell, senior purchasing buyer bu yer.. “Premature tooling wear in the middle of a part run is disruptive. Our part runs vary and we punch a lot of different materials and thicknesses, everything from aluminum and mild steel to stainless steel. So continuous work flow minimizing press downtime for tool maintenance is a challenge we take seriously and try to improve on because it influences our quality and productivity.” Getting Longer Life From Tougher Tougher Punches
Figure 1
Augur Metal Products punches hundreds of holes in stainless steel sheets for commercial separators. Holding a punched panel is Joe Shotwell (left), senior purchasing buyer, and Pat Walker (right), press operator.
The company performed a trial run using Mate Precision Tooling’s Tooling’s Strippit punches made of DuraSteel™ in an existing guide assembly to see if it could improve the hit count. “We “We didn’t have to touch the Mate punch until well after perforating 40 of the 10-gauge stainless steel panels,” said press operator Pat Walker. Walker. “All 40 of the panels had between 650 and 750 holes punched in them. The holes h oles are cleaner with less burr on them. And we’re getting three to four times the tool life with the new Mate punches.” “Stainless is very abrasive to punch, creating a high degree of friction and heat in the punch when it penetrates pene trates the material,” explained Tim Kraus, Mate sales representative. “Stainless dulls ordinary tools very quickly, especially at higher press speeds. Even if you slow the machine down, the abrasive effect continues and wears out the tool prematurely. prematurely. You lose productivity two ways—with lower press speed and by having to maintain the tooling frequently.” frequently.”
SOCIETY4PAKSWISSIANS The new punches resist the abrasive effects of the stainless material and reduce heat buildup in the punch. In addition to the DuraSteel punches, a special tool coating called Maxima™ was used to coat the punch. The coating bonds with the substrate and adds both durability and lubricity. lubricity. Punch Anatomy In addition to the DuraSteel punch and Maxima coating, the tools design affects productivity. productivity. For example, punch points are machined with a 1/4-degree back taper to reduce friction during the stripping phase of the punching cycle, which further extends tool life. Also, slug pulling is a longtime problem in the punching process, and thus the use of a special die design to counter this foe is useful. During punching the slug can pull back out of the die and then interfere with the next punching cycle. This is generically called slug pulling. Mate’s Slug Free® die is designed with a slight hourglass shape that causes a pressure point that acts like a one-way door to keep the slug from pulling back out of the die. Once the slug is squeezed through the pressure point, it is free to fall down the slug chute as it should and away from where it could cause problems. Using the new punches, Augur says it was able to increase press speed by 20 percent. Shotwell added that switching to the new ne w Mate tooling actually cost 10 percent less than the old tooling. “When you add up the longer tool life, increased press output, and less downtime for tool sharpening, you’ve really improved overall ove rall productivity and profitability on that job.”
Is metal roofing fabrication right for your shop? How to ensure your roll forming operation is a good fit By Paul Williams April 10, 2007
SOCIETY4PAKSWISSIANS When deciding wheher or not to produce roofing panels, you need to determine your ROI, based on if you can use existing equipment or need new equipment, the required panel appearance; possible line configuration; and material handling options.
In recent years the metal building industries have grown substantially. substantially. According to the Metal Roofing Alliance, the residential metal roofing market doubled its market share from 3 percent to 6 percent in five years. To To take advantage of this growth, more fabricators are increasing the versatility of their manufacturing capabilities by adding to or expanding the metal building products p roducts they offer. offer. Besides the more commonly produced metal studs, fabricators have been adding metal roofing and accessories to their current product lineups. The roofing panels come in many different types, with the more common ones being R, A, AG, corrugated, standing seam, and roof decks (see Figures 1, 2, and 3).
Figure 1,2,3
Roofing panels come in many different types, with the more commone ones being R (left)A,AG,corrugated (center),standing seam, and roof decking (right).
Existing or New Equipment? When deciding whether or not to produce these panels either as an expanded line or a new product, you must decide if your return on investment (ROI) makes sense for your business model. The rule of thumb is if you must run at least 500,000 linear feet of sheet metal to justify purchasing a new, new, complete roll forming line. If you have an existing roll forming line and are planning to run fewer than 500,000 linear feet of sheet metal, you must calculate the current capacity of your line to see if the new components can be run on it. You You might be able to retool your existing line, which can be a big cost savings.
SOCIETY4PAKSWISSIANS Of course, the type of product you are going to run and its requirements (number of passes, horizontal spacing, roll space, and so on) will dictate whether you can run it on existing equipment. Your Your tooling vendors should be able to help you with this determination. If you do not have an existing roll forming line or have insufficient capacity on your current equipment, you will need to purchase a new, complete line. New lines come in many configurations; some are high-speed, in-plant machines while others are less capital-intensive feed-to-stop and portable units for smaller footage requirements. The portable machines usually are entry-level, with capacities limited to the smaller footage requirements of on-site fabrication.
Panel Appearance Roof and wall panels are highly visible "appearance" components. Most are fabricated from prepainted coil, so care must be taken to avoid damaging the coil's coating during the roll forming process (see lead image). This is achieved by having enough roll tooling passes and by chromed roll tooling. In addition, roll forming can contribute to oil canning, which is the waviness in the flat areas of roofing and siding panels. pan els. Generally, Generally, the period and amplitude of the wave depend on the continuous width of the flat, so that must be monitored closely. closely. The panels need to be straight, especially on the sides of standing seam panels, so that they can be joined. Therefore, flare must be minimized. R, A, AG, and other panels run on wide roll formers (44- to 48-inch-wide roll space mills) that produce a panel with 36-in.-wide coverage. The most common standing seam panel widths are 12 and 18 in., and there is no center forming. To To change widths quickly, you can produce standing seam panels on a duplex-style mill. The panels also can be run on conventional, raft-style roll formers. Portable mills have made big inroads in this market, because contractors can produce panels on-site, oil canning and all, and put them right on the roof.
Line Configurations Panel roll forming lines can be configured con figured in a couple of different ways. One is a start-stop line. The material starts moving by ramping up to speed and then decelerates and stops when it is time to cut. This type of line typically is inexpensive overall, because you do not have to fly the cutoff die. However, since the line has to stop, total throughput is limited. The line might run at a top speed of 100 feet per minute, but the average line speed for the day might be only 60 FPM. A continuous roll forming line runs constantly con stantly.. However, the overall cost c ost usually is higher than on a start-stop line, because you must add a flying cutoff configuration.
SOCIETY4PAKSWISSIANS With either of these configurations, you can add a precut/shear die or a postcut die (see Figure 4). Most new panel lines have a precut die. Precut dies use a common stationary or flying cutoff set for the maximum width, which provides versatility. Even a common stacker can be applied. You can change part widths (such as from 36-in. to 24-in. coverage) with a simple stock guide adjustment and coil change and no die changeout.
Figure 4
Most new panel lines have a precut shear die (top), which use a common stationary or flying cutoff set for the maximum width. Typically Typically,, you will get a better overall profile with a postcut die (bottom) because you eliminate some of the additional flare that can occur during precutting. Depending on the panel type, a postcut die might require a die insert changeout or complete die changeover. Depending on the panel type, a postcut die might require a die insert changeout or complete die changeover. When running precut products, you need to be careful not to add flare on the ingoing and outgoing ends of the material—a common occurrence on precut lines. With a postcut die, you will typically get a better overall profile because you eliminate some of the additional flare that can occur during precutting. Also, depending on the panel profile and the roll tooling design, you might be able to use a common cutoff die by simply changing the material strip width. For uncommon shapes, a cutting blade or entire die changeover might be required. Roll tooling change is an issue because the sets have a lot of rolls. Rafting, double-wide roll formers, two-part roll formers, and machines with combination tool sets can help minimize the machine downtime. However, making the roll forming system more complex to decrease downtime usually increases the overall machine cost.
Material Handling Options To further customize your line, you can add different material handling options at the feeding end. There are more options o ptions than a typical uncoiler (in a continuous-feed con tinuous-feed line) or hand-feeding sheets (in a precut line). You can use coil cars, coil upenders, turnstiles, and stacking systems to help decrease changeover time. Quick coil change is important, because the faster you can feed new materials and different colors of coils into the roll forming line, the more panels you can run overall.
SOCIETY4PAKSWISSIANS The most common choice for the exit end of a panel roll forming mill has been a drop stacker. Another option is a magnetic stacker. While it costs more, it involves less maintenance. Additional building products that can be roll formed on dedicated machines are soffits, fascia, gutter guards, and drip edges. Most of these lend themselves to being produced on precut or postcut roll forming lines, with the same benefits b enefits and limitations as panel manufacturing. For an in-depth analysis of metal roofing panels for your specific application, it's best to contact a roll forming equipment manufacturer.
Worn out roll forming tooling and no drawings? Reverse-engineer it By Steve Ebel and River City Roll Form Inc., Contributing Con tributing Writer March 25, 2004 You may have found yourself saying, "I need to make an engineering change to my roll form tooling, but I don't have the roll tooling designs or drawings." Maybe you have a product change; or the tooling is worn out, chipped, or broken; or your company just needs to improve the tooling. When you are faced with this situation, you have to start at the beginning, basically, and reverse-engineer the complete set of roll form tooling. Recut or Replace Tooling? Depending on a couple of factors, the roll form tooling may be recut and dropped, or decreased, in diameter to eliminate wear. The first consideration is the vertical range of your roll form equipment. The vertical range (centers) is the distance between the top spindle and the bottom spindle, and a nd on most machines it is adjustable (see Figure 1). A large vertical range allows for recutting of the roll, but a very small vertical range does not allow for diameter changes, which means the roll tooling must be replaced when it becomes worn.
SOCIETY4PAKSWISSIANS The second consideration is spindle wear. If the roll form tooling has been run without keys in it, the bores of the roll tooling may be worn more than the specifications allow, allow, which means the bores must be replaced or reconditioned. (Keys are the square pieces of cold-rolled steel that are inserted into the keyways of the roll tooling and the spindles to prevent the roll tooling from spinning on the spindles.) If the bores are overworn because they were allowed to spin on the spindle of the roll former, they will have to be ground, then hard-chromed, and ground again to achieve the precision fit required between the bore on the roll tooling and the spindles on the roll former. You need to gather as much information about your roll form tooling and equipment as possible before you can get started. Measure and record: • • • •
Horizontal centers. Vertical centers (minimum and maximum). Spindle diameter (keyway size). Roll space (base to centerline of bottom spindle).
Tooling Material
Figure 1
Measurements must be taken at the vertical centers, horizontal centers, spindle diameter, amd roll space.
It is important to know what steel grade the roll form tooling was made of originally. originally. In the past many man y sets of roll form tooling were made out of tool steels that would case-harden only when heattreated, meaning that the hardened surface was only about 1¼32 inch deep. Roll form tooling constructed this way cannot be recut; it has to be replaced. If the roll form tooling is made out of tool steel that can be through-hardened, the chances of being able to recut it are better. Tooling Construction
Figure 2
Itâ??s also important to know how your current cu rrent roll form tooling is Split contruction is built. Many times roll form tooling is built in a way that allows it to better-suited for recutting than one be recut easily ea sily.. A roll roll tooling set that is built with many splits or piece construction. individual pieces is better-suited for recutting than a set that has a one-piece roll construction (see Figure 2). One-piece roll construction does not allow for easy changes, and if a change or wear in the roll form tooling is extensive, replacement is required. Product Drawing
SOCIETY4PAKSWISSIANS The roll designer reviews the product drawing d rawing and final profile to generate the new roll form tooling drawing. Once the designer has this information, he can determine the practicality of changing the roll form tooling. At this point the roll form tooling has to be shadow-graphed and measured (see introductory photo ). Each pass and each roll must be put into an optical comparator that projects an image scaled 10 times the original size onto a screen. This image has to be traced by hand to examine the current condition of the roll form tooling and compared to the product drawing. Typically Typically this can be done in about a week, depending depend ing on the size of the roll form tooling and the number of forming passes. Companies that offer this service can work with the customer to minimize the amount of lost production produc tion time by doing a few passes of roll form tooling at a time. After the shadow-graph tracing is complete, the roll diameter, roll width, angles, and bore size have to be measured and recorded. This information is used in conjunction with the tracing to Figure 3
develop the CAD files for each roll and forming pass. At this point the roll designer also looks at the tracing to determine the amount of wear and how much the roll diameters have to be decreased to eliminate the wear or chips in the roll form tooling. If some of the rolls are worn more than the others, the de designer signer may elect to replace a few rolls rather than recut the entire set. Once all this information is collected and the decision is made to recut or replace the roll form tooling, the designer uses CAD to draw the roll form tooling flower (see Figure 3). After the flower pattern is determined, the roll designer inputs the data from the tracings and the measurements into the CAD system to produce the roll form tooling design. The math Figure 4 The CAD drawings that are developed must show data generated will be used in the CNC turning measurements, specs, and details for each pass. pa ss. centers to recut or make new rolls as needed (see Figure 4).
SOCIETY4PAKSWISSIANS If the roll former has additional stations, usually extra passes can be added at strategic spots that can help reduce wear, improve part quality, quality, or reduce production problems. For example, if a lot of forming is being done between passes 5 and 6, an extra pass can be added between these passes to help slow down the forming. These types of ideas can help improve production issues and part quality. quality. Auxiliary Tooling Tooling or o r Fixtures If you have added side roll stands, supports, or straighteners to work in conjunction with the roll form tooling, the roll designer needs to have as much information about abou t them as possible so they can be made to fit if any changes or replacements are needed. Obviously, a lot of time and effort go into reverse-engineering a set of roll form tooling and reproducing the design. However, once the design is complete, performing an engineering change, replacing or recutting damaged tooling, or duplicating a set of tooling will be easier the next time.
Die Basics 101: Part XVI By Art Hedrick, Contributing Writer October 9, 2007 This article continues the discussion of bending in stamping operations. It focuses on rotary and reverse U bending and addresses the advantages and disadvantages of rotary bending. Descriptions of and links to the first 15 parts in this series can be found at the end of this article. Part XV of this series about stamping die fundamentals described several bending bend ing methods—wipe, coin relief, pivot, and V bending. It also discussed d iscussed springback and how to compensate for it when using these methods. This article focuses on other bending processes. Keep in mind that the key to success is to design the bending ben ding process so that it can be easily, easily, quickly, and safely adjusted to allow for material variables.
Rotary Bending Rotary bending perhaps is one of the most popular and effective ways of creating a precision bend. Rotary benders, also known commercially as Ready Benders® or AccuBend™ benders, have many advantages over conventional wipe bending methods. First, let's examine how they work. Rotary or rocker benders consist of a foundation found ation block, often referred to as the saddle. The saddle has ha s a spring-loaded V-shape V-shape component called the rocker. This rocker rotates
SOCIETY4PAKSWISSIANS about its centerline and performs the bending action. It acts as both a holding pad and the bending mechanism. Although this type of bender can be installed in almost any direction with respect to the ram travel, it most commonly is fastened to the upper die shoe. As the bender moves down, the rocker makes contact with the sheet metal. One contact point acts as a holding pad, while the opposite contact con tact point rotates, creating the bending action. a ction. After After the bend is completed and on the press's return stroke, the spring forces the rocker to return back to its original or idle position (Figure 1).
Figure 1
Rotary bending has some advantages over other methods. The most advantageous feature is the simplicity of adjustment. Changes in the bend angle can be made simply by shimming or grinding the height of o f the assembly. assembly. Doing so takes very little time, and time is money. Advantages.
Rotary benders can bend as much as 120 degrees and are well-suited to bending highstrength material. One company in Sweden has ha s successfully created two 90-degree return bends in steel with yield strength of 980 mega pascals. This translates into steel that by U.S. standards has a yield strength of more than 142,000 pounds per square inch (PSI)— five times stronger than low-carbon steel. Attempting to make such a bend in a conventional wipe-bending operation most certainly would be impossible. Another advantage is that, unlike conventional wipe bending, rotary benders require much lower forces to create the bend. Anywhere from a 40 percent to 80 percent reduction in force can be expected. This makes this method ideal for producing long, heavy-gauge, large parts, such as truck and semi frame rails.
SOCIETY4PAKSWISSIANS You can expect less hole distortion in rotary bending. Consider a hole that is pierced p ierced in a flat blank and later bent into a vertical wall. During conventional bending, this hole can be subjected to a great deal of tension, which causes the hole to distort. Because rocker benders fold the metal around the punch, hole distortion is eliminated (Figure 2).
Figure 2
Inserting rockers with a special hard plastic called Delrin® can ca n make them nonmarking, which is desirable when bending cosmetic-quality stainless steel or prepainted materials. Rotary benders can used to bend up or down. They also can be placed on cam slides. Despite the many advantages, rotary benders do have some disadvantages. First, they can be quite expensive; however, consider the advantages of the reduction in downtime and frustration. Overall, they often pay for themselves in a short period of time. Disadvantages.
SOCIETY4PAKSWISSIANS Figure 3
Poor Candidate for Rotary Bending
Also consider that you most likely will not need an a n external pad, which reduces die cost. Often the true cost of designing and building a conventional wipe bending die is much greater than the rocker bender. Don't confuse cost with value. In my opinion, rotary benders are worth every penny. Because these benders have moving parts, there is a risk of galling up and failing to rotate. This can be prevented by b y periodically cleaning and lubricating them. Remember that rotary benders bende rs can be used for straight-line bending only. only. Avoid Avoid using them to bend special-shaped trim lines that do not allow for simultaneous punch contact. con tact. Angled corners are not good candidates for rocker benders (Figure 3). Overall, I highly recommend using rotary benders for appropriate applications. a pplications. They are available commercially from a few reputable suppliers.
Reverse U Bending Reverse U bending is a unique but effective way of obtaining either a 90-degree bend or a bend with a slight negative angle. This process utilizes a high-pressure pad with an insert that can be adjusted in height by shimming or grinding it. The insert causes the part to bow upward in the center of the punch where a void has been created. Raising or lowering the insert changes the severity of the bow. Keep in mind that this bow must be created with the pressure exerted by b y the pad. This often requires the use of high-pressure gas springs. After the bow has been created, the pad moves downward and the bends are established. Upon punch removal, the part has a tendency to spring back in the center, which causes the bends to "toe in." This method works well with materials that exhibit a great deal of springback. If the metal permanently deforms in the center bowed area, it may be necessary to push the part back flat in order to achieve a 90-degree angle (Figure 4).
SOCIETY4PAKSWISSIANS Figure 4
Reverse U Bending Process Remember that the true key to bending success is to design the tool in such a fashion that it can be quickly, quickly, safely, safely, and accurately adjusted with respect to ever-changing incoming variables. Avoid Avoid using the grinding and welding process whenever possible.
Die Basics 101: Part XIV By Art Hedrick, Contributing Writer June 12, 2007 Fineblanking and GRIPflow® are cold metal extrusion processes used to produce what appear to be blanked parts. These processes are alternatives to casting, forging, and machining. This article explains these processes. Descriptions of and links to the first 13 parts in this series can be found at the end of this article. Although fineblanking and GRIPflow® often are categorized as metal cutting operations, they more closely resemble a cold metal extrusion process that tha t creates what appears to be a blanked part. The processes can be defined simply as methods in which a part is squeezed from the strip.
Figure 1
Results of Conventional Cutting Unlike parts made with conventional metal cutting methods, the parts made using fineblanking and GRIPflow have little or no fracture zone (Figure 1). In other words, these parts appear to have smooth, square machined edges.
These processes also can produce parts with very close flatness and dimensional tolerances and roughness of about 2 to 3 µm, which means that, in many cases, postprocessing operations such as grinding and milling can be eliminated.
SOCIETY4PAKSWISSIANS Parts commonly made using fineblanking and GRIPflow include gears g ears and parts that require close flatness tolerances or a square cut edge. These processes also can pierce holes with diameters as small as one-third of the metal's thickness and very close to the part's edge. Before these methods were available, the metal had to be shaved in one or several shaving operations to achieve a smooth cut edge. Shaving in a die often produces slivers and debris that can create tool problems and product defects.
Fineblanking Invented in Switzerland in the 1920s, fineblanking, unlike conventional stamping methods, utilizes a special triple-action hydraulic press called a fineblanking press. Fineblanking requires the use of extreme-pressure pads. These high-pressure pads hold the metal flat during the cutting process and an d keep the metal from plastically p lastically deforming during punch entry. entry. In fineblanking presses, a V-ring is incorporated into one o ne of the high-pressure pads. This V-ring also is commonly referred to as a stinger or impingement ring. Before the punch contacts con tacts the part, the V-ring V-ring impales the metal. It surrounds the part perimeter and functions both to trap the metal from moving outward and push p ush the metal inward toward the punch. This action reduces reduc es the rollover that occurs at the part's p art's cut edge. Using high-pressure pads combined with the stinger ring and close clearances keeps the metal from fracturing and creates a smooth edge (Figure 2). Because the part is held extremely tight between the high-pressure pads during cutting, part distortion is minimal.
Figure 2
Fineblanking Process
SOCIETY4PAKSWISSIANS Unlike conventional cutting operations that use approximately 10 percent of the metal's thickness for the cutting clearance, fineblanking operations usually use clearances less than 0.0005 in. per p er side. This small-clearance requirement combined with high pressure also contributes to the fully sheared part edge. Once again, don't confuse fineblanking with a cutting operation. It's not a cutting operation at all; it is more like a cold extruding process. The slug (part) is pushed or extruded from strip held so tightly between high-pressure holding plates and a nd pads that the metal cannot bulge or plastically p lastically deform during the process. These high-pressure pads fit precisely around all cutting components. Fineblanking can be used to produce parts as thick as 0.5 in. from a variety of metals.
GRIPflow Not to be confused with fineblanking, the GRIPflow process does not use a stinger or impingement ring to stop outward metal movement move ment but relies solely on hydraulically applied pressure to the blank. The pressure is applied through precision-guided pressure pads.
Figure 3
GRIPflow Part Source: Ebway Corp. Think of the GRIPflow process as similar to compound blanking. However, unlike a compound blanking operation, GRIPflow uses very small cutting clearances between each of the cutting components. This small clearance, combined with high blank holding pressures and precision clearances between all moving components, produces a smoothedged part that can be held to very tight dimensional tolerances (Figure 3). Once again, keep in mind that GRIPflow is not a metal cutting process but a cold extruding process. The cutting sections do not have ha ve cutting shear ground on them. It is difficult to tell the difference between a part that was fineblanked and one made using the GRIPflow process just by looking at them. Unlike fineblanking, GRIPflow does
SOCIETY4PAKSWISSIANS not require a triple-action press. Because it uses hydraulic cylinders mounted in the die, the process is best-suited to a hydraulic action press. Both fineblanking and the GRIPflow process now are being used to produce many parts previously made by more costly processes, such as casting, forging, and machining. Because other minor forming operations can be combined with these special processes, they both lend themselves to many man y geometries. Keep in mind that each process has its own advantages and disadvantages. GRIPflow is a registered trademark of EBway EBway Corp.
Die Basics 101 -- Part XIII By Art Hedrick, Contributing Writer April 10, 2007 Pinch, breakout, and shimmy trimming are cutting methods often used in stamping operations. This article, which is a continuation of a series on die basics, discusses these processes. Descriptions of and links to the first 12 pparts arts in this series can be found at the end of this article. Various specialty metal cutting methods are used in stamping operations. Among them are pinch, breakout, and shimmy. shimmy.
Figure 1
Pinch trimming die design
Pinch Trimming Pinch trimming is a special method in which the vertical walls of a drawn or stretched vessel are cut by pinching the metal between two hardened tool steel die sections. In most cases, the clearance between the die sections is as little as possible (Figure 1). Unlike a conventional metal cutting process, no shearing or fracturing takes place in pinch trimming. Items such as deep-drawn cans often are pinch trimmed. Although pinch trimming is a very popular method, because the metal basically is pinched off, a very sharp burr usually remains on the part ( Figure 2). This burr must often be removed by b y tumbling the parts in a tub containing abrasives.
SOCIETY4PAKSWISSIANS Pinch trimming also places a great load on the sides of the die sections, which results in high wear. Most pinch trimming operations require a great deal of maintenance. Breakout Trimming
Figure 2
Result of pinch trimming
Breakout trimming is a specialty metal trimming process in which the metal is forced to fracture or break free from the vessel's flange. If you are accustomed to conventional cutting operations, this process most certainly may look harebrained to you. Unlike a conventional metal cutting process, the lower die section has a 45-degree angle ground on its edge. This angle has two basic functions: func tions: first, to allow the cup to fully nest in the lower die, and second,. to force the flange to bend upward slightly. slightly. The cutting clearance also is much greater in breakout trimming than the clearance commonly used in conventional cutting operations. This additional clearance causes leverage action, but does not allow for the metal to be bent into a vertical wall. However rest assured, this process works well, especially for metals that severely work harden (Figure 3). Breakout trimming takes advantage of the metal's work hardening and reduced thickness in a given localized zone. This method works best for round or axial symmetrical drawn parts.
Figure 3
Break out trimming
For breakout trimming to work effectively, effectively, the drawn cup must be properly prepared for the process. The inside radius on the cup's flange must be reduced to a dead sharp corner before using this method. This is achieved by drawing the cup deeper in the drawing operation or compressing it back over a dead sharp corner on the die section (Figure 4). Doing so reduces thickness in the radius and allows work hardening to take place. After the cup has been prepared properly, it can be introduced into the breakout trimming process, in which the cup flange will be forced upward, causing the metal to break at the dead sharp corner (Figure 5). Because the cup flange is
Figure 4
Creating a small radius
SOCIETY4PAKSWISSIANS round, as it is pushed upward it is forced into radial compression. This compression works to your advantage by forcing the cup to be fractured out of the flange. Breakout trimming does not produce a burr as large as that produced by pinch trimming. Also, because the loads on the tool steel sections are minimal, the die requires less frequent maintenance. However keep in mind that this method can be used only in situations in which the metal must be cut at the intersection of the flange and the cup's vertical wall. Shimmy Trimming Shimmy trimming is a unique metal trimming process in which a series of specially designed cams are used Figure 5 to force the part to move side to side. Unlike conventional cam trimming, the part does do es not remain stationary, stationary, but rather moves horizontally in the die. It moves in such as fashion that it can be trimmed true to the surface of the vessel. Trimming 90 degrees or true to surface results in a much cleaner cut and considerably lower burrs than pinch trimming. A great advantage of shimmy dies is that they can cut the entire perimeter of a part in a single press stroke. Unlike conventional pinch trimming, a shimmy trimming operation is not restricted to straight line cuts. Features such as notches, curved cuts, as well as a various other cuts can be made. Many common items such as cigarette lighters and gun shells are made using the shimmy trimming process. Shimmy trimming operations also can be designed to cut metal as thick as 0.250 Figure 6 in. and, unlike conventional pinch Parts trimmed with a shimmy trim die trimming, can keep the original metal Images courtesy of Vulcan Tool Tool Corporation thickness in the trimmed area. Not like conventional cutting operations, shimmy dies require a pressure system such as a press cushion or a nitrogen gas manifold (Figure 6). Which metal cutting operation a die design engineer chooses is based on many factors, including allowable burr height, parts volumes, metal type and thickness, and trim line geometry. geometry. No single trimming operation is best for all scenarios. The next article in this series will continue the discussion of metal cutting.
Die Basics 101: Part XII
SOCIETY4PAKSWISSIANS By Art Hedrick, Contributing Writer February 13, 2007 Part XI of this series covering stamping die fundamentals defined slug pulling and discussed some underlying reasons that it occurs. This article describes some methods for resolving slug pulling problems. Descriptions of and links to the first 10 parts in this series can be found at the end of this article. Slug pulling, which occurs when scrap metal—the slug—sticks to the punch face upon withdrawal and comes out of the button, or lower matrix, is a serious problem that can damage parts and dies. Various Various methods can help reduce the occurrence of slug pulling.
Air Vents Putting air vents in cutting and piercing sections most likely will not completely stop cutting slugs from pulling, but it's a good start. This is because trapped air that creates vacuum pockets is a major cause of slug pulling. It is good die-building practice to drill air vents in all cutting punches whenever possible, especially if they are piercing punches.
Spring Pins
Figure 1
Spring Ejectors and Air Vents Vents Images courtesy of Dayton Progress
SOCIETY4PAKSWISSIANS A common, popular method for preventing slugs from pulling is to use a pierce punch with a spring-loaded ejector pin. However, this method is effective only if the punch is large enough to accept a spring pin. The spring-loaded pin pushes slugs from the punch point and into the matrix. Keep in mind that to maximize the spring pin's effectiveness, it must be accompanied by an air vent. This can be achieved by drilling an oversized hole for the pin and allowing the trapped air to escape around the spring pin. Spring pins work well in large dies containing large pierce punches, punc hes, but they do not lend themselves well to small-die, high-speed operations. Many commercial punch manufactures can provide these types t ypes of punches for you. Some commercially available punches even have a special wire retainer that allows the maintenance technician to depress the spring pin, lock it in place with a special retention pin, and grind the punch with the spring depressed. This capability allows the punch to have the same amount of spring travel as a new punch (Figure 1).
Reduce the Punch-to-Die Clearance Although reducing the cutting clearance shortens the life of the punch and matrix, it helps minimize slug pulling. This is because reducing cutting clearance forces the slug in compression during cutting. After the cutting is completed, the slug decompresses in the matrix for an interference fit. For short-term runs and low-production parts, reducing the clearance may be your answer; however, for high-production dies, it is recommended that you use an engineered cutting clearance combined with an alternate method for slug retention.
Special Die Inserts, Buttons, and Matrix Alterations Many commercially available inserts orbuttons can help address slug pulling problems. p roblems. Some common commercial names are "slug huggers" or "slug-control buttons" (Figure 2).
SOCIETY4PAKSWISSIANS
Figure 2
Commercial Slug Control Buttons A slug-control button consists of two small slots machined at an angle in each side of the matrix. These slots cause a burr to be generated g enerated on the slug. The burr is forced downward at an angle, wedging the slug in the matrix. A slug-hugger button has barbs in the matrix that impale themselves into the slug. Both of these methods work well and are highly recommended.
A reverse-tapered "bell mouth" button also works well. Most die buttons have a bell mouth taper machined into them, with the hole diameter increasing toward the bottom of the button. Although it may seem strange to use a button with a hole in the matrix that gets slightly smaller as it nears the clearance opening, this is an effective slug retention method. The reverse taper holds the slugs in compression in the matrix. Keep in mind that tha t in most piercing operations, 0.0005 inch to 0.001 in. is more than sufficient taper. Too Too much taper and compression can cause the matrix to split (Figure 3).
Figure 3
Alternate Slug Control Buttons
SOCIETY4PAKSWISSIANS
Vacuum Units Commercially available vacuum units can be incorporated in your piercing operation. These units create a vacuum and pull the slug downward into the matrix. In a pinch, try a simple wet and dry vacuum. In my experience, it works fairly well. However, keep in mind that these vacuums typically are not meant to run for hours and hours. Even the higher-quality models burn up quickly.
Other Ideas Although it may be somewhat crude, using a weld spatter technique on the inside of a button can be b e a relatively effective slug-pulling remedy remed y. Commercially available deposit machines work best to execute this application. These special deposit machines deposit tiny barbs on the inside of the button. These barbs impale themselves into the slug and help prevent it from pulling upward. These portable application machines have significant advantages over ordinary weld spatter. spatter. First, they can deposit tungsten or vanadium carbide on the button surface, which decreases button wear and increases slug-retention life. Second, the deposits can be made accurately with as little heat as possible. This helps to reduce tool steel and button damage. Deposit amounts can be carefully controlled. Keep in mind that each cutting and piercing operation may require a different slug pulling method. The key is to remember that one pulled slug is one too many. Even a single pulled slug can result in extensive die damage. Don't risk ignoring the issue: An ounce of prevention is worth a pound of cure!
Future Future articles in this series will cover specialty cutting methods, such as pinch, breakout, and shimmy trimming, as well as tricks for piercing multiple layers and on angular suDie Basics 101: Part X By Art Hedrick, Contributing Writer October 10, 2006 This article, Part X of a series covering stamping die fundamentals, begins an in-depth look at the metal cutting process. It covers piercing and cutting clearance and discusses some common piercing misconceptions. Descriptions of and links to the first nine articles in this series can be found at the end of this article.
SOCIETY4PAKSWISSIANS Cutting is the most severe metalworking process that takes place in a die and shouldn't be taken lightly. Cutting Basics Cutting metal requires great force. For example, it takes approximately 78,000 lbs. of pressure to cut a 10-in.-diameter blank from 0.100-in.-thick 0.10 0-in.-thick mild steel. Consequently, Consequently, the punch, die, and press must absorb overwhelming shock. Overshocking the press and die components usually is what causes them to fail prematurely. prematurely. If you work in a shop that blanks heavy metals, you know kn ow what I mean. You can hear and feel the press shock. Doing everything you can to reduce the unnecessary loading and shocking is important. Factors such as cutting clearance and shear angles contribute significantly to the amount of force required. They also affect the amount of shock that is generated. Piercing Misconceptions If you participated in a tool and die apprenticeship, you probably were taught the following rules for piercing punches: • • •
The punch determines the hole size. The cutting clearance always should be even (equal) around the punch. 10 percent of the metal's thickness is a good cutting clearance for each side of the punch.
These are good starting guidelines for cutting, but they aren't entirely true. Let's examine each misconception. The punch determines the hole size —Although the punch produces a hole that is very
close to its actual diameter, altering the clearance between the punch and the button b utton (sometimes referred to as the matrix) also affects the hole size. The simple truth is that a hole can be made slightly larger or smaller than the punch diameter by increasing or decreasing the cutting clearance. This is because of the way that the metal deforms before be fore the cutting actually takes place. Think of the metal that you're cutting as Silly Putty® or a rubbery plastic. If the clearance between the cutting punch and the button is insufficient, it will cause the metal to compress or bulge out away awa y from the punch before the cutting takes place. After the slug is created, the metal grips the punch sides. This increased friction between the sides of the punch and the metal raises the amount of force necessary to strip or pull the punch from the metal. The insufficient clearance between the punch and the button means that a greater force is needed to create the hole. Inadequate clearance also increases the load on the edges of the punch and the matrix, which causes premature edge breakdown.
SOCIETY4PAKSWISSIANS After the punch is removed, the metal that once was compressed decompresses and collapses around the void area (the hole). The result is a hole that is smaller than the punch's diameter (Figure 1).
Figure 1
Insufficient Cutting Clearance If the clearance between the punch and button is increased, the metal is pulled inward in slight tension into the button. After the slug is created, the metal pulls away from the edges of the punch, resulting in a hole that is slightly larger than the pierce punch. pun ch. Increasing the cutting clearance also reduces the cutting force needed to create the hole. In addition, because the hole is slightly larger than the punch, the force needed nee ded to strip the metal from the punch is greatly reduced (Figure 2).
Figure 2
Using Increased Cutting Clearance Keep in mind that changing the clearance does not affect the hole size to a great extent— about 0.001 in. to 0.002 in. Although it might seem small, this change can reduce the friction generated during punch withdrawal significantly and extend the punch life. The cutting clearance always should be equal around your punches —Once again,
unless you are piercing only round holes, this statement is not entirely true.
Cutting clearances should change around the punch perimeter with respect to the punch geometry. Let me explain using this example: If you are piercing a square hole, you may notice that the corners of the punches are the first areas to break down. Once the corners break down, the entire punch must be sharpened. Ever wonder why the corners break
SOCIETY4PAKSWISSIANS down first? It's because this is the area that is subjected to the highest cutting loads. Very Very simply, wherever there is a small radial feature in a cut (nothing is worse than a dead sharp corner), the compressive forces will be greater. greater. Excessive compression can be compensated for by increasing the cutting clearance in areas with small radial features or sharp corners. Increasing the clearance in these areas helps to increase punch and an d button life and reduce the probability of a large corner burr. A good rule of thumb is to increase the clearance in the corners to approximately 1.5 times the normal clearance. An even better scenario is to avoid avo id dead sharp corners whenever possible (Figure 3).
Figure 3
Increasing Cutting Clearances in Corners 10 percent of the metal's thickness is a good cutting clearance for each side of the punch —Once again, this statement isn't always true. While 10 percent is by far the most
popular cutting clearance used, it most certainly is not always the ideal cutting clearance. Cutting clearances can range from as little as 0.5 percent up to as much as 25 percent of the metal's thickness per side. Among the many factors that determine the best cutting clearance are the metal's thickness and hardness and the punch size and geometry. For example, the ideal cutting clearance for piercing a 0.500-in.-diameter round hole in a sheet of 0.100-in.-thick 300 series stainless steel is about 13 percent of the metal's thickness per side, or 0.013 in. per side. This calculates to a total clearance of 0.026 in. However, changing from a 0.500-in.-diameter punch to a 0.100-in.-diameter punch requires more cutting clearance, from 13 percent to 20 percent per side. This is because the smaller punch has a smaller radius, and compressive forces congregate at the smallest radial feature of a cut (just as in the rectangular punch example noted above). Metal type also affects cutting clearance selection. Harder, higher-strength materials require more cutting clearance, while softer metals, such as aluminum, require smaller cutting clearances. As you can see, metal cutting is slightly more complicated than often perceived. Understanding the many variables and how ho w they affect the cutting process are key.
SOCIETY4PAKSWISSIANS The next article in this series will continue the discussion about cutting. Topics Topics to be covered in the next and subsequent articles include methods for preventing slug pulling and punch breakage; specialty cutting methods, such as pinch, breakout, and shim trimming; and tricks for piercing multiple layers and piercing on an angular surface.
Die Basics 101: Part IX By Art Hedrick, Contributing Writer August 8, 2006 This installment in the Die Basics 101 series picks up where Part VIII left off in describing the mechanical properties and behavioral b ehavioral characteristics of metals used in stamping operations. Among the topics discussed are strain, springback, stress, stretch distribution, n value, r value, and surface topography. Editor's Note: This article—Part IX of a series covering stamping die fundamentals— continues the discussion of mechanical properties as well as behavioral characteristics of metals. Part VIII expanded upon Part VII 's 's overview of metals used in stamping. Part VI explained specialty die components. Parts IV and Part Part V covered common stamping Part III discussed several different production die components. Part production methods used to produce stamped parts. Part II covered various forming operations, and Part Part I explained what a die is and described several metal cutting operations.
Figure 1
Strain and Thickness Distribution Part VIII of this series discussed some of the specific mechanical properties of metals— ductility, ductility, elongation percentage, tensile and a nd yield strength, and hardness—and how to derive these properties. This article describes other important mechanical properties, as well as a few behavioral characteristics.
SOCIETY4PAKSWISSIANS Strain Strain can be defined simply as a measurable deformation of the metal. In other words, metal must be "strained" in order to change its shape. Strains can be positive po sitive (pulling the metal apart, or tension) or negative (pushing the metal together, or compression.) Strains also can be permanent (plastic) or recoverable (elastic). The result of elastic straining commonly is referred to as springback, or elastic recovery. recovery. Remember, every metal type wants to return to its original shape when it's deformed. The amount the metal springs back is a function of its mechanical properties. When engineers refer to part areas that are "high strain," they typically are referring to areas that have been subjected to substantial stretch or compression. Figure 1 shows a simulation image of a part that has been stretched. Each color represents a different type and amount of strain. Some of the strains are positive and others are negative. Stress Stress is simply the result of straining the metal. When subjected to stress, metal incurs internal changes that cause it to spring back or deform nonuniformly. nonuniformly. Trapped stresses within a part often result in a loss of flatness or other geometric characteristics. All cut or formed parts incur stress. Stretch Distribution Stretch distribution is a very important mechanical property. property. A metal's stretch distribution characteristics control how much surface area of the stretched metal is permanently deformed. Stretch distribution is determined primarily by checking the metal's thickness when it's deformed in tension during the tensile testing process. The more uniform the Figure 2 thickness distribution, the better the Stretch Distribution / Tensile Test stretch distribution. Stretch distribution also is partially expressed in the metal's n value. Figure 2 shows different stretch distribution results. The red areas of the sample test coupon represent areas that have been stretched. n Value To understand n value, otherwise known as the work or strain hardening exponent, you must understand that every time metal is exposed to permanent deformation, work hardening occurs. It's the same thing that happens when you bend a coat hanger back and forth. As you bend the hanger, it gets harder and harder to bend. It also becomes more difficult to bend it in the same place. This increase in strength is the result of work or
SOCIETY4PAKSWISSIANS strain hardening. However, if you continue to bend the hanger in the same spot, it will eventually fail. Ironic as it may seem, materials need to work-harden to achieve both good stretchability and stretch distribution. How they work-harden is the key ke y. The n value of a material can be defined fundamentally as the metal's stretchability; however, it also is an expression of a material's stretch distribution characteristics. Perhaps one of the most important mechanical mechan ical properties to consider if the stamped part requires a great deal of stretch, the n value is expressed numerically in numbers from 0.100 to 0.300 and usually is carried out two or three decimal d ecimal places. The higher the number, the greater the metal's stretchability and stretch distribution. Higher-strength metals, such as spring steel, have very v ery low n values, while metals such as those used for making oil pans and other o ther deep-formed parts usually exhibit higher n values. The metal's n value also is a key mechanical value used in creating forming limit diagrams. (This will be discussed in subsequent parts of this series.) r Value The metal's r value is defined metallurgically as the plastic strain ratio. To understand this concept, you must clearly know the difference between stretching and drawing. Stretching is a metal forming process in which the metal is forced into tension. This results in an increase in surface area. Items such as most automobile hoods and fenders are made using this process. Drawing is the displacement of metal into a cavity or over a punch by means of plastic flow or feeding the metal. Items such as large cans, oil pans, and deep-formed parts usually are made using this process.
Figure 3
Plastic Strain Ratio r Value The metal's r value can be defined simply as the metal's ability to flow. It also is expressed numerically using a value from 1 to 2, which usually is carried out two decimal de cimal places. The greater the r value, the more drawable the metal (Figure 3). The metal's r value is not uniform throughout the sheet. Most metals have different r values with respect to the metal's rolling direction. Testing for a metal's r value requires tensile testing in three different directions—with the rolling direction, against the rolling
SOCIETY4PAKSWISSIANS direction, and at 45 degrees to the rolling direction. The test results usually are averaged and expressed as the r bar, or average of the r values. v alues. Differences in the plastic strain ratio result in earring of the metal when being drawn. For example, when drawing a round shell from a round blank, the results will be a near ne ar square Figure 4 bottom on the flange of the cup. This Earring Caused by Differences in the Metal’s r effect (Figure 4) is caused by Value different amounts of metal flow with respect to the metal's Surface Topography A metal's surface topography, topography, defined simply as the metal surface finish, is created mainly during the metal rolling process. Surface topography is an important metal characteristic. When being drawn, metals often require a surface finish that has the ability to hold lubricant. Surface topography is determined with a measuring tool called a profilometer. This wraps up the discussion of sheet metal characteristics. The next article in this series will focus on metal cutting. By Art Hedrick, Contributing Writer April 11, 2006 Although many metals are used in stamping, all fall into one of two basic categories— ca tegories— ferrous and nonferrous. All metals have certain characteristics that must be considered when determining which stamping dies, production processes, and equipment to use. This article introduces the most basic metals and their properties. Editor's Note: This article—Part VII of a series covering cover ing stamping die fundamentals—is fund amentals—is an overview of metals used in stamping. Part VI explained specialty die components. Parts IV and V covered common stamping die components. Part III discussed several different production methods used to produce stamped parts. Part II covered various forming operations, and Part I explained what a die is and
described several metal cutting operations.
Previous articles in this series focused on stamping dies and production methods. This article discusses stamping materials—both ferrous and nonferrous.
SOCIETY4PAKSWISSIANS To process, design, and build a successful stamping die, it is necessary to fully understand the behavioral characteristics of the specific material to be cut and formed. For example, if you are forming 5000 series aluminum and you follow the same process you use for deep drawing steel, the operation most likely will fail—not because aluminum is bad, it's just different from steel. Each metal has its own unique un ique mechanical characteristics. The metal type that the die is forming and cutting often determines the tool steel that must be used, as well as how ho w many operations are required. In addition, different d ifferent metal types require different lubricants, press speeds, and capacities. Because stampers are end users of metals, this article focuses on selecting and understanding the end-product behavior only and not the metal-making process. Two Metal Types Although there are literally thousands of metals that can be stamped, all fall within two basic categories— ferrous and nonferrous. Ferrous metals contain iron, and nonferrous metals are those without iron. Steel is a classic ferrous metal because beca use it is derived essentially from iron ore. Aluminum, however, contains no iron and is classified as a nonferrous metal. With the exception of a few exotic specialty metals, ferrous metals are magnetic and a nd nonferrous metals are nonmagnetic. Because nonferrous metals do not contain iron, they are less likely to deteriorate through oxidation or rusting. Some commonly stamped nonferrous metals are aluminum, brass, bronze, gold, silver, silver, tin, and copper coppe r. Aluminum is a very popular metal for applications in which strength, weight, and corrosion resistance are factors. Aluminum is approximately one-third the weight of steel. Although hundreds of alloyed steels exist, plain carbon steel is by far the most commonly stamped ferrous metal. Steel Basics Carbon is a basic element of o f the steelmaking process. In its raw form, carbon could cou ld be described as a chunk of coal or pencil lead. A piece of coal buried a mile or so beneath bene ath the surface of the earth and subjected to intense heat and pressure for about a thousand years yields what? A diamond. A diamond is nothing more than pure, compressed carbon. (Yes, (Yes, "Carbon is a girl's best friend." Just make sure that it's natural, highly compressed carbon that you are giving her.) From this basic knowledge of carbon, it is easy to deduce that the more carbon present in the steel, typically the stronger and less formable it will be. For example, exa mple, tool steel used in manufacturing dies contains far more carbon than the sheet metal being processed. Keep in mind that the carbon content of a particular p articular metal does not fully determine the metal's mechanical properties. Carbon content is only one factor.
SOCIETY4PAKSWISSIANS Alloys An alloy is a homogeneous compound or mixture of two or more metals that enhances the metal's chemical, mechanical, or physical properties. When combined, the metals must be compatible Figure 1 and resist separation under normal conditions. For example, two common alloys added to steel are chrome and nickel. Chrome is very hard and resists oxidation, and so does nickel. Adding chrome and nickel to steel produces stainless steel. These added alloys enable the stainless steel to resist oxidation. If you have purchased stainless steel flatware recently, you may have noticed different grades are available. These grades usually are designated as good, better, and best. The main difference in the quality depends primarily on the alloy content. con tent. The numbers that you see on the packaging, such as 18/8 or 18/10, refer to the percentage of chromium (18 percent) and nickel (8 percent p ercent or 10 percent) in the stainless steel. Chromium is known for its stain resistance, and nickel is known for its high luster and shine. Higher alloy numbers mean higher quality and cost. Alloys can be introduced into both ferrous and nonferrous metals. Many aluminum alloys are available today toda y. A very common steel type used in the automotive industry is highstrength, low-alloy steel (HSLA). Alloys are combined with medium carbon steel to give the metal good load-carrying ability and reasonable formability. formability. These mechanical properties make HSLA a good candidate for frame rails and other automotive structural parts that require strength. The number of alloyed metals used in stamping are far too numerous to mention in this article. The thing to remember is that alloyed metals are a combination or mixture of two or more metals that create a new metal with special characteristics.
Figure 2
Plain Carbon Steel Plain carbon steel can be defined as pure steel, meaning that it contains no intentionally added alloys. Plain carbon steel—among the most popular steel types used in stamping today—usually is assigned a four-digit number, such as 1006, 1020, 1050, and 1080. To determine the steel's carbon content, simply place an imaginary decimal place between the four digits and read the last two digits as a percentage of 1 percent. For example, 1010 steel contains 10 1/100 of 1 percent carbon, or 0.10 carbon (see Figure 1). The more carbon in the steel, the harder it will be to cut and form. Metals with increased carbon can be hardened further by heating them to a critical temperature and cooling
SOCIETY4PAKSWISSIANS them quickly in the proper quenching medium. Processing harder metals requires dies made from tougher, more wear-resistant tool steels. Also, greater force is needed ne eded to cut and form the metal. Knowing the metal's carbon content can help you make a better decision about the appropriate tool steel and press capacity. Figure 2 shows a few typical applications with respect to the steel's carbon content. This article covered very basic metal types and properties only. only. The next article in this series will discuss the mechanical characteristics of different metals in more detail. It also will explain how the metal selection affects the die processing method and die materials. By Art Hedrick, Contributing Writer February 7, 2006 In-die tapping units, rotary benders, pierce nut units, un its, HYDROCAM®s, and threadforming punches/buttons are among the specialty dies that can help reduce the number of required operations and costs to produce holes in stamped parts. This article discusses these components and their applications. Editor's Note: This article—Part VI of a series covering stamping die fundamentals— discusses specialty die components. Parts IV and V covered common stamping die components. Part III discussed several different production methods used to produce stamped parts. Part II covered various Part I explained forming operations, and Part what a die is and described several metal cutting operations.
Previous articles in this series discussed common stamping die components. This article focuses on less common specialty components found only in certain dies, most of which are available from various suppliers. In-die Tapping Units
Figure 1
Inidie Tapping Units Image courtesy of Danly IEM.
Many dies produce parts that contain holes or extrusions that will be tapped or threaded to hold a fastener. fastener. These holes often are tapped in the die rather than in a separate, offline o ffline operation. In-die tapping units use a series of helix-style he lix-style shafts and gears to transfer linear motion (press ram) into rotary motion. The mechanical rotary motion can be press ram-driven, or it can be created by special electronic servo-drive motors. Besides moving downward, the tap spins and creates the threaded hole. Unlike a regular cutting tap, an a n in-die tapping unit uses special roll forming taps. Instead of removing chips, roll forming taps gradually deform the metal into the shape of a
SOCIETY4PAKSWISSIANS thread. Using a standard cutting tap in an in-die tapping unit would create a cutting chip removal problem. Because the work hardens during the metal deformation process, an in-die tapped hole's strength can be similar to a standard cut thread's strength. The difference is cost— c ost— using an in-die tapping unit instead of an offline tapping process can reduce costs significantly (see Figure 1). Rotary Benders Rotary benders, often referred to as rocker benders, are specialty metal bending units that feature a rotary action producing V-grooved cylinder. cylinder. This cylinder is spring loaded and secured into a special retainer called a saddle. As the die closes and the cylinder makes contact Figure 2 with the sheet metal, it rotates about its Image courtesy of Danly IEM centerline and creates the bend. Rotary benders can be used to create straight-line bends only. Unlike conventional metal bending equipment, rocker benders require no additional pressure pad. Rocker benders can be easily adjusted and require less force than conventional bending methods. When inserted with a special hard plastic, they are nonmarking and can overbend the metal to create an acute or less than 90-degree angle. They also can create double bends (Figure 2). Pierce Nut Units Fasteners, such as screws, nuts and rivets, can be inserted into a stamped part in various ways. Using a pierce nut unit currently cu rrently is a common method. This special mechanical unit (Figure 3) both pierces a hole and fastens a threaded nut to the stamped part.
Figure 3
SOCIETY4PAKSWISSIANS Pierce Nut Installation Unit Image courtesy of Multifastener Corp.
Pierce nut units can feed fasteners in several different ways and can be incorporated easily in progressive, line, and transfer dies. Unlike tapping, in which the hole relies on the amount of thread engagement that can be achieved by the specific extrusion length, pierce nut units can work with a variety of nut sizes, strengths, and thread series. Pierce nut units can be used in almost any hole-piercing operation and are very popular in both the automotive and other industries. HYDROCAMs Activated by press ram-driven hydraulic cylinders, HYDROCAMs (Figure 4) pierce holes and create special forms in die areas that are inaccessible using standard cams. Using HYDROCAMs can reduce the number of stamping operations necessary, as well as the die cost.
Figure 4
HYDROCAM Assembly Image courtesy of Ready Technology. Technology.
The drive unit can be placed almost anywhere beneath the press ram and can be used to activate one of several cams. Because these cams run on hydraulics, they can achieve a great force. HYDROCAMs also can be adjusted easily to fine-tune the timing to execute specialty cutting and forming operations. Thread-forming Punches/Buttons Thread-forming punches and buttons (Figure 5) both pierce and form the metal into a special shape. The specially shaped pierced hole h ole functions to hold a variety of screws and increases the force necessary to pull the screw out o ut of the sheet metal.
SOCIETY4PAKSWISSIANS
Figure 5 Image courtesy of Danly IEM.
The punches and buttons can be incorporated into standard ball lock retainers, or they can be the headed type. Because the metal simply is being pierced and formed, no press speed reduction is necessary. necessary. Holes created with special thread-forming punches and buttons have improved holding ability over putting a screw into a flat piece of sheet metal. Metal cutting and forming methods are virtually endless and limited only by the imagination. Each die has its own special function. To To list all commercially available and custom-made die components available would be nearly impossible. Part VII of this series will discuss sheet metal properties. By Art Hedrick, Contributing Writer October 11, 2005 Stamping dies can comprise many components. This article discusses the basic components, including die plates, shoes, die sets, guide pins, bushings, heel blocks, heel plates, screws, dowels, and keys. This article— Part Part IV of a series covering stamping die fundamentals—explains the purpose and composition of common stamping die components. Part III discussed several different production methods used to produce stamped parts. Part II covered various forming operations, and Part I explained what a die is and described several metal cutting operations. While many specialty components can be used in manufacturing dies, most dies contain certain common components. Die Plates, Shoes, and Die Sets
SOCIETY4PAKSWISSIANS Die plates, shoes, and die sets are steel or aluminum plates that correspond to the size of the die. They serve as the foundation for mounting the working die components. These parts must be machined so that they are parallel and flat within a critical tolerance. The machining methods are milling Figure 1 and grinding. Although Various die set types grinding is the most popular, a milled surface now can be obtained that is as accurate as a ground surface. Most die shoes are made from steel. Aluminum also is a popular die shoe material. Aluminum is one-third the weight of steel, it can be machined very quickly, and special alloys can be added to it to give it greater compressive strength than low-carbon steel. Aluminum also is a great metal for shock adsorption, which makes it a good choice for blanking dies. The upper and lower die shoes assembled together with guide pins create the die set. The lower die shoe often has machined mach ined or flame-cut holes that allow slugs and scrap created in the die to fall freely through the die shoe onto the press bed. The holes also may serve as clearances for gas springs and other die components. The die shoe thickness is based on how much force can be expected during cutting and forming. For example, a coining die, one that compresses metal by squeezing it between an upper and lower die section, requires a much thicker die shoe than a simple bending die (Figure 1). Guide Pins and Bushings Guide pins, sometimes referred to as guide posts or pillars, p illars, function together with guide bushings to align both the upper and lower die shoes precisely. They are precision-ground components, often manufactured within 0.0001 in. Although numerous specialty mounting methods can be used to install these components, there are only o nly two basic types of guide pins and bushings—friction b ushings—friction pins and ball bearing-style pins. Friction pins are precision-ground pins that are slightly smaller than the guide bushing's inside diameter. Pins are made from hardened tool steel, while bushings often are made from or lined with a special wear-resistant material called aluminum-bronze. The aluminum-bronze may contain graphite plugs that help to reduce friction and wear that occur to the pins and bushings. Friction pins also help to heel the die shoes and prevent them from moving from side to side.
SOCIETY4PAKSWISSIANS
Figure 2
CVarious CVarious guide pins p ins and bushings Precision or ball bearing-style guide pins comprise precision-hardened pins, ball cages, ball bearings, and bushings. Unlike friction pins, these pins ride on a series of ball bearings contained in a special aluminum ball cage that permits the bearings to rotate without falling out. These pins have several advantages. First, friction is reduced so the die can run at faster speeds without generating excessive friction and heat. Second, they allow the diemaker to separate the upper and lower die shoes easily. easily. Third, because they use ball bearings, they can be b e manufactured with greater accuracy than friction pins (Figure 2). Remember, guide pins are meant to align the upper and lower die shoes, not to align a poorly maintained or sloppy ram in a press! Some companies try to compensate for a
poorly maintained press by adding oversized guide pins or grinding the guide pin ends to a cone shape. Care must be taken when flipping die shoes over so that the guide pins are not bent. Heel Blocks and Heel Plates Heel blocks are special steel blocks that are precision-machined, screwed, doweled, and often welded to both the upper and lower die shoes. They contain components called wear plates and function to adsorb any side thrust that may be generated during the Figure 3
Heel blocks
SOCIETY4PAKSWISSIANS cutting and forming process. They are especially important if the generated gene rated force is onedirectional. Too Too much force generated from one direction only can cause the guide pins to deflect, which results in misalignment of critical cutting and forming components. Most heel blocks have steel heel plates, and the heel block on the opposite shoe has a wear plate made from aluminum bronze or some other dissimilar metal. The plate selection process is critical. Using two opposing plates made of the same metal type can result in high friction, heat, and eventually galling or cold welding of the wear plates. Heel blocks can be used to heel the die in any or all directions. Box heels often are used to heel the die in all directions ( Figure 3). Screws, Dowels, and Keys Screws fasten and secure the working components to both the upper- and lower-die shoes. The socket head cap screw is the most popular fastener used in stamping dies. This hardened tool steel screw, often referred to as an an Allen head screw, screw, offers superior holding power and strength. Dowels are hardened, precisionground pins that precisely locate the Figure 4 die section or component in its proper Keys, dowels and screws location on the die shoe. Although dowels have much heeling ability, their main function is to locate the die section properly. properly. Keys are small, rectangular blocks of precision-ground steel that are inserted into a milled pocket in the die shoes and sections called keyways. Keys locate and heel h eel die sections and components (Figure 4). While these are the most common, other components can be used in manufacturing stamping dies. These will be discussed in Part V of this series. By Art Hedrick, Contributing Writer December 13, 2005 Stamping dies comprise many components. Continuing the discussion of common stamping die components began in Part IV of this series, this article focuses on pads, including stripper, pressure, and drawing; the methods used to secure them—spools, shoulder bolts, keepers, and retainers; and springs—gas, coil, and urethane. Editors Note: This article—Part V of a series covering stamping die fundamentals— continues the discussion about common stamping die components that began in Part IV .
SOCIETY4PAKSWISSIANS Part III discussed
several different production methods used to produce stamped parts. Part II covered various forming operations, and Part Part I explained what a die is and described several metal cutting operations.
Many specialty components can be used in dies, but the most commonly used are die plates, shoes, die sets, guide pins, bushings, heel blocks, heel plates, screws, dowels, and keys—all of which were explained in Part IV of this series. This article focuses on other common components—pads, retainers, and springs. Pads
Figure 1
A pad is simply a pressure-loaded plate, either flat or contoured, that holds, controls, or strips the metal during the cutting and forming process. Several types of pads are used in stamping dies. Depending on their function, pads can be made from soft low-carbon steel or hardened tool steel. Contoured pads must fit very closely to the mating die section. Precision requirements determine whether the pads are positioned with guide pins and bushings or left unguided. Stripper Pads/ Plates. Stripper pads are flat or contoured, spring-loaded plates that pull, or strip, the metal off the cutting punches. When it's cut, metal naturally tends to collapse around the body bod y or shank of the cutting punches; this is especially true during piercing. The stripper pad surrounds the cutting punches pu nches and mounts to the upper up per die shoe. As the punch exits the lower die, the spring-loaded pad holds the metal down flush with the lower die section, which allows the cutting cu tting punches to withdraw from the sheet metal or piece part. Often stripper pads are inserted with a small block of steel called a pad window. This pad window usually is small and lightweight and can be removed easily to allow the die maintenance technician to remove the ball lock-style pierce punch from the retainer without removing the entire stripper pad. Stripper pads also function to hold the metal flat or to the desired shape during the cutting process ( Figure 1). Pressure Pads/ Plates . During the wipe bending process, the metal must be held down
tightly to the lower die section before the forming punch contacts the metal. Pressure pads must apply a force that is at a t least equivalent to the bending force. Most pressure pads use high-pressure coil or gas springs (Figure 1). When loaded with very high pressure springs, contoured or flat pads also can form sheet metal. These pad types often are referred to as power punches (Figure 2).
SOCIETY4PAKSWISSIANS
Figure 2
Figure 3
Draw Pads. Draw pads control metal flow during the
drawing process. In drawing, the amount of pressure, or downward force, exerted on the sheet metal determines de termines how much metal is allowed to flow and enter en ter the draw die cavity. cavity. Too much pressure may stop the metal from flowing and cause splitting; too little downward force may allow excess metal to flow inward and cause loose metal or wrinkling. Draw pads, often referred to as binders or blank holders usually are made from hardened tool steel. They can be flat or contoured, depending on the piece part shape. Most drawing dies use a single draw pad; pad ; however, in special cases, some use two (Figure 3). Spools, Shoulder Bolts, and Keepers Spools, shoulder bolts, and keepers are used to fasten pads to the die shoes while allowing them to move up and down. They are secured to either the top or bottom die shoe with screws and often dowels for precision location. Of all of the components used for securing pads, spools are the most common, especially in larger dies (Figure 1 and Figure 4).
Figure 4
Retainers
SOCIETY4PAKSWISSIANS Retainers hold or secure cutting or forming die components to both the upper and lower die shoes. One of the most popular retainers is a ball-lock retainer, a high-precision, accurately manufactured die component that secures and aligns both cutting and forming punches. It uses a spring-loaded ball bearing to locate and secure the punches, which feature a precisely machined teardrop or ball seat . The spring-loaded ball bearing locks into the teardrop shape and prevents the punches from coming out of the retainer.
Figure 5
The advantage of ball-lock retainers is that they allow the die maintenance technician tech nician to remove and reinstall punches quickly. The punch is removed by depressing the springloaded ball bearing and pulling up on the punch. Specialty retainers also can be made to hold and align irregular punch shapes, as well as headed-style punches and pilot pins (Figure 5). Springs Springs supply the force needed to hold, strip, or form metal. Many different springs are used in stamping dies. Spring selection is based on o n many factors, including the required force and travel, the spring's life expectancy expec tancy,, and, of course, cost. Among the most popular are gas springs, which, when filled with nitrogen, can supply a great deal of force. They also have an excellent life expectancy.
Figure 6
SOCIETY4PAKSWISSIANS Other types are coil and urethane springs, often called marshmallow springs (Figure 6). Coil springs are very popular when a reasonable amount of force is needed and budget constraints are present. Urethane springs work well in short-run or prototype stamping operations. They also are inexpensive. The next part of this series will cover even more common stamping die components By Art Hedrick, Contributing Writer April 11, 2005 When I conduct conferences, it isn't unusual to have one or two attendees who are new to the stamping die and pressworking world. Some are young new hires trying to learn about stamping, and others are individuals who have been transferred from a different department and thrown to the wolves in the stamping department.
Figure 1
This article is the first in a series intended to introduce beginner toolmakers, die maintenance technicians, engineers, engineers, and press technicians to stamping. The series will define a die as well as a stamping operation. It will also discuss cutting and forming operations, components and functions, and different methods used to stamp parts. What Is a Stamping Die? A stamping die is a special, one-of-a-kind precision tool that cuts and forms sheet metal into a desired shape or profile. The die's cutting and forming sections typically are made from special types of hardenable steel called tool steel. Dies also can contain cutting and forming sections made from carbide or various other hard, wear-resistant materials. Stamping is a cold-forming operation, which means that no heat is introduced into the die or the sheet material intentionally. However, because heat is generated from friction during the cutting and forming process, stamped parts often exit the dies very hot.. Figure 2 Dies range in size from those used to make Typical Cut Edge of a Stamped Part microelectronics, which can fit in the palm of your hand, to those that are 20 ft. square and 10 ft. thick that are used to make entire automobile body sides.
The part a stamping operation produces is called a piece part (see Figure 1). Certain dies can make more than one piece part per cycle and can cycle as fast as 1,500 cycles (strokes) per minute. Force from a press enables the die to perform. How Many Die Types Exist? There are many kinds of stamping dies, all of which perform two basic operations— cutting, forming, or both. Manually or robotically loaded dies are referred to as line dies. Progressive and transfer dies are fully automated. Cutting Cutting is perhaps the most common operation performed in a stamping die. The metal is severed by placing it between two bypassing tool steel sections that have a small gap between them. This gap, or distance, is called the cutting clearance. Figure 3
Cutting clearances change with respect to the type of cutting operation Trimming being performed, the metal's properties, and the desired edge condition of the piece part. The cutting clearance often is expressed as a percentage of the metal's thickness. The most common cutting clearance used is about 10 percent of the metal's thickness. Very high force is needed to cut metal. The process often introduces substantial substantial shock to the die and press. In most cutting operations, the metal is stressed to the point of failure, which produces a cut edge with a shiny portion referred to as the cut band, or shear, and a portion called the fracture zone, or break line (see Figure 2).
SOCIETY4PAKSWISSIANS There are many different cutting operations, each with a special purpose. Some common operations are: Trimming—The outer perimeter of the formed part or flat
sheet metal is cut away to give the piece part the desired profile. The excess material usually is discarded as scrap (see Figure 3).
Figure 4 Notching
Notching—Usually associated with progressive dies, notching is a process in which a cutting operation is performed progressively on the outside of a sheet metal strip to create a given strip profile (see Figure 4).
Blanking—A dual-purpose cutting operation usually
performed on a larger scale, blanking is used in operations in which the slug is saved for further pressworking. It also is used to cut finished piece parts free from the sheet metal. The profiled sheet metal slug removed from the sheet by this process is called the blank, or starting piece of sheet metal that will be cut or formed later (see Figure 5). Piercing—Often called perforating, piercing is a metal
cutting operation that produces a round, square, or specialshaped hole in flat sheet metal or a formed part. The main difference between piercing and blanking is that in blanking, the slug is used, and in piercing the slug is discarded as scrap. The cutting punch that produces the hole is called the pierce punch, and the hole the punch enters is called the matrix (see Figure 6). Lancing—In lancing, the metal is sliced or slit in an effort
to free up metal without separating it from the strip. Lancing often is done in progressive dies to create a part carrier called a flex or stretch web (see Figure 7). Shearing—Shearing slices or cuts the metal along a straight line. This method commonly is used to produce rectangular and square blanks (see Figure 8).
Part II of this series will discuss forming dies and stamping processes.
Reducing scrap, inventory costs with coil optimization software Maximize material usage By Lloyd Wolf April 10, 2007
Coil optimization software is a valuable tool that fabricators can use to attack the problems of high scrap and high inventory. It offers the ability to quickly and easily make sound decisions regarding the purchase and use of master coil
SOCIETY4PAKSWISSIANS sizes. By using computers and specialized optimization algorithms, fabricators can minimize manual selection of coil sizes.
Specialized coil optimization software analyzes the parts to be made and determines the optimal coil sizes (widths) to purchase and maintain in inventory. inventory. Multicut blanking line photo courtesy of Red Bud Industries, Red Bud, Ill.
Metal fabrication is one of the most competitive industries in the U.S. Fabricators are always looking for new ways to decrease manufacturing costs to maintain profitability and a competitive edge. Identifying and implementing implementing cost-reduction opportunities often mean the difference between long-term survival and plant closure. Many companies report that raw steel can represent as much as 70 percent of total manufacturing costs. Therefore, reducing scrap and inventory costs are at the center of many cost-reduction efforts. Even the smallest reduction in these costs can have a huge impact on the company's financial bottom line. Specialized coil optimization optimization software helps analyze the parts to be made and determine the optimal coil sizes (widths) to purchase and maintain in inventory.
The Coil Handling Process Master coils that fabricators purchase from mills and service centers typically are from 30 to 72 inches wide (see Figure 1). The master coils are decoiled and processed through a series of cut-to-length or multicut blanking operations to yield rectangular blanks.
Figure 1 Master coils 30 to 72 inches wide are processed through a series of cut-to-length or multicut blanking operations to yield rectangular blanks.
The process begins when a master coil is loaded onto a cut-to-length or multicut blanking line. As the coil is unrolled, the length is sheared, or cut to length. The blanks generated from the cut-to-length operation are sent to a manual shear, where the coil's width is cut in a secondary shearing operation. The rectangular blanks generated from these operations are then sent to the fabrication, welding, paint, and assembly departments to create the finished part. If the coil is on a multicut blanking line (a cut-to-length line with slitter blades), the blank's width also is slit at the same time the length is being cut. The difference between the width of the master coil and the sum of the blank widths across the coil is scrap. It is dumped into a scrap hopper and resold for only a few pennies per pound. Cutting from master coils can result in inefficient material utilization, because, typically, typically, hundreds of rectangular fabricated parts—each with unique dimensions—must be cut from only a few master coil sizes. To make the math even more complex, each part has its own production requirements: Some parts may be produced in very high volumes—more than 100,000 pieces annually. annually. Other parts may be needed in very low volumes—as few as 100 pieces annually. A coil size that utilizes material efficiently for one part number often is inefficient for another part number. For example, four 12-in.-wide parts placed across a 48-in.-wide coil results in 100 percent material utilization and 0 percent scrap. However, four 10-in.-wide parts placed across the same 48-in.-wide coil results in about 17 percent scrap. Three 15-in.-wide parts placed across the 48-in.-wide coil results in more than 6 percent scrap.
Many Coils, Many Foils One method some fabricators use to reduce scrap is to increase the number of different master master coil sizes that they purchase and maintain in inventory to increase the chance of maximizing material utilization. utilization. Unfortunately, Unfortunately, this method of scrap reduction conflicts with just-in-time (JIT) manufacturing and low coil inventory goals. With many different coil sizes in inventory, inventory, each coil's usage is reduced. Also, this increases inventory carrying costs, because the coils tend to sit idle in inventory for extended time periods. Purchasing and maintaining numerous different coil sizes also force more frequent setups and changeovers on the cut-to-length line. This is because the more coils that are in inventory, the less likely that the coil required for the next shop order will be the same as the coil required for the last. In addition, purchasing many coil sizes reduces the purchasing power of volume discounts. Another method some companies use to reduce material costs is to purchase standard-size master coils, typically 30, 48, 60, and 72 in. wide. These are common sizes, readily available from many suppliers. Accordingly, Accordingly, they are sold for several cents per pound less than the "special"master "special"master coil sizes. However, in some instances, this method can be penny-wise and dollar-foolish, because many parts may not fit efficiently into these standard coil sizes. If 5 percent can be saved on the purchase price per pound, then an extra 2 percent or 3 percent
SOCIETY4PAKSWISSIANS scrap might be acceptable. But does it make sense to save 5 percent on the purchase price per pound with a scrap rate that is 10 percent to 15 percent higher than it would be with special master coil sizes?
Manual Calculations Fabricators try to minimize the amount of scrap they produce by selecting coil sizes that best fit the part sizes. However, However, for the large number of different part sizes that most fabricators produce, a nearly infinite number of solutions could be considered as to which coil sizes —and combinations of those sizes—;would provide the lowest overall scrap. Selecting the most desirable coil sizes typically means relying on personal experience or a set of complex manual calculations using spreadsheets. These calculations calculations can take several days or even months to perform, especially when a different set of calculations must be performed for each unique material specification (gauge, grade, chemistry, chemistry, and so on). Unfortunately, during that time, product line and mix changes may render those results invalid. Also, without having knowledge of complex optimization algorithms, fabricators may base their calculations on invalid assumptions. Further complicating manual calculations calculations are that purchase prices and part rotation often vary as the coil width changes, because a premium is charged for narrower coils, while discounts are provided for wider coils. Second, if grain direction does not matter, each part can be considered both with-the-grain and rotated. This factor alone more than doubles the number of possible solutions.
Optimization Software Specialized coil optimization software can help fabricators attack the problems of high scrap and high inventory. The software analyzes forecast production requirements for a set of parts, manufacturing constraints, and material and manufacturing costs. It determines the optimal coil sizes (widths) to purchase and maintain in inventory, and it shows how to cut parts with lower scrap, lower cost, and fewer coil sizes.
Figure 2 The parts database stores part blank information—such as part number, width, length, forecast demand, and rotatability— for each material specification.
Because of powerful optimization algorithms, the software can effectively effectively consider the cost of every possible combination of coil sizes that can be used—more than could ever be considered manually. manually. It finds the optimal coil sizes, thus reducing scrap loss and the number of different master coil sizes.
Typical Typical Optimization Process The user starts an optimization optimization study by providing parts and constraint information information for the material type to be optimized. The parts database (see Figure 2) is a spreadsheet-like window where part blank information information is stored for each material specification. Information typically includes part number, width, length, forecast demand, and rotatability. rotatability. This may be entered directly by the user, copied and pasted from other software, or imported from other s ystems via file transfer.
Figure 3 The costs and constraints database is where equipment limits, material costs, and manufacturing costs are specified.
The costs and constraints database (see Figure 3) is where equipment limits, material costs, and manufacturing costs are specified. Equipment constraints include maximum and minimum coil widths, the quantity of slitter blades, and edge-trim allowance. Using a material cost table, the user can specify the purchase price per pound for varying ranges of coil widths, along with the reimbursement for scrap.
SOCIETY4PAKSWISSIANS Costs for material handling and labor also can be broken out. Constraint information needs to be set up only once for various material specifications and does not require modification modification for each optimization study. study. Once that data is input, the user starts the optimization routine. The software automatically determines the optimal master coil sizes in less than five minutes, typically (see Figure 4). About halfway through the optimization process, the optimal coil sizes are displayed. The user can continue with the optimal master coil sizes, or other sizes may be entered to facilitate "what if"scenarios. When the calculations are finished, the optimization results can be reviewed both on-screen and in printed reports. The cost and scrap summary report provides summary information such as total scrap, total cost, and total weight for different master coil sizes.
Figure 4 During the optimization routine, the software automatically determines the optimal master coil sizes. Other sizes may be entered to facilitate “what if” scenarios.
For example, if only one coil size were selected, what would be its width? What would be the scrap rate? What would be the overall cost? If two coil sizes were selected, what would be the width and volume of each, the overall scrap rate, and overall cost? Having more coil sizes will result in less scrap, but other, intangible costs would also increase at the same time, offsetting the material savings. If adding an additional coil size saves an extra $25,000 per year in scrap, that probably makes sense. But if the savings were only an additional $500 per year, then the additional, intangible intangible inventory costs would probably far exceed the material savings. Using the cost and scrap summary, summary, it is fairly easy to decide on the solution containing the optimal number of master coil sizes to use, considering scrap, material costs, and inventory all together. Once the number of master coil sizes is decided, a part assignment report can be viewed on-screen or printed. This report shows which parts are assigned to which master coil for the selected solution, and the corresponding number of pieces cut across the coil width. This report typically is used by the engineering department to update bills of materials and routings in the company's manufacturing software system.
Typical Typical Investment, Savings, and Ongoing Periodic Analysis The initial investment in coil optimization optimization software typically is from $15,000 to $25,000 per manufacturing location—depending location—depending on the number of users, the amount of user training, and the need for any customization. Ongoing annual costs for software maintenance and support are typically 15 percent to 20 percent of the initial investment. Depending on the annual steel tonnage the company needs, material costs, and the part mix, annual savings typically are from $30,000 to $200,000. Because operating costs and material costs tend to increase over time, annual savings typically increases too. Because the mix of parts can change each year, as older product lines are discontinued and new product lines and changes are introduced, the optimal coil sizes also may change. Barring any major product changes, typically a company will use the optimization software to reevaluate master coil sizes about once each year to see how any changes in part mix have affected the optimal coil sizes. If part demand and mix have changed significantly, significantly, different coil sizes likely will be recommended. If a year from now the results from a new optimization optimization study show that changing two of the four coil sizes for a material specification specification yields a $25,000 savings, then it probably makes sense to change those sizes. If, however, changing the sizes would produce only a $2,500 savings, meaning that the part mix has not changed much and the prior coil sizes still "fit"the parts fairly well, then it may make sense to simply keep the current sizes, because there will be some cost associated with the time and effort to switch. n
Leaving the lab behind: Australian students move stamping research to the plant By Michael Cardew-Hall, Peter Hodgson, and Noel Miller, Contributing Writers April 24, 2001 Stamping Technology Technology for Automotive Manufacturing Manufacturing Processes (STAMP) is a novel type of research program developed in Australia. The unique aspect of this program is that r esearch is conducted for industry inside actual companies--a radical departure from traditional research, which typically involves experimentation in laboratories. This research model is well-suited to the manufacturing manufacturing industry, particularly in Australia, where small and medium-size companies are predominant. The Need for Assistance STAMP was was launched in mid-1997 as a collaborative venture between two Australian universities–The universities–The Australian National University and Deakin University--and Ford Motor Company, along with three of its suppliers, BHP Steel Ltd., Castrol Pty Ltd., and Imag Australia. The program was created to address some specific needs of the collaborating partners in the general areas of stamping and sheet metal forming. As many other stamping professionals throughout the world do, these partners perceived stamping as a black art and believed that problems experienced with new or ongoing parts could be solved only by experts with many years of experience. While this had been the
SOCIETY4PAKSWISSIANS mode of operation for many years at these plants, the continuing need to be efficient and competitive had resulted in the loss of many experienced personnel through downsizing and early retirement. The black art needed to be replaced by more scientific approaches, and new experts with sound understanding needed to be trained and brought into the industry. It also was recognized that day-to-day pressures present in stamping operations do not allow long-term projects to be addressed. These projects may have great potential benefit to a plant's operational effectiveness, effectiveness, but they often require extensive background research, experimentation, experimentation, analysis, and reflection on results–a luxury to busy plant engineers. When STAMP was initiated, the Ford Stamping Plant in Geelong, Victoria, Australia, was working with a number of separate universities on disparate, sometimes overlapping projects. It was identified that by drawing together the strengths of several institutions and suppliers into a virtual center structure comprising existing industrial and academic facilities, a focused approach could be adopted to meet identified needs. It also provided plant personnel with a single window for access to knowledge and expertise. The Model Universities and the stamping industry working together is nothing new. What is novel is the model used within STAMP. Projects are designed for university research students, who usually are enrolled in t wo-year Master of Engineering (and occasionally Ph.D.) research degree programs. The length of the projects allows significant problems to be addressed. The students are in the plant setting for more than 80 percent of their time, working alongside plant personnel. They dress the same as company employees and attend regular operational meetings so that they can better understand the motivations and problems that the plant personnel experience. To To maintain the academic nature of their work, students also spend periods of time, either one day a week or longer blocks, at their university campus to read, work on problems using university facilities, or consult academics. In addition to having an academic supervisor, each student is assigned an industrial supervisor, who typically is a line manager in the plant, and a technical mentor, who helps with the day-to-day facilitation of the project. Both people are key to the success of the students' project. Students meet with their academic supervisors either on the university campus or in the plant. The academics are regular visitors to the plant, spending, on average, one day there every three weeks. Students have access to production presses to carry out experiments in context, rather than in the abstract in a university laboratory, laboratory, and findings are likely to yield direct benefits to the operations. In addition to production plants, the students have access to a number of small presses set aside for their use. These have a wider variety of instrumentation and allow students to carry out more fundamental experiments. The stamping lines and individual presses are considered to be part of the experimental facilities available to the STAMP program. The plant-based experimentation experimentation is supported by university-based testing facilities and workshops as needed. While some projects involve large amounts of experimentation, others focus on the use of computer-aided engineering and manufacturing (CAEM) and finite element modeling methods to improve process understanding and limit problems. Students have access to two UNIXbased engineering workstations located in the Ford plant. These run CAD, CAEM, and metal forming simulation software and are connected via a microwave link to the university network. This link effectively effectively allows a minicampus to exist within the plant. In addition to the plant-based students, one or two research students work at their university on more long-term projects. They create another avenue of communication for the students in the plant. Further support is provided b y a postdoctoral fellow and two research engineers who spend extended periods of time in the plant when projects require them. Two committees manage the STAMP activities. Both are chaired by senior plant personnel and meet every six weeks: 1. The technical committee is r esponsible for defining, monitoring, and controlling the projects. It includes some plant personnel, particularly the technical mentors and industrial supervisors, as well as all of the collaborating industrial partners, academics, and students. The projects are identified and scoped by the industrial partners and the academic colleagues. This ensures that a balance is maintained between addressing real problems and academic merit and integrity. 2. The management committee oversees the financial and resource management of the program. It provides guidance on the students’ career development beyond the life of their project. Each year, an independent review of the program's activities is carried out. Each student presents his or her work to an audience of plant personnel, senior academics from the two universities who are not associated with the program, and an eminent professor who has worked extensively in the sheet metal forming area. This group provides an important quality check and critical feedback on the direction and nature of the work being done. Benefits At the technical level, this program allows relatively long-term projects to be addressed that normally would be too long for production personnel to be involved in. Because the research is carried out in context, project input and output remain relevant. Researchers are able to understand the limitations limitations of current processes and organizational structures. Through this program, the partners can attract and retain well-qualified, motivated technical technical staff within the manufacturing manufacturing sector. Development and retention of graduates within the partner organizations is a major focus of STAMP, and each student is viewed as a potential employee. Students are recruited through a competitive interview and assessment process. The program attracts both fresh graduates and those who have been in graduate training programs and want a higher degree and more technical work experience in an industrial environment. A side benefit is that findings and real-world problems can be incorporated into the undergraduate engineering programs at the two universities. Guest speakers now are regularly invited to speak to undergraduate students, providing a knowledge path from industry to the university. The structure and organization of the program have created a multidisciplinary multidisciplinary team. There is an open environment for the discussion of ideas and problems. This is partly due to the individuals involved, but also to the high level of commitment shown by the participating companies and universities. Specific Outcomes Each project has three outcome measures:
SOCIETY4PAKSWISSIANS 1. Improvement in process/increase in technical knowledge base in the plant. This is a key outcome. Each thesis generated by the students must have an appendix of how the results will be adopted by the industry partner. Projects completed to date have reduced lubricant and die coating costs, increased practical understanding of forming bake-hardenable steels, enabled viewing of the deep-drawing process as a system, and more. 2. New employees. To date, all of the graduates either have been employed by the partner companies or have gone to supplier organizations upon completion of their projects. 3. Publication of academic works. The industrial partners recognize the academic partners’ need to publish scholarly articles. Much of the work that is not of a sensitive nature has been published in international journals or presented at conferences. In addition to Figure 1 being presented at public conferences, One significant project result has been the development of a knowledge capture and dissemination the work carried out within STAMP is system called Simpress, which initially was developed by research engineers in conjunction with the regularly reported to the industrial student projects as a way to use project outcomes as useful tools in the plant. partners' global headquarters in the U.S. through various technical stamping forums. While project results have significantly improved understanding understanding of the stamping process in the plant, the most significant outcome has been the development of a knowledge capture and dissemination system called Simpress. This system initially was developed by research engineers in conjunction with the student projects as a way to use project results as useful tools in the plant (see Figure 1). Developed in close cooperation with staff and students in the plant, the system now forms the basis of a wider knowledge-capture system for stamping operations. It has been designed to allow knowledge and methods from student projects to be incorporated in a modular fashion
