Water jet machining
ABSTRACT Since commercialized in the late 1970’s, water jet technology has been
elevated from a mere niche cutter to a precision machine tool competing on an equal footing footing with conven conventio tional nal tools, tools, includ including ing but but not limited limited to EDM, EDM, lasers lasers,, CNC CNC machining, ultrasonic, and photo chemical etching. Nowadays, water jet technology has been highly automated with PC based based CAD/C CAD/CAM AM softwa software re that contro controls ls and operate operatess the hardw hardware are (pump (pump,, nozzle, nozzle, abrasive feeding, traverse, and accessories) for precision machining. Most machine error sources have been minimized for optimum operations. Abrasive-water jets (AWJs) are capable of machining most materials up to about 0.2 m thick with a taper error less than 2 arc minutes, true edge +/- 50 μm regularly (+/- 20 am in special cases). In many cases, AWJ-machined parts could be used directly for system assembly with no need for secondary treatment. For extremely precise parts, AWJ could be used to fabricate netshap shaped ed parts parts that that only only requ require ire an addi additio tional nal light light trim trimmi ming ng to meet meet strin stringe gent nt specifications. For very tough materials, the use of AWJ for net shaping often helps to minimize the wear of expensive contact tools (e.g., diamond coated drill bits), leading to improved productivity and significant cost saving (reduction of work stoppage, part rejection, and tool replacement due to an increase in tool life). For fatigue-critical applic applicatio ations, ns, low-cos low-cost, t, second secondary ary dry-gr dry-grit it blastin blasting g proces processes ses have have been been shown shown to successfully induce residual compressive stresses on AWJ-machined edges of aircraft metals, improving their fatigue lives at least three times over those of CNC-milled counterparts. In addition, a flash abrasive-water jet (FAWJ) was developed to superheat the high-pressure water that evaporates upon exiting, leading to a reduction in building up of static pressure inside blind holes, mitigating damage to delicate materials such as composites and laminates. This paper overviews about the importance of water jet cutting machines. Mainly concentrated on working process of water jet machines and wide range range of their their applic applicatio ations ns in differe different nt challe challengi nging ng indust industrie ries. s. And And also also compar compared ed different machining operations with water jet machining process.
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Water jet machining
INTRODUCTION.
Doff r In the battle to reduce costs, engineering and manufacturing departments are constantly on the lookout for an edge. The water jet process provides many unique capabilities and advantages that can prove very effective in the cost battle. Learning more about the water jet technology will give us an opportunity to put these cost-cutting capabilities to work. Beyond cost cutting, the water jet process is recognized as the most versatile and fastest growing process in the world. Water jets are used in high production applications across the globe. They compliment other technologies such as milling, laser, EDM, plasma and routers. No poisonous gases or liquids are used in water jet cutting, and water jets do not create hazardous materials or vapors. No heat effected zones or mechanical stresses are left on a water jet cut surface. It is truly a versatile, productive, cold cutting process. The water jet has shown that it can do things that other technologies simply cannot. From cutting whisper, thin details in stone, glass and metals; to rapid whole drilling of titanium; for cutting of food, to the killing of pathogens in beverages and dips, the water jet has proven itself unique. THEORY OF WATER JET CUTTING
Most water jet cutting theories explain water jet cutting as a form of micro erosion as described here. Water jet cutting works by forcing a large volume of water through a small orifice in the nozzle. The constant volume of water traveling through a reduced cross sectional area causes the particles to rapidly accelerate. This accelerated stream leaving the nozzle impacts the material to be cut. The extreme pressure of the accelerated water particles contacts a small area of the work piece. In this small area the work piece develops small cracks due to stream impact. The water jet washes away the material that "erodes" from the surface of the work piece. The crack caused by the water jet impact is now exposed to the water jet. The extreme pressure and impact of particles in the following stream cause the small crack to propagate until the material is cut through.
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Powering the Water jet
The water jet intensifier pump acts as an amplifier as it converts the energy from the low-pressure hydraulic fluid into ultra-high pressure water. The hydraulic system provides fluid power to a reciprocating piston in the intensifier center section. A limit switch, located at each end of the piston travel, signals the electronic controls to shift the directional control valve and reverse the piston direction. The intensifier assembly, with a plunger on each side of the piston, generates pressure in both directions. As one side of the intensifier is in the inlet stroke, the opposite side is generating ultra-high pressure output. During the plunger inlet stroke, filtered water enters the high pressure cylinder through the check value assembly. After the plunger reverses direction, the water is compressed and exits as ultra-high pressure water and then enters the pressure vessel (attenuator). The attenuator smoothes pressure fluctuations from the intensifier and delivers a constant and steady stream of ultra-high pressure water to the cutting or cleaning tool.
Types of water jet cutting 1. Water jet cutting 2. Abrasive water cutting
Water jet cutting:
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Water jet cutting machines cut with a jet of water so powerful that it cuts cleanly and precisely through material in a single pass without shredding or crushing it. In the formation of the jet stream, water is pressurized up to 90,000 psi (6,200 bar) by a Jet Edge hydraulically-driven water jet intensifier pump. The pressurized water passes through an attenuator which stabilizes the jet stream. The water jet cutting action takes place as a result of the ultra-high pressure (UHP) water being forced through a pre-mounted orifice as small as .003 in (.076 mm). The pressurized water exits the orifice at extremely high velocities as a coherent water jet stream that produces a clean cut. Water jet cuts with a narrow kerfs, so parts can be tightly nested, maximizing material usage. The compact, lightweight cutting head is designed for reliability in high cycle, on/off applications. When coupled with a Jet Edge motion control system, water jet cutting provides extremely accurate cuts with a high degree of repeatability over a wide range of materials and shapes. Cutting with water increases production rates on paper products, woven or non-woven textiles and similar materials without shredding or damage associated with conventional processing methods. The water jet stream cuts flexible materials quickly and accurately and overcomes distortion encountered from compression during conventional die cutting.
Water jets cut materials such as: • • • • • • • •
Plastics Corrugated Cardboard Insulation Rubber Food Non-woven’s Paper Automotive Carpeting and Headliners
Abrasive water jet cutting:
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Abrasive water jet cutting machines (abrasive jets) use a combination of water and garnet to cut through materials considered "unmachineable" by conventional cutting methods. Using small amounts of water while eliminating the friction caused by tool-to-part contact, abrasive water jet cutting avoids thermal damage or heat-affected zones (HAZ) which can adversely affect metallurgic properties in materials being cut. The ability to pierce through material also eliminates the need and cost of drilling starter holes. Because abrasive jet cuts with a narrow kerfs, parts can be tightly nested, maximizing material usage. Abrasive water jets can cut through materials ranging from 1/16 inch (1.6 mm) to 12 inches (305 mm) thick. Jet Edge precision water jets are capable of +/- 0.001" linear positional accuracy and +/- 0.001" repeatability. When coupled with a Jet Edge motion control system, abrasive jet cutting provides extremely accurate cuts with a high degree of repeatability over a wide range of materials and shapes. Abrasive water jet is excellent for the cutting of complex shapes, and in fragile materials such as glass, the high failure rate due to breakage and chipping of corners during conventional processing is virtually eliminated. Whatever your industrial need, abrasive jet is an accurate, flexible, and efficient cutting system.
Abrasive water jets cut materials such as: • • • • • • • •
Titanium Brass Aluminum Stone Inconel (R) Steel Glass Composites
Components used: • • • • • • • •
Hydraulic pump Intensifier Attenuator Piston cylinder Electric motor Nozzle Orifice Abrasive particles
A technology that redefines economic efficiency – cost-effective
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production of prototypes and small series
A CAD file (in all common formats) of the part to be created is read in for the water jet cutting process or created directly in the user software. The cutting plan specifies the cutting parameters for the various sections of the contour, including feed motion speed and pressure. The material to be processed is positioned on the system and cutting can begin. Thus, water jet cutting impresses with extremely short programming and setup times as well as efficient cutting times. Water jet cutting systems can be equipped with several cutting heads, and if necessary, several parts can be produced at the same time. Water jet cutting systems provide users with previously unknown flexibility and economic efficiency. From individual and prototype production to small series on through to large series, all orders can be produced cost-effectively and fast, and this with a nearly unlimited range of materials. Furthermore, since water jet cutting is a “cold” cutting process, the material is not subject to any thermal or processing forces.
3-axis CAD/CAM The 3-axis CAD/CAM allows the cost effective production of simple three dimensional shaped parts. The clamping fixture required for this is constructed automatically by the software and can be produced using the same water jet cutting system.
Machining center:
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Basic equipment used for water jet cutting consists of:CNC guide machine, PC based programmable controller or microprocessor based control, structural steel base, servo drive system, "X/Y" carriage, cantilever arm, motorized "Z" axis, catch tank, cutting table, work piece support grid/material, filtration system, high pressure pumps, pressure intensifiers, abrasive material disposal/removal system, injector to draw abrasives into cutting stream, mixing chamber, cutting nozzle (varying orifice size), abrasive removal system, chiller (optional).
Comparison and advantages: Amazing Quality Finish
Compared to saw cutting, routing, plasma cut, and laser cutting; Water jet cut finish stands alone. With a smoother, more sandblasted look, free of burnt edges, chips, burrs, and slag: it can save you in unnecessary finishing costs. Water jet cutting is in fact considered a “finish cut” and is typically used for signs and displays, most popular for its esthetics. This transposes over for many different industries because the finish is typically the smoothest and cleanest.
No Heat Affected Zone
Unlike laser or plasma cutting that could cause burning or melting, where the cut areas material can become chemically altered due to heat, Water jet cut parts remain unaffected, due to the fact that water is the medium being used. Water is well known for its insulation and absorption of heat. This can be very critical on applications where the material cannot show any signs of burning or discoloration, or on materials that cannot be cut with laser due to burning; with toxins released into the atmosphere. With water jet, very little heat is created, generated or even transferred to the part. This is extremely handy for working on tool steels, , stainless steels exotic alloys and other metals where heat could actually change the properties of the metal. Also true for plastics, acrylics, composites, laminates and phenolics.
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The final result is that no heat affected zone (HAZ) on the material is created. With the absence of a HAZ, you can secondary machine without hardening the material, generating poisonous fumes, recasting, or warping. You can also machine parts that have already been heat treated. No Mechanical Stresses
The very nature of Water jet cutting places no mechanical stresses into the work-piece. No side pressures are created because water jet pressure is forced downward, forcing the material onto the table, therefore clamping and featuring is very minimal and could practically be non-existent. Because there is no metal on metal contact not heat created, water jet machining does not introduce any stresses into the material as well
Water jets vs. Lasers Laser cutting uses a laser focused onto the material intended to melt, burn and vaporize the material. The laser can be comprised of gas (such as CO2) or solidstate. The beam can be static, where the material progresses in front of the laser, or the laser can move across the material. Advantages of water jets Cut more materials! •
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Water jets can cut reflective materials like copper and aluminum that lasers cannot. Water jets can cut a wide range of material with no change in setup. Water jets can cut heat sensitive materials that lasers will ruin. No heat-affected zone! (HAZ)
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Water jet cutting does not heat your part. There is no thermal distortion, which can occur with lasers. Water jets do not change the properties of the material. Environmentally friendly
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Abrasive jets typically use garnet as the abrasive material. Garnet is non-reactive that is biologically inert. No noxious fumes, (vaporized metal) and no risk of fires. Material Uniformity not important!
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Lasers need the material to be relatively flat (uniform). When cutting over uneven surfaces, focus can be lost thus losing cutting power. Modern Pressures of water jet exceed 60,000 psi which posses a more consistent cutting power over uneven material. Better tolerances on thicker parts
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Water jetting offers better tolerances on parts thicker than 0.5" (12 mm). Thicker materials
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Water jets easily handle from through 10". Lasers lose practicality at cutting thicknesses of 0.5" Better edge finish
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Due to the nature of Water jetting, cuts have a fine sand-blasted surface finish. Laser cuts tend to have a rougher edge, which may need additional machining operations to clean up.
Water jets vs. Electrical Discharge Machining (EDM) EDM is when an electrical arc rapidly discharges between an electrode and the work-piece material. The series of arcs removes metal by melting it and vaporizing it, essentially eroding the metal using electricity. Particles are flushed away by circulating non-conducting fluid (de-ionized water). EDM is more capable of intricate shapes in hardened metals that are extremely difficult to machine using traditional methods. Advantages of water jets Many parts that an EDM would do can be done faster and cheaper on an abrasive jet, if the tolerances are not extreme. • • •
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New Water jet technology allows for tolerances of up to +/-.003"! Abrasive jets are much faster than EDM, which slowly removes the metal. Non-conductive materials that EDM cannot touch, such as glass, wood, plastic, and ceramic are a breeze for water jet. There is almost no limit to the type of materials that can be machined with water jets.
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Uniformity of material not important A water jet will retain much of its cutting power over uneven material. Such material changes would cause wire EDM to lose consistency. Water jets make their own pierce holes For Wire EDM, a hole needs to be in the material, which has to be done by separate process. Water jets can pierce their own material which requires no additional featuring. Make bigger parts The water jet table / tank capacity is much larger and can handle a much larger sheet than the typical EDM work table. •
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Water jets vs. Plasma & Flame Cutting Plasma cutting involves a pressurized stream of gas which is blown at high speed while an electrical arc is introduced. This causes some of the gas to become hot plasma. The gas is 27,000° F (15,000° C) which melts the metal it comes into contact with. Advantages of water jets •
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Water jet can cut materials that do not easily melt (Granite, Cement, Ceramic) or that are destroyed by melting (many laminates, aluminums, exotics). Precision is enhanced by no slag or left over melted metal along the cutting edge as left by Plasma.
Water jets vs. CNC Milling CNC Milling can perform a variety of operations on material such as cutting, drilling, lathing, and planning. Modern mills are six-axis machines that can perform complex sequences rapidly and precisely. Advantages of water jets •
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Water jets can machine brittle materials, pre-hardened materials, and difficult materials such as Titanium, Has alloy, Inconel, Stainless and Hardened Tool Steels that CNC Milling does not exceed in cutting. Water jets are frequently used for complimenting or replacing milling operations. Used for roughing out parts prior to milling, or for providing secondary machining on parts that just came off the mill.
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APPLICATIONS OF WATERJET CUTTING
Flexible water jet cutting technology is used in practically all sectors of industry: Aerospace, residential and industrial construction, mechanical engineering, the glass industry, the wood, textiles and paper industries, the automotive and its supplier industries, and the electrical, electronic and foodstuffs industries. Unlike traditional thermal cutting methods, water jet cutting technology wins friends with its high level of cost-effectiveness and flexibility. The most diverse materials, from metal via plastics up to and including granite, can be quickly and precisely worked using a high-pressure jet of water. Material thickness of 150 mm or more present no difficulties to our cutting processes. The water jet achieves optimum cut-edge qualities on both simple and extremely complex contours. General 2D applications:
• Sheet metal: Stainless steel, carbon steel, high-alloy nickel steels, aluminum, titanium, copper • Building: Decorative stone, marble, granite, tiles, plasterboard, glass and mineral wool • Glass: Laminated glass, safety glass, and bulletproof glass • Foodstuffs: Baked goods, deep-frozen products and fish • Paper: Cardboard, corrugated cardboard, printing papers • Miscellaneous: Plywood, leather, textiles, composites, rubber, plastics, sealing materials and foams . 3D and robot applications: • Abrasive: Titanium, aluminum and stainless steel motor-vehicle components, turbine blades, decorative stone or marble. • Pure water: Motor-vehicle elements such as carpets, door-trims, fenders, dashboards, instrument panels, rear shelves. 8. CONCLUSIONS AND FUTURE SCOPE
Since its development, water jet machining has seen many improvements in its design. Water jet cutting technology is one of the fastest growing major machine tool processes in the world due to its versatility and ease of operation. Manufacturers are realizing that there are virtually no limits to what water jets are capable of cutting and machining. Machine shops of all sizes are realizing greater efficiency and productivity by implementing UHP water jets in their operations. Water jets are becoming the machine tool of choice for many shops. Since abrasive water jet (AWJ) technology was first invented by Flow in the early 1980s, the technology has rapidly evolved with continuous research and development. What makes water jets so popular? Water jets require few secondary operations, produce net-shaped parts with no heat-affected zone, heat distortion, or mechanical stresses caused by other cutting methods, can cut with a narrow kerfs, and can provide better usage of raw material since parts can be tightly nested. As a result of the Flow Master PC control system and intuitive operation, water jets are extremely easy to use. Typically, operators can be trained in hours and are producing high quality parts in hours. Additionally, water jets can cut virtually any
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material, leaving a satin-smooth edge. These benefits add up to significant cost savings per part in industries that have traditionally defined productivity by cost per hour. The latest development in the field of water jet cutting is the use of super water for cutting, which enhances both abrasive and non-abrasive water jet cutting.
