Optimization of Metal removal rate in end milling Using Taguchi and Anova method.

OPTIMIZATION OF METAL REMOVAL RATE IN END MILLING TAGUCHI AND ANOVA METHOD

1.2

VERTICAL

MILLING

MACHINE:

Fig 1.1 vertical milling machine

Milling machines can be found in a variety of sizes and designs, yet they still possess the same main components that enable the work piece to be moved in three directions relative to the tool. These components include the following: Base and column - The base of a milling machine is simply the platform that sits on the

ground and supports the machine. A large column is attached to the base and connects to the other components. Table - The work piece that will be milled is mounted onto a platform called the table,

which typically has "T" shaped slots along its surface. The work piece may be secured in a fixture called a vise, which is secured into the T-slots, or the work piece can be clamped directly into these slots. The table provides the horizontal motion of the work piece in the X-direction by sliding along a platform beneath it, called the saddle. Saddle - The saddle is the platform that supports the table and allows its longitudinal

motion. The saddle is also able to move and provides the horizontal motion of the work piece in the Y-direction by sliding transversely along another platform called the knee.

DEPT OF MECHANICAL ENGG, CMRCET

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Knee - The knee is the platform that supports the saddle and the table. In most milling

machines, sometimes called column and knee milling machines, the knee provides the vertical motion (Z direction) of the work piece. The knee can move vertically along the column, thus moving the work piece vertically while the cutter remains stationary above it. However, in a fixed bed machine, the knee is fixed while the cutter moves vertically in order to cut the work piece.

1.3 HORIZONTAL MILLING MACHINE: A horizontal mill has the same sort of x – y table, but the cutters are mounted on a horizontal arbor across the table. Many horizontal mills also feature a built-in rotary table that allows milling at various angles; this feature is called a universal table. While endmills and the other types of tools available to a vertical mill may be used in a horizontal mill, their real advantage lies in arbor-mounted cutters, called side and face mills, which have a cross section rather like a circular saw, but are generally wider and smaller in diameter. Because the cutters have good support from the arbor and have a larger cross-sectional area than an end mill, quite heavy cuts can be taken enabling rapid material removal rates. These are used to mill grooves and slots. Plain mills are used to shape flat surfaces. Several cutters may be ganged together on the arbor to mill a complex shape of slots and planes. Special S pecial cutters cu tters can also cut grooves, bevels, radii, or indeed any section desired. These specialty cutters tend to be expensive. Simplex mills have one spindle, and duplex mills have two. It is also easier to cut gear s on a horizontal mill. Some horizontal milling machines are equipped with a power-take-off provision on the table. This allows the table feed to be synchronized to a rotary fixture, enabling the milling of spiral features such as hypoid gears.


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FIG.1.2 HORIZONTAL MILLING MACHINE

1.4 CUTTING TOOLS AND ITS MATERIALS: A cutting tool (or cutter) is any tool that is used to remove material from the work piece by means of shear deformation. Cutting may be accomplished by single-point or multipoint tools. Single-point tools are used in turning, shaping, plaining and similar operations, and remove material by means of one cutting edge. Milling and drilling tools are often multipoint tools. Grinding tools are also multipoint tools. Each grain of abrasive functions as a microscopic single-point cutting edge and shea rs a tiny chip. Cutting tools must be made of a material harder than harder than the material which is to be cut, and the tool must be able to withstand the heat generated in the metal-cutting process. Also, the tool must have a specific geometry, with clearance angles designed so that the cutting edge can contact the work piece without the rest of the tool dragging on the work piece surface. The angle of the cutting face is also important, as is the flute width, number of flutes or teeth, and margin size. In order to have a long working life, all of the above must be optimized, plus the speeds and feeds at which the tool is run. MATERIALS:

To produce a quality product cutting tool must have three characteristics:


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Hardness — Hardness — hardness hardness and strength at high temperatures. Toughness — Toughness — toughness, toughness, so that tools don‘t chip or fracture. Wear resistance Wear resistance — — having having acceptable tool life before needing to be replaced. Cutting tool materials can be divided into two main categories: stable and unstable. Unstable materials (usually steels) are substances that start at a relatively low hardness point and are then heat treated to promote the growth of hard particles (usually carbides) inside the original matrix, which increases the overall hardness of the material at the expense of some its original toughness. Since heat is the mechanism to alter the structure of the substance and at the same time the cutting action produces a lot of heat, such substances is inherently unstable under machining conditions. Stable materials (usually tungsten carbide) are substances that remain relatively stable under the heat produced by most machining conditions, as they don't attain their hardness through heat. They wear down due to abrasion, but generally don't change their properties much during use. Most stable materials are hard enough to break before flexing, which makes them very fragile. To avoid chipping at the cutting edge, most tools made of such materials are finished with a slightly blunt edge, which results in higher cutting forces due to an increased shear area. Fragility combined with high cutting forces results in most stable materials being unsuitable for use in anything but large, he avy and stiff machinery. Unstable materials, being generally softer and thus tougher, generally can stand a bit of flexing without breaking, which makes them much more suitable for unfavorable machining conditions, such as those encountered i n hand tools and light machinery. machiner y. Tool material

Properties

Unstable. Very inexpensive. Extremely sensitive to heat. Mostly obsolete in Carbon

today's commercial machining, although it is still commonly found in non-

steels

intensive applications such as hobbyist or MRO machining, where economy-grade drill bits, taps and dies, hacksaw blades, and reamers are still usually made of it (because of its affordability). Hardness up to about


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HRC 65. Sharp cutting edges possible.

High speed steel(HSS) steel(HSS)

Unstable. Inexpensive. Retains hardness at moderate temperatures. The most common cutting tool material used today. Used extensively on drill bits and taps. Hardness up to about HRC 67. Sharp cutting edges possible.

Unstable. Moderately expensive. The high cobalt versions of high speed steel are very resistant to heat and thus excellent for machining abrasive HSS cobalt

and/or work hardening materials such as titanium and stainless steel. Used extensively on milling cutters and drill bits. Hardness up to about HRC 70. Sharp cutting edges possible.

Cast

cobalt

alloys

Stable. Expensive. Somewhat fragile. Despite its stability it doesn't allow for high machining speed due to low hardness. Not used much. Hardness up to about HRC 65. Sharp cutting edges possible.

Stable. Moderately expensive. The most common material used in the industry today. It is offered in several "grades" containing different Cemented carbide

proportions of tungsten carbide and binder (usually cobalt). High r esistance to abrasion. High solubility in iron requires the additions of tantalum of tantalum carbide and niobium carbide for steel usage. Its main use is in turning tool bits although it is very common in milling cutters and saw blades. Hardness up to about HRC 90. Sharp edges generally not recommended.

Stable. Moderately inexpensive. Chemically inert and extremely resistant to Ceramics

heat, ceramics are usually desirable in high speed applications, the only drawback being their high fragility. Ceramics are considered unpredictable under un favourable conditions. The most common ceramic materials are


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based on alumina (aluminium oxide), silicon nitride and silicon carbide. Used almost exclusively on turning tool bits. Hardness up to about HRC 93. Sharp cutting edges and positive rake angles are to be avoided.

1.5 SELECTION OF A MILLING CUTTER Selecting a milling cutter is not a simple task. There are many variables, opinions and lore to consider, but essentially the machinist is trying to choose a tool which will cut the material to the required specification for the least cost. The cost of the job is a combination of the price of the tool, the time taken by the milling machine, and the time taken by the machinist. Often, for jobs of a large number of parts, and days of machining time, the cost of the tool is lowest of the three costs. Material: High speed steel (HSS) cutters are the least-expensive and shortest-lived cutters.

Cobalt steel is an improvement on HSS and generally can be run 10% faster . Carbide tools are more expensive than steel, but last longer, and can be run much faster, so prove more economical in the long run. HSS tools are perfectly adequate for many applications. The progression from HSS to cobalt steel to carbide could be viewed as very good, even better, and the best. Diameter: Larger tools can remove material faster than small ones, therefore the largest possible

cutter that will fit in the job is usually chosen. When milling an internal contour, or concave external contours, the diameter is limited by the size of internal curves. The radius of the cutter must be less than or equal to the radius of the smallest arc. Flutes: More flutes allows a higher feed rate, because there is less material removed per flute.

But because the core diameter increases, there is less room for swarf, so a balance must be chosen. Coating: Coatings, such as titanium nitride, also increase initial cost but reduce wear and

increase tool life. Helix angle: High helix angles are typically best for soft metals, and low helix angles for hard

or tough metals.

1.6 WORK HOLDING METHOD:


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In the machining of a complex component, it is usually started off with the milling of a rectangular block. To ensure that each surface of the rectangular block is perpendicular to its neighbouring surfaces, the following points should be noted:

The vice jaws and the work piece must be free from burrs, chips, and cutting fluid.



Smaller work piece should be supported by parallel bars to provide the supporting datum.



Round bar must be placed between the work piece and the movable jaw to ensure that the work piece is in perfect contact conta ct with the fix jaw.



The vice handle should be tightened by hand to avoid over clamping of the work piece as well as the vice. Hide face hammer should be used to assure that the work piece is in perfect contact with the supporting base.



On completion of the milling of the first face, the work piece should be unloaded, deburred, and cleaned before the next operation.



To machine the second and the third faces, the work piece should be clamped with its preceding machined surface facing against the fix jaw of the vice.



Similar clamping method can be applied in the machining of the fourth face.



Yet it can also be clamped on the vice without the round bar



Both ends of the work piece can be machined with the periphery flutes of the cutter using up cut milling.

FIG.1.3 Holding Method by Using a Machine Vice


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1.7 TYPES OF MILLING CUTTERS Different types of cutters that can be used in ho rizontal milling are those listed below. Plane (helical) mill Form relieved mill Staggered tooth mill Double angle mill Another operation known as a straddle milling is also possible with a horizontal milling machine. This form of milling refers to the use of multiple cutters attached to the arbor and used simultaneously. Straddle milling can be used to form a complex feature with a single

cut.

For vertical milling machines, the cutters take a very different form. The cutter teeth cover only a portion of the tool, while the remaining length is a smooth surface, called the shank. The shank is the section of the cutter that is secured inside the collet, for attachment to the spindle. Also, many vertical cutters are designed to cut using both the sides and the bottom of the cutter. Listed below are several common vertical cutters. Flat end mill Ball end mill Chamfer mill Face mill Twist drill Reamer

1.8 END MILLS: An end mill is a type of milling of milling cutter, a cutting tool used in industrial milling applications. It is distinguished from the drill bit in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, a milling bit can generally cut in all directions, though some cannot cut axially. Endmills are used in milling applications such as profile milling, tracer milling, face milling, and plunging.


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FIG.1.4 END MILLS

Several broad categories of end- and face-milling tools exist, such as centre-cutting versus non-centre-cutting and categorization by number of flutes; by helix angle; by material; and by coating material. Each category may be further divided by specific application and special geometry. It is becoming increasingly common for traditional solid endmills to be replaced by more cost-effective inserted cutting tools (which, though more expensive initially, reduce toolchange times and allow for the easy replacement of worn or broken cutting edges rather than the entire tool). End mills are sold in both imperial and metric shank and cutting diameters

1.8.1 END MILLING: End Milling is the milling of a flat surface with the axis of the cutter perpendicular to the machining surface .


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FIG 1.5 End Milling

1.9 CONVENTIONAL MILLING: The chip thickness starts at zero thickness, and increases up to the maximum. The cut is so light at the beginning that the tool does not cut, but slides across the surface of the material, until sufficient pressure is built up and the tooth suddenly bites and begins to cut. This deforms the material (at point A on the diagram, left), work hardening it, and dulling the tool. The sliding and biting behaviour leaves a poor finish on the material.

1.10 CLIMB MILLING: Each tooth engages the material at a definite point, and the width of the cut starts at the maximum and decreases to zero. The chips are disposed behind the cutter, leading to easier scraps removal. The tooth does not rub on the material, and so tool life may be longer. However, climb milling can apply larger loads to the machine, and so is not recommended for older milling machines, or machines which are not in good condition. This type of milling is used predominantly on mills with a backlash eliminator.


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1.11 MILLING OPERATIONS: During the process cycle, a variety of operations may be performed to the work piece to yield the desired part shape. The following operations are each defined by the type of cutter used and the path of that cutter to remove material from the work piece. a) End milling : An end mill makes either peripheral or slot cuts, determined by the step-over

distance, across the work piece in order to machine a specified feature, such as a profile, slot, pocket, or even a complex surface contour. The depth of the feature may be machined in a single pass or may be reached by machining at a smaller axial depth of cut and making multiple passes

Fig 1.7 End milling b) Chamfer milling: A chamfer end mill makes a peripheral cut along an edge of the work

piece or a feature to create an angled surface, known as a chamfer. This chamfer, typically with a 45 degree angle, can be machined on either the exterior or interior of a part and can follow either a straight or curved path.

Fig 1.8 chamfer milling


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C) Face milling: A face mill machines a flat surface of the work piece in order to provide a

smooth finish. The depth of the face, typically very small, may be machined in a single pass or may be reached by machining at a smaller axial depth of cut and making multiple passes.

Fig 1.9 Face milling d) Drilling: A drill enters the work piece axially and cuts a hole with a diameter equal to that

of the tool. A drilling operation can produce a blind hole, which extends to some depth inside the work piece, or a through hole, which extends completely through the work piece.

Fig 1.10 Drilling e) Boring: A boring tool enters the work piece axially and cuts along an internal surface to

form different features. The boring tool is a single-point cutting tool, which can be set to cut the desired diameter by using an adjustable boring head. Boring is commonly performed after drilling a hole in order to enlarge the diameter or obtain more precise dimensions.


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Fig 1.11 boring f) Counter boring: A counter bore tool enters the work piece axially and enlarges the top

portion of an existing hole to the diameter of the tool. Counter boring is often performed after drilling to provide space for the head of a fastener, such as a bolt, to sit below the surface of a part. The counter boring tool has a pilot on the end to guide it straight into the existing hole.

Fig 1.12 Counter boring g) Countersinking: A countersink tool enters the work piece axially and enlarges the top

portion of an existing hole to a cone-shaped opening. Countersinking is often p erformed after drilling to provide space for the head of a fastener, such as a screw, to sit flush with the work piece surface. Common included angles for a countersink include 60, 82, 90, 100, 118, and 120 degrees.

Fig 1.13 Countersinking


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h) Reaming: A reamer enters the work piece axially and enlarges an existing hole to the

diameter of the tool. Reaming removes a minimal amount of material and is often performed after drilling to obtain both a more accurate diameter and a smoother internal finish.

Fig 1.14 Reaming i) Tapping : A tap enters the work piece axially and cuts internal threads into an existing hole.

The existing hole is typically drilled by the required tap drill size that will accommodate the desired tap. Threads may be cut to a specified depth inside the whole (bottom tap) or the complete depth of a through hole (through tap).

1.12 CUTTING PARAMETER In milling, the speed and motion of the cutting tool is

specified through several parameters. These parameters are selected for each operation based upon the work piece material, tool material, tool size, and more. a) Cutting feed: The distance that the cutting tool or work piece advances during one revolution of the spindle and tool, measured in inches per revolution (IPR). In some operations the tool feeds into the work piece and in others the work piece feeds into the tool. For a multi-point tool, the cutting feed is also equal to the feed per tooth, measured in inches per tooth (IPT), and multiplied by the number of teeth on the cutting tool. b) Cutting speed: The speed of the work piece surface relative to the edge of the cutting tool during a cut, measured in surface feet per minute (SFM). c) Spindle speed: The rotational speed of the spindle and tool in revolutions per minute


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(RPM). The spindle speed is equal to the cutting speed divided by the circumference of the tool. d) Feed rate: The speed of the cutting tool's movement relative to the work piece as the tool makes a cut. The feed rate is measured in inches per minute (IPM) and is the product of the cutting feed (IPR) and the spindle speed (RPM). e) Axial depth of cut: The depth of the tool along its axis in the work piece as it makes a cut. A large axial depth of cut will require a low feed rate, or else it will result in a high load on the tool and reduce the tool life. Therefore, a feature is typically machined in several passes as the tool moves to the specified axial ax ial depth of cut for each pass. f) Radial depth of cut: The depth of the tool along its radius in the work piece as it makes a cut. If the radial depth of cut is less than the tool radius, the tool is only partially engaged and is making a peripheral cut. If the radial depth of cut is equal to the tool diameter, the cutting tool is fully engaged and is making a slot cut. A large radial depth of cut will require a low feed rate, or else it will result in a high load on the tool and reduce the tool life. Therefore, a feature is often machined in several steps as the tool moves over the step-over distance, and makes another cut at the radial depth of cut.

Peripheral cut

Slot cut

Fig 1.16 peripheral cut

Fig 1.17 slot cut


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1.13 DEFECTS

Most defects in milling are inaccuracies in a feature's dimensions or surface roughness. There are several possible causes for these defects, including the following: a) Incorrect cutting parameters: If the cutting parameters such as the feed rate, spindle speed, or axial depth of cut are too high, the surface of the work piece will be rougher than desired and may contain scratch marks or even burn marks. Also, a large depth of cut may result in vibration of the cutter and cause inaccuracies in the cut. b) Dull cutter: As a cutter is used, the teeth will wear down and become dull. A dull cutter is less capable of making precision cuts. c) Unsecured work piece: If the work piece is not securely clamped in the fixture, the friction of milling may cause it to shift and alter the desired cuts

1.14 METAL CUTTING 

The purpose of metal cutting operation commonly called machining is to produce a desired shape, size, and finish of a component by removing the excess material in the form of chips from a block of material.



A cutting tool exerts a compressive force on the work piece which stresses the work material beyond its yield point and therefore the material deform plastically and shears off.



CHIPS: The sheared material begins to flow along the cutting tool face in the form of small pieces called chips. The applied compressive forces which leads to the formation of chips is cutting force.


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Fig 1.18 Metal cutting

1.14.1 TYPES OF CHIPS: 

Continuous chip



Continuous chip with built up edge



Non homogeneous chip



Discontinuous chip



CONTINUOUS CHIPS: This type of chip is produced when ductile materials such

as Aluminum, copper, Wrought Iron, and Mild steel are machined at normal cutting speeds. This type of chip is produced when there is low friction between chip and tool face. 

CONTINOUS CHIPS WITH BUILD UP EDGE : When high friction exists

between chip and the tool, the chip material, which in turn leads to the building up of o f layer upon layer of chip material. Thus the built up material is referred to as a built up


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edge. 

DISCONTINUOUS CHIP: This type of chip is produced while machining brittle

materials such as cast iron or cast brass but may also be produced when machining ductile materials at very low speeds and high feeds. For brittle materials discontinuous chip is associated with fair surface finish lower power consumption and reasonable tool life. 

NON HOMOGENEOUS CHIP: These chips are formed by notches on the free side

of the chip and they formed due to non uniform strain in the material during chip formation. 1.15 MATERIAL REMOVAL RATE MEASUREMENT

Material removal rate (MRR) has been calculated from the difference of weight of work piece before and after experiment.

MRR= W1-W2/densiy*time mm3/min

Where W1= initial weight of the specimen W2= final weight of the specimen Density is in grams per cubic volume density of mild steel is (7.8 x 10-3g/mm3). The weight of the work piece has been measured in a high precision digital balance meter which can measure up to the accuracy of 10-4 g and thus eliminates the possibility of large error while calculating material removal.


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FIG1.19 Digital Balance meter

STOPWATCH: A stop watch is a handled time piece designed to measure the amount of time elapsed from a particular time when activated to when the piece is deactivated. A large digital version of a stopwatch designed for viewing at a distance, as in a sports stadium is called stop clock.


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In our project we used it for measuring the machining time, that is time required to complete one pass of the spindle, with desired speed, feed and depth of cut. It is preferred because of its accuracy.

1.16 TOOL HOLDING DEVICE USED:

Fig 5.6 Collet Collet is a cone-shaped sleeve used for holding circular or rod like pieces in milling or other machine. A collet is a metal band placed around a cutting tool to prevent it from splitting. In manufacturing, a collet is a type of chuck used to hold cylindrical objects in milling. This type of chuck is a metal cone-like device that surrounds the work piece and applies an equal amount of holding pressure to the entire circumference o f the piece. Typically found on milling, grinders and lathe machines, the collet is know for its extreme accuracy. Much more accurate than a multi-jaw type chuck, the collet holds the work piece to exacting tolerances. Its downside is that it typically fits only one size of work piece. The chuck is, however, very easily changed when the need to work on a different size of stock arises.


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While the collet is designed to primarily work with round stock, octagonal, square and even hexagonal work pieces can be used in the chuck. Many manufacturers utilize this type of chuck when completing very precise operations and doing very detailed work. Special emergency-type collets can be machined to hold different shapes of stock as well as different sizes. Collet chucks

Fig 5.7 Collet chucks Chucks are made of special hardened steel to withstand many use cycles, as would be typical in a high-volume manufacturing environment. There are, however, collets made of brass and even nylon n ylon that can be custom made to hold h old special work pieces. These chucks can also be made in step models that are machined to hold shorter pieces that have a larger diameter than the standard size chuck. There are several advantages to using a collet chuck over a self-centering or multi-jaw type chuck. To decipher which type of chuck to use there are some key points to consider. Spindle speed is crucial to chuck choice. A high-speed tooling requires the lower mass chuck


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over the higher mass and weight of a self-centering chuck. The lighter weight and less mass allows the chuck to accelerate in a much faster manner. When working on a large run order or creating many identical pieces, the collet allows for easy stock changing and precise holding. Also, when the parts are of a diameter of less than three inches, this type of chuck is preferred due to its holding power and easy operating tendencies. When making multiple operation cuts on a work piece, the collet provides a much tighter clamping tolerance, thereby ensuring that the outcome of the different steps will be precise.

1.17 OBJECTIVES OF EXPERIMENT : This project was developed to study about the cutting parameter in milling using end mills with dampers. The main purposes of this project a re listed below:

a) To study about the influence of Spindle speed on material removal rate on mild steel.

b) To design a series of experiment using the help of Design of Experiments (DOE) layout.

c) To study about the best combination of solution for maximizing the Material Removal Rate (MRR) with Taguchi Method and analyzing the obtained values values by using ANOVA.

1.18 SCOPE OF EXPERIMENT: Literature depicts that a considerable amount of work has been carried out by previous investigators for modeling, simulation and parametric optimization of metal cutting properties of the product in milling operation. Issues related to metal cutting or metal removal rate, are studied. A part from optimizing a single response, multi objective optimization problems have also been solved using Taguchi method.


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CHAPTER 2 LITERATURE REWIEW

Traditionally, the selection of cutting conditions for metal cutting is left to the machine operator. In such cases, the experience of the operator plays a major role, but even for a skilled operator it is very difficult to attain the optimum values each time. Machining parameters in metal turning are cutting speed, feed rate and depth of cut. The setting of these parameters determines the quality characteristics of turned parts. Following the pioneering work of Taylor (1907) and his famous tool life equation, different analytical and experimental approaches for the optimization of machining parameters have been investigated. Brewer (1966) suggested the use of Lagrangian multipliers for optimization of the constrained problem of unit cost, with cutting power as the main constraint. Bhattacharya et al (1970) optimized the unit cost for turning, subject to the constraints of surface roughness and cutting power by the use of Lagrange‘s Lagrange‘s method. Walvekar & Lambert (1970) discussed the use of geometric programming to selection of machining variables. They optimized cutting speed and feed rate to yield minimum production cost. Petropoulos (1973) investigated optimal selection of machining rate variables, viz. cutting speed and feed rate, by geometric programming. A constrained unit cost problem in turning was optimized by machining SAE 1045 steel with a cemented carbide tool of ISO P-10 grade. Sundaram (1978) applied a goal-programming technique in metal cutting for selecting levels of machining parameters in a fine turning operation on AISI 4140 steel using cemented tungsten carbide tools. Ermer & Kromodiharajo (1981) developed a multi-step mathematical


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Optimization of machining techniques model to solve a constrained multi-pass machining problem. They concluded that in some cases with certain constant total depths of cut, multi-pass machining was more economical than single-pass machining, if depth of cut for each pass was properly allocated. They used high speed steel (HSS) cutting tools to machine carbon steel. For a given combination of tool and work material, the search for the optimum was confined to a feed rate versus depth-ofdepth-of-cut cut plane defined by the chip-breaking chip-breaking constraint. Some of the other constraints considered include power available, work holding, surface finish and dimensional accuracy. Tsai (1986) studied the relationship between the multi-pass machining and single-pass machining. He presented the concept of a break-even point, i.e. there is always a point, a certain value of depth of cut, at which single-pass and double-pass machining are equally effective. When the depth of cut drops below the break-even point, the single-pass is more economical than the double-pass, and when the depth of cut rises above this breakeven point, double-pass is better. Carbide tools are used to turn the carbon steel work material. Surface finish and machine power were taken as the constraints while optimizing cutting speed and feed rate for a given depth of cut. Agapiou (1992) formulated single-pass and multi-pass machining operations. Production cost and total time were taken as objectives and a weighting factor was assigned to prioritize the two objectives in the objective function. He optimized the number of passes, depth of cut, cutting speed and feed rate in his model, through a multi-stage solution process called dynamic programming. Several physical constraints were considered and applied in his model. In his solution methodology, every cutting pass is independent of the previous pass; hence the optimality for each pass is not reached simultaneously. Prasad et al (1997) reported the development of an optimization module for determining process parameters for turning operations as part of a PC-based generative CAPP system.


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The work piece materials considered in their study include steels, cast iron, aluminum, copper and brass. HSS and carbide tool materials are considered in this study. The minimization of production time is taken as the basis for formulating the objective function. The constraints considered in this study include power, surface finish, tolerance, and work piece rigidity, range of cutting speed, maximum and minimum depths of cut and total depth of cut. Improved mathematical models are formulated by modifying the tolerance and work piece rigidity constraints for multi-pass turning operations. The formulated models are solved by the combination of geometric and linear programming techniques. The first concept of High Speed Machining (1931) was presented by Carl J Salomon [1], who is considered as the father of high speed machining. The results of his experiments, carried out on non-ferrous metals such as Aluminum, Copper and Bronze, using helical milling cutters at speeds up to 18067 m/min (surface meters per minute) revealed that with the increase of cutting speed, the cutting temperature increases up to a maximum value close to the melting point of the material and then decreases with further increase in speed [2]. This implies that there is a possibility of gaining the advantage of high speeds without the limitations due to heat generation.

As explained by King

& Vaughn [2], subsequent researchers were unable to find

experimentally, the decreasing nature of temperature with increasing speed and they tried to verify this by studying the experimental method that Salomon used. Schmidt [3] criticized Salomon‘s test results and he claimed that the temperature-speed temperature-speed plot presented by Salomon is valid only for the temperatures found to the left of the peak value. Since the cutting temperature increases with cutting speed there is a limitation on the tool as the temperature reaches the melting point of the material. Resht [4] studied ultra-high speed machining and theoretically analysed the variation of tool-chip interface temperature with the speed. As the heat generated at the tool-chip interface must be conducted into the chip, the rate of heat conducted away has to be increased. Therefore he predicted that the tool-chip interface temperature increases to a peak with the cutting speed and developed a mathematical model for prediction. His work was confirmed later by tests by McGee [5]


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on high speed milling of Aluminum (at 3000m/min) and revealed the possibility of taking the advantage of high speed machining, as there will not be further increase in temperature beyond the melting temperature of the material, provided that the tool can withstand the temperature. These studies show that the temperature Salomon was referring to, can be the tool-chip interface temperature rather than the temperature at the shear zone. McGee [5] investigated high-speed end milling of Aluminum alloys and derived optimum cutting parameters for three types of Aluminum alloys using the results of empirical methods. For 6061-T651 Aluminum alloy it was shown that the optimum machining parameters as; feed of 0.200.25 mm/tooth and speed of 2,225 m/min for end milling. He concluded that carbide tools are preferred for Al alloys and finally that the HSM is a cost effective process and these results are of great importance for the industry. Tugrul et al [6] investigated the flat end milling operation and used Finite Element Method (FEM) simulations to predict chip formation, cutting temperatures, tool stresses and cutting forces. They used P20 steel as the material and plain Tungsten carbide as the tool for this special straight cutting edge end milling process and cutting conditions were; cutting speed of 200 m/min, feeds of 0.1 and 0.155 mm/tooth. The comparison of the predicted two force components (measured with the rotation angle) with the experimental results, showed a satisfactory agreement except a deviation shown for some angles. They considered this as successful at this 2D stage as the deviation was no t present at all the angles. A study by Mativenga and Hon [7] considered the dynamic force signals generated in end-milling operation in a rotational speed range of 3750 – 31500 rpm. These experimental dynamic force signals have been studied using a real-time data acquisition system and in addition to the force components, the amplitude-frequency plots have been studied to characterize the occurrence of peaks in the force signal.. Another finding of the study was that in single tooth ball-nose end milling of H13 tool steel, as the tool traverses over the swept angle of the cut, cut, the force doesn‘t build to a maximum following a DEPT OF MECHANICAL ENGG, CMRCET

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sinusoidal function but it builds up to a maximum by a series of distinct peaks. It has been found that the tooth passing frequency is responsible for the most significant and base mode in the force harmonic signal.


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CHAPTER 3 REDUCTION OF VIBRATIONS IN MILLING CUTTER

3.1 MILLING CUTTER CHATTER

Eliminating chatter or noisy vibration in mold making and other cavity milling operations pays off in greater productivity. It increases metal removal rates, enhances surface finishes with fewer finishing steps and reduces scrap. Eliminating vibration also reduces wear on cutting tools and machining centers to minimize machine downtime. Poor fixturing, work holding and machine maintenance all contribute to vibration and its associated problems. The best way to quiet chatter is often a combination of remedies. However, machine operators and manufacturing engineers generally look first at their cutting tools. A knowledgeable supplier of both segmented and solid carbide cutting tools can integrate total solutions to stop the chatter. Vibration in cavity milling creates uneven wear on cutting tools and shortens tool life. While index able insert milling cutters and solid carbide end mills differ in construction, they are both vulnerable to chatter and share some common vibration remedies. Index able insert milling cutters are generally available in diameters down to one-half inch. They use replaceable inserts with a choice of geometries and coatings. Smaller openings call for solid carbide end mills with two, three or four cutting edges. There are steps that users can take to end vibration with both milling cutters and end mills. a) Use cutters with fewer inserts: Although it may seem counterintuitive, the first step to reducing chatter in milling operations is to switch to a cutter with fewer teeth. In general, the coarser the cutter pitch, the lesser the chance of harmonic vibration. Sometimes, replacing a 16-tooth cutter with a 12-tooth tool ends chatter altogether. A differential-pitch cutter may be required in more difficult cases to eliminate troublesome harmonics.


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The larger the cutter, the better the performance will be. Conditions permitting, larger cutters provide more choices about how to approach the work piece. Varying the relative position often helps damp vibration. Manufacturing engineers should try to keep the cutter diameter 20 to 50 percent larger than the width of the cut. The cutter should be sized so that no more than two-thirds of the inserts are engaged in the cut at any time. These guidelines help produce an ideal entry angle, thereby reducing cutting forces and vibration. b) Optimize insert geometry: The shape of the cutting inserts often determines their vibration tendency. Round inserts are most vibration prone, while those with 45-degree lead angles are the least prone to chatter. The smaller the entry angles of the cutting edge to the work, the lower the tendency tendenc y to vibrate. Cutting tool specifies can reduce overall cutting force and resulting vibration by using positive rake insert geometry. The shearing action of positive rake cutters reduces cutting pressure by more than 20 percent versus zero- or negative-rake milling tools. The sharper edge and angle of entry of this type of insert also helps to reduce the power needed to penetrate the surface of the work piece. c) Choose inserts coatings carefully: Coatings on inserts perform many functions, but their primary jobs are protecting against heat, maintaining lubricity and preventing buildup on the insert. To reduce edge rounding and chatter, you should look to replace inserts protected by thick CVD coatings with those wearing thinner PVD coatings. Though C VD treatments are formulated for wear resistance, PVD coatings provide a sharper insert edge and a more positive rake angle to help minimize vibration. 3.1.1 STIFFER TOOLS, LESS VIBRATION

The same anti-vibration principles true for index able milling cutters also apply to solid end mills. To reduce vibration, users should select end mills with fewer teeth and a high helix. A steeper helix corresponds to a more positive rake. A shallow helix is equivalent to a negative rake. To minimize vibration, end mill users should examine using helix angles from 30 to 60 degrees relative to the centerline of the tool.


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a) Minimize length; maximize diameter: In addition to positive rake and high helix angles, both milling cutters and end mills should be as stiff as possible. Machine operators and manufacturing engineers should do everything possible to minimize the bending or deflection of cutting tools. A rule of thumb t humb states that reducing the length of o f the tool by 20 percent reduces the amount of bending in the tool by 50 percent. Likewise, increasing the diameter of a cutting tool by 20 percent cuts deflection in half. In practical terms, this usually means that you should try to use the largest diameter tool you can to do the job. In addition to large diameter tools, try to use the shortest tool possible for each application. Many operators tend to choose a tool that meets the most demanding case on a work piece requiring multiple operations. For a work piece with several hole depths, the same long tool selected to make the deepest hole is also used to make shallower penetrations. Using a longer-than-necessary tool in shallow holes contributes instability to the entire operation and invites chatter. Programming the machine to use the right tool for each step minimizes vibration and maximizes productivity for th e entire job. 3.1.2 FEEDS, SPEEDS AND ANGLES

a) Maintain feed pressure per tooth: To minimize vibration, don't try to go easy on tools by reducing feed pressure. Too light a feed allows the tool to slip and is just as prone to generate vibration as too heavy a feed pressure. Use the loading recommended by the tool supplier to minimize chatter and maximize tool life. b) Increase feed rate: Machine operators commonly respond to a vibration problem by reducing the cutting speed and leaving the table feed alone. Speeding up the machine or the feed may seem like a recipe for disaster. However, an increase in feed at the same rpm may turn out to be the ideal solution. Anyone who has experienced harmonic vibrations in a car on the highway knows either speeding up or slowing down can end the noise. Similar experimentation can counter the complex harmonics of milling chatter. c) Vary entry points: Moving the centerline of the cutter slightly too either side of the entry point on the work piece can often reduce the tendency to chatter or vibrate. The offset creates a finer entry angle and prevents forces from oscillating from one side of the


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cutter to the other. For a two- to three-inch face mill, the offset may be 3/16". For a oneinch end mill, the offset may be 0.0050". Again, experimentation can determine the lowvibration setting.

3.2 TOOLHOLDING OPTIONS a) Balance and true cutting tools: Cavity milling operators seeking to minimize vibration should make sure that their tool is properly balanced and that it is mounted true to the spindle center. Strategies for connecting the tool to the machining center vary widely. Especially on milling jobs with long overhang, machine operators should avoid tool holders that rely only on setscrews or keyways to transmission of torque. Modern tool holding solutions, like a modular tool holding system, can help ensure balance and true mounting One system reduces tool run out to less than eighty millionths of an inch. The holder design maintains 100 percent contact in the clamping area where torque is transmitted to the tool. For shanked tools, a hydro mechanical chuck improves tool balance and stability, and thereby reduces uncontrolled vibration.

3.3 INTEGRATED SOLUTION Chatter is the product of every element in the cavity milling process, including the tools, the machine and the work piece. The total system remedy is to eliminate all vibration sources that can lead to harmonic responses. Run the job on the "tightest" machine available. The more that the machine's ways and spindle are tight and robust, the less vibration will occur. Keep the structure rigid from spindle to cutting edge. Clamp the part to minimize movement, vibration and deflection. Add support close to the areas to be machined. Vibration is most likely in work pieces with a long overhang. As a rule of thumb, whenever a cutter's shank aspect ratio - its length-to-diameter ratio - exceeds three to one, the risk of vibration rises rapidly. With ratios over five to one, vibration-damping adapters/extenders and modular tool holders can help. Unlike solid adapters that transmit vibrations readily, today's vibration-damping adapters have an internal chamber


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containing a heavy body suspended on rubber bushings. Machine operators should position the milling cutter as close to the tuned adapter as possible. Tooling is just one element in the campaign against vibration.

3.4 FRICTION DAMPERS Self-excited vibration in cutting tools has been a significant problem in the area of highspeed machining due to its detrimental effect on the tool and the machined surface. Theoretical models were developed and the magnitude of frictional work produced by the damper was obtained by optimizing the physical dimensions of the design. Three different tools, solid, hollow, and damped, were selected for investigation and were fabricated with identical profiles. Initial tests to understand the tool characteristics were performed by measuring the frequency response function (FRF) of the tools. The effect of spindle speeds on the dynamic behavior of the spindle/holder/tool at the tool point was studied by obtaining the rotating FRF at different speeds. Stability lobes were obtained based on the measurements and the difference in stability limits between the static and rotating FRF measurements was plotted. The effect of the damper on the cutting tool dynamics, compared with the solid and the hollow tools, was also determined based on measured FRFs at the tool point .To verify the preliminary results, a series of cutting tests were performed on the three tools, and a method to identify the stability limits was developed by recording the audio signal during the cut. The results were then plotted to show the the effect of spindle spindle speed on stability limits providing a measure of performance of the three tools. The concept of frictional damping was verified when the damped tool achieved a sixty-six percent improvement in cutting depth over the solid tool. The results also showed that lobes developed from dynamic measurements are more realistic than statically generated, non-rotating FRFs. Finite element analysis can also be used to analyze complex systems for stress and displacement. ANSYS was used to perform the analysis. The damper model was created as an extruded cylinder slit along its length and was assembled coaxially inside a hollow shaft. While the results obtained from the theoretical model explain the behavior


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of the damper inside the tool, cutting tests must be performed on the tool-damper assembly to see the effect of the damper on tool stability. Frictional work predicted from the theoretical model is just an approximation of work magnitude that could be obtained from the damper design. This is because theoretical models sometimes tend to overlook the actual testing conditions and may result in overestimating the values. To verify the analytical results cutting tests were performed. In an effort to control vibration in cutting tools, a method is developed to stabilize the high frequency chatter vibration in end mills by employing a friction damper. It is observed that end mills during machining, when unstable, produced chatter frequency of more than 1 KHz. This caused a reduced tool life and a bad surface quality on the machined surface. In order to improve the tool life and to reduce chatter, implemented a frictional dampers are introduced. Frictional damper is proposed for suppression of chatter in slender end mill tool. This damper is made of a core and multi fingered hollow cylinder .The core is press fitted into the hollow cylinder and they both are press fitted into an axial hole inside the tool. This combination produces the resisting frictional stress against the stress reaction. An analytical model including accurate modeling of friction in sliding and pre-sliding region is developed for this damper. Finally, the optimal damped tool with damper inside is fabricated and experimentally tested in comparison with traditional tool. The results show a considerable improvement in tool performance. An acceptable agreement between analytical and experimental results is obtained which show the effectiveness of damped tool in improvement of tool performance. The damping caused by the structure in the model is due to the principle of axial shear in beams. It is well known from the elementary engineering subject called Mechanics of Material, that beams undergo internal shear deformation along their axes during bending. Members of a composite beam that are not securely fixed together will slide over each other in proportion to their distance from the neutral axis of the composite beam. It is this same sliding which would occur in the model beam while bending as long as the neutral axis of the internal members, or fingers, does not coincide with the neutral axis of the composite beam. DEPT OF MECHANICAL ENGG, CMRCET

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CHAPTER-4

4.1 PROCESS VARIABLES: Milling operates on the principle of rotary motion. A milling cutter is spun about an axis while a

work piece is advanced through it in such a way that the blades of the cutter are

able to to shave chips chips of material with each pass. There are many variables affect the cutting process like spindle speed, feed, hardness of the work piece, properties of the tool, properties of the work piece, In the present experimental study, spindle speed, feed rate, type of tool and depth of cut have been considered as process variables.

Spindle speed: The spindle speed is the rotational frequency of the spindle measured in

revolutions per minute (RPM), Excessive spindle speed may cause premature tool wear, and can cause tool chatter, all of which can lead to potentially dangerous conditions. Using the correct spindle speed and tool will greatly enhance the tool life and quality of surface finish.

Feed rate: Feed rate is the velocity at which cutter is fed, that is advanced against the

work piece units are measured in millimeters per revolution, feed rate is dependent on 

Type of tool.



Quantity of material to be removed.



Power available at spindle.



Strength of the work piece.

If the feed is given opposite to the direction of milling tool, this means the teeth of the tool are pulling the chips out. In this type of feed chips are small and have a very low force in contact this result in tool wear and rough surface finish. Counter to the above if the feed is given given towards the direction of rotating tool, tool, then continuous chip formation will take place which results in smooth surface finish.


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Axial depth of cut: Cutting speed and feed rate come together with depth of cut that

means it is the volume of the material removed per unit time. Type of tool: This also plays a prominent role in metal removal rate, In this experimental

study we used two (solid, hollow) different types of tools including one, two, three, four, five dampers. Since dampers help us to minimize the vibrations of tool. Dampers: A damper is a mechanical device designed to dissipate mechanical energy, or

It is a device that counters the effects of inertia and other forces of motion. The damper does not negate the forces but it absorbs.

Fig 4.1 dampers 4.2 EQUIPMENT USED: a)Universal Knee-type milling machine: It is a mini type milling machine used for

milling on flat surfaces, inclined face face and vertical surface and slots by employing disc cutters, angular cutters, formed cutters, face metal milling and end milling cutters. When mounted in vertical attachments it can perform various operations.


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MACHINE SPECIFICATIONS :

Machine number in machine tools lab=03 Manufactured by – Masters machine tools and traders. Model- 02 Serial Number-02


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Fig 4.2 vertical milling machine b) Cutting tool used : HSS M8 with 19.05 mm diameter with four flutes Tool material used-HSS-These are basically high carbon steel with significant quantities

of tungsten, Molybdenum, Chromium, Vanadium and Cobalt. These alloying elements improve hardness, harden ability, toughness and wear resistance. They also improve high temperature properties. These steels retain the keenness of the cutting edge and hardness up to 600 Celsius degrees, thereby permitting much higher cutting speeds. There are two types of

high speed steel. T type for tungsten predominant alloy alloy and M

type for Molybdenum predominate alloy. According AISI (American Iron and Steel Institute) designation Molybdenum HSS are slightly tougher than tungsten

variety.

Presence of chromium improves harden ability, vanadium improves abrasion resistance. Grind ability decreases with higher percentage of vanadium.HSS are used for single point tools, milling cutters drills, broaches, shavers, taps and tool bits. c) Work piece used:


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AISI MS bar with 50*50 dimensions. (Length=50 and breadth =50)

Fig 4.3 work piece

4.4 end mill This is the solid end mill used in our experiment


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4.3 EXPERIMENTAL PROCESS: Following is the plan of experiment a) Checking and preparing the vertical knee-type milling machine ready for performing the

milling operation.

b) Mild steel was the metal used in this study project with young's modulus of 210Gpa and density of 7.8 grams per cubic meter. Of dimensions 50mm both length and breadth. c) Servo pat was used as the lubricant fluid for this experiment. Then after Measure the weight of each block by using the high precision digital balance meter before machining. d)Fix the solid end mill in the spring collets chuck, Set the spindle speed to desired rpm as per the given values by using two levers as shown in below figure. e)Similarly feed is adjusted according given values by using the lever make sure that before adjusting the speed machine should be in power off mode. f) Clamp the work piece in machine vice tightly, so that it may not vibrate while performing at higher speeds. g) Now switch on the power and let the spindle run, make sure that spindle should not touch the work piece at this stage, slowly rotate the knee handle such that knee rises which in turn lifts the work table. h)When work piece is made in contact with the tool, at this stage give the axial depth of cut at required value and keep the feed in automatic mode measure the machining time while performing milling using stop watch. i) Note down the speed, feed rate, depth of cut and machining time. After completion of slot we should measure the weight of the spe cimen again. j) Repeat the experiment with hollow end mill and also using all five dampers and note each experimental value.


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This is the spindle speed chart which is attached to the side of column. By using these two levers we can adjust the spindle speed of the machine.

4.5 spindle speed chart

Following this shows feed chart which lies just below the speed levers, by using this we can adjust the feed of the machine.

4.6 feed chart DEPT OF MECHANICAL ENGG, CMRCET

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Fig 4.7 slot cutting

This is the figure of machining operation,we can see the chips formatoin in this figure. After performing machining operation the work piece resemble as below, we should again measure the weight of each specimen again by same digital balance meter.The MRR values are calculated by using above mentioned formula .

Fig4.8 Slotted work piece DEPT OF MECHANICAL ENGG, CMRCET

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Optimal machining parameter were carried out by setting of spindle speed, feed rate, and depth of cut in the range of as follows and essential parameters of the experiment are:

S pindle speed (rpm)

100 to 960.

Feed rate

(mm per min)

18

Depth of cut

(mm)

0.1 to 0.5.

Type of tool

to 45.

Solid end mill Hollow with one damper. Hollow with two dampers. Hollow with three dampers. Hollow with three dampers. Hollow with four dampers. Hollow with five dampers.

4.4 DESIGN OF EXPERIMENT: 4.4.1Design of Experiments (DOE) :Techniques enables designers to determine simultaneously the individual and interactive effects of many factors that could affect the output results in any design. DOE also provides a full insight of interaction between design elements; therefore, it helps turn any standard design into robust one. Simply put, DOE helps to pin point the sensitive parts and sensitive areas in designs that cause problems in yield. Designers are then able to fix these problems and produce robust and higher yield designs prior going into production. Design of experiments is a powerful tool that can be used in a variety experimental situations. DOE allows for multiple input factors to be manipulated determining their effect on a desired output. By manipulating multiple inputs at the same time, DOE can


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identify important interactions that may be missed when experimenting with one factor at a time. All possible combinations can be investigated or only a portion of possible combinations. We use DOE when more than one input factor is suspended of influencing an output.

4.4.2Orthogonal 4.4.2Orthogonal array: Orthogonal array is a black box testing technique which is a systematic, statistical way of software testing It is used when the number of inputs to the system is relatively small, but too large to allow for exhaustive testing of every possible input to the systems It is particularly effective in finding errors associated with faulty logic within computer software systems. Orthogonal arrays can be applied in user interface testing, system testing, regression testing, configuration testing and performance testing. The experimental layout for the machining using L18 orthogonal array was used in this study. This array having four control parameters, and eighteen combinations of type of tool speed, feed and depth of cut In Taguchi method, most all of the observed values are calculated on the "higher is better", thus in this study the observed values of MRR were set to maximum. Each experimental trial was performed and noted down the obtained result. Next the optimization of the observed values was determined by comparing the standard analysis of variance (ANOVA) which was based on the taguchi method.


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CHAPTER 5 DESIGN OF EXPERIMENT 5.1Design of Experiments (DOE) :Techniques enables designers to determine simultaneously the individual and interactive effects of many factors that could affect the output results in any design. DOE also provides a full insight of interaction between design elements; therefore, it helps turn any standard design into robust one. Simply put, DOE helps to pin point the sensitive parts and sensitive areas in designs that cause problems in yield. Designers are then able to fix these problems and produce robust and higher yield designs prior going into production. Design of experiments is a powerful tool that can be used in a variety experimental situations. DOE allows for multiple input factors to be manipulated determining their effect on a desired output. By manipulating multiple inputs at the same time, DOE can identify important interactions that may be missed when experimenting with one factor at a time. All possible combinations can be investigated or only a portion of possible combinations. We use DOE when more than one input factor is suspended of influencing an output.

5.2Orthogonal 5.2Orthogonal array: Orthogonal array is a black box testing technique which is a systematic, statistical way of software testing It is used when the number of inputs to the system is relatively small, but too large to allow for exhaustive testing of every possible input to the systems It is particularly effective in finding errors associated with faulty logic within computer software systems. Orthogonal arrays can be applied in user interface testing, system testing, regression testing, configuration testing and performance testing. The experimental layout for the machining using L18 orthogonal array was used in this study. This array having four control parameters, and eighteen combinations of type of tool speed, feed and depth of cut In Taguchi method, most all of the observed values are calculated on the "higher is better", thus in this study the observed values of MRR were


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set to maximum. Each experimental trial was performed and noted down the obtained result. Next the optimization of the observed values was determined by comparing the standard analysis of variance (ANOVA) which was based on the taguchi method.

5.3 TAGUCHI METHOD Taguchi methods are statically methods developed by Genichi taguchi to improve the

quality

of

manufactured

goods,

and

more

recently

also

applied

to

engineering, biotechnology marketing and advertising. Professional statisticians have welcomed the goals and improvements brought about by Taguchi methods, particularly by Taguchi's development of designs for studying variation. Concepts of Robust Design The main principles behind the Taguchi method for robust design are: 1) Robustness is first, adjusting average to meet the target is last. 2) To improve product quality, parameter design is first, tolerance design is last. This "two-step" optimization technique utilizes the idea that improving the functionality of a process will reduce the variability. thus resulting in more precise control of the product quality. To incorporate the Taguchi method into product improvement engineering, three design criteria must be considered: System Design: Development of a system to meet a defined objective Parameter Design: Selection and optimization of controllable parameters within the

system Tolerance Design: Determination of limitations in variability for each parameter

System design is the most important criteria because the system functionality is the main indication of whether the defined objective can be met with reproducible results. Selecting an adequate system design is also the most difficult task because the


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functionality of the system cannot be confirmed without results, obtained from the parameter design. The parameter design is the second most important criteria because it is used to optimize the system and reduce variability in the product, but requires experimentation or simulation, so it must be done with maximum efficiency. The tolerance design is the last criterion for improving product quality because only after the system is defined and optimized can the product quality limitation be set. Using these criteria to build a new process or develop a new product is a systematic approach for robust design because one can apply this approach to many different applications or industries (flexibility) and obtain results with less variabiality (reproducibility). Product/System Design

The first concept in robust design of a product or process system is the selection of the technical means in order to meet a specific objective function. An example of an objective function may be to modify an existing washer's design to meet the consumer's need for a higher efficiency washer that minimizes energy usage. In designing a process system or developing a new product, it is critical to remember that a greater amount of control variables (a more complex system) will allow for improvement in a larger number of subsections in that system or product. Each control variable is then selected by an engineer in terms of its generic function. The selection of the generic function must serve to meet the requirements of the objective function. From the previous example, choosing to add a temperature control system, timed rinse cycle, and lower power agitator to create a more energy efficient washer would serve as the generic functions. The two different categories of decision-making strategies employed by engineers to aid in the proper selection of the generic functions are: 1. Error-free implementation using a collection of past knowledge and ex perience 2. Generation of new design information used for improving quality, reliability, performance of the product/process as well as reducing the associated cost The three generic functions used in the washer design above stem from the second category because improving efficiency is an important customer need.


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Another consideration in system design occurs when integrating an existing and new process system. The degree of improvement in product quality depends on the complexity of both the individual and integrated systems. For example, when adding a temperature control (TC) system to an existing washer design, the reduction in energy usage is dependent on a variety of factors. 

Compatibility of the TC system with the current washer design



Material of component parts used in the TC system

 

Number of settings in the TC system Controllability of the temperature

For the last two factors, if there are only three temperature settings (High, Medium, and Low) and the degree of temperature control must be maintained with 1 degree of the setpoint, then the system may not be complex enough to see an appreciable improvement in the energy reduction of the washer. Parameter Design

Once the product or system design is chosen, optimal setting for the control parameters are determined using one of two approaches; develop a prototype or run a simulation. The main objective of either approach is to find the settings that have the greatest reduction in variability of the product quality. The first approach requires experimentation (with inexpensive raw materials or parts) under certain conditions (usually specified by the customer), while the second approach is completed using the same conditions, but does not require costly experiments. If experimentation is performed, to increase efficiency, using an orthogonal array allows for quickly determining the most concise experimental test method with fewest number of trials. If the results from either approach meet the system objective under the specified conditions, the study of the system's robustness is complete. At this point, the product quality target can be adjusted in the tolerance design of the system. Tolerance Design

Tolerance design for a system is a methodology for finding acceptable limits of variability in the quality of a product. In order to understand the methodology outlined DEPT OF MECHANICAL ENGG, CMRCET

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below, it is first necessary to determine what is meant by "quality". There are four different types of quality; origin, upstream, midstream, and downstream quality. "Origin" quality refers to the robustness of developing a group or family of products, whereas "upstream" quality are the characteristics of one product. For example, the characteristics of the robotic arm (used for welding) are considered an origin quality because they can be used in multiple applications, such as welding car parts, steel vessels, machinery, etc. The quality of a robotic arm used for welding the frame of a car is considered of the "upstream" type, since it is specific to one particular application. "Midstream" quality refers to the product specifications (i.e. purity, size of particles, length), which can be measured before the product is sent to the customer. From the previous example, the actual welds on the frame are considered the midstream quality. "Downstream" quality refers to the product quality seen by the customer (i.e. performance, color, efficiency). The performance of the welds (how well they hold the frame together) is an example of downstream quality. The first two types (origin and upstream quality) are adjusted in parameter and system design, while the last two types (midstream and downstream quality) can be adjusted using tolerance design. Improvement in the downstream quality is accomplished by modifying the midstream quality (i.e. tightening the tolerance). However, to determine if the decrease in the variability of a product specification is worth the cost, the loss function must be analyzed, which is done by finding the Signalto-Noise ratio. 5.4 SIGNAL- TO-NOISE RATIO:

Quality engineering is in essence the evaluation of functionality and the concept of a measure known as the signal-to-noise ratio (SN ratio) is employed for this purpose. The concept of the SN ratio has in itself been in the communication industry for almost a century but due to the efforts and breakthroughs made by Taguchi in generalizing this concept, it is now commonly used for the evaluation of measurement systems as well as for the function of products and processes. Conceptually, the SN ratio is the ratio of signal to noise in terms of power. More specifically, it is the ratio of the magnitude of energy used for the objective function to the magnitude of energy consumed for variability. The SN ratio can also be viewed as the ratio of sensitivity to variability and is typically measured in units of decibels (dB). For example, a value of 30dB indicates that DEPT OF MECHANICAL ENGG, CMRCET

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the magnitude of the signal is 1000 times more powerful than the power of noise. Thus, the larger the SN ratio, the better the quality. The SN ratio typically highlights the interactions between the signal factor, the control factor, and noise factors and when used along with orthogonal arrays enable one to avoid undesirable interactions between control factors. The input-to-output relationship is studied in a measurement system where the true value of the object is the input and the result of the measurement is the output. A good measurement system must fulfill the following criteria. Firstly, the result of measurement must be proportional to the true value and thus the input/output relationship is linear. Secondly, a good system must be sensitive to various inputs and as a result the desired effect is that slope showing the input/output relationships must be steep. Finally, a desired criterion is that variability is small. All three criteria are lumped into a single index when a SN ratio is used to evaluate a measurement system and thus allows easy evaluation and improvement of a system by using these ratios. To better understand Taguchi design, the procedure of the Taguchi design is described in Fig.5.1. The complete procedure in Taguchi design method can be divided into three stages: system design, parameter design, and tolerance design (shown in Fig. 1).Of the three design stages, the second stage – stage – the the parameter design – design – is is the most important stage It has been widely applied in the US US and Japan with with great success for

optimizing

industrial/production processes. The stage of Taguchi parameter design requires that the factors affecting quality characteristics in the manufacturing process have been determined. The major goal of this stage is to identify the optimal cutting conditions that yield the highest material removal rate .


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Fig.5.1. Taguchi design procedure

The steps included in the Taguchi parameter design are: 

selecting the proper orthogonal array (OA) according to the numbers of controllable factors (parameters)



running experiments based on the OA



analyzing data



identifying the optimum condition;



Conducting confirmation runs with the optimal levels of all the parameters.

The details regarding these steps will be described in the section of experimental design. 5.5 ANVOA 5.5.1Definition of 'Analysis Of Variance - ANOVA'

A statistical analysis tool that separates the total variability found within a data set into two components: random and systematic factors. The random factors do not have any statistical influence on the given data set, while the systematic factors do. The ANOVA DEPT OF MECHANICAL ENGG, CMRCET

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test is used to determine the impact independent variables have on the dependent variable in a regression analysis.

5.5.2Analysis of variance (ANOVA):Purpose: The reason for doing an ANOVA is to see if there is any difference between groups on some variable. For example, you might have data on student performance in non-assessed tutorial exercises as well as their final grading. You are interested in seeing if tutorial performance is related to final grade. Anova allows you to break up the group according to the grade and then see if performance is different across these grades. Anova is available for both parametric (score data) and non-parametric (ranking/ordering) data. 5.5.3` Types of anova: One-way between groups:

The example given above is called a one-way between groups model. You are looking at the differences between the groups. There is only one grouping (final grade) which you are using to define the groups. This is the simplest version of anova. This type of anova can also be used to compare variables between different groups - tutorial performance from different intakes. One-way repeated measures:

A one way repeated measures anova is used when you have a single group on which you have measured something a few times. For example, you may have a test of understanding of classes. You give this test at the beginning of the topic, at the end of the topic and then at the end of the subject. You would use a one-way repeated measures anova to see if student performance on the test changed over time.


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Two-way between groups:

A two-way between groups anova is used to look at complex groupings. For example, the grades by tutorial analysis could be extended to see if overseas students performed differently to local students what you would have from this form of anova is: the effect of final grade the effect of overseas versus local the interaction between final grade and overseas/local each of the main effects are one-way tests the interaction effect is simply asking "is there any significant difference in performance when you take. Final grade and overseas/local acting together" Two-way repeated measures: This version of anova simple uses the repeated measures structure includes an interaction effect. In the example given for one-way between groups, you could add gender and see if there was any joint effect of gender and time of testing - i.e. Do males and females differ in the amount they remember absorb over time. Nonparametric and parametric anova is available for score or interval data as parametric anova. This is the type of anova you do from the standard menu options in a statistical package. The non-parametric version is usually found under the heading "nonparametric test". It is used when you have rank or ordered data.

5.6 EXPERIMENTAL SETUP AND CONDITIONS

The experiments were carried out into two stages. Initially the mild steel material parts are machined using milling machine with end mill cutter. Then the material removal rate profile was investigated. The material mat erial removal rate values were recorded reco rded for at different cutting speeds, feeds and depth of cuts. Tests were performed at different spindle speeds. Three cutting speeds were selected and the results obtained where chatter was initiated and observed. The details of these experimental conditions are shown in Table 8.1.


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S.No.

TYPE OF TOOL

SPEED FEED

DOC

1

solid end mill

385

18

0.25

2

solid end mill

685

29

0.35

3

solid end mill

960

45

0.5

4

hollow with one damper

385

18

0.35

5


685

29

0.5

6


960

45

0.25

7

hollow with two damper

385

29

0.25

8


685

45

0.35

9


960

18

0.5

385

45

0.5

685

18

0.25

960

29

0.35

385

29

0.5

685

45

0.25

960

18

0.35

hollow 10

three

with

four

with

four

damper hollow

15

with

damper hollow

14

three

damper hollow

13

with

damper hollow

12

three

damper hollow

11

with

damper

with

four


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hollow 16

with

with

385

45

0.35

685

18

0.5

960

29

0.25

five

damper hollow

18

five

damper hollow

17

with

five

damper

The experiments were carried out on vertical milling machine. Each experiment was repeated using a new cutting edge every time to obtain accurate reading of surface roughness. The physical and mechanical properties of work piece are 50mm in length, 25mm in width. The work piece material is Mild steel. The end milling cutter is of High Speed Steel (HSS). 5.7 EXPERIMENTAL DESIGN 5.7.1. Orthogonal array and experimental factors

Following the procedure described in Fig. 1, the first step in the Taguchi method is to select a proper orthogonal array. The standardized Taguchi-based experimental design, a L18(6*1 3*3) orthogonal array was used in this study and is shown in Table 1. A total of eighteen experimental runs must be conducted, using the combination of levels for each control factor as indicated in Table 2. The control factors are the basic controlled parameters used in a milling operation. The spindle speeds and type of tools were selected from within the range of parameters for milling of mild steel. The feed and depth of cut used for milling mild steel work pieces are var ying. 5.7.2. Experimental set-up and procedure

After the orthogonal array has been selected, the second step in Taguchi parameter design (see Fig.1) is running the experiment. This experiment was conducted using the hardware listed as follows:


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• End Milling Machine: • Cutting tools: Solid tool, Hollow tool with one damper, Hollow tool with two dampers, Hollow tool with three dampers, Hollow tool with four dampers, Hollow tool with five dampers. Table 5.2 Factors and level values used for orthogonal array L18 TYPE OF TOOL

SPEED

FEED

DOC

MRR

1

1

1

1

15.0829

1

2

2

2

106.7382

1

3

3

3

267.9697

2

1

1

2

117.3878

2

2

2

3

200.9368

2

3

3

1

187.6923

3

1

2

1

107.2369

3

2

3

2

169.5616

3

3

1

3

128.2051

4

1

3

3

163.6439

4

2

1

1

79.5625

4

3

2

2

112.0297

5

1

2

3

188.7464

5

2

3

1

96.6792

5

3

1

2

107.2191

6

1

3

2

251.1986

6

2

1

3

127.8166

6

3

2

1

88.9501

Orthogonal array L18 is shown in following table

Above mentioned table is the orthogonal array of L18 with metal removal rate values.


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Table 5.3 Orthogonal array TY PE O F TO OL

SPE ED

FE ED

D OC

1

1

1

1

1

2

2

2

1

3

3

3

2

1

1

2

2

2

2

3

2

3

3

1

3

1

2

1

3

2

3

2

3

3

1

3

4

1

3

3

4

2

1

1

4

3

2

2

5

1

2

3

5

2

3

1

5

3

1

2

6

1

3

2

6

2

1

3

6

3

2

1

5.8 RESULTS AND DISCUSSIONS

Mild steel work piece of 50mm X 50mm X 25mm is machined on vertical milling machine with an end milling cutter of 19.05mm diameter and 125mm length at a feed of 18mm,29mm,41mm and depth of cut of 0.25mm,0.35mm,0.5mm and at various speeds of 385 rpm, 685 rpm, 960 rpm. In the Taguchi method, the term ‗signal‘ represents the desirable value (mean) for the output characteristic and the term ‗noise‘ represents the undesirable undesirable value for the output characteristic. Taguchi uses the S/N ratio to measure the quality characteristic deviating from the desired value. There are several S/N ratios available depending on type of characteristic: ―lower is better ‖ (LB), ―nominal is best‖ best‖ (NB), or or ―higher is better‖ (HB). ―Larger is ―Larger is better ‖ S/N ratio was used in this study because more metal removal rate was


Page 61


desirable Quality characteristic of the larger is better is calculated in the following equation. The Larger-The-Better: If the number of minutes per dollar customers get from their cellular phone service provider is critical to quality, the customers will want to get the

maximum number of minutes they can for every eve ry dollar they spend on their phone p hone bills. If the lifetime of a battery is critical to quality, the customers will want their batteries to last forever. The longer the battery lasts, the better it is. The Signal-To-Noise ratio for the bigger-the-better is: S/N = -10*log (mean square of the inverse of the response)

Where S/N= Signal to noise ratio that is desired to undesired ratio. Y=Metal removal rate of the nth experiment. This formula is used to calculate the metal removal rate of the desired work piece. Experiments are conducted in the order given by Taguchi method and material removal rate values are measured and tabulated. TABLE 5.4.

MRR parameter S/N values for machining mild steel work piece at feed of 18mm,29 mm,41mm and depth of cut of 0.25mm,0.35mm,0.5 m for Solid tool, Hollow tool with one damper, Hollow tool with two dampers, Hollow tool with three dampers, Hollow tool with four dampers, Hollow tool with five dampers inserts at eighteen runs.


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TYPE OF TOOL

solid end mill solid end mill solid end mill hollow with one damper hollow with one damper hollow with one damper hollow with two damper hollow with two damper hollow with two damper hollow with three damper hollow with three damper hollow with three damper hollow with four damper hollow with four damper hollow with four damper hollow with five damper hollow with five damper hollow with five damper

SPEED

FEED

DOC

MRR

SNRA1

385

18

0.25

15.0829

23.5697

685

29

0.35

106.7382

40.5664

960

41

0.5

267.9697

48.56171

385

18

0.35

117.3878

41.39246

685

29

0.5

200.9368

46.06119

960

41

0.25

187.6923

45.46893

385

29

0.25

107.2369

40.60689

685

41

0.35

169.5616

44.58655

960

18

0.5

128.2051

42.15811

385

41

0.5

163.6439

44.278

685

18

0.25

79 79.5625

38.01417

960

29

0.35

112.0297

40.98666

385

29

0.5

188.7464

45.51757

685

41

0.25

96 96.6792

39.70666

960

18

0.35

107.2191

40.60544

385

41

0.35

251.1986

48.00034

685

18

0.5

127.8166

42.13175

960

29

0.25

88 88.9501

38.98293

From the table we can understand that S/N ratio is maximum for solid end mill at maximum depth and maximum speed. After calculating S/N Ratios, the effect of control parameters on S/N ratio is shown below. This is the overall SN ratios for different parameters namely tool, speed, feed, Depth of cut.


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Main Effects Plot for SN ratios

Data Means TYPE OF TOOL

46

SPEED

44 42 s o 40 i t a 38 r N S f o n 46 a e M44

1

2

3

4

5

6

1

FEED

2

3

DO C

42 40 38 1

2

3

1

2

3

Signal-to-noise: Larger is better

There is large variation in S/N ratio due to variation in speed. As speed increases S/N ratio increases gradually, There is considerable variation in S/N ratio because of type of tool. It varies from tool to tool, It records high S/N ratio for hollow with one dampers and low with solid tool and average value for three dampered tool. There is slight variation in S/N ratio because of feed. feed that is as feed increases S/N ratio increases, It records nearly 10 at 45mm/min of feed. There is slight variation in S/N ratio because of depth of cut. that is as depth of cut increases S/N ratio increases. Therefore at 0.5 S/N ratio is larger .


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TABLE 5.5 SUMMARY OF ANOVA RESULTS Taguchi Design

Taguchi Orthogonal Array Design L18(6**1 ,3**3) Factors: 4 Runs:

18

Columns of L18(6**1 3**6) Array 1234 Taguchi Analysis: MRR versus TYPE OF TOOL, SPEED, FEED, DOC

Response Table for Signal to Noise Ratios ―Larger is better ‖ LEVEL

TOOL

SPEED

FEED

DOC

1

37.57

40.56

37.98

37.72

2

44.31

41.84

42.12

42.69

3

42.45

42.79

45.10

44.78

4

41.09

5

41.94

6

43.04


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DELTA

6.74

2.23

7.12

7.06

RANK

3

4

1

2

5.9 Main Effects Plot for SN ratios General Linear Model: MRR versus TYPE OF TOOL, SPEED, FEED, DOC

FACTORS

TYPES

LEVELS

VALUES

TYPE OF TOOL

FIXED

6

1,2,3,4,5,6

SPEED

FIXED

3

1,2,3

FEED

FIXED

3

1,2,3

DOC

FIXED

3

1,2,3


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Analysis of Variance for MRR, using Adjusted SS for Tests

SOURCE

DF

TYPE OF 5

SEQ SS

ADJ SS

ADJ MS

F

P

5259

5259

1052

0.48

0.780

TOOL SPEED

2

1027

1027

514

0.24

0.797

FEED

2

26564

26564

13282

6.09

0.036

DOC

2

21169

21169

10585

4.85

0.056

ERROR

6

13093

13093

2182

TOOL

17

67113

Predicted Optimal S/N value from Taguchi = 51.783 Predicted metal removal rate value Corresponding to S/N =388.47gms/min Experimental metal removal rate value = 380.12 gms/min


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CHAPTER 6 6.1 CONCLUSION: In the present work, multi-response optimization problem has been solved by searching an optimal parametric combination, capable of producing high quality milled product in a relatively lesser time. This work has shown the feasibility of machining mild steel by end milling with a HSS tool. Taguchi has been used to determine the main effects, significant factors and optimum machining condition to the performance of Mild steel.



The mach inability of mild steel when subjected to milling operation using high speed cutting steel tools is studied. Machining parameters, metal removalrate were investigated.



The results indicated that the metal removal rate increases with increasing cutting speed and feed. The selection of appropriate cutting conditions and the use of sharp cutting tools with adequate edge preparation is critical to achieve good metal cutting.



Friction damper will lead to increase in the material removing rate in the milling process by increasing stable chatter free depth of cut. It can also cause better surface finish that is investigated here.



From the results obtained, it was found that the damped tool outperformed both the solid and the hollow tool. Hence the overall performance of the damped tool with one damper inserts was exceptional compared to solid milling cutter, hollow milling cutter.



Metal removal rate is achieved under the optimal cutting parameters indicated that of the parameter settings used in this study, those identified as optimal through Taguchi parameter design were able to produce the best metal cutting in this milling operation.



The optimal levels for the controllable factors were spindle speed 960 rpm, feed rate 45 mm/min, depth of cut 0.5 mm and hollow end mill with one damper. Compared with the experiment results in Table, the optimal metal removal rate of


Page 68


the 18 confirmation samples 388.47 gms/min. which was very close to the optimal value of metal removal rate is 380.12 gms/min gms/min by Taguchi Method Method 

The material removal rate, on the other hand, depends on both axial and radial depth of cuts and thus both limits have to be considered in order to maximize the productivity.



It is shown that maximum material removal rate is is obtained using the optimal axial and radial depth which also depends on other factors like speed and feed.



The application of the method is demonstrated on a slotting experiment where significant material removal rate is obtained using the optimal parameters.

Based on the result presented here, we can conclude that, the feed rate of end milling tool mainly affects the Metal removal rate.


Page 69


References: [1] Salomon, C., Critical Machining Velocities. 1931: German Patent No. 523594. [2] King, R.I. and R.L. Vaughn. A synoptic review of High-speed machining from Salomon to to

the present present in High speed machining : presented presented at the winter winter annual

meeting of the American Society of Mechanical Engineers 1984. New Orleans, Louisiana: ASME (345 E. 47th St., New York 10017): p. 1-13. [3] Schmidt, A.O. Machine Tool Engineering: Today's Facts and Fictions. in High speed machining : presented at the winter annual meeting of the American Society of Mechanical Engineers 1984. New Orleans, Louisiana: ASME (345 E. 47th St., New York 10017): p. 69-82. [4] Recht, R.F., The feasibility of Ultra -High-Speed Machining. 1960, University of Denver. [5]

A treatise on milling and milling machines. Cincinnati, Ohio: Cincinnati Milling

Machine Company. 1922. Retrieved 2013-01-28 [6] De Vries, D. (1910), Milling machines and milling practice: a practical manual for the use of manufacturers, engineering students and practical men, London: E. & F.N. Spon. Coedition, New York, Spon & Chamberlain, 1910. [7] Robert H. Todd, Dell K. Allen, Leo Alting, "Manufacturing Processes Reference Guide", Industrial Press Inc., New York, 1994 pg 49-53 [8] Brown & Sharpe. "Brown and Sharpe Speeds and Feeds Chart". Automatic Screw Machine Handbook. Providence, R.I.: Brown & Sharpe Manufacturing Co. [9] rown & Sharpe 2. "Cam & Tool Design: Surface Cutting Speeds Chart". Automatic Screw Machine Handbook. Providence, R.I.: Brown & Sharpe Manufacturing Co.


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[10] Brown & Sharpe 3. "Machinebility of Materials, Composition and Machinability Chart". Automatic Screw Scre w Machine Handbook. Providence, R.I.: R. I.: Brown & Sharpe Manufacturing Co

[11] Tlusty. J Polacek, J.. and Polacek, M. The stability of Machine Tools against self Excited vibrations in Machining. ASME International research in production engineering. [12] J.A.Mc Geough ―Advanced Methods of Machining‖, Chapman and Hall, Newyork, 1998 [13]Ranjit K.Roy ―A Premier On the Taguchi Method‖ Van Nostrand Reinhold, Newyork,1996.


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Optimization of Metal removal rate in end milling Using Taguchi and Anova method.

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