surface roughness optimization using taguchi and anova method

Surface Roughness Optimization in End Milling using Taguchi method and ANOVA

CHAPTER 1

MILLING

1.1 INTRODUCTION

1.1.1 Milling Machines

Milling machines were first invented and developed by Eli Whitney to mass produce

interchangeable musket parts. Although crude, these machines assisted man in

maintaining accuracy and uniformity while duplicating parts that could not be

manufactured with the use of a file. Development and improvements of the milling

machine and components continued, which resulted in the manufacturing of heavier

arbors and high speed steel and carbide cutters. These components allowed the operator to

remove metal faster, and with more accuracy, than previous machines. Variations of

milling machines were also developed to perform special milling operations. During this

era, computerized machines have been developed to alleviate errors and provide better

quality in the finished product.

Milling-Milling is the process of cutting away material by feeding a workpiece past a

rotating multiple tooth cutter. The cutting action of the many teeth around the milling

cutter provides a fast method of machining. The machined surface may be flat,angular, or

curved. The surface may also be milled to any combination of shapes. The machine for

holding the workpiece, rotating the cutter, and feeding it is known as the Milling machine.

The type of milling machine most commonly found in student shops is a vertical spindle

machine with a swiveling head. The spindle can be fed up and down with a quill feed lever

on the head. Most milling machines are equipped with power feed for one or more axes.

Power feed is smoother than manual feed and, therefore, can produce a better surface

finish. Power feed also reduces operator fatigue on long cuts.

The Machine Tool – In the present climate many different configurations of machine tool

exist .Some machines have the table/work piece stationary whilst the X,Y and Z axes move

Department of Mechanical engineering CMRCET

http://www.mfg.mtu.edu/marc/primers/milling/millmach.html


and others may be constructed to allow the work piece/table to be the moving part whilst

the axes are fixed.

In any condition the X, Y and Z-axes directions are always configured the same.

Fig: 1.1 MACHINE TOOL

The X-axis is always considered as the longest axis,where X+ will be the table motioning

to the left and X- to the right. The Y-axis moves from front to back of the machine with the

table motioning towards the operator as the Y+(positive) direction and away being the Y-

(negative) direction. The Z-axis where the tool normally is located,has the positive Z+

(positive) axis motioning up and away from the workpiece/table and Z-(negative)direction

down towards the workpiece/table.

1.2 CLASSIFICATION OF MILLING

Peripheral Milling: In peripheral (or slab) milling, the milled surface is generated by teeth

located on the periphery of the cutter body. The axis of cutter rotation is generally in a

plane parallel to the work piece surface to be machined.



Fig:1.2 Peripheral Milling

Face Milling: In face milling, the cutter is mounted on a spindle having an axis of rotation

perpendicular to the work piece surface. The milled surface results from the action of

cutting edges located on the periphery and face of the cutter.

Fig:1.3 Face Milling

End Milling: The cutter in end milling generally rotates on an axis vertical to the work

piece. It can be tilted to machine tapered surfaces. Cutting teeth are located on both the end

face of the cutter and the periphery of the cutter body.

Fig: 1.4 End Milling



1.2.1 METHODS OF MILLING

Up Milling: Up milling is also referred to as conventional milling. The direction of the

cutter rotation opposes the feed motion. For example, if the cutter rotates clockwise , the

workpiece is fed to the right in up milling.

Fig:1.5 Up milling

Down Milling:Down milling is also referred to as climb milling. The direction of cutter

rotation is same as the feed motion. For example, if the cutter rotates counterclockwise ,

the workpiece is fed to the right in down milling.

Fig: 1.6 Down Milling

The chip formation in down milling is opposite to the chip formation in up milling. The

figure for down milling shows that the cutter tooth is almost parallel to the top surface of

the workpiece. The cutter tooth begins to mill the full chip thickness. Then the chip

thickness gradually decreases.



Other milling operations are shown in the figure.

Fig:1.7 Types of Milling Operations

1.3 WORKING PRINCIPLES OF MILLING MACHINE

The workpiece is holding on the worktable of the machine. The table movement controls

the feed of workpiece against the rotating cutter. The cutter is mounted on a spindle or

arbor and revolves at high speed. Except for rotation of the cutter has no other motion. As

the workpiece advances, the cutter teeth remove the metal from the surface of workpiece

and the desired shape is produced.



Fig: 1.8 Working Principle of Milling Machine

1.3.1 Principle parts of a 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 vice, 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.

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.

Arbor - It holds rotating milling cutters rigidly and mounted on the spindle. Sometimes

arbor is supported at maximum distance from support of overhanging arm like a cantilever,

it is called stub arbor. Locking provisions are provided in the arbor assembly to ensure its

reliability.

Fig:1.9 Vertical milling machines

1.3.2 Manual vertical milling machine

The above components of the milling machine can be oriented either vertically or

horizontally, creating two very distinct forms of milling machine. A horizontal milling

machine uses a cutter that is mounted on a horizontal shaft, called an arbor, above the work

piece. For this reason, horizontal milling is sometimes referred to as arbor milling. The

arbor is supported on one side by an over arm, which is connected to the column, and on

the other side by the spindle. The spindle is driven by a motor and therefore rotates the



arbor. During milling, the cutter rotates along a horizontal axis and the side of the cutter

removes material from the work piece.

A vertical milling machine, on the other hand, orients the cutter vertically. The cutter is

secured inside a piece called a collet, which is then attached to the vertically oriented

spindle. The spindle is located inside the milling head, which is attached to the column.

Milling machines can also be classified by the type of control that is used. A manual

milling machine requires the operator to control the motion of the cutter during the milling

operation. The operator adjusts the position of the cutter by using hand cranks that move

the table, saddle, and knee.

Milling machines are also able to be computer controlled, in which case they are referred

to as a computer numerical control (CNC) milling machine. CNC milling machines move

the work piece and cutter based on commands that are preprogrammed and offer very high

precision. The programs that are written are often called G-codes or NC-codes. Many CNC

milling machines also contain another axis of motion besides the standard X-Y-Z motion.

The angle of the spindle and cutter can be changed, allowing for even more complex

shapes to be milled.

The tooling that is required for milling is a sharp cutter that will be rotated by the spindle.

The cutter is a cylindrical tool with sharp teeth spaced around the exterior. The spaces

between the teeth are called flutes and allow the material chips to move away from

the work piece.

The teeth may be straight along the side of the cutter, but are more commonly arranged in

a helix. The helix angle reduces the load on the teeth by distributing the forces. Also, the

number of teeth on a cutter varies. A larger number of teeth will provide a better surface

finish. The cutters that can be used for milling operations are highly diverse, thus allowing

for the formation of a variety of features. While these cutters differ greatly in diameter,

length, and by the shape of the cut they will form, they also differ based upon their

orientation, whether they will be used horizontally or vertically.

A cutter that will be used in a horizontal milling machine will have the teeth extend along

the entire length of the tool. The interior of the tool will be hollow so that it can be

mounted onto the arbor.



Tool materials in common use

High Carbon Steel: Contains 1 - 1.4% carbon with some addition of chromium

and tungsten to improve wear resistance. The steel begins to lose its hardness at

about 250° C, and is not favored for modern machining operations where high

speeds and heavy cuts are usually employed.

High Speed Steel (H.S.S.): Steel, which has a hot hardness value of about 600°C,

possesses good strength and shock resistant properties. It is commonly used for

single point lathe cutting tools and multi point cutting tools such as drills, reamers

and milling cutters.

Cemented Carbides: An extremely hard material made from tungsten powder.

Carbide tools are usually used in the form of brazed or clamped tips. High cutting

speeds may be used and materials difficult to cut with HSS may be readily

machined using carbide tipped tool.

1.4 Cutting parameters

As you proceed to the process of metal cutting, the relative ‘speed’ of work piece rotation

and ‘feed’ rates of the cutting tool coupled to the material to be cut must be given your

serious attention. This relationship is of paramount importance if items are to be

manufactured in a cost-effective way in the minimum time, in accordance with the laid

down specifications for quality of surface finish and accuracy. You, as a potential

supervisory /management level engineer, must take particular note of these important

parameters and ensure that you gain a fundamental understanding of factors involved.

Cutting Speed

All materials have an optimum Cutting Speed and it is defined as the speed at which a

point on the surface of the work passes the cutting edge or point of the tool and is normally

given in meters/min. To calculate the spindle Speed required,



Where:

N = Spindle Speed (RPM)

CS = Cutting Speed (m/min)

d = Diameter of Work piece (mm)

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.

Spindle speed: The rotational speed of the spindle and tool in revolutions per minute

(RPM). The spindle speed is equal to the cutting speed divided by the circumference of the

tool.

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).

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 depth of cut for each pass.

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.



1.5 Milling cutters

Milling cutters are cutting tools typically used in milling machines or machining centres

to perform milling operations. Special milling cutters are designed to perform special

operations which may be combination of several conventional operations. Standard

milling cutters are the conventional cutters which are classified as given below.

Plain Milling Cutters: These cutters are cylindrical in shape having teeth on their

circumference. These are used to produce flat surfaces parallel to axis of rotation. Plain

milling cutter is shown in Figure 1.5. Depending upon the size and applications plain

milling cutters are categorized as light duty, heavy duty and helical plain milling cutters.

Side Milling Cutters: Side milling cutters are used to remove metals from the side of

workpiece. These cutters have teeth on the periphery and on its sides. These are further

categorized as plain side milling cutters having straight circumferential teeth. Staggered

teeth side milling cutters having alternate teeth with opposite helix angle providing more

chip space. Half side milling cutters have straight or helical teeth on its circumference and

on its one side only. Circumferential teeth do the actual cutting of metal while side teeth do

the finishing work.

Interlocking side milling cutter has teeth of two half side milling cutter which are

made to interlock to form one unit.

Metal Slitting Saw: These cutters are like plain or side milling cutters having very small

width. These are used for parting off or slotting operations. Metal slitting saw is shown in

Figure 1.6. It is of two types. If teeth of this saw resembles with plain milling cutter, it is

called plain milling slitting saw. If its teeth matches with staggered teeth side milling

cutter, it is called staggered teeth slitting saw.

Angle Milling Cutter:These cutters have conical surfaces with cutting edges over them.



These are used to machine angles other than 90o. Two types of angle milling cutters are

available single angle milling cutter and double angle milling cutter.

End Mill: End mills are used for cutting slots, small holes and light milling operations.

These cutters have teeth on their end as well as an periphery. The cutting teeth may be

straight or helical. Depending upon the shape of their shank, these are categorized as

discussed below.

Taper Shank Mill: Taper shank mill have tapered shank.

Straight Shank Mill: Straight shank mill having straight shank.

Shell End Mills: These are normally used for face milling operation. Cutters of different

sizes can be accommodated on a single common shank.

‘T’ Slot Milling Cutters: These are the special form of milling cutters used to produce

„T‟ shaped slots in the work piece. These have cutting edges on their periphery and both

sides.

Fly cutters: Fly cutters are the simplest form of cutters used to make contoured surfaces.

These cutters are the single cutting point cutting tools.

Convex Milling Cutters: These cutters have profile outwards at their circumference and

used to generate concave semicircular surface on the work piece.

Concave Milling Cutters: These milling cutters have teeth profile curve in words on their

circumference. These are used to generate convex semicircular surfaces.

Corner Rounding Milling Cutters: These cutters have teeth curved inwards. These

milling cutters are used to form contours of quarter circle. These are main used in making

round corners and round edges of the work piece.

Gear Cutter: These cutters are used in making gears on milling machine. Gear cutting is

an operation which cannot be done otherwise. These cutters have shape of the teeth which

are to be reproduced on the gear blank. Different gear cutters are used to make teeth with

involutes profile or cycloidal profile. A gear cutter is used to cut a range of gear size with a

fixed tooth profile.



Thread Milling Cutter: These cutters are designated to mill threads of specific form and

size on the work piece. These cutters may be with parallel shank of tapered shank and

mainly used to make worms.

Top and Reamer Cutter: Top and reamer cutters are the cutters of double angle type,

these are normally used to make grooves and flutes in taps or reamers. Taps and reamers

are used as thread cutting tools for softer material work pieces.

Fig: 1.10 Types of Milling Cutters

1.6 END MILL CUTTERS

1.6.1 Tool Geometry

An end mill is a type 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. End mills are used in milling applications such as profile

milling, tracer milling, face milling, and plunging.



A - mill size or cutting diameter

B - shank diameter

C - length of cut or flute length

D - overall length

Fig: 1.11 Tool geometry of End mill cutters

Angular Edge - That cutting edge that is a straight line, forming an angle with the

cutter axis. The surface produced by a cutting edge of this type will not be flat as is

the case with a helical cutting edge.

Axial Run out - The difference between the highest and lowest indicator reading

taken at the face of a cutter near the outer diameter.

Chamfer - A short relieved flat installed where the periphery and face of a cutter

meet. Used to strengthen the otherwise weak corner.

Chip Breakers - Special geometry of the rake face that causes the chip to curl

tightly and break.



Chip Splitters - Notches in the circumference of a Corn cob style End mill cutter

resulting in narrow chips. Suitable for rough machining.

Core Diameter - The diameter of a cylinder (or cone shape with tapered End mills)

tangent to the flutes at the deepest point.

Counter bore - A recess in a non-end cutting tool to facilitate grinding.

Cutter Sweep (Run out) - Material removed by the fluting cutter (or grinding

wheel) at the end of the flute.

Cutting Edge (A) - The leading edge of the cutter tooth. The intersection of two

finely finished surfaces, generally of an included angle of less than 90 degrees.

Cutting Edge Angle - The angle formed by the cutting edge and the tool axis.

Differential pitch cutters - A specifically designed variation in the radial spacing of

the cutter teeth. This provides a variation in tooth spacing and can be beneficial in

reducing chatter. This concept is based on reducing the harmonic effect of the tool

contacting the part in an exact moment of vibration.

Entrance Angle - The angle formed by a line through the center of the cutter at 90

to the direction of feed and a radial line through the initial point of contact. As this

angle approaches 90 degrees the shock loading is increased.

Entrance Angle: Ramp-in - Angle or radius value to enter the cutter into the part

surface

Fillet - The radius at the bottom of the flute, from which core diameter is found.

Flute - Space between cutting teeth providing chip space and regrinding capabilities. The

number of cutting edges. Sometimes referred to as "teeth" or "gullet". The number on an

end mill will determine the feed rate.



Fig: 1.12 Flute

Flute Length - Length of flutes or grooves. Often used incorrectly to denote cutting

length.

Shank - Projecting portion of cutter which locates and drives the cutter from the

machine spindle or adapter

Straight Shank - Cylindrical shank, with or without driving flats or notches, often

seen on carbide end mills

Weldon Shank - Industry name for a specific type of shank with a drive and

location flat. The flat on the cutter provides positive ( non slip ) driving surface to

the End mill.

Tooth - The cutting edge of the End mill.

Tooth Face - Also known as the Rake Face. The portion of the tooth upon which

the tooth meets the part.

1.7 END MILL TECHNICAL FEATURES

Back taper - A slight taper resulting in the shank end of the cutting diameter being

smaller than the cutting end. This condition aids not only the plunging or drilling

condition but also tends to compensate for deflection.

Clearance - Space created by the removal of additional tool material from behind

the relief angle.



Fig: 1.13 Clearance of End Mill

Clearance Angle - The angle formed by the cleared surface and line tangent to the

cutting edge.

o Clearance: Primary (1st angle, 5°-9°) - Relief adjacent to the cutting edge.

o Clearance: Secondary (2nd angle, 14°-17°) - Relief adjacent to cutting edge

o Clearance: Tertiary (3rd) - Additional relief clearance provided adjacent to

the secondary angle.

Concave - Small hollow required on the end face of an End mill. This feature is

produced by a Dish angle produced on the cutter.

Convex - An outward projection radius feature on the end face of a Ball mill.

Dish Angle - The angle formed by the end cutting edge and a plane perpendicular to the

cutter axis. Dish ensures that a flat surface is produced by the cutter.



Fig: 1.14 Different angles shown in an End Mill

Gash (Notch) - The secondary cuts on a tool to provide chip space at corners and

ends. The space forming the end cutting edge, which is used when feeding axially.

Gash angle - The relief angle of the gash feature.

Gash width - The width of the gash feature. The space between cutting edges,

which provides chip space and resharpening capabilities. Sometimes called the

flute.

Heel - The back edge of the relieved land. It is the surface of the tooth trailing the

cutting edge.

Helical - A cutting edge or flute which progresses uniformly around a cylindrical

surface in an axial direction. The normal helical direction is a right direction spiral.

Helix Angle - The angle formed by a line tangent to the helix and a plane through

the axis of the cutter or the cutting edge angle which a helical cutting edge makes

with a plane containing the axis of a cylindrical cutter.

Hook - A term used to refer to a concave condition of a tooth face. This term

implies a curved surface rather than a straight surface. Hook must be measured at

the cutting edge, making measurement difficult.



Land - The narrow surface of a profile sharpened cutter tooth immediately behind

the cutting edge,

o (A) Cylindrical - a narrow portion of the peripheral land, adjacent to the

cutting edge, having no radial relief.

o (B) Relieved - A portion of the land adjacent to the cutting edge, which

provides relief.

Lead - The axial advance of a helical cutting edge in one revolution.

Lead = (Cutter diameter x Pi) / Tangent Helix Angle

Length of Cut (Flute Length) - The effective axial length of the peripheral cutting

edge which has been relieved to cut.

Radial Rake angle - The angle made by the rake face and a radius measured in a plane

normal to the axis.

Fig : 1.15 Tool terminology



Rake - The angular relationship between the tooth face or a tangent to the tooth

face at a given point and a reference plane or line. An angular feature ground onto

the surface of an end mill.

o Axial rake - The angle formed by a plane passing through the axis and a line

coinciding with or tangent to the tooth face.

o Effective rake - The rake angle influencing chip formation most is that

measured normal to the cutting edge. The effective rake angle is greatly

affected by the radial and axial rakes only when corner angles are involved.

o Helical rake - For most purposes the terms helical and axial rake can be

used interchangeably. It is the inclination of the tooth face with reference to

a plane through the cutter axis.

o Negative Rake - Exists when the initial contact between tool and workpiece

occurs at a point or line on the tooth other than the cutting edge. The rake

surface leads the cutting edge.

o Positive Rake - Exists when the initial contact between the cutter and the

work piece occurs at the cutting edge. The cutting edge leads the rake surface.

Fig: 1.16 Rake



Relief-Space - Provided by removing material immediately behind the cutting edge.

Done to eliminate the possibility of heeling or rubbing.

o Axial angle relief - The angle made by a line tangent to the relieved surface

at the end cutting edge and a plane normal to the axis.

o Axial relief - The relief measured in the axial direction between a plane

perpendicular to the axis at the cutting edge and the relieved surface. Helps

to prevent rubbing as the corner wears.

o Concave relief - The relieved surface behind the cutting edge having a

concave form. Produced by a grinding wheel set at 90 degrees to the cutter

axis.

o Eccentric relief - The relieved surface behind the cutting edge having a

convex form. Produced by a type I wheel presented at an angle to the cutter

axis.

o End relief - Relief on the end of an end mill. Needed only for plunging

cutters and to relieve rubbing as the result of corner wear.

o Flat relief - The relieved surface behind the cutting edge having a flat

surface produced by the face of a cup wheel.

o Radial relief - Relief in a radial direction measured in the plane of rotation.

It can be measured by the amount of indicator drop at a given radius in a

given amount of angular rotation.

Tangential rake angle - The angle made by a line tangent to a hooked tooth at the

cutting edge and a radius passing through the same point in plane normal to the

axis.



CHAPTER 2

LITERATURE STUDY

Researchers in the area of high-speed milling have implemented various chatter

recognition techniques. Professor Jiri Tlusty[1] developed a method that detects chatter

during machining, and in turn, suggests a new speed for the same depth. Cobb [2] found

after testing, that impact dampers served better in controlling the vibrations. The types

ofimpact dampers used were a spring/mass liquid impact damper and a tapered impact

damper. Smith[3], Keyvanmanesh[4], and Cheng[5] did an extensive research in

understanding the dynamic characteristics of the tool and spindle to control chatter during

machining.

Cook et al. [6] developed damping mechanisms to control vibrations on

traffic signal structures. Traffic signal structures that are subjected to cyclic loading due to



the wind and fast moving vehicles, sometimes, result in premature fatigue failures. They

investigated this problem and proposed devices to provide damping to the structures. The

research damper model was based on the work done by Slocum [7] on damping bending in

beams. In his book, Slocum introduced the concept of friction damping between layered

elements. The book explains that, when two cantilevered beams stacked on top of each

other undergo bending there occur a relative shear motion between the inner surfaces of the

layered elements causing friction energy to be produced at the interface, which in turn,

used to reduce the deflection of the layered beam. One of his patented works [8]

implements this idea. He developed a method to damp bending vibrations in beams and

similar structures T. Schmitz, J.C. Ziegert, C. Stanislaus [9] Charles Stanislaus predicted

that the stable cutting regions are a critical requirement for high-speed milling operations.

M.Alauddin, M.A.EL Baradie, M.S.J.Hashmi [10] has revealed that when the cutting speed

is increased, productivity can be maximized, and surface quality can be improved. F.

Ismail and E.G. Kubica [11] proposed the maximum quantity of material that can be

removed by the milling operation which is often limited by the stability of the cutting

process, and not by the power available on the machine. Smith and Dilio[12] have

described a control strategy for chatter suppression by adjusting the spindle speed to

operate in high stability lobe. Experimentally, they achieved a remarkable increase in metal

removal rates. Weck et al [13] attempted to assess the merits of using the spindle speed

modulation and for that matter any other technique for chatter suppression, one needs to

detect the onset chatter reliably. M. Liang, T.Yeap, A. Hermansyah [14] reported a fuzzy

logic approach for chatter suppression in end milling processes. Vibration energy and the

peak value of vibration frequency spectrum are jointly used as chatter indicators and inputs

to the proposed fuzzy controller.

Kosuke Nagaya, Jyoji Kobayasi, Katuhito Ima i [15] gave a method of

micro-vibration control of milling machine heads by use of vibration absorber. An auto-

tuning vibration absorber is presented in which the absorber creates anti-resonance state.

Ziegert John C. Stanislaus Charles, Schmitz Tony L. Streling [16] Robert found that the

limiting chatter free depth of cut in milling is dependent on dynamic stiffness of the tool or

spindle system. N.H.Kim, K.K.Choi, J.S.Chen and Y.H.Park [17] proposed a continuum-

based shape design sensitivity formulation for a frictional contact problem with arigid body

using mesh less method. Tony L. Schmitz, John C. Ziegert, [18] Charles Stanislaus



predicted that the stable cutting regions are a critical requirement for high-speed milling

operations. Sridhar et al [19] presented the first detailed mathematical model with time

varying cutting force coefficients. Budak and Altintas [20] derived the finite order

characteristic equation for the stability analysis in milling. Recent investigation performed

by Alauddin [21] has revealed that when the cutting speed is increased, productivity can be

maximized, and surface quality can be improved. According to Hasegawa [22] surface

finish can be characterized by various parameters such as average roughness (Ra),

smoothening depth (Rp), root mean square (Rq), and maximum peak-to-valley height (Rt).

EI-Baradie [23] and Bandyopad [24] have shown that by increasing cutting speed, the

productivity can be maximized, an and the surface quality can be improved. S. Rajesham et

al.[25] stresses that Process knowledge is the prerequisite to applying Taguchi Method/D

O E. W.H. Yang, Y.S. Tarng [26] highlighted on the Taguchi method, a powerful tool to

design optimization for quality, is used to find the optimal cutting parameters for turning

operations. J.Z. Zhang et al [27] says that Taguchi design is an efficient and effective

experimental method in which a response variable can be optimized, given various control

and noise factors, using fewer resources than a factorial design.

Several efforts were made to reduce the chatter on the products produced by the

milling process. Sridhar et al [28] presented the first detailed mathematical model with

time varying cutting force coefficients..

Engelhardt et al [29] have been demonstrated the technique of spindle speed

modulation to be very effective in suppressing chatter in milling at regular cutting speeds.

The speed modulation parameters are application specific and may not be suitable for

entire job. The static force variation that results from modulated feed per tooth could

produce undesirable effects where constant speed cutting may suffice. Hence this

technique on its own lacks broad applicability..

Weck et al [30] attempted to assess the merits of using the spindle speed

modulation and for that matter any other technique for chatter suppression, one needs to

detect the onset chatter reliably. This blurring is amplified drastically when applying

certain chatter suppression techniques like spindle speed modulation method. The limit of

stability is defined as the axial depth of cut at which chatter commences.



T. Schmitz et al [31] predicted that the stable cutting regions are a critical

requirement for high-speed milling operations. J.C.Ziegert et al (2004) found that the

limiting chatter-free depth of cut in milling is dependent on dynamic stiffness of the tool or

spindle system. A method for increasing the dynamic stiffness by providing additional

damping is demonstrated. The proposed damper is multi-fingered cylindrical insert placed

in an interior bore located inside conventional milling cutters. Spindle rotation forces these

flexible fingers against the inner surface of the tool, bending of the tool during cutting

dissipate energy through friction, leading to improved damping and dynamic stiffness. This

presents an analytical model of the damper, experimental measurements of tool response

and comparison between stable cutting depths using both conventional tool and with the

damping insert.

P.Ravi kumar and G.Krishna mohana Rao [32] conducted experiments on end

milling in aluminium and mild steel using solid end milling cutters .It was observed that

surface roughness decreases as the cutting speed increases.

P.Ravi Kumar and G.Krishna mohana Rao [33] conducted experiments on damper

inserted end milling cutters . Influence of cutting speed and type of damping insert on the

roughness of surface produced by damper inserted end mill cutter was studied. Taguchi

method was applied and found that hollow end milling cutter with 2 dampers was

optimum.

In the present study, experiments are conducted on work material Cast iron to

investigate the effect of damper inserted end milling tools on surface roughness.



CHAPTER 3

REDUCTION OF VIBRATION IN MILLING CUTTERS

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 indexable insert milling cutters and solid carbide end mills differ in construction,

they are both vulnerable to chatter and share some common vibration remedies. Indexable

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.

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 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 build-



up 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 CVD

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 indexable 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.

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 states that reducing the length of 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 the 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 centreline 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

cutter to the other. For a two- to three-inch face mill, the offset may be 3/16". For a one-

inch end mill, the offset may be 0.0050". Again, experimentation can determine the low-

vibration 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 centre. Strategies for connecting the tool to the machining centre 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 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 INTRODUCTION TO FRICTION DAMPERS

Self-excited vibration in cutting tools has been a significant problem in the area of high-

speed 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 effect

of 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.

.

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 modelling 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.

3.4.1Friction damper inserts:-



Fig: 3.1 Solid End mill tool Fig: 3.2 Hollow

End mill Tool

Testing was performed on the solid end mill, and later the dampers were inserted

into the hollow tool, and the tests were repeated. The damper insert had fingers and was

constructed from a 9.5 mm diameter mild steel blank. The damper insert was slit down

76mm of its 105mm length by wire electro discharge machining in order to form the

separate fingers. As shown in the figures tools with one, two, three, four and five dampers

are chosen, so that different interactions between independent variables could be

effectively investigated. The diameter of the damper insert was such that the solid portion

provided a light press fit into the tool body.



Fig:3.3 Hollow tool with one damper

Fig:3.4 Two dampers to be inserted in a Hollow Tool

Fig:3.5 Three Dampers to be inserted in a Hollow Tool

For the purpose of the project and to obtain better results dampers with four and five slots

in number were fabricated using Wire Cut EDM machining process. Dampers with



increased number of slots have increased area of friction surface which increases the

amount of energy dissipation and hence reduced chatter and vibration.

Fig:3.6 Four dampers fabricated using wire cut EDM machining process

Fig:3.7 Five dampers fabricated using wire cut EDM machining process

3.5 WIRE CUT EDM MACHINING:



Wire EDM (Vertical EDM's kid brother), is not the new kid on the block. It was

introduced in the late 1960s', and has revolutionized the tool and die, mold, and

metalworking industries. It is probably the most exciting and diversified machine tool

developed for this industry in the last fifty years, and has numerous advantages to offer.

The accuracy, surface finish and time required to complete a job is extremely

predictable, making it much easier to quote.

PRINCIPLE OF WIRE ELECTRICAL DISCHARGE MACHINING

The Spark Theory on a wire EDM is basically the same as that of the vertical EDM

process. In wire EDM, the conductive materials are machined with a series of electrical

discharges (sparks) that are produced between an accurately positioned moving wire (the

electrode) and the workpiece. High frequency pulses of alternating or direct current is

discharged from the wire to the workpiece with a very small spark gap through an

insulated dielectric fluid (water). Many sparks can be observed at one time. This is

because actual discharges can occur more than one hundred thousand times per second,

with discharge sparks lasting in the range of 1/1,000,000 of a second or less. The volume

of metal removed during this short period of spark discharge depends on the desired

cutting speed and the surface finish required.

The heat of each electrical spark, estimated at around 15,000 to 21,000 Fahrenheit,

erodes away a tiny bit of material that is vaporized and melted from the workpiece.

(Some of the wire material is also eroded away) These particles (chips) are flushed away

from the cut with a stream of de-ionized water through the top and bottom flushing



nozzles. The water also prevents heat build-up in the workpiece. Without this cooling,

thermal expansion of the part would affect size and positional accuracy. Keep in mind

that it is the ON and OFF time of the spark that is repeated over and over that removes

material, not just the flow of electric current.

STARTING A CUT FROM THE EDGE OF A WORKPIECE

When starting a cut from the edge of a workpiece, cutting a form tool, slicing a tube

or bar stock, or starting a cut from a large diameter start hole, is a slower process without

submerged machining capabilities. There is a greater risk of breaking a wire if the flush

is not set properly or if too much power is used. This condition is greatly reduced when

cutting the part submerged.

Fig 3.8 working of wire EDM 3.6 REDUCING VIBRATIONS AND CHATTER IN END MILLING:



When chatter occurs, it can be self-sustaining until the problem is corrected. Chatter

causes poor finish on the part, and will damage and significantly reduce the life of end

mills. Carbide end mills are particularly susceptible to damage.

3.6.1 Typical methods to reduce chatter include reducing cutting forces by:

Reducing the number of flutes. Decreasing the chipload per tooth by reducing the feed or increasing the speed or

RPM. Reducing the axial or radial depth of cut.

Though these steps will reduce chatter, slowing down the cutting process is not always the best course of action, and reducing the chipload can be detrimental to the cutter.

3.6.2 First steps are to improve rigidity and stability:

Use a larger end mill with a larger core diameter. Use end mills with reduced clearance or a small circular margin. Use the shortest overhang from spindle nose to tip of tool. Use stub length end mills where possible Use balanced tool holders. Rework fixture to hold the workpiece more securely. Reprogram the cutter path to shift cutting forces into stiffer portions of the

workpiece. Look for ways to improve spindle speeds then adjust feed accordingly.

Chatter is common when machining corners. As the end mill enters the corner, the

percentage of engagement increases the number of teeth in the cut. This drastically

increases the cutting forces, causing chatter. To reduce chatter when machining corners,

consider using circular interpolation to produce a bigger corner radius than indicated by the

part print. Then remove the remaining stock with a smaller end mill using circular

interpolation.



CHAPTER 4

SURFACE ROUGHNESS

4.1 INTRODUCTION

Characterization of surface topography is important in applications involving friction,

lubrication, and wear (Thomas, 1999). In general, it has been found that friction increases

with average roughness. Roughness parameters are, therefore, important in applications

such as automobile brake linings, floor surfaces, and tires. The effect of roughness on

lubrication has also been studied to determine its impact on issues regarding lubrication of

sliding surfaces, compliant surfaces, and roller bearing fatigue. Finally, some researchers

have found a correlation between initial roughness of sliding surfaces and their wear rate.

Such correlations have been used to predict failure time of contact surfaces.

Another area where surface roughness plays a critical role is contact resistance (Thomas,

1999). Thermal or electrical conduction between two surfaces in contact occurs only



through certain regions. In the case of thermal conduction, for example, the heat flow lines

are squeezed together at the areas of contact, which results in a distortion

Fig:4.1 .Contact resistance due to construction of flow lines of the isothermal lines,

Thermal contact resistance is an important issue in space applications, such as

satellites,

Where the heat generated by the electronic devices can only are driven away by

conduction. Surface roughness is also a topic of interest in fluid dynamics (Thomas, 1999).

The roughness of the interior surface of pipes affects flow parameters, such as the

Reynolds number, which is used to evaluate the flow regime (i.e., laminar or turbulent).

The performance of ships is also affected by roughness in the form of skin friction, which

can account for 80-90% of the total flow resistance. In addition, the power consumption

can increase as much as 40% during the service life of a ship as a result of increased

Surface roughness caused by paint cracking, hull corrosion and fouling. The examples

mentioned above are just a few of the applications in which surface roughness has to be

carefully considered. However, the influence of roughness extends to various engineering

concerns such as noise and vibration control, dimensional tolerance, abrasive processes,

bioengineering, and geomorphometry (Thomas, 1999).



4.1.1 Surface Finish:

Surface finish is the allowable deviation from a perfectly flat surface that is made

by some manufacturing process

4.1.2 Terminology of surface roughness

Surface: The boundary that separates an object from another object, substance, or

space.

Real Surface: The actual boundary of an object. Its deviations from the nominal

surface stem from the processes that produce the surface.

Measured Surface: A representation of the real surface obtained by the use of a

measuring instrument.

Nominal Surface: The intended surface boundary (exclusive of any intended

surface roughness), the shape and extent of which is usually shown and

dimensioned on a drawing or descriptive specification (Figure 1.8).

Flaws: Flaws, or defects, are random irregularities, such as scratches, cracks,

holes, depressions, seams, tears, or inclusions as shown in Figure 1.8.

Lay: Lay, or directionality, is the direction of the predominant surface pattern and

is usually visible to the naked eye. Lay direction has been shown in Figure 1.8.

Roughness: It is defined as closely spaced, irregular deviations on a scale smaller

than that of waviness. Roughness may be superimposed on waviness. Roughness is

expressed in terms of its height, its width, and its distance on the surface along

which it is measured.(figure 1.8.1)



Fig 4.2 schematic diagram of surface characteristics

Waviness: It is a recurrent deviation from a flat surface, much like waves on the

surface of water. It is measured and described in terms of the space between

adjacent crests of the waves (waviness width) and height between the crests and

valleys of the waves (waviness height). Waviness can be caused by,

Deflections of tools, dies, or the work piece,

Forces or temperature sufficient to cause warping,

Uneven lubrication,

Vibration, or

Any periodic mechanical or thermal variations in the system during manufacturing

operations.



Fig 4.3 schematic diagram of surface characteristics

4.2 DEFINITION AND PARAMETERS

The concept of roughness is often described with terms such as ‘uneven’, ‘irregular’, ‘coarse in texture’, ‘broken by prominences’, and other similar ones (Thomas, 1999). Surface roughness is a measure of the texture of a surface. It is quantified by the vertical deviations of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small the surface is smooth. Roughness is typically considered to be the high frequency, short wavelength component of a measured surface.

Roughness plays an important role in determining how a real object will interact with its environment. Rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces . Roughness is often a good predictor of the performance of a mechanical component, since irregularities in the surface may form nucleation sites for cracks or corrosion. On the other hand, roughness may promote adhesion.

Although roughness is often undesirable, it is difficult and expensive to control in manufacturing. Decreasing the roughness of a surface will usually increase exponentially its manufacturing costs. This often results in a trade-off between the manufacturing cost of a component and its performance in application.

There are many different roughness parameters in use, but Ra is by far the most common. Other common parameters include Rz, Rq, and Rsk.



Parameters

Ra is the arithmetic average of the absolute values and Rt is the range of the collected roughness data points.

The average roughness, Ra, is expressed in units of height. In the Imperial (English) system, 1 Ra is typically expressed in "millionths" of an inch. This is also referred to as "microinches" or sometimes just as "micro" The parameters are by far the most common surface roughness parameters found in the India on mechanical engineering drawings and in technical literature.

Table 4.1 surface roughness parameters


Parameter Description Formula

Ra arithmetic average of absolute values

Rq, RRMS root mean squared

Rv maximum valley depth

Rp maximum peak height

Rt Maximum Height of the Profile

Rsk Skewness

http://en.wikipedia.org/wiki/Range


The Parameter that we dwell upon the most is Average Roughness –Ra: -

• Roughness average (Ra): This parameter is also known as the arithmetic mean

roughness value, AA (arithmetic average) or CLA (centre line average). Ra as shown in

thefig is universally recognized and the most used international parameter of roughness.

Fig 4.4 Roughness average of surface texture

Where Ra = the arithmetic average deviation from the mean line

L = the sampling length

y = the ordinate of the profile curve

It is the arithmetic mean of the departure of the roughness profile from the mean line.

An example of the surface profile is shown in Figure 6.6.

Fig: 4.5 Surface profile



4.3 MEASURMENT TECHNIQUES

Surface finish may be measured in two ways: contact and non-contact methods. Contact

methods involve dragging a measurement stylus across the surface; these instruments are

called profilometers. Non-contact methods include: interferometer, confocal

microscopy, focus variation, structured light, electrical capacitance, electron microscopy,

and photogrammetry.

The most common method is to use a diamond stylus profilometer. The stylus is run

perpendicular to the lay of the surface.

4.3.1 Taylsurf instrument:

The Taylor-Hobson Talysurf.

The Talysurf is an electronic instrument working on carrier modulating principle. This

instrument also gives the same information as the previous instrument, but much more

rapidly and accurately. This instrument as also the previous one records the static

displacement of the stylus and is dynamic instrument like profile meter.

The measuring head of this instrument consists of a diamond stylus of about 0.002 mm tip

radius and skid or shoe which is drawn across the surface by means of a motorized driving

unit (gearbox), which provides three motorized speeds giving respectively x 20 and x 100

horizontal magnification and a speed suitable for average reading. A neutral position in

which the pick-up can be traversed manually is also provided. In this case the arm carrying

the stylus

forms an armature which pivots about the centre piece of E-shaped stamping as shown in

Fig. 11.9. On two legs of (outer pole pieces) the J5-shaped stamping there are coils

carrying an a.c. current. These two coils with other two resistances form an oscillator. As

the armature is pivoted about the central leg, any movement of the stylus causes the air gap

to vary and thus the amplitude of the original a. c. current flowing in the coils is

modulated. The output of the bridge thus consists of modulation only as shown in Fig.


http://en.wikipedia.org/wiki/Diamond

http://en.wikipedia.org/wiki/Photogrammetry

http://en.wikipedia.org/wiki/Electron_microscopy

http://en.wikipedia.org/wiki/Electrical_capacitance

http://en.wikipedia.org/wiki/Structured_light

http://en.wikipedia.org/wiki/Focus_variation

http://en.wikipedia.org/wiki/Confocal_microscopy

http://en.wikipedia.org/wiki/Confocal_microscopy

http://en.wikipedia.org/wiki/Interferometry

http://en.wikipedia.org/wiki/Profilometer

http://en.wikipedia.org/wiki/Stylus


Fig. 4.6 Schematic Layout of Talysurf.

This is further demodulated so that the current now is directly proportional to the vertical

displacement of the stylus only. The demodulated output is caused to operate a pen

recorder to produce a permanent record and a meter to give a numerical assessment

directly. In recorder of this statement the marking medium is an electric discharge through

a specially treated paper which blackens at the point of the stylus, so this has no distortion

due to drag and the record strictly rectilinear one.

Now-a-days microprocessors have made available complete statistical multi-trace systems

measuring several places over a given area and can provide standard deviations and

average over area-type readings and define complete surface characterization. These

systems lend themselves to research applications where specialized programming can

achieve autocorrelation, power spectrum analysis and peak curvature.

Stylus

Phonograph needles, though used in some cases are found to be too large and too heavily

loaded. It also causes damage. Diamond styli are used universally. Some of them are cones

of 90° include dangle and tip radius 4-12 urn. A popular stylus with truncated pyramid is

shown in Fig. 11.10. The angle between the faces is 90°. The short edge is parallel to the

direction of motion. Thus this stylus cannot resolve a wavelength shorter than 6 \xm, and

integrates over a narrow strip of surface 8 \im wide.


http://lh3.ggpht.com/_X6JnoL0U4BY/S01_5bJc5NI/AAAAAAAAFA8/LOVAEh7UPa4/s1600-h/tmp3F55_thumb1.png


It may be noted that this pick up has finite dimensions, and it is constrained to move in a

nearly vertical plane, relative to the moving pickup. Thus the stylus cannot record re-

entrant features, an unimportant drawback for engineering investigations as re-entrant

structures are absent on most machined surfaces. This stylus will fail to follow peaks and

valley faithfully and produces a distorted record of the surface.

Since the dimensions of the stylus are finite, so also is the load on it. The load is of the

order of 70 mg force. But as the area of contact is too small, the local pressure may be

sufficiently high to cause significant local elastic downward deformation of the surface

under examination.

Fig: 4.7 Talysurf

4.3.2 Principle:

Fig 4.8 Principle of talysurf

A profile measurement device is usually based on a tactile measurement principle.

The surface is measured by moving a stylus across the surface. As the stylus moves up and



down along the surface, a transducer converts these movements into a signal which is then

transformed into a roughness number and usually a visually displayed profile. Multiple

profiles can often be combined to form a surface representation.

CHAPTER 5



METHODOLOGY

5.1 CHATTER DETECTION AND SUPPRESSION

Chatter is generally classified in two categories: primary and secondary. Primary chatter

can be caused by the cutting process itself (i.e. by friction between the tool and the

workpiece, by thermo-mechanical effects on the chip formation or by mode coupling).

Secondary chatter may be caused by the regeneration of waviness on the workpiece

surface.

This regenerative effect is the most important cause of chatter. For this reason it has

become a convention and been followed by a lot of the publications that ’’chatter’’ only

refers to regenerative chatter. However, it has to be mentioned that it is possible to

distinguish between frictional chatter, thermo-mechanical chatter and mode coupling

chatter and regenerative chatter depending on the self-excitation mechanism that causes the

vibration.

Frictional chatter occurs when rubbing on the clearance face excites vibration in the

direction of the cutting force Fc and limits in the thrust force Ft direction.

Thermo-mechanical chatter occurs due to the temperature and strain rate in the

plastic deformation zone.

Mode coupling chatter exists if vibration in the thrust force direction generates

vibration in the cutting force direction and vice versa. This result in simultaneous vibration

in the cutting and thrust force directions .Physically, it is caused by a number of sources

such as friction on the rake and clearance surfaces, chip thickness variation, shear angle

oscillations and regeneration effect.

Regenerative chatter is the most common form of selfxcited vibration. It can occur

often because most metal cutting operations involve overlapping cuts which can be a

source of vibration amplification .The cutter vibrations leave a wavy surface. During

milling the external tooth in cut attacks this wavy surface and generates an wavy

surface .The chip thickness and, hence ,the force on the cutting tool vary due to the phase

difference between the wave left by the previous teeth (in turning it is the surface left after

the previous revolution) and the wave left by the current ones . This phenomenon can



greatly amplify vibrations, become dominant and build up chatter. If the relative phase

difference is zero, the dynamic chip thickness is also zero. If the relative phase is p, the

dynamic chip thickness variation is maximum. Consequently, the force on the cutter

depends, among other factors, on the displacement of the previous tooth.

At high speeds, the stabilizing effect of process damping diminishes, making the

process more prone to chatter. Process damping usually occurs at low spindle speeds and

provides the stability due to the short undulations left on the part’s surface by high-

frequency vibrations. These surface waves interfere with the cutting tool flank face and

dampen the cutting tool vibration.

Fig: 5.1 Regeneration of waviness in a milling model with two degrees of freedom.

5.1.1 Strategy for ensuring stable machining processes:

In detecting, identifying ,avoiding, preventing, reducing ,controlling, or suppressing chatter

a review of the great deal of literature regarding the chatter problem leads to a existing

method ,in which modifying certain machine tool elements to passively change the

behaviour of the system composed of the machine tool, the cutting tool and tool holder.



In this method, the design of the machine tool is changed to improve its performance

against vibration or on the use of extra devices that can absorb extra energy or disrupt the

regenerative effect. Examples of these are passive damping devices installed in machine

tool elements with lower rigidity: friction dampers, mass dampers or tuned dampers. This

is focused on ensuring chatter-free operations by using passive strategies to damp, reduce

and control the phenomenon.

To reduce the excessive vibrations of an end-mill cutter, a mechanical damper is

introduced into a cylindrical hole in the centre of a standard end-milling cutter to dissipate

chatter energy in the form of friction. Chatter is a highly complex phenomenon due to the

diversity of elements that can compose the dynamic system and its behaviour the cutting

tool, the tool holder, the work piece material, the machine tool structure and the cutting

parameters. Predicting its occurrence is still the subject of much research, even though the

regenerative effect, the main cause of chatter, was identified and studied very early on.

Moreover, chatter can occur in different metal removal processes: milling, turning, drilling,

boring, broaching and grinding.

Chatter occurrence has several negative effects:

Poor surface quality.

Unacceptable inaccuracy.

Excessive noise.

Disproportionate tool wear.

Machine tool damage.

Reduced material removal rate (MRR).

Increased costs in terms of production time.

Waste of materials.

Waste of energy.

Environmental impact in terms of materials and energy.

Costs of recycling ,reprocessing or dumping non-valid final parts to recycling

points

For these reasons, chatter avoidance is a topic of enormous interest. In workshops, machine

tool operators often select conservative cutting parameters to avoid chatter and, in some



cases, additional manual operations are required to clean chatter marks left on the part

surface. This common practice usually results in a decrease in productivity.

Chatter causes poor surface quality, therefore an investigation is made to test

surface roughness of work piece with solid end milling cuter, hollow milling cutter and

damper inserted milling cutters at various.

5.2 FRICTION DAMPER STRUCTURE

Friction damper is to increase the damping in end mills used for high-speed milling by the

addition of internal features into the tool. The increased damping is achieved by hollowing

the tool body and inserting a multi fingered damper into the center opening. The fingers on

the damper insert are created by cutting axial slits along most of the length of a cylinder

whose outer diameter matches the inner diameter of the tool body, thus forming multiple

fingers a damper may also be inserted into a solid end mill that has a blind hole in the non-

fluted end.

When the tool bends, the neutral surface of the outer cylindrical tool body is

located on the tool centreline. However, the fingers will bend with their neutral surfaces

passing through their own centroids. The net result is that the axial strain experienced on

the outer surface of the fingers will be different than the axial strain experienced on the

inner surface of the tool body, causing a relative sliding between them. When the tool

rotates at high speed, large centrifugal forces press the fingers against the inner surface of

the tool body. Press fitting causes an enhanced pressure between the parts that makes the

effect of damper more sensible. This is because of increasing the amount of frictional force

between the surfaces. The effect of press fit pressure seems to be much more than

centrifugal effect. Wire electro discharge machining is used to form fingers of the damper.

The damper was primarily designed to fit into the tool through a blind hole made

on the shank. When the tool rotates, the centrifugal forces generated at high speeds tend to

push the fingers of the damper outwards against the inner surface of the tool shank. During

this event, when the tool experiences bending vibrations, the fingers slide over the inner



surface of the tool body. The relative sliding is proportional to the distance from the neutral

axis of the tool to the neutral axis of the individual fingers. The frictional forces,

Which arise during this sliding of the fingers over the inner surface of the tool body?

Dissipate energy and produce damping.

Two designs of the damper were developed in this research. The second is a

modified design, which was developed to attempt to improve the damper performance.

Since both the designs were based on same fundamental concept, the basic equations for

calculating the friction work remain the same except that the second model has a much-

simplified geometry and assumes that the contact between the tool’s inner surface and the

damper is only at the end. The equations for calculating the frictional work will be derived

for the original model followed by the modified equations that were used to calculate the

frictional work of the new design.

Of course, when the center section of a tool is removed, the stiffness will decrease.

This stiffness loss must, at minimum, be compensated by increases in the damping ratio

provided by the centrifugal damper. However, the stiffness loss is minimal for holes of

reasonable size. For example, in the tools developed for this work, the diameter of the

central hole is one-half of the outer diameters of the tool body, which reduces the bending

stiffness of the tool by only 7%. The frictional forces, which arise during this sliding of the

fingers over the inner surface of the tool body, dissipate energy and produce damping.

CHAPTER 6



DESIGN OF EXPERIMENTS

A Design of Experiment (DOE) is a structured, organized method for determining the

relationship between factors affecting a process and the output of that process.

Other Definitions:

1. Conducting and analysing controlled tests to evaluate the factors that control the value

of a parameter or group of parameters.

2. "Design of Experiments" (DOE) refers to experimental methods used to quantify

indeterminate measurements of factors and interactions between factors statistically

through observance of forced changes made methodically as directed by mathematically

systematic tables.

Design of Experiment Techniques

1. Factorial Design

2. Response Surface methodology

3. Mixture Design

4. Taguchi Design

Among those we had selected Taguchi Design for optimizing surface finish and cutting

forces in end milling Operation.

6.1 Introduction to Taguchi Method

Competitive crisis in manufacturing during the 1970’s and 1980’s that gave rise to

the modern quality movement, leading to the introduction of Taguchi methods to the U.S.

in the 1980’s. Taguchi’s method is a system of design engineering to increase quality.

Taguchi Methods refers to a collection of principles which make up the framework of a

continually evolving approach to quality. Taguchi Methods of Quality Engineering design

is built around three integral elements, the loss function, signal-to-noise ratio, and

orthogonal arrays, which are each closely related to the definition of quality.

6.1.1 Taguchi design phases

To achieve economical product quality design, Taguchi proposed three phases:

1. System design,



2. Parameter design,

3. Tolerance design.

1. Systems Design: Systems design identifies the basic elements of the design, which

will produce the desired output, such as the best combination of processes and

materials, selection of machine, the type of tool are considered.

2. Parameter Design: Parameter design determines the most appropriate, optimizing

set of parameters covering these design elements by identifying the "settings" of

each parameter which will minimize variation from the target performance of the

product.

3. Tolerance Design: Tolerance design finally identifies the components of the

design which are sensitive in terms of affecting the quality of the product and

establishes tolerance limits which will give the required level of variation in the

design.

Fig 6.1 Taguchi design phases

6.2 Taguchi approach


SYSTEMS DESIGN

PARAMETER DESIGN

TOLERANCE DESIGN

ENGINEERING EXPERTIZE

Establishment of basic design and engineering concepts

Establishment of design target –dimensions, properties, statistical design and sensitivity analysis

Establish tolerances, statistical tolerance & design


The objective of the robust design is to find the controllable process parameter

settings for which noise or variation has a minimal effect on the product's or process's

functional characteristics. It is to be noted that the aim is not to find the parameter settings

for the uncontrollable noise variables, but the controllable design variables. To attain this

objective, the control parameters, also known as inner array variables, are systematically

varied as stipulated by the inner orthogonal array. For each experiment of the inner array, a

series of new experiments are conducted by varying the level settings of the uncontrollable

noise variables. The level combinations of noise variables are done using the outer

orthogonal array.

The influence of noise on the performance characteristics can be found using the

ratio. Where S is the standard deviation of the performance parameters for each inner array

experiment and N is the total number of experiment in the outer orthogonal array. This

ratio indicates the functional variation due to noise. Using this result, it is possible to

predict which control parameter settings will make the process insensitive to noise.

Taguchi method focuses on Robust Design through use of

Signal-To-Noise ratio

Orthogonal arrays.

6.2.1 Signal-To-Noise Ratio

The signal-to-noise concept is closely related to the robustness of a product design.

A Robust Design or product delivers strong ‘signal’. It performs its expected function and

can cope with variations (“noise”), both internal and external. In signal-to-Noise Ratio,

signal represents the desirable value and noise represents the undesirable value.

Uses

o S/N ratios can be used to get closer to a given target value, or to reduce variation in

the product's quality characteristic(s).

o Signal-To-Noise ratio is used to measure controllable factors that can have such a

negative effect on the performance of design.

o They lead to optimum through monotonic function

o They help improve additives of the effects.



o To quantify the quality.

There are 3 Signal-to-Noise ratios of common interest for optimization of Static

Problems. The formulae for signal to noise ratio are designed so that an experimenter can

always select the largest factor level setting to optimize the quality characteristic of an

experiment. Therefore a method of calculating the Signal-To-Noise ratio we had gone for

quality characteristic.

They are

1. Smaller-The-Better,

2. Larger-The-Better,

3. Nominal-The-Best.

The Smaller-The-Better: Impurity in drinking water is critical to quality. The less

impurities customers find in their in their drinking water, the better it is. Vibrations

are critical to quality for a car, the less vibration the customers feel while driving

their cars the better, the more attractive the cars are.

The Signal-To-Noise ratio for the Smaller-The-Better is:

S/N = -10 *log (mean square of the response)

.

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 dollar they spend on their

phone 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)



.

Nominal-The-Best:

When a manufacturer is building mating parts, he would want every part to match

the predetermined target. For instance when he is creating pistons that need to be anchored

on a given part of a machine, failure to have the length of the piston to match a

predetermined size will result in it being either too small or too long resulting in lowering

the quality of the machine. In that case, the manufacturer wants all the parts to match their

target.

When a customer buys ceramic tiles to decorate his bathroom, the size of the tiles is

critical to quality, having tiles that do not match the predetermined target will result in

them not being correctly lined up against the bathroom walls.

The S/N equation for the Nominal-The-Best is:

S/N = 10 * log (the square of the mean divided by the variance)

.

6.2.2 Orthogonal Arrays

Introduction:

In order to reduce the total number of experiments “sir Ronald Fisher” developed

the solution:” orthogonal arrays”. The orthogonal array can be thought of as a distillation

mechanism through which the engineers experiment passes (Ealey, 1998). The array

allows the engineer to vary multiple variables at one time and obtain the effects which that

set of variables has an average and the dispersion.

Taguchi employs design experiments using specially constructed table, known as

"Orthogonal Arrays (OA)" to treat the design process, such that the quality is build into the

product during the product design stage. Orthogonal Arrays (OA) are a special set of Latin

squares, constructed by Taguchi to lay out the product design experiments.



An orthogonal array is a type of experiment where the columns for the independent

variables are “orthogonal” to one another. Orthogonal arrays are employed to study the

effect of several control factors. Orthogonal arrays are used to investigate quality.

Orthogonal arrays are not unique to Taguchi. They were discovered considerably

earlier (Bendell, 1998). However Taguchi has simplified their use by providing tabulated

sets of standard orthogonal arrays and corresponding linear graphs to fit specific projects

(ASI, 1989; Taguchi and Kenishi, 1987).

A typical orthogonal Array:Sno A B C

1 1 1 1

2 1 2 2

3 1 3 3

4 2 1 3

5 2 2 1

6 2 3 2

7 3 1 2

8 3 2 3

9 3 3 1

Table 6.1 L9 Orthogonal array

In this array the columns are mutually orthogonal. That is for any pair of columns

all combination of factors occurs; and they occur an equal number of times. Here there are

4 parameters, A, B, and C each at three levels. This is called an ‘L9’ design; with the 9

indication the nine rows, configurations, or prototypes to be tested. Specific test

characteristics for each experimental evaluation are identified in the associated row of the

table. Thus L9 (34) means that nine experiments are to be carried out to study four variables

with three levels. There are greater savings in testing for larger arrays.

6.2.3 Minimum number of experiments to be conducted

The design of experiments using the orthogonal array is, in most cases, efficient when

compared to many other statistical designs. The minimum number of experiments that are



required to conduct the Taguchi method can be calculated based on the degrees of freedom

approach.

For example, in case of 8 independent variables study having 1 independent variable with

2 levels and remaining 7 independent variables with 3 levels (L18 orthogonal array), the

minimum number of experiments required based on the above equation are 16. Because of

the balancing property of the orthogonal arrays, the total number of experiments shall be

multiple of 2 and 3. Hence the number of experiments for the above case is 18.

Application of Orthogonal Array

Taguchi's OA analysis is used to produce the best parameters for the optimum

design process, with the least number of experiments.

OA is usually applied in the design of engineering products, test and quality

development, and process development.

Advantages and disadvantages of orthogonal array:

Conclusions valid over the entire region spanned by the control factors and their

settings

Large saving in the experiment effort

Analysis is easy

OA techniques are not applicable, such as a process involving influencing factors

that vary in time and cannot be quantified exactly.

6.3 Steps in Taguchi Methodology

Taguchi method is a scientifically disciplined mechanism for evaluating and

implementing improvements in products, processes, materials, equipment, and facilities.

These improvements are aimed at improving the desired characteristics and simultaneously

reducing the number of defects by studying the key variables controlling the process and

optimizing the procedures or design to yield the best results. Taguchi proposed a standard

procedure for applying his method for optimizing any process.



Fig 6.2 Steps in Taguchi methodology

6.3.1 Determine the Quality Characteristic to be optimized

The first step in the Taguchi method is to determine the quality characteristic to be

optimized. The quality characteristic is a parameter whose variation has a critical effect on

product quality. It is output or the response variable to be observed. Examples are weight,

cost, corrosion, target thickness, surface roughness, strength of a structure, and

electromagnetic radiation etc.

6.3.2 Identify the Noise Factors and Test Conditions

The next step is to identify the noise factors that can have a negative impact on

system performance and quality. Noise factors are those parameters which are either



uncontrollable or are too expensive to control. Noise factors include variations in

environmental operating conditions, deterioration of components with usage, and variation

in response between products of same design with the same input.

6.3.3 Identify the Control Parameters and Their Alternative Levels

The third step is to identify the control parameters thought to have significant

effects on the quality characteristic. Control parameters are those design factors that can be

set and maintained. The levels for each test parameter must be chosen at this point. The

number of levels, with associated test values, for each test parameter defines the

experimental region.

6.3.4 Design the Matrix Experiment and Define the Data Analysis Procedure

The next step is to design the matrix experiment and define the data analysis

procedure. First, the appropriate orthogonal arrays for the noise and control parameters to

fit a specific study are selected. Taguchi provides many standard orthogonal arrays and

corresponding linear graphs for this purpose.

After selecting the appropriate orthogonal arrays, a procedure to simulate the

variation in the quality characteristic due to the noise factors needs to be defined. A

common approach is the use of Monte Carlo simulation. However, for an accurate

estimation of the mean and variance, Monte Carlo simulation requires a large number of

testing conditions which can be expensive and time consuming. As an alternative, Taguchi

proposes orthogonal array based simulation to evaluate the mean and the variance of a

product response resulting from variations in noise factors as shown in fig. the results of

the experiment for each combination of control and noise array experiment are denoted by

Yii.

6.3.5 Conduct the Matrix Experiment

The next step is to conduct the matrix experiment and record the results. The Taguchi

method can be used in any situation where there is a controllable process. The controllable

process can be an actual hardware experiment, systems of mathematical equations, or

computer models that can adequately model the response of many products and processes.



6.3.6 Analyze the Data and Determine the Optimum Levels

After the experiments have been conducted, the optimal test parameter configuration

within the experiment design must be determined. To analyze the results, the Taguchi

method sues a statistical measure of performance called signal-to-noise (S/N) ratio

borrowed from electrical control theory. The S/N ratio developed by Dr. Taguchi is a

performance measure to choose control levels that best cope with noise. The S/N ratio

takes both the mean and the variability into account. In its simplest form S/N ratio is the

ratio of the mean (signal) to the standard deviation (noise). The S/N equation depends on

the criterion for the quality characteristic to be optimized. While there are many different

possible S/N ratios, three of them are considered standard and are generally applicable in

the situations below.

6.3.7 Predict the Performance at these Levels

Using the Taguchi method for parameter design, the predicted optimum setting need

not correspond to one of the rows o f the matrix experiment. This is often the case when

highly fractioned designs are used therefore, as the final step; an experimental

confirmation is run using the predicted optimum levels for the control parameters being

studied.

6.4 Analysis Of Variance (Anova)

Analysis of variance (ANOVA) is a statistical method for determining the existence

of differences among several population means. While the aim of ANOVA is the detect

differences among several populations means, the technique requires the analysis of

different forms of variance associated with the random samples under study- hence the

name analysis of variance.

The original ideas analysis of variance was developed by the English Statistician Sir

Ronald A. Fisher during the first part of this century. Much of the early work in this area

dealt with agricultural experiments where crops were given different treatments, such as

being grown using different kinds of fertilizers. The researchers wanted to determine

whether all treatments under study were equally effective or whether some treatments were

better than others.



CHAPTER 7

EXPERIMENTAL SETUP

To experimentally test the performance of the damper insert, two end mills are

designed. The tool is made of high speed steel (HSS) with 19.05mm outer diameter,

125mm length, and has 4 cutting flutes. Their external geometry was identical. One of the

tool had an internal blind hole of 9.5mm diameter with a length of 105 mm.

7.1 EXPERIMENTAL SETUP AND CONDITIONS

The experiment was carried out into two stages.

I. Cast Iron pieces of 50*50*35mm were used as the workpieces for the machining

process. Longitudinal slots were machined on the work piece by varying 4 parameters.

Fig 7.1 slot cutting on Cast Iron



Tests were performed at different spindle Speeds, Feeds and Depth of cuts for each tool. In

total there were about 6 different tools with various damper inserts for the present study.

The tools were

1) Solid End mill tool

2) Hollow End mill tool with one damper insert

3) Hollow End mill tool with two damper inserts

4) Hollow End mill tool with three damper inserts

5) Hollow End mill tool with four damper inserts

6) Hollow End mill tool with five damper inserts

Three prominent cutting speeds were selected among the 9 standard milling speeds, they

were 385Rpm, 685Rpm and 960Rpm. Similarly three Feed values were selected namely

18mm/min, 29mm/min and 41mm/min and three depth of cuts which are 0.25mm, 0.35mm

and 0.5mm. Taguchi's orthogonal array suggests a suitable combination of Speeds, Feeds

and Depth of cuts (doc) with the tool and damper arrangements. For the purpose of

variation of speeds, feeds and doc's with the various tools the Taguchi design gives outputs

as various combinations of these four parameters. Thus tests begin with each combination

of Type of tool, Feed, Speed and Depth of cut.

Consider the following table:-The details of these experimental conditions are shown

S.No. TYPE OF TOOL SPEED FEED DOC1 solid end mill 385 18 0.252 solid end mill 685 29 0.353 solid end mill 960 41 0.54 hollow with one damper 385 18 0.355 hollow with one damper 685 29 0.56 hollow with one damper 960 41 0.257 hollow with two damper 385 29 0.258 hollow with two damper 685 41 0.359 hollow with two damper 960 18 0.5

10hollow with three

damper 385 41 0.5

11hollow with three

damper 685 18 0.25

12hollow with three

damper 960 29 0.3513 hollow with four damper 385 29 0.514 hollow with four damper 685 41 0.25



15 hollow with four damper 960 18 0.3516 hollow with five damper 385 41 0.3517 hollow with five damper 685 18 0.518 hollow with five damper 960 29 0.25

Table : 7.1 Experimental Details for Surface Roughness Analysis

II. After machining with the different cutting conditions, the surface roughness were

measured using surface measuring instrument TALYSURF shown in Figure.

Fig: 7.2 Taly Surf

Fig: 7.3 Surface roughness analysis



The experiments were carried out on vertical milling machine. The physical and

mechanical properties of work piece are 50mm in length, 50mm in width and 35mm in

thickness. The work piece material is Cast Iron. The end milling cutter is of High Speed

Steel (HSS).



CHAPTER 8

RESULTS AND DISCUSSIONS

The Cast Iron work piece of 50mm X 50mm is machined on vertical milling

machine with an end milling cutter of 19.05mm diameter and 125mm length at varying

feeds speeds and depth of cuts. Each individual slot or cut imparts a certain texture on the

newly exposed surface of the work piece. The slot is tested with a Talysurf instrument to

find the Average Surface Roughness (Ra). The Roughness values for each corresponding

tool, speed, feed and depth of cut is tabulated. Taguchi design identifies 18 unique

combinations of type of tool, feed, doc and speed.

S.No. TYPE OF TOOL SPEED FEED DOC Ra1 solid end mill 385 18 0.25 5.65 2 solid end mill 685 29 0.35 3.833 solid end mill 960 41 0.5 3.944 hollow with one damper 385 18 0.35 2.525 hollow with one damper 685 29 0.5 3.366 hollow with one damper 960 41 0.25 3.717 hollow with two damper 385 29 0.25 3.668 hollow with two damper 685 41 0.35 3.819 hollow with two damper 960 18 0.5 3.08

10 hollow with three damper 385 41 0.5 4.1511 hollow with three damper 685 18 0.25 3.3412 hollow with three damper 960 29 0.35 3.6913 hollow with four damper 385 29 0.5 4.8114 hollow with four damper 685 41 0.25 3.9115 hollow with four damper 960 18 0.35 3.3316 hollow with five damper 385 41 0.35 2.6717 hollow with five damper 685 18 0.5 2.3618 hollow with five damper 960 29 0.25 2.25

Table 8.1 Tabulated values of surface roughness at various cutting speeds, feeds, Doc’s with different tool inserts

Table 8.1 Depicts the variation of surface roughness Ra with cutting speed, feed and depth

of cut. It shows the influence of number of damper inserts also. Among all the tools used,

cutter with five fingered input resulted in better surface finish. This may be due to the



increased area of friction surface which increases the amount of energy dissipation and

hence reduced chatter and vibration. When the tool bends, the neutral surface of the outer

cylindrical tool body is located on the tool center line. However, the fingers will bend with

their neutral surfaces passing through their own centroids. The net result is that the axial

strain experienced on the outer surface of the fingers will be different than the axial strain

experienced on the inner surface of the tool body, causing a relative sliding between them.

When the tool rotates at high speed, large centrifugal forces press the fingers against the

inner surface of the tool body. Press fitting causes an enhanced pressure between the parts

that makes the effect of damper more sensible. This is because of increasing the amount of

frictional force between the surfaces. The effect of press fit pressure seems to be much

more than centrifugal effect.

8.1 .TAGUCHI DESIGN METHOD:-

To better understand Taguchi design, the procedure of the Taguchi design is described in

the Fig. The complete procedure in Taguchi design method can be divided into three

stages: system design, parameter design, and tolerance design Of the three design stages,

the second stage – the parameter design – is the most important stage.

Fig:8.1 Taguchi Design



8.2 Orthogonal array and experimental factors:-

Following the procedure described in the Fig, the first step in the Taguchi method is to

select a proper orthogonal array. A L18 orthogonal array was used in this study and is

shown in Table. This basic design makes use of up to four control factors, with three levels

each. A total of eighteen experimental runs must be conducted.

Table specifications -Taguchi Orthogonal Array Design

L18 (6**1 3**3)

Factors: 4Runs: 18

Table 8.2-Orthogonal array

Trial No. Type of tool Speed Feed Depth of cut1 1 1 1 12 1 2 2 23 1 3 3 34 2 1 1 25 2 2 2 36 2 3 3 17 3 1 2 18 3 2 3 29 3 3 1 310 4 1 3 311 4 2 1 112 4 3 2 213 5 1 2 314 5 2 3 115 5 3 1 216 6 1 3 217 6 2 1 318 6 3 2 1

8.3 Experimental set-up and procedure

After the orthogonal array has been selected, the second step in Taguchi parameter design

is running the experiment. This experiment was conducted using the hardware listed as

follows:

• End Milling Machine



• Surface roughness measurement device: Taly surf (measures Ra in μm; stylus travel 0.4

mm).

• Cutting tools

8.4 Results of Taguchi analysis:-

In the Taguchi method, the term ‘signal’ represents the desirable value (mean) for the

output characteristic and the term ‘noise’ represents the undesirable value for the output

characteristic. Taguchi uses the S/N ratio to measure the quality characteristic deviating

from the desired value. Smaller is better S/N ratio was used in this study because less

surface roughness was desirable.

Quality characteristic of the smaller is better is calculated in the following equation

Experiments are conducted in the order given by Taguchi method and surface roughness

values are measured and tabulated.

TYPE OF TOOL SPEED FEED DOC Ra SNRA1

1 1 1 1 5.65 -15.0411 2 2 2 3.83 -11.6641 3 3 3 3.94 -11.90992 1 1 2 2.52 -8.028012 2 2 3 3.36 -10.52682 3 3 1 3.71 -11.38753 1 2 1 3.66 -11.26963 2 3 2 3.81 -11.61853 3 1 3 3.08 -9.771014 1 3 3 4.15 -12.3614 2 1 1 3.34 -10.47494 3 2 2 3.69 -11.34055 1 2 3 4.81 -13.64295 2 3 1 3.91 -11.84355 3 1 2 3.33 -10.44896 1 3 2 2.67 -8.530236 2 1 3 2.36 -7.458246 3 2 1 2.25 -7.04365

Table- 8.3 Surface roughness parameter, Roughness average Ra values, S/N values for

machining the Cast Iron work piece at eighteen runs



On analysing the data, inference can be made that the S/N ratio keeps decreasing with more number of dampers inserted into the hollow end mill tool on account of the vibration energy absorbed as friction.

After calculating S/N Ratios, the effect of control parameters on S/N ratio is shown below.

Figure:8.2 Graph of S/N to various factors

According to Taguchi design:-

Factor levels for predictions

TYPE OF TOOL SPEED FEED DOC 6 3 1 2

Predicted S/N Ratio = -6.07629



According to Taguchi method, the optimum value of surface roughness can be obtained with the 6th tool, the 3rd speed, the 1st feed and the 2nd depth of cut. From the orthogonal array,Factor levels for predictions

TYPE OF TOOL SPEED FEED DOCHollow end mill with 5 damper 960rpm 18mm/min 0.35mm

8.5 SUMMARY OF ANOVA RESULTS

TABLE 8.4.Analysis of Variance

Source DF Seq SS Adj SS Adj MS F PTYPE OF

TOOL5 7.4665 7.4665 1.4933 3.46 0.081

SPEED 2 1.1370 1.1370 0.5685 1.32 0.335

FEED 2 0.3188 0.3188 0.1594 0.37 0.706

DOC 2 0.6235 0.6235 0.3118 0.72 0.523

Error 6 2.5860 2.5860 0.4310

Total 17 12.1319

S = 0.656510 R-Sq = 78.68% R-Sq(adj) = 39.60%

Predicted Optimal S/N value from Taguchi method= -6.07629

Predicted Surface roughness value Corresponding to S/N = -6.07629 is 2.012 µm

Experimental surface roughness value = 2.35 µm



CONCLUSIONS

In the present study, experiments are conducted on work material Cast iron to

investigate the effect of damper inserted end milling tools on surface roughness.

The results indicated that the surface roughness decreases with increasing cutting

speed. The selection of appropriate cutting conditions and the use of sharp cutting

tools with adequate edge preparation are critical to achieve good surface finish.

Friction damper will lead to increase in the material removing rate in the milling

process via 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 the

solid tool. Hence the overall performance of the damped tool with five damper

inserts was exceptional compared to the rest of the tools and consequently the solid

end mill tool.

Surface finish achievement of the confirmation runs 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 surface roughness in this milling operation.

The optimal levels for the controllable factors were spindle speed 960 rpm, feed

rate 28 mm/rev, depth of cut 0.35 mm. Compared with the experiment results in

Table 8.1, the optimal surface roughness of the 18 confirmation samples 2.35µm.

which was very close to the smallest value optimal value of surface roughness

2.012 µm by Taguchi method .



References

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[3] Smith, Kevin Scott, 1985, “Chatter, Forced Vibrations, And Accuracy In High- SpeedMilling,” Master’s Thesis, Mechanical Engineering, University of Florida,Gainesville.

[4] Keyvanmanesh, Amir, 1990, “Evaluation of Chatter Detection and Control System,” Master’s Thesis, Mechanical Engineering, University of Florida, Gainesville, FL.

[5] Cheng, E., 1992, “A Chatter-Free Pocketing Routine For Any Two-And-A Half-Dimensional Pocket With Islands,” Master’s Thesis, Mechanical Engineering, University ofFlorida, Gainesville, FL.

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surface roughness optimization using taguchi and anova method

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