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Chapter 1
INTRODUCTION
1.1 Background
In the Metal removal process, the cutting tool can be used until their cutting edges
produce parts within the specified surface finish and dimensional tolerances. When the
quality of cutting edge is lost because of the wear, the tool has reached its life limit and must
be replaced. This contributes to increased machining cost. To reduce the machining cost,
improve production rate and achieve world class efficiency it is essential to optimize every
possibilities.
The ultimate failure is understood to have taken place when the tool has worn out and
can machine no more and could break under the cutting forces enhanced due to the blunt
cutting edge. The Gradual wear that leads to this ultimate failure is unavoidable but
controllable. On the other hand a tool could fail due to many avoidable causes which we
would call as premature failure.
To achieve optimum tool life and reduce production cost, we need to optimize all the
cutting parameters. Depths of cut are also one of those parameters, in this study we are
focusing on influence of radial depth of cut or width of cut on tool wear and temperature.
1.2Company Introduction
1.2.1 History
In 1938, after years of research, metallurgist Philip M. McKenna created a tungsten-
titanium carbide alloy for cutting tools that provided a productivity breakthrough in the
machining of steel. "Kennametal" tools cut faster and lasted longer, and thereby facilitated
metalworking in products from automobiles to airliners to machinery. With his invention,
Philip started the McKenna Metals Company in Latrobe, Pennsylvania. Later renamed to
Kennametal, the corporation has become a world leader in the metalworking industry and
remains headquartered in Latrobe.
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McKenna Metal's first full-year sales, with a staff of 12 employees, totaled to about
$30,000. But World War II saw American heavy industry shift into high gear. Kennametal's
annual sales approached $10 million and employment was nearly 900 as the company's tools
were used extensively in the war-time economy.
When the wartime boom ended, Kennametal sought new ways to exploit the
toughness and wear resistance of tungsten carbide alloys. In the mid-1940s, the company
pioneered the use of carbide tooling for mining, which led to the development of the
continuous mining machine. Kennametal also found uses for tungsten carbide in demanding
specialty applications where resistance to wear was vital, such as in valves, dies, drill bits and
snow plough blades.
1.2.2 About Kennametal
Kennametal delivers productivity to customers seeking peak performance in
demanding environments by providing innovative custom and standard wear-resistant
solutions. This proven productivity is enabled through our advanced materials sciences and
application knowledge. Our commitment to a sustainable environment provides additional
value to our customers. Kennametals portfolio of well-respected brand names and broad
global presence enable us to help customers of all sizes in virtually every geography drive
success at every stage of their value chain. Strategically aligned across our two core
businesses - Industrial and Infrastructure - our products and services touch nearly everymanufacturing process. People around the globe can see and touch these results throughout
many aspects of their day, from the light switch they turn on to the car they drive.
Kennametal of United States of America acquired Widia India on 30th August 2002,
which is number one in Germany and India. Thus Widia enjoys the multifaceted expertise of
Kennametal. Widia (India) was incorporated in the state of Karnataka with its registered at
Bangalore on the 21st September 1964 with technical and financial collaboration from Krupp
Widia, GMBH, West Germany.
The Bangalore division went on stream in 1967 and has grown by leaps and bounds
since, then, from rupees 7.1 lakhs turnover at inception, the company has notched up an
impressive rupees 375 crores in 2010, with an active involvement of employees and officers
company as grown to greater heights and continues to be the market leader despite tough
competition, both domestic and global.
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Keeping pace with the modernization and emerging technological trends new
products are aggressively introduced. Widia (India) Ltd decided to manufacture machine
tools including CNC machines. The machine tool division Widma was thus found
specializing in the special purpose machines, to suit specific requirements of customers.
Kennametal has been named a four-time best-practice partner for excellence in our
world-class product development and portfolio management processes by the APQC, a non-
profit organization and internationally recognized leader in benchmarking, knowledge
management, measurement and quality programs.
1.2.3 Company Overview
Founded in 1938
Nearly 11,000 employees worldwide
Annual sales are approximately $2.4 billion
Headquartered in Latrobe, Pennsylvania, USA
Operations in over 60 countries
First or second in every market we serve
Global market leader in tooling for the mining and highway construction industries.
1.2.4 Products
The major products produce in Kennametal are metal forming tools, metal cutting
tools, which includes inserts, carbide bodies, gun drills, and end mills. Kennametal provides
the industry's best metalworking tools using advanced tungsten carbide, ceramics, and high-
speed steel materials.
Kennametal specializes in solving the unique wear problems by engineering and
manufacturing customized protective systems made of the world's toughest materials.
Kennametal is focused on delivering value to the customers for many different applications
that offer long life, maintain tolerance through multiple-use cycles, and deliver superior
overall performance. Our applications specialists can help in the design and manufacture for
your custom tooling requirements. Our customers report that our high-quality tungsten
carbide parts last a minimum of 10 times longer than steel in most applications.
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Fig.1.1: milling cutters Fig.1.2: Indexable milling cutters
Fig.1.3: Solid end mills Fig.1.4: Turning tools Fig.1.5: Inserts
(Courtesy: Kennametal Inc.)
1.3 Objectives
The main objective is to study the Effect of machining parameter and develop an
optimal machining strategy to ensure optimum tool life and production cost in face milling
operation.
Steps to achieve the objectives
To carry out literature survey on face milling, effect of machining parameters on thesurface roughness, tool wear, material removal rate and coatings.
Face milling experiment to analyze the effect by varying the radial depth of cut (Ae)and keeping constant axial depth of cut (Ap) on tool life. (When Ae=80%, 50% and
20%)
Analyze the Effect of Varying parameter on temperature and forces by Finite elementMethod using Third wave AdvantEdge software. (Ae=80% and 20%)
Identify the best strategy for enhanced tool life and production rate.
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Chapter 2
MILLING
2.1 Fundamentals of Metal Cutting2.1.1 Machining
Machining is a term used to describe a variety of material removal processes in which
a cutting tool removes unwanted material from a work piece to produce the desired shape.
The work piece is typically cut from a larger piece of stock, which is available in a variety of
standard shapes, such as flat sheets, solid bars, hollow tubes, and shaped beams. Machining
can also be performed on an existing part, such as a casting or forging.
2.1.2 Metal Removal Process
Mechanicalo Single-point cutting
TurningPlanning and shaping
o Multi-point cuttingMillingDrillingBroachingSawing
o Abrasive machiningGrindingHoningLappingUltrasonic machiningAbrasive jet machining
Chemicalo Chemical machiningo Electrochemical machining (ECM)
http://www.custompartnet.com/wu/turninghttp://www.custompartnet.com/wu/turninghttp://www.custompartnet.com/wu/millinghttp://www.custompartnet.com/wu/millinghttp://www.custompartnet.com/wu/hole-makinghttp://www.custompartnet.com/wu/hole-makinghttp://www.custompartnet.com/wu/hole-makinghttp://www.custompartnet.com/wu/millinghttp://www.custompartnet.com/wu/turning -
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Thermalo Torch cuttingo Electrical discharge machining (EDM)o High energy beam machining
The popular process out of the above listed process with respect to material removal rate is
Turning Milling Drilling
In this course work we are more focusing on Milling Process.
2.2 Milling
Modern milling is a very universal machining method. During the past few years,
hand-in-hand with machine tool developments, milling has evolved into a method that
machines a very broad range of configurations. The choice of methods today in multi-axis
machinery is no longer straightforward in addition to all the conventional applications,
milling is a strong contender for producing holes, cavities, surfaces that used to be turned,
threads, etc. Tooling developments have also contributed to the new possibilities along with
the gains in productivity, reliability and quality consistency that have been made in indexable
Insert and solid carbide technology. Milling is principally metal cutting performed with a
rotating, multi-edge cutting tool which performs programmed feed movements against a
work piece in almost any direction. It is this cutting action that makes milling such an
efficient and versatile machining method. Each of the cutting edges removes a certain
amount of metal, with a limited In-cut engagement, making chip formation and evacuation a
secondary concern. Most frequently still, milling is applied to generate flat faces as in face
milling - but other forms and surfaces are increasing steadily as the number of five-axismachining centers and multi-task machines grow.
2.2.1 Basic Milling Operations
A milling cutter will basically employ one or a combination of the following basic
cutting actions: (s) Radial, (n) Peripheral and (v) Axial.
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(a) Radial (b) Peripheral (c) AxialFig. 2.1: milling operations
There are two milling process being followed
Up milling (conventional milling) Down milling (climb milling)
2.2.2 Up milling (Conventional milling)In up milling the cutter starts with zero chip thickness which increases as the cut
proceeds. At start the cutter in fact rubs against the work piece surface before actually
beginning to cut. The rubbing action generates heat at the interface. As a result, the newly
formed chip may get welded on to the rake face of the cutter tooth, thereby producing a
scratch on the work piece surface. Since the work piece motion is against the force exerted
by the cutter, any backlash present in the lead-screw of the table does not affect the process.
2.2.3 Down milling (Climb milling)In down milling (climb milling), the chip thickness is maximum at the beginning of
the cut and gradually reduces to zero. If the work piece is a casting, the rough sandy surface
can easily abrade and make the tool blunt. The process is however good for finishing cuts.There should not be any looseness or play between the nut and lead screws of the machine
table, as otherwise the work piece would be pulled in by the cutter and this would increase
the chip thickness to such an extent that it could break the cutter tooth. Compared to up
milling, the average chip thickness is higher in this process for given values of feed and
cutting speed and there is less power consumption.
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a) b)
Fig. 2.2: a) Up milling (conventional) and b) Down milling (climb)
2.3 Milling Cutter GeometryMilling cutter geometry is comprised of three major elements
Rake Angle, Clearance Angles and Lead Angle
Fig. 2.3: Radial and axial rake angle (courtesy: Kennametal Inc.)
2.3.1 Radial Rake Angle
The radial rake angle of a milling cutter is the angle formed in a diametric plane
between the face of the tooth and a radial line passing through the cutting edge. This may be
positive, negative, or zero degree.
Impact of Radial Rake Angles
1. Cutting Forces Amount of force Direction of cutting forces
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Radial clearance
2. Strength of the Cutting Edge3. Controls the radial direction of Chip Flow4. Has a major impact on radial clearance
Impact on cutting Edges Strength
Cutting forces enter the cutting edge at right angles to the rake surface. Radial rake angles absorb the impact of interruption on each revolution of the cutter.
Positive Radial Rake:The Positive radial rake exposes cutting edge to transfer rupture.
Negative Radial Rake:The Negative radial rake places the cutting edge into compression.
Chip flow Characteristics in Positive Radial Rake
Chip flow is inboard, up the incline plane formed by the positive radial rake. Cutter tends to recut chips Chips tend to weld to the chip slot Finish is marred by chip flow
Chip flow Characteristics in Negative Radial Rake
Chips clear the periphery.
Chips are thicker. Chip flow is outboard along the negative incline plane.
2.3.2 Radial Clearance
Fig. 2.4: Radial clearance in milling cutter (courtesy: Kennametal Inc.)
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The cutter is designed to provide a set amount of clearance (based on work piecesmaterial) under the heel of the insert.
The smaller the cutter diameter the greater the negative rake required to generate theprescribed clearance.
As diameter of the clearance increased the radial rake becomes more negative.
2.3.3 Lead Angle (Bevel Angle)Lead angle is dependent on work piece configuration, machine rigidity and fixture
rigidity. Lead angle controls the direction of cutting forces, chip thickness and nose radius
impacts on the lead angles.
2.3.4 Axial Rake Angle or Helical Rake
When a milling cutter has helical teeth, that is, when its cutting edge is formed along
a helix about the cutter axis, the resulting rake is called helical rake. If the cutting edge is
straight, its rake is axial rake. The axial rake or helical rake angle is the angle formed
between the line of the peripheral cutting edge and the axis of the cutter, when looking
radially at the point of intersection. This applies in the case of helical mills, half-side mills,
staggered tooth mills, face mills, and metal slitting saws having face cutting edges.
Axial Rake angle controls the cutting forces generated by the cutter.
Cutting forces decrease as the axial rake angle becomes more positive. Controls the axial direction of chip flow
Fig. 2.5: Nomenclature of Face milling cutter
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2.4 Milling Parameter
There are three major cutting parameters to be controlled in any milling operation.
These three parameters are cutting speed, feed rate and depth of cut. These parameters are
described below.
2.4.1 Cutting Speed
Cutting speed of a milling cutter is its peripheral linear speed resulting from
operation. It is expressed in meters per minute. The cutting speed can be derived from the
above formula.
Vc = Dn/1000 m/min (2.1)
where D= Diameter of milling cutter (mm)Vc= Cutting speed (linear) (meter per minute, m/min)n= Cutter speed in revolution per minute.
2.4.2 Feed Rate
It is the rate with which the work piece under process advances under the revolving
milling cutter. It is known that revolving cutter remains stationary and feed is given to the
work piece through worktable. Generally feed is expressed in three ways.
Feed per Tooth
It is the distance traveled by the work piece (its advance) between engagement by the
two successive teeth. It is expressed as mm/tooth and denoted by fz.
Feed per Revolution
Travel of work piece during one revolution of milling cutter. It is expressed as
mm/rev. and denoted by frev
Feed per Unit of Time
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Feed can also be expressed as feed/minute or feed/sec. It is the distance advances by
the work piece in unit time fm.
Above described three feed rates are mutually convertible.
fm= n x frev (2.2)
where n= rpm of cutter.
It can be extended further as
fm= n x frev = Z x n x fz (2.3)
where Z= Number of teeth in milling cutter.
2.4.3 Depth of Cut
Depth of cut in milling operation is the measure of penetration of cutter into the work
piece. It is thickness of the material removed in one pairs of cutter under process. One pairs
of cutter means when cutter completes the milling operation from one end of the work piece
to another end.
a) Axial depth of cut is axial advance of milling cutter into work piece. Axial depth is
represented by Ap and measured in mm.
(b) Radial depth is radial advance of milling cutter into work piece. Its also called as width
of cut, represented by Ae and measured in mm.
Fig. 2.6: milling process showing radial(Ae) and axial depth of cut (Ap)
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Coarse Pitch Cutter has less number of teeth compared to Fine Pitch Cutter and used for
larger depths of cut.
Fine Pitch Cutter has more teeth engagement with less chip clearance and used for lighter
Depths of cut.
Effect of Pitch on Feed: A simple calculation shows the effect of pitch on feed
Metal Removal rate of Coarse Pitch= 7 teeth x 0.127 mm/tooth x 500 RPM = 444.5 mm3/min
Metal Removal rate of Fine Pitch = 12 teeth x 0.127 mm/tooth x 500 RPM = 762 mm3/min
2.5.4 Cutter Hand
There are two types: LH cutter and RH Cutter
LH cutter is application specific and RH Cutter is most widely used for General purpose
2.5.5 Geometry
Fig. 2.10: Insert geometry (courtesy: Kennametal Inc.)
Edge Preparation
There are mainly 4 types of Edges preparations
Fig. 2.11: Edge configuration of insert (courtesy: Kennametal Inc.)
Out of above four types of edges we choose Honed Edge because of uniform
distribution of cutting forces.
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2.5.6 Carbon and Cobalt contents for machining Steel work piece
Fig. 2.12: Effect of carbon and cobalt (courtesy: Kennametal Inc.)
More the percentage of tungsten (wc) more is the wear and thermal shock resistance. The
strength of the insert increases with percentage of cobalt (co).
2.6 Factors affecting the machining parameters
Attention should be paid on the factors that are influencing the cutting parameters
cutting speed, feed rate and depth of cut.
2.6.1 Factors affecting speed
Work piece Hardness Work piece Condition (scale, sand) Condition of the Machine Horsepower Available Ability of the Grade to withstand Heat (Hot Hardness)
2.6.2 Factors affecting feed rates
Machine Horsepower Machine Rigidity and Fixture Rigidity Positive vs. Negative Geometry Cutter Pitch Surface Finish Required
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2.6.3 Factors affecting Depth of cut
Machine Horsepower Machine Rigidity and Fixture Rigidity Material to be Removed
2.7 Cutting Tool Materials
The cutting tool materials that are commonly used are:
Plain carbon and low alloy steels High-speed steels Cemented carbide, cermet and coated carbide
Ceramics Synthetic diamond (Poly Crystalline Diamond-PCD) and cubic boron nitride
(CBN)
Fig. 2.13: Cutting tool materials, speed vs. feed, doc (courtesy: Kennametal Inc.)
2.7.1 Evolution of Cutting Tool Materials
1910-1920: High speed steel 1920s: Cemented carbide 1950s: Cermet (TiC-based) 1960s: Alumina-based ceramic
Speed
(Thermal
Deformatio
n Resist)
Feed, DoC, Interruptions (Fracture resistance)
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1970: CVD coated carbide 1980: First engineered carbide
substrate (cobalt-enrichment)
1982: First SiAlON ceramic 1985: First PVD coated carbide Mid 80s: Modern cermets (TiCN-based) Late 80s: SiC whisker reinforced Al2O3 ceramic Early 90s: Advanced Sialons Mid 90s: Thin film diamond coated carbide Late 90s: PVD coated PCBN 2000: Advanced Pre-coat & post-coat treatments
2.7.2 Commonly used cutting tool materials
Common cutting tool materials are described below:
Carbon steels:
Carbon steels have been used since the 1880s for cutting tools. However carbon steels
start to soften at a temperature of about 180oC. This limitation means that such tools are
rarely used for metal cutting operations.
Plain carbon steel tools, containing about 0.9% carbon and about 1% manganese,
hardened to about 62 Rc, are widely used for woodworking and they can be used in a router
to machine aluminum sheet up to about 3mm thick.
High speed steels (HSS):
HSS tools are so named because they were developed to cut at higher speeds. These
steel have excellent hardenability and retain harness upto 650 oC. F.W. Taylor and M.White
in 1900 developed this steel for the first time. It typically contains 12-18% tungsten, 4-5.5%
chromium as principal alloying elements and retained hardness upto red heat temperature.
Other common alloying elements are vanadium, molybdenum and cobalt.
There are two basic types of high speed steels, tungsten (T-series) and molybdenum
(M-series).
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Most grades contain about 0.5% molybdenum and 4- 12% cobalt. It was soon
discovered that molybdenum (smaller proportions) could be substituted for most of the
tungsten resulting in a more economical formulation which had better abrasion resistance
than the T series and undergoes less distortion during heat treatment.
Consequently about 95% of all HSS tools are made from M series grades. These
contain 5 - 10% molybdenum, 1.5 - 10% tungsten, 1 - 4% vanadium, 4% Chromium and
many grades contain 5 - 10% cobalt.
HSS tools are tough and suitable for interrupted cutting and are used to manufacture
tools of complex shape such as drills, reamers, taps, dies and gear cutters. Tools may also be
coated to improve wear resistance. HSS accounts for the largest tonnage of tool materials
currently used. Typical cutting speeds: 10 - 60 m/min.
Cast non-ferrous alloys:
Introduced in early 1915 by Ellwood Hynes. These materials have the following
principal elements with specified ranges, 40 - 50% cobalt, 15-35% chromium, 1-4% carbon
and 10 - 25% tungsten. These alloys are cast and ground to the desired shape, they are not as
tough as HSS and are sensitive to shock loading but resist shock better than carbides. It is
recommended for deep continuous rough cuts at relatively high feed rates and speeds as
much as twice those possible with HSS. They can retain harness up to 950 oC. It is not heat
treatable and has maximum hardness values of 55 - 64 Rc. These tools are used only in
special applications (formed tools).
Carbides:
Also known as cemented carbides or sintered carbides were introduced commercially
in 1930s and have high hardness over a wide range of temperatures, high thermal
conductivity, high Young's modulus making them effective tool and die materials for a range
of applications. The two groups used for machining are tungsten carbide and titanium
carbide; both types may be coated or uncoated. Tungsten carbide particles (1-5 m) are
bonded together in a cobalt matrix using powder metallurgy. The powder is pressed and
sintered to the required insert shape. A wide range of grades are available for different
applications. The proportion of cobalt (the usual matrix material) present has a significant
effect on the properties of carbide tools. 3 - 6% matrix of cobalt gives greater hardness while
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6 - 15% matrix of cobalt gives a greater toughness while decreasing the hardness, wear
resistance and strength. Tungsten carbide tools are commonly used for machining steels, cast
irons and abrasive non-ferrous materials. Titanium carbide has a higher wear resistance than
tungsten but is not as tough. With a nickel-molybdenum alloy as the matrix, Tic is suitable
for machining at higher speeds than those which can be used for tungsten carbide. Typical
cutting speeds are: 30 - 150 m/min or 100 - 250 when coated.
Cemented Carbides
Fig. 2.14: Magnified image of cemented carbide (courtesy: Kennametal Inc.)
The dark colored object is tungsten carbide and the light colored object is cobalt.
Composition / Grain Size vs. Properties
3 - 12% Cobalt and 1-5 m carbide grain size
Fig. 2.15: Grain size (courtesy: Kennametal Inc.)
Above fig. 2.15, shows microscopy images of the coarse grain size of about 5 m
and fine grain size of about 1 m. With increase in grain size and cobalt content resistance
decreases and toughness increases.
WC grain size
Coarse grained (5 m)Fine grained (1 m)
WC (tungsten carbide)
Co (Cobalt)
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Table 2.1: Grain size nomenclature (courtesy: Kennametal Inc.)
Grain Size Range Nomenclature
< 0.2 Nano
0.20.5 Ultrafine
0.50.8 Submicron
0.81.3 Fine
1.32.5 Medium
2.56.0 Coarse
> 6.0 Extra Coarse
Cermets:Developed in the 1960s, these typically contain 70% aluminum oxide and 30%
titanium carbide. Some formulation contains molybdenum carbide, niobium carbide and
tantalum carbide. Their performance is between those of carbides and ceramics and coatings
seem to offer few benefits. Typical cutting speeds: 150 - 350 m/min.
Ceramics:
Alumina Introduced in the early 1950s, two classes are used for cutting tools: fine
grained high purity aluminum oxide (Al2O3) and silicon nitride (Si3N4) are pressed into
insert tip shapes and sintered at high temperatures. Additions of titanium carbide and
zirconium oxide (ZrO2) may be made to improve properties. But while ZrO2 improves the
fracture toughness, it reduces the hardness and thermal conductivity. Silicon carbide (SiC)
whiskers may be added to give better toughness and improved thermal shock resistance. The
tips have high abrasion resistance and hot hardness and their superior chemical stability
compared to HSS and carbides means they are less likely to adhere to the metals during
cutting and consequently have a lower tendency to form a built up edge. Their main
weakness is low toughness and negative rake angles are often used to avoid chipping due to
their low tensile strengths. Stiff machine tools and work set ups should be used when
machining with ceramic tips as otherwise vibration is likely to lead to premature failure of
the tip. Typical cutting speeds: 150-650 m/min.
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Silicon Nitride:
In the 1970s a tool material based on silicon nitride was developed, these may also
contain aluminum oxide, yttrium oxide and titanium carbide. SiN has an affinity for iron and
is not suitable for machining steels. A specific type is 'Sialon', containing the elements:
silicon, aluminum, oxygen and nitrogen. This has higher thermal shock resistance than
silicon nitride and is recommended for machining cast irons and nickel based super alloys at
intermediate cutting speeds.
Cubic Boron Nitride (CBN):
Introduced in the early 1960s, this is the second hardest material available after
diamond. CBN tools may be used either in the form of small solid tips or or as a 0.5 to 1 mm
thick layer of of polycrystalline boron nitride sintered onto a carbide substrate underpressure. In the latter case the carbide provides shock resistance and the cBN layer provides
very high wear resistance and cutting edge strength. Cubic boron nitride is the standard
choice for machining alloy and tool steels with a hardness of 50 Rc or higher.
Typical cutting speeds: 30 - 310 m/min.
Diamond:
The hardest known substance is diamond. Although single crystal diamond has been
used as a tool, they are brittle and need to be mounted at the correct crystal orientation to
obtain optimal tool life. Single crystal diamond tools have been mainly replaced by
polycrystalline diamond (PCD). This consists of very small synthetic crystals fused by a high
temperature high pressure process to a thickness of between 0.5 and 1mm and bonded to a
carbide substrate. The result is similar to CBN tools. The random orientation of the diamond
crystals prevents the propagation of cracks, improving toughness. Because of its reactivity,
PCD is not suitable for machining plain carbon steels or nickel, titanium and cobalt based
alloys. PCD is most suited to light uninterrupted finishing cuts at almost any speed and is
mainly used for very high speed machining of aluminum - silicon alloys, composites and
other non - metallic materials.
Typical cutting speeds: 200 - 2000 m/min.
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2.7.3 Desirable characteristics of Cutting tool material
Hot hardness: The hardness, strength, and wear resistance of the tool are maintained at the
temperatures encountered in machining operations. This ensures that the tool does not
undergo any plastic deformation and, thus, retains its shape and sharpness.
Toughness and impact strength (mechanical shock): Impact forces on the tool encountered
repeatedly in interrupted cutting operations (such milling, turning on a lathe, or due to
vibration and chatter during machining) do not chip or fracture the tool.
Thermal shock resistance: To withstand the rapid temperature cycling encountered in
interrupted cutting.
Wear resistance: An acceptable tool life is obtained before the tool has to be replaced.
Chemical stability and inertness: With respect to the material being machined, to avoid or
minimize any adverse reactions, adhesion, and toolchip diffusion that would contribute to
tool wear.
2.8 Coating for cutting tool materialsCoatings are frequently applied to carbide tool tips to improve tool life, productivity,
work piece surface finish. More than 65% of metal cutting inserts sold globally are coated.
There are two important Coating process
Chemical Vapor Deposition (CVD) Physical Vapor Deposition (PVD)
2.8.1 Chemical Vapor Deposition (CVD)
It is an atmosphere controlled process conducted at elevated temperatures (~1000 C)
in a CVD reactor. During this process, thin-film coatings are formed as the result of
reactions between various gaseous phases and the heated surface of substrates within the
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CVD reactor. As different gases are transported through the reactor, distinct coating layers
are formed on the tooling substrate. For example,
TiN is formed as a result of the following chemical reaction:
TiCl4 + N2 + H2 1000 C TiN + 4 HCl + H2.
Titanium carbide (TiC) is formed as the result of the following chemical reaction: TiCl4 +
CH4 + H2 1030 C TiC + 4 HCl + H2.
The final product of these reactions is a hard, wear-resistant coating that exhibits a
chemical and metallurgical bond to the substrate. CVD coatings provide excellent resistance
to the types of wear and galling typically seen during many metal-forming applications.
Fig. 2.16: Axial feed CVD (courtesy: Kennametal Inc.)
2.8.2 Physical Vapor Deposition (PVD)
Physical Vapor Deposition, or PVD, is a term used to describe a family of relatively
low temperature (500 C) vacuum coating processes that involve the generation of positively
charged ions through various methods. Reactive gases are introduced into the chamber to
Reactive gases Vacuum
Pump
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create various compounds. The positively charges ions are attracted to a negative bias given
to the tool substrates. This attraction results in a dense thin-film layer with an extremely
strong physical bond to the tool substrate
Features of PVD coatings
Both Monolayer and multilayer is possible Crack fee coating Fine grained & smoother than CVD coatings Compressive residual stress Can apply over the sharp edges Line-of-Sight processrequires tool fixture rotation
Fig. 2.17: Physical vapor deposition (courtesy: Kennametal Inc.)
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2.8.3 Properties of Coating
Chemical stability Improved hot hardness Microstructure Adhesion Coating thickness Residual stress (CVD-Tensile Stress, PVD-Compressive stress) Surface roughness Visual appearance
Table 2.2: Comparison between PVD and CVD Coating
PVD CVD
Full Name Physical Vapor Deposition Chemical Vapor Deposition
Process Temperature Low, 300 to 600 C High, 1000+ C
Coating Thickness 2 M to 8 M 2 M to 14 M
Material used
TiN, TiCN, TiAlN,TiB2,
TiN-TiAlN
High temperature
(~1000C) TiC, TiCN, TiN,
Al2O3, Diamond
multi-layers, nano-layer
coatings
Medium temperature
(~850C) TiCN, ZrCN
Plasma assisted CVD
(~600C) TiN, TiCN,
TiAlN
Multiple Layers No Yes
Applications Drilling, Milling Turning, Milling
Tools with Sharp Edges Threading, Grooving
Residual Stress Compressive Stress Tensile Stress
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2.9 Categories of Tool failure
Abrasive Wear
1) Flank Wear
Mechanical Failure
1) Chipping1a. Flank Chipping
1b. Rake Face Chipping
2) Depth of Cut notching3) Fracture
Heat Failure
1) Built up Edge1a. Rake Surface
1b. Flank Surface
2) Thermal Cracking3) Crater Wear4) Thermal Deformation
2.9.1 Abrasive Wear
Abrasive wear occurs as a result of the interaction between the work piece and the
cutting edge. This interaction results in the abrading away of relief on the flank of the tool.
This loss of relief is referred to as a wear land.
It depends on the hardness, elastic properties and Geometry of the two mating
surfaces.
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The larger the amount of elastic deformation a surface can sustain, the greater will be
its resistance to abrasion. A Brittle material like cast iron causes more of abrasion wear than
ductile steel.
It must also be noted that any material transferred from one surface to another which
is highly strain hardened could add to the abrasive wear. Further, the oxidation of the nascent
metal produces hard oxide particles which again contribute to the abrasive wear.
The width of the wear land is determined by the amount of contact between the
cutting edge and the work piece.
Fig. 2.18: wear land (courtesy: Kennametal Inc.)
Flank Wear
Fig. 2.19: Flank wear in insert (courtesy: Kennametal Inc.)
Flank: Is the Flat Surface of an insert perpendicular to the rake face
The cutting force normal to the direction of velocity keeps the tool pressed against the
wok piece. The friction between clearance face and the machined surface progressively
flattens the cutting edge. A flat wear land is produced on the clearance face extending from
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the cutting edge along the clearance face. As the length of the wear land increases friction
and heat generated in cutting increased and leads to further wear.
When the wear land reaches a critical value cutting becomes difficult. It leaves a
Burnished mark on the surface. More energy is required to remove the same amount of
material. Flank wear is mostly caused by abrasion of the flank and worsened by higher
temperatures caused at elevated speeds and cutting tool pressure.
Flank wear is the desired tool failure mechanism and it is the only mechanism that
can be predictable
Fig. 2.20: Flank and Crater wear on the tool clearance face (courtesy: Kennametal Inc.)
2.9.2 Mechanical Failures
Mechanical failures occurs from Insert wear caused by intense physical contact
between an insert and a work piece
Main Mechanical Failures are
1) Chipping 2) Notching 3) Fracture
Chipping
Tool wear results in the loss of small slivers from the cutting edge of the tool.
Chipping is also called frittering.
There are two Types of Chipping: 1) Flank Chipping 2) Rake Face Chipping
Flank Chipping or Mechanical Chipping
Mechanical Chipping occurs when small particles of the cutting edge are broken
away rather than being abraded away in abrasive wear.
Crater Wear
Flank Wear
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This happens when the mechanical load exceeds the strength of the cutting edge.
Mechanical chipping is common in operations having variable shock loads, such as
interrupted cuts. Chipping causes the cutting edge to be ragged altering both the rake face
and flank clearance. This ragged edge is less inefficient, causing forces and temperature to
increase, resulting in significantly reduced tool life.
Mechanical chipping is often the result of an unstable setup. i.e., a tool holder or
boring bar extended to far past the ideal length/diameter ratio, unsupported work pieces etc..,
Mechanical chipping is best identified by observing the size of the chip on both the
rake surface and the flank surface. The forces are normally exerted down onto the rake
surface producing a smaller chip on the rake surface and a larger chip on the flank surface
Fig. 2.21: Flank Chipping (mechanical chipping) (courtesy: Kennametal Inc.)
Rake Face Chipping: occurs due to Thermal Expansion and Radial Cutting Forces.
Chipping occurs when work pieces or cutting edge interface does not have adequate
clearance to facilitate an effective cut. This may be result of misapplication of a cutting tool
with inadequate clearance for the work pieces material being cut.
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Rake Surface Flank Surface Rake Face Chipping
Fig. 2.22: Rake face Chipping (observed on rake and flank surface) (courtesy: Kennametal
Inc.)
Depth Of Cutting Notching
Fig. 2.23: Depth of cut notching (courtesy: Kennametal Inc.)
It was described that the hardness of the chip and a thin layer of the machined surface
were significantly harder than the bulk material.
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It may be visualized that in turning, the tool will have its tip in the bulk of the material; but
at the distance equaling the depth of cut, the tool will be cutting through some significantly
harder material (the work hardened layer) causing a notch to appear on the flank face, called
the depth of cut notch.
Depending on the shape and geometry of the tool, the notch wear can be highly
influential on tool life or be completely insignificant compared with other modes of wear.
Effect
Localized failure at the depth of cut line. Localized Chipping and Localized Cratering
Typical with Stainless Steel, high temperature alloys a all work-hardening materials Typical when the work pieces have scale or a hardened surface.
Depth-of-Cut Notching can be minimized by following Methods
by CVD coatings by Cobalt enriched grades Increased lead angle (thins the chip reducing forces) Use tapered cuts
Fracture
Fig. 2.24: Failure due to fracture
Tool Fracture occurs when the tool is unable to support the cutting force over the
tool-chip contact area and results in loss of only a small part of tool. It is called as Chipping
or Breakage
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It is Common in interrupted cuts and in non-rigid setups.
Chipping and Breakage can be minimized by using
Tougher cutting tool material: Cobalt enriched grades higher cobalt TiC, & TaC grades
Stronger geometrya. By using Negative rake rather than the positive rakeb. Increasing Tool Nose
Maximize rigidity Reduced metal removal rate
2.9.3 Heat Related Failure
Below are Heat related Failures occurring in Cutting tool.
1) Built Up Edge 2) Thermal Cracking 3) Cratering 4) Thermal Deformation
Built-Up Edge
Fig. 2.25: Built up edge on insert (courtesy: Kennametal Inc.)
Built-up Edge is also called as Adhesion. This occurs due to welding between the tool
and chip (i.e. work material is deposited on the rake and flank face of the tool) at the
asperities and the subsequent breakage of the welds. When weld breaks it plucks away
material from the tool. We can expect that this wear will be inversely proportional to the
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hardness of the work material and directly proportional to the normal stress on the sliding
surface.
It is the product of the localized high temperature and extreme pressure at the tool and
chip interface.
It depends on the Normal face between the sliding surfaces and the apparent area of contact.
It is dependent upon the Relative hardness of the chip and tool.
Built-up edge is not stable and will slough off periodically, adhering to the chip or
passing through the tool and adhering to the machined surface.
Generally adhesion occurs on soft, gummy work pieces materials.
Rake Face
Fig. 2.26: Built up edge in Rake face (courtesy: Kennametal Inc.)
Welding of work pieces material to the rake face of the cutting tool Loss of effective geometry causes increases in cutting forces and eventual tool
breakage
Minimizing Built Up Edge
Using higher cutting speed- At high speeds, that is at high tool-chip interfacetemperatures, the welds between tool and chip would be predominantly temperature
welds. There is insufficient time for pressure welds to occur. Temperature welds
being soft will separate easily. No built up edge is formed. However there is small
amount of material plucked off from tool surface.
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PVD Coating by using materials like TiC, TiN: TiC and Tin have lesser affinity tosteel to form built-up edge. Moreover low wettability of these materials by ferrous
material reduces built-up edge formation. The edges are uniformly coated hence there
is less chance of adherence property
Polished edges: Adherence property is weaker at polished surfaces. Using Coolant: Coolant washes away built up material at earlier stages. by using positive rake : Area of contact is minimum. by Minimizing the flank wear
Flank Face Builtup Edge
This is normally associated with inadequate clearance angles under the cutting edge.Soft Springy materials tend to spring-back afterbeing cut and rub the flank of the tool.
Fig. 2.27: Built up edge in flank face (courtesy: Kennametal Inc.)
Thermal-Mechanical Cracking
Thermal Cracking
This thermal cracking is Evenly-spaced cracks perpendicular to the cutting edge
It is commonly observed in milling and interrupted cutting. Caused by variations in temperature in milling induce cyclic thermal shock as the
surface layer of tool repeatedly expands and contracts due to heating and cooling of
the edge
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Minimizing Thermal Cracking
Thermal Cracking can be minimized by following method:
Using Tougher, more thermal-shock-resistant tool material Use a grade with more TaC content Higher cobalt content carbide grade Avoid coolant if possible or assure a steady supply By reduced cutting speed.
Cratering
Fig. 2.28: Crater wear on insert (courtesy: Kennametal Inc.)
Cratering are Tool wear characterized by a concave depression in the rake face of the
cutting tool. Cratering is also called crater wear.
Cratering are Typical in machining carbon steels at elevated speeds. This are Caused by extreme heat & pressure of chip
Involves diffusion or dissolution of tool material into the chip
Minimizing Crater Wear
Crater Wear can be minimized by following methods: By Reduce Cutting speed (by reduced spindle speed) By using Higher TiC Content grade By Lower cobalt grade By Use of CVD coated grades - Al2O3 & TiC
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Thermal Deformation
Fig. 2.29: Thermal deformation (courtesy: Kennametal Inc.)
It is also called as plastic deformation and takes place as a result of combination of
high temperature and high pressures on the cutting edge.
When the cutting edge loses its hot hardness the forces created by the feed rate cause
the cutting edge to deform. The amount of thermal deformation is in direct proportion to the
depth of cut and feed rate.
It is typical in machining alloy steels at elevated speeds. Results in Bulging or blunting of the tool edge.
Minimizing Thermal Deformation
By Use of grades with higher TaC content By Use of grades with lower cobalt content By Using CVD coated grades - Al2O3 & TiC
2.10 Tool Life
The length of time that a cutting tool can function properly before it begins to fail
Taylors Tool life equation
Vc Tn= Ct (2.4)
Where, T is time in minutes,
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Ct is constant and varies with tool and work material, tool geometry
Exponent n determines the slope of the tool life curve and depends primarily on the tool
material
Vc is cutting speed in m/min
Some of the more common criteria for judging the end point of tool life are
1) Width of wear land i.e. occurrence of a certain width of wear land.2) Depth of crater wear i.e. occurrence of a certain depth of crater wear.3) Increase of cutting force, or power consumption, by a certain amount.4) Increase of radial force on the tool by a certain amount.5)
Increase of feed force by a certain amount.
6) Sudden change in finish and dimension of work piece.
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Chapter 3
LITERATURE REVIEW
3.1 Historical background
The history of cutting tools began during the industrial revolution in 1800 AD, but the
first cutting tool was cast using a crucible method in 1740. In 1868 R. mushet found by
adding tungsten we can increase hardness and tool life (air quenching). F.W. Taylor in
Pennsylvania did the most basic research in metal cutting between 1880-1905 and invented
High speed steel cutting tools. The initial development of cemented and sintered carbides
occurred in Germany in 1920s by osram study society for electrical lighting to replace
diamonds as a material for machining metal. Later the license was transferred to Krupp,
essen, germany at the end of 1925. In 1926 Krupp brings sintered carbide on to the market
under the name of WIDIA (in german acronym for Wie Diamant, means like diamond in
English).
3.2 Overview
There are many researches done in field of Metal Cutting application. The importance
is being to reduce production cost by Enhancing the tool life and material removal rate.
This is possible by optimizing the 1) Machining Parameters like cutting speed, feed
and depths of cut (axial and radial). 2) By optimizing the Insert geometries like shape, cutting
edges, rake angles 3) By various coatings.
Mr. Milon D Selvam, research scholar at karpagam university has optimized the four
machining parameters i.e., number of passes, depth of cut, spindle speed and feed rate by
using CNC vertical machining center with fanuc control. Workpiece material was Mild steel,
processed using zinc coated carbide cutting tool inserts (diameter 25mm face milling cutter).
Optimization was done using taguchis L9 orthogonal array and was fine-tuned with genetic
algorithm. The optimum machining parameters were, number of Passes = 3, Depth of cut =
0.1162mm, Spindle speed = 1999 rpm, Feed rate = 497.7 mm/min. The surface roughness
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evaluated through taguchi technique is 0.975 m and 0.88 m. It is observed that all the four
parameters are predominantly contributing to the response[1].
In face milling of hardened steel (EN 90MnCrV8) the influence of cutting parameter
(i.e., cutting speed, feed rate and depth of cut) on cutting forces studied by Milenko sekulic
using taguchi method shows that among all the significant parameters, depth of cut is the
most significant parameter [2].
An experimental investigation made to find out optimum milling parameters for
machining EN8 steel using Seco R220.53-0125-09-8c tool holder with diameter 125mm face
milling cutter shows the optimum value for face milling is Cutting speed = 285 m/min, feed
rate = 0.27 mm/rev and depth of cut = 0.4 mm (for Surface roughness of 0.690 m). Alsoauthor concludes the cutting speed is statistically significant factors influencing the surface
roughness in milling process [3].
There is growing demand for superior quality production for its functional aspects, the
surface roughness here play a significant role. An Experimental investigation was conducted
by Nitin agarwal on effect of machining parameters on the surface quality of aluminum alloy
in CNC milling operation with HSS Tool. The Spindle speed, feed rate and depth of cut was
independent variable and surface roughness parameter is taken as dependent variable. The
speed considered was 800, 1000 and 1200 rpm. Feed range from 200 to 500 in steps of 100
mm/min. Depth of cut 0.25, 0.50 and 0.75 respectively. Experiment concluded that
1) The surface roughness could be efficiently calculated by using spindle speed, feedrate and axial depth of cut as the input variables.
2) Considering the individual parameters, depth of cut has been established as mostinfluencing parameter, followed by feed rate and spindle speed.
3) As the depth of cut influences the surface roughness considerably for a given feedrate, the increase in feed rate causes the surface roughness to increase. For lower
depth of cut, the feed rate increases with surface roughness [4].
Further Mathematical Relationship (1st order and 2nd order quadratic equations using
Design expert ver. 6.0) was developed between the tool life in end milling of hard material
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(AISI -D2) and the machining variable by using the experimental results of Response surface
Methodology (RSM). These model can be safely used to predict the tool life of machined
part of AISI D2 tool steel under the specified conditions, speed range = 40 80 m/min,
Depth of cut range is 0.52mm and feed range is 0.050.1 mm/tooth [5].
Another, study on the influence of cutting conditions cutting speed, feed velocity
and feed per tooth - on tool life and surface finish of the work piece in the face milling of flat
surfaces. Aiming to achieve this goal, several milling experiments were carried out with
different cutting speeds, feed velocities and feeds per tooth. In the first phase of the
experiments, cutting speed was varied without varying feed velocity, which caused a
variation in feed per tooth. In the second phase of the experiments, cutting speed and feed
velocity were varied in such a way that feed per tooth was kept constant. Tool flank wear andsurface roughness of the work piece were measured as cutting time elapsed. The main
conclusions of this work are that a) cutting speed has a strong influence on tool life,
regardless of whether feed velocity or feed per tooth varies and b) an increase in surface
roughness of the work piece is not closely related to an increase in wear of the primary
cutting edge [6].
One of the research studied on Performances of tool life and surface roughness on AISI
D2 Steel (58 HRc) using Indexable ball nose End mills employing carbide, cermet tools and
solid carbide ball nose end mills. Author carries out experiment to find Tool Wear
Mechanism (Chipping, Adhesion and attrition) with process parameters (Tool life and
Surface Roughness) by Taguchi and ANOVA Method shows that Best parameters found for
finish machining are Cutting speed 204 m\min, depth of cut = 0.2mm and width of cut =
0.2mm. He also suggests hard machining can potentially be an alternative to grinding and
EDM with a scope to improve productivity, increased flexibility decreased capital expenses
and reduced environmental waste [7].
Other experiment conducted on the Influence of the mechanical properties like
Tensile strength and hardness of the work piece material (DIN 42CrM04 (JUS C4732)
having tensile strength of 975 MPa, Hardness=265 BHN, Cutting tool Material HM P25,
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Vc=89.17 m/min, ap=1mm) have a significant influences the cutting force in face milling
and cutting energy in machining [8].
The Influence of radial depth or radial engagement is least touched subject. Shen yang of
Tianjin university did experimental investigation on Effect of radial depth on vibration and
surface roughness in face milling of austenitic stainless steel (AISI304) using Indexable
cemented carbide milling cutters (speed and feed were fixed). The results shows the
amplitude of vibration acceleration increased with the increasing radial depth up to 80mm,
also the vibration frequency varied with the radial depth. The minimum surface finish was
found radial depth was equaled to 40mm [9].
Further, Multi-Layer Hard Coating on Cutting Tools also enhances the tool life.Studies are also done comparing the performance of different Titanium based coatings like
Titanium nitride (TiN) Titanium carbon nitride (TiCN) and Titanium Alumina nitride
(TiALN) using Taguchi method shows that TiCN hard coating has best performance (Tool
Life) among above on AISI 1045 Carbon Steel in Face Milling operation [10].
In comparison with coating performance produced by PVD (TiN-TiALN) and CVD
(TiN-Al203-TiCN) process on carbide insert for face milling operation on TC6 (Difficult to
cut, Titanium machining) work piece under the dry condition, several tool life test and tool
wear experiments were conducted using 5-axis machining center. The effect of varying
cutting speeds on cutting forces, surface roughness and chip formation was investigated.
Surface roughness had small rise by increasing cutting speed from 50 to 140 m/min. Also
increase in feed rates, keeping constant speed and depth of cut shows increase in surface
roughness. With the force fluctuation due to increase in cutting speed shows increased
surface roughness. Chip formation and its morphology are the important features of metal
cutting process. When cutting speed increases from 50 to 140 m/min the chip deformed from
curling to ribbon shape.
It was noticed that crater wear and fracture were major types of rake wear found in common.
In milling process, the rake face of cutting tool can produce dramatic friction, high
temperature and high pressure. When cutting edge is in contact with the chip or work piece
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or both, the plastic flow occurs on surface material which in detrimental to the abrasive
resistance of cutting tool.
Further from SEM investigation it is observed that the coatings on cutting edges were
removed, this is because of continual impact between rake face of cutting tool and the work
piece in milling process. Another reason is friction between coating layer and chip [11].
An study conducted to develop an optimization technique to determine the
coefficients of the extended Taylor tool life equation in milling. The best set of cutting
conditions that yield the fastest convergence for the coefficients of the extended Taylor tool
life equation and associated confidence intervals for the coefficients was determined. This
was done by obtaining the minimum ratio (NC) between maximum and minimum singular
values of the sensitivity matrix of tool life related to variation of machine parameters. Theycompared their technique to the commonly used fractional factorial technique used to
determine the coefficients of the Taylor tool life equation during dry face milling of AISI
1045 rolled steel (mean hardness of 197 HB) with triple
TiN/TiC/TiN coated carbide inserts (ISO P45-M35 class). The mean percentage error
and standard deviation between tool life values was higher for the fractional factorial
technique compared to the optimization procedure. The same study was repeated for AISI
304 stainless. However, it was found that mean percentage error between tool life estimates
obtained for AISI 304 stainless steel was 46 % compared to 10 % for AISI 1045 steel. It was
found that irregular flank wear patterns and variations in work piece material composition in
the case of AISI 304 stainless steel caused more variation in tool life estimates compared to
AISI 1045 steel [12].
Other study on effect of wear for honed radius edges shows that increase in edge
radius tends to increase in wear rate, especially at the initial cut in wear phase. The uncut
chip thickness is less than or equal to the edge radius, forces actually decreases substantially
with flank wear until most of the edge radius has been worn out [13].
Finite element method based simulation is attracting researchers for the better
understanding of the chip formation mechanism, heat generation in the metal cutting zones,
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tool-chip interfacial frictional characteristics. Prediction of temperature and stress
distribution plays a vital role in enhancing the tool life.
Study on FEM Simulation of Edge rounded insert for machining AISI 1045 steel by
using dynamic explicit arbitrary lagrangian eulerian method yields results that are highly
essential in predicting residual stresses, temperature and other property on machined surface
[14].
Study on tool chip interfacial friction properties by using analysis of machining was
carried on by several temperature models for calculating the average temperatures at primary
and secondary deformation zones and present comparisons with the experimental data
obtained for AISI 1045 steel through assessment of machining models activity. The proposed
methodology was utilized to measure forces and chip thickness obtained through a basicorthogonal cutting test. This conveniently determined the work material flow stress at the
primary deformation zone and interfacial friction characteristics along the tool rake face [15].
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Chapter 4
METHODOLOGY
Metal cutting operation, Face milling, cutting tool materials, Different mode of
cutting tool failure, parameters affecting the face milling operation, optimization methods
were studied by literature survey.
Observations were made on different milling operation and strategies used in
Kennametal metal cutting lab and production shops. Manufacturing process of tool holders,
Tungsten carbide cutting tools were documented.
Going through different catalog and journals, literature we got to know that there was
not many experiments conducted in optimizing the radial depth of cut (Ae) to achieve better
tool life and Material removal rate. Most of the experiments conducted to improve tool life
were by optimizing the
a). machining parameters like Feed, Speed and Axial depth of cut
b). by optimizing the cutting tool geometry
c). by varying different types of coatings
This made us to conduct an experiment to achieve optimum tool life and reduce
production cost by optimizing the machining parameters considering radial depth of cut.
4.1 Design of Experiment
The Four variable used for the design of experiments are cutting speed, feed, axial
depth of cut and radial depth of cut. The experiment is carried under dry condition.
The minimum cutting speed (Vc) of 170 m/min is taken as constant, the effective feed
per tooth (fz) or chip load is 0.16 mm and axial depth of cut (Ap) is kept constant to 3mm
throughout the experimentation. The only parameter varied is Radial depth of cut which
contributes more to material removal rate. The radial depth of cut (Ae) is varied at 20%, 50%
and 80% of cutting diameter and its influence on power consumption, surface roughness
(Ra), Material removal rate and tool wear.
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Fig. 4.1: Flow chart of Experimentation
Developing a milling
strategy for optimum
tool life
Finite Element Analysis
Selection of Cuttin Tool
Selection of work piece
Pre-processor
Work piece modeling
Enter Process parameter
Simulation
Post Process
Experimentation
Prepare insert (Edge honing)
Hc Test, Check Honed
Radius, Laser Marking,
Edge check.
Lab Test (Machining)
Results and Discussion
Conclusion
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Chapter 5
EXPERIMENTATION
The lab experimentation was conducted in Kennametals metal cutting lab and Finite
element analysis was carried on Third Wave AdvantEdge 2D at CAE team, Kennametal.
5.1 Selection of Cutting tools
Manufacturer: Widia
Cutter: M690
Diameter: 63mm
Insert: SDMT 1204 PDR-MH
Coating: TN7535
Suitable for machining C45 (AISI 1045) carbon steel.
Table 5.1:, Insert ISO Designation
S D M T
ShapeClearanceangle Tolerance Features
Square 15 degree 0.06 mm
12 04 PDR MH
Size ThicknessPositiveDegree,Right Hand
Positive geometry and
stable cutting edges,problem free machiningof a wide range ofmaterials12.7 mm 4 mm
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Fig.5.1: Selection of milling insert for M690 cutter. (From widia catalog pg. 278)
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Table 5.2: Insert Grade Description (From widia catalog pg. 327)
Table 5.3: Selection of feed per tooth and Cutting speed (From widia catalog pg. 327)
Select P-2 for C45 (AISI 1045) material
Feed per tooth (fz, mm) = 0.1 to 0.3
Cutting Speed (Vc, m/min) = 165 to 250
Insert Grade Grade Description
TN 7535HC-P35
Coated Carbide Insert,MT-CVD/CVD processwith TicN-Al203-TiNmultilayer coating forLight and Mediummachining for steels andnodular cast iron
fz
Vc
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5.2 Work piece
Table 5.4: Work piece material specification
5.2.1 Dimensions of the work pieces
Fig.5.2: Work piece (modeled and drafted in NX6)
Material Size: 150 x 150 x 300 mm
Work piece Material C45 steel (DIN)
Equivalent AISI 1045 steel
Hardness 201 BHN
Chemical composition
C 0.43
Si0.4
(maximum)
Mn 0.5
Cr+Mo+Ni0.63
(maximum)
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5.2.2 Work piece Hardness Test
(a)
(b) (c)
Fig.5.3: a) Equo tip Portable hardness tester b) Hardness measuring c) Ball indenter d)
Measured hardness value (courtesy: Kennametal Inc.)
(d)
Hardness was checked in two different places using portable equo tip instrument, the
brinells hardness value was observed to be in range of 183 to 201 BHN. We consider the
higher hardness number i.e. 201 BHN
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5.3 Vertical Milling Center Specification
Fig.5.4: Vertical Machining Center (from Mazak catalog)
Table 5.5: Machine specification
Manufacturer Mazak
Model FJV-200
Type Vertical Machining Center
Control Mazatrol 640M
Maximum Power 22 KW
Maximum RPM 12000 rpm
Maximum Travel X= 550mm, Y= 400mm, Z= 400mmWork holding Machine Vice
ATC 40
Table specification Width= 450mm, Length = 800mm
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5.4 Pre-Metal Cutting Test
5.4.1 Edge preparation
Edge preparation type: Radius (Honed)
Table 5.6: Edge round value check
Insert 1 Radius in mm
Edge-1 0.054
Edge-2 0.0548
Edge-3 0.058
Edge-4 0.059
Insert 2 Radius in mm
Edge-1 0.0572Edge-2 0.0616
Edge-3 0.0606
Edge-4 0.0592
Fig.5.5: Edge Hone radius measurement unit (courtesy: Kennametal Inc.)
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Fig. 5.6: Honed radius measuring setup (courtesy: Kennametal Inc.)
Insert hone radius is checked in Kennametal facility to ensure that the manufactured
value lies within limits. All Insert were well within limit.
5.4.2 Weight of the Insert
Fig.5.7: Insert weight (courtesy: Kennametal Inc.)
Initial Insert weight was measured using precision weighing machine, the measured
weight was observed to be 6.991 gms.
5.4.3 Coercive Field Strength
Coercive field strength Hc is the necessary force required to completely demagnetize
a magnet, Higher the number the better the magnetism property.
Coercivity is usually measured in oersted or ampere/meter units and is denoted by Hc.
Coercive field strength is also called as the magnetic field strength
Our specimen (SDMT1204-PDR-MH) has Coercive field strength (Hc)=147.3 oe.
Insert
Measuring Probe
Insert
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Coercive force is within the range.
Fig. 5.8: Foerster koerzmat HCJ meter (Coercive field strength measurement device)
5.4.4 Laser Marking of Insert
Fig.5.9: Laser Marking Machine (courtesy: Kennametal Inc.)
Laser marking is done to identify the cutting edges.
Insert
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Assembling Insert (SDMT1204 PDR-MH) to milling tool holder (M690)
Fig.5.10: Assembly of insert with cutter (courtesy: Kennametal Inc.)
Assembly of the insert to the cutter is done using the specified hardware parts. One
more insert is used as backup insert to avoid accident due to failure of primary insert.
Fig. 5.11: Mitutoyo Surface roughness testing device (tally surf) (courtesy: Kennametal Inc.)
Device specification
Measuring range : 12.5mm
Measuring speed : 0.25 mm/s
Traversing direction : Backward Detector
Detecting method : Skid measurement (differential inductance)
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5.4.5 Initial Images
Fig. 5.12: Optical Microscope (courtesy: Kennametal Inc.)
The Ram opticals Sprint MVP 200 optical microscope is used to measure wear.
Optical microscope comes with motorized precision XYZ stages, high resolution zoom
optics, color metrology camera, LED coaxial light and Measure-X metrology software.
Fig. 5.13: Optical measuring setup to measure wear (courtesy: Kennametal Inc.)
The magnification used for measurement is 50x.
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Insert 1. Initial images of Edge-1
Facet (crater face) Flank face
Nose Radius Rake Face
Initial images of Edge-2
Facet (crater face) Flank face
Nose Radius Rake Face
Fig. 5.14: Insert1- Initial images of edge -1 and edge-2 (magnification 50x) (courtesy:
Kennametal Inc.)
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Insert 2, Initial images of Edge-2
Facet (crater face) Flank face
Nose Radius Rake Face
Initial images of Edge-4
Facet (crater face) Flank face
Nose Radius Rake Face
Fig. 5.15: Insert2- Initial images of edge -2 and edge-4 (magnification 50x) (courtesy:
Kennametal Inc.)
Prior to running the experiment on machining, each cutting insert was wiped down
with cleaning agent and Initial images are captured in optical microscope to compare the
image with subsequent images and also to ensure that the edges are free from defects.
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Chapter 6
FINITE ELEMENT ANALYSIS
Finite element method based modeling and simulation is attracting researchers for
better understanding. We have used Third wave AdvantEdge software tool for Finite element
analysis purpose.
6.1 Third wave AdvantEdge
Third wave AdvantEdge from Minneapolis is a special program written for
machining simulations. This is developed based on the dynamic explicit lagrangian
formulation. It is the ideal tool for the companies that manufacture and design cutting tools
for the metalworking industry. The model is built by selecting the type of machining
operation and defining the necessary process parameters. Since we are focusing on face
milling operation the process parameter are feed, spindle speed, axial depth of cut, radial
depth of cut, length of cut and initial temperature of the work piece.
The model created by Third Wave AdvantEdge is also thermo-mechanically coupled.
In Third Wave AdvantEdge, a staggered procedure is adopted for the purpose of coupling the
thermal and mechanical equations. Geometrically identical meshes for the thermal and
mechanical models are used. Mechanical and thermal computations are staggered, assuming
the constant Temperature during the mechanical step and constant heat generation during the
thermal step.
A mechanical step is taken first based on the current distribution of temperature, and
the heat generated is computed from plastic working and frictional heat generation. The heat
thus computed is transferred to the thermal mesh and the temperatures are recomputed by
recourse to the forward-Euler algorithm. The resulting temperatures are transferred to themechanical mesh and incorporated into the thermal-softening model, which completes one
time stepping cycle.
Certain assumptions are made to simulate the complex procedure of metal cutting with
FEM as listed below. These assumptions are used to define the problem to be solved as well
as to apply the boundary and loading conditions:
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a) The cutting speed is constant.b) The cutting velocity vector is normal to the cutting edge.c) The work piece material is a homogeneous polycrystalline, isotropic and
incompressible solid.
d) The work piece is set at a reference temperature of 20 C at the beginning of thesimulation.
e) The machine tool is perfectly rigid and no influence of machine tool dynamics onmachining is considered.
f) The friction is constant at tool-chip interaction and tool-work piece interaction.
The model created by Third Wave AdvantEdge is also thermo-mechanically coupled.
In Third Wave AdvantEdge, a staggered procedure is adopted for the purpose of coupling thethermal and mechanical equations. Geometrically identical meshes for the thermal and
mechanical models are used. Mechanical and thermal computations are staggered, assuming
the constant Temperature during the mechanical step and constant heat generation during the
thermal step.
A mechanical step is taken first based on the current distribution of temperature, and the heat
generated is computed from plastic working and frictional heat generation. The heat thus
computed is transferred to the thermal mesh and the temperatures are recomputed by
recourse to the forward-Euler algorithm. The resulting temperatures are transferred to the
mechanical mesh and incorporated into the thermal-softening model, which completes one
time stepping cycle.
Certain assumptions are made to simulate the complex procedure of metal cutting with
FEM as listed below. These assumptions are used to define the problem to be solved as well
as to apply the boundary and loading conditions:
g) The cutting speed is constant.h) The width of cut is larger than the feed (plane strain condition), and both are constant.i) The cutting velocity vector is normal to the cutting edge.j) The work piece material is a homogeneous polycrystalline, isotropic, and
incompressible solid.
k) The work piece is set at a reference temperature of 20 C at the beginning of thesimulation.
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l) The machine tool is perfectly rigid and no influence of machine tool dynamics onmachining is considered.
m)The friction is constant at tool-chip interaction and tool-work piece interaction.
The finite deformation formulation used in Third Wave AdvantEdge incorporates the
hybrid triangular elements for spatial discretization. The element has three corners. The
separation of nodes, thus forming the chip from the work piece during a cutting simulation, is
achieved by continuous re-meshing. Therefore, during the metal-cutting process, the work
piece material is allowed to flow around the cutting tool edge and when the elements in the
vicinity become distorted, Third Wave AdvantEdg