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Cutting Tool Materials-Manufacturing techniquies v2.4

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Characteristics of cutting tool :
Hardness (Elevated temperatures)
Toughness (Impact forces on tool in interrupted
Wear resistance (tool life to be considered)
Chemical stability or inertness (to avoid adverse
Cutting Tool Materials
The selection of cutting tool material and grade is an important
factor to consider when planning a successful metal cutting
A basic knowledge of each cutting tool material and its
performance is therefore important so that the correct selection
for each application can be made. Considerations include the
workpiece material to be machined, the component type and
shape, machining conditions and the level of surface quality
required for each operation. Source: http://www.azom.com/details.asp?ArticleID=268&head=Sialons#_Cutting_Tools
Cutting Tool Materials
Tool bits (inserts) generally
made of seven materials:
High-speed steel,
Cast alloy (such as stellite),
Cemented carbide,
Cubic Boron Nitride,
Polycrystalline Diamond.
Cutting Tool Properties
Hot Hardness
Hardness of
various cuttingtool materials as a
function of
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Wear Resistance
Able to maintain sharpened edge throughout
the cutting operation,
Same as abrasive resistance.
Shock Resistance
Able to take the cutting loads and forces.
Shape and Configuration
Should be available for use in different sizes and shapes.
Letter Symbols Specifying
The Designation of Hard Cutting
Hard metals:
HW Uncoated hard metal containing primarily
tungsten carbide (WC).
Uncoated hard metal, also called cermet ,
containing primarily titanium carbides (TIC) or
titanium nitrides (TIN) or both.
Hard metals as above, but coated.
Carbon and Medium
Alloy Steels
Oldest of tool materials;
Used for: drills, taps, broaches, reamers;
Inexpensive, easily shaped, sharpened;
No sufficient hardness and wear resistance;
Limited to low cutting speed operation.
High speed steels (HSS)
Hardened to various depths,
Good wear resistance,
Suitable for high positive rake angle tools.
High Speed Steel
May contain combinations of tungsten, chromium,
vanadium, molybdenum, cobalt,
Can take heavy cuts, withstand shock and maintain
sharp cutting edge under red heat.
Generally two types (general purpose):
Molybdenum-base (Group M),
Tungsten-base (Group T).
Cobalt added if more red hardness desired.
M-series - Contains 10% molybdenum,
chromium, vanadium, tungsten, cobalt
 Higher, abrasion resistance,
 H.S.S. are majorly made of M-series.
T-series - 12 % - 18 % tungsten,
chromium, vanadium & cobalt
 undergoes less distortion during heat
H.S.S. available in wrought ,cast &
sintered (Powder metallurgy)
 Coated for better performance,
 Subjected to surface treatments
such as case-hardening for
improved hardness and wear
resistance or steam treatment at
elevated temperatures,
 High speed steels account for
largest tonnage
High Speed Steels (HSS)
 Good wear resistance
 Relatively inexpensive
Suitable for:
 High positive rake tools (small angles)
 Interrupted cuts
 Tools subjected to vibration and chatter (indent)
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Typical Wear Patterns on Highspeed-steel Uncoated and Titaniumnitride Coated Tools
Schematic illustration of typical wear patterns of high-speedsteel uncoated and titanium-nitride coated tools. Note that flank
wear is significantly lower for the coated tool.
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Cast-cobalt Alloys
Commonly known as stellite tools:
Composition ranges – 38% - 53 % cobalt, 30%33% chromium, 10%-20% tungsten
Good wear resistance (higher hardness)
Less tough than high-speed steels and sensitive to
impact forces
Less suitable than high-speed steels for interrupted
cutting operations
Continuous roughing cuts – relatively high
g=feeds & speeds
Finishing cuts are at lower feed and depth of cut
Cast Alloy
Usually contain 25% to 35% chromium, 4% to
25% tungsten and 1% to 3% carbon
Remainder cobalt
High hardness
High resistance to wear
Excellent red-hardness
Operate 2 ½ times speed of high-speed steel
Weaker and more brittle than high-speed steel
Cutting tool materials have different combinations
of hardness, toughness and wear resistance, and
are divided into numerous grades with specific
properties. Generally , a cutting tool material that is
successful in its application should be:
 Hard, to resist flank wear and deformation
 Tough, to resist bulk breakage
 Non-reactive with the workpiece material
 Chemically stable, to resist oxidation and
 Resistant to sudden thermal changes.
Cemented Carbide
Definition and properties
Cemented carbide is a powdery metallurgical material; a composite of
tungsten carbide (WC) particles and a binder rich in metallic cobalt (Co).
Cemented carbides for metal cutting applications consist of more than 80% of
hard phase WC. Additional cubic carbonitrides are other important
components, especially in gradient sintered grades.
The cemented carbide body is formed, either through powder pressing or
injection moulding techniques, into a body, which is then sintered to full
WC grain size is one of the most important parameters for adjusting
the hardness/toughness relationship of a grade; the finer grain size
means higher hardness at a given binder phase content.
The amount and composition of the Co-rich binder controls the grade’s
toughness and resistance to plastic deformation. At equal WC grain size,
an increased amount of binder will result in a tougher grade, which is
more prone to plastic deformation wear. A binder content that is too low
may result in a brittle material.
Cubic carbonitrides, also referred to as γ-phase, are generally added to
increase hot hardness and to form gradients.
Gradients are used to combine improved plastic deformation resistance
with edge toughness. Cubic carbonitrides concentrated in the cutting
edge improve the hot hardness where it is needed. Beyond the cutting
edge, a binder rich in tungsten carbide structure inhibits cracks and chip
hammering fractures.
Medium to coarse WC grain size Medium to
coarse WC grain sizes provide the cemented
carbides with a superior combination of high hot
hardness and toughness. These are used in
combination with CVD or PVD coatings in
grades for all areas.
Fine or submicron WC grain size Fine or
submicron WC grain sizes are used for sharp
cutting edges with a PVD coating to further
improve the strength of the sharp edge. They
also benefit from a superior resistance to
thermal and mechanical cyclic loads. Typical
applications are solid carbide drills, solid
carbide end mills, parting off and grooving
inserts, milling and grades for finishing.
Cemented carbide with gradient The beneficial
dual property of gradients is successfully
applied in combination with CVD coatings in
many first choice grades for turning, and parting
and grooving in steels and stainless steels.
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Uncoated Cemented
Carbide (HW)
Definition and properties
Uncoated cemented
represent a very small
total assortment. These
straight WC/Co or have
cubic carbonitrides.
carbide grades
proportion of the
grades are either
a high volume of
Typical applications are machining of
HRSA (heat resistant super alloys) or
titanium alloys and turning hardened
materials at low speed.
The wear rate of uncoated cemented
carbide grades is rapid yet controlled, with
a self-sharpening action.
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Cermet (CT)
Definition and properties
A cermet is a cemented carbide with titanium based
hard particles. The name cermet combines the
words ceramic and metal. Originally, cermets were
composites of TiC and nickel. Modern cermets are
nickel-free and have a designed structure of
titanium carbonitride Ti(C,N) core particles, a
second hard phase of (Ti,Nb,W)(C,N) and a W-rich
cobalt binder.
Ti(C,N) adds wear resistance to the grade, the
second hard phase increases the plastic
deformation resistance, and the amount of cobalt
controls the toughness.
In comparison to cemented carbide, cermet has
improved wear resistance and reduced smearing
tendencies. On the other hand, it also has lower
compressive strength and inferior thermal shock
resistance. Cermet can also be PVD coats for
improve wear resistance.
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Cermet grades are used in smearing applications where built-up
edge is a problem. Its self-sharpening wear pattern keeps cutting
forces low even after long periods in cut. In finishing operations,
this enables a long tool life and close tolerances, and results in
shiny surfaces.
Typical applications are finishing in stainless steels, nodular cast
irons, low carbon steels and ferritic steels. Cermets can also be
applied for trouble shooting in all ferrous materials.
Use low feed and depth of cut.
Change the insert edge when flank wear reaches 0.3 mm.
Avoid thermal cracks and fractures by machining without coolant.
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Coated Cemented Carbide
Coated cemented carbide currently represents 80-90% of all
cutting tool inserts.
Its success as a tool material is due to its unique combination
of wear resistance and toughness, and its ability to be formed
in complex shapes.
Coated cemented carbide combines cemented carbide with a
coating. Together they form a grade which is customized for its
Coated cemented carbide grades are
the first choice for a wide variety of tools
and applications.
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Coating Materials
Titanium nitride (TiN)
Titanium carbide (TiC)
Titanium Carbonitride (TiCN)
Aluminum oxide (Al2O3), thickness range – 2-15 µm
Techniques used:
Chemical –vapor deposition (CVD)
Plasma assisted CVD
Physical-vapor deposition(PVD)
Medium –temperature chemical- vapor deposition(MTCVD)
Coating – CVD
Definition and properties:
CVD stands for Chemical Vapor Deposition. The
CVD coating is generated by chemical reactions at
temperatures of 700-1050°C.
CVD coatings have high wear resistance and
excellent adhesion to cemented carbide.
The first CVD coated cemented carbide was the
single layer titanium carbide coating (TiC).
Alumina coatings (Al2O3) and titanium nitride (TiN)
coatings were introduced later. More recently, the
modern titanium carbonitride coatings (MT-Ti(C,N)
or MT-TiCN, also called MT-CVD) were developed
to improve grade properties through their ability to
keep the cemented carbide interface intact.
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Modern CVD coatings combine MT-Ti(C,N), Al2O3 and TiN. The coating
properties have been continuously improved for adhesion, toughness and
wear properties through microstructural optimizations and posttreatments.
MT-Ti(C,N) - Its hardness provides abrasive wear resistance,resulting in
reduced flank wear.
CVD-Al2O3 – Chemically inert with low thermal conductivity , making it
resistant to crater wear. It also acts as a thermal barrier to improve plastic
deformation resistance.
CVD-TiN - Improves wear resistance and is used for wear detection.
Post-treatments - Improve edge toughness in interrupted cuts and reduce
smearing tendencies.
CVD coated grades are the first choice in a wide range of
applications where wear resistance is important.
Such applications are found in general turning and boring of steel,
with crater wear resistance offered by the thick CVD coatings;
general turning of stainless steels and for milling grades in: ISO P
(steel), ISO M (stainless steel), ISO K(cast iron) .
For drilling, CVD grades are usually used in the peripheral insert.
ISO Classification of Carbide
Cutting Tools
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Most cost effective, versatile tool used
in manufacturing
Two major types of carbides
(Tungsten and Titanium)
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Coating – PVD
Definition and properties
Physical Vapor Deposition (PVD) coatings are
formed at relatively low temperatures (400-600°C).
The process involves the evaporation of a metal
which reacts with, for example, nitrogen to form a
hard nitride coating on the cutting tool surface.
PVD coatings add wear resistance to a grade due
to their hardness. Their compressive stresses also
add edge toughness and comb crack resistance.
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The main PVD-coating constituents are described below. Modern
coatings are combinations of these constituents in sequenced
layers and/or lamellar coatings. Lamellar coatings have numerous
thin layers, in the nanometer range, which make the coating even
PVD-TiN - Titanium nitride was the first PVD coating. It has all-round
properties and a golden color.
PVD-Ti(C,N) - Titanium carbonitride is harder than TiN and adds flank wear
PVD-(Ti,Al)N - Titanium aluminium nitride has high hardness in combination
with oxidation resistance, which improves overall wear resistance.
PVD-oxide - Is used for its chemical inertness and enhanced crater wear
Multi Phase Coatings
Reduces abrasion and chemical reactivity
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Diamond Coated Tools
 Use of Polycrystalline diamond as a coating,
 Difficult to adhere diamond film to substrate,
 Thin-film diamond coated inserts now commercially
 Thin films deposited on substrate with PVD & CVD
 Thick films obtained by growing large sheet of pure
 Diamond coated tools particularly effective in
machining non-ferrous and abrasive materials.
New Coating Materials
 Titanium carbo nitride (TiCN)
 Titanium Aluminum Nitride(TiAlN)
 Chromium Based coatings
 Chromium carbide
 Zirconium Nitride (ZrN)
 Hafnium nitride (HfN)
Recent developments gives nano-coating & composite coating
Ion Implementation :
 Ions placed into the surface of cutting tool
 No change in the dimensions of tool
 Nitrogen-ion Implanted carbide tools used for alloy steels & stainless
 Xeon – ion implantation of tools as under development
PVD coated grades are recommended for tough, yet sharp,
cutting edges, as well as in smearing materials.
Such applications are widespread and include all solid end mills
and drills, and a majority of grades for grooving, threading and
milling. PVD-coated grades are also extensively used for
finishing applications and as the central insert grade in drilling.
Letter Symbols Specifying
The Designation of Hard Cutting
CA Oxide ceramics containing primarily aluminium
oxide (Al2O3).
CM Mixed ceramics containing primarily aluminium
oxide (Al2O3) but containing components other than
CN Nitride ceramics containing primarily silicon nitride
CC Ceramics as above, but coated.
Ceramic (CA, CM, CN, CC)
Definition and properties
All ceramic cutting tools have excellent wear resistance at high cutting speeds.
There are a range of ceramic grades available for a variety of applications.
Oxide ceramics are aluminium oxide based (Al2O3), with added zirconia
(ZrO2) for crack inhibition. This generates a material that is chemically very
stable, but which lacks thermal shock resistance.
(1) Mixed ceramics are particle reinforced through the addition of cubic
carbides or carbonitrides (TiC, Ti(C,N)). This improves toughness and thermal
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Whisker-reinforced ceramics use silicon carbide whiskers (SiCw) to
dramatically increase toughness and enable the use of coolant.
Whisker-reinforced ceramics are ideal for machining Ni-based alloys.
(3) Silicon nitride ceramics (Si3N4) represent another group of ceramic
materials. Their elongated crystals form a self-reinforced material with
high toughness. Silicon nitride grades are successful in grey cast iron,
but a lack of chemical stability limits their use in other workpiece
 Have good hardness
Good thermal shock resistance
Good for machining cast irons
and nickel based super alloys
Sialon (SiAlON) grades combine the strength of a self-reinforced
silicon nitride network with enhanced chemical stability. Sialon grades
are ideal for machining heat resistant super alloys (HRSA).
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Sialon Applications
Seals and bearings
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CC620 Oxide ceramic for high speed finishing of grey cast iron in stable and
dry conditions.
CC6050 Mixed ceramic for light, continuous finishing in hardened materials.
CC650 Mixed ceramic for high speed finishing of grey cast irons and
hardened materials, and for semi-finishing operations in HRSA with low
toughness demands.
CC670 Whisker ceramic with excellent toughness for turning, grooving and
milling of Ni-based alloys . Can also be used for hard part turning in
unfavorable conditions.
CC6190 Silicon nitride grade for rough to finish turning and high speed dry
milling of cast iron, perlitic nodular
CC6090 cast irons and hardened cast irons.
CC6090 Coated silicon nitride grade for light roughing to finish turning of cast
GC1690 Sialon grade for optimized performance when turning pre-machined
HRSA in stable conditions.
CC6060 Predictable wear due to good notch wear resistance.
CC6065 Particle reinforced Sialon for turning operations in HRSA that
demand tough inserts.
Letter Symbols Specifying The
Designation of Hard Cutting
DP Polycrystalline diamond*
Boron nitride:
BN Cubic boron nitride*
*(Polycrystalline diamond and cubic boron nitride are also
called superhard cutting materials ).
Polycrystalline Cubic Boron
Nitride, CBN (BN)
Definition and properties
Polycrystalline cubic boron nitride, CBN, is a
material with excellent hot hardness that can be
used at very high cutting speeds. It also exhibits
good toughness and thermal shock resistance.
Modern CBN grades are ceramic composites
with a CBN content of 40-65%. The ceramic
binder adds wear resistance to the CBN, which
is otherwise prone to chemical wear. Another
group of grades are the high content CBN
grades, with 85% to almost 100% CBN. These
grades may have a metallic binder to improve
their toughness.
CBN is brazed onto a cemented carbide carrier
to form an insert. The Safe-Lok™ technology
further enhances the bondage of CBN cutting
tips on negative inserts
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CBN grades are largely used for finish turning of hardened steels,
with a hardness over 45 HRC. Above 55 HRC, CBN is the only
cutting tool which can replace traditionally used grinding methods.
Softer steels, below 45 HRC, contain a higher amount of ferrite,
which has a negative effect on the wear resistance of CBN.
CBN can also be used for high speed roughing of grey cast irons in
both turning and milling operations.
CB7015 PVD coated CBN grade with ceramic binder for continuous
turning, and light interrupted cuts in hardened steels.
CB7025 CBN grade with ceramic binder for interrupted cuts and high
toughness demands when turning hardened steels.
CB7050 High content CBN grade with metallic binder for heavy
interrupted cuts in hardened steels and for finishing grey cast iron. PVD
coated .hardness demands when turning hardened steels.
 Hardest known substance
 Low friction, high wear resistance
 Ability to maintain sharp cutting edge
 Single crystal diamond of various carats used
for special applications
 Machining copper—front precision optical
mirrors for ( SDI)
 Diamond is brittle , tool shape & sharpened is
 Low rake angle used for string cutting edge
Polycrystalline Diamond, PCD (DP)
Definition and properties
PCD is a composite of diamond particles sintered
together with a metallic binder. Diamond is the
hardest, and therefore the most abrasion resistant, of
all materials. As a cutting tool, it has good wear
resistance but it lacks chemical stability at high
temperatures and dissolves easily in iron.
PCD grade for finishing and semi-finishing of non-ferrous and
non-metallic materials in turning and milling.
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(PCD) Tools
 Used for wire drawing of fine wires,
 Small synthesis crystal fused by high pressure and
 Bonded to a carbide substrate,
 Diamond tools can be used for any speed,
 Suitable for light un-interrupted finishing cuts,
 To avoid tool fracture single crystal diamond is to
be re-sharpened as it becomes dull,
 Also used as an abrasive in grinding and polishing
Diamond Edge Saw Blade
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Diamond Tip Drill Bits
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Properties for Groups of Tool
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Relative Time Required To Machine With
Various Cutting-tool Materials
Relative time required to machine with various cutting-tool materials, indicating the year the tool
materials were first introduced. Note that machining time has been reduced by two orders of
magnitude with a hundred years. Source: Courtesy of Sandvik.
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Inserts And Toolholders
 Individual cutting tools with several
cutting points
 A square insert has 8 cutting points
 The holes in the inserts are
standardized for interchangeability
Typical carbide inserts with various shapes and chip-breaker
features: Round inserts are also available, as can be seen in
The holes in the inserts are standardized for interchangeability
in toolholders. Source: Courtesy of Kyocera Engineered
Ceramics, Inc.
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
CARBIDES - Insert Attachment
Methods of attaching
inserts to toolholders:
 Clamping
 Wing lockpins
 Examples of inserts
attached to toolholders with
threadless lockpins, which
are secured with side
 Insert brazed on a tool
Methods of mounting inserts on
toolholders: (a) clamping and (b) wing
lockpins. (c) Examples of inserts
mounted with threadless lockpins,
which are secured with side screws.
Source: Courtesy of Valenite.
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Insert Edge Properties
Relative edge strength and tendency for
chipping of inserts with various shapes.
Strength refers to the cutting edge indicated
by the included angles. Source: Courtesy of
Kennametal, Inc.
Insert shape affects strength of
cutting edge
To further improve edge
strength and prevent chipping,
all insert edges are usually
honed, chamfered, or
produced with a negative land.
Edge preparation for inserts to improve
edge strength. Source: Courtesy of
Kennametal, Inc.
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Insert Edge Properties
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Wear on Cutting Edges
To understand the advantages and limitations of each
material, it is important to have some knowledge of the different
wear mechanisms to which cutting tools are subjected.
Flank wear
The most common type of wear and the preferred
wear type, as it offers predictable and stable tool life.
Flank wear occurs due to abrasion, caused by hard
constituents in the workpiece material.
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Built-up edge (BUE)
This wear type is caused by pressure welding of
the chip to the insert. It is most common when
machining sticky materials, such as low carbon
steel, stainless steel and aluminium. Low cutting
speed increases the formation of built-up edge.
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Notch wear
Insert wear characterized by excessive
localized damage on both the rake face and
flank of the insert at the depth of cut line.
Caused by adhesion (pressure welding of
chips) and a deformation hardened surface. A
common wear type when machining stainless
Plastic deformation
Plastic deformation takes place when the tool
material is softened. This occurs when the
cutting temperature is too high for a certain
grade. In general, harder grades and thicker
coatings improve resistance to plastic
deformation wear.
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Thermal cracks
When the temperature at the cutting edge
changes rapidly from hot to cold, multiple cracks
may appear perpendicular to the cutting edge.
Thermal cracks are related to interrupted cuts,
common in milling operations, and are
aggravated by the use of coolant.
Mechanic, impact force
Edge chipping/breakage
Chipping or breakage is the result of an overload
of mechanical tensile stresses. These stresses
can be due to a number of reasons, such as chip
hammering, a depth of cut or feed that is too
high, sand inclusions in the workpiece material,
built-up edge, vibrations or excessive wear on
the insert.
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Tool-life curves for a variety of
cutting-tool materials. The negative
inverse of the slope of these curves is
the exponent n in the Taylor tool-life
equation and C is the cutting speed at
T = 1 min, ranging from about 200 to
10,000 ft./min in this figure.
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Allowable Average Wear Land
for Cutting Tools
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Types of Wear Seen in Cutting
(a) Schematic illustration of types of wear observed on various cutting tools. (b) Schematic
illustrations of catastrophic tool failures. A wide range of parameters influence these wear and
failure patterns. Source: Courtesy of V. C. Venkatesh.
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Surface Finish
Factors Affecting Surface Finish:
Nose radius of tool
Cutting speed
Rigidity of machining operation
Temperature generated during machining
Direct relationship between temperature of
workpiece and quality of surface finish
High temperature yields rough surface finish
Metal particles tend to adhere to cutting tool and form
built-up edge
Cooling work material reduces temperature of
cutting-tool edge
Result in better surface finish
Machined Surfaces Produced
on Steel
Machined surfaces produced on steel (highly magnified), as observed with a scanning
electron microscope: (a) turned surface and (b) surface produced by shaping. Source:
Courtesy of J. T. Black and S. Ramalingam.
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Dull Tool in Orthogonal
Schematic illustration of a dull tool with respect to the depth of cut in orthogonal machining
(exaggerated). Note that the tool has a positive rake angle, but as the depth of cut decreases, the
rake angle effectively can become negative. The tool then simply rides over the workpiece
(without cutting) and burnishes its surface; this action raises the workpiece temperature and
causes surface residual stresses.
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Feed Marks on a Turned
Surface roughness:
w here
f fe e d
R  to o l - n o s e ra d iu s
Schematic illustration of feed marks on a surface
being turned (exaggerated).
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Effects of Cutting Fluids
Perform three important functions
Reduce temperature of cutting action
Reduce friction of chips sliding along tool face
Decrease tool wear and increase tool life
Three types of cutting fluids
Cutting oils
Emulsifiable (soluble) oils
Chemical (synthetic) cutting fluids
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Cutting Fluids
Generally used for machining: steel, alloy
steel, brass and bronze with high-speed
steel cutting tools
Not used with cemented-carbide tools
 If used, great quantities of cutting fluid are
applied to ensure uniform temperatures to
prevent carbide inserts from cracking
Not generally used with cast iron, aluminum,
and magnesium alloys.
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Cutting Fluids
Purpose of cutting fluids:
Reduce friction and wear
Cool cutting zone
Flush chips away from the cutting zone
Protect the machined surface from
environmental corrosion
These factors improve tool life and help
make a better more efficient cut.
Image of cutting
fluid and its
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Cutting Fluids
 Lubricants reduce friction
 Coolants effectively reduce high temperatures of
tools/ work pieces
 At times, using a cutting fluid may cause the
material to become “curly”, which concentrates the
heat closer to the tip. This is detrimental because
it decreases the tool’s life.
 It is these defects that have turned machinists to
“near-dry machining”
Cutting Fluids
Types of cutting fluids:
Oils : mineral, animal, vegetable, compounded, and
synthetic oils. Only used in operations where temp
rise is ins ignificant.
Em uls ions : mixture of oil and water and additives.
Good for operations where temperature rise is
s ignificant.
S e m is ynthe tics : chemical emulsions containing little
mineral oil diluted in water with additives that reduce
size of particles.
S ynthe tics : chemicals with additives, diluted in water,
without oil.
Image of a “synthetic”
cutting fluid.
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Cutting Fluids
Methods of Application
Flooding: most common; rates of up to 225
L/min for multi-tooth cutters; poor visibility; 1002000 Psi.
Mist: most effective w/ water based fluids;
requires venting but is popular because of
good visibility; similar to using an aerolsol can;
10- 80 Psi.
High-pressure systems: use a powerful
jet/nozzle to target the hot area; 800- 5000 Psi;
can be used as a chip-breaker to clear debris
Through the cutting tool system: passages
are made in the tool/ tool handle that allow for
a direct route for the coolant to the hot area.
Cutting Fluids
Special Considerations for use of cutting
Machines need to be washed after fluids have been
Used cutting fluids may undergo chemical changes.
Settling, skimming, centrifuging and filtering help to
avoid any bad effects they may cause.
Cutting fluids containing:
Sulfur should not be used on Nickel based alloys.
Chlorine should not be used with Titanium
Cutting Fluids
Through the cutting tool system flooding method
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Cutting Fluids
Multi-Jet Delivery System Flooding Method
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Proper Methods of Applying
Cutting Fluids
Schematic illustration of the proper methods of applying cutting fluids
(flooding) in various machining operations: (a) turning, (b) milling, (c)
thread grinding, and (d) drilling.
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid., ISBN 0-13-148965-8. © 2006 Pearson
Education, Inc., Upper Saddle River, NJ. All rights reserved.
Near-dry and Dry Machining
Introduced in 1990’s to minimize use of metalworking
In these processes, chips are removed from the cutting
zone by application of pressurized air.
Dry machining:
Used for turning, milling, and gear cutting on steels, steel alloys,
and cast irons.
Near-dry cutting:
The application of a mist of a mixture of water and cutting fluid
(vegetable oil) inserted through the spindle of the machine tool.
Near-dry and Dry Machining
Cryogenic Machining
Cryogenic gases such as nitrogen and carbon dioxide are
used as a coolant. They are shot through a small nozzle at
temperatures around -200 C; good for tool life, good for the
Image of a liquid nitrogen
cooling system.
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Machinability is defined in terms of:
1. Surface finish and surface integrity of machined part
2. Tool life
3. Force and power required
4. The level of difficulty in chip control
Good machinability indicates
good surface finish and surface integrity
a long tool life
and low force and power requirements
Note, continuous chips should be avoided for good
Results of (Free-machining)
Three main machining characteristics
become evident
Tool life is increased
Better surface finish produced
Lower power consumption required for machining
Machinability ratings (indexes)
These have been used also to determine machinability
available for each type of material and its condition
not used much anymore due to misleading nature
e.g.: AISI 1112 steel with a rating of 100:
for a tool life of 60 min,
choose 30 m/min cutting speed (for machining this material)
These are mostly qualitative aspects - not sufficient to
guide operator to machining parts economically
Other guides for various materials should include:
cutting speed, feed, depth of cut, cutting tools and
shape, cutting fluids
Grain Structure
Machinability of metal affected by its
Ductility and shear strength modified greatly by
operations such as annealing, normalizing and
stress relieving
Certain chemical and physical modifications of
steel improve machinability
Addition of phosphorus, sulphur, lead, or sodium
Cold working, which modifies ductility
Machinability here discussed for the following:
Ferrous Metals (e.g. steels, stainless steels, cast iron, etc.),
Nonferrous Metals (e.g. aluminum, copper, magnesium),
Miscellaneous Materials (e.g. thermoplastics, ceramics),
Thermally assisted machining.
Machinability of Ferrous Metals: Steels
Carbon steels have a wide range of machinability
If a carbon steel is too ductile, chip formation can produce
built-up edge, leading to poor surface finish
If too hard, it can cause abrasive wear of the tool because of
the presence of carbides in the steel
Cold-worked carbon steels: preferred machinability
Machinability of Ferrous
Steels (cont)
Free-machining steels: contain sulfur + phosphorus
Sulfur forms: manganese sulfide inclusions
Important to choose size, shape, distribution of inclusions
These act as stress raisers in primary shear zone, chips are
small, break easily (i.e. machinability ↑)
Phosphorus has two major-desirable-effects
1. Strengthens ferrite - better chip formation, surface finish ↑
2. Increases hardness - short (non-continuous chips)
Note, soft steels have low machinability since have tendency
to form BUE - poor surface finish
Machinability of Ferrous
Steels (cont)
Leaded steels (e.g. 10L45 steel)
High percentage of lead solidifies at the tips of manganese
sulfide inclusions,
Lead acts as a solid lubricant (due to low shear strength) at
tool-chip interface during cutting,
It also acts: liquid lubricant when temp. is high in front of tool,
It also ↓ shear stress at primary shear zone - ↓ forces and ↓
power consumption,
Lead is, however, dangerous environmental toxin, there’s
trend to eliminate use of lead in steel: “lead-free steels”,
Good substitutes: bismuth, tin (but performance is lower).
Low-carbon (Machine)
Large areas of ferrite interspersed with
small areas of pearlite
Ferrite: soft, high ductility and low strength
Pearlite: low ductility and high strength
 Combination of ferrite and iron carbide
More desirable microstructure in steel is
when pearlite well distributed instead of in
High-carbon (Tool) Steel
Greater amount of pearlite because of
higher carbon content
More difficult to machine steel efficiently
Desirable to anneal these steels to alter
Improves machining qualities
Machinability of Ferrous
Steels (cont)
Calcium-deoxidized steels
They contain oxide flakes of calcium silicates (CaSO)
these reduce the strength of the secondary shear zone
they also decrease tool–chip interface friction and wear
- temp. increases are lower- less crater wear
Alloy steels
They have a large variety of compositions and hardnesses
machinability can’t be generalized
but they have higher hardness and other properties
Can be used to produce good surface finish, integrity,
dimensional accuracy
Alloy Steel
Combinations of two or more metals.
Generally slightly more difficult to machine than
low-or high-carbon steels.
To improve machining qualities
Combinations of sulfur and lead or sulfur and manganese in
proper proportions added,
Combination of normalizing and annealing.
Machining of stainless steel greatly eased by
addition of selenium
Machinability of Ferrous
Effects of Various Elements in Steels
Presence of aluminum and silicon is harmful in steels
Reason: combine with oxygen to form aluminum oxide and
silicates, which are hard and abrasive -tool wear increases
and machinability is reduced
Note that as machinability↑, other properties may ↓
e.g. lead causes embrittlement of steel at high temp.
(although has no effect at room temp.)
e.g. sulfur can reduce hot workability of steel
Machinability of Ferrous
Stainless Steels
 Austenitic (300 series) steels are difficult to machine (needs
machine tool with high stiffness to avoid chatter)
 Ferritic stainless steels (also 300 series) have good
 Martensitic (400 series) steels are abrasive, tend to form BUE
 Precipitation-hardening stainless steels: strong and abrasive,
require hard, abrasion-resistant tool
Cast Irons
Gray irons: machinable, but abrasive (esp. pearlite)
Nodular, malleable irons: machinable with hard materials
Cast Iron
Consists generally of ferrite, iron carbide, and
free carbon
Microstructure controlled by addition of alloys,
method of casting, rate of cooling, and heat
White cast iron cooled rapidly after casting
hard and brittle (formation of hard iron carbide)
Gray cast iron cooled gradually
composed by compound pearlite, fine ferrite, iron carbide and
flakes of graphite (softer)
Cast Iron
Machining slightly difficult due to iron carbide
and presence of sand on outer surface of
Microstructure altered through annealing
Iron carbide broken down into graphitic carbon and ferrite
 Easier to machine
Addition of silicon, sulfur and manganese gives
cast iron different qualities.
Machinability of
Nonferrous Metals
very easy to machine
but softer grades: form BUE, poor surface finish recommend
high cutting speeds, high rake and relief angles
requires machining in a controlled environment
this is due to toxicity of fine particles produced in machining
Cobalt-based alloys
abrasive and work hardening
require sharp, abrasion-resistant tool materials, and low feeds
and speeds
can be difficult to machine because of BUE formation
Pure aluminum generally more difficult to
machine than aluminum alloys
Produces long stringy chips and harder on cutting tool
Aluminum alloys
Cut at high speeds, yield good surface finish
Hardened and tempered alloys easier to machine
Silicon in alloy makes it difficult to machine
 Chips tear from work (poor surface)
Heavy, soft, reddish-colored metal refined from
copper ore (copper sulfide)
High electrical and thermal conductivity
Good corrosion resistance and strength
Easily welded, brazed or soldered
Very ductile
Anneal: heat at 650º C and quench in water
Does not machine well: long chips clog flutes of
cutting tool
Coolant should be used to minimize heat
Copper-based Alloys:
Alloy of copper and zinc with good corrosion
resistance, easily formed, machines, and cast
Several forms of brass
Alpha brasses: up to 36% zinc, suitable for cold working
Alpha 1 beta brasses: Contain 54%-62% copper and used in hot
Small amounts of tin or antimony added to
minimize pitting effect of salt water
Used for water and gas line fittings, tubings,
tanks, radiator cores, and rivets
Copper-based Alloys:
Alloys of copper and tin which contain up to
12% of principal alloying element
Exception: copper-zinc alloys
90% copper, 10% tin, and very small amount of phosphorus
High strength, toughness, corrosion resistance
Used for lock washers, cotter pins, springs and clutch discs
Copper-based Alloys:
Silicon-bronze (copper-silicon alloy)
Contains less than 5% silicon
Strongest of work-hardenable copper alloys
Mechanical properties of machine steel and corrosion resistance
of copper
Used for tanks, pressure vessels, and hydraulic pressure lines
Copper-based Alloys:
Aluminum-bronze (copper-aluminum
Contains between 4% and 11% aluminum
Other elements added
 Iron and nickel (both up to 5%) increases strength
 Silicon (up to 2%) improves machinability
 Manganese promotes soundness in casting
Good corrosion resistance and strength
Used for condenser tubes, pressure vessels, nuts
and bolts
Copper-based Alloys:
Beryllium-bronze (copper and beryllium)
Contains up to 2% beryllium
Easily formed in annealed condition
High tensile strength and fatigue strength in hardened
Used for surgical instruments, bolts, nuts, and screws
Machinability of Nonferrous
very easy to machine, good surface finish, prolonged tool life
Caution: high rate of oxidation and fire danger
Titanium and its alloys
have very poor thermal conductivity, high temp. rise and
BUE, difficult to machine
brittle, strong, and very abrasive, machinability is low
Good machinability
Requires cooling cutting fluid (danger of explosion, fire)
Machinability of
Miscellaneous Materials
Machining requires sharp tools with positive rake angles, large
relief angles, small depths of cut and feed and high speeds
Cooling also required to keep chips from sticking to tools
Polymer-matrix composites:
Very abrasive , difficult to machine
Also, requires careful handling; avoid touching, inhaling fibers
Metal-matrix and ceramic-matrix composites
Can be difficult to machine depending on the properties of the
matrix material and the reinforcing fibers
Requires sharp, hard, abrasion-resistant tools
Machinability Of
Miscellaneous Materials
Have steadily improving machinability (e.g. nanoceramics)
Require appropriate processing paramters
Properties vary with grain direction, type of chips and surfaces
vary significantly depending on the type of wood and its
Basic requirements: sharp tools, high cutting speeds
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