Cutting Tool Materials 220
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Class Outline
Objectives
Important Cutting Tool Properties
The Balance of Properties
Carbon Tool Steels
High-Speed Steel
Uses of High-Speed Steel
Tool Treatment Methods
Carbides
Carbide Coatings
Uses of Carbides
Indexable Inserts
Nonferrous Cast Alloys
Ceramics
Cubic Boron Nitride
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Diamonds
Common Tool Choices
Specialized Tool Choices
Class Outline
Objectives
Important Cutting Tool Properties
The Balance of Properties
Carbon Tool Steels
High-Speed Steel
Uses of High-Speed Steel
Tool Treatment Methods
Carbides
Carbide Coatings
Uses of Carbides
Indexable Inserts
Nonferrous Cast Alloys
Ceramics
Cubic Boron Nitride
Diamonds
Common Tool Choices
Specialized Tool Choices
Summary
Objetivos
Importancia de las herramientas de carburo
¿Qué es el carburo?
Lesson: 1/18
Objectives
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Identify important properties for cutting tools.
Describe the balance of tool properties.
Describe carbon tool steels.
Identify the major types of high-speed steel.
Describe high-speed steel tools.
Describe treatments available for high-speed
steel.
Identify the major types of carbides.
Describe the role of coatings for carbides.
Describe carbide tools.
Explain how an indexable insert works.
Describe cast alloy tools.
Describe ceramic tools.
Describe cubic boron nitride tools.
Describe diamond tools.
Explain common variables in cutting tool
selection.
Describe why specialty tool materials are chosen.
Copyright © 2009 Tooling U, LLC. All Rights Reserved.
Figure 1. Cutting tool materials involve a balance between hardness and
toughness.
Lesson: 1/18
Objectives
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Identify important properties for cutting tools.
Describe the balance of tool properties.
Describe carbon tool steels.
Identify the major types of high-speed steel.
Describe high-speed steel tools.
Describe treatments available for high-speed
steel.
Identify the major types of carbides.
Describe the role of coatings for carbides.
Describe carbide tools.
Explain how an indexable insert works.
Describe cast alloy tools.
Describe ceramic tools.
Describe cubic boron nitride tools.
Describe diamond tools.
Explain common variables in cutting tool
selection.
Describe why specialty tool materials are chosen.
Figure 1. Cutting tool materials involve a balance between hardness and
toughness.
Figure 2. An assortment of carbide cutting inserts.
Figure 3. A high-speed steel end mill.
Copyright © 2009 Tooling U, LLC. All Rights Reserved.
Lesson: 2/18
Important Cutting Tool Properties
Effective cutting tools combine a handful of valuable properties. The key properties of
cutting tool materials are hardness, toughness, and wear resistance.
A cutting tool must be hard so that it can remove metal without scratching or eroding. It
must be tough so that it does not fracture or fail during the operation, as shown in
Figure 1. Finally, the tool must be wear resistant so that it maintains its cutting edge for
a reasonable length of time.
Keep in mind that a cutting tool must exhibit these properties at high temperatures,
sometimes over 1000°F (538°C). During any machining operation, the removal of metal
from the workpiece generates friction and heat. The faster the removal of metal, the
greater the amount of heat that is generated. Consequently, cutting tool materials that
remain hard, tough, and wear resistant at high temperatures are most effective during
machining operations.
Figure 1. The sudden fracturing of a cutting tool
is a serious failure that should be avoided.
Lesson: 3/18
The Balance of Properties
No single cutting material excels at all of the necessary properties. Most often, the
selection of a cutting material involves the tradeoff of one property for another.
Some of the most common cutting tool materials are very tough. In other words, they
can take a healthy amount of abuse before they finally fail. However, tough tools may
not have the necessary hardness for machining certain workpiece materials. Older
machines, such as the lathe in Figure 1, often require tougher tools.
Generally speaking, the harder the cutting tool material, the less toughness that same
material exhibits. A harder cutting tool allows you to machine harder workpiece
materials at higher speeds. However, harder tools also require more powerful and more
rigid machines, such as the machine in Figure 2. Otherwise, these brittle materials will
fracture or crack during machining.
Cutting material selection involves a careful balance between toughness and hardness.
The workpiece material and machine tool will dictate the cutting material with the best
balance of these properties. Also, the cost of the tool material is always a key factor.
Figure 1. Older machines require tools with
excellent toughness.
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Figure 2. Modern machines are powerful, rigid, and
Lesson: 3/18
The Balance of Properties
No single cutting material excels at all of the necessary properties. Most often, the
selection of a cutting material involves the tradeoff of one property for another.
Some of the most common cutting tool materials are very tough. In other words, they
can take a healthy amount of abuse before they finally fail. However, tough tools may
not have the necessary hardness for machining certain workpiece materials. Older
machines, such as the lathe in Figure 1, often require tougher tools.
Generally speaking, the harder the cutting tool material, the less toughness that same
material exhibits. A harder cutting tool allows you to machine harder workpiece
materials at higher speeds. However, harder tools also require more powerful and more
rigid machines, such as the machine in Figure 2. Otherwise, these brittle materials will
fracture or crack during machining.
Cutting material selection involves a careful balance between toughness and hardness.
The workpiece material and machine tool will dictate the cutting material with the best
balance of these properties. Also, the cost of the tool material is always a key factor.
Figure 1. Older machines require tools with
excellent toughness.
Figure 2. Modern machines are powerful, rigid, and
can support harder tool materials.
Lesson: 4/18
Carbon Tool Steels
Before 1870, the only available type of cutting tool material was plain carbon steel. One of the
major disadvantages of plain carbon steel is that it loses its hardness at even modest cutting
temperatures. Consequently, most machining was done at very low speeds.
To increase cutting speeds, manufacturers developed various carbon tool steels. These steels
contain combinations of manganese, silicon, and/or chromium, as shown in Figure 1. Small
additions of these alloying elements helped to improve their performance. Most tool steels are
heat treated to create their special properties.
Carbon tool steels have some key disadvantages by today’s cutting tool standards. Nowadays,
tool steels are often used to make inexpensive drills, taps, and reamers. High production
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cutting jobs require harder tool materials that can handle higher speeds and temperatures.
Figure 1. Contents of sample tool steel
Lesson: 4/18
Carbon Tool Steels
Before 1870, the only available type of cutting tool material was plain carbon steel. One of the
major disadvantages of plain carbon steel is that it loses its hardness at even modest cutting
temperatures. Consequently, most machining was done at very low speeds.
To increase cutting speeds, manufacturers developed various carbon tool steels. These steels
contain combinations of manganese, silicon, and/or chromium, as shown in Figure 1. Small
additions of these alloying elements helped to improve their performance. Most tool steels are
heat treated to create their special properties.
Carbon tool steels have some key disadvantages by today’s cutting tool standards. Nowadays,
tool steels are often used to make inexpensive drills, taps, and reamers. High production
cutting jobs require harder tool materials that can handle higher speeds and temperatures.
Figure 1. Contents of sample tool steel
grades.
Lesson: 5/18
High-Speed Steel
One of today’s most common groups of cutting tool materials is high-speed steel (HSS).
Though high-speed steel was first introduced around 1900, it is still used in today’s shops.
As with the carbon tool steels that preceded these materials, HSS contains a balance of varying
alloying elements. Generally speaking, HSS can be divided into these two major groups:
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Tungsten high-speed steels were the first HSS tools created that used tungsten as a
primary alloying element. Figure 1 lists the contents of two HSS tungsten grades.
Molybdenum high-speed steels later contained molybdenum as an alloying element to
reduce the amounts of costly tungsten. Figure 2 shows the composition of two HSS
molybdenum grades.
Both of these groups of high-speed steel are still available today. HSS tools are either
wrought or sintered. During sintering, a fine powder of HSS is pressed and heated to create
the final solidified shape. Sintered HSS tools cost more, but they tend to be harder, tougher,
and more wear resistant.
Figure 1. Sample contents of tungsten
HSS.
Figure 2. Sample contents of molybdenum
HSS.
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Lesson: 5/18
High-Speed Steel
One of today’s most common groups of cutting tool materials is high-speed steel (HSS).
Though high-speed steel was first introduced around 1900, it is still used in today’s shops.
As with the carbon tool steels that preceded these materials, HSS contains a balance of varying
alloying elements. Generally speaking, HSS can be divided into these two major groups:
l
l
Tungsten high-speed steels were the first HSS tools created that used tungsten as a
primary alloying element. Figure 1 lists the contents of two HSS tungsten grades.
Molybdenum high-speed steels later contained molybdenum as an alloying element to
reduce the amounts of costly tungsten. Figure 2 shows the composition of two HSS
molybdenum grades.
Both of these groups of high-speed steel are still available today. HSS tools are either
wrought or sintered. During sintering, a fine powder of HSS is pressed and heated to create
the final solidified shape. Sintered HSS tools cost more, but they tend to be harder, tougher,
and more wear resistant.
Figure 1. Sample contents of tungsten
HSS.
Figure 2. Sample contents of molybdenum
HSS.
Lesson: 6/18
Uses of High-Speed Steel
Generally speaking, manufacturers choose to use HSS tools for their toughness and low cost.
High-speed steel cutting tools are not considered "hard" cutting tools. Many other cutting
materials offer greater hardness. However, HSS tools are able to take a substantial amount of
abuse before finally failing.
Certain machining situations may require the use of HSS tools, such as the end mill in Figure 1.
Older and less rigid machines typically require HSS tools. Other cutting materials cannot
withstand the slower cutting speeds and less stable tool setups that accompany older machines.
Also, HSS tools are useful for performing interrupted cuts, such as those during milling
operations. The HSS cutting materials are able to withstand the temperature fluctuations and
shock that occurs during interrupted cutting. Workpieces that still have a heavy surface scale
from hot working are also effectively machined by HSS tools.
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Figure 1. A high-speed steel end mill.
Lesson: 6/18
Uses of High-Speed Steel
Generally speaking, manufacturers choose to use HSS tools for their toughness and low cost.
High-speed steel cutting tools are not considered "hard" cutting tools. Many other cutting
materials offer greater hardness. However, HSS tools are able to take a substantial amount of
abuse before finally failing.
Certain machining situations may require the use of HSS tools, such as the end mill in Figure 1.
Older and less rigid machines typically require HSS tools. Other cutting materials cannot
withstand the slower cutting speeds and less stable tool setups that accompany older machines.
Also, HSS tools are useful for performing interrupted cuts, such as those during milling
operations. The HSS cutting materials are able to withstand the temperature fluctuations and
shock that occurs during interrupted cutting. Workpieces that still have a heavy surface scale
from hot working are also effectively machined by HSS tools.
Figure 1. A high-speed steel end mill.
Lesson: 7/18
Tool Treatment Methods
The metallic composition of the tungsten-based high-speed steels has remained the same
for over a century. However, as technology improves, the quality of the HSS tools
improves as well. Most HSS tools have benefited from improvements in both heat
treatment and coating methods.
Figure 1 shows a furnace used for heat treatment. By adjusting the temperature of the
metal, manufacturers can control the hardness of HSS tools. The cutting tool can be
shaped in its softer state and then heat treated to harden the tool exterior. HSS tools
can harden well below the surface of the tool.
Many HSS tools are also coated with titanium nitride (TiN) through a physical vapor
deposition (PVD) process. During this process, small atoms of TiN are turned into a
vapor gas and deposited on the tool surface. This film is only 0.0002 in. thick (0.0051
mm), which is less than 1/10 the thickness of a human hair. Even this thin layer improves
the life of the cutting tool.
Figure 1. A furnace used to heat treat products.
(Courtesy of Okubo-Gear.)
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Lesson: 8/18
Lesson: 7/18
Tool Treatment Methods
The metallic composition of the tungsten-based high-speed steels has remained the same
for over a century. However, as technology improves, the quality of the HSS tools
improves as well. Most HSS tools have benefited from improvements in both heat
treatment and coating methods.
Figure 1 shows a furnace used for heat treatment. By adjusting the temperature of the
metal, manufacturers can control the hardness of HSS tools. The cutting tool can be
shaped in its softer state and then heat treated to harden the tool exterior. HSS tools
can harden well below the surface of the tool.
Many HSS tools are also coated with titanium nitride (TiN) through a physical vapor
deposition (PVD) process. During this process, small atoms of TiN are turned into a
vapor gas and deposited on the tool surface. This film is only 0.0002 in. thick (0.0051
mm), which is less than 1/10 the thickness of a human hair. Even this thin layer improves
the life of the cutting tool.
Figure 1. A furnace used to heat treat products.
(Courtesy of Okubo-Gear.)
Lesson: 8/18
Carbides
Without question, the most common cutting tool materials are the various cemented carbides,
or simply carbides. You may also see these tools referred to as sintered carbides. Almost every
high-production machine shop relies on cutting tools made from carbides. Figure 1 shows a
range of carbide insert shapes.
The original carbide cutting tools contained tungsten carbide (WC). Early carbide tools were
harder than high-speed steel. However, the original carbide tools quickly developed a crater
when machining the various grades of steel. Figure 2 illustrates cratering. To reduce this
tendency, manufacturers developed carbide tools that combined tungsten carbide with titanium
carbide (TiC). Carbide tools made exclusively with titanium carbide are also available.
Cemented carbide tools are actually a type of cermet. The term "cermet" is short for "ceramic in
a metallic binder." In other words, tiny ceramic particles are embedded in a metal base.
Nowadays, carbide tools offer some of the most effective means for machining steel.
Figure 1. An assortment of carbide
inserts.
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Lesson: 8/18
Carbides
Without question, the most common cutting tool materials are the various cemented carbides,
or simply carbides. You may also see these tools referred to as sintered carbides. Almost every
high-production machine shop relies on cutting tools made from carbides. Figure 1 shows a
range of carbide insert shapes.
The original carbide cutting tools contained tungsten carbide (WC). Early carbide tools were
harder than high-speed steel. However, the original carbide tools quickly developed a crater
when machining the various grades of steel. Figure 2 illustrates cratering. To reduce this
tendency, manufacturers developed carbide tools that combined tungsten carbide with titanium
carbide (TiC). Carbide tools made exclusively with titanium carbide are also available.
Cemented carbide tools are actually a type of cermet. The term "cermet" is short for "ceramic in
a metallic binder." In other words, tiny ceramic particles are embedded in a metal base.
Nowadays, carbide tools offer some of the most effective means for machining steel.
Figure 1. An assortment of carbide
inserts.
Figure 2. Close-up image of crater
formation.
Lesson: 9/18
Carbide Coatings
As is the case with HSS tools, carbide tools are available either coated or uncoated. About
85% of the carbide tools sold today are coated, mostly through chemical vapor
deposition (CVD) and physical vapor deposition (PVD) processes. Figure 1 illustrates the
three most popular carbide coatings:
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Titanium nitride (TiN) reduces the friction between the workpiece and cutting tool.
Aluminum oxide (Al2O3) helps to prevent the abrasive wear of the tool.
Titanium carbide (TiC) strengthens the bond between the coating and the material.
The
special
coatings
added
to carbide
tools
can triple the life of the tool by increasing
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© 2009
Tooling
U, LLC.
All Rights
Reserved.
hardness and wear resistance and reducing friction. Carbide tools can combine three or
more layers of different coating materials, as shown in Figure 2. Coatings can also increase
the productivity of tooling by allowing operation at higher speeds without a compromise in
Lesson: 9/18
Carbide Coatings
As is the case with HSS tools, carbide tools are available either coated or uncoated. About
85% of the carbide tools sold today are coated, mostly through chemical vapor
deposition (CVD) and physical vapor deposition (PVD) processes. Figure 1 illustrates the
three most popular carbide coatings:
l
l
l
Titanium nitride (TiN) reduces the friction between the workpiece and cutting tool.
Aluminum oxide (Al2O3) helps to prevent the abrasive wear of the tool.
Titanium carbide (TiC) strengthens the bond between the coating and the material.
The special coatings added to carbide tools can triple the life of the tool by increasing
hardness and wear resistance and reducing friction. Carbide tools can combine three or
more layers of different coating materials, as shown in Figure 2. Coatings can also increase
the productivity of tooling by allowing operation at higher speeds without a compromise in
tool wear.
Figure 1. Most inserts are coated with different
layers of material.
Figure 2. Modern carbides have layers of
alternating coating materials.
Lesson: 10/18
Uses of Carbides
In today’s high-production machine shops, carbide tools are used constantly. When this
cutting material was first introduced during World War II, it was too brittle for most
machines. Eventually, the methods for producing carbide tools improved, and the
development of modern CNC machines provided a more sturdy setup and faster cutting
speeds. Figure 1 shows a CNC machine that uses carbide tooling.
Carbide tools work hand in hand with CNC machines. These tools are much harder than
HSS tools, and they can cut at higher temperatures and faster speeds. Nowadays, coated
carbide tools are used to machine all sorts of steels, stainless steels, and cast irons. Some
nonferrous alloys can be machined with carbides as well.
The major drawback of carbide tools is cost. Carbides are more expensive than HSS tools.
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© 2009
Tooling
U, LLC.
Rights Reserved.
They
are also
more
brittle
thanAll
high-speed
steel, and they require machines to run at high
cutting speeds. However, the effectiveness of carbide tools often justifies the extra cost.
Figure 1. CNC turning centers hold multiple
carbide insert tools in a turret.
Lesson: 10/18
Uses of Carbides
In today’s high-production machine shops, carbide tools are used constantly. When this
cutting material was first introduced during World War II, it was too brittle for most
machines. Eventually, the methods for producing carbide tools improved, and the
development of modern CNC machines provided a more sturdy setup and faster cutting
speeds. Figure 1 shows a CNC machine that uses carbide tooling.
Carbide tools work hand in hand with CNC machines. These tools are much harder than
HSS tools, and they can cut at higher temperatures and faster speeds. Nowadays, coated
carbide tools are used to machine all sorts of steels, stainless steels, and cast irons. Some
nonferrous alloys can be machined with carbides as well.
The major drawback of carbide tools is cost. Carbides are more expensive than HSS tools.
They are also more brittle than high-speed steel, and they require machines to run at high
cutting speeds. However, the effectiveness of carbide tools often justifies the extra cost.
Figure 1. CNC turning centers hold multiple
carbide insert tools in a turret.
Lesson: 11/18
Indexable Inserts
The first carbide tools were made by brazing a thin wafer of carbide onto a steel shank. Once
the tool wore out, the machinist had to remove it from its holder, regrind it, and reposition the
tool. These collective steps were time consuming.
The desire to save time led to the development of indexable inserts, which are small wafer-like
tools with several cutting edges. Once an edge wears out, the machinist removes the insert,
turns it to position a new, sharp cutting edge, and clamps the insert back in the holder. There is
no need to remove the tool from its holder for regrinding. Figure 1 shows an indexable carbide
insert.
The modern carbide tool is designed as a "throwaway" insert. These inserts are used individually
as single-point tools or collectively in multi-point tools such as the face mill in Figure 2. After
they wear out on all the cutting surfaces, carbide tools are often recycled to preserve their
expensive contents.
Figure 1. An indexable insert in its
toolholder.
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Figure 2. A face mill with multiple inserts.
Lesson: 11/18
Indexable Inserts
The first carbide tools were made by brazing a thin wafer of carbide onto a steel shank. Once
the tool wore out, the machinist had to remove it from its holder, regrind it, and reposition the
tool. These collective steps were time consuming.
The desire to save time led to the development of indexable inserts, which are small wafer-like
tools with several cutting edges. Once an edge wears out, the machinist removes the insert,
turns it to position a new, sharp cutting edge, and clamps the insert back in the holder. There is
no need to remove the tool from its holder for regrinding. Figure 1 shows an indexable carbide
insert.
The modern carbide tool is designed as a "throwaway" insert. These inserts are used individually
as single-point tools or collectively in multi-point tools such as the face mill in Figure 2. After
they wear out on all the cutting surfaces, carbide tools are often recycled to preserve their
expensive contents.
Figure 1. An indexable insert in its
toolholder.
Figure 2. A face mill with multiple inserts.
Lesson: 12/18
Nonferrous Cast Alloys
Before carbide tools gained in popularity, nonferrous cast alloys were used to machine
harder materials. Cast alloy tools cannot be softened or hardened by heat treatment. They
must be directly cast and ground to the desired shape. These materials contain percentages
of tungsten and cobalt, which tend to be expensive. Tools made from these cast alloys are
marketed under various trade names.
At room temperature, cast alloys have the same hardness as high-speed steel. However, cast
alloys maintain their hardness and wear resistance at higher temperatures. Consequently,
cutting tools made from cast alloys have a hardness that bridges the gap between tool steels
and carbide tools, as shown in Figure 1.
For the most part, cast alloy tools have been replaced by carbides. Cast alloys are difficult to
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Tooling
U, LLC. All
Rights Reserved.
manufacture,
and
they contain
expensive
elements. In most cases, carbide tools offer
improved cutting properties for less cost.
Figure 1. Cast alloys offer less hardness
than carbides.
Lesson: 12/18
Nonferrous Cast Alloys
Before carbide tools gained in popularity, nonferrous cast alloys were used to machine
harder materials. Cast alloy tools cannot be softened or hardened by heat treatment. They
must be directly cast and ground to the desired shape. These materials contain percentages
of tungsten and cobalt, which tend to be expensive. Tools made from these cast alloys are
marketed under various trade names.
At room temperature, cast alloys have the same hardness as high-speed steel. However, cast
alloys maintain their hardness and wear resistance at higher temperatures. Consequently,
cutting tools made from cast alloys have a hardness that bridges the gap between tool steels
and carbide tools, as shown in Figure 1.
For the most part, cast alloy tools have been replaced by carbides. Cast alloys are difficult to
manufacture, and they contain expensive elements. In most cases, carbide tools offer
improved cutting properties for less cost.
Figure 1. Cast alloys offer less hardness
than carbides.
Lesson: 13/18
Ceramics
In addition to high-speed steel and carbide tools, there are more "specialty" tool materials
available. Cutting tools with even greater hardness include the ceramics.
Ceramic cutting tools are harder than carbide tools. They can cut at higher speeds, and they can
handle very hard workpiece materials and high temperatures. Also, these tool materials are
available as indexable inserts, as shown in Figure 1. Ceramic tools are excellent for machining
alloy steels and cast iron parts, such as the part shown in Figure 2.
Though they are harder than carbides, ceramic tools are not effective as all-purpose tools. The
increased hardness leads to increased brittleness. Consequently, ceramics require very rigid
machines that are capable of high cutting speeds. Most ceramics are not suitable for interrupted
cutting. Nevertheless, as technology advances and better machines are manufactured, ceramic
tools may become more common in the future.
Figure 1. Ceramic inserts.
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Lesson: 13/18
Ceramics
In addition to high-speed steel and carbide tools, there are more "specialty" tool materials
available. Cutting tools with even greater hardness include the ceramics.
Ceramic cutting tools are harder than carbide tools. They can cut at higher speeds, and they can
handle very hard workpiece materials and high temperatures. Also, these tool materials are
available as indexable inserts, as shown in Figure 1. Ceramic tools are excellent for machining
alloy steels and cast iron parts, such as the part shown in Figure 2.
Though they are harder than carbides, ceramic tools are not effective as all-purpose tools. The
increased hardness leads to increased brittleness. Consequently, ceramics require very rigid
machines that are capable of high cutting speeds. Most ceramics are not suitable for interrupted
cutting. Nevertheless, as technology advances and better machines are manufactured, ceramic
tools may become more common in the future.
Figure 1. Ceramic inserts.
Figure 2. A part made of cast iron.
Lesson: 14/18
Cubic Boron Nitride
One of the most advanced cutting materials is cubic boron nitride (CBN), which is
shown in Figure 1. Cubic boron nitride is extremely hard; only diamond offers greater
hardness. Figure 2 compares the hardness of CBN to other tool materials. CBN maintains
this hardness at extremely high temperatures, from 1800°F (982°C) and higher.
CBN tools can remove the material from a workpiece at five times the rate of carbide
tools. Workpiece materials that are difficult to machine may require CBN tools. These
tools
can ©
be2009
used
to efficiently
machine
the harder grades of steel, tools steels, cast
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Tooling
U, LLC. All
Rights Reserved.
irons, and superalloys.
Lesson: 14/18
Cubic Boron Nitride
One of the most advanced cutting materials is cubic boron nitride (CBN), which is
shown in Figure 1. Cubic boron nitride is extremely hard; only diamond offers greater
hardness. Figure 2 compares the hardness of CBN to other tool materials. CBN maintains
this hardness at extremely high temperatures, from 1800°F (982°C) and higher.
CBN tools can remove the material from a workpiece at five times the rate of carbide
tools. Workpiece materials that are difficult to machine may require CBN tools. These
tools can be used to efficiently machine the harder grades of steel, tools steels, cast
irons, and superalloys.
If CBN tools are often more efficient than carbide tools, why aren’t they used more
frequently? Cubic boron nitride is very expensive. Manufacturers are forced to pay for the
extra performance. Plus, the increased hardness creates increased brittleness. CBN tools
require very rigid and powerful machines to prevent chipping or fracture of these
expensive tools.
Figure 1. CBN inserts in their matching
toolholders.
Figure 2. A comparison of hardness values for
specialty cutting tool materials.
Lesson: 15/18
Diamonds
Diamond cutting tools represent the combination of extremes. These are the hardest
available tools with excellent wear resistance. They are also the most brittle and expensive
tools as well.
Diamond is available as natural single-crystal diamond and as polycrystalline diamond
(PCD). Figures 1 and 2 show PCD inserts. Polycrystalline diamond is a manufactured product.
It is certainly not a substitute for jewelry, but it offers almost the same hardness and wear
resistance as its natural, single-crystal counterpart.
The biggest problem with diamond is its inability to machine ferrous metals. Diamond is a
special
formation
of carbon,
and
metals contain carbon as well. If diamond is used on
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U, LLC.
Allferrous
Rights Reserved.
these metals, it reverts to graphite at higher temperatures. Instead, CBN tools are best
used on ferrous metals when the hardest available tools are necessary.
Figure 1. An insert that is coated with PCD at
Lesson: 15/18
Diamonds
Diamond cutting tools represent the combination of extremes. These are the hardest
available tools with excellent wear resistance. They are also the most brittle and expensive
tools as well.
Diamond is available as natural single-crystal diamond and as polycrystalline diamond
(PCD). Figures 1 and 2 show PCD inserts. Polycrystalline diamond is a manufactured product.
It is certainly not a substitute for jewelry, but it offers almost the same hardness and wear
resistance as its natural, single-crystal counterpart.
The biggest problem with diamond is its inability to machine ferrous metals. Diamond is a
special formation of carbon, and ferrous metals contain carbon as well. If diamond is used on
these metals, it reverts to graphite at higher temperatures. Instead, CBN tools are best
used on ferrous metals when the hardest available tools are necessary.
Diamond tools do have their uses. They can effectively machine materials such as fiberglass,
plastics, and various aluminum and copper alloys. The tight tolerances necessary for optical
instruments and jewelry demand diamond cutting tools.
Figure 1. An insert that is coated with PCD at
the tip.
Figure 2. A PCD insert is often used for
finishing operations.
Lesson: 16/18
Common Tool Choices
The material of the workpiece determines the most appropriate cutting tool material. Softer
workpiece materials can be machined with the more common cutting tool materials.
However, workpiece materials that are very hard or that are unusually gummy will require a
more specialized cutting tool material with increased hardness.
The two most common tool materials are high-speed steel and coated carbides. HSS
materials are relatively inexpensive, and they create cutting tools with excellent toughness.
The common grades of plain carbon steel are effectively machined with HSS tools. Also,
HSS tools can effectively handle the built-up edge that develops when machining gummy
metals. Figure 1 shows a built-up edge on a carbide insert.
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2009
U, LLC.
All Rights
Reserved.
For
most ©
jobs
onTooling
fast, rigid
machine
tools
like the newer CNC machines, the material of
choice is usually indexable inserts made of carbide. Nowadays, most carbide tools are
coated for extra wear resistance and hardness. Though carbides are more expensive than
Lesson: 16/18
Common Tool Choices
The material of the workpiece determines the most appropriate cutting tool material. Softer
workpiece materials can be machined with the more common cutting tool materials.
However, workpiece materials that are very hard or that are unusually gummy will require a
more specialized cutting tool material with increased hardness.
The two most common tool materials are high-speed steel and coated carbides. HSS
materials are relatively inexpensive, and they create cutting tools with excellent toughness.
The common grades of plain carbon steel are effectively machined with HSS tools. Also,
HSS tools can effectively handle the built-up edge that develops when machining gummy
metals. Figure 1 shows a built-up edge on a carbide insert.
For most jobs on fast, rigid machine tools like the newer CNC machines, the material of
choice is usually indexable inserts made of carbide. Nowadays, most carbide tools are
coated for extra wear resistance and hardness. Though carbides are more expensive than
HSS tools, the increased tool life often makes them the more economical choice.
Figure 1. Gummy materials may result in a
built-up edge on the insert.
Lesson: 17/18
Specialized Tool Choices
In most cases, HSS tools or coated carbide tools are reasonable choices for the more
common machining operations. However, parts made from extra-hard or unusual materials
may require cutting tools made from a more specialized material as well.
Generally speaking, manufacturers purchase more expensive cutting tools for their extra
hardness. Tools made from ceramics, cubic boron nitride, and diamond are all harder than the
typical coated carbide. However, extra hardness comes at an extra cost. Also, cutting tools
with increased hardness are more brittle. Figure 1 shows the relationship between hardness
and toughness.
When using the more specialized types of cutting tool materials, the overall cost must justify
the more expensive choice. Brittle tools require the more expensive machines to use them
properly at higher speeds. Manufacturers can perform calculations that help them to project
the cost of using various tool materials over time. Ideally, parts should be produced with
minimum cost per cut.
Figure 1. Harder tools have less toughness
and vice versa.
Copyright © 2009 Tooling U, LLC. All Rights Reserved.
Lesson: 17/18
Specialized Tool Choices
In most cases, HSS tools or coated carbide tools are reasonable choices for the more
common machining operations. However, parts made from extra-hard or unusual materials
may require cutting tools made from a more specialized material as well.
Generally speaking, manufacturers purchase more expensive cutting tools for their extra
hardness. Tools made from ceramics, cubic boron nitride, and diamond are all harder than the
typical coated carbide. However, extra hardness comes at an extra cost. Also, cutting tools
with increased hardness are more brittle. Figure 1 shows the relationship between hardness
and toughness.
When using the more specialized types of cutting tool materials, the overall cost must justify
the more expensive choice. Brittle tools require the more expensive machines to use them
properly at higher speeds. Manufacturers can perform calculations that help them to project
the cost of using various tool materials over time. Ideally, parts should be produced with
minimum cost per cut.
Figure 1. Harder tools have less toughness
and vice versa.
Lesson: 18/18
Summary
Effective cutting tools combine a handful of valuable properties: hardness, toughness,
and wear resistance. Cutting material selection involves a careful balance between
toughness and hardness. The type of workpiece material mostly dictates the cutting
material with the best balance of these properties.
Manufacturers typically choose to use HSS tools based on their toughness and low
cost. Most HSS tools have benefited from improvements in both heat treatment and
coating methods.
Carbide tools offer some of the most effective means for machining steel at higher
speeds. Coatings are frequently used on carbide tools to reduce wear and increase
hardness. Carbide inserts help save setup time.
Ceramic cutting tools are harder than carbide tools, and they cut at higher speeds.
Cubic boron nitride can be used to machine exceptionally hard metals. Though diamond
is the hardest substance, it cannot cut ferrous metals.
Figure 1. HSS is often used to make drills, taps,
and reamers.
Copyright © 2009 Tooling U, LLC. All Rights Reserved.
Lesson: 18/18
Summary
Effective cutting tools combine a handful of valuable properties: hardness, toughness,
and wear resistance. Cutting material selection involves a careful balance between
toughness and hardness. The type of workpiece material mostly dictates the cutting
material with the best balance of these properties.
Manufacturers typically choose to use HSS tools based on their toughness and low
cost. Most HSS tools have benefited from improvements in both heat treatment and
coating methods.
Carbide tools offer some of the most effective means for machining steel at higher
speeds. Coatings are frequently used on carbide tools to reduce wear and increase
hardness. Carbide inserts help save setup time.
Ceramic cutting tools are harder than carbide tools, and they cut at higher speeds.
Cubic boron nitride can be used to machine exceptionally hard metals. Though diamond
is the hardest substance, it cannot cut ferrous metals.
Figure 1. HSS is often used to make drills, taps,
and reamers.
Figure 2. Carbide tools are often coated with
layers of special materials.
Figure 3. Ceramic inserts can be used to machine
cast iron and certain alloys.
Class Vocabulary
Definition
Copyright Term
© 2009 Tooling U, LLC. All Rights Reserved.
aluminum oxide Al2O3. A common coating element for carbide tools because it reduces abrasive wear of the tool.
brazing A joining process that is used to combine dissimilar metals at temperatures lower than welding.
Class Vocabulary
Term
Definition
aluminum oxide Al2O3. A common coating element for carbide tools because it reduces abrasive wear of the tool.
brazing A joining process that is used to combine dissimilar metals at temperatures lower than welding.
built-up edge The unwanted rough edge on a cutting tool that is created by workpiece material welding onto the tool during cutting.
Gummy metals often produce a built-up edge.
carbide The most common cutting tool material that is used to make both indexable inserts and solid cutting tools. Carbide
tools are often coated.
carbon tool steel A type of steel designed with improved wear resistance, toughness, and strength.
cast Metal that has been poured as a liquid into a mold and cooled into a solid shape.
ceramic A hard, brittle material that can withstand high temperatures. Ceramic cutting tools require high cutting speeds and
rigid machinery.
cermet Any cutting tool material consisting of ceramic particles in a metallic binder. Cemented carbide tools are a type of
cermet.
chemical vapor A special process that uses chemical reactions to coat a cutting tool at the atomic level with fine layers of coating
deposition material. Carbide tools are coated by chemical vapor deposition.
chromium A shiny, hard, steel-gray metal used in ferrous alloys to add hardness and wear resistance to steel.
CNC machine A machine controlled by a computer that runs special programs to manufacture a workpiece. CNC machines are very
rigid and are capable of fast cutting speeds.
cobalt A hard, gray, brittle metal that is a key alloying element in many nonferrous cast alloys.
crater A depression that forms on the face of a cutting tool above the cutting edge during machining.
cubic boron nitride A type of cutting tool material offering a hardness that is second only to diamond. CBN tools are very effective at
machining most steels and cast irons, but they are also very expensive.
ferrous metal A metal that contains iron.
graphite A soft, black formation of carbon. If diamond is subjected to high temperatures, it may revert to graphite.
gummy Excessively soft and difficult to machine. Gummy metals produce long, stringy chips.
hardness The ability of a metal to resist penetration and scratching.
heat treatment The heating and cooling processes used to change the structure of a material and alter its mechanical properties.
high-speed steel A common cutting tool material that is relatively inexpensive and that offers excellent toughness. Many HSS tools are
coated.
hot working The shaping of metal at temperatures above its recrystallization phase. Hot working typically leaves a tough, scaly
surface on the metal.
indexable insert A cutting bit that has multiple cutting edges. Once a cutting edge is excessively worn, it can be indexed to another
edge, or the insert can be replaced.
interrupted cut A cut in which one or more edges of the cutting tool are not in constant contact with the workpiece surface.
manganese A hard, brittle, gray-white metal used in ferrous alloys to add strength and hardness to steel and other metals.
molybdenum A hard, silvery white metal used in ferrous alloys to add toughness, creep strength, and wear resistance to steel.
Molybdenum is an effective substitute for tungsten.
nonferrous alloy An alloy that does not intentionally contain iron.
nonferrous cast alloy A type of cutting tool material that is relatively expensive and that must be directly cast into shape. Nonferrous cast
alloy tools have largely been replaced by carbide.
physical vapor A special process that bombards the surface with coating particles to produce fine layers of coating. HSS and carbide
deposition tools are coated by physical vapor deposition.
plain carbon steel The basic type of steel, which contains less than 3 percent of elements other than iron and carbon.
polycrystalline
The manufactured formation of diamond that has a hardness approaching natural diamond.
diamond
silicon A dark gray metal with a blue tinge that is added to alloys to improve hot-forming properties.
single-crystal
The natural formation of diamond that is the hardest known material. Single-crystal diamond is extremely brittle.
diamond
sintered Powdered metal that has been pressed and heated to create a solid shape. Sintered metals create very uniform
contents.
superalloy An alloy consisting of numerous alloying elements that is very expensive and designed to exhibit certain mechanical
properties at elevated temperatures.
titanium carbide TiC. A more recent material used to make carbide cutting tools that offers improved chemical stability and crater
resistance.
titanium nitride
tolerance
toughness
tungsten
TiN. A compound used to coat high-speed steel and carbide tools to reduce friction.
The unwanted but acceptable deviation from the desired dimension.
The ability of a metal to absorb energy without breaking or fracturing.
A gray metal that is very strong at elevated temperatures and is a key alloy for many cutting tools. Tungsten is
relatively expensive.
tungsten carbide The original material used to make carbide cutting tools.
wear resistance The ability of a metal to resist the gradual wearing away caused by abrasion and friction.
wrought Solid metal that has been bent, hammered, or physically formed into a desired shape.
Copyright © 2009 Tooling U, LLC. All Rights Reserved.
wrought Solid metal that has been bent, hammered, or physically formed into a desired shape.
Copyright © 2009 Tooling U, LLC. All Rights Reserved.