Chapter (1)

CUTTING TOOL MATERIALS

 TOPICS :

„ Introduction „ Cubic Boron Nitride

„ Carbon and medium „ Silicon Nitride
alloy steels based ceramics
„ High speed steels „ Diamond
„ Cast-cobalt alloys „ Whisker-reinforced
„ Carbides tool materials
„ Coated tools
„ Alumina-based
ceramics
 Introduction:
Characteristics of cutting tool :
„ Hardness (resistance to wear)

„ Hot hardness (capacity to retain hardness at high

temperatures
„ Toughness (resistance to impact forces on tool in
interrupted operations)
„ Chemical stability or inertness (to avoid adverse
reactions)
 Cutting tool materials

„ Carbon & medium alloy steels

„ High speed steels
„ Cast-cobalt alloys
„ Carbides
„ Coated tools
„ Alumina-based ceramics
„ Cubic boron nitride
„ Silicon-nitride-base ceramics
„ Diamond
„ Whisker-reinforced materials
Carbon and Medium alloy steels :

„ Oldest of tool materials

„ Used for drills taps, broaches, reamers
„ Inexpensive, easily shaped, sharpened
„ No sufficient wear resistance
„ Limited to hand tools and low cutting speed
operation. (Red hardness temp.: 200° C)

High speed steels (HSS)

„ Hardened to various depths
„ Good wear resistance
„ Suitable for high positive rake angle tools
Two basic types of HSS
„ Molybdenum (M-series)
„ Tungsten (T-series)

M-series (6-6-4-2): Contains 6% molybdenum, 6% tungsten,

4% chromium, 2% vanadium & cobalt
„ Higher, abrasion resistance
„ H.S.S. are majorly made of M-series

T-series (18-4-1): Contains 18 % tungsten, 4% chromium, 1%

vanadium & cobalt
„ undergoes less distortion during heat treating
„ 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 (Red hardness temp.: 650° C)

 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
 Carbides :

(Hot hardness temp.: 1000° C)

„ These carbides are also known as cemented or

sintered carbides
„ High elastic modulus, thermal conductivity
„ Low thermal expansion

2-groups of carbides used for machining operations

„ tungsten carbide

„ titanium carbide
 Tungsten Carbide

„ Composite material consisting of tungsten-carbide particles

bonded together

„ Alternate name is cemented carbides

„ Manufactured with powder metallurgy techniques

„ Particles 1-5 µm in size are pressed & sintered to desired

shape in a H2 atmosphere furnace at 1550°C

„ Amount of cobalt present affects properties of carbide tools

„ As cobalt content increases – strength, hardness & wear

resistance increases
 Titanium carbide

„ Titanium carbide has higher wear resistance

than tungsten carbide

„ Nickel-Molybdenum alloy as matrix – Tic

suitable for machining hard materials

„ Steels & cast irons

„ Speeds higher than those for tungsten

carbide
Cutting tool materials – HSS alloying
Element Properties

Tungsten Increases hot hardness

Hard carbides formed, improving abrasion resistance

Molybdenum Increases hot hardness

Hard carbides formed, improving abrasion resistance

Chromium Depth hardenability during heat treat

Hard carbides formed, improving abrasion resistance
Some corrosion resistance

Vanadium Combines with carbon for wear resistance

Retards grain growth for better toughness

Cobalt Increases hot hardness, toughness

Carbon Hardening element

Forms carbides
Inserts
 Inserts

„ Individual cutting tool with severed cutting points

„ Clamped on tool shanks with locking mechanisms
„ Inserts also brazed to the tools
„ Clamping is preferred method for securing an insert
„ Carbide Inserts available in various shapes-Square,
Triangle, Diamond and round
„ Strength depends on the shape
„ Inserts honed, chamfered or produced with negative
land to improve edge strength
Insert Attachment

Fig : Methods of
attaching inserts to
toolholders : (a)
Clamping and (b)
Wing lockpins. (c)
Examples of inserts
attached to
toolholders with
threadless lockpins,
which are secured
with side screws.
Edge Strength
Fig : Relative edge
strength and
tendency for chipping
and breaking of
inserts with various
shapes. Strength
refers to the cutting
edge shown by the
included angles.

Fig : edge preparation of

inserts to improve edge
strength.
 Chip breakers:
Purpose :
„ Eliminating long chips

„ Controlling chip flow during machining

„ Reducing vibration & heat generated

„ Selection depends on feed and depth

of cut, work piece material and type
of chip produced during cutting
 Coated tools :

- High strength and toughness but generally

abrasive and chemically reactive with tool
materials

- (Hot hardness temp.: 1100° C)

Unique Properties :
¾ Lower Friction

¾ High resistance to cracks and wear

¾ High Cutting speeds and low time & costs

¾ Longer tool life

Coating materials
„ Titanium nitride (TiN)
„ Titanium carbide (Tic)
„ Titanium Carbonitride (TicN)
„ Aluminum oxide (Al2O3)
„ Diamond coating
Thickness range: 2-15 µm (80-600 µin)

Techniques used :
„ Chemical –vapor deposition (CVD)
Plasma assisted CVD
„ Physical-vapor deposition(PVD)
„ Medium –temperature chemical- vapor
deposition(MTCVD)
 Properties for Group of Materials

Fig : Ranges of properties

for various groups of
tool materials.
 Cutting tool Characteristics for coating :

„ High hardness
„ Chemical stability
„ Low thermal conductivity
„ Good bonding
„ Little or no Porosity

Titanium nitride (TiN) coating :

„ Low friction coefficients
„ High hardness
„ Resistance to high temperatures
„ Good adhesion to substrate
„ High life of high speed-steel tools

Titanium carbide (TiC) coating:

„ Titanium carbide coatings on tungsten-carbide inserts have high flank
wear resistance.
 Ceramics :

„ Low thermal conductivity ,resistance ,high temperature

„ Resistance to flank wear and crater wear
„ Ceramics are suitable materials for tools
„ Al2O3 (most commonly used)

Multi Phase Coatings :

„ First layer –Should bond well with substrate
„ Outer layer – Resist wear and have low thermal
conductivity
„ Intermediate layer – Bond well & compatible with both
layers
„ Coatings of alternating multipurpose layers are also
formed.
Multiphase Coatings

Fig : Multiphase coatings on a

tungsten-carbide
substrate. Three
alternating layers of
aluminum oxide are
separated by very thin
layers of titanium nitride.
Inserts with as many as
thirteen layers of
coatings have been
made. Coating thick
nesses are typically in
the range of 2 to 10 µm.
 Diamond Coated tools :

„ Use of Polycrystalline diamond as a coating

„ Difficult to adhere diamond film to substrate
„ Thin-film diamond coated inserts now
commercially available
„ Thin films deposited on substrate with PVD & CVD
techniques
„ Thick films obtained by growing large sheet of
pure diamond
„ 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)
¾ 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
steels
„ Xeon – ion implantation of tools as under development
 Alumina-Based ceramics:
„ Cold-Pressed Into insert shapes under high pressure and
sintered at high temperature
„ High Abrasion resistance and hot hardness (1200°C)
„ Chemically stable than high speed steels & carbides
„ So less tendency to adhere to metals
„ Good surface finish obtained in cutting cast iron and steels
„ Negative rake-angle preferred to avoid chipping due to poor
tensile strength

Cermets, Black or Hot- Pressed :

„ 70% aluminum oxide & 30 % titanium carbide
„ cermets(ceramics & metal)
„ Cermets contain molybdenum carbide, niobium carbide and
tantalum carbide.
 Cubic boron Nitride ( CBN ) :
„ Made by bonding (0.5-1.0 mm) Layer of poly crystalline cubic
boron nitride to a carbide substrate by sintering under
pressure
„ While carbide provides shock resistance CBN layer provides
high resistance and cutting edge strength
„ Cubic boron nitride tools are made in small sizes without
substrate

Fig : (a) Construction of a polycrystalline cubic boron nitride or a diamond layer on a tungsten-carbide insert.
(b) Inserts with polycrystalline cubic boron nitride tips (top row) and solid polycrystalline CBN inserts
(bottom row).
 Silicon-Nitride based ceramics (SiN)

„ They consists various addition of Aluminum Oxide ythrium oxide,

titanium carbide

„ SiN have toughness, hot hardened & good thermal – shock

resistance

„ SiN base material is Silicon

„ High thermal & shock resistance

„ Recommended for machining cast iron and nickel based super

alloys at intermediate cutting speeds
 Diamond :

„ 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
important
„ Low rake angle used for string cutting edge
 Polycrystalline-Diamond ( PCD ) Tools:

„ Used for wire drawing of fine wires

„ Small synthesis crystal fused by high pressure and
temperature
„ Bonded to a carbide substrate
„ Diamond tools can be used fir 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
operations
 Whisker –reinforced & Nanocrystalline
tool materials

New tool materials with enhanced properties :

„ High fracture toughness

„ Resistance to thermal shock
„ Cutting –edge strength
„ Hot hardness
 Whiskers used as reinforcing fibers :

„ Examples: Silicon-nitride base tools reinforced

with silicon-carbide (SiC)

„ Aluminum oxide based tools reinforced with

silicon-carbide with ferrous metals makes SiC-
reinforced tools

„ Progress in nanomaterial has lead to the

development of cutting tools

„ Made of fine grained structures as (micro grain)

carbides
 Cutting-Tool Reconditioning

„ When tools get worned, they are reconditioned for further

use
„ Reconditioning also involves recoating used tools with
titanium nitride
Web site:

http://www.staff.zu.edu.eg/awafa/