CUTTING TOOL SELECTION

1. CUTTING- TOOL MATERIALS
AND CUTTING FLUIDS
Presented by
NAME : S.ARUNKUMAR
YEAR : IV YEAR
DEPARTMENT : MECHANICAL ENGINEERING
COLLEGE : SUDHARASAN ENGG COLLEGE

2. Cutting-Tool Materials and Cutting Fluids

3. Introduction
• Cutting Tool Characteristics:
1. Maintaining hardness, strength, and wear resistance at elevated
temperatures. This property ensures that the tool does not
undergo any plastic deformation and thus retains its shape and
sharpness.
2. Toughness and impact strength (or mechanical shock resistance),
so that impact forces on the tool that are encountered repeatedly
in interrupted cutting operations or forces due to vibration and
chatter during machining do not chip or fracture the tool.
3. Thermal Shock resistance to withstand the rapid temperature
cycling encountered in interrupted cutting.
4. Wear resistance so that an acceptable tool life is obtained before
replacement is necessary.
5. Chemical stability to avoid or minimize any adverse reactions,
adhesion, and tool-chip diffusion.

4. Introduction
• Tool Materials Categories:
1. High-speed steels
2. Cast-cobalt alloys
3. Carbides
4. Coated tools
5. Alumina-based ceramics
6. Cubic boron nitride
7. Silicon-nitride-base ceramics
8. Diamond
9. Whisker-reinforced materials

5. Hardness of Cutting
Tool Materials as a
Function of
Temperature
Figure 22.1 The hardness of
various cutting-tool materials as a
function of temperature (hot
hardness). The wide range in
each group of materials is due to
the variety of tool compositions
and treatments available for that
group.

6. General Properties of Tool Materials

7. General Properties of Tool Materials
• The properties listed in the first column are useful in
determining desirable tool-material characteristics for a
particular application. For example,
• Hardness and strength are important with respect to the
mechanical properties of the workpiece material to be
machined.
• Impact strength is important in making interrupted cuts in
machining, such as in milling.
• Melting temperature of the tool material is important as
compared to the temperatures developed in the cutting zone.
• The physical properties of thermal conductivity and coefficient
of thermal expansion are important in determining the
resistance of the tool materials to thermal fatigue and shock.

8. Operating Characteristics of
Cutting-Tool Materials

9. HIGH SPEED STEELS
• Good wear resistance, relatively inexpensive
• Because of their toughness and high resistance to fracture, HSS are
especially suitable for:
1. high +ve rake-angle tools
2. interrupted cuts
3. machine tools with low stiffness that are subjected to vibration
and chatter.
• HSS tools are available in wrought, cast, and sintered forms
• They can be coated for improved performance
• HSS tools may also be subjected to:
a. surface treatments for improved hardness and wear resistance
such as case hardening for improved hardness and wear resistance
b. steam treatment at elevated temperatures to develop a black oxide
layer for improved performance including a reduced tendency for
built-up edge formation

10. HIGH SPEED STEELS
• Two basic types of HSS:
1. Molybdenum (M series)
• Up to about 10% Mo, with Cr, Vn, W, Co as alloying elements
2. Tungsten (T series)
• 12% -18% W, with Cr, Vn, and Co as alloying elements
• M series generally has higher abrasion resistance than T series,
undergoes less distortion during heat treating, and is less
expensive

11. HIGH SPEED STEELS
• Example 22.1: List the major alloying elements in HSS and
describe their effects in cutting tools
• Chromium improves toughness, wear resistance, and high-
temperature strength.
• Vanadium improves toughness, abrasion resistance, and hot
hardness.
• Tungsten and cobalt have similar effects, namely, improved
strength and hot hardness.
• Molybdenum improves wear resistance, toughness, and high-
temperature strength and hardness.

12. CAST-COBALT ALLOYS
• 38%-53% Co, 30%-33% Cr, and 10%-20%W
• High hardness, good wear resistance, can maintain their
hardness at elevated temperatures
• They are not as tough as HSS and are sensitive to impact forces
Stellite Tools
• These alloys are cast and ground into relatively simple tool
shapes.
• used only for special applications that involve deep continuous
roughing cuts at relatively high feeds and speeds, as much as
twice the rates possible with HSS

13. CARBIDES
• The previous tools possess the required toughness, impact strength,
and thermal shock resistance, but they also have important
limitations, particularly with respect to strength and hot hardness.
• Carbides have:
a. Hardness over a wide range of temperatures.
b. high elastic modulus and thermal conductivity.
c. low thermal expansion.
Tungsten carbide (WC):
• Composite material consisting of WC particles bonded together in
a cobalt matrix
• Manufactured with powder-metallurgy techniques
• WC particles, 1-5 μm in size
• As Co content increases, the strength, hardness, and wear
resistance of WC decrease, while its toughness increases because
of the higher toughness of cobalt

14. CARBIDES
Titanium Carbide (TiC):
• Higher wear resistance than WC but is not as tough
• With a nickel-molybdenum alloy as the matrix, TiC is suitable
for machining hard materials, mainly steels and cast irons, and
for cutting at speeds higher than those for WC.

15. COATED TOOLS
• Because of their unique properties, such as lower friction and
higher resistance to cracks and wear, coated tools can be used
at high cutting speeds, reducing both the time required for
machining operations and costs.
• Coated tools can have tool lives 10 times longer than those of
uncoated tools.

16. Relative Time Required to Machine
with Various Cutting-Tool Materials
Figure 22.6 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.

17. COATED TOOLS - Coating Materials
Titanium Nitride coating (gold in color):
• low friction coefficient, high hardness, resistance to high
temp, and good adhesion to the substrate.
• perform well at higher cutting speeds and feeds
• Flank wear is significantly lower than that of uncoated tools
• do not perform as well at low cutting speeds because the
coating can be worn off by chip adhesion
Titanium Carbide coatings:
• on tungsten-carbide inserts have high flank-wear resistance
in machining abrasive materials

18. Typical Wear Patterns on High-
Speed-Steel Uncoated and
Titanium-Nitride Coated Tools
Figure 22.7 Schematic illustration of typical wear patterns of
high-speed-steel uncoated and titanium-nitride coated tools.
Note that flank wear is significantly lower for the coated tool.

19. COATED TOOLS - Coating Materials
Ceramics Coatings:
• Chemical inertness
• Low thermal conductivity
• Resistance to high temperature
• Resistance to flank and crater wear
• Most commonly used ceramic coating aluminum oxide
(Al2O3). However oxide coating generally bond weakly to
the substrate.

20. COATED TOOLS - Coating Materials
Multiphase Coatings:
•Functions of coatings:
1.TiN: low friction
2.Al2O3: high thermal stability
3.TiCN: fiber reinforced with a good balance of resistance to
flank and crater wear for interrupted cutting
4.A thin carbide substrate: high fracture toughness
5.A thick carbide substrate: hard and resistant to plastic
deformation at high temperatures.