Tool life is measured by the time period from when a tool starts cutting until failure or until it needs resharpening. Tool life can be measured in units of time, number of pieces cut, volume of material removed, or length of cut. Tools typically fail due to high temperatures, mechanical impacts, or gradual wear. Wear occurs on the flank and crater faces of tools and is caused by abrasion, diffusion, electrochemical reactions, and other mechanisms. Factors like cutting speed, workpiece properties, tool geometry, and cooling influence tool life.

1. Presented by:-
Mobashir Kashani
(121116048)
Shubham Khandelwal
(121116054)

2. Tool Life
 Useful cutting life of tool expressed in time
 Time period measured from start of cut to failure
of the tool
 Time period between two consecutive
resharpenings or replacements.

3. Ways of measuring tool life
 No. of pieces of work machined
 Total volume of material removed
 Total length of cut.
 Limiting value of surface finish
 Increase in cutting forces
 Dimensional accuracy
 Overheating and fuming
 Presence of chatter

4. Modes of tool failure
1. Temperature failure
a. Plastic deformation of Cutting Edge (CE) due to
high temp
b. Cracking at the CE due to thermal stresses.
2. Rupture of the tool point
a. Chipping of tool edge due to mechanical impact
b. Crumbling of CE due to Built up Edge (BUE)
3. Gradual wear at tool point
a. Flank wear
b. Crater wear

5. Tool wear
 Tool wear causes the tool to lose its original
shape- ineffective cutting
 Tool needs to be resharpened

6. Causes of Tool Wear
1. Attrition wear
2. Diffusion wear
3. Abrasive wear
4. Electrochemical wear
5. Chemical wear
6. Plastic deformation
7. Thermal cracking

7. Attrition wear
 At low cutting speeds
 Flow of material past cutting edge is irregular and
less stream lined
 BUE formed and discontinuous contact with the
tool
 Fragments of tool are torn from the tool surface
intermittently
 High
 Slow and interrupted cutting
 Presence of vibrations
 Found in carbide tools at low cutting speeds

8. Diffusion wear
 Diffusion of metal & carbon atoms from the tool
surface into the w/p & chip.
 Due to
 High temp
 High pressure
 Rapid flow of chip & w/p past the tool
 Diffusion rate depends on the metallurgical
relationship
 Significant in carbide tools.

9. Abrasive wear
 Due to
 Presence of hard materials in w/p material.
 Strain hardening induced in the chip & w/p due to
plastic deformation.
 Contributes to flank wear
 Effect can be reduced by fine grain size of the
tool & lower percentage of cobalt

10. Electrochemical wear
 When ions are passed b/w tool & w/p
 Oxidation of the tool surface
 Break down of tool material @ chip tool interface

11. Chemical wear
 Interaction b/w tool and work material
 Plastics with carbide tools
 Cutting fluid

12. Plastic Deformation
 When high compressive stresses acts on tool
rake face- tool deformed downways – reduces
relief angle
 Modifies tool geometry and accelerates other
wear processes

13. Thermal cracking
 Due to cyclic thermal stresses at cutting edge
 Comb cracks
 Transverse cracks
 Chipping of tool

14. Geometry of tool wear
 Flank wear (edge wear)
 Crater wear (face wear)

15. Flank Wear
 Tool slides over the surface of the work piece and
friction is developed
 Due to Friction and abrasion.
 Adhesion between work piece & tool- BUE
 Starts at CE and starts widening along the
clearance face
 Independent of cutting conditions and tool / work
piece materials
 Brittle and discontinuous chip
 Increases as speed is increased.

16.  Primary stage rapid
wear due to very high
stress at tool point
 Wear rate is more or
less linear in the
secondary stage
 Tertiary stage wear
rate increases rapidly
resulting in
catastrophic failure.

17. Crater wear
 Direct contact of tool and w/p
 Forms cavity
 Ductile materials – continuous chips
 Initiates rapid rupture near to nose
 Leads to
 weakening of the tool
 Increase in cutting temp
 Cutting forces & friction

18. Measurement of tool life
 Time for Total destruction in case of HSS or time
to produce 0.75 mm wear for carbide tools
 Tool life expressed by Taylor’s eqn
 VTb = C
 V = cutting speed in cm/min
 T= tool life in min
 b= const= 0.1 for HSS
 C= 50 for HSS
 Cemented carbide : b=0.125, C=100
 Tool life expressed in volume of metal removed
 L = TVfd

19. Measurement of tool life
 Diamond Indentor technique
 Radioactive techniques
 Test at elevated cutting speeds
 Facing tests
 Test with low wear criterion

20. Factors affecting tool life
1. Cutting speed
2. Physical properties of w/p
3. Area of cut
4. Ratio of feed to depth of cut
5. Shape and angles of tool
6. Tool material and its heat treatment
7. Nature and quantity of coolants
8. Rigidity of tool and wp