1. UNIT-I THEORY OF METAL CUTTING

2. Tool Wear (Failure) Tool wear occurs due to factors such as: Forces
Temperatures
Sliding action b/w tool & work piece
They are classified as
Face wear
Flank wear
Nose wear
Face wear
Flank wear
Nose wear

3. Tool Wear (Failure) Face wear
Friction caused when chip flows on face of tool
Cavity is formed – crater wear
If cavities are increased, tool will be broken
Flank wear
Caused by abrasion
Occurs on the side & flanks of the cutting tool
Cannot produce finished surface
Nose wear
Occurs at the nose of the tool
If nose wear, friction b/w the tool & work piece will be more
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4. TOOL –LIFE
Tool-life is the time elapsed between two successive grinding of a cutting tool. Tool-life may be measured in the following ways:
Number of pieces machined between tool sharpening.
Time of actual operation, viz., the time the tool is in contact with the job.
Total time of operation.
Equivalent cutting speed.
Volume of material removed between tool sharpening.

5. FACTORS AFFECTING TOOL LIFE
Cutting speed
Depth of cut
Tool geometry
Type of machining
Coolant
Feed
Tool material
Work piece material
Rigidity of machine
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6. Tool Wear & Failure - Factors
Cutting speed
When machining with high speed, high temp. will be developed b/w work piece & tool
Hardness will be reduced
Feed
Life of tool depends on the amount of metal removed per minute
Depth of cut
Correct depth should be used to increase tool life
Tool material
Tool life depends on the tool material.
Carbide tools have more life than high speed steel & carbon steel.

7. Tool Wear & Failure - Factors
Tool geometry
Geometry should be perfect
Large rake angle reduce the tool cross section
Head absorbing area will also be reduced
Increase in nose radius improves tool life
Rigidity of machine
Strongly fitted tool on rigid m/c will have more life
Coolant
Coolant absorb heat produced during machining
It reduces friction & temp
Tool life will be increased

8. MACHINABILITY
Machinability depends on: 1. Chemical composition of work piece material. 2. Micro-structure. 3. Mechanical properties. 4. Physical properties. 5. Cutting conditions.

9. Evaluation of machinability
1. Tool-life between grinds. 2. Value of cutting forces. 3. Quality of surface finish. 4. Form and size of chips. 5. Temperature of cutting. 6. Rate of cutting under a standard force. 7. Rate of metal removal.

10. SURFACE FINISH
Cutting speed
Feed
Depth of cut