Following are the factors affecting tool life.
- Cutting speed
- Feed and Depth of cut
- Tool material
- Tool geometry
- Work material
- Nature of cut
- The rigidity of the machine tool work system
- Cutting fluids
The most important variable influencing tool life is cutting speed.
Tool life decreases with cutting speed according to the relationship v r’ = C.
Feed and Depth of cut
Another tool life equation proposed includes feed and depth of cut in addition to cutting speed V.
Tool materials that can withstand high cutting temperatures while retaining mechanical properties and geometry will have a longer life.
High hardness gives the tool good wear resistance but reduces its toughness and shock resistance.
Higher thermal shock resistance, thermal conductivity, and low coefficient of thermal expansion materials result in longer tool life.
Tool life is affected by the geometry of the tool in the following ways:
- A greater positive rake angle reduces cutting forces and heat generation, resulting in longer tool life.
- However, increasing the rake angle has an inverse effect on tool strength and reduces the area of heat conduction, potentially leading to early tool failure.
- Relief or clearance angle helps to increase tool life by preventing rubbing of the tool flank’ against the work. Larger angles, once again, mechanically weaken the tool.
- Cutting edge angles have a similar effect on tool life.
- The nose radius improves the surface finish and tool strength. As a result, tool life is extended.
Harder work materials require more power and wear on the tool, resulting in shorter tool life. Tool wear is increased by impurities or hard constituents in the work material. Scales and oxide layers present on the work material are highly abrasive and reduce tool life. Pure metals tend to adhere to the tool surface, resulting in high friction and wear rates and shorter tool life.
Nature of cut
When compared to continuous cutting, intermittent cutting reduces tool life. Shock loading caused by work surface discontinuities or hard spots reduces tool life.
The rigidity of the machine tool work system
During the machining operation, both the machine tool and the workpiece should remain rigid.
Any vibrations produced may result in intermittent cutting, variations in cutting forces, and shock rather than continuous cutting, reducing tool life.
Cutting fluids reduce forces and transfer heat away from the tool, extending tool life; moreover, cutting fluids also aid in the reduction of friction, the improvement of surface finish, and the removal of chips.
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