Surface caused by friction and abrasion and is considered normal wear. Edge breakdown is also caused by the tearing away of minute carbide particles by the built-up edge (Figure F-30). The cutting edge is usually chipped or broken in this case. Lack of rigidity, too much feed, or too slow a speed results in chipped or broken inserts (Figure F-31).
Tiny projections on the cutting edges of new inserts often break down and reduce tool life. Some machinists hone the edges of new inserts to increase tool life. However, if this practice is not carried out correctly, the tool can be damaged and actually have a lowered tool life. For this reason, some insert tool manufacturers provide prehoned carbide tools. Machine shop students should not hone the edges of their tools until they have gained more experience in the field.
Thermal shock, caused by sudden heating and cooling, is the cracking and checking of a tool that leads to breakage (Figure F-32). This condition is most likely to occur when an inadequate amount of coolant is used. It is better to machine dry if the work and tool cannot be kept flooded with coolant. If edge wear occurs:
1. Decrease the machining speed.
2. Increase the feed.
3. change to a harder , more wear-resistant carbide grage.
If the cutting edge is chipped or broken:
1. Increase the speed.
2. Decrease the feed and/or depth of cut.
3. Change to a tougher grade carbide insert.
4. Use a negative rake.
5. Hone the cutting edge before use.
6. Check the rigidity and tool overhang.
When there is a buildup on the cutting edge:
1. Increase the speed.
2. Change to a positive rake tool.
3. Change to a grade containing titanium.
For cutting edge notching (flank wear):
1. Increase the side cutting edge angle.
2. Decrease the feed.
Cratering (Figure F-33) is the result of high temperatures and pressured that cause the steel chip to weld itself to the tungsten Carbide and tear out small particles of the tool material. The addition of titanium carbide to the mixture of tungsten carbide and cobalt provides an antiweld quality, but there is some loss in abrasive wear and strength in these tools.
Surface caused by friction and abrasion and is considered normal wear. Edge breakdown is also caused by the tearing away of minute carbide particles by the built-up edge (Figure F-30). The cutting edge is usually chipped or broken in this case. Lack of rigidity, too much feed, or too slow a speed results in chipped or broken inserts (Figure F-31).
Tiny projections on the cutting edges of new inserts often break down and reduce tool life. Some machinists hone the edges of new inserts to increase tool life. However, if this practice is not carried out correctly, the tool can be damaged and actually have a lowered tool life. For this reason, some insert tool manufacturers provide prehoned carbide tools. Machine shop students should not hone the edges of their tools until they have gained more experience in the field.
Thermal shock, caused by sudden heating and cooling, is the cracking and checking of a tool that leads to breakage (Figure F-32). This condition is most likely to occur when an inadequate amount of coolant is used. It is better to machine dry if the work and tool cannot be kept flooded with coolant. If edge wear occurs:
1. Decrease the machining speed.
2. Increase the feed.
3. change to a harder , more wear-resistant carbide grage.
If the cutting edge is chipped or broken:
1. Increase the speed.
2. Decrease the feed and/or depth of cut.
3. Change to a tougher grade carbide insert.
4. Use a negative rake.
5. Hone the cutting edge before use.
6. Check the rigidity and tool overhang.
When there is a buildup on the cutting edge:
1. Increase the speed.
2. Change to a positive rake tool.
3. Change to a grade containing titanium.
For cutting edge notching (flank wear):
1. Increase the side cutting edge angle.
2. Decrease the feed.
Cratering (Figure F-33) is the result of high temperatures and pressured that cause the steel chip to weld itself to the tungsten Carbide and tear out small particles of the tool material. The addition of titanium carbide to the mixture of tungsten carbide and cobalt provides an antiweld quality, but there is some loss in abrasive wear and strength in these tools.
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