Wear is caused by simultaneous mechanical and thermal stress on the cutting wedge. The major causes are as follows:
a = Diffusion
b = Mechanical abrasion
c = Scaling/oxidation
d = Built-up edge formation
Dark grey = cutting speed (vc)
Red = feed (f)
Light grey = cutting depth (ap)
With the increasing cutting temperature, both thermal causes of wear (oxidation and diffusion) prevail.
The cutting temperature and wear depend heavily upon the machining conditions.
Applying hard material layers to carbide tools reduces wear. The advantages of a hard material layer are a reduction in
Abrasion on the flank: normal wear after a certain period of operation.
| Possible causes | Solution |
|---|---|
| Cutting speed too high | Reduce cutting speed |
| Wear resistance | Select a carbide grade with a higher wear resistance |
| Feed not adapted to application | Bring feed into the right relationship with cutting speed and cutting depth (increase feed) |
Increased mechanical stress on the cutting edge may result in carbide particles breaking off.
| Possible causes | Solution |
|---|---|
| Grade with too high a wear resistance | Use tougher grade |
| Vibration | Use negative cutting edge geometry with a chip breaker |
| Feed or cutting depth is too high | Adapt cutting values |
| Interrupted cut | Use tougher grade or more stable geometry |
| Chip stroke | Use different chip breaker |
No cracks at 90° to the cutting edge.
| Possible causes | Solution |
|---|---|
| Changing cutting temperature, thermal shock |
Use grade resistant to cracking at right angles to the cutting edge |
| Incorrect cooling | Use a generous amount of cooling lubricant or dry mill |
| High tensile materials | Select suitable cutting parameters |
| Cutting speed too high | Reduce cutting speed |
Material builds up if the chip does not flow correctly due to the cutting temperature being too low.
| Possible causes | Solution |
|---|---|
| Cutting speed too low | Increase cutting speed |
| Rake angle too small | Increase rake angle |
| Incorrect cutting material | Use TiN coating |
| Missing coolant/lubrication | Use thicker emulsions |
Necking at maximum depth of cut.
| Possible causes | Solution |
|---|---|
| Work-hardening materials (e.g. super alloys) | Reduce cutting speed |
| Casting and forging skin | Use smaller setting angle |
| Burr formation | Change the working position of the milling cutter |
If a cutting insert is overloaded, insert breakage may occur.
| Possible causes | Solution |
|---|---|
| Overload of carbide grade | Use tougher cutting material or adapt cutting parameters |
| Lack of stability | Use chamfer for edge protection |
| Wedge angle too small | Increase rounding of cutting edge |
| Excessive notch wear | Use more stable geometry and adapt cutting parameters |
| Shock type changes in cutting force | Reduce feed |
The outgoing hot chip is causing cratering of the cutting insert on the clamping surface.
| Possible causes | Solution |
|---|---|
| Cutting speed, feed or both are too high | Reduce cutting speed and/or feed |
| Rake angle too low | Use different geometry |
| Carbide grade does not have enough wear resistance | Use more wear-resistant grade |
| Incorrectly supplied coolant | Increase quantity and/or pressure of coolant, check supply |
High machining temperature with simultaneous mechanical stress can lead to plastic deformation.
| Possible causes | Solution |
|---|---|
| Working temperature too high, softening of the base material | Reduce cutting speed |
| Damage to the coating | Select a carbide grade with a higher wear resistance |
| Chip breaker too narrow | Use different geometry |