Types of wear and causes during bar peeling

Causes of wear

Wear is caused by simultaneous mechanical and thermal stress on the cutting wedge. The major causes are as follows:

  • Mechanical abrasion
  • Shearing of pressure-welded points
  • Oxidation processes
  • Diffusion

a = Diffusion

b = Mechanical abrasion

c = Scaling/oxidation

d = Built-up edge formation

Dark grey = cutting speed (ap)

Red = feed (f)

Light grey = cutting depth (vc)

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.

How a hard material layer works

Applying hard material layers to carbide tools reduces wear. The advantages of a hard material layer are a reduction in

  • Friction
  • Heating
  • Oxidation
  • Diffusion

Types of wear

Flank wear

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)

Edge breakages

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

Crack at right angles to the cutting edge

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

Built-up edge formation

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

Notch wear

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

Insert breakage

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

Crater wear

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

Plastic deformation

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