For the purpose of controlling tool wear one must understand the various mechanisms of wear, that the cutting tool undergoes under different conditions.

The common mechanisms of cutting tool wear are:

1] Mechanical wear.

• Thermally insensitive type; like abrasion, chipping and delamination.

• Thermally insensitive type; like adhesion, fracturing, flaking etc.

2] Thermochemical wear.

• Macro-diffusion by mass dissolution.

• Micro-diffusion by atomic migration.

3] Chemical wear.

4] Galvanic wear.

In diffusion wear the material from the tool at its rubbing surfaces, particularly at the rake surface gradually diffuses into the following chip wither in bulk or atom by atom when the tool material has chemical affinity or solid solubility towards the work material. The rate of such tool increases with the increase in temperature at the cutting zone.

Diffusion wear becomes predominant when the cutting temperature becomes very high due to high cutting velocity and high strength of the work material. Chemical wear, leading to damages like grooving wear may occur if the tool material is not enough chemically stable against the work material and/or the atmospheric gases.

Galvanic wear, based on electrochemical dissolution, seldom occurs when both the work tool materials are electrically conductive, cutting zone temperature is high and the cutting fluid acts as an electrolyte. The usual pattern or geometry o wear of turning and face milling inserts are typically shown in Figure.1 (a and b) and Fig.2 respectively.

In addition of ultimate failure o the tool, the following effects are also caused by the growing tool – wear:

• Increase in cutting forces and power consumption mainly due to the principal flank wear.

• Increase in dimensional deviation and surface roughness mainly due to wear of the tool tips and auxiliary flank wear ($V_s$)

• Odd sound and vibration.

• Worsening surface integrity.

• Mechanically weakening of the tool tip.