Mechanism of Wear

Mechanism of Wear

Mechanism of Wear - The fundamental nature of the mechanism of wear can be very different under different conditions. In metal cutting the following basic causes of wear are known.

(i) In adhesion wear, the wear is caused by the fracture of welded asperity junctions between the two metals. In metal cutting, junctions between the chip and tool materials are formed as part of the friction mechanism; when these junctions are fractured, small fragments of tool material can be torn out and carried away on the underside of the chip or on the new workpiece surface.

(ii) In abrasion wear, the wear occurs when hard particles on the underside of the chip pass over the tool face and remove tool material by mechanical action.

These hard particles may be highly strain hardened fragments of an unstable built up edge, fragments of the hard tool material removed by adhesion wear or hard constituents in the work material.

(iii) Diffusion wear, occurs by solid state diffusion mechanism in which atoms in a metallic crystal lattice move from a region of high atomic concentration to one of low concentration.

In metal cutting, where intimate contact between the work and tool materials occurs and high temperatures exist, diffusion can occur where atoms move from the tool material to work material.

This process, which takes place within a very narrow reaction zone at the interface between the workpiece and tool materials, causes a weakening of the surface structure of the tool.