Tribological Factors

A finished workpiece is often designed to be part of a moving mechanism where wear or friction might become an important issue. Finishing operations therefore should to be selected based on their consequences on the wear resistance of the parts, their friction coefficient, their hardness, and so on (Ref 15, 16).

Wear. The influence of finishing method on the run-in of AISI A10 and AISI 4140 steel cams has been demonstrated (Ref 44). The wear mechanisms involved were found to be strongly dependent on the surface finishing method used (milling, grinding, ion nitriding, or blasting) as well as the microstructure of the steel. Interestingly, this study also clearly demonstrated the advantage of computer-controlled finishing machines over their analog counterparts as far as wear is concerned.

Friction. A study of the break-in period of automotive components demonstrated that honing and lapping operations can reduce the initial friction of cylinder liners and cam shafts (Ref 45).

Hardness. As many studies have demonstrated (e.g., Ref 17), surface hardening resulting from a finishing operation can lead to significant improvement in the fatigue life of a component.

A good understanding of the micromechanisms associated with a finishing technique might bring some significant mechanical advantages. Of course, a tradeoff might have to be made. In Ref 44, for instance, the lower wear of nitrided and bead-blasted cams had to be judged against a decrease in their dynamic performance, compared with that of ground cams.

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