Friction and Deformation Behaviors of ~60-μm Stainless Steel Micro-balls for Application in Small Precision Devices

The friction and deformation behaviors of ~60-μm-diameter stainless steel micro-balls were assessed under various rolling conditions against Si specimens. In the friction tests, the micro-balls were placed between a stationary flat silicon specimen on the top and a flat or grooved silicon specimen at the bottom that was made to move in a reciprocating motion. Rectangular- and V-shaped grooves were fabricated on the silicon specimen by a photolithographic process, and the effect of groove shape on the frictional behavior of the micro-balls was investigated. Friction coefficient of 0.01 could be successfully achieved when proper rolling was attained. It was found that the number of micro-balls was not a critical factor as long as more than three balls were placed between the two flat Si specimens. Furthermore, rectangular-shaped groove resulted in lower friction than V-shaped groove. This was due to severe deformation of the micro-ball which led to increase in the contact area when the V-shaped groove was used. The results of this work were expected to aid in the development of miniature bearings for applications in small precision systems.