Experimental study on size effect of dry friction in meso/micro-upsetting process

In this work, the cylindrical upsetting experiments of pure copper under meso and micro scale were carried out, and the effects of specimen size, grain size, and tool surface roughness on dry friction in meso/micro-forming process were studied. The results show that even in the case of no lubrication, the so called size effect on friction behavior still exists in meso/micro-upsetting process. In order to study the mechanism of the size effect on friction behavior, the ratio of specimen size D to grain size d (t = D/d) is introduced as a scale parameter. A higher friction factor on the contact surface is found as the ratio t is higher in the experimental results. The effects of tool surface roughness on friction behavior were also studied through the upsetting tests under disks in different surface roughness in our work. And a rising trend of friction factor on the contact surface is observed with the increasing of tool surface roughness. The increase ratio of friction factor is chosen to study the effects of tool surface roughness on friction. It turns out that the increase ratio of friction factor is larger for the smaller specimen, and the degree of friction size effect decreases with the increasing of tool surface roughness.