Change of Contact Condition in Multiple-Stage Cold Forging

In multiple-stage cold forging using a parts-former machine, lubricant oil is needed on the ends of billets after cropping. The oil is trapped by a squeeze action and it is sometimes supplied from valleys of roughness serving as oil pits. Naturally, the surface roughness on the billets must affect lubrication, but data on surfaces of practical billets is not sufficient for estimating the lubrication condition for designers of tools and processes. The authors sampled some practical billets in two typical kinds of multiple-stage cold forging. Changing distributions of surface roughness and the contact ratios are exemplified.