Die-Workpiece Interfacial Behaviors in Axisymmetric Forging Processes with Flat Dies

A new piezo-viscous, average flow model combined with an advanced slab method is used to investigate the lubrication in axisymmetric forging processes with flat dies. Interactions between lubricant transport and surface roughness are studied. Influence of friction on the outward motion of the workpiece is also considered. It is shown that the lubricant is transported outward in a speed slower than half the surface speed, and the film thickness is smaller than the case of the smooth surface if asperity contact is not severe. However, when asperity contact is pronounced, the lubricant pressure distribution is quite different from the prior research. Mixed lubrication is observed in most of the region where asperity contact occurs. Boundary lubrication can only be found in a narrow area near the workpiece edge.