A Study of the Lubrication Behavior of Solid Lubricants in the Upsetting Process

Four kinds of solid lubricants were tested in order to examine the frictional characteristics and the yield shear stress by the friction testing apparatus developed by the authors. The frictional shear stresses $τf$ increased approximate linearly with the punch pressure p in every solid lubricant, and the friction coefficients μ were approximately constant. The yield shear stress k was also increased with the punch pressure p. In order to investigate lubrication behaviors of solid lubricants in upsetting processes, FEM simulations for upsetting of circular plates have been carried out. Some experimental upsetting tests of circular plate were tried using some kinds of solid lubricants. It has been confirmed that the solid lubricants can lubricate successfully without metal-to-metal contact when $μD$ at the interface between tool and solid lubricant is relatively low and $μM$ at the interface between work piece and solid lubricant is relatively high. On the other hand, metal-to-metal contact occurs easily at the peripheral regions of the work piece, when $μD$ is relatively high and $μM$ is relatively low. [S0742-4787(00)00804-3]