Effects of Surface Finish and Die Temperature on Friction and Lubrication in Forging

Abstract

In this study, ring compression test was conducted to investigate i) effects of surface topography on friction and lubrication at room temperature with both dry and lubricated conditions, and ii) the effect of die temperature on friction and lubrication by differentiating temperatures of die and ring samples. Findings from experiments and FE results lead to develop a pressure-dependent variable friction model that concurrently changes friction factor during the forming stroke and different contact surface areas. The constant frictional model and this variable friction model were used in FE simulations of ring compression. The prediction results were compared with experimental results in details. The use of variable friction model gave very good correlations of the final ring geometry than other constant friction models in comparison to experiments. This implies that the pressure-dependent variable friction model can better characterize the interfacial friction condition in cold forging applications. In the ring compression with heated dies, the temperature rise was found to degrade the performance of lubricant, which resulted in the tapered shape ring. Therefore, the effect of surface topography and die temperature on interfacial friction condition with lubricant viscosity should be considered for the improved friction model for FE simulations of forging processes with high stroking rates.