Characterization of cooling heat transfer for various coolant conditions in warm forging process

Because of the elevated temperatures in the warm or hot forging processes, the temperature of tools plays a major role in their service life. To increase tool life in warm or hot forging processes, forging conditions such as lubricants, cooling methods, tool material, heat treatment of tools and workpiece temperature should be optimized. All of these conditions are closely related to the temperature of active tools, so it is difficult to determine which factors are dominant and which ones require an accurate prediction of temperature changes in order to be changed. In warm or hot forging processes, the amount of heat generation by plastic deformation, heat transfer between workpiece and tools and the coolant cooling rate are essential for predicting the exact temperature of the workpiece and active tools. In this research, to determine the convective heat transfer coefficient with respect to different lubricants, the temperature of surface and lubricant was measured using flowing cooling experiments for the heat treated tools made of H13 steel. The convective heat transfer coefficients were calculated using both the measured temperature and inverse method algorithm. The calculations were performed using MPL code, which was developed for thermo-mechanical plastic deformation analysis. The calculated convective heat transfer coefficient was used in finite element analysis and verified.