Effect of tool temperature deviations on the stress distribution of hot die forging tool for gear blanks

Abstract

Tool preform and heating deviations in the operations of forging instruments that significantly affect the part and tool life are usually set in constant in various numerical forging process researches. It is desirable to find the variation effect of these factors on the tool life represented by the stress and/or strain distributions. A numerical method for the tool heating deviations on the stress distribution of a four-stage hot die forging was proposed. A Latin hypercube sampling was applied on the numerical mapping from the hot die forging process parameters (dimensions, temperatures, and time-to-displacement law for the tool’s forming impulse and hole drilling) to the index of the tool stress distribution. The numerical mapping integrated three types of finite element analyses, i.e., the tool heat transferring in cooling, tool thermal expansion and the forging of four gear blanks. The gear blanks took the kinematic plastic material model and the tool took multi-temperature bilinear model. The gear blanks were 900 ºC. The nominal tool temperatures for the four stages were respectively 260, 170, 170 and 335 ºC. The variation of the tool temperature was set to be 10 percent of the nominal tool temperature. Simulation and experiment reveal the effect of part and tool heating deviations on the index of stress distribution of a four stage hot die forging process for gear blanks. The stress variation is about 19% of the mean value and these maximum stress points are on a circle of the third tool. The effect of part and tool heating deviations should be taken into the further process design.