An investigation of involute and lead deflection in hot precision forging of gears

A theoretical model is presented in the paper for predicting involute profile deflection in hot precision forging of gears. This model is a function of a number of material and processing parameters, including the thermal expansion of the die, thermal contraction of workpiece, elastic expansion of the die during forging, and workpiece recovery after ejection. To improve the accuracy of the hot forged gear tooth, an equation set to define modified involute that is used to design the die tooth has been proposed based on the model. The distribution of deflection along the involute was also predicted using the commercial FE code, PRO-E. The deflection characteristic of the toothed die through the tooth width was analyzed by combining the theoretical method and FEM to investigate the non-uniform deflection. The dimension of the forged gears was measured using a gear measurement machine WGT3000. A close agreement between predicted and measured tooth involute profiles was obtained, which validated the involute deflection prediction model. The measured lead error also verified the model for deflection non-uniformity through the tooth width. The results can provide a guide for die tooth designs to improve the dimensional accuracy of hot forged gear teeth.