Abstract
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.
Highlights
The market demand for gears has been increased significantly in recent years [1]
The idea of relief axis and relief hole based on a divided flow principle was used in gear forging by Kondo et al [9] to reduce forming load and contribute to complete die filling
A new cold precision forging process proposed by Wang et al [10] suggested that the spur gear forging process should be divided into two steps, which improved the filling of the teeth and reduced the forging load by 30 % [10]
Summary
The market demand for gears has been increased significantly in recent years [1]. High accuracy, productivity, and the capability in gear manufacturing have been receiving significant attentions [2]. Choi et al [14] forged spur gears made of alloy steel (SCM415) with inside relief in two steps of forging process Their proposed method decreases forging load and improves forging accuracy to fourth and fifth classes in the Korean industrial standard, which is close to the accuracy of a machined spur gear [15]. Another process, known as cold ironing, which is used to obtain high surface finish and accuracy, was investigated by Stone et al [16] and Chang et al [17] as a postprocess for net-shape manufacturing of gears, which has improved the accuracy of hot forged gears significantly. The measured lead profile verified the model, which was used to predict the nonuniform deflection through the tooth width
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