Distortions induced by heat treatment of automotive bevel gears

Bevel gears are widely used in the automotive industry and are manufactured by machining or cold forging. Recently, many kinds of gears have been produced by forging in order to enhance the mechanical properties of the gears and the productivity of the process. Developments in forging technology are the reason for the increased usage. However, a critical problem of the forged gears is the dimensional change or distortion caused by elastic recovery after forging, and relief of the residual stresses during subsequent heat treatments. Distortion is of great concern to the manufacturers of precision parts, because it influences directly the dimensional accuracy and the grade of carburized bevel gears. In the present paper, distortion due to heat treatment of bevel gears is investigated. Distortions of forged gears and machined gears are measured and compared. Numerical analysis is used to simulate the complete heat treatment process for the machined gears and shows good agreement with the experimental measurements.