Sensitivity Study of Press Quench Process and Concept of Tooling Design for Reduced Distortion by Modeling

摘要

Press quenching is designed to harden steel gears while minimizing distortion, and the process is especially applied for hardening large diameter thin-wall gears, face gears, and bevel gears. The dimensional control aims at maintaining flatness, out-of-round, straightness, and consistency of radial size. The press quench tooling and the process design have been mainly experience-based, using a trial and error approach for implementation of new processes, new gear materials, and gear configurations. Both the out-of-round distortion and the radial distortion, including straightness and size change of thin-wall gears, are critical due to the maximum allowed grinding amount of the carburized case. Factors affecting the dimensional consistency of a press quench process can be classified as originating from gear/material conditions or the process parameters. The gear/material conditions include the variations of the initial gear dimensions, carbon distribution, residual stresses, and material microstructures prior to hardening. The press quench process parameters include the heating rate, austenitizing temperature, applied load type, load amount, load location on the part from the tooling, friction between the tooling and the gear, and the quench rate, etc. All these factors may lead to inconsistent distortion, including the size and shape in quench-hardened parts. In this paper, the effects of several critical factors on the dimensional inconsistency are analyzed using the heat treatment modeling software DANTE. The analysis results indicate that the current press quench with expander design does not effectively maintain a consistent radial size for thin-wall gears after hardening. By replacing the expander with an oversized plug, the effects of austenitizing temperature, cooling rate, and initial gear size on the distortion are analyzed, and the press quench with plug design leads to consistent radial size. This concept of tooling design is demonstrated by modeling a hardening process for a simplified thin-wall spiral bevel gear made of carburized AISI 9310 steel.