Study on Residual Stress and Load Bearing Capacity of Induction Hardened Gears

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Eddy current distribution and amount of heat originated from induction heating of a circular bar were caculated by means of FEM electromagnetic field analysis method, and the validity of this FEM program was confirmed by comparing the results by the FEM with those by the theoretical equatin. An electromagnetic fied analysis, a heat conduction analysis and an elastic-plastic stress analysis of the shafts during induction heating and water cooling processes with uniform cross-section and with semicircular notch were carried out by the FEM, considering changes of the magnetic ermeability, the resistivity, the thermal expansion coefficient and the yield stress with the temperature. The effects f the electric pwer, the frequency, the heating time, the diameter and the notch on the residual stress of the shaft were examined.A heat conduction analysis and an elastic-plastic stress analysis in case-hardening process of the thin-rimmed spur gear were carried out by the FEM, considering changes … More of the thermal expansion coefficient and the yield stress with the temperature and the carbon content distribution. The effects of the case depth, the parts (tooth and/or bore) of hardening, the rim thickness and the standard pressure angle on the residual stress of the gear were examined.The main results obtained from this investigation are summarized as follows.1. In the induction hardening process of the shaft, the time t_h taken for the surface temperature to reach the hardening teperature decreases with increasing electric power and frequency, and the temperature difference T_s-T_c between the surface and the center of the shaft increases. The time t_h increases with increasing diameter of shaft and the temperature difference T_s-T_c decreases. 2. There is an optimum induction hardening condition (electric power, frequency and heating time) for the residua stress of the ahaft due to induction hardening. 3. The axial residual stress sigma_z near the notch bottom of the shaft with semicircular notch due to induction hardening is fairly small compared with that of the straight part for short heating time, but approaches to sigma_z of the straight part with increasing heating time. 4. Residual stress at Hofer's critical section of the spur gear due to case-hardening decreases with rim thickness and increases with standard pressure angle (20ﾟ(〕SY.ltoreq.〔)alpha_0(〕SY.ltoreq.〔)27ﾟ). There is an optimum case depth for residual stress of the spur gear due t case-hardening. Less