Study on Optimum Coil Design and Hardening Condition for Gear Induction Hardening

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An electromagnetic field analysis, a heat conduction analysis and an elastic-plastic stress analysis during induction heating and water cooling processes of shaft with uniform cross-section and shouldered shaft were carried out by the axisymmetric FEM, considering changes of the magnetic permeability, the resistivity, the thermal expansion coefficient and the yield stress with the temperature. Optimum hardening condition and coil configuration for residual stress and hardened layer were examined. 3D-FEM program for calculations of induced current density, temperature and stress during induction hardening process was developed. Residual stresses and hardened layer of gear due to single and dual frequency induction hardening were calculated by means of the FEM program, and then optimum induction hardening method for residual stress and hardened layer of gear were examined.The main results obtained from this investigation are summarized as follows.1.A chart to determine the optimum heatin … More g condition of electric power P and frequency f for residual stress due to the induction hardening of shaft with uniform cross-section was derived.2.Effective case depth of Hv=550(Hv : Vickers hardness number) due to the induction hardening of shaft with uniform cross-section increase at the middle of shaft and decreases at the end of shaft with decreasing lィイD2cィエD2, P and F (lィイD2cィエD2 : coil length).3.Axial and circumferential residual stresses σィイD2zィエD2ィイD1*ィエD1, σィイD2θィエD2ィイD1*ィエD1 of the shouldered shaft due to the induction hardening using the coil with constant inner diameter become large compressive stresses at the shaft surface only of smaller diameter in the case of lower f and the shaft surface only of larger diameter in the case of higher f.4.Surface σィイD2zィエD2ィイD1*ィエD1, σィイD2θィエD2ィイD1*ィエD1 of the shouldered shaft become large compressive stresses along the length of the shaft by carrying out the dual frequency induction hardening.5.Hardened layer of shouldered shaft occurs along the length of the shaft to certain shoulder height by carrying out the dual frequency induction hardening, and for larger shoulder height the coil must be overhung from the shaft end of smaller diameter.6.The position of maximum temperature at the end of induction heating process of gear becomes the tooth bottom of the end of face width irrespective of P and f in the case of narrower face width b, but becomes the tooth bottom of the middle of face width for lower f and the tooth tip of the middle of face width for higher f in the case of wider b.7.Contour lines of temperature at the end of induction heating process become lines along tooth profile by carrying out the dual frequency induction hardening, and residual stress and hardened layer occur along the tooth profile. Less