Optimization of Gear Strength Using Heat Treatment Simulation

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In this research, an optimization of gear strength using heat treatment simulation was investigated. A heat conduction analysis and an elastic-plastic stress analysis during the case-carburizing process of the thick- and thin-rimmed spur gears and the helical gears were carried out by the simulator for the case-carburizing developed by the researchers. Bending fatigue tests and impact tests were carried out. Effects of the case depth, the case-carburized part, the rim and web thicknesses, the tempering and the helix angle on the residual stress, the bending fatigue strength and the impact breaking energy were determined. In the case of induction hardened gears, a suitable profile of hardened layer and pre-treatment condition for bending fatigue strength of induction hardened gears were investigated. In the first, residual stresses and hardened layers of gears induction hardened under various heating conditions were calculated by means of the induction- hardening simulator, which had be … More en developed by authors. Measurements of hardened layers and bending fatigue tests of gears induction hardenedunder various heating conditions were carried out. Calculated hardened layers were compared with measured ones. The optimum heating condition for the bending fatigue strength of induction-hardened gears was examined. In the next step, the hardness measurement and the observation of macro- and micro- structure of hardened layer, and the bending fatigue test of induction-hardened gears made of as-rolled and thermally refined S35C and S45C steels were carried out for various heating conditions, and then profiles of hardened layer and S-N curves were obtained. Effects of the pre-treatment and the heating condition (electric power P, frequency f and heating time th) on profiles and micro-structures of hardened layer of the gears were examined. The relationship among the bending fatigue strength, the profile of hardened layer and the hardness distribution and the micro-structure at the Hofer's critical section of tooth root fillet was determined. The suitable profile of hardened layer and the pre-treatment condition for the bending fatigue strength of induction hardened S35C and S45C steel gears were indicated. Less