Optimum design of process parameters to minimize distortion during gas quenching process

During the gas quenching process, the process parameters can be classified as observable and controllable parameters. The controllable process parameters include the preheated temperature of the component, the temperature of the circulated gas, and as considered in this paper, the heat transfer coefficient between the component and the circulated gas. The surface of the component is divided into several regions, and different values of heat transfer coefficient are imposed on each region. The values of beat transfer coefficient are used as design variables in optimization. The objective in this research is to minimize the distortion caused by quenching. Large distortions after quenching will increase the cost due to the post quenching processes, such as grinding and hot rectification. Constraints on the residual stresses and surface hardness distribution are imposed to improve the service properties. The commercial finite element software, DEFORM-HT, is used to predict the material responses during the quenching process. The response surface method is used to obtain the analytical models of the objective function and constraints in terms of the design variables. Once the closed-form response surface models are obtained, a design optimization tool, DOT (Design Optimization Tool), is used to search for the optimum design point. This paper summarizes the methodology used to optimize the gas quenching process together with an application of steel axisymmetric disk example.