A Coupling Response Surfaces Methodology of Multiple Constraints (CRSMMC) for parameters optimization of broach tool in broaching of heat-resistant steel X12CrMoWVNb N-10-1-1

Abstract

Broaching fir-slots on the turbine discs is regarded as one of the key processes and the most difficult machining operations due to complex geometry and very tight tolerances. The heat-resistant steel X12CrMoWVNb N-10-1-1 is widely used as material in power-generation turbines. However, the manufacturability of the heat-resistant steel poses enormous challenges to the turbine plants. Subjected to several constraints including broaching force, broaching surface quality and broaching tool’s structure strength, machining efficiency, broaching tool’s life, and so on; the broaching process is mainly influenced by cutting speed, rake angle, clearance angle, and rise per tooth (RPT) of broach tool. A flexible evaluation method for multiple constraints, CRSMMC, is presented to acquire optimization parameters of broach tool for machining heat-resistant steel. Rake angle, clearance angle and rise per tooth (RPT) are designed as three factors by using the central composite design (CCD) method. In addition, broaching experiments of heat-resistant steel X12CrMoWVNb N-10-1-1 were performed in order to set up the model. In addition, the influences of broaches parameters on constraints were studied. The results indicated that the rise per tooth (RPT) was the dominant factor under the constraints of surface roughness and cutting force. Moreover, the predicted values obtained by CRSMMC were in good agreement with the experimental values, which indicated that CRSMMC was an effective method for broach tool’s parameters optimization in broaching of heat-resistant steel X12CrMoWVNb N-10-1-1.