On the workpiece setup optimization for five-axis machining with RTCP function

Abstract

Nonlinear errors in five-axis machining process are caused due to the nonlinear motions of the rotational axes, which are inevitable. For the RT-type machine tool, the workpiece setup location on the working table has a direct effect on the nonlinear errors, thus there must be an optimal setup position which can reduce the nonlinear errors. Today’s five-axis machine tools are mostly equipped the with the RTCP (rotational tool center point) function, with which the NC program becomes independent from the workpiece setup. In this paper, we have focused on finding the optimal workpiece setup for the RT-type machine tool with RTCP function, more specifically, the Mikron UCP 600 five-axis machine tool in our lab. The kinematics of the machine tool is briefly analyzed. Based on that, the nonlinear error evaluation method with RTCP interpolation is derived. With this method, nonlinear errors can actually be considered as a function of the workpiece setup position. Then, the particle swarm optimization (PSO) is applied to find the optimal workpiece setup, in which a mutation operation is used since PSO traps into local optimum easily. The proposed optimal workpiece setup method is implemented and tested. Example results show that the optimal setup with least nonlinear errors can be found. Some interesting results also show that the nonlinear errors are not sensitive with the z component of the workpiece setup vector. The proposed optimization is nearly zero-cost and easy to both understand and implement, yet has a potential to reduce the nonlinear errors and thus to improve the accuracy of five-axis machining.