Investigation of rotary axes geometric performance of a five-axis machine tool using a double ball bar through dual axes coordinated motion

Abstract

The accuracy of coordinated motion involving multiple axes of five-axis machining is critical to surface finish quality and geometric tolerances. However, the lack of existing criteria to benchmark such accuracy causes severe problems in maintaining machining accuracy. Therefore, this paper proposes a novel method to identify the geometric performance of rotary axes of a five-axis machine tool with a tilting head and a rotary table using a double ball bar (DBB). A new measuring trajectory only involving two rotary axes simultaneous movement is presented. A DBB was employed to sample the complex motion, causing a semi-conical surface in a 3D space formed by the DBB poses. The asynchronisation between the resultant speed of the spindle tool cup during the B- and C-axes coordinated motion and the DBB sampling rate has been resolved, enabling the true reflection of machine tool error conditions. Simulation models were built to compare with the testing results, suggesting the estimation of PIGEs of both rotary axes. Disagreements in the simulation and experimental results were analysed and possible reasons causing such disagreements were given. The results show that the compensation of the PIGEs diagnosed with the proposed method will significantly enhance the coordinated motion of the B- and C-axes and result in geometric accuracy improvement due to the promotion of the geometric and kinematic behaviour of the target five-axis machine tool.