An optimized single-point offset method for reducing the theoretical error of S-shaped test piece

Abstract

The S-shaped test piece is utilized to comprehensively detect the machining accuracy of multi-axis machine tools. However, due to the existence of the influence of theoretical error for S-shaped test piece on the acceptance of multi-axis machine tools, therefore, a new methodology to reduce the theoretical error is proposed in this study. Firstly, the uniform double cubic B-spline surface model is applied to a surface representation. By utilizing this model, a model of the S-shaped test piece is established. Furthermore, the distribution of the twist angle at the selected three section lines is obtained. Meanwhile, the influence of twist angle on the theoretical error of S-shaped test pieces is analyzed. Then, the single-point offset (SPO) method is analyzed, which has some drawbacks. In order to significantly reduce the theoretical error of S-shaped test piece, the optimized single-point offset (OSPO) method is proposed. Moreover, the tool path of the S-shaped test piece is generated by CAD/CAM software based on the OSPO method. Finally, in order to verify the feasibility of the presented method, a machining and measurement experiment is carried out on the gantry-type five-axis milling machine tool (XKAS2525) and coordinate measuring machine (CMM) based on the S-shaped test piece, respectively. Experiment results show that the average theoretical error of S-shaped test pieces based on the OSPO method is reduced by about 50.1% than that on the SPO method. In addition, the vast majority of theoretical errors based on the OSPO method are approximately less than 5 μm, which can be negligible. It is therefore reasonable to conclude that, compared with the SPO method, the proposed method in this paper can avoid the influence of theoretical error on the acceptance of multi-axis machine tools intuitively and efficiently.