Methods for Improving the Accuracy and Repeatability

Significant improvements have been made in the performance of CNC machine tools due to the active research over the last several decades. However, the research and understanding on chucking accuracy have not been adequate. Nor has any systematic methods been reported for on chucking accuracy, especially in terms of the repeatability and the accuracy in the position of a chucked workpiece. The needs for the improvements in chucking accuracy has been existed since chucking has been the bottleneck in the form accuracy of a workpiece as the accuracy of machine tools improved significantly over the last several decades. However, the need was not very strong since turning has not been considered as the finishing process for the production of precision mechanical components such as bearings and shafts. After recent studies have demonstrated the benefits of hard turning in terms of surface integrity over other abrasive machining processes as a finishing process, a strong need emerged to improve chucking accuracy to enable the implementation of finish hard turning for the production of precision mechanical components. In this study, systematic methods for improving the accuracy and repeatability in the position of a chucked workpiece have been sought. Factors affecting the positioning accuracy and repeatability of a chucked workpiece have been identified. In addition, the characteristics of these factors, as well as their effect on chucking accuracy, were given. From the results, a chucking error map that summarizes the relations between these factors and the positioning error of a chucked workpiece was created. A series of error reduction experiments were carried out based on the results of the earlier works. The experimental results showed the possibility that the knowledge created in this study could be used effectively to improve the positioning accuracy and repeatability of parts in chucking and other work/tool holding operations.