Methods for Improving Chucking Accuracy

Abstract

Since recent studies have demonstrated the benefits of hard turning over other abrasive machining processes as a finishing process in terms of surface integrity, a strong need has existed to improve the performance of chucking. It is because the poor repeatability and accuracy in the positioning of chucked workpieces became the major bottleneck in the implementation of finish hard turning for precision mechanical components. However, the understanding of chucking has not been adequate nor has any systematic method been reported for improving chucking accuracy. In this paper, all the major factors that affect the positioning accuracy and repeatability of a chucked workpiece have been identified by error budgeting and systematic measurements. In addition, the characteristics of these factors as well as their effect on chucking accuracy were investigated. From the results, a chucking error map that summarizes the relations between these factors and the positioning error of a chucked workpiece was developed. Then, a series of experiments were carried out to test the effectiveness of the error budget. The results demonstrated that the knowledge on these factors was accurate and it could be effectively used to improve the positioning accuracy and repeatability of a range of cylindrical workpieces in chucking. It was also shown that hard turning alone, without any extra machining process, could satisfy the same level of concentricity, which is currently achieved by finish grinding when chucking accuracy was improved by the method developed. Even if this study was originally intended for the implementation of finish hard turning for replacing finish grinding, the methods developed in this study can be used to improve the final form accuracy of cylindrical workpieces in other finishing processes including grinding, if any work holding devices similar to chucks are used to hold the workpieces. The methodology and the procedures for improving chucking accuracy are covered in a pending patent by the authors.