Methods for improving chucking accuracy of a cylindrical workpiece in finish hard turning.

摘要

A strong need has existed to develop a hard turning process that can replace grinding as a finishing process, due to its huge benefits in surface integrity and manufacturing flexibility over finish grinding and superfinishing. Due to the significant advances in machine tool accuracy and cutting tool material properties, chucking, which has not been improved significantly over the last several decades, has become the weakest link in the whole machine processing system. However, the understanding of chucking accuracy is lacking, nor is any systematic research on the improvement of chucking accuracy is available in literature. In this study, methods which enable evaluating, and improving chucking accuracy of a cylindrical workpiece were developed. This study performed systematic error identification and the analyses of the characteristics of the factors that affect chucking accuracy. Then, the formulations of the relation between the measurable factors and the chucking error were carried out as well as a chucking error map. From these analyses and formulations, methods for compensating the error components on chucking accuracy were developed. The methods were tested using the rings of a taper-roller bearing. From the tests of the methods, it was proven that hard turning alone, without any other finishing process such as grinding, can satisfy the same level of form accuracy that is currently achieved by finish grinding. With the developed chucking methods and strategies, the concentricity error could be reduced significantly or eliminated. For the case studied, we achieved about 20 times improvement in concentricity and 30 times in repeatability. The knowledge, created by this research on the improvement of chucking accuracy, can be applied to other operations requiring precision holding of a workpiece or a tool, as well as to general turning operations.