Compensation of reference surface errors in the machining of free form features

Abstract

One of the major sources of error in machining operations is the inaccurate positioning of the workpiece in the fixture. Generally, the surface of the workpiece that is in contact with the fixture locators is used as a workpiece reference surface (WRS). Errors in the WRS can lead to improper placing of the workpiece in the fixture and, in turn, to inaccurate machining operations. In this paper, a method is introduced that eliminates the effect of WRS errors on machined features produced in a milling operation. In the proposed method the positioning of the workpiece with consideration of WRS errors is mathematically modelled using homogenous transformation matrices. This model is then used to compensate the effect of WRS errors by modifying the machining toolpath. A post-processing workpiece error compensation module is developed that modifies the initial NC-codes that are generated from a CAM system. The presented method is verified using the simulation software NX and VERICUT and experimental studies. The results confirm that this method can be used to successfully compensate these kinds of errors.