Prediction of Workpiece Location Error Due to Fixture Geometric Errors and Fixture-Workpiece Compliance

Abstract

Workpiece location relative to the cutting tool is affected by the accuracy of part placement in the fixture. A number of error sources are known to contribute to the resulting workpiece location error, which can lead to poor part quality. The major sources include fixture geometric error and elastic deformation of the fixture and workpiece due to fixturing forces. In this paper, workpiece location error is predicted by modeling the process of part loading (given fixture geometric variations) and clamping (given deformations at the contact points) in a machining fixture. Linear elastic models for the fixture elements, contact mechanics models at the region of contact, and the flexibility influence coefficient method for the bulk elasticity of the workpiece have been used to model the compliance of the entire fixture-workpiece system. The deformations at the contact points are obtained by solving a constrained optimization model. The effect of geometric errors and compliance on workpiece location error is examined using part response points as a measure of quality, through examples involving a 3-2-1 machining fixture.