Modeling of Workpiece Location Error Due to Fixture Geometric Error and Fixture-Workpiece Compliance

Abstract

Several fixture-related error sources contribute to workpiece location error in a machining system. Inaccurate part placement in the fixture relative to the cutting tool, for example, can negatively affect the quality of the part. In this paper, the following major sources of error are considered: fixture geometric error and elastic deformation of the fixture and workpiece due to fixturing forces. The 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 for the contact regions, and flexibility influence coefficients to capture 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. Experimental validation is also provided for several fixture-workpiece variable levels using a 3-2-1 machining fixture.