Improved Algorithm for Tolerance-Based Stiffness Optimization of Machining Fixtures

Current fixture design methods rely extensively on heuristics and lack a formal engineering approach to determine the necessary stiffness, dimensions, etc. This paper presents a model for stiffness optimization of machining fixtures based on the tolerance limit specified for the machined part surface. Specifically, the model allows systematic determination of the optimum fixture stiffness needed to keep the contribution of fixture deflection to the machined feature tolerance within a designer-specified level. Based on the stiffness optimization model presented here, the optimum dimensions of the fixture elements can also be determined. The model development relies on rigid body analysis methods, contact mechanics principles, and consideration of bulk elasticity of the fixture. The model is generic enough to be used for the design of dedicated or flexible fixtures consisting of mechanical elements. Two examples, one involving a pin-array type flexible fixture and another involving a dedicated fixture, are presented to illustrate the applicability of the model.