| A systematic approach to optimally configure the layout of machining fixtures for prismatic parts is presented. The overall structure of this work consists of (1) modeling the fixture-workpiece structure using FEM, (2) developing design optimization model for fixture design, (3) constructing an optimum design scheme involving selection of optimization codes and integration with the ANSYS program, and (4) conducting case studies to implement, evaluate and verify the proposed methodologies, techniques, and assumptions, respectively.; The workpiece is considered as not only a rigid body in kinematic and static analyses, but also a nonrigid body to account for deformation. The finite element method is used to model the fixture-workpiece system and calculate the workpiece deflections. The optimization model is structured for improving machined component precision. The objective function to be minimized is defined as the maximum workpiece deflection. The design variables are identified as the positions of locators and clamps, and the magnitude of clamping forces. The types of constraints include state variable constraints and design variable boundary constraints. Three optimization techniques, with completely different characteristics in the structure, are applied to solving the fixture design problem. They are (1) the ellipsoid method, (2) the feasible directions method and (3) the augmented Lagrange multiplier method. Computational efficiency and solution precision are the two criteria used to evaluate their performance on the fixture design.; The outcomes from cases studied show that the optimum design model is able to deal with sequentially implemented machining operations, and feasible for three-dimensional applications. The feasible directions method is computationally most efficient, while the ellipsoid method is the best for solution precision criterion. The augmented Lagrange multiplier method proved to have generally poor computational efficiency and failed to converge in one case. |
