Research On Design Optimization Technology In Computer Aided Fixture Design

Fixtures are used to locate, clamp and support a workpiece in machining. A poor choice of the positions of fixture elements and clamping force(s) can lead to undesirable workpiece deformation and low dimensional/form accuracy of the workpiece. Traditionally, the design of a fixture relies heavily on the designer's expertise and experience and it is not esay to assure an optimal fixture plan. So this design method can't meet the need of precision thin-walled workpiece. Based on genetic algorithm (GA) and finite element method (FEM), this paper studies on the fixture optimization technology in computer aided fixture design. The main work is as follows.Firstly, the whole structure of computer aided fixture design system and fixture optimization function were analysed. And fixture optimization procedure is presented based on GA and FEM, where GA is used as optimization algorithm and FEM is used to calculate the objective function value for GA procedure. This paper was focused on the control of parameters, how to deal with the constraint conditions and how to speed up the optimization process when GA is used in fixture optimization. In addition, how to create a parametric workpiece-fixture system finite element model taking cutting force, clamping force(s), friction and chip removal into account after having chosed an appropriate workpiece-fixture contact model was also studied.Secondly, single objective fixture optimization method aiming at minimizing the maximum maching deformation is presented. And a multi-objective fixture optimization method is also put forward which aims at maximizing the deformation distribution uniformity along the cutting path additionally comparing with single objective fixture optimization. And it is proved the multi-objective optimization method can get the better solution than what the single objective optimization method gets.Thirdly, how to obtain the alterable clamping force(s) was studied. Based on the optimized fixture layout, GA and FEM are used to obtain an optimal clamping force(s) in each case which the cutting path is cutted into. And finally a group of optimized clamping force(s) along the cutting path is obtained. It is proved that this method is effective by simulation.Finally, based on SolidWorks and exiting computer aided modular fixture rapid design system, the fixture optimization function module is developed. Using APDL to edit parametric workpiece-fixture system finite element model files, MATLAB lanuage to edit GA program and VC++6.0 as development tool, ANSYS, MATLAB and SolidWorks are integrated in the module.