Research On Clamping Optimization Of Workpiece Using Genetic Algorithm And Finite Element Method

Fixtures are used to locate, support and completely constrain a workpiece during a machining operation. Because the experience fixture design can't adapt the demand of production increasingly, so a simultaneous clamping optimization technology of fixture layout and clamping force used genetic algorithm (GA) and finite element method (FEM) is put forward. The main work is as follows.Firstly, a mathematical model based on the positioning principle is established, and six positioning validity criterions are obtained according to it. Through the solution of the rank of jacobian matrix, we can judge the validity of some positioning scheme. At the same time, a clamping stability mathematical model based on the three constraint conditions of clamping stability is established. By means of the linear programming technology, a criterion is established to verify the clamping stability of workpiece, and realize the solution of clamping stability model with non-friction and friction individually.Secondly, genetic algorithm and its application in the clamping optimization are introduced. A coding method which takes the fixture layout and clamping force as a design variable is proposed to get the global optimal solution. An adaptive GA is applied for the purpose of improving the early convergence and late search dullness in GA. Meanwhile, a method of speeding up clamping optimization is proposed, and the interface between GA and finite element soft-ANSYS is described.Thirdly, the key technologies of workpiece clamping optimization in ANSYS are researched. For example, in order to speed up the optimal rate and prevent the occurrence of non-convergence, springs are used instead of the contact between workpiece and fixture, and continuous interpolation is used to transfer the contact point to the nearest one or several nodes. Meanwhile, take the step surface contact between cutting tool and workpiece instead of the cylindrical surface contact, the cutting forces are even acted on the step surface, and the element death and birth technology is used for the simulation of chip removal.Lastly, the clamping optimization model aiming at minimizing the maximum machining deformation is presented based on the GA and FEM. A method that using linear programming technology in the GA is presented, which not only ensures the stability of workpiece but also decrease the optimization time. It is shown through an example that this method yields a design far superior to the experiential one and is proved to be efficient.