Simultaneous Optimization Of Fixture Layout And The Application Sequences And Analysis Of Stability

The fixture is playing the vital role in process of mechanical machining for it directly affect the quality of products, productivity and cost. The workpiece is deformable during the process of clamping and instable in machining. Then the simultaneous optimization procedure of fixture layout and the application sequences by using genetic algorithm is put forward. Meanwhile, modeling and application of workpiece stability based on the linear programming method is proposed. These two methods can decrease the deformation of workpiece effectively and ensure the stability during the process of fixing, claming and machining.Firstly, the theoretical basis of fixture optimization is introduced. The principle of the minimum complementary energy, genetic algorithm and linear programming method are discussed. Contact is replaced by springs whose deformation is used to simulate contact deformation of workpiece and fixture element.Secondly, the model of workpiece stability is established which is based on mechanics and linear programming method. By means of the linear approximation of the friction cone and variable transformation, a quantitive criterion is established to verify the workpiece stability and the model of stability is solved. The model is simple, versatile and applicable to a variety of clamping ways, as well as the analysis for workpiece stability. It can not only solve the problem of workpiece stability in the early stages of fixture design, but also provide a theoretical basis for computer-aided fixture design(CAFD).Thirdly, a mathematical model is established to analyze the relationship among clamping sequences, contact force and incremental nodal displacement. A static equilibrium equation of clamping device system is derived at every clamping step. According to the principle of the minimum complementary energy and coulomb friction law, an optimization model is formulated. Then the simultaneous optimization procedure of fixture layout and the application sequences is put forward.Finally, three practical example are used to verify the validity of the proposed approach. The first one is the frictionless workpiece stability. The second one is the frictional workpiece stability. The results of the two examples show that the proposed method, in addition to the verification of the workpiece stability, can be used to study the feasibility of the magnitude and clamping sequence. The third example carries on the simulation analysis to the thin-walled aluminum alloy pieces. The results show that this method can solve the problem in step by step optimization and traditional optimization. It ensure the globally optimal solution and decrease the deformation of workpiece enormously.