Investigation On The Reverse Direction Step Decrease Planning Method Of Clamping Forces

In the machining process, the workpiece fixturing is necessary to machine a workpiece.Due to the influence of the external loads, such as the cutting force, the cutting torque, and so forth, on the workpiece, the workpiece will translate along the machine tool or rotate about the machine tool, even it can fly out from the machine tool to cause accidents.Therefore, the fixturing stability of workpiece is the prerequisite to guarantee the machining accuracy of workpiece. It can directly affect the machining quality, production efficiency and the manufacturing cost. In addition, with the development of economy, the demands of the society on the product are higher and higher. Consequently, the enterprises must to the greatest extent carry out the reduction of the product design period as well as the improvement of the product quality. Computer Aided Fixture Design(CAFD) can greatly shorten the time of fixture design. With the rapid development of computer technology,CAFD becomes a research hotspot in the domestic and abroad manufacturing fields.However, the automatic planning of clamping force is a "bottleneck" which can prevent CAFD system from the practicality. Therefore, in combination of the mechanical model of workpiece fixturing layout, the linear programming technique is adopted to establish the analysis model and its solution technology of the force existence and the force feasibility.These proposed analysis model can be used to judge the existence of clamping forces as well as the feasibility of clamping forces. By discretizing the feasible interval of clamping forces, the reverse direction step decrease planning algorithm is created for the determination of clamping forces. The proposed method can not only be employed to design the clamping forces for workpieces with complex surfaces, but also to realize the program for design automation of clamping forces. Obviously, it is of important research value and great realistic significance to raise the manufacturing level. The main contents of this thesis are as follows:First of all, the research purpose and significance is clarified in addition to the research significance. The state-of-art of computer-aided fixture design is further analyzed and concluded. The research methods and innovation points are introduced in this thesis.Secondly, according to the forced status of the workpiece in the fixturing layout, its static equilibrium equation can be formulized under the condition of the unidirectional constraints. Moreover, by means of linear programming technology, fixturing stability analysis model is established for the workpiece. Under the condition of the given positionand direction of fixels, gravity and machining forces, the analysis method of the existence of the clamping force is concluded. Again, aiming at the existence of clamping force, the analysis method of feasibility of clamping force is built according to the known position and direction of fixels, gravity force, machining forces, and magnitudes of clamping forces.Thirdly, by introducing the discretization idea into the feasible interval of clamping force, the reverse direction step decrease planning algorithm is established for the determination of clamping forces. Above all, the analysis method of the existence of clamping force can be used to judge whether the fixturing layout has reasonable clamping forces or not. If it has no clamping forces, the design process is over. Otherwise, the analysis method of the feasibility of clamping forces can be used to judge the feasibility status between the adjacent two clamping forces. When they are the same as each other, the next clamping force will be achieved by adding the same step to the current clamping force.Otherwise, the next clamping force will be obtained by decreasing the half step from the current clamping force. By so doing, the critical value/ interval of clamping forces can be determined until the absolute value of the current step is less than its given threshold value.Finally, the research work of this thesis is summarized. It is more important, the future research direction is described.