Research On The Springback Control Methods In High Strength Sheet U-shaped Parts Stamping Forming

Automobile industry is one of the important symbols to judge measure a country's industrial level. In recent years, for reasons of security, economic and environmental considerations, vehicles (especially cars) lightweight gradually become one of the trends of automobile industrial development, high-strength steel is large-scale applicated in the manufacture of automobile body. In the early 1980s ,the United States and Japan have begun to use high-strength low-alloy steel to reduce the automobile's weight of 20% to 40% .Automobile body using high-strength steels have reached the average ratio of 23.3% in Japan since 1992, which Nissan Motor Co. reached more than 30%. Domestic automobile manufacturers also changed the original vehicle parts material to high-strength steel in oder to reduce automobile's weight and improve safety. The yield limit of high strength steel is so high that the plastic deformation is not completable in the process of forming ,which makes the springback of parts more after forming, especially in the U-shaped part sheet metal forming ,springback deploys more significantly. A lot of automotive structure parts are U-shaped pieces, such as frame girders, beams, as well as collision boxes. Springback seriously impacts on the production's dimensional accuracy. The effective measures to control springback is been urgently needed in the actual production.During the research of this paper , Firstly, Based on the research to the mold compensation method, which had been used to control the rebound of the U-shaped part in the practice production, obtained the parameter formula of die compensation under three kind of materials models, such as ideal spring- plastic material model, linear hardening material model, exponent sign hardening material model. The compensation die was designed to confirm the formula under three kinds of hardening material model as well. The result indicates the formula under exponent sign hardening material model has a higher precision, and it can better control the spring-back of U-shape part according to the formula values for the Die parameters.Secondly, combining with one factory's production of the automobile carline as the research object, proposed using two times bending method to control the high strength steel U-shape carline's springback, based on detailed analysis bending mechanism and the U shape bending characteristic. Beside used the finite element analysis method to made the feasibility analysis of two times bending, also carried on the corresponding experimental confirmation. The result indicates two times bending method can effectively control carline's springback and make the components achieve the specification.Finaly, established the springback prediction model about the high strength steel U-shape by using finite element simulation technology and the data processing linear return technology. And confirmed prediction model with the production components. The results proves the prediction model may be effective forecast the tendency of springback, and the control method of springback has been introduced combine with prediction model.