Research On The Algorithms Of Blank Unfolding And Spring-back Simulation For Sheet Metal Parts

Sheet metal parts are widely used in many fields such as automobile industry, aviation industry and electronic and electric industry for its light weight, high strength and mass production performance. Numerical simulation is adopted extensively in the stamping field with the development of computer technology. Considering that the accuracy of blank shape will definitely influence the forming precision of parts, and spring-back is very common since there is always bend forming in sheet metal forming process, this article mainly researches on the algorithms of blank unfolding and spring-back simulation according to the forming characteristics based on one-step inverse analysis.For the unfolding algorithm of sheet metal parts, there are two basic algorithms based on one-step inverse analysis presented in this paper. One is the self-adaptive algorithm of equivalent resistance, the other is the unfolding algorithm for stamping parts with process features. In this new unfolding algorithm, the effect of blank holders can be fully considered especially for deep drawing. For the stamping parts with undercutting regions, the initial guess mesh is generated in triangle mesh parameterization way which is robust for undercutting regions and efficient for most parts. For the parts containing un-deformed process features in forming area, the improved algorithm firstly separates the process features away. Then, traditional one-step inverse analysis is used to unfold the rest of the forming area. The process features are treated as rigid body which can be transformed by rotation and translation.For the spring-back problem in bend forming process, the current simulation method is mainly based on the plastic incremental theory which is inefficient. One spring-back finite element formulation is derived based on the plastic total strain theory and DKT12 elements after relative displacement of forming part is obtained by one-step inverse analysis in this article. This method improves solving efficiency greatly. Although the precision is declined slightly, the method still has good prediction of spring-back at the early design stage.In the end, two typical and complex sheet metal parts are taken as examples to verify the accuracy and efficiency of the above mentioned algorithms of blank unfolding and spring-back simulation.