Research On Wrinkle And Springback Of Saddle Surface During Multi-point Forming Under Force-displacement Separated Control

Multi-point forming is a new technology of flexible sheet metal forming and has a broad application prospect. Multi-point forming under force-displacement separated control can not only make forces and displacements of matrix elements separated and controlled separately, but also ensure that the plate can be constrained by matrix elements fully and controllably. In this paper, the method of combining the numerical simulation and experiment was adopted to study wrinkle and springback of saddle surface during multi-point forming under force-displacement separated control.Based on the simulation platform of ABAQUS, the forming and springback processes of saddle surface were simulated after the model of multi-point forming under force-displacement separated control was established. Wrinkle of saddle surface was studied through the forming results of Numerical simulation. Firstly, wrinkle of saddle surface was described and the reason was analyzed. Then the influence of saddle surface parameters, curvature radius and thicknesses on wrinkle of saddle surface was studied. At the same time, methods were put forward to suppress wrinkle according to the phenomenon in the model. The results show that in multi-point forming under force-displacement separated control, the two directions of saddle surface can量t deform at the same time and the direction which gives priority to deformation is prone to occur wrinkled. The wrinkle depths of the double curvature directions of saddle surface decrease with the increasing saddle surface parameters, curvature radius and thicknesses. Increasing the sheet forming force reduces wrinkle significantly but difficult to eliminate. There is almost no wrinkle on plates after staggering matrix elements, and combined with increasing forces improve the quality of sheet metal forming effectively.Through the numerical simulation results of springback of saddle surface, the influence of saddle surface parameters, curvature radius and thicknesses on springback of saddle surface was studied with the forming force of1000N. The change of springback of saddle surface with different forming forces was also analyzed. The results show that when the forming force is small, in the two curvature directions of saddle surface, the direction of bigger curvature mainly occur positive springback and is the principal direction of springback, which affects the direction of smaller curvature and makes it to occur negative springback. With the greater difference of curvature radius of the two curvature directions, the primary and secondary relationship is more obvious. Different curvature radius or thicknesses do not change the relationship with a constant saddle surface parameter. Along with the rising of the forming force, the primary and secondary relationship of springback changes gradually, which is to say the direction of smaller curvature becomes the main direction of springback and mainly occur positive springback, while the direction of bigger curvature becomes the secondary direction of springback. With the larger forming force, the trend is more obvious.Finally, experiments of multi-point forming under force-displacement separated control were carried on. The quality of sheet metal forming in the experiment was analyzed and springback of saddle surface was studied. The results show that in the experiment, the springback of the direction which gives priority to deformation of saddle surface is consistent with the simulation result. The direction later forming is prone to appear the phenomenon of insufficient forming, which shows positive springback. With the greater deformation extent, the forming is more inadequate and the positive springback is greater. The conclusion above has a certain guiding significance for the actual production practice.