Study On The Mechanism Of Plastic Deformation In The Chain Die Forming Of Variable Cross Section Steels

Chain die forming is a new sheet metal forming process,it is developed on the basis of the traditional roll forming,chain die forming can increase the deformation zone length in the process of sheet metal forming by introducing virtual "Large diameter roller", and reduce the the longitudinal strain of sheet metal forming process, which can effectively reduce sheet metal forming defects, such as the edge wave, distortion, warping.The finite anylisis model of variable cross-section chain die forming process was established in this thesis.At first,the accuracy of the simulation model was confirmed through comparing strain measured from experiment and simulation model. The results show that:the equivalent plastic strain are larger in corner area of variable cross-section part, it has a larger Mises stress after forming; the arc area of the flange have larger longitudinal strain, the tensile deformation occurs in concave arc area, compression deformation occurs in convex arc area.The effects of process parameters on longitudinal strain was studied in variable cross-section chain die forming process, the process parameters of material properties, flange height, sheet thickness, flange bending radius of variable cross-section was selected, each process parameters takes three levels, establish four factors and three levels orthogonal experiment. Through range analysis of orthogonal experiment to determine the value of Range R of each process parameters, orthogonal test results showed that:the flange height has the strongest sensitivity in longitudinal strain, and longitudinal strain increases with the flange height; sheet thickness has the weakest sensitivity in longitudinal strain of variable cross-section chain die forming.Analized the reasons for the web bow of the variable cross-section with chain die forming process. The result show that:in the web of variable cross-section,the longitudinal and shear stresses in the upper surface and lower surface are in the opposite direction, so that the longitudinal bending of the web area occurs.The influence of forming angle, flange height, material properties, and other parameters of variable cross-section forming on the web bow was studied, the material properties of the variable cross-section chain die forming have a large influence on web bow, forming angle and flange height have small impact on variable cross-section chain die forming web bow.A static implicit algorithm Abaqus model of variable cross-section chain die forming is established.The stress and strain state of corner area, the arc area of the flange and other key areas of the variable cross-section part are analyzed.Compared the springback values measured in finite anylisis model with the bending springback values calculated from empirical formulas, the springback value of simulation is agree with the springback value calculated from the empirical formulas.Therefore,the finite element model can effectively predict springback in variable cross-section chain die forming process, the model can offer the theory of die optimization design.