Surface Reconstruction of the “False” Tools to Compensate for the Springback in Sheet Forming Process

Abstract

In sheet forming process the springback after the tool withdraw often causes a deformed geometry. In order to obtain the desired geometry, the spring-back effect should be compensated by the modified tools, called false tools in this study. In the numerical simulation, the forming process simulation gives a FE part mesh which fits well the tools and then the springback simulation gives a deformed mesh which has the same nodes and element connectivity as the part mesh. A displacement adjustment of the nodes on the part mesh in the opposite direction of the springback deformation leads to a false mesh . This mesh defines the geometry of the false tools which will be used in the next forming and springback simulations until a part with desired dimensions is obtained. In this paper, we propose a technique of surface reconstruction in order to facilitate the parametric shape optimization and tool manufacturing. In our technique of surface reconstruction, we discritize the tools' surfaces one by one by a triangle mesh and move these nodes (sample points) onto the false mesh in keeping their local surface coordinates, then we project them on to a local quadratic surface, finally we reconstruct Nurbs surfaces using the moved nodes on the false mesh . The main idea is to take a surface of the initial design tools or a newly created Nurbs as the reference surface and move its control points in order to obtain a new surface (surface of false tool) that is very close to the false mesh . The surfaces of the false tools are created one by one by minimizing the gaps between the new surfaces and the moved sample points on the false mesh in keeping the sample points' normal on the border of two surfaces. The Nurbs surface creation is fulfilled on the Open CASCADE platform and the numerical simulations are carried out in ABAQUS.