A methodology for the 3D stress analysis and the design of layered sheet metal forming tools joined by screws

In sheet metal forming industry, several experimental trials have been carried out successfully in the last 10 years, to demonstrate the feasibility of layered forming tools, by various rapid prototyping techniques. Recently, a layered stamping punch, based on the Stratoconception® process, was produced in a Craft European project Fastool and used successfully to produce some parts. The layered punch was joined using several screws in addition to an epoxy adhesive. Numerical simulation softwares allowing for 3D stress analysis of the layered tools are needed to evaluate their deformation and the various solutions of an assembly system. In this context, the authors proposed and developed a simplified numerical procedure, based on two steps, for the 3D stress analysis of deformable tools (layered or not). In addition, an optimization procedure, based on design of experiments and response surface method, has been established in order to optimize the screw positions, which are crucial in the aim of achieving the required high strength and life duration of the assembly technique by screws. The results show the feasibility of the developed procedure in the context of industrial applications, the potential interest of the optimization of the screw positions is also outlined.