The use of finite element analysis in the development of closed-die forging processes is widely established in industry. However, the simulated and the real workpiece dimensions differ from each other in a significant way. As a result, multi-stage dies in particular often need to undergo an experimental time-consuming optimization process on the production machine which leads in conjunction with the unproductive downtime of the press to high overall costs.
The aforementioned problems are mainly caused by non-realistic modeling of press behavior within the forging simulation. Such simulations do not consider the relative displacements between the upper and the lower die that occur in the press due to process loads. In the case of multi-stage forging processes with two or more stages in tool contact at any one point in time, the interactions between the forging process and the machine are considerably more complex due to the individual tool stages influencing each other. Forging simulation systems available today do not, however, offer adequate ways of modeling these interactions taking place between the multi-stage process and the press. They provide no possibility, therefore, of achieving simulation-aided tool optimization in order to minimize the
efforts and costs involved in trial-and-error optimization processes. In order to consider the interactions between the process and the machine, and to improve the accuracy of the forging simulation, a method was developed at the WZL at RWTH Aachen University that allows the coupling of the forging simulation (Forge®) with external machine tool simulation systems and nonlinear-elastic press models. This method of coupled simulation was integrated into a software tool and may be used for single-stage as well as for multi-stage processes in closed-die forging operations. The method makes it possible to reconstruct the development of forging errors caused by the press machine for single- and multi-stage processes by simulation. The simulation results of multi-stage processes show that the aforementioned complex interactions may be simulated correctly. Besides the analysis of machine-specific workpiece failure, verified examples show that the coupled simulation may also be used to carry out a tool stress analysis. This allows simulation-aided optimization of the dies as early as the design stage as well as individual adaptation to the particular production press well in advance of the test phase of the dies on the press.
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