Iterative preform design technique by tracing the material flow along the deformation path - Application to piston forging

Abstract

Purpose - In the finite element analysis of a hot forging process, it is difficult to design an optimal preform because of highly nonlinear characteristics of design variables. In this paper, a new preform design method which can reduce the forming load and the die wear by removing the flash is developed and applied to the pre form design of a piston. Design/methodology/approach - After finite element analyses of hot forging processes, if the final product is found to have excessive flash and cause high die wear, a new preform design technique, so-called iterative preform design technique is applied to obtain an optimal preform design. From the results of FE simulations, a boundary region at the outlet of the flash is first selected. Then, by tracing the section along the deformation path to the initial billet, it is possible to obtain a mapped section boundary in the initial billet. After updating the initial shape by removing the exterior region of the mapped section boundary, a finite element simulation is carried out with the updated initial shape. Iterations should be continued until a desired result is obtained. Findings - It has been confirmed that the proposed preform design technique has a negligible effect on the initial forgeability of the workpiece. It is expected that the tool life will be increased, because the forming load and die wear are reduced as the number of iterations are increased. Moreover, because the preform design reduces the flash, it thereby reduces the waste of material. Originality/value - In the 3D finite element analysis of a hot forging process, several optimal preform design techniques have been developed. However, it is difficult to use the techniques in general problems because it is difficult to formulate cost functions, which mainly depend on the experience and physical insight of the designer. In addition, tremendous time is consumed in optimizing a problem as a large number of iterations are required in minimizing the objective function. The proposed preform design technique is simple enough to apply to general hot forging problems involving excessive flash. The proposed preform design technique is an offline method and easy to apply to any other analysis program, including commercial programs.