Numerical simulation of the superplastic moving die forming process with a modified membrane finite element method

In superplastic forming, a number of processes have been developed and designed to reduce the thickness deviation that is inevitable in simple female-die forming. Some of the forming processes require tool movements for better thickness distribution than simple female forming. It is common to use techniques based on male tool movement for relatively deep and complex shapes. The process has to deal with the optimum pressure cycle considering the moving die, the thickness distribution and the final shape. Calculation of the thickness distribution is a key for the optimum process design to produce good quality parts of uniform thickness distribution. In this paper, superplastic forming processes with a moving die are simulated with the finite element method (FEM) with modified membrane elements in the convective coordinate system. The numerical result provides the optimum pressure cycle and intermediate deformed shapes with the variation of the forming time as well as the thickness distribution. The result is compared with that obtained from simple female-die forming to demonstrate that the thickness distribution with a moving die is more uniform than that with a simple female die. The analysis enables accurate prediction of the thickness distribution in blow forming processes with a moving die.