Metal forming is complex; hence conducting computer simulations with reasonable turn around time requires a number of assumptions and simplifications of the physical reality. Since a number of commercial software codes are now available for metal forming simulation, it is very important that the underlying assumptions are well understood. It is not a simple case of one code being “better” than another; rather it is to understand the results and to apply them effectively.
The goal of this investigation was to compare the simulation results between a full bending formulation (FBF) code and a modified membrane formulation (MMF) code, with particular emphasis on how friction should be “treated”. The strategy followed was to simulate the stamping of a simple U-channel FEA first in the FBF code and then to adjust the MMF results to be comparable by changing the friction coefficient. (The full bending code has been previously quantitatively correlated to many soft and hard tool stampings.)
Two levels of sheet thickness, boundary conditions and FBF friction coefficient were used, resulting in a matrix of 32 simulations performed for each software. The results indicate that the values of the friction coefficients used in the MMF code have to be lower for lock conditions but much higher for draw conditions. It is believed that these differences are due to an underestimation of the bending stiffness components in the MMF. For applications where the bending stiffness is important, for example, metal sliding over a radius with a r/t less than 6-8, the effects are significant and the results need to be interpreted with this understanding in mind.