Input Parameters for Springback Simulation using LS-DYNA
Bradley N. Maker Xinhai Zhu Livermore Software Technology Corporation June, 2001 LS-DYNA has been applied to springback simulation by a large number of users, with generally mixed results. Some results have demonstrated 70% accuracy or better, while others have been entirely misleading. In order to eliminate inconsistent results, this report presents a standard procedure for conducting springback simulations with LS-DYNA. The “seamless” and “dynain” methods for springback are described, followed by a description of general implicit springback problem set-up. Recommendations are given for anticipating and improving springback prediction accuracy. Wherever possible, LS-DYNA keyword input data is shown to clarify the presentation. Recommended input parameters are identified in boldface type and included in boxed keyword input syntax for quick reference. A boldface zero value is entered for required input data which is model specific, such as the termination time term.

The Forming Simulation
Results from the forming simulation provide the starting point for the springback simulation. The most important factor in springback accuracy is the accuracy of the forming simulation. This is essential! If trouble occurs during springback, look for the cause in the forming analysis. In explicit forming simulations, run time can and should be greatly decreased using mass scaling and/or artificially high tool velocity. Both these methods introduce artificial dynamic effects, which must be minimized to reasonable levels in an engineering sense. A single independent parameter describing artificial dynamic effect is the number of explicit time steps (cycles) taken per millimeter of tool motion. Relatively more cycles per millimeter are required when the forming process allows large unrestrained sheet motion. An example is the crash forming process, which uses no binders. Relatively fewer cycles per millimeter are necessary...