Introduction of a New Function, (CONTROL_FORMING_SCRAP_FALL),in LS-DYNA & Its Applications in Scrap Fall Simulation

In stamping plants, one of the most common defects is scrap fall failure, in which some of the trimmed scraps do not fall according to the designed chutes or intended path. The scrap fall failure can damage dies or/and panels and cause stamping production line shutdown, which could easily result in millions of dollars lost. This paper is focused on developing effective analytical tools to detect potential scrap fall failures in tool/die design stages. Scrap cutting/separation from its parent sheet metal is an important step in properly simulating the scrap falling sequence. There are several critical characteristics which need to be properly captured by an analytical method in order to "detect" scrap fall errors. First, many broken-off scraps carry the initial kinematics and dynamics from the upper moving trim steel through contact during the trim process. Second, the trimming action is not simultaneous along the trim curve even in most simple direct trims. In complex cases such as multiple direct trim processes or mixture of direct trim and cam trim, the sequence of the scrap separation is very different from one design to another. In addition to the scrap separation sequence and the initial kinematics and dynamics of the scrap, contact between scrap and low trim steel and post is another very critical factor to the trajectory of the scrap fall. Some efforts ([1], [2], and [3]) have been made to understand and detect the root causes of scrap fall issues. To our best knowledge, there are no methods available today which could consider all three above factors accurately. Therefore, simulation results from those methods might not yield the results observed in the stamping plants (refering to some cases presented in the paper). To capture above mentioned three characteristics in simulation of scrap fall, a new function, called CONTROL_FORMING_SCRAP_FALL in LS-DYNA, has been jointly developed by Ford and LSTC. In this paper, we will first reveal the basic parameters employed in the new function, and illustrate how they are used to simulate the scrap separation & falling with a few simple cases. Then, several complex examples will be shown to illustrate how the new function along w/ LS-DYNA existing capabilities to be able to simulate real trimming processes accurately (to capture above mentioned three key characteristics) and detect scrap fall failures.