Modeling Drawbeads in Deep Drawing Simulations

Abstract

The numerical simulation has become an indispensable tool in the design, production and process set up of deep drawn parts. The advantages of these tools are nowadays well known. If the numerical model correctly describes both the technological procedure and process parameters, the use of numerical simulation allows to save time, money and effort. One of the challenges to guarantee this correlation between the numerical models and the real process conditions is the drawbead modeling. Drawbeads are often used in sheet metal forming processes to provide a better control of the material flow. Numerically there are still numerous difficulties to accurately model and describe drawbeads’ geometries and actions. Due to such difficulties, most of the numerical strategies used in finite element codes simply replace the real drawbead by an “equivalent drawbead model”. The majority of these models are based on the analysis of a 2-D model of the physical drawbead. The drawbead geometry is simplified to an artificial line where a restraining and a lift force are associated with. More complex models are based on an algorithm that acts on the finite elements that cross the artificial line in order to update both thinning and strain and stress states. The first drawback of these strategies is associated with its accuracy if in the real process the drawbead is not linear or the deformation process is not close to plain strain state. The second drawback is associated with the fact that the clamping phase disappears, and in this phase the drawbeads can induce some state variables change in nodes that aren’t close to the artificial line. In this work, two different kinds of forming processes that require the modeling of a drawbead are analyzed. In the first, a bulge test example, the drawbead acts to eliminate any gliding between the blank and the drawbead. The second example is the U shape geometry according to the Benchmark#3 (Stage 1) proposed in the framework of Numisheet’2005 conference. In this example the drawbead acts only to control the material inflow, but the material passing through the drawbead will be included in the final formed part [1]. Simulation results of these examples with the physical drawbead model, with an “equivalent drawbead model” and with no drawbead are analyzed. All simulations were performed with the implicit finite element code DD3IMP.