Towards Efficient Modelling Of Macro And Micro Tool Deformations In Sheet Metal Forming

During forming, the deep drawing press and tools undergo large loads, and even though they are extremely sturdy\ud structures, deformations occur. This causes changes in the geometry of the tool surface and the gap width between the tools.\ud The deep drawing process can be very sensitive to these deformations. Tool and press deformations can be split into two\ud categories. The deflection of the press bed-plate or slide and global deformation in the deep drawing tools are referred to as\ud macro press deformation. Micro-deformation occurs directly at the surfaces of the forming tools and is one or two orders\ud lower in magnitude.\ud The goal is to include tool deformation in a FE forming simulation. This is not principally problematic, however, the FE\ud meshes become very large, causing an extremely large increase in numerical effort. In this paper, various methods are\ud discussed to include tool elasticity phenomena with acceptable cost. For macro deformation, modal methods or ’deformable\ud rigid bodies’ provide interesting possibilities. Static condensation is also a well known method to reduce the number of DOFs,\ud however the increasing bandwidth of the stiffness matrix limits this method severely, and decreased calculation times are not\ud expected. At the moment, modeling Micro-deformation remains unfeasible. Theoretically, it can be taken into account, but\ud the results may not be reliable due to the limited size of the tool meshes and due to approximations in the contact algorithms

Compensation of deep drawing tools for springback and tool-deformation

Manual tool reworking is one of the most time-consuming stages in the\ud preparation of a deep drawing process. Finite Elements (FE) analyses are now widely\ud applied to test the feasibility of the forming process, and with the increasing accuracy of the\ud results, even the springback of a blank can be predicted. In this paper, the results of an FE\ud analysis are used to carry out tool compensation for both springback and tool/press\ud deformations. Especially when high-strength steels are used, or when large body panels are\ud produced, tool compensation in the digital domain helps to reduce work and save time in the\ud press workshop. A successful compensation depends on accurate and efficient FE-prediction,\ud as well as a flexible and process-oriented compensation algorithm. This paper is divided in\ud two sections. The first section deals with efficient modeling of tool/press deformations, but\ud does not discuss compensation. The second section is focused on springback, but here the\ud focus is on the compensation algorithm instead of the springback phenomenon itself

Tool And Blank Interaction In The Cross-Die Forming Process

The deformation of the press and the forming tools during a deep drawing process is small. However, it has a significant influence on the formed product, since the draw-in is affected significantly by this deformation. This effect is demonstrated for the cross-die forming process. The process was simulated using the commercial code ABAQUS, comparing different models for the forming tools and blank. The simulated process behaves quite differently when rigid or deformable tools are applied. In the latter case, so-called tool-spacers absorb a significant part of the blankholder load, resulting in a stronger draw-in of the blank. In all cases, the results depended heavily on the blank element type and on numerical settings for the contact algorithm. These should be treated with great care when accurate results are required

Equivalent drawbead performance in deep drawing simulations

Drawbeads are applied in the deep drawing process to improve the control of the material flow\ud during the forming operation. In simulations of the deep drawing process these drawbeads can be replaced by\ud an equivalent drawbead model. In this paper the usage of an equivalent drawbead model in the finite element\ud code DiekA is described. The input for this equivalent drawbead model is served by experiments or by a 2D\ud plane strain drawbead simulation. Simulations and experiments of the deep drawing of a rectangular product\ud are performed to test the equivalent drawbead model performance. The overall conclusion reads that a real\ud drawbead geometry can succesfully be replaced by the equivalent drawbead mode

Advanced sheet metal forming

Weight reduction of vehicles can be achieved by using high strength steels or aluminum. The formability of aluminum can be improved by applying the forming process at elevated temperatures. A thermo-mechanically coupled material model and shell element is developed to accurately simulate the forming process at elevated temperatures. The use of high strength steels enlarges the risk of wrinkling. Wrinkling indicators are developed which are used to drive a local mesh refinement procedure to be able to properly capture wrinkling. Besides, to intensify the use of implicit finite element codes for solving large-scale problems, a method is developed which decreases the computational time of implicit codes by factors. The method is based on introducing inertia effects into the implicit finite element code. It is concluded that the computation time is decreased by a factor 5-10 for large-scale problems