Springback is a major problem in the deep drawing process. When the tools are released after the forming stage, the product springs back due to the action of internal stresses. In many cases the shape deviation is too large and springback compensation is needed: the tools of the deep drawing process are changed so, that the product becomes geometrically accurate after springback. In this paper, two different ways of geometric optimization are presented, the Smooth Displacement Adjustment (SDA) method and the Surface Controlled Overbending (SCO) method. Both methods use results from a finite elements deep drawing simulation for the optimization of the tool shape. The methods are demonstrated on an industrial product. The results are satisfactory, but it is shown that both methods still need to be improved and that the FE simulation needs to become more reliable to allow industrial application.

Numerical simulations are being deployed widely for product design. However, the accuracy of the numerical tools is not yet always sufficiently accurate and reliable. This article focuses on the current state and recent developments in different stages of product design: springback prediction, springback compensation and optimization by finite element (FE) analysis. To improve the springback prediction by FE analysis, guidelines regarding the mesh discretization are provided and a new through-thickness integration scheme for shell elements is launched. In the next stage of virtual product design the product is compensated for springback. Currently, deformations due to springback are manually compensated in the industry. Here, a procedure to automatically compensate the tool geometry, including the CAD description, is presented and it is successfully applied to an industrial automotive part. The last stage in virtual product design comprises optimization. This article presents an optimization scheme which is capable of designing optimal and robust metal forming processes efficiently. r

Now that Finite Element springback prediction has become possible, springback compensation can also be carried out in the context of a forming simulation, before actual production tools are made. The Displacement Adjustment (DA) and Springforward (SF) methods were applied to an analytical bar stretchbending model, in order to gain insight about the influence of material, process and geometrical parameters on springback and compensation. The DA method was investigated in both a one-step and iterative variant. In one-step DA, a compensation factor is required. This factor can be directly calculated for the analytical model. The results can be used as a guideline for industrial processes, where such a calculation is not possible. Finally, it was shown that iterative DA leads to better tool shapes than SF, and that practical and computational problems make the use of SF impossible in an industrial context.

Computer-aided engineering (CAE) has significantly expedited product development in the automotive industry. In the process design and planning of deep drawing processes, computer-aided design tools and finite element (FE) simulations are used together in order to achieve a high-quality product within an acceptable time-span. Here, finding the right shape for the forming tools is one of the most important tasks. However, when the tools are manufactured and tested on the prototype press the quality of the prototype parts rarely satisfies the requirements straightaway. Therefore, manual reworking of the forming tools is required. Because reworking is highly time-consuming and because a lot of experience is required by the tool technicians, this is the most significant bottleneck in the process-planning today.

Abstract. Upon unloading after the forming stage, a sheet metal product will spring back due to internal stresses. Springback is a major problem for process-planning engineers. In industrial practise, deformations due to springback are compensated manually, by doing extensive measurements on prototype parts, and altering the tool geometry by hand. This is a time consuming and costly operation. In this paper the application of two compensation algorithms, based on the finite element simulation of the forming process are discussed. The smooth displacement adjustment (SDA) method and the springforward (SF) method have been applied to several industrial products, such as the NUMISHEET 2005 benchmark#1. With the SDA method successful compensations have been carried out. For the SF method some principal problems remain.

An overview of sheet metal forming simulations with enhanced assumed strain elements AIP Conf. Proc. 908, 741 (2007); An advanced constitutive model in the sheet metal forming simulation: the Teodosiu microstructural model and the Cazacu Barlat yield criterion AIP Conf.Abstract. During forming, the deep drawing press and tools undergo large loads, and even though they are extremely sturdy structures, deformations occur. This causes changes in the geometry of the tool surface and the gap width between the tools. The deep drawing process can be very sensitive to these deformations. Tool and press deformations can be split into two categories. The deflection of the press bed-plate or slide and global deformation in the deep drawing tools are referred to as macro press deformation. Micro-deformation occurs directly at the surfaces of the forming tools and is one or two orders lower in magnitude.The goal is to include tool deformation in a FE forming simulation. This is not principally problematic, however, the FE meshes become very large, causing an extremely large increase in numerical effort. In this paper, various methods are discussed to include tool elasticity phenomena with acceptable cost. For macro deformation, modal methods or 'deformable rigid bodies' provide interesting possibilities. Static condensation is also a well known method to reduce the number of DOFs, however the increasing bandwidth of the stiffness matrix limits this method severely, and decreased calculation times are not expected. At the moment, modeling Micro-deformation remains unfeasible. Theoretically, it can be taken into account, but the results may not be reliable due to the limited size of the tool meshes and due to approximations in the contact algorithms.

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.

No abstract