Fuel cell technology offers a sustainable power supply solution for heavy-duty vehicles, aviation and shipping as well as stationary application. Manufacturing of metallic bipolar plates (MBPP) as a key component of fuel cells is nowadays one of the main topics in production-based research and processing industry. One reason for this is that although stamping of thin stainless-steel foils enables an economic large-scale production of metallic bipolar plates, tooling and press technologies required for embossing and shear cut operations are highly demanding and thus continuously being developed. Particular challenges are posed by the embossing of the complex flow field structure, which can cause forming defects and pronounced springback phenomena.
The use of finite element (FE [12], [16]) simulations to conduct a virtual validation of the forming process for sheet metal parts has been introduced in the mid 1990s and is state of the art in the automotive industry today. Two challenging tasks for determination of feasibility of a tool design and its process parameters [17] are the prediction of the material behavior during the forming process and the springback of the final part [2,3,4].
Novelis is a world leader in aluminium flat rolled products and a major supplier to the beverage can-making industry. As such, Novelis is deeply involved in supporting the can-making industry to help shaping a more sustainable future together. Reducing the amount of metal used for each beverage can is a major driver for improving sustainability of the beverage can packaging, thus Novelis is actively investigating and developing state of the art modelling tools and approaches to support further optimization of the beverage can.
To reduce cost and increase the efficiency of D&I food cans, a lighter can with the same axial stability and paneling resistance is required. Axial stability depends on wall thickness, bead geometry (mainly bead depth) and tensile strength in the wall, whereas paneling resistance is a function of wall thickness, Young’s modulus and bead geometry (mainly bead depth), with the bead depth having an opposite influence on paneling resistance and axial stability. FEA is used to find a bead geometry that satisfies both the paneling resistance and axial stability requirements. For a stable calculation of the paneling resistance, perturbation in the form of an eigenmode is required. The calculation time is significantly reduced by using an implicit solver with arc length method. When simulating axial stability, accurate modeling of the beginning of the flow curve is required. A weight reduction of 5% can be achieved by using next-generation high-strength D&I steel grades (e.g. rasselstein® D&I Solid).
Hollow embossing rolling constitutes a promising forming technology for metallic bipolar plates due to the high achievable production rates. The simulation-based process optimization is impeded by the incremental forming character and modeling of fine channel structures, which leads to large model sizes and computation times. This paper presents a shell-based finite element modeling approach using LS-DYNA© for bipolar plate forming simulation. Essential boundary conditions of the modeling are discussed, and recommended setting parameters are derived.
Sheet metal forming simulations are crucial in various industries, such as automotive, aerospace, and construction. These simulations are commonly carried out using Reissner-Mindlin shell elements, which involve certain simplifying assumptions about zero normal stress in shell normal direction and cross-sectional fibers remaining straight during deformation [1]. Because of this, the material model needs to be modified and no three-dimensional material model can be used. However, in critical forming situations such as bending with small radii relative to the sheet thickness, these assumptions do not hold, resulting in inaccurate simulation results. To address this issue, a higher-order 3D-shell element that incorporates a full three-dimensional constitutive model and that can account for cross-sectional warping and higher-order strain distributions has been developed [2].
Forming limit curves (FLCs) are widely used for the feasibility analysis of deep drawn steel components and the final tool design. The experimental determination of the FLC is usually based on Nakajima tests, which are evaluated according to the ISO 12004-2 standard with the intersection line method. In recent years the additional determination with the time dependent method [1] is used since it more accurately describes the increased forming potential of modern high ductility steel grades found in practical experiments.
Novelis is a world leader in aluminium flat rolled products and a major supplier to the beverage can-making industry. As such, Novelis is deeply involved in supporting the can-making industry to help shaping a more sustainable future together. Reducing the amount of metal used for each beverage can is a major driver for improving sustainability of the beverage can packaging, thus Novelis is actively investigating and developing state of the art modelling tools and approaches to support further optimization of the beverage can.
This two-part series focuses on the industrial application of higher-order 3D-shell elements and anisotropic 3D yield functions in sheet metal forming simulations. In the second part, the effect of plastic anisotropy with respect to the in-plane and out-of-plane behaviour on sheet metal forming simulations is analysed. To this end, parameters of the anisotropic 3D yield function Yld2004-18p were identified by a crystal plasticity modelling approach for an AA6014-T4 aluminium alloy. Different loading conditions related to the plane and full stress state were carried out to study the plastic anisotropy with respect to the in-plane and out-of-plane behaviour.
Numerical study on a new forming method for manufacturing large metallic bipolar plates