Investigation of viscous pressure forming for 6K21-T4 aluminum alloy car panels

Abstract

Aluminum alloy car panels are difficult-to-form, complex components, with low formability at room temperature and high springback, and are easily scraped after forming. Although several advanced forming technologies have been developed to improve the formability of aluminum alloys, currently, there are no viable and cost-effective methods for the manufacture of high-quality aluminum alloy car panels. In this paper, a newly-developed flexible die forming approach called viscous pressure forming (VPF) is proposed to manufacture car hoods with scaled-down dimensions. The use of VPF technology provides decreased springback and improved surface quality, and manufacturing expense can be decreased by taking advantage of the characteristics of this technology. Both forming experiments and the finite element method (FEM) were adopted to investigate the forming of the panels and to verify the accuracy of the simulation model. The FEM was then used to further investigate key forming process parameters, such as sheet blank shape and blank holder force (BHF), particularly their role in the main defect of local wall thinning. Results indicated that the maximum thinning of a formed hood was 32.4 % when using an initial sheet blank under a constant BHF of 40 kN, while it decreased by 41.7 % when using the optimized sheet blank under variable BHF with segmented binders. This is mainly because material flow can be efficiently controlled under variable BHF. VPF technology combined with an appropriate sheet blank and variable BHF is an advantageous approach for manufacturing high-quality aluminum alloy car panels.