Formability of coated vinyl on sheet metal during deep drawing process

• A finite element model for laminated sheet metals was established using GTN model.
• Fracture characteristics of polymer films and adhesive were simulated by GTN model.
• The numerical model was verified using tensile tests and rectangular deep drawing.
• Forming limit curves of VCM were predicted using the verified numerical model.

In this study, the formability of vinyl coated metal (VCM) which is sheet metal coated with PET and PVC was studied. VCM has excellent appearances because of the artificial pattern named hairline and is used in home appliances such as washing machines and refrigerators. However, there are problems in the formability of VCM because PET film fracture or delamination occurs when VCM is formed (in particular, in drawing processes) in some cases. To predict the formability of VCM, a finite element numerical model that expressed material damage was established using GTN (Gurson–Tvergaard–Needleman) damage model. Individual materials that would constitute VCM were determined through tensile test based reverse engineering. The numerical model was verified using the results of VCM tensile tests and rectangular deep drawing tests and a good congruence between the results obtained from the numerical model and actual phenomena was identified. In addition, the mechanism for PET films to reach fracture early compared to their elongation in VCM forming was identified. Furthermore, bending processes were simulated using the verified numerical model to examine damage behaviors of VCM according to process variables and Nakazima test was simulated to draw forming limit curves and evaluate the formability of VCM.