Prediction of delamination and tearing during stamping of polymer-coated metal sheet

The objective of this study is to design a stamping process for polymer-coated metal (PCM) sheets to prevent defects such as delamination and tearing. A defect diagram composed of the delamination limit curve and the tearing limit curve of the PCM sheet is developed for determining the safe region. Similar to the forming limit diagram, the defect diagram is constructed using the critical major and minor strains at which defects occur in various deformation modes. Experiments are performed for establishing the defect diagram of the PCM sheet by means of the limit dome height test and square cup deep-drawing test. A cross-hatched specimen is employed for estimating the delamination of the polymer layer from the steel substrate. Based on the defect diagram, a finite element analysis (FEA) of the stamping process is conducted to determine a forming condition without delamination and tearing. The effectiveness of the stamping process designed on the basis of the developed defect diagram is verified by a forming experiment. Comparison of the FEA results and experimental results reveals that the defect diagram is efficient and suitable for the design of the actual stamping process using PCM sheets.