Tearing criterion and process window of hot metal gas forming for AA6063 cylindrical stepped tubes
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Hot metal gas forming (HMGF) with axial feeding presents unique features that enable the complex and further expansion of workpieces that are characterized by minimal defects, such as wrinkles and tears. In this study, the effects of process parameters on the HMGF of aluminum alloy 6063 for the production of cylindrical stepped tubes were investigated through experimental tests and finite element simulations. The effects of applied axial feeding, temperature, and pressure on the thickness distribution of specimens and the percentage of die filling were studied. Pressure and axial feeding were applied gradually with a linear increase over a period of 600 s. The second derivative of the specimens’ thickness strain with respect to time was used as a criterion for predicting tearing. The results were then used to plot the process window of HMGF. The obtained stress distributions showed that a gradual increase in gas pressure increased tensile stress in the forming zone, thereby facilitating the elimination of wrinkles created during axial feeding. Increasing temperature reduced the extent of successful deformation but decreased pressure, thus increasing the percentage of die filling.
KeywordsHot metal gas forming FEM Process window Cylindrical stepped tube Tearing criteria AA6063
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