Gas dynamics analysis of an air pocket in the metal-stamping process

Abstract

Metal stamping is widely used in the mass production process utilized in the automobile industry. During the stamping process, air may be trapped between the draw die and the panel and/or between the punch and the panel. The pressure of the trapped air pocket builds up as the punch moves downwards. The high pressure of the air pocket induces imperfections on the panel surface and creates a situation where an extremely high tonnage of punch is required to reach the home position. To prevent these problems, many air ventilation holes are drilled through the draw die and the punch. However, most die makers drill excessive air ventilation holes on a trial-and-error basis and waste labour time and cost. The present work has developed a mathematical formulation for computing the pressure of the air pocket at a given cross-sectional area of air ventilation holes, which is based on the ideal gas with an isentropic relation. The pressure of the air pocket was compared with the commercial computational fluid dynamics (CFD) code and experiments. It was found that the pressure agreed well with the results of the CFD code and experiments. The present work also used inverse design methodology to calculate the cross-sectional area of the air ventilation holes, which did not exceed the prescribed maximum pressure of the air pocket.