Effect of punching die angular clearance on punched hole quality of S275 mild steel sheet metal

Abstract

Metal punching processes are widely used in mass production because of their simplicity, high levels of productivity, and low costs. The quality of the product made by punching greatly depends on various processing parameters such as the tool geometries, sheet material properties, punching conditions, punch and die material properties, and tooling wears. In this study, the effects of die clearance angles and die opening sizes were compared on the accuracy and quality of punched holes produced on 1.4-mm thick S275 mild steel metal sheet. A total of nine punching dies were made with die clearance angles of 0.25°, 0.50°, and 0.75° for each die opening sizes of o20.225 mm, o13.225 mm, and o12.225 mm. The burr formations and die weight losses were monitored for 10th, 50th, 100th, 500th, and 1000th strokes. The results show that the die weight loss, indicative of wear, increases as the number of strokes increase, with the most losses at the initial stages of the punching process (10th–50th strokes). The lowest weight loss was obtained for dies with 0.75° angular clearance, corresponding to the lowest wear occurrence. The low wear indicates that the shearing edge remains relatively sharp and thus able to produce good quality holes. Thus, for producing good quality holes and increasing tool life, it is recommended that an angular clearance of 0.75° is considered in the design of punching dies.