A Study on Hole Flanging Mechanism to Improve Geometrical Accuracy

Hole flanging is a process that consists of hole piercing and forming a hole flanging with a punch bending and pushing material around hole to form a flange. One of a major problem that arises after the hole flanging process is the formation of uneven ends of the hole flange. In case the work requires high accuracy, time and production costs increase to smooth the surface. In this study, the influence of the punch geometry on the shape accuracy of the finished workpiece from the hole flanging process was studied by investigating punches with various shapes, including conical punch with 60-degree, conical punch with 120-degree, flat punch and hemispherical punch. According to the finite element simulation, it was found that the uneven tip of the hole edge on the workpiece was caused by the inclined face of the punch contacting and pushing against the edge of the drill hole at the beginning of the forming process, and by the punch dragging the remaining material at the end of the forming process. From the analysis of the behavior of expanding the hole to the flange area, it was found that changing the shape of the punch alone could not reduce the uneven tip of the workpiece flange. Therefore, the researcher proposed a method to improve the quality of forming the hole expansion by pressing the edge of the drill hole with a punch and designed a new punch, which resulted in a reduction of the uneven tip of the hole flange.