Evaluation of the minimum distance of the hole position in the V-die bending process

Hole precision and hole roundness after bending are very important, especially for bent part assemblies using the hole assembly technique. In the past, determining the minimum distance of the hole location (d_min) was considered useful for retaining the hole roundness; however, this d_min determination overestimated this value. Thus, a primary challenge in present research is to determine whether d_min is suitable for the V-die bending process. Investigations were carried out by using the finite element method (FEM) and laboratory experiments. The V-die bending model, including the workpiece thickness (ranging from 2 mm to 6 mm), bend angle (ranging from 30° to 150°), bend radius (ranging from 3 mm to 30 mm), and workpiece material (aluminum, A1100-O(JIS) and low-carbon cold rolled steel (SPCC(JIS)) were examined. The newly developed equation for d_min is a function of the workpiece thickness, bend angle and bend radius; this is different from the previous determination of d_min, where only the bend radius and workpiece thickness were considered. The d_min values using the previous equation were estimated, but the proposed formula was more accurate. Specifically, compared with the previously used formula, the new formula provides shorter d_min values of approximately 20% and 15% in the cases of 90° and 150° bend angles, respectively. The experiments were carried out, and the experimental d_min values were in good agreement with the d_min values using the newly developed equation. Therefore, to achieve the desired precise hole after bending, the use of newly developed d_min equation is strongly recommended.