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 (dmin) was considered useful for
retaining the hole roundness; however, this dmin determination overestimated this value. Thus, a primary challenge in pre
sent research is to determine whether dmin 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 dmin is a function of the workpiece thickness, bend angle and bend radius; this is dif
ferent from the previous determination of dmin, where only the bend radius and workpiece thickness were considered.
The dmin 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 dmin values of approximately 20% and 15%
in the cases of 90° and 150° bend angles, respectively. The experiments were carried out, and the experimental dmin
values were in good agreement with the dmin values using the newly developed equation. Therefore, to achieve the desired
precise hole after bending, the use of newly developed dmin equation is strongly recommended.