Press brake bending/Part II: Bending allowance in air bending

摘要

During air bending a sheet is placed on the die, and a press's ram descends and bends the sheet into a V shape (see Figure la). The process is common because dies don't need to be changed to achieve different bending angles. For a given die opening, the bend angle is determined by the punch stroke. Various air bending parameters tress, strain, bending moment, bend force, springback, and bend allowance-can affect the process. During bending the outer fiber of the sheet material, indicated by radius R^ is in tension while the inner fiber, indicated by R_i, is in compression (see Figure lb). The length of the fibers in tension increases while the length of those in compression decreases. Between Ro and R. is the neutral axis. Fibers along this axis are under neither tension nor compression; their length does not change. In the unbent sheet, the neutral axis coincides with the sheets centerline. However, as the sheet undergoes bending, the neutral axis shifts toward the inner radius, R_i (see Figure lb).