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1. Radius of punch fillet rp
When the relative bending radius r/t of the bending part is less than 5 ~ 8 and not less than rmin/t (Table 3-3), the fillet radius of the punch is taken as the fillet radius of the bending part, that is, RP = R; if r/t is less than rmin/t, it should be taken as rp≥rmin, and the bending part should be bent into a larger fillet radius first, and then the forming process should be adopted to meet the fillet radius requirements of the bending part.
When the relative bending radius of the bending part is r/t≥ 10, and the accuracy requirement is high, the resilience of the fillet radius should be considered. Rp is calculated according to formula 3-, and should be modified according to the rebound value after die test.
2. Radius rd of concave die fillet?
The radius of fillet on both sides of the die should be the same, otherwise the blank will be offset when bending. Rd should not be too small, otherwise the bending arm of bending moment will decrease, and the sliding resistance of the blank will increase when it is pulled into the die, which will easily scratch or indentation the surface of the bending part; But when rd is too large, it will affect the accuracy of blank positioning. In production, the radius rd of concave die fillet is usually selected according to the material thickness:
When t ≤2mm, rd = (3 ~ 6) t.
When t =2~4mm, rd = (2 ~ 3) t.
When t > 4 mm, rd =2t.
For V-shaped bending die, according to the thinning of bending deformation zone, the bottom can be provided with unloading groove or fillet radius RD ′ = (0.6 ~ 0.8) (RP+T).