We use Bystronic 320 tonne pressbrakes to fold 100s of tonnes of steel a year. I use the following settings in Solidworks and advise our clients to do the same.
Mild Steel K-Factors for 90° Folds
1mm, R1mm, K-Factor 0.2733
2mm, R2mm, K-Factor 0.2733
3mm, R3.84mm, K-Factor 0.4
4mm, R5.12mm, K-Factor 0.4
5mm, R6.4mm, K-Factor 0.4
6mm, R8mm, K-Factor 0.4
8mm, R9.6mm, K-Factor 0.4
10mm, R12.8mm, K-Factor 0.4
12mm, R16mm, K-Factor 0.4
15mm, R24mm K-Factor 0.5
Plate Rolling, All Thickness, K-Factor 0.5
Accuracy using these settings is +/- 0.25mm on S275, S355, DD11, DC01.
Basically the radius is the material thickness x 8, which equates to the vee size to be used. Then this is multiplied by 0.16 to get the inside bend radius (e.g. 4mm x 8 = Vee32, 32 x 0.16 = R5.12)
It would be interesting to know what other users of Solidworks use in their bend settings?