1.What are the core formulas and general principles?
For the most commonly used ordinary low-carbon cold-rolled steel sheets (such as SPCC, DC01, Q235, etc.):
When the bending line is perpendicular to the rolling direction, the minimum safe bending radius is typically R ≥ 0.5t ~ 1.0t.
This means that for a 1mm thick sheet, its minimum inner bending radius is approximately between 0.5mm and 1mm.
Corresponding to the "outer angle" of a 90-degree bend, this usually means that a very sharp right angle can be formed (the outer angle is not a rounded corner), but there is a corresponding small radius at the inner angle.
2.How does material thickness affect the minimum bending radius?
The greater the thickness, the greater the difference in deformation between the inner and outer sides during bending, and the larger the minimum radius required. This is the most important influencing factor.
3.How do material grade and condition affect the minimum bending radius?
Soft state (annealed state): such as SPCC-SD (extra soft), with excellent plasticity; minimum radius (R) can reach 0.2t or less.
Semi-hard and hard state: such as SPCC-1/2H and 1H, due to work hardening, plasticity decreases, and the minimum radius (R) needs to be increased to 1t or even more than 2t.
High-strength steel: such as high-strength IF steel, duplex steel (DP), and martensitic steel (MS), the higher the strength, the lower the plasticity, and the larger the minimum radius (R) requirement (can reach 2t~4t or even greater).
4.How do the bending direction and rolling direction affect the minimum bending radius?
Bending line perpendicular to the rolling direction: This is the optimal direction, as the material has good ductility along the rolling direction, resulting in the smallest bending radius.
Bending line parallel to the rolling direction: Material properties are poorer in this direction, making it prone to cracking. The minimum bending radius needs to be increased, typically recommended to be 1.5 to 2 times that of the perpendicular direction.
5.How do process conditions affect the minimum bending radius?
Die clearance and fillet radius: The width of the lower die's V-shaped opening and the fillet radius of the upper die (punch) tip directly affect the forming effect. An excessively small punch fillet radius will exacerbate localized stress.
Bending speed: Excessive bending speed may reduce material flowability and increase the risk of cracking.
Edge condition: Burred edges after shearing or punching, if located in the outer tension zone, will become stress concentration points, easily leading to cracking. Burred edges should be placed on the inner side (compression zone) or deburred first.