Free Engineering Tool
Compare a selected inside bend radius with typical material-specific starting ranges. See R/t, outside radius and a suggested V-die reference.
Use this check before finalising a flat pattern or press-brake route. It distinguishes the common starting range from the more conservative end where cracking or springback risk may require a trial bend.
The minimum bend radius in sheet metal is the smallest inside radius that can be formed without unacceptable cracking, orange peeling or loss of function, commonly expressed as a multiple of sheet thickness t. A practical starting range is about 1t for mild steel and aluminium 5052, 1.5t-2t for stainless steel 304, 2t-3t for aluminium 6061-T6, and roughly 0.5t-1t for soft copper. The controlling ratio is R/t, where R is the inside radius and t is thickness. Lower R/t raises strain on the outside surface and changes springback, bend allowance and V-die behaviour. Grain direction, temper, edge quality, surface condition and bending method can move the safe limit. Treat the table as a review range, not a guarantee. Zhejiang Balford Mechatronics Co., Ltd. evaluates forming routes at its 12,000 m² production facility and confirms critical radii with representative trial bends.
The radius is inside the typical range but below its conservative end. A trial bend is advisable for stainless or high-strength materials.
Minimum bend radius is not a single universal material constant. Surface condition, rolling direction, temper, bend line, tooling, springback and required residual stress all affect the safe limit.
The calculator compares the drawing's inside radius with a material-specific multiple of sheet thickness.
| Material | Typical R/t range | Main condition |
|---|---|---|
| Mild / low-carbon steel | 1.0t–1.2t | Annealed or normal forming grade |
| Stainless steel 304 | 1.5t–2.0t | Springback and work hardening |
| Aluminium 5052-H32 | 1.0t–1.5t | Temper and grain direction |
| Aluminium 6061-T6 | 2.0t–3.0t | Higher cracking risk at tight radius |
| Copper, soft | 0.5t–1.0t | Temper dependent |
| Brass | 0.8t–1.5t | Temper dependent |
| Spring / high-strength steel | 1.5t–2.5t | Strength and edge quality |
Broad process-review ranges, not material specifications. Use the material certificate and a representative trial bend for production release.
A 2 mm mild-steel part with a 2 mm inside radius has R/t = 1.0. Using the 1.0t–1.2t starting range, the selected radius is at the minimum end and a trial bend should confirm cracking, springback and final radius. The outside radius is 2 + 2 = 4 mm.
Bend radius is the curvature of the formed sheet. The inside bend radius is measured on the inner surface next to the punch, while the outside radius is the inside radius plus sheet thickness. Drawings and press-brake programmes normally specify the inside radius.
A practical estimate is minimum inside radius = material factor × sheet thickness. The factor is commonly around 1t for mild steel and aluminium 5052, about 1.5t–2t for stainless 304 and about 2t–3t for aluminium 6061-T6. Material temper, grain direction and edge condition can change the limit.
R/t is the inside radius divided by sheet thickness. It describes how tightly the material is being bent relative to its thickness. Low R/t raises outer-fibre strain and cracking risk; it also changes springback, bend allowance and the useful V-die range.
Yes. Bending some aluminium and high-strength materials parallel to the rolling direction can raise cracking risk. Where possible, orient the bend line across the grain and confirm the safe radius with a trial part, especially for 6061-T6 or high-strength steel.
No. It is a starting range for process review, not a material certification. Actual acceptance depends on material certificate, temper, surface condition, bend line, tooling, springback and the required inspection. Establish the production radius with a representative first-article bend.
Send the drawing, material grade and temper, thickness, bend line, required radius and surface requirement. Send the drawing to shawn@balford.net. We normally reply within 24 hours, China Standard Time.