Learn about minimum bend radii for different materials and thicknesses. Understand how to prevent cracking, design for manufacturability, and select appropriate radii.
Introduction
The minimum bend radius is critical in sheet metal design. Bending below the tolerable radius causes cracking. At Fulei Metal, we help clients specify appropriate bend radii.
What Determines Minimum Bend Radius?
Material ductility, thickness, temper, grain direction, and edge condition all determine the minimum radius. Ductile materials tolerate tighter radii. Thicker materials need proportionally larger radii. Annealed tempers allow smaller radii. Bending across grain is safer.
Minimum Bend Radius by Material
Mild Steel
Rule: 0.8 times thickness across grain. For 1 mm: 0.8 mm. For 2 mm: 1.5 mm. For 3 mm: 2.4 mm. For 5 mm: 4.0 mm. For 10 mm: 8.0 mm.
Stainless Steel
Rule: 1.0 times thickness. Excellent ductility (40-60% elongation). For 1 mm: 1.0 mm. For 3 mm: 3.0 mm. For 5 mm: 5.0 mm.
Aluminum
Varies by alloy. Soft alloys (5005-O): 0.5-1.0 times thickness. Medium (5052-H32): 1.0-1.5 times. Hard (6061-T6): 1.5-3.0 times.
Galvanized Steel
Base metal: 0.8-1.0 times. To prevent coating cracking: 1.0-1.2 times.
Consequences of Bending Below Minimum
Cracking on the outside of the bend. Reduced strength from micro-cracks. Coating damage. Aesthetic defects.
Designing for Appropriate Bend Radii
Use standard radii (0.5, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 8.0, 10.0 mm). Design with material in mind. Consider grain direction. Add bend relief. Avoid multiple tight bends in sequence.
Testing Bend Feasibility
Always perform test bends for new materials, unusual thicknesses, or tight radii. Cut a sample, bend, inspect for cracking. Test both grain directions if unknown.
Common Mistakes
Specifying radius equals zero (impossible). Underestimating aluminum requirements. Ignoring grain direction. Not testing new materials.
Conclusion
Understanding and specifying appropriate minimum bend radii prevents cracking. At Fulei Metal, our experience enables us to advise on appropriate radii and produce bends meeting structural and aesthetic requirements.