1. Match the Material to the Bending Requirement
Prioritize galvanized sheet with low yield strength and high elongation - bending performance is closely related to plasticity.
Deep-drawing-grade galvanized sheet typically has elongation ≥38% and yield ≤180 MPa (typical values) - suitable for complex bends.
Structural-grade sheet has higher yield and lower elongation - suitable only for simple bends; avoid large angles and small radii.
Select sheet with a uniform galvanizing layer and strong adhesion; avoid scratches, pitting or peeling - these defects act as stress-concentration points during bending.
2. Optimise the Process Parameters
2.1 Bend radius (operating references).
Ordinary mild galvanized sheet: minimum inner radius ≥0.5×t (for 2 mm sheet, R ≥1 mm); high-strength sheet: 1.5–2×t. For small radii, use pre-bending or step-bending to release stress gradually.
2.2 Angle and speed.
Avoid bending beyond 90° in one pass; bend in stages to reduce local stress concentration. Avoid excessive speed, which can cause brittle cracking from insufficient plastic deformation.
2.3 Die and gap.
Keep the die cutting edge smooth; adjust the upper/lower die gap to 1.0–1.2×t (too little gap compresses and cracks; too much causes wrinkling).
3. Pre- and Post-Treatment
For cold-rolled or work-hardened galvanized sheet, low-temperature stress relief (150–200 °C for 1–2 h, base metal only) eliminates internal stress and improves plasticity; avoid pre-bending deformation during transport.
If minor coating cracks appear after bending (base metal undamaged), apply passivation (prefer chromium-free passivation per current EU REACH rules) or anti-rust paint to prevent rust spread; if the base metal cracks, replace the sheet and re-evaluate the process.
4. Avoid Human-Factor Cracking
Bend perpendicular to the rolling direction - plasticity is greater along the rolling direction (lengthwise) than across the width; if bending along the rolling direction is unavoidable, increase the bend radius.
Smooth burrs or shear marks on edges and corners before bending - otherwise they become cracking points under stress.
5. Core Principle
Choose the right materials, optimise parameters and standardise operations - adjusted to the sheet's yield strength and elongation plus the bending angle and radius. Verify difficult bends (small radius, large angle) by trial bending first; give priority to deep-drawing sheet combined with annealing for the most demanding cases.
6.Quality inspection of galvanized steel sheets
