Manufacturing Process
Curling
卷边 / 翻边
Rolling the edge of sheet metal into a rounded rim to add stiffness, remove sharp edges and improve part safety.
Process Steps
- Edge trimmed to width
- Curl die rolls edge
- Radius and profile checked
- Edge hardness/quality inspected
What is curling?
Direct answer: curling rolls the edge of a sheet metal part into a loop or a tube. It rounds a sharp edge, stiffens the part, and in some designs forms the hinge or the rolled rim you would otherwise weld on.
Curling, hemming and beading are not the same
| Edge treatment | What happens | Result |
|---|---|---|
| Curl (roll) | The edge is rolled into an open or closed loop | Rounded, stiff edge; can be a hinge or a rim |
| Hem | The edge is folded 180° back on itself and flattened | Thick double edge with no gap; no exposed burr |
| Bead | A groove is formed into the surface, not the edge | Stiffening and appearance |
Designers often use the words interchangeably, and the difference matters: a hem has no gap and doubles the edge thickness, while a curl leaves the inside of the roll open.
What decides whether a curl is possible
- Inside diameter of the curl. As a rule the inside radius should be at least 1–2× the material thickness; tighter curls crack at the outside of the roll.
- Edge length. The material has to be long enough to form the circumference you want — curling does not create material.
- Material. Mild steel and soft aluminium curl easily; stainless needs a larger radius; coated stock can crack at the coating.
- Direction of the burr. Rolling a burr to the inside hides it; rolling it to the outside leaves it visible.
Where it is used
- Rolled rims on covers, cups and housings — a safe edge and a stiff one in a single operation.
- Hinge knuckles: a series of curls on alternating parts forms an interlocking hinge.
- Stiffening the free edge of a bracket or a panel.
Frequently asked
What is the minimum curl radius?
Roughly 1–2× the material thickness for the inside radius of the roll. Tighter than that, the outside of the curl starts to crack.
Can a curled edge be plated?
Yes, but a closed curl traps solution and can bleed plating salts afterwards. Where the part will be plated, an open curl, a small gap, or a drain consideration avoids staining after the fact.
Do I need a special die for curling?
The curl is usually formed inside the stamping tool with a curling slide or a forming station. It is a tooling feature rather than a separate machine operation.
Curling or hemming for a safe edge?
A hem gives a thinner, tighter edge with no gap and is common on enclosures. A curl gives a rounder, stiffer edge with an open inside, and is the usual choice for a rim or a hinge knuckle.
Related: metal bending · trimming · deburring · deep drawing · precision stamping