Curling is a sheet metal forming operation in which the edge of a metal sheet is rolled into a circular or curved shape.
It is mainly done to remove sharp edges and improve safety and appearance.
Curling also increases the strength and stiffness of the sheet edge.
In this article:
Curling in Sheet Metal
What is Curling?
Curling is a sheet metal forming operation in which the edge of a sheet is rolled into a circular or curved shape to remove sharp edges and increase strength.
👉 No material is removed
👉 Edge is rolled into a loop or circular form
👉 Improves safety and stiffness
Curling is commonly used in containers, lids, and panels.
Working Principle
Step-by-step Process:
- Sheet is placed in curling die.
- A forming tool applies pressure to the edge.
- The edge gradually bends and rolls.
- Final rounded edge is formed.
Main Components
1. Curling Die
- Has groove matching desired curl shape
2. Punch / Roller
- Applies forming force
3. Press Machine
- Mechanical or hydraulic
Purpose of Curling
✔ Removes sharp edges
✔ Increases rigidity
✔ Improves appearance
✔ Makes edge safe for handling
Important Parameters
- Curl diameter
- Sheet thickness
- Material ductility
- Clearance between die and tool
Proper control prevents:
❌ Cracking
❌ Wrinkling
❌ Flattening of curl
Types of Curling
1. Open Curl
Edge rolled partially.
2. Closed Curl
Edge rolled into full circular loop.
3. Beaded Edge
Small rounded edge for stiffness.
Applications
- Food and beverage cans
- Drum containers
- Sheet metal lids
- Automotive panels
- Household appliances
Advantages
✔ Safe edges
✔ Improved strength
✔ Better appearance
✔ No material waste
Disadvantages
✖ Requires precise tool design
✖ Not suitable for brittle materials
✖ Additional operation increases cost
Curling vs Hemming
| Feature | Curling | Hemming |
|---|---|---|
| Edge Shape | Circular | Folded flat |
| Purpose | Safety & stiffness | Joining & strengthening |
| Appearance | Rounded | Flat folded |
Summary
- Curling is an edge forming process.
- Used to remove sharp edges.
- No material is cut.
- Improves stiffness and safety.
- Used mainly in can manufacturing.
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