Hemming is a sheet metal operation in which the edge of the sheet is folded over onto itself.
It is mainly used to eliminate sharp edges and improve strength and appearance.
Hemming is commonly used in automobile body panels and enclosures.
In this article:
Hemming in Sheet Metal
What is Hemming?
Hemming is a sheet metal forming operation in which the edge of a sheet is folded over onto itself (usually 180°) to increase stiffness, improve safety, or join two sheets together.
👉 No material is removed
👉 Edge is folded flat
👉 Improves strength and appearance
Hemming is widely used in automobile body panels and appliance covers.
Working Principle
Step-by-step Process:
- Flanging – Edge is first bent to about 90°.
- Pre-hemming – Edge is bent further (≈ 135°).
- Final hemming – Edge is completely folded to 180°.
Main Components
1. Punch
Applies bending force.
2. Die
Supports sheet during folding.
3. Press Machine / Hemming Tool
Mechanical or hydraulic system.
Purpose of Hemming
✔ Removes sharp edges
✔ Increases rigidity
✔ Improves appearance
✔ Joins two sheets together (in some cases)
✔ Reduces vibration
Important Parameters
- Sheet thickness
- Bend radius
- Material ductility
- Clearance
Proper design prevents:
❌ Cracking
❌ Surface marks
❌ Wrinkling
Types of Hemming
1. Open Hem
Small gap between folded layers.
2. Closed Hem
Folded tightly without gap.
3. Teardrop Hem
Rounded hem to avoid cracking in thick sheets.
4. Rope Hem
Wire inserted inside hem for strength.
Applications
- Automobile doors
- Car hoods and trunk lids
- Washing machine panels
- Refrigerator doors
- Metal enclosures
Advantages
✔ Strong edges
✔ Safe handling
✔ Improved appearance
✔ Good stiffness
Disadvantages
✖ Additional operation increases cost
✖ Not suitable for brittle materials
✖ Requires accurate tool alignment
Hemming vs Curling
| Feature | Hemming | Curling |
|---|---|---|
| Edge Shape | Folded flat | Rolled circular |
| Angle | 180° fold | Circular loop |
| Purpose | Joining & stiffness | Safety & smooth edge |
Summary:
- Hemming is an edge folding operation.
- Usually done in stages (flanging → pre-hem → final hem).
- No material removal.
- Common in automotive industries.
- Improves strength and safety.
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