Short answer: A hemmed edge can make a stamped part safer to handle, stiffer, cleaner in appearance, and less sensitive to exposed burrs. The RFQ should define hem type, material thickness, inside radius, visible face, coating or paint route, edge gap, cracking limits, final dimensions, and whether the hem is functional, cosmetic, or both.
Hemmed edges appear on covers, guards, panels, appliance parts, brackets, hand-contact edges, and enclosure features. A hem can hide a cut edge and add stiffness, but it can also trap coating, crack at corners, change final size, and require extra forming stations.
Use this page with the edge break specification guide, burr control guide, શીટ મેટલ enclosure DFM guide, and DFM review before tooling guide.
Hem design choices before quoting
| Choice | Why it matters | RFQ detail |
|---|---|---|
| Open hem | Easier to form and less likely to trap coating, but may leave a visible gap. | Gap limit, edge direction, and visible side. |
| Closed hem | Cleaner appearance and safer edge, but higher cracking and thickness buildup risk. | Material ductility, radius, and crack acceptance. |
| Teardrop hem | Can reduce cracking on thicker or harder material. | Allowed shape, final envelope, and tooling route. |
| Corner treatment | Corners can split, overlap, or create sharp pockets. | Relief, notch, radius, and cosmetic standard. |
Pick the hem for the function
A hand-contact edge may need a closed or nearly closed hem so the user never touches a sharp sheared edge. A stiffening flange may only need an open hem or return. A cosmetic cover may care more about outside appearance, rack marks, and coating buildup than maximum strength.
Do not add a hem only because the edge looks nicer in CAD. It changes blank size, forming sequence, press tonnage, springback, and inspection. If the part also has holes, slots, louvers, or tabs near the hem, review spacing with the punched holes and slots guide and process sequence checklist.
Watch material and finish limits
Ductile low-carbon steel may hem more easily than hard stainless, HSLA steel, or some aluminum tempers. Tight folds can crack at the outside surface or leave a raised witness line. Grain direction, burr side, coating thickness, and corner relief all matter.
If the part is powder coated, painted, plated, or pre-coated, define whether the hem is formed before or after finishing. A closed hem can trap liquid, cleaning residue, or powder. A post-coated hem may chip during forming. Connect the decision to the powder coating masking guide and pre-coated steel guide.
RFQ details to include
- Drawing with hem type, visible face, inside radius, edge gap, corner relief, and final envelope dimension.
- Material grade, thickness, temper, coating state, grain direction, and whether substitution is allowed.
- Function of the hem: safe edge, stiffness, cosmetic surface, assembly stop, cover lip, or mating feature.
- Acceptable cracking, witness marks, waviness, coating buildup, and gap variation.
- Inspection method for final size, edge safety, appearance, and fit in the mating assembly.
- Annual volume, sample quantity, tooling budget, and packaging protection for hemmed edges.
How to approve hem samples
First samples should be checked by function, not only by dimensions. Handle the edge, fit the mating part, check corner relief, inspect coating or plating at the fold, and confirm whether the hem changes flatness or hole location. If the hem is visible, approve a cosmetic master sample.
Also ask whether the hem will be measured from the outside envelope, inside return, or mating face. Different measurement points can make good samples look wrong on paper.
Send drawings, material, finish, and hem intent through the contact page. If you are not sure which hem type fits the part, use the RFQ form to ask for an open versus closed hem review with tooling impact and sample risks listed.
A સપ્લાયર answer should name the forming route and the likely risk points. That answer is more useful than a simple yes, because hem quality depends on material behavior, tooling sequence, corner design, and finishing route.
FAQ
What is a hemmed edge on a stamped part?
A hemmed edge folds the sheet edge back on itself to improve handling safety, stiffness, appearance, or fit with a mating part.
Is a closed hem always better than an open hem?
No. Closed hems can look cleaner, but they may crack, trap coating, or add thickness. Open or teardrop hems may be better for some materials.
Does powder coating affect hem design?
Yes. Coating thickness, trapped powder, chipped edges, and masked areas should be reviewed before selecting the hem type and sequence.
What should be sent for a hemmed edge RFQ?
Send drawings, material, thickness, hem type, visible surface, finish, gap or radius limits, corner relief, volume, and sample approval needs.