Sheet metal hemming folds an edge back onto itself to create a safer, stronger, and cleaner border. It is common in panels, covers, doors, automotive parts, enclosures, and consumer products.
A hem can remove sharp edges, improve stiffness, hide a raw cut edge, and help two sheets join together. The process must be planned with bend radius, material thickness, grain direction, and tooling clearance in mind.
Quick Guide to Sheet Metal Hemming
| Item | Purpose | Manufacturing Note |
|---|---|---|
| Open hem | Edge is folded but leaves a small gap | Useful when material may crack if flattened |
| Closed hem | Edge is folded flat | Clean appearance but higher forming stress |
| Teardrop hem | Rounded internal gap | Good for harder or thicker materials |
| Rope hem | Rolled circular edge | Adds stiffness and safer handling |
Process Selection Notes
The best process depends on material, geometry, tolerance, quantity, surface finish, heat effects, burr requirements, and whether the part needs secondary machining or finishing.
- Match the process to the material and geometry.
- Confirm critical dimensions before quoting.
- Plan finishing and inspection before production.
- Use prototypes to validate fit when the assembly risk is high.
Common Applications
Sheet Metal Hemming is relevant for prototypes, custom components, fixtures, low-volume manufacturing, maintenance parts, and engineering projects where function, cost, and lead time must be balanced.
Cost Factors
Cost usually depends on setup time, material price, number of operations, tool access, tolerance requirements, surface finish, inspection depth, and batch quantity.
Design and Sourcing Notes
The safest design approach is to define the part’s function first, then assign tolerances only where they affect assembly, movement, sealing, safety, or long-term performance.
- Avoid unnecessary tight tolerances on non-critical surfaces.
- Keep internal corners, hole depths, wall thickness, and tool access realistic.
- Call out cosmetic surfaces separately from functional surfaces.
- Include material, finish, quantity, and inspection notes in the RFQ package.
Quality Checks That Matter
Quality control may include visual inspection, dimensional measurement, thread checks, gauge checks, flatness checks, runout checks, surface finish checks, or CMM inspection depending on the part’s risk and function.
Related MTSPi Resources
FAQ
What is the main consideration for sheet metal hemming?
The main consideration is whether the design, material, and process can meet the functional requirements without adding unnecessary cost or risk.
Can MTSPi help with custom parts for this topic?
Yes. MTSPi can review drawings, material requirements, tolerances, finishing, and inspection needs for custom CNC machined or related manufacturing parts.
What should I send for a quote?
Send 3D CAD, 2D drawings, material grade, quantity, surface finish requirements, tolerance notes, and any critical assembly information.
