Hemming

Hemming folds sheet metal edges over onto themselves to create smooth, stiff, and safe edges, often for cosmetic panels and lightweight structural reinforcement.

Overview

Hemming, or edge folding, forms a sheet metal edge by folding it back onto itself, usually in one or two stages (pre-hem and final hem). The process removes sharp edges, increases local stiffness, and improves cosmetic appearance without adding separate hardware. It’s common in automotive body panels, appliances, and enclosures where users will see or touch the edge.

Use hemming when you need a safe, rounded edge, a clean visual line, or a stiffened flange in thin-gauge sheet. It also works for mechanically joining two sheets along an edge. Tradeoffs include higher tooling and setup cost than simple bends, more sensitivity to material thickness and coating variation, and potential distortion if the flange is too short or the radius is too tight. Expect practical limits on hem width, material thickness, and corner details, and plan for slightly looser dimensional control than standard press brake bends due to material springback and stack-up.

Common Materials

  • Mild steel CRS
  • Galvanized steel
  • Aluminum 5052
  • Aluminum 6061
  • Stainless steel 304
  • Copper

Tolerances

±0.010"

Applications

  • Automotive body panels and door hems
  • Appliance doors and front panels
  • Sheet metal enclosures and covers
  • Machine guards with safe edges
  • Architectural trim and fascia panels
  • HVAC plenums and duct access panels

When to Choose Hemming

Use hemming when you need smooth, safe, and cosmetically clean edges or local stiffness in thin sheet metal without adding extra parts. It fits best for thin-gauge panels, doors, and covers at low to high production volumes where a consistent edge condition matters more than ultra-tight dimensional accuracy. It also works well for joining two overlapping sheets along a shared edge.

vs Press Brake Bending

Choose hemming instead of a simple press brake bend when edge safety, stiffness, or appearance is critical, such as user-touch surfaces or visible panel seams. Bends create a single flange; hems fold the flange back, thickening and rounding the edge but with more forming steps and slightly looser dimensional control.

vs Roll Bending

Pick hemming over roll bending when you need a finished edge on relatively straight or mildly curved panels, not large sweeping radii. Roll bending is for forming curves across the panel; hemming is for treating the edge to improve safety, stiffness, or cosmetics.

vs Spot Welding

Use hemming instead of spot welding when you can mechanically join overlapping sheet edges along a continuous line and want a clean, hardware-free seam. Hems avoid weld spatter and heat-affected zones but require appropriate flange geometry and are limited to edge joints, not internal locations.

vs Adhesive Bonding

Choose hemming over adhesive bonding when you want an immediate, mechanical edge joint without cure time or surface prep. Adhesives can supplement hems for stiffness and sealing, but a pure hem is faster to assemble and more robust against contamination at the joint line.

Design Considerations

  • Make hem flange length at least 3–4× material thickness to avoid cracking, excessive thinning, and inconsistent closure
  • Specify hem type (open, closed, teardrop) and target gap or overlap so the shop can choose correct tooling and setup
  • Avoid very tight inside radii; use a minimum bend radius of at least 1× material thickness, more for high-strength or coated steels
  • Add corner reliefs or notches where hems wrap around corners to prevent material bulging and tearing
  • Call out which surfaces are cosmetic and acceptable hem marks or witness lines to guide tool selection and fixturing
  • Provide flat patterns with bend deductions or K-factors appropriate for the material and thickness so hem length and edge positions are achievable