Hemming

Hemming folds a sheet metal edge back onto itself to create a smooth, stiffened, safer edge with improved durability and appearance.

Overview

Hemming (edge folding) forms a sheet metal edge by bending it past 90° and flattening it onto itself, typically creating a 180° fold. The result is a rounded, closed edge that increases edge stiffness, removes sharpness, and can trap or cover raw edges for better cosmetics and corrosion resistance.

Choose hemming for panels, covers, and enclosures where touch safety, edge quality, and rigidity matter more than tight dimensional control. Hems are often done after other forming operations, and the hem geometry is sensitive to material temper, grain direction, coating, and edge condition.

Tradeoffs: hemming adds tooling and handling steps, can print/mark cosmetic surfaces, and is prone to cracking on tight inside radii—especially in harder tempers or thick stock. Hem size and flatness vary with springback and material thickness; plan for wider process tolerances than a simple bend.

Common Materials

  • Aluminum 5052-H32
  • Aluminum 6061-T6
  • Mild steel (CRS)
  • Galvanized steel
  • Stainless steel 304

Tolerances

±0.010" to ±0.030"

Applications

  • Automotive door and hood outer panel hems
  • HVAC sheet metal panels with safe edges
  • Electrical enclosure doors and covers
  • Appliance skins and trim panels
  • Cabinet and rack side panels

When to Choose Hemming

Hemming fits parts that need a smooth, safe edge and added edge stiffness, especially on thin-to-medium gauge sheet metal panels. It works well in medium to high volumes where consistent edge appearance matters. Plan hemming early in the forming sequence so flanges, reliefs, and cosmetic surfaces are compatible with the tooling.

vs Press Brake Bending

Choose hemming when you need a doubled-over edge for safety, stiffness, or a finished appearance rather than a single-angle flange. A hem also hides the raw edge and can reduce edge flutter on large panels. Expect more process sensitivity and wider edge-location variation than a straightforward brake bend.

vs Roll Bending

Choose hemming when the goal is a closed, flattened edge, not a large-radius curvature across the whole part. Roll bending sets global curvature; hemming is a localized edge feature that improves edge rigidity and touch safety. Hemming is better for panels and skins where only the perimeter needs reinforcement.

vs Curling (Edge Rolling)

Choose hemming when you want a compact, flattened double thickness at the edge rather than an open curl with a larger outside radius. Hems can be lower-profile and easier to stack/fit against adjacent parts. Curling is often better when you need a wire edge or a rounder, more uniform radius for handling.

vs Beading

Choose hemming when reinforcement is needed at the perimeter and edge safety/cosmetics are key. Beads stiffen a panel without doubling thickness at the edge and are usually placed away from the perimeter. Hemming is preferred when the edge itself must be durable and smooth.

Design Considerations

  • Size the hem leg length to suit material thickness and tooling; very short hems increase cracking and dimensional variation
  • Add corner reliefs and bend reliefs where hems intersect to prevent tearing and bulging
  • Call out cosmetic-side requirements and allow for tool marking; specify protective film if surface appearance is critical
  • Avoid hemming across holes, slots, or emboss features near the edge; keep adequate edge distance to prevent distortion
  • Specify material temper and grain direction when cracking risk is high, especially for aluminum and stainless
  • Define whether the hem is open, closed, or teardrop and include target inside radius/flattening requirement to quote accurately