Key principles.
180° fold
Tight 180° fold, both sides touch. Cosmetic finish. Standard for visible edges.
180° fold with gap
180° fold but gap remains. Used as stiffener, easier to fabricate.
135° partial
Partial fold (135°). Compromise — visible from one side, easier to make than closed hem.
1-2× thickness
Hem bend requires sufficient radius to avoid cracking. 1-2× material thickness typical.
At least 4× thickness
Hem flange (folded portion length) ≥ 4× material thickness for strength.
Ductile better
Ductile materials hem easier. 5052 aluminum excellent. 6061 OK with care. Stainless work-hardens but workable.
FAQ
Hem stiffens the edge, eliminates sharp burrs, looks finished. Appropriate for visible/handled edges.
Single 90° bend: simple flange. Hem: complete fold over. Different aesthetic and function.
Cut edge has square corner. Hemmed edge has small radius. Smoother finish, safer to handle.
Hem adds bending operation. ~10-30% added cost vs simple cut edge.
Most cold-formable sheet (aluminum, mild steel, 304/316L stainless). Not work-hardened or brittle materials.
Visual inspection — uniform fold, no cracks, no marking. Critical edge inspection if cosmetic.
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