Sheet Metal Fabrication Basics
Cutting, bending, forming, welding and stamping — and how parts are quoted flat
Sheet metal starts as flat stock and becomes a part through cutting (laser, punch, waterjet) and bending (press brake), with secondary forming, welding and hardware. Every quote is derived from the flat pattern — the unfolded geometry — so 3D models must be bend-aware. Standard tolerance is ±0.3 mm on cut and ±0.5 mm on formed dimensions; costs are driven by thickness, bend count, hardware and finish.
1. Cutting processes
Laser cutting is the default for most sheet parts: kerf 0.1–0.3 mm, edge quality good, thickness 0.5–12 mm in steel/aluminum/stainless. Punching (CNC turret) is faster for high-volume repetitive holes; waterjet cuts thick or heat-sensitive materials but slower and costlier.
Minimum hole ≈ sheet thickness (punch) or 0.8 mm (laser); hole-to-edge ≥ 1.5× thickness. Cut edges are slightly tapered (laser) or sheared (punch) — specify deburring or edge-breaking where fingers will touch.
2. Bending and forming
Press-brake bending forms the flat into 3D: minimum inside radius ≈ thickness for air bending, and bend length up to ~3 m on large brakes. Springback varies with material and temper — formed tolerances run ±0.3–0.5 mm. Bend reliefs (3–6 mm) prevent tearing at corners.
Forming operations add depth: hemming (rolled edges), countersinks, louvering, embossing and coining. Each adds a setup cost; minimize distinct bend radii on a part to keep the brake setup short.
3. Hardware, welding and finishing
Captive hardware (PEM® studs/nuts/standoffs) is pressed in after forming; specify the standard panel thickness range. Welding (MIG/TIG/spot) joins parts and weldments; weld distortion is real — keep weldment tolerances ≥ ±0.5 mm and put welds on non-visible faces.
Finishes: powder coat (25–100 µm), zinc plating, anodizing (aluminum), passivation (stainless), plus silkscreen labels. Finish covers cut edges, so deburr before coating for a clean line.
4. How sheet parts are quoted
The engine unfolds the flat, then prices: material area × thickness × density × price index, plus laser time, bend count × bend rate, hardware items, welding minutes, finish area and tooling (flat/blank dies for volume). Quantity tiers discount setup-heavy small runs.
Design for the flat: model bends with a consistent K-factor, avoid bends too close to holes (≥ 2× thickness), keep bend lines away from hardware, and let the drawing state bend radius and direction.
Quick reference
| Parameter | Typical range |
|---|---|
| Thickness | 0.6–6.35 mm (0.024–0.250 in) |
| Cut tolerance | ±0.13–0.3 mm (laser) |
| Formed tolerance | ±0.3–0.5 mm |
| Min bend radius | = thickness (air bend) |
| Max part size | ~3000 mm (laser), 1250 mm bend |
| Min hole | 0.8 mm laser / 1×t punch |
| Corner relief | 3–6 mm |
| Finish thickness | Powder 25–100 µm |
Sources & references
- ISO 2768-1:1989
- ASTM A1008 / A240 / B209 (stock)
- Xometry Learning Center — Sheet Metal Basics (public engineering reference)