Sheet Metal Fabrication Design Guide
Design sheet metal parts that bend, punch, and form cleanly
Sheet metal fabrication is one of the most cost-effective manufacturing processes for enclosures, brackets, chassis, and structural components. But the process has real constraints — minimum bend radii, hole-to-edge distances, springback compensation, and grain direction all affect quality and cost. This guide helps you design parts that work the first time.
Core Design Principles
Think Flat First
Every sheet metal part starts as a flat blank. If it can't unfold without overlapping, it can't be made.
Respect Bend Limits
Minimum bend radius depends on material and thickness. Going too tight causes cracking on the outer surface.
Maintain Clearances
Holes, slots, and features near bends or edges distort during forming. Keep proper distances.
Design for Assembly
Tab-and-slot, PEM inserts, and self-locating features reduce assembly time and cost.
DFM Rules & Guidelines
Bend Radius
Too-tight bends crack the outer surface. The minimum depends on material ductility and thickness.
Minimum inside bend radius = 1× material thickness for aluminum, 1.5× for stainless steel. Use consistent bend radii throughout the part.
Bend radius less than the material thickness. Mixing multiple different bend radii (requires tooling changes).
Hole-to-Bend Distance
Holes too close to a bend line distort during forming, becoming oval or tearing.
Minimum distance from hole edge to bend line = 2.5× material thickness + bend radius. Use relief cuts if holes must be closer.
Placing holes within 2× material thickness of a bend. Slots parallel and close to bend lines.
Hole-to-Edge Distance
Holes too close to an edge cause the edge to bulge or the hole to deform during punching.
Minimum: 2× material thickness from hole edge to part edge. For oblong holes: 3× thickness.
Holes within 1× material thickness of any edge.
Minimum Flange Length
Short flanges cannot grip in the brake die, leading to inconsistent bends or slipping.
Minimum flange = 4× material thickness (never less than 6 mm). For hems: minimum flat = 4× thickness + bend radius.
Flanges shorter than 3× material thickness. Return flanges without adequate clearance for tooling.
Tab-and-Slot Design
Self-locating tabs and slots simplify assembly, reduce fixturing, and enable tack welding without jigs.
Tab width: 1.5–2× material thickness. Slot clearance: 0.1–0.2 mm per side. Add a small lead-in radius on slot corners.
Tabs wider than 3× material thickness (hard to insert). Zero clearance (interference during assembly).
Tolerances
Sheet metal tolerances are wider than CNC. Cumulative bend tolerance stacks up across multiple bends.
±0.1 mm for laser-cut features. ±0.2 mm for punch features. ±0.3–0.5 mm for formed/bent dimensions. Specify datums for critical features.
Expecting ±0.05 mm on bent dimensions. Accumulating tolerance across 4+ bends without datum references.
⚠️ Common Design Mistakes
- ⚠ Not accounting for bend deduction — the flat pattern length is NOT the sum of the flange lengths.
- ⚠ Placing hardware inserts (PEM nuts) too close to bends — they interfere with the brake tooling.
- ⚠ Designing parts with internal features that can't be reached by a punch or laser — always check tool access.
- ⚠ Forgetting grain direction — bends parallel to the grain are more likely to crack, especially in aluminum.
- ⚠ Not providing a flat pattern — if your CAD model can't unfold, the shop has to guess at your K-factor.
💡 Pro Tips
- ▸ Use standard sheet thicknesses (0.9, 1.2, 1.5, 2.0, 3.0 mm) to avoid material surcharges.
- ▸ Add corner reliefs at bend intersections — a small notch prevents tearing and creates cleaner bends.
- ▸ Self-clinching PEM fasteners (nuts, studs, standoffs) are cheaper than welding threaded bosses.
- ▸ Design for nesting: rectangular blanks waste less material than complex outlines. Material cost often dominates.
- ▸ If you need paint or powder coat, specify it early — it affects hole tolerances (coating adds 0.05–0.1 mm).
Ready to get started with Sheet Metal?
Upload your design and get a quote with DFM feedback from our engineering team.