Sheet Metal DFM Checklist: 12 Design Rules That Cut Prototype Cost

Most sheet metal cost overruns trace back to a handful of repeatable design mistakes — bend radii that don't match tooling, holes punched too close to bends, and features that force secondary welding or machining. This is the same 12-point checklist our engineers run on every SkillsProto quote before a number goes out.

Bends: radius, direction, and the k-factor

Design inside bend radii equal to or slightly greater than material thickness (1× t is the safe default for steel and aluminum). Keep all bends in the same direction to avoid part flip-overs on the press brake — every reorientation adds setup time. Remember that bends near each other need relief: leave at least the material thickness between a bend and an adjacent edge or feature.

Holes, slots and their distance to bends

• Hole diameter ≥ material thickness (preferably 1.5×) to avoid tool breakage
• Keep holes/slots ≥ 2.5× thickness + bend radius away from the bend line
• Holes closer than that will distort when the flange forms — or require post-bend drilling
• Countersinks: limit depth to 50–75 % of thickness; never countersink through

Uniform thickness is a hard constraint

Unlike machined parts, a bent sheet metal component must keep one thickness throughout. If your CAD shows stepped thicknesses, either split it into two parts joined with fasteners/welding, or rework as a machined enclosure. Also watch tolerance expectations: bending holds ±0.1–0.3 mm per flange, not the ±0.02 mm of CNC machining.

Features that quietly double cost

The usual suspects: lances and louvered vents (custom tooling), tight internal corners (need relief cuts or come back as cracks), hardware too close to bends (installation dies can't reach), and cosmetic surfaces specified on the inside face where tool marks are unavoidable. Each is fixable in minutes at the design stage — and expensive after the first article.

Finishes and quantities we optimize for

For prototypes we laser-cut, bend, and finish in-house: powder coating for enclosures, anodizing or zinc plating for functional parts, and silk-screened branding where needed. Typical SkillsProto lead time is 3–7 working days for 1–100 pieces, scaling smoothly into low-volume production with the same fixtures. Upload DXF plus STEP and our DFM report flags every bend and hole-distance issue before you pay for it.