Metal Stamping Design Guide
Design stamped parts for high yield, low scrap, and long tool life
Metal stamping produces high-volume parts at extremely low per-unit cost — but tooling is expensive and unforgiving. A progressive die can cost $20,000–$200,000, and a design mistake found after the die is built can mean weeks of delay and five-figure rework costs. These DFM rules help you avoid the most expensive mistakes.
Core Design Principles
Strip Layout Efficiency
Parts are stamped from a continuous strip. The shape of the part and carrier design determines material utilization.
Minimize Stations
Each forming/cutting operation needs a die station. Fewer stations = simpler die = lower tooling cost.
Respect Material Limits
Every material has a maximum draw ratio, bend radius, and stretch limit. Exceeding them causes cracks and tearing.
Design for Die Maintenance
Punches wear, springs break. Design features that allow easy replacement of wear components.
DFM Rules & Guidelines
Minimum Hole Size
Small holes require small punches that are fragile and wear quickly, increasing maintenance costs.
Minimum hole diameter = 1× material thickness (round holes). Minimum slot width = 1.5× material thickness. Use standard punch sizes.
Holes smaller than material thickness. Non-round holes smaller than 1.5× thickness.
Hole-to-Edge & Hole-to-Hole
Insufficient spacing between holes or edges causes slug pulling, die damage, and distorted parts.
Hole edge to part edge: ≥ 2× material thickness. Hole edge to hole edge: ≥ 2× material thickness. Hole edge to bend: ≥ 2.5× thickness + bend radius.
Spacing less than 1× thickness. Holes that intersect the trim line.
Bend Radius & Relief
Bends that are too tight crack. Bends without relief slots tear at the intersection of the bend and edge.
Minimum inside bend radius: 1× thickness for mild steel, 1.5× for stainless, 0.5× for copper. Add relief notches at bend intersections.
Zero-radius bends. Bends without relief cuts at the ends. Bends parallel to grain direction in hard materials.
Draw Depth
Deep draws require multiple stations and risk thinning, wrinkling, and tearing. Shallower draws are more reliable.
Maximum draw depth = 1× blank diameter for round cups (first draw). Use stepped draws for deeper parts. Maintain minimum bottom thickness.
Draw ratios exceeding material limits in a single station. Sharp corners at the draw radius (causes tearing).
Feature Spacing
Features too close together weaken the die and cause interference between forming operations in progressive dies.
Minimum feature-to-feature spacing: 3× material thickness. Carrier strip width: ≥ 2× thickness (minimum 3 mm).
Crowding features into minimum spacing. Placing forming features adjacent to trim edges.
Tolerances
Stamping tolerances depend on material, thickness, and the number of forming operations.
±0.1 mm for blanked dimensions. ±0.15 mm for formed features. ±0.3 mm for drawn depths. ±1° for bend angles.
CNC-level tolerances on stamped features. Tolerance callouts that ignore springback.
⚠️ Common Design Mistakes
- ⚠ Designing parts with features too close to the trim edge — causes slug pulling and burrs on critical surfaces.
- ⚠ Not accounting for springback — bends in high-strength steel can spring back 3–5°, requiring overbend compensation.
- ⚠ Creating asymmetric strip layouts — wastes material and complicates die design.
- ⚠ Specifying burr-free on all edges — burr direction is inherent to the process. Specify burr side if it matters.
- ⚠ Ignoring grain direction — bend performance and surface finish depend heavily on orientation relative to the rolling direction.
💡 Pro Tips
- ▸ Design parts that nest or tile efficiently on the strip — material typically accounts for 40–60% of stamped part cost.
- ▸ Add pilot holes to your design for strip registration — your die maker will add them anyway, but proactive placement avoids conflicts.
- ▸ If a feature is purely cosmetic, consider embossing (cheaper) vs. machining (expensive secondary operation).
- ▸ For volumes under 10,000, consider compound dies or even laser+brake (no die cost) before investing in progressive tooling.
- ▸ Provide a flat pattern AND a 3D model. Die designers need both. Specify which dimensions are critical on the formed part.
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