Design for Manufacturability (DFM) Guide
Practical guidelines to optimize powder metallurgy part designs for cost, quality, and production efficiency. Use these rules to reduce tooling risk and avoid avoidable rework.
Key DFM Guidelines
Draft Angles
Draft angles help parts eject cleanly from the die and reduce tooling wear.
- External surfaces: 0.5-1.5 degrees
- Internal holes: 1.0-2.0 degrees
- Complex features: 0.5-1.0 degrees
Wall Thickness
More uniform wall sections improve density consistency and reduce sintering distortion.
- General parts: >= 1.5 mm
- Small parts under 25 mm: >= 1.0 mm
- Large parts over 100 mm: >= 3.0 mm
- Recommended maximum thickness: <= 25 mm
Holes and Cavities
Features parallel to the pressing direction are easiest to compact and most cost-effective.
- Axial hole minimum diameter: >= 1.5 mm
- Maximum hole depth: <= 4 x diameter
- Blind hole minimum depth: >= 1.0 mm
Fillets and Radii
Generous radii improve powder flow, reduce stress concentration, and extend die life.
- Internal corners: >= 0.3 mm, preferably 0.8-1.5 mm
- External corners: >= 0.5 mm
- Use smooth transitions between thick and thin sections
Common DFM Mistakes to Avoid
Ignoring Sintering Shrinkage
PM parts typically shrink about 1-2% during sintering. Tooling must include material-specific compensation.
Sharp Internal Corners
Sharp corners create stress concentration and can accelerate die chipping or cracking.
Adjacent Thin and Thick Sections
Abrupt section changes can create density variation and increase distortion or crack risk.
Deep Narrow Slots
Difficult powder filling and weak punches make narrow slots risky. Keep slot width at or above 1.5 mm when possible.
Expecting Threads Directly from Pressing
Most threads still need tapping, rolling, or another secondary operation after sintering.
Tolerance and Shrinkage Guidelines
Achievable Tolerance Grades (ISO 286)
| Condition | ISO Grade | Typical Range |
|---|---|---|
| As-sintered (standard) | IT8-11 | +/-0.3% to +/-0.5% |
| As-sintered (precision) | IT7-8 | +/-0.2% to +/-0.3% |
| After sizing or coining | IT6-7 | +/-0.05% to +/-0.1% |
Typical Material Shrinkage Rates
| Material | Linear Shrinkage | Tool Compensation |
|---|---|---|
| Iron-based (F-0000) | 1.2-1.5% | Scale factor 1.012-1.015 |
| Copper steel (FC-0205) | 1.0-1.3% | Scale factor 1.010-1.013 |
| Nickel steel (FN-0205) | 1.0-1.3% | Scale factor 1.010-1.013 |
| Stainless steel (316L) | 1.3-1.6% | Scale factor 1.013-1.016 |