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Should I use powdered metal or CNC machining?
Machine from bar below about 5,000 parts a year: there is no tooling and parts are fully dense. Above about 10,000 parts a year, powdered metal is often much cheaper for gears, cams, sprockets and complex flat profiles: after a $5,000–$50,000 compaction tool, it uses about 97% of the material and needs little or no machining.
Which is cheaper at your quantity?
The same spur gear, each process in a suitable material (FN-0205 and 6061-T6).
| Quantity | Powdered metal | CNC machining |
|---|---|---|
| 10 | $884 | $70.30 |
| 50 | $177 | $27.80 |
| 100 | $88.40 | $21.90 |
| 500 | $17.70 | $14.80 |
| 1,000 | $8.94 | $13.10 |
| 5,000 | $2.19 | $12.00 |
| 10,000 | $1.35 | $11.90 |
| 50,000 | $0.67 | $11.90 |
| 100,000 | $0.59 | $11.90 |
Where each pays off
Powdered metal
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- Tooling
- 6–12 weeks
- First article
- 2–3 weeks after tooling
- Production
- 4–8 weeks per release
About ±0.001 in per in (±0.1%) as sintered; about ±0.0005 in (±0.013 mm) after sizing
Production machining, turning, and sawing
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- First article
- 1–3 weeks
- Production
- 2–6 weeks per release
±0.005 in (±0.13 mm), or ISO 2768-m
Which should you pick?
Pick Powdered metal when
- You need 10,000 or more gears, cams, sprockets or clutch plates a year
- The part is a self-lubricating, oil-impregnated bushing
- A complex flat profile would take heavy machining
- Loads are moderate, with heat treat to HRC 20–43 apparent
Pick CNC machining when
- Volume is under about 5,000 parts a year
- Full-density fatigue or impact strength is required
- The part has cross holes, threads or side undercuts
- Tight tolerances are needed in every direction
Key differences
| Powdered metal | CNC machining | |
|---|---|---|
| Tooling | $5,000–$50,000; 6–12 weeks | None |
| Material utilization | About 97% | Everything outside the part becomes chips |
| Density | 82–92% of wrought steel | Fully dense |
| Ductility | Under 1–2% elongation as sintered | Wrought ductility |
| Geometry | Features along the pressing axis; length to diameter about 3:1 maximum | Almost any feature a tool can reach |
| Tolerance | Radial ±0.001 in per in (±0.1%); ±0.0005 in (±0.013 mm) after sizing; height ±0.003–0.005 in (±0.08–0.13 mm) | ±0.005 in (±0.13 mm) standard; ±0.001 in (±0.025 mm) critical |
| Plating | Resin impregnate first to seal pores | Plate directly |
Questions
Is powdered metal as strong as machined steel?
Not quite. As-sintered FC-0208-50 runs about 60 ksi (410 MPa) tensile, close to hot-rolled low-carbon steel, but with under 1% elongation. Heat-treated grades exceed 100 ksi (690 MPa). For impact-loaded parts, wrought steel is the better call.
Can powdered metal parts be machined?
Yes. Cross holes, threads and undercuts are added by secondary machining. If a part needs many of them, screw machining or CNC machining from bar may be simpler.
What is the minimum volume for powdered metal?
Most PM programs need about 5,000–10,000 parts a year to pay back tooling and setup. Compaction tooling usually lasts hundreds of thousands to millions of parts.
Try both on your part.
The builder prices the same geometry in every suitable process and material, with DFM for each.