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Should I forge my part or machine it from bar?
Machine from bar for prototypes, fewer than about 500 parts a year, and lightly loaded parts. Forge when volume reaches several hundred to a few thousand parts a year and the part sees fatigue or shock: closed-die tooling, typically $5,000–$60,000, makes a near-net blank with grain flow that follows the contour, and machining finishes functional surfaces to ±0.001 in (±0.025 mm).
Which is cheaper at your quantity?
The same flanged bushing, each process in a suitable material (4140 and 4140).
| Quantity | Forging | CNC machining |
|---|---|---|
| 10 | $1,014 | $68.80 |
| 50 | $203 | $27.30 |
| 100 | $102 | $21.50 |
| 500 | $22.10 | $14.50 |
| 1,000 | $12.00 | $12.90 |
| 5,000 | $4.02 | $11.80 |
| 10,000 | $3.02 | $11.70 |
| 50,000 | $2.21 | $11.70 |
| 100,000 | $2.11 | $11.70 |
Where each pays off
Forging
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- Tooling
- 6–12 weeks
- First article
- 2–4 weeks after tooling
- Production
- 4–10 weeks per release, including heat treat and machining
±0.010–0.030 in (±0.25–0.8 mm), plus die wear and mismatch allowances
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 Forging when
- The part carries fatigue, shock or impact loads
- Volume is 500 parts or more a year
- Machining from bar would waste much of the stock
- Grain flow should follow the load path
Pick CNC machining when
- You need prototypes or fewer than about 500 parts a year
- The design is still changing
- Loads are light
- The part is round and close to bar size, with little stock removal
Key differences
| Forging | CNC machining | |
|---|---|---|
| Grain flow | Follows the part contour | Cut through at shoulders and contour changes |
| Tooling | $5,000–$60,000; 6–12 weeks | None |
| Material purchase | By the pound, plus 20–40% flash | Bar or plate; everything outside the part becomes chips |
| Tolerance | As-forged ±0.010–0.030 in (±0.25–0.8 mm); machined features ±0.001 in (±0.025 mm) | ±0.005 in (±0.13 mm) standard; ±0.001 in (±0.025 mm) critical |
| Production lead time | 4–10 weeks including heat treat and machining | 2–6 weeks |
| Draft | 5–7° on steel forged surfaces | None |
Questions
Is a forged part stronger than a machined part?
In fatigue and impact, usually yes. Both start from wrought metal, but machining from bar cuts through the grain at shoulders, while forging bends the grain to follow the contour. Static strength of the same alloy and heat treat is similar.
Do forgings still need machining?
Almost always on functional surfaces. Forgers leave 0.060–0.125 in (1.5–3.2 mm) of stock per machined surface, and bores, faces and threads are finished to ±0.001 in (±0.025 mm) or tighter.
How do I move a machined part to a forging?
Add draft, generous fillets and machining stock, place the parting line on the largest cross section, and separate as-forged and machined tolerances on the drawing, with datums on machined features.
Try both on your part.
The builder prices the same geometry in every suitable process and material, with DFM for each.