3D Printing vs CNC vs Injection Moulding: When to Use Each Process?

Executive summary

The general rule: 3D printing for prototypes and short runs, CNC for high precision or non-printable materials, injection for high volumes where tooling cost is amortised.

Direct comparison

Criterion	FDM 3D Printing	CNC	Injection
Setup cost	None	Low–Medium	High (tooling)
Cost per part (high qty)	Medium	High	Very low
Lead time	24h–3 days	3–10 days	6–12 weeks
Geometric complexity	Very high	Medium	Medium
Tolerâncias típicas	±0,1–0,3 mm	±0,01–0,05 mm	±0,05–0,1 mm
Available materials	FDM polymers	Metal, plastic, composite	Most thermoplastics
Volume mínimo económico	1 peça	1 peça	500–2,000 parts
Design iteration	Very fast	Fast	Slow and expensive

FDM 3D Printing — speed and flexibility

FDM 3D printing has zero setup cost. Unbeatable for functional prototypes, low-volume parts and complex geometries.

Strengths: 24h delivery, no tooling, free geometries, fast iteration.

Limitations: Z-axis anisotropy; ±0.1–0.3 mm tolerances; visible layer lines without post-processing.

CNC — precision and premium materials

CNC is the right process for tight tolerances, metal or aluminium, or high-quality surface finishes.

When to choose CNC: metal parts, high-precision fits, quality metric threads.

Limitations: geometry limited by tool access; cost doesn't scale for high volumes.

Injection moulding — industrial scale

Injection moulding is the reference process for mass production of plastics. Tooling cost (€5,000–€80,000) is amortised over a large number of parts.

When to choose injection: volumes above 1,000–5,000 units/year, stable geometry.

Limitations: tooling costs €5,000–€80,000 and takes 6–12 weeks; design changes are expensive.

Hybrid strategy

The most efficient product teams use all three processes throughout the product lifecycle:

1. Phase 1 — Concept: FDM 3D printing for form and fit validation. Multiple iterations in days.
2. Phase 2 — Functional validation: 3D printing with technical materials for real mechanical testing.
3. Phase 3 — Pre-series: CNC or 3D printing for first 50–200 units while tooling is being made.
4. Phase 4 — Production: injection for high volumes. 3D printing for variants and spare parts.

Decision table by volume

Annual volume	Recommended process	Note
1–10 peças	3D Printing	24h delivery, zero setup cost
10–100 peças	3D Printing or CNC	Depends on material and tolerances
100–500 peças	3D Printing (plastic) / CNC (metal)	Injection not yet economical
500–2.000 peças	Case by case analysis	Crossover point — calculate total cost
>2,000 parts	Injection moulding	Tooling amortised, low unit cost