Last updated: 2026-09-05 · 5 min read

Injection Molding vs. CNC Machining — Which Process Delivers Lower Cost Per Part at Your Production Volume, and What Are the Quality and Lead-Time Trade-Offs?

Injection molding has high upfront cost ($15,000–$80,000 mold) but low per-part cost ($0.10–$2.00). CNC machining has no mold cost but high per-part cost ($5–$50+ per part). The break-even: at 500–5,000 parts, injection molding becomes cheaper than CNC. Below 500 parts: CNC is faster and more economical. Above 10,000 parts: injection molding delivers 80–95% lower cost per part.

  • Cost structure: injection molding requires a mold ($15,000–$80,000 depending on complexity, cavity count and steel), then each part costs $0.10–$2.00 (resin + cycle time + overhead). CNC machining has no tooling cost, but each part is machined individually at $5–$50+ per part (material + machine time + operator). For 100 parts: CNC = $500–$5,000, injection = $15,000 mold + $10–$200 parts = $15,010–$15,200. For 100,000 parts: CNC = $500,000–$5,000,000, injection = $30,000 mold + $10,000–$200,000 = $40,000–$230,000. Injection wins at volume.
  • Lead time: CNC delivers parts in 1–5 days (no tooling needed). Injection molding requires 6–12 weeks for mold build + 1–2 weeks for T1 sampling. For urgent prototypes or bridge production under 500 parts: CNC is faster. For production above 10,000 parts: the 8–14 week lead time for injection molding is offset by the lower per-part cost and the ability to produce all parts in days once the mold is running. The decision depends on urgency vs. volume.
  • Part quality: CNC machining achieves tighter tolerances (±0.01mm) and better surface finish from the machine (Ra 0.8–3.2 µm). Injection molding tolerances: ±0.05–0.15mm (depends on resin shrinkage and mold precision). However, injection molding produces near-net-shape parts with minimal secondary operations. CNC parts often require multiple setups (3-axis, 5-axis, turning) for complex geometry, each adding cost and time. For complex 3D shapes with internal features: injection molding is more capable (undercuts, thin walls, living hinges).

How Do Injection Molding and CNC Machining Compare on Cost, Speed and Capability?

Factor Injection Molding CNC Machining
Upfront cost $15,000–$80,000 (mold) $0 (no tooling)
Per-part cost $0.10–$2.00 $5–$50+
Break-even volume 500–5,000 parts Under 500 parts
Lead time (first parts) 6–12 weeks (mold build) 1–5 days
Tolerance ±0.05–0.15mm ±0.01mm
Surface finish SPI A1–D3 (mold dependent) Ra 0.8–3.2 µm (as-machined)
Material options Thermoplastics only Metals + plastics + composites
Complex geometry Excellent (undercuts, thin walls) Limited (tool access)
Best for Production above 5,000 parts Prototypes, under 500 parts

The decision rule: if you need 1–100 parts in 1–5 days: CNC machining. If you need 100–5,000 parts and can wait 2–4 weeks: CNC or rapid tooling (aluminum mold). If you need 5,000+ parts and can wait 8–14 weeks: injection molding delivers the lowest cost per part. The break-even depends on part complexity, material and tolerance — a detailed cost comparison is needed for each program.

Rapid tooling — aluminum molds ($8,000–$15,000, 3–4 weeks) that bridge the gap between CNC prototyping and full production molds. Life: 5,000–20,000 shots. For 500–5,000 parts: rapid tooling delivers injection-molding economics without the full steel mold investment. The aluminum vs. steel guide covers the material trade-offs in detail.

What Three Factors Determine Whether Injection Molding or CNC Is the Right Process?

  1. Calculate the total cost at your production volume — this is the primary decision driver. Total cost = upfront tooling + (per-part cost × quantity). For a $30,000 mold at $0.50/part vs. CNC at $10/part: break-even at $30,000 ÷ ($10 − $0.50) = 3,158 parts. If you need 10,000 parts: injection = $30,000 + $5,000 = $35,000 vs. CNC = $100,000. If you need 500 parts: injection = $30,000 + $250 = $30,250 vs. CNC = $5,000. CNC wins below break-even; injection wins above.
  2. Evaluate the lead time requirement — CNC delivers in days, injection in weeks. If the parts are needed for a trade show, functional test or investor demo in 1–2 weeks: CNC machining is the only option. If the timeline allows 8–14 weeks for mold build and sampling: injection molding delivers lower per-part cost. For programs that need both: use CNC for prototypes (validate design) and injection molding for production (scale at lower cost). This two-stage approach is common in product development.
  3. Assess the part geometry — complex 3D shapes favor injection, simple blocks favor CNC. Injection molding excels at complex geometry: thin walls (0.5–1.5mm), living hinges, snap fits, undercuts (with slides), and internal features (ribs, bosses). CNC machining is limited by tool access — deep pockets, thin walls and complex internal features are difficult or impossible to machine. For simple blocks, plates and cylindrical parts: CNC is faster and more precise. For complex enclosures, housings and mechanical parts: injection molding is more capable.

Near-net-shape — a manufacturing process that produces parts very close to final dimensions, requiring minimal secondary machining. Injection molding is near-net-shape: the part comes out of the mold within ±0.05–0.15mm of final size. CNC machining starts from a block and removes material to reach final dimensions — more waste, more machine time. The mold cost amortization guide shows how near-net-shape production lowers per-part cost at volume.

Injection vs. CNC: injection = $15k–$80k mold + $0.10–$2/part. CNC = $0 tooling + $5–$50/part. Break-even: 500–5,000 parts. CNC: 1–5 day lead, ±0.01mm tolerance. Injection: 8–14 week lead, ±0.05–0.15mm. Under 500 parts: CNC. Over 10,000: injection.

  • Total cost at volume calculated — tooling + per-part × quantity for both processes.
  • Lead time requirement clear — days = CNC; weeks = injection molding.
  • Geometry complexity assessed — undercuts, thin walls, living hinges = injection.
  • Tolerance vs. process capability — ±0.01mm = CNC; ±0.05mm = injection.
  • Break-even volume identified — typically 500–5,000 parts.

Frequently Asked Questions

Can I use CNC-machined parts for production runs of 10,000 or more?

Technically yes, but it is rarely economical. At 10,000 parts: CNC at $10/part = $100,000 vs. injection molding at $30,000 mold + $0.50/part = $35,000. The injection-molded parts cost 65% less. CNC makes sense for 10,000+ parts only when: the material is not available in injection-grade resin (e.g., certain metals or composites), the tolerance is tighter than injection can hold (±0.01mm), or the volume is uncertain and the mold investment is too risky. For most thermoplastic parts at 10,000+: injection molding is the lower-cost process.

What is rapid tooling and how does it compare to CNC and full production molds?

Rapid tooling uses aluminum molds (instead of hardened steel) to reduce mold cost and lead time. Aluminum mold: $8,000–$15,000, 3–4 weeks delivery, 5,000–20,000 shot life. This fills the gap between CNC (no tooling, 1–5 days, $5–$50/part) and full production molds ($15,000–$80,000, 8–14 weeks, $0.10–$2/part). For 500–5,000 parts: rapid tooling delivers injection-molding economics without the full mold investment. Above 20,000 parts: the aluminum mold wears and a hardened steel mold is needed.

How do tolerances compare between injection molding and CNC machining?

CNC machining holds ±0.01mm (0.0005″) consistently, and ±0.005mm on simple features. Injection molding holds ±0.05–0.15mm (0.002–0.006″), depending on resin shrinkage, mold precision and part geometry. Semi-crystalline resins (PP, PA, POM) shrink more (1.5–2.5%) and are harder to hold tightly. Amorphous resins (PC, ABS, PS) shrink less (0.4–0.7%) and hold tighter tolerances. For parts requiring ±0.01mm: CNC is the default choice. For ±0.05mm or looser: injection molding is capable and more economical at volume.

Key Takeaways

  • Injection: $15k–$80k mold + $0.10–$2/part. CNC: $0 + $5–$50/part.
  • Break-even: 500–5,000 parts (depends on part cost).
  • CNC: 1–5 day lead, ±0.01mm. Injection: 8–14 weeks, ±0.05mm.
  • Under 500 parts: CNC. Over 10,000: injection molding.

Send the part drawing, material and annual volume — the review compares injection molding vs. CNC machining on total cost, lead time and tolerance capability, and recommends the process that delivers the lowest cost per part for your production program.

Sources: Plastics Technology — Injection Molding vs. CNC Machining: Cost Comparison · Manufacturing.net — Choosing Between Prototyping and Production Processes · Society of Manufacturing Engineers (SME) — Process Selection for Plastic Parts · MoldMaking Technology — Rapid Tooling vs. CNC: Bridging the Gap · ThomasNet — Injection Molding vs. Machining: When to Switch

— Arthur, Tooling Engineer at aCatMould