CNC Machining vs Injection Moulding Australia
The right manufacturing process depends on your volume, timeline, and budget. Here is a practical guide to choosing between CNC machining and injection moulding — with Australian cost benchmarks and volume crossover analysis.
CNC Machining vs Injection Moulding: At a Glance
Use this table for a quick side-by-side comparison before deciding which process suits your requirements.
| Factor | CNC Machining | Injection Moulding |
|---|---|---|
| Tooling cost | None | $3,000–$100,000+ |
| Tooling lead time | None | 3–8 weeks |
| Per-part cost (low volume) | Low–Medium | High (tooling amortised) |
| Per-part cost (high volume) | High | Very low ($1–$20) |
| Break-even volume | — | Typically 200–2,000 pieces |
| Typical lead time (parts) | 7–14 days | 4–12 weeks (incl. tooling) |
| Materials | Metals + all plastics | Thermoplastics only |
| Tolerances | ±0.01–0.05mm | ±0.1–0.3mm typical |
| Design changes | Free (no tooling) | Expensive (tool modification) |
| Best for | Prototypes, low–mid volume, metals | High-volume plastic parts |
Understanding the Volume Crossover
The crossover point — where injection moulding becomes cheaper than CNC machining — depends on tooling cost and per-part cost differential.
Simple Part
For simple consumer product parts in ABS or PP — crossover occurs very quickly.
Medium Complexity
Multi-cavity tools reduce tooling cost per cavity. Consider family moulds for related parts.
Complex Part
Complex tooling with side actions, hot runner systems. DFM critical before committing to tooling.
The Recommended Product Development Path
Most successful products follow the same path: CNC machined prototypes first, then injection moulding tooling once the design is validated.
CNC Prototype
Machine 1–5 parts in target plastic or aluminium. Validate design, fit, and function. Fast and cheap to iterate.
Design Validation
Test, refine, and finalise design. Any changes are free — just update the drawing. No tooling wasted.
Pre-Production Run
Machine 10–50 parts for market testing, regulatory approval, or beta customer supply. Bridge before tooling.
Injection Moulding Tooling
Once design is locked and volume justifies it, commission tooling. Transition to production moulding.
CNC vs Injection Moulding FAQ
What is the main difference between CNC machining and injection moulding?
CNC machining is a subtractive process — material is removed from solid billet using cutting tools. There is no tooling cost. Parts can be produced in any material available in billet or bar stock form. Injection moulding is a net-shape forming process — molten plastic is injected into a steel mould under high pressure. The mould (tooling) costs $3,000–$100,000+ AUD depending on complexity, but once the tool is made, per-part cost for plastic parts drops dramatically compared to CNC machining. The key decision factor is volume: CNC machining is cheaper at low volumes, injection moulding becomes cheaper above a volume crossover point.
At what volume does injection moulding become cheaper than CNC machining?
The crossover volume depends on part complexity and tooling cost. A simple part with $5,000 AUD tooling and a CNC machining cost of $100/part vs injection moulding at $5/part would break even at 52 parts (tooling cost recovered at 52 pieces). At 100 parts, total injection moulding cost is $5,500 (tool + parts) vs $10,000 CNC; at 500 parts, $7,500 vs $50,000. For typical plastic consumer or industrial parts: the crossover is usually 100–500 pieces for simple parts, and 500–2,000 pieces for complex parts with expensive tooling. Below the crossover, CNC machined plastic is cheaper. Above it, injection moulding wins decisively.
When should I choose CNC machining over injection moulding?
Choose CNC machining when: volume is below the injection moulding break-even point (typically < 200–500 pieces); you need the part quickly (injection moulding tool lead time is typically 3–8 weeks, CNC is 1–2 weeks); you need a metal part (CNC machines any metal; injection moulding is plastic-only); you need tight tolerances not achievable in moulded plastic; you are still iterating on the design (tooling is expensive to modify); you need a one-off prototype or spare part; or the part geometry prevents tool extraction (undercuts, re-entrant features without complex side actions).
When should I choose injection moulding over CNC machining?
Choose injection moulding when: volume is above 500+ pieces per year and the design is finalised; the part is plastic and can tolerate the slightly looser tolerances of moulding; you need low per-unit cost at volume — moulded plastic parts often cost $1–$20 each vs $50–$500 for CNC machined equivalents; the part has thin walls that would be expensive or fragile to machine; you need production-grade resins (glass-filled nylon, ABS/PC blends) that machine poorly; or the part has complex organic shapes better suited to moulding.
Can CNC machining be used as a bridge before committing to injection moulding tooling?
Yes — and this is the recommended approach for most product development programmes. CNC machined plastic prototypes allow design validation, functional testing, and market testing before the significant investment in injection moulding tooling. CNC machined parts can be produced in the same engineering-grade plastics (Delrin, PEEK, Nylon, ABS) that will be used in the final moulded part, giving representative mechanical performance. Once the design is validated and volume justifies tooling investment, transition to injection moulding for production. This approach eliminates costly tooling changes driven by design errors.
What materials are available for CNC machined plastic parts?
A wide range of engineering-grade plastics are available for CNC machining: Delrin / POM (Acetal) — excellent machinability, good dimensional stability, self-lubricating; PEEK — high temperature, chemical resistant, FDA-compliant grades available; Nylon PA6/PA66 — good wear resistance, moderate cost; Polycarbonate — transparent grades available, impact resistant; HDPE and UHMWPE — food-grade grades, excellent chemical resistance; PTFE — non-stick, excellent chemical resistance; PVC — corrosion-resistant for fluid handling; and ABS — general purpose, paintable. Not all of these are available as injection moulding grades.
Does Rapid Manufacturing supply both CNC machined parts and injection moulded parts?
Yes. Rapid Manufacturing is a managed supply service covering multiple manufacturing processes — CNC machining for prototypes and low-volume production, and injection moulding for higher-volume plastic parts. When you submit a drawing, we will advise on the most appropriate process based on your volume, timeline, and budget. We manage tooling procurement, mould trials, and production supply through our injection moulding supplier network.
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