CNC vs Injection Moulding: How Quantity Changes the Decision
Quantity changes the balance between tooling, unit cost, lead time and design flexibility.
The problem: selecting a process too early
A part that can be machined may also be injection moulded, but the investment logic is different. CNC removes material from stock and can avoid dedicated moulds. Injection moulding requires the part and tooling to be developed as one system.
Unit price alone is not enough. Setup, programming, tooling, validation, scrap, expected design changes and logistics must be considered together with batch size and annual demand.
When each option becomes relevant
CNC machining
- Initial or changing batches.
- Geometry still under validation.
- No dedicated mould investment.
- High-value or customised parts.
Injection moulding
- Volume can support tooling.
- Geometry is sufficiently stable.
- Repeatable production cycles matter.
- Functions can be integrated into fewer parts.
Use scenarios, not a single number
Compare a pilot batch, a probable demand and a growth scenario. For each one, include upfront investment, recurring cost, lead time, expected changes and the risk of obsolete tooling.
A product may start with CNC machining and later be redesigned for injection moulding. It may also remain machined when personalisation, product value or uncertain demand make flexibility more important.
Educational example: a technical enclosure
Educational example, not a client case. For an initial batch of 80 units, a team compares two machined halves with a redesign for injection moulding. CNC allows changes after early tests. Injection moulding requires draft angles, wall thickness, ribs and ejection to be resolved before tooling.
The team machines the pilot batch and records assembly time and interface performance. If demand stabilises, those results provide a stronger basis for a tooling decision.
FAQ
Is there a universal minimum quantity for injection moulding?
No. It depends on part size, complexity, material, tooling, cycle and product life.
Can the same geometry be used for both processes?
Usually not without adjustments. Tool access, radii, wall thickness and draft follow different constraints.
Select the process from function, scale and investment
Órbita compares manufacturing scenarios and prepares products for supplier quotations.
