Quick answer
Injection moulding becomes cheaper when lower unit cost outweighs tooling cost.
Example: GBP6,500 / (GBP18 - GBP0.70) = roughly 376 units. That figure is only useful if the design and forecast are stable enough to trust.
Break-even volume is the point where a process with a higher upfront investment but lower recurring unit cost overtakes a process that is cheap to start but expensive to repeat. Injection moulding usually wins late, not early. That does not make it wrong. It makes it timing-sensitive.
The wrong question teams often ask
“When is moulding cheaper?” sounds precise, but it hides the real issue: “When is moulding safer and more profitable than the alternatives?” Cost alone is not enough. A route that looks cheapest at 20,000 units can still be the wrong move if you only sell 4,000, change the geometry twice, or need to ship pilot builds before tooling is ready.
Break-even is not a number to memorise. It is a timing decision about when your confidence in the product becomes strong enough to justify commitment.
Example calculation
Assume 3D printing costs GBP18 per part with no tooling, while injection moulding costs GBP0.70 per part with a GBP6,500 tool. The cost gap per part is GBP17.30. On paper, the moulded route starts to win at roughly 376 units.
That sounds early, but only if the design is stable, the forecast is credible, and the first few hundred parts will not be scrapped by engineering changes.
What each manufacturing route is buying you
| Process | What you gain | What you give up | Typical trigger to move on |
|---|---|---|---|
| 3D printing | Speed, flexibility, almost no setup commitment | High unit cost, weaker cosmetic and process repeatability | When learning slows and recurring unit cost starts to dominate |
| CNC machining | Durable parts, predictable quality, useful functional prototypes | Moderate cost and slower repetition at higher quantities | When volume grows beyond the point where machining remains economical |
| Vacuum casting | Bridge-volume flexibility and better appearance than many prototype routes | Limited life and not the final production process | When demand and geometry justify real production tooling |
| Injection moulding | Lowest recurring cost and repeatable scale production | High upfront commitment and painful late-stage changes | When both demand and product architecture are genuinely stable |
Five questions to answer before cutting steel
- How strong is the forecast, and who owns that confidence?
- What is the cost of one major geometry change after tooling starts?
- Can a bridge process carry the first launch or pilot batch more safely?
- Are the quality and finish requirements already stable enough to tool against?
- Does the team have enough cash and lead-time tolerance to absorb tooling delays?
Common decision traps
Interactive tool
The Manufacturing Payoff Visualiser is most useful when you compare several scenarios instead of chasing a single answer. Run at least three cases:
- a conservative demand scenario
- your expected case
- an optimistic case with a more stable design and better process efficiency
Then compare the cost curves against what you know about launch timing, cash, and engineering maturity. That is where the real decision sits.