The break-even usually sits between 1,000 and 10,000 pieces per year, depending on geometry and material. Below 1,000 SLS is almost always cheaper (no mould). Above 10,000 stable PA12 parts, injection moulding wins. Complex geometry, varying variants or a time-sensitive launch push the break-even to higher volume.
The math in principle
Injection moulding has high fixed costs (mould €10,000-50,000+, qualification, material tests) and low marginal cost per piece (€1-5). 3D printing has no fixed cost and higher marginal cost (€10-50 per PA12 part).
Break-even is where total costs are equal: (mould + N x moulded per-piece cost) = (N x 3D print per-piece cost). Mould of €30,000 and €4 difference per piece: break-even = 7,500 pieces.
Why it is not a sharp line
Four factors shift the break-even.
Geometry complexity. Complex parts stay favourable for SLS longer because an injection mould gets more expensive.
Material choice. With PA 950 HD SLS per-piece drops 35%. SLS stays competitive longer.
Design iteration. If you are still iterating, every design change is a tool rework of weeks and €5,000+. SLS gets structurally cheaper.
Time to market. 2-3 months mould wait costs you market momentum.
On complex or evolving designs the break-even can sit above 30,000+ pieces; on simple stable PA12 parts as low as 3,000.
The hybrid strategy that often wins
You do not have to pick one. Most common: SLS for bridge production during the first 6-12 months while you have the mould built.
Benefits: no waiting for tooling, design can still adapt to first customer feedback without tool rework, cash-out of the mould shifts to when you know the product runs. Once injection is up, SLS goes off for the main product. You can keep SLS for exceptions, variants and fast replacements.
Want to run this math on your case? Talk to an engineer.