The difference in one sentence
With 3D printing you pay per part and have no set-up costs. With injection moulding you pay for a mould first and then a low price per part. Everything in this article follows from those two cost structures.
Cost structure of 3D printing
A 3D printer builds every part directly from your CAD file. There's no tooling, so the first part costs about the same as the hundredth. The price depends mainly on the part's volume and the material.
For functional plastic parts in series, MJF is often the logical technology. At Makernaut, MJF starts from €0.45/cm³, and PA12 Grey MJF from €0.52/cm³, excl. VAT.
Worked example: a PA12 housing
A small housing has a volume of 30 cm³. In PA12 Grey MJF that's 30 cm³ × €0.52/cm³ = from €15.60 per part, excl. VAT and finishing. For 50 parts that comes to from €780.00, with no mould and no set-up costs.
Volume × material price is a starting point. You'll see your actual price, including any finishing, in Quotebase.
Cost structure of injection moulding
In injection moulding, molten plastic is injected under high pressure into a metal mould. That mould is a one-off investment, made specifically for your part. Once it's ready, the machine produces parts at a high rate, at a low price per part.
What the mould costs depends on:
- the size and complexity of the part, with undercuts that need slides or cores;
- the number of cavities: more parts per cycle means a pricier mould but a lower unit price;
- the mould material: aluminium for small series, pre-hardened steel for medium and hardened steel for large series;
- the surface requirements, such as high gloss or a texture.
We deliberately don't quote amounts here: a mould is always bespoke. Through Makernaut's ISO 9001-certified partners, you get a custom quote within one working day.
Working out the break-even point
The break-even point is the volume at which both processes cost the same. Below it, 3D printing is cheaper; above it, injection moulding. You calculate it like this:
Break-even volume = mould cost ÷ (price per printed part − price per moulded part)
The reasoning: suppose a printed part costs a certain amount more than a moulded part. Every part you mould instead of print 'earns back' that difference. As soon as those savings add up to the cost of the mould, you've reached the break-even point.
Three practical lessons follow from that:
- Small parts push the break-even point up: a small volume is cheap to print, so the difference per part is small.
- Complex shapes push it up too: they make the mould more expensive, while a printer doesn't care about undercuts.
- Large, simple parts pull it down: lots of volume makes every print expensive, and a simple mould is relatively affordable.
More than just price
| Criterion | 3D printing | Injection moulding |
|---|---|---|
| Set-up costs | None | Mould |
| Price per part | Higher, nearly constant | Low, falls with volume |
| Design changes | Upload a new file | Modify or remake the mould |
| Design freedom | Very high, including internal channels | Draft angles and even walls needed |
| Materials | PA12, resins, TPU and more | Wide range: ABS, PC, PP, POM, PA and more |
| Surface | Depends on the technology, often with finishing | As the mould: smooth or textured |
A design made for 3D printing can't always be moulded as is. If you plan to switch later, design with draft angles and even wall thicknesses from the start.
Bridge options between printing and moulding
Between the first prototype and full injection production there are often months of testing, tweaking and early sales. Two processes cover that phase.
MJF series
MJF produces strong, functional PA12 parts without a mould. Because many parts fit in one build volume, it suits series work. You can change your design between batches without any tooling cost.
Vacuum casting
Vacuum casting uses a silicone mould made around a printed master. The PU parts look like moulded parts, including in clear or rubber-like grades. It typically pays off for small series; one mould typically lasts 20 to 25 castings.
How to choose
- Choose 3D printing if your design is still changing, your volume is small or the shape is hard to mould.
- Choose MJF series for functional PA12 parts in volume, without a mould.
- Choose vacuum casting for a small series that has to look like a moulded part.
- Choose injection moulding when your design is frozen and your volume is past the break-even point.
Not sure? Get both a print price and an injection moulding quote. With those two figures you can fill in the formula above and see straight away where your volume sits.