3D printing vs injection moulding for business parts
Both processes make plastic parts, but they suit different stages and volumes. Here's how I think about the choice for functional business parts.
The main difference: tooling
Injection moulding needs a mould tool made before the first part. Once the tool exists, each part can be produced quickly and consistently, which is why moulding is usually the better route for stable designs at high volumes.
FDM 3D printing builds each part in layers straight from your digital file, so there is no tool to make. That makes it practical for short runs and repeat batches where buying a mould would not make sense yet.
When your design changes
With FDM, a revised file can be printed in the next batch without changing any tooling. Every revision still needs care: I review the new file, prepare it again, and if the change affects fit or function I may suggest a new sample and a new quote. More on changing a design between batches.
Moulds can often be modified rather than replaced. Mould makers commonly plan for this by designing "steel-safe" (or "metal-safe"): removing metal from a tool is usually possible, adding it back is much harder. So some changes, like a thicker wall or an added rib, can often be machined into an existing tool, while others, such as making a wall thinner or changing the parting line, usually mean significant rework or a new tool.
Finish, strength and materials
- Finish: FDM parts show fine layer lines. If you need a smooth cosmetic surface straight from the process, moulding (or a different printing process) may suit you better.
- Strength: FDM parts are anisotropic: usually weaker across their layers than along them. Print orientation matters, and mechanically critical parts need testing in real use.
- Materials: I print in PLA, PETG, ASA and TPU. Moulding offers a very wide range of grades. How a part performs depends on the process and the specific material grade, so compare like with like.
Using both
Many products don't have to choose once and for all. Printed batches can carry you while a design is still changing or volumes are modest; if the design settles and volumes grow, moulding may become the better option. A part designed for printing may need design-for-moulding changes, such as draft angles and even wall thicknesses, before it can be moulded, so plan for that step.
If I think moulding or another process would suit your part better, I'll tell you.
Not sure which process suits your part?
Send me your file and quantity. I'll tell you honestly whether batch FDM printing makes sense, or whether moulding or another process would suit it better.
How to send your fileMore guides
Or email me at info@stourworks.co.uk