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3D printing vs injection molding for low-volume parts
How to decide between printing and molding when you need tens or hundreds of parts, not a million.
3D printing is usually the better choice for one-offs, prototypes and small batches, or while the design is still changing — there's no tooling and parts ship in days. Injection molding wins when you need many identical parts or the part has to be in a production plastic like PP or HDPE. Mithril's printed resin molds make short molding runs practical without the cost of a steel tool.
The real difference: tooling
A printed part costs about the same whether you order one or fifty, because there's nothing to build first. A molded part needs a mold before the first part exists, but every part after that is fast and inexpensive. So the question isn't which process is better — it's how many parts you need and whether the design is final.
Traditional steel molds can cost thousands and take weeks. We print mold cavities in-house instead, which brings tooling cost and lead time down far enough that a short run can make sense.
Side by side
| 3D printing | Injection molding (printed molds) | |
|---|---|---|
| Upfront cost | None | One-time mold cost |
| Cost per part | Roughly flat at any quantity | Drops as quantity goes up |
| Typical lead time | 3–5 days | 7–15 days |
| Materials | FDM filaments and SLA resins | Delrin, PP, ABS, TPU, PE, HDPE |
| Design changes | Free — just send a new file | Usually needs a new or modified mold |
| Best for | Prototypes, one-offs, small batches, changing designs | Short runs, bridge production, parts that must be in production plastic |
How to decide
- Is the design still changing? Print it. Molding a design that's about to change wastes the tool.
- Does it have to be PP, HDPE or another production plastic? Mold it — those materials aren't printable the same way.
- How many do you need? The more identical parts, the more molding pays off. Where the crossover falls depends on the part's size and complexity, so we'll quote both.
- Need parts now and more later? Print the first batch while the mold is made — that's bridge production.
Planning to mold? Draft angles, even wall thickness and generous radii make a big difference. Our Design for Manufacturing guide covers the basics.
Questions
How many parts before injection molding is worth it?
It depends on the part's size, complexity and material. Send the file and quantity and we'll quote printing and molding so you can see where the crossover is for your part.
Can I start with 3D printing and switch to molding later?
Yes. Many customers print prototypes and the first parts, then move to molding once the design is final and quantities grow.
Do I need to change my design for molding?
Often a little. Molded parts need draft angles so they release from the mold, and even wall thickness to avoid sink and warping. We review every file and flag what needs to change.
What are printed resin molds?
Mold cavities printed in-house from resin instead of machined from steel. They cost less and are ready faster, which makes them a good fit for short runs and bridge production.
Not sure which way to go?
Send the file and the quantity you need, and we'll tell you whether to print or mold — and why.