3D-Printed Injection Molds May Actually Be Practical

If you want to make one plastic thing, turn to 3D printing. If you want to make thousands of the same plastic thing, turn to injection molding. But the physical molds used for injection molding are notoriously expensive — easily tens of thousands of dollars. Conventional wisdom says they need to be machined from suitable metal, like hardened steel. However, Manuel Maeder demonstrated in a recent video that it can be practical to 3D print injection molds.

Maeder is using a TARS (Tiny Automatic Recycling System), which is a small desktop injection molding machine that he designed for recycling plastic. TARS is pretty intriguing in its own right, as industrial injection molding machines are very large and very expensive.

If you’re going to try 3D printing injection molds, you’ll probably want something like TARS. A manufacturer isn’t going to accept your 3D-printed molds, so you’ll need to get through the whole process with your own equipment.

There isn’t anything complicated about the process itself. Just print the mold in something like PETG-CF, coat it in a release spray, then inject your plastic. You’ll want to inject appropriate plastic — something that won’t stick to the PETG-CF and that has a lower glass transition temperature.

Of course, this has several limitations and disadvantages. Among those, the most obvious is very low durability. Injection molding requires a lot of heat and pressure, neither of which are good for the 3D-printed molds. They’ll quickly deform and deteriorate. Based on Maeder’s tests and demonstrations, I think you’d be unlikely to get more than a dozen injection-molded parts from each mold.

My opinion is that this entire process could be improved pretty dramatically with resin 3D printing instead of FFF (Fused Filament Fabrication) 3D printing. They would have much better surface finishes without layer lines and would also hold up better to the heat.

But in a pinch for small runs, even FFF 3D-printed molds can work and save you a small fortune — if you have a TARS machine or something similar.