Can You 3d Print Injection Molds for Plastic Injection Molding?


3d printing is a fantastic new technology that has taken the home manufacturing world by storm. With these machines, you can produce quality plastic models in a few hours, all from a machine which easily sits on your desk. They’re simply amazing.

You can 3d print injection molds to be used with injection molding setups. You will need an aluminum mold frame to put the 3d printed mold halves into, and then use an injection molder that melts the plastic and injects it into the mold. This can be a good way to balance the slow nature of 3d printing with the desire to produce quality plastic parts.

Plastic injection molding, at the industrial level, can be expensive, but there are smaller setups that can be used in the home. Many of us went to high schools that had small injection mold setups for use in making small plastic items. My high school produced small plastic footballs with an aluminum mold.

The Concept of 3d Printing For Injection Molding

Formlabs made news recently when it published a White Paper (a document that explores a concept, rather than a blueprint for how to do that concept). You can read it here:

It caused a stir in my local maker group here in the US Southwest. For game pieces for tabletop games, the best quality come from plastic model kits. 3d printing has come a very long way, and with DLP resin printers, we’re at a point where the quality of the models produced is near the quality of those vaunted plastic model kits.

Essentially, the discussion centered around the ability to make plastic injection parts at home. First, you’d need an injection molding machine. Sure, the industrial variants of these can be staggeringly expensive (not to mention large and take a lot of electricity to run). There are, however, smaller injection molding setups that you can purchase that can fit in a home or small workshop. These home-sized setups use human power to inject molten plastic into sandwich molds (two mold halves squeezed together in a frame). Once the two halves cool, the halves can be separated and a freshly minted plastic part is left.

The problem has always been the molds themselves. There are some commercially available small aluminum molds for sale that can get you some designs, but for us gamers, they are never the right designs. We want that specific figure, or vehicle model, or scale model howitzer for the game that we’re playing. And we want 50 of them, not five, and not 500 (or that ballpark).

Formlabs’ White Paper described a method of taking a rigid aluminum mold frame, with a hollow center, and 3d printing molds that will fit in the hollow center. The mold has to be a negative of the thing that you want to print. Instead of making a figure, you’re making a block of plastic with a hole that’s the shape of the figure. Further, you’re printing two half-molds, that, when they’re squeezed together, form a hole in the shape of that figure. The aluminum mold frame is there so that the mold doesn’t deform when hot plastic, under pressure, is injected into that hole in the shape of the figure.

It’s a nice marrying of 3d printing and home plastic injection molding. Depending on the required temperature, pressure and complexity of the models to be produced, you can get anywhere from 20 to 100 copies of a model before the mold is worn out and not useful any more. When that happens, simply reprint the 3d mold halves, and get back to it! It’s a pretty neat idea!

Produce 3d Printed Injection Mold Halves

You’re going to need to become familiar with 3d Computer Aided Design (CAD) software at this point. Eventually, it’s possible these mold halves will become available on places like Thingiverse.Com or other STL sites. But that’s not true yet.

Instead, you’ll have to take a 3d design and modify it. For those with a good working knowledge of CAD software, this isn’t actually too hard. You’ll make a 3d block, take your model, and “embed” it in the block (virtually, of course). Once you’ve created a cavity, your job them will be to split the block in half, creating the two halves of the mold.

A video is worth several thousand words (is that how the saying goes?) Here’s a link to a good YouTube video on the concept:

Equipment to 3d Print Molds and Injection Molding

The first thing you’ll need is a home-sized injection system to produce the parts once you’ve got a mold. The Formlabs White Paper references the Galomb model, below:

This is a nice injection molder with a heating hopper (to melt the plastic), and a clamping system to secure a small mold frame in place. The mold frame will have a hole for the injection nozzle to marry up to, and the molten plastic is pressured into that hole via the pull-down plunger on the machine. Pulling down generates the necessary pressure to squeeze the plastic into the mold to form the part.

For high quality mold halves (that are detailed, smooth and will create good quality parts), you’ll want to use a DLP resin printer. The Elegoo Mars or the AnyCubic Photon are both good examples of printers that can produce excellent results here, and both are sub-$300.00USD. Of course, in the White Paper, Formlabs references a Formlab printer. It, of course, is also an excellent choice, but at a higher price point.

For mold frames, you can find these available for jewelry making online. They’re normally below $50.00USD. Here are two sources that have multiple sizes.

It’s likely easier to find the injection molding system and a good mold frame or two that will fit, then design and print the 3d printed inserts. 3d design can be tailored to whatever size is perfect for your mold frame. It may be more difficult to look for a mold frame to fit your pre-existing molds (unless you happen to have designed your molds to fit standard mold frame sizes).

Mold Materials for 3d Printed Molds

To withstand the heat of melted plastic, you’re going to want to print in a material that’s resistant to heat. PLA, ABS and regular UV 3d Printing Resin all have melting points down where they may deform with the melted plastic in plastic injection molding. Instead, go with a more heat resistant filament or resin. Here are two (the first for DLP resin 3d printers and the second for FDM filament 3d printers). Their heat resistance is much higher than regular plastic or resin, so it’ll hold up much better to injection molding.

Related Questions

Is 3d printing cheaper than injection molding?

No, 3d printing is more expensive when you are injection producing large numbers of parts. However, for small numbers, like up to 10, it can be cheaper to simply print the design 10 times. A 3d printer is likely a lot cheaper than a plastic injection molding machine, with a DLP resin printer costing under $300.00USD and prints created for under $2.00USD in material. Compare with a Galomb Model B-100 Injection Molder at $4490.00USD, but prints for under $0.20USD per.

Can I 3d print rubber?

No, but you can come close. You can print with a flexible filament (called thermoplastic polyurethane, or TPU) with an FDM filament printer. The flexible filament is slightly more expensive than PLA filament, but is readily available in a number of colors. Check out YOYI TPU filament on Amazon.Com for an idea of a flexible filament. 
https://www.amazon.com/YOYI-Flexible-Filament-Tolerance-Green/dp/B07TLBJVBZ/ref=asc_df_B01M63ZVUJ/?tag=hyprod-20&linkCode=df0&hvadid=241975559923&hvpos=1o1&hvnetw=g&hvrand=4815559895983151328&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9030797&hvtargid=aud-801381245258%3Apla-451730562937&th=1

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