Recycled Plastic Compression Molding With 3D-Printed Molds

Recycling plastic at home using 3D printed molds is relatively accessible these days, but if you do not wish to invest a lot of money into specialized equipment, what’s the most minimal setup that you can get away with? In a recent [future things] video DIY plastic recycling is explored using only equipment that the average home is likely to have around.

Lest anyone complain, you should always wear PPE such as gloves and a suitable respirator whenever you’re dealing with hot plastic in this manner, just to avoid a trip to the emergency room. Once taken care of that issue, there are a few ways of doing molding, with compression molding being one of the most straightforward types.

With compression molding you got two halves of a mold, of which one compresses the material inside the other half. This means that you do not require any complex devices like with injection molding, just a toaster oven or equivalent to melt the plastic, which is LDPE in this example. The scrap plastic is placed in a silicone cup before it’s heated so that it doesn’t stick to the container.

The wad of goopy plastic is then put inside the bottom part of the mold before the top part is put in place and squeezed by hand until molten plastic comes out of the overflow opening(s). After letting it fully cool down, the mold is opened and the part released. Although the demonstrated process can be improved upon, it seems to work well enough if you are aware of the limitations. In terms of costs and parts required it’s definitely hard to come up with a cheaper way to do plastic molding.

3 thoughts on “Recycled Plastic Compression Molding With 3D-Printed Molds

    1. Honestly this seems much easier to do than any kind of art resin injection with 3D printed moulds that i can do. I’ve made silicone parts with 3D printed moulds as well, and they too turn out well. I really believe 3D printing is of great utility for making one off moulds for parts that’s you will make probably only a dozen or so of. I seldom see people using 3D printers for making moulds though, that’s a gripe i have

      But that’s nothing against when my father “borrows” my soldering iron with its nice and clean, properly tinned hakko tip and uses it to melt holes into a plastic project box. Never, never loan out your tools, at least the ones you cherish

  1. Great video and concept. I work as a machinist making commercial compression molds and have learned a lot about the design nuances. In particular I’d like to suggest incorporating a “shear edge” around the perimeter of your cavities so that the two halves act like a pair of scissors to automatically trim the flashing away at the end of the compression stroke.

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