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Exploring mould making for localised plastic recycling


We are all aware that globally we have a plastics problem, with less than 16% of plastics being recycled and the rest being burnt or sent to landfill. Localised plastic recycling is a movement to decentralise the recycling of plastic waste, with small businesses collecting and sorting plastic waste on a community scale before turning it directly into new products. This movement is spearheaded by Precious Plastic, I'd highly recommend checking out their YouTube channel if you've not come across them before.

This community is doing amazing work, turning plastic waste into new products, but a problem I consistently came across when speaking to them was mould making. They generally have small-scale injection moulding machines to produce new products from shredded waste plastic, but producing the moulds for this process is difficult and expensive. Moulds are normally CNC machined from metal blocks, costing anywhere from £500 to £5,000 pounds. This means members of the community often don't want to risk trying out new products as they don't know if a new mould will work properly or if the part will work as intended, or if they'll even be a demand for their new product. So they default to buying off-the-shelf moulds for simple objects like flower pots, rather than creating something new and interesting. I wanted to see whether 3D printing could be used to make mould-making accessible and affordable so that these recyclers could make and experiment with moulds and push the boundaries of what is possible with locally recycled plastic.


Typical off-the-shelf flower pot mould (image credit Plasticpreneur)


My project has involved a large amount of experimentation in this area. I started with simple FDM 3D printed moulds, which can work at low temperatures, especially by using filaments such as Nylon which are relatively temperature resistant. I quickly moved on to using 3D forms as moulds-of-moulds, this allows you to easily 3D the form you want and then make a mould of it from a more temperature resistant material. I explored options like silicones, plasters, polyurethanes and cast pewter metal but found the most promising to be casting epoxy resin.


A lot of my experimentation focused on the use of electroplating to create a metal surface layer for the moulds. I found that this greatly improved the surface quality of the parts produced, helped make the parts release more easily from the mould, and helped separate the mould from the 3D printed form. Using electroplating in combination with the mould-of-a-mould technique worked incredibly well, as the copper surface exactly replicates the surface of the 3D print giving a very smooth and precise surface. If you electroplate a regular mould the metal layer grows unevenly, giving unpredictable tolerances and amplifying imperfections. When a mould-of-a-mould is electroplated and then filled with epoxy resin, the resin also adheres directly to the metal giving a very strong connection. Normally when electroplating plastics there is a layer of conductive paint between the plastic and the metal which limits the adhesion strength. This strong adhesion is definitely necessary when producing an injection mould.


To test these moulds I've been using a benchtop injection moulding machine based on a design by BusterBeagle3D. I'd highly recommend giving it a look if you're interested in experimenting with injection moulding plastics. It does have quite a small shot-size, and so I produced mainly small moulds, often for a plastic button as this was a small but challenging geometry.


Early Process

Based on these experiments I settled on an early process that seems to be relatively effective:


I'm now in the process of refining this method to make it more straightforward, fast, and reliable. I look forward to sharing more about that once the project is complete!

I'm an Innovation Design Engineering post-graduate student, studying at the Royal College of Art and Imperial College London. I previously studied Mechanical Engineering at the University of Cambridge. I love taking a hands-on experimental approach to design and using engineering principles to solve design problems.
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