Reduce, Reuse, Injection Mold

Many people have the means now to create little plastic objects thanks to 3D printing. However, injection molding is far less common. Another uncommon tech is plastic recycling, although we do occasionally see people converting waste plastic into filament. [Manuel] wants to solve both of those problems and created an injection molder specifically for recycling.

The machine — Smart Injector — is automated thanks to an Arduino. It’s pretty complex mechanically, so in addition to CAD models there are several PDF guides and a ton of pictures showing how it all goes together.

According to the documentation, the extrusion screw can provide 51 Nm of torque with a 48V supply using a NEMA34 stepper and a 6:1 gearbox. The machine can make an iPhone 8 cover in about 4 minutes and costs about  1000 Euro to build.

Of course, melting and extruding plastic isn’t the big trick. That lies in clamping the mold. That step is done with a threaded rod and a NEMA17 stepper. Then again, the other trick is developing your molds which need to have an ejection mechanism specific to the molded part.

While some people might be put off by the statement that the machine still needs some manual intervention due to unresolved clogging and clamping problems. We’ll bet that will be a challenge to Hackaday readers who will be happy to help resolve those issues.

If you build it, we’d love to hear about it. The project reminded us a lot of another iPhone case maker we saw a few years back, although some of the links there are dead. If you want to practice with something cheaper, try hot glue and some ingenuity.

34 thoughts on “Reduce, Reuse, Injection Mold

  1. Please remember that almost all plastic is made from crude oil, plastic recycling has therefore an ecological viability and it would be unwise to take the problems with recycling as an excuse just to convert the plastic into CO2.

    Also please remember that the petro-chemical industry (and this is far from being just “fuels”) takes in recycled plastic.

    Also please remember that plastic is an umbrella term for a wide variety of materials just to name a few ABS, PP, PE, PC with different levels of recyclability

    And please remember if one just posts a statement and provides no argumentation might scam you.

          1. > Because it works better?

            Depends how “better” is defined.

            > Multi-use bottles (sterilzation, distribution)?

            Thinking creates more economy, keeps people busier and from being wastoids getting into who knows what. Less dependency on oil and non-renewable resources.

            > Plastic/wax coated paper (die in less than a week)?

            Was a way… not certain what you mean by “die in less than a week?”

    1. There are also a lot of variations, for each type of plastic. There is no way to sort out each, perfectly. Injection molding can be temperamental, and can take a while to dial-in, just in house re-grind. The only variation is the colorant added. We never ran 100% re-grind either, seldom exceed 40%. In production, you want every cycle, to produce perfect parts. It’s a huge lose of time and production, and also a risk of clogging, or damage to the machines. I’m sure there are uses for recycled plastics, but doubt they’ll replace virgin material to any great extent.

  2. Burning it to gain back some of its energy is probably the most environmentally responsible course of action. But good luck explaining that. I mean the average person should be more afraid of bananas radioactive potassium that nuclear power.

  3. While it may be “flashy” to make Iphone cases, it doesn´t seem like a hard plastic case would protect the phone that much.

    One use where I believe recycled plastic could help would be with sewage tubes and fittings. It is something that does not involve the requirements of food-safety, and also doesn´t need the other additives ( flame retardants, etc ) that are needed in electrical fittings ( tubes, boxes, even lamp fixtures and whatever ) .

    1. But aren’t because it is cheaper to produce things from new plastic. The cost of sorting, cleaning, and processing while also dealing with higher defects and reduced qualities make recycled plastic often more expensive than new plastic.

        1. That’s not a cost that the manufacturer has to bear. That gets foisted onto consumers (recycling fees) and local waste management facilities. So they don’t care what happens to the old plastic. They’ll just buy the cheaper new plastic.

        2. but dumping it in the ocean is not supposed to happen. in the EU there are no landfills (besides for super toxic stuff) and all trash is burned in local facilities to generate electricity and heat.
          but to correctly burn the trash they either need to add additional oil/gas or just mix in the right amount of plastic trash. its called thermal recycling and its the most economic way to use plastics.

          there is some recycling going on, PET bottles are basically recyclet 100% and turned into clothing. you would never use recycled plastic to make food containers, you want virgin material for that for safety reasons.

      1. its actually easy to recycle plastics into less valuable products. you can basically take mixed plastic trash, heat it up and press it into a gigantic mould to make a bench, road splitter, lots of other parts. the resulting material is a brownish, rather inhomogeneous block of plastic that often cant even hold its own weight in the summer, it doesnt rot so it does make a useful product, but technically its downcycling not recycling.

        pet bottles are pretty much 100% turned into fabric, because its easy to separate and clean.

        there also is almost 100% recycling going on in the production line itself, cutoffs, out of spec parts and runners are ground down and reused.

  4. The clamping force of a mouse trying to hold back a tidal wave. There is a reason why even the smallest of injection moulding machines have a hydraulic ram putting over 1 ton of force on mould.

  5. Nice build!

    From the video, it looks like they are running the nozzle temperature very hot for typical recyclables (HDPE, PP). This is probably needed to get the viscosity down to where the relatively low torque motor/gearbox can drive it.

    Aside from saving the planet, an injection machine is a useful addition to the tool box. You can build a manual machine for under $150 and make everything from raw stock, to mechanical parts, and some limited quantity promotional/decorative items. The creativity comes in how you generate the mold for a low cost (without industrial CNC). It is useful to generate parts without some of the directional strength issues of printed parts.

    The downside is you start picking your laundry detergent by how cool the bottle color is.

    1. Recycled HDPE and PE prices are fluctuating pretty heavily right now but usually they hover around $550/ton. And with a price like that you have to be ignorant to suggest it doesn’t make sense to recycle.

  6. When recycling thermoplastics the properties of the remelt can be made close to 100% virgin plastic by including 10 to 15 % virgin plastic with the recycled.

    Plastic bottles are made by first injection molding a preform. Those have the finished neck ring and threads while the rest is a short, thick walled tube with a closed bottom. For PET beverage bottles they’re typically at least four layers. Virgin PET inside, an oxygen barrier, recycled PET (thickest layer) and recycled, recycled+virgin, or all virgin PET outside. When clamped into a mold and blown with hot air, the layers all stretch and thin out.

    The only number that really matters in recycling is the % of post-consumer content. In many industries, papers, metals, plastics, and wood, recycling has been done since their beginnings.

    Paper mills have always taken their edge cuts, rough ends, and breakage and tossed it all back into the start of the process, either re-run for the same type paper or mixed for cardboard or formed packaging material.

    Metal refineries take waste and extra bits and put it back into the smelters.
    Back when double hung windows used heavy sash weights and wall clocks were weight driven, iron foundries would at the end of a crucible or end of the day, cast up a bunch of those weights, or weights for farm equipment, anything that just needed to be heavy and not structural. All that mattered was the weight, not the physical properties, so if there was a chunk of slag in, no problem.

    Plastics factories have always taken the failed shots, sprues, runners and anything else not part of the finished product and run them through a pelletizer to mix in with the virgin plastic. In that use case the re-run is just a fraction of the total.

    Lumber mills use sawdust and short cuts and pieces too crappy for lumber to run boilers or generators or it gets formed into particleboard or oriented strand board. If you see sheets of OSB with “Recycled” on it, It’s a pretty fair bet not a bit of it came from lumber salvaged from old houses.

    But starting in the late 1970’s these long done practices became “recycling”.

    So if you see 100% recycled on a product and nowhere does if say Post-Consumer, the recycling claim is BS, it’s just greenwashing industry standard re-processing they’ve always done.

    One product that really shows its recycled nature is the Starrett CS1-25 Re-Tape 25 foot tape measure. The housing is a grey plastic with visible bits of metal embedded, which are supposed to be from ground up metal tape measure housings.
    I bet they’re from housings that didn’t pass internal quality control. Getting enough old tape measure returned to have enough material for regular production of this product would be a logistical mess, plus all the dirt and other crud that would have to be cleaned off, along with disassembling the old measures. I’ve seen one in person, didn’t feel like any of the metal chunks were exposed on the surface, perhaps they use a double shot or over-molding process that puts a thin clear layer on the outside.

  7. I think a lot of us forget about the ‘Reduce’ of the 3 R’s. I would posit that many of us could remove more plastic from the ecosystem by simply reducing our consumption rather than building contraptions like this. If this project was framed as a “Cool DIY Injection Molding Machine” I’d be all about it, but acting like it is recycling on any meaningful level is, um, well, very optimistic.

  8. Screw that, how about using upcycled/recycled/reformed plastic for a shelter for impoverished locations? Or for the homeless? You want to feel good about the process, make stackable bricks that can make a wall for a decent shelter in temperate areas.

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