Hackaday Prize 2022: Recycled Plastic Skateboard Decks Demonstrate Small-Scale Injection Molding

Injection molding is usually focused on high-volume production, but that doesn’t always need to be the case. The Recycled Plastic Skateboard Deck project centers on the use of injection molding for a relatively low-volume production line using open-source tooling.

RPSD is part of the Precious Plastics ecosystem and uses the existing and open-source shredder and extruder to turn locally-sourced plastic waste into melted plastic. The core of the tooling is in the aluminum CNC-machined top, bottom, and edge mold sections bolted to a thick steel support structure that give the skateboard deck its shape. The edge section defines the deck’s perimeter, and 64 cartridge heaters are inserted into it to bring the mold up to temperature. The mold is mounted on a scissor lift mechanism to allow it to be aligned with the extruder, and temperature control electronics are housed in a laser-cut metal enclosure, which is bolted to the base of the mold structure.

To be clear, this is not a cheap way to make a couple of skateboard decks, but rather a way for small shops to do injection molded decks in-house. At ~$7500 for the components of this relatively large mold, excluding the extruder, you’d still have to sell quite a few decks to make it economically viable.

Although small-scale injection molding has become a lot more accessible, the cost of machined metal molds will remain high for the foreseeable future. However, if you only need small, flexible parts, you could probably do it for under $50 using 3D printed molds and silicone.

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Injection Molds: Aluminum Or Resin?

[JohnSL] and his friend both have injection molding machines. They decided to compare the aluminum molds they usually use with some 3D printed molds created with a resin printer. They used two different resins, one on each side of the mold. You can see a video of the results below.

One half of the mold used ordinary resin while the other side used a resin that is made to hold up to higher temperatures. As you might expect, the lower-temperature resin didn’t stand up well to molten plastic. However, the higher temperature resin did somewhat better. It makes sense, though, that an aluminum mold draws more heat out of the plastic which is helpful in the molding process.

The higher temperature — and more expensive — resin did seem to hold up rather well, though. Of course, this was just to test. In real life, you’d want to use the better resin throughout.

No surprise, the resin molds didn’t last nearly as long as a proper mold. After 70 shots, the mold was worn beyond what you’d want to use. So not necessarily something you’d want to use for a real production run, but it should be enough for a quick prototype before you go to the expense of creating a proper mold.

We wonder if there are some other tricks to get better results. A comment from [TheCrafsMan] suggests that clear resin UV cures better, and that might produce better results. In fact, there are a lot of interesting comments on the video from people who have varied experiences trying to do the same thing.

If nothing else, watching the mill cut through the aluminum around the 15-minute mark is always interesting to watch.  If you don’t already have an injection molding setup, you can always build one. We’ve seen more than one design.

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Injekto Injection Machine Reaches 2.0

Last time we looked in on Injekto — a homemade plastic injection machine — it was at version 1.0. A recent video from the team that you can see below shows version 2 which is much improved and can work with 3D printed molds. Injection molding takes a lot of pressure and the machine certainly looks stout with lots of machined aluminum.

If you want to skip the build process, you can skip up to around the 9-minute mark. That’s where they show a machined mold and a 3D printed mold being used with the machine.

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Used Facemasks Turned Into Rapid Antigen Tests With Injection Molding

Here’s a little eye-opener for you: next time you’re taking a walk, cast your eyes to the ground for a bit and see how far you can go without spotting a carelessly discarded face mask. In our experience, it’s no more than a block or two, especially if you live near a school. Masks and other disposal artifacts of the COVID-19 pandemic have turned into a menace, and uncounted billions of the things will be clogging up landfills, waterways, and byways for decades to come.

Unless they can be recycled into something useful, of course, like the plastic cases used for rapid antigen tests. This comes to us by way of [Ric Real] from the Design and Manufacturing Futures lab at the University of Bristol in the UK. If any of this sounds or looks familiar, refer back to October when the same team presented a method for turning old masks into 3D printer filament. The current work is an extension of that, but feeds the polypropylene pellets recovered from the old masks into a desktop injection molding machine.

The injection molding machine is fitted with 3D-printed molds for the shells of lateral flow devices (LFD) used for COVID-19 rapid antigen testing. The mold tooling was designed in Fusion 360 and printed on an Elegoo Mars MSLA printer using a high-strength, temperature-resistant resin. The molds stood up to the manual injection molding process pretty well, making good-quality parts in the familiar blue and white colors of the starting material. It’s obviously a proof of concept, but it’s good to see someone putting some thought into what we can do with the megatonnes of plastic waste generated by the pandemic response.

DIY Injection Molder Built From A Cheap Pneumatic Press

[Kurt Schaefer] was watching YouTube videos of people making molds for injection molding purposes using what he considered to be the toy 3018 CNC machines, and looking at the results, decided he needed a piece of the action. However, once you have molds, the next obvious issue to address is lack of access to an injection molding machine. But these things are expensive. As luck would have it, you can get a nice-looking pneumatic press for less than $350, and with a little more money spent, [Kurt] found he could convert it into a functional injection molding machine (video, embedded below), and get some half-decent results out of it.

After ordering the press on eBay, what eventually arrived was quite a mess, having clearly been inadequately packed for its weight, and had sustained some damage in transit. Despite this, it seemed the functional bits were fine, so [Kurt] decided to press on with the build. The first obvious change is the requirement of a heated chamber to deal with the feedstock material. Using an off-the-shelf injection molding chamber by buster beagle 3D, only a few standoffs and a support bracket needed machining in order to complete the mechanics. A common PID controller available from the usual suppliers, with some heat bands wrapped around the chamber, dealt with the injection temperature requirements, and some 3D printed enclosures wrapped it all up neatly.

After some initial wobbles, and a couple of hacks to the design, [Kurt] got some pretty good results out of this simple setup, and it appears to be pretty tune-able and repeatable, which will help maintain the quality of those results. In short, a neat hack of easy to get parts, and perhaps a welcome addition to a hackerspace near you?

3D printed parts are available on the Thingiverse page, as well as a Fusion360 CAD model. The shopping list for parts can be found in the video description, if you want to have a go at reproducing this.

We’ve seen a few DIY injection molding attempts over the years, like this slick plastic molding setup. Here’s one with 3D-printed molds, and if you just need something the right shape, you could just injection mold with a hot glue.

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injecto doing it's thing

Tiny Homemade Injection Molder

With 3D printing continually gaining ground, some hackers might not see the need for traditional injection molding. After all, you can tweak the code or the model and print dozens of different iterations with fairly minimal lead time. Things get trickier when you need to print hundreds or thousands of the same thing and that ten-hour print time adds up quickly. [Actionbox] built a tiny injection molder they dubbed INJEKTO to speed up their manufacturing.

The design was optimized to be accessible as it is held together with brackets and cheap aluminum flat stock. The hardest part to source is the heating chamber, as it is a piece of turned aluminum. A PID controller keeps the temperature relatively stable and heats the plastic pellets you can dump in the top. Next, you’ll need an external air compressor to power the dual 2″ pneumatic pistons. The pistons push the plastic out of the spring-loaded extruder nozzle. [Actionbox] is already planning on a second version with 4″ pistons that provide significantly more force to extrude larger amounts of plastic as the current version tops out at about 27 grams.

Injection molding still needs a heavy-duty mold to inject into, which can be hard to machine. So until we can 3D print an injection mold, this multi-head 3D printer is something in between a 3D printer and an injection molder, as it can print a dozen of the same thing, speeding up that print time.

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THICC GBA SP Mod Gets Easy Install Ahead Of Release

Back in August we covered a unique modification for the Nintendo Game Boy Advance SP which replaced the handheld’s rear panel with an expanded version that had enough internal volume for an upgraded battery, a Bluetooth audio transmitter, and support for both Qi wireless and USB-C charging. The downside was that getting the 10 mm 3D printed “backpack” installed wasn’t exactly the most user-friendly operation.

But today we’re happy to report that the dream team behind the so-called THICC BOI SP have not only made some huge improvements to the mod, but that they intend to release it as a commercial kit in the next few months. The trick to making this considerable upgrade a bit more forgiving is the use of a bespoke flat flex cable that easily allows the user to solder up all the necessary test points and connections, as well as a custom PCB that pulls together all the hardware required.

In the video below, [Tito] of Macho Nacho Productions goes over the latest version of the mod he’s been working on with [Kyle] and [Helder], and provides a complete step-by-step installation tutorial to give viewers an idea of what they’ll be in for once the kit goes on sale. While it’s still a fairly involved modification, the new design is surprisingly approachable. As we’ve seen with previous console modifications, the use of flat flex technology means the installation shouldn’t pose much of a challenge for anyone with soldering experience.

The flat flex cable allows for an exceptionally clean install.

Some may be put off by the fact that the replacement rear panel is even thicker this time around, but hopefully the unprecedented runtime made possible by the monstrous 4,500 mAh LiPo battery pack hiding inside the retrofit unit will help ease any discomfort (physical or otherwise) you may have from carrying around the chunkier case. Even with power-hungry accouterments like an aftermarket IPS display and a flash cart, the new battery can keep your SP running for nearly 20 hours. If you still haven’t beaten Metroid: Zero Mission by then, it’s time to take a break and reflect on your life anyway.

According to [Tito], the logistical challenges and considerable upfront costs involved in getting the new rear panels injection molded in ABS is the major roadblock holding the release of the kit back right now. The current prototypes, which appear to have been 3D printed in resin, simply don’t match the look and feel of the GBA SP’s original case well enough to be a viable option. A crowd funding campaign should get them over that initial hump, and we’ll be keeping an eye out for more updates as things move along towards production.

The previous version of this mod was impressive enough as a one-off project, but we’re excited to see the team taking the next steps towards making this compelling evolution of the GBA more widely available. It’s a fantastic example of what’s possible for small teams, or even individuals, when you leverage all the tools in the modern hardware hacking arsenal.

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