Lessons Learned: Plastic Injection Molding For Products

October 14, 2023 by 19 Comments

Injection molding is one of the technologies that makes the world go round. But what does it actually look like to go through the whole process to get a part made? [Achim Haug] wrote up a blog post that does a fantastic job of explaining what to expect when getting plastic enclosures injection molded in China.

These air quality monitors required a two-part enclosure.

Injection molding a part requires making a custom mold, which is then used by an injection molding machine in a shop to crank out parts. These are two separate jobs, but in China the typical business model is for a supplier to quote a price for both the mold as well as the part production. [Achim] describes not only what navigating that whole process was like, but also goes into detail on what important lessons were learned and shares important tips.

One of the biggest takeaways is to design the part with injection molding in mind right from the start. That means things like avoiding undercuts and changes in part thickness, as well as thinking about where the inevitable mold line will end up.

[Achim] found that hiring a been-there-done-that mold expert as a consultant to review things was a huge help, and well worth the money. As with any serious engineering undertaking, apparently small features or changes can have an outsized impact on costs, and an expert can recognize and navigate those.

In the end, [Achim] says that getting their air quality monitor enclosures injection molded was a great experience and they are very happy with the results, so long as one is willing to put the work in up front. Once the mold has been made, downstream changes can be very costly to make.

[Achim]’s beginning-to-end overview is bound to be useful to anyone looking to actually navigate the process, and we have a few other resources to point you to if you’re curious to learn more. There are basic design concerns to keep in mind when designing parts to make moving to injection molding easier. Some injection molding techniques have even proven useful for 3D printing, such as using crush ribs to accommodate inserted hardware like bearings. Finally, shadow lines can help give an enclosure a consistent look, while helping to conceal mold lines.

Making An Injection Mold For Yourself

August 28, 2023 by 29 Comments

Injection molding is the obvious onward step from 3D printing when the making of a few plastic parts becomes their series manufacture. The problem with injection molding is though, that making a mold can be prohibitively expensive. Has the advent of affordable CNC machining changed that? [Teaching Tech] takes a look, and machines a mold for part of a bicycle bracket.

With a diversion into home-made silicone seals for the injection molding machine, he proceeds to machine the mold itself from a block of aluminium. It’s a basic introduction to mold construction for those of us who’ve never ventured in this direction before, and it provides some interesting lessons. As we’d expect he does a rough machining pass before returning with a ball-end tool to smooth off those curves, but there’s a lesson in measuring rather than believing the paperwork. The tool he used was a bit smaller then the spec, so his path left some rough edges that had to be returned to. Otherwise the use of a removable pair of bolts to form holes in the finished part is we guess obvious after watching the video, but it’s something we learned as injection molding newbies.

This video follows on from a previous one we also covered, in which we’re introduced to the machine itself.

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Repairing A Home Injection Molding Machine

August 5, 2023 by 10 Comments

When [Michael] over at the Teaching Tech YouTube channel bought a hobby injection molding machine a long time ago, one of the plans he had with it was to use it for grinding up waste bits of PLA filament for injection molding. Since the machine was bought from a US shop and [Michael] is based in Australia it required some modifications to adapt it to the local 220+ VAC mains, followed by adding a PID temperature controller and a small compressor to provide the compressed air rather than from a large shop compressor.

Although [Michael] had discussed using the machine for PLA with the seller to confirm that this would work, a user error meant that the now defective unit had been sitting idly for many years, until recently.

Since the machine had been gathering dust and rust in the garage, fixing the machine up took a complete teardown to remove corrosion and resolve other issues. After this the original fault was identified, which turned out to be a shorted wire near the heater which had been turned up to a too high temperature, leading to the release of magic smoke and banishment of the machine to the Pit of Despair, AKA the shadowy depths of one’s garage.

In this first installment, [Michael] cleaned up the machine and restored it to a working state. In the next part injection molding will be attempted again, which should give some idea of the feasibility of turning scraps of PLA and failed 3D prints into smooth injection molded parts, assuming you have the CNC machine or patience to carve out the requisite molds, of course.

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

October 21, 2022 by 25 Comments

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?

June 27, 2022 by 11 Comments

[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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Used Facemasks Turned Into Rapid Antigen Tests With Injection Molding

March 24, 2022 by 15 Comments

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

March 6, 2022 by 10 Comments

[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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