How to build your own injection molding machine (2023) | Hacker News Reader

How to build your own injection molding machine (2023)

machinedesign.com

87 pointsdanboarder35 comments

Though this is cool and I appreciate the ethos here the article doesn't really spell it out.

All the cost, difficulty, time and money in injection molding is in the molds. They are expensive.

When done well they can make 1000's of parts if not more.

It's a great project, an amazing POC. There is the potential for small scale (garage sized) manufacturing to exist, the equipment is the cost of a (nice) car...

1000 pieces is a soft tool Millions are expected out of hard tooling.

I think the small scale, as in the footprint, is the point. They’d be much better off buying a used IMM if they want production parts but those are huge compared to TFA’s design.

If they can make their own molds at a machine shop, this could hit the sweet spot for a product that’s too high volume for 3d printing but not enough to justify a professional mold. Set it up and run it once a week to make a few hundred parts, that type of schedule. Just practical enough for a hacker-run lifestyle business.

I wonder if it might be possible to make moulds out of other materials for hobby-scale things?

For example, a mould which is made of plaster/concrete with an inner layer of silicone?

That would be pretty easy/cheap to manufacture. You'd use a 3d plastic printer ($150), dip the print in casting silicone, then float the result in concrete, with the concrete surface being the parting line.

Then use a scalpel to cut the silicone along the parting line and add more concrete to make the other half of your mould.

The design the buster beagle uses is an aluminum box you drop your molds into after printing them. Though this idea is interesting, I think, for people who are injecting with variable size molds that a single casing would not suffice for.

A desktop CNC at that scale to make simple stuff like casing boxes is probably going to be more affordable and less hassle/mess than your suggested setup pretty quick though.

Desktop is definitely not going to be good enough to make aluminum molds themselves though. I think you need a 5 axis CNC for that. Surprisingly my makerspace actually has one of those and I considered learning how to use it but decided against it.

In practice however on these molding setups I’ve found you are already kind of constrained on your mold sizes a lot simply by virtue of your machine’s volume capacity. The one I have goes up to 3 cubic inches, but in practice you can’t use all of that capacity and you get weird/bad results for too small of capacity too so the actual ranges of shot volume I can produce in a mold are actually constrained to something like 1-2.5 cubic inches

1000's would for most molds be considered a failure and very much excessive wear. You'd normally look for orders of magnitude more than that.

It's only a Three-Dimensional inversion of an intricate model that requires very precise depths and must be reusable for hundreds of thousands of jobs. How hard can it be?

And where both the material and the mold shrink at different rates and it would be nice if the product released from the mold after the injection phase. At most a weekend's work ;)

There are many videos on YouTube using 3d printed resin moulds.

Total cost to do this is roughly (2021 USD when I went through this)

$1000-1500 USD to build out a buster beagle with COTS components $700 for an anycubic photon plus a an anycubic treatment chamber $300 for all the ancillary materials like resin (Siraya tech is a great option), mold spray, pellets (purchased off eBay), $30 toaster oven from Walmart to keep the molds warm, etc etc

Design your molds in fusion 360 and print them on the Anycubic

So if you are patient and have more time than money it is theoretically possible to have a full fledged injection molding machine with up to 3 cubic inches (50 mL) in your garage for under $2000 USD

It takes a lot of time and research to do this properly however. Designing the mold has lots of caveats and is very custom work. This process is not at all as simple as operating an FDM printer, there are a ton more variables and failure modes that go into injection molding so you have to be able to create an environment where you control all of them.

One thing that could probably save a lot of time and heartache for people on this journey is finding someone on fiverr to design the mold for you for a few hundred bucks rather than trying to teach yourself some hardcore industrial engineering concepts. But it’s doable, I read an injection molding book and was able to produce something that worked after leveling up my Fusion 360 skills.

I do want to underscore that yeah, as your comment implies, even though recently the money component has significantly improved with innovative designs like these that use COTS components the time and difficulty part is still there. Injection molding is not for the faint of heart, it’s definitely one of the more hardcore industrial processes out there. I have seen the endgame of this journey so I am happy to answer any other questions if people have them

How long did your molds last? PTFE and PTFE with glass? What kinds of plastic.

Molds last between 150-500 shots depending on all sorts of factors in my experience. Once you have the design dialed printing a copy of the mold is not terribly expensive, however, takes several hours and perhaps $5-10 of resin. Buster beagle sells an aluminum casing to surround the mold that greatly increases the life of it since the vast majority of the beating it takes is from pressure from the clamps.

Not sure if you are talking about the PTFE molding process or not but this is just straight single shot injection molding, though it is possible to design multi shot processes with this setup. It’s just more complicated.

I used polypropylene which imo everyone should start with first because it’s by far the easiest to work with and pretty easily sourced off of eBay. It’s suitable for a wide variety of components for indoor use. For outdoor use you would want something like polycarbonate. I think working with polycarbonate would not be as lucrative in a home machine and here’s why: temp and pressures for polycarbonate are often a bit harder to achieve and the temps you need for molding polycarbonate are often at the upper limits of what these resins used to make the resin molds will tolerate. I think it’s possible though, but requires careful selection of a particular polycarbonate with the correct thermoplastic properties (such as lower melt temp) to operate within the acceptable ranges of your setup.

Need more coffee before questions!

Were you using a PTFE release agent? Like this: https://www.antiseize.com/PTFE-SPRAY-HEAVY-COAT-Anti-Seize-L...

Polypropylene... Did this have (fiber)glass added?

No though I know people have literally just used stuff like PAM in the past. Mine was a purpose made mold release agent that I picked up off McMaster Carr. They sell a lot of different ones

The polypropylene I’ve used does not have fiberglass added. Though there are a LOT of options for thermoplastics, both ready made and custom mixed/compounded. You really learn to just go straight to the data sheet when thermoplastic shopping because that has all the relevant info you need

> All the cost, difficulty, time and money in injection molding is in the molds. They are expensive.

You can 3D print high-temp resin, place it in an aluminum carrier and shoot roughly 20-50 parts.

This kind of machine is a really good match for that.

This project Precious Plastic shares machine design, resources and a store to encourage localized recycling within communities. They are already globalised if your interested there may be a project near you https://www.preciousplastic.com/

Great guys but the design they offer is a lever operated machine which IMO does not give you the consistency you need for production runs. The problem is that your arm applies an inconsistent amount of pressure whereas a pneumatic machine like the one from OP does not. I looked at their design and the holipress when I looked at low cost benchtop molders and that was one reason I decided against them. I actually built a lever machine first and disassembled it when I wasn’t happy with the results

Can injection moulding be done into a hot mould which is later cooled down?

Clearly a cold mould is better for mass production speed, but if you had a hot mould then you could probably just use a 3d printers nozzle and low pressure to do the injection - or even just keep the whole mould in an oven and pour plastic pellets in.

That's more or less how it is done. Thermal cycling of the molds is one of the bigger factors in determining the operational life of a mold. Moldmaking is a very advanced art, the people that do this have a formidable array of software at their disposal to model how the mold and the plastic will behave as well as a massive amount of accumulated trade knowledge. I know several, one of which is outstanding and in very high demand because he can reduce the number of trials to a minimum. Materials science is nice compared to software because you can actually learn something and build on it for a whole career instead of the next five to 10 after which you have to re-learn everything.

I have my own injection molding machine in my garage, DIY all the way. Everything about molding is precise, and it has to be, it’s not nearly as forgiving as FDM printing in terms of failure modes. To achieve what you are describing I have two molds that I rotate in and out of a toaster oven, not kidding. Every thermoplastic pellet has a detailed data sheet on expected temps and the like and mold temp is simply one of those.

Just FYI this machine can only inject 44ml of plastic. It makes tiny parts. Great progress for DIYers though!

That's true but it's already quite impressive at that and usually when you have something working the path forward is incremental so I think over time you'll see larger and more capable units.

Buster beagle sells a variant that goes up to 50 mL but once you get beyond that I think the price point is going to significantly increase. You need more pressure and capacity that an off the shelf air compressor might be able to give, for instance. So unless the availability of COTS stuff changes I think there is somewhat of a ceiling of capacity you can get at this price point

Hm... this has me thinking though and I'm already wondering if I shouldn't try my hands at a prototype, the key I think is that if you don't have to go fast that that's enough of a requirements change that you may be able to take another path.

Yeah I would not really invest the time in this kind of setup unless you are sure you want to be doing production runs out of your garage/LI setup. One easy use case off the top of my head is if you’re trying to be allowed to put “Made in USA” on your product or you otherwise have some requirement that it be manufactured here vs simply assembled.

That being said given the low cost (money) it’s also a worthwhile thing to look into because it’s so low cost. Which might be what you’re implying here, could build out a machine and even if it no longer meets your requirements down the road it’s not really a big deal because of the low monetary investment. If you’re handy that’s probably acceptable. You’ll end up knowing enough about the machine that you could probably make adjustments to it to meet some possible changing requirements down the road as well.

Or just buy the real deal: https://www.ebay.com/itm/325965381740

I find it hard to believe it's only $62 shipping.

This article could be vastly improved by adding some sketches and diagrams.

They don't really talk about why. When would you want to switch to this over using 3D printing for prototyping?

If you just need a few parts (likely at home), waiting for the 3D printer seems a lot easier?

I think small[er] scale injection molding has a ton of potential for local/recycled/lower volume projects that 3d printing isn't necessarily suited for. Brothersmakes [1] sells recycled plastic combs and more using a similar process, products that really wouldn't work well with any modern 3d printer. I've seen similar projects for disc golf discs as well from TrashPanda. [2] The market for hyper-local small scale products is growing, and I think downscaling injection molding fits in well to this. I could order a custom steel mold (that I've designed) from a machine shop for a few hundred bucks, and with an injection machine and a supply of some plastics, conceivably make a few thousands parts on a relatively short time scale, with minimal manual labor.

[1] https://www.brothersmake.com [2] https://youtube.com/@TrashPandaDiscGolf?si=LWdw3gV9rtNQdlUD

Thank you for this! I just started exactly this! I bought a couple injection molding machines and started Golden Gate Molders. We injection mold parts right here in the SOMA neighborhood of San Francisco! Not only do we use traditional metal tools, we also provide 3d printed tooling options for lower volume prototype tools.

www.goldengatemolders.com

Very cool, just subscribed to your mailing list. As a mechanical design engineer, I'm a bit jealous! Good luck with your endeavor

If your part is small enough you can do small scale (several hundreds to low 1000s) of your units in house for a machine so cheap money wise to build that it’s better than outsourcing even without the QC concerns. Also even prototyping sometimes gets old on the 3D printer when you have a 5 hour per you need to make 10-20 of that you could do in an hour with the molding machine.

Though IMO faster prototyping is not a good reason for getting a molding machine, it’s just a nice bonus. There are plenty of shops in the USA you can send your STL file to and they will print a bunch of them for a reasonable price. The real reason that you want a molding machine is fast small scale production runs because oftentimes what you produce on a 3D printer is either not professional looking enough to sell (the lines look very hobbyist) or FDM cannot achieve your product requirements long term (outdoor plastic enclosures, for example, need waterproofing with FDM but not with molded parts)

Injected plastic can be much stronger than 3D printed stuff. It also has a much wider choice of material properties.

weird, the linked video from the article is their original design, but then the auto-play after it takes the viewer to the "v2" they repeatedly reference in the first video: https://www.youtube.com/watch?v=M28Pbrm7wzE

Can this do clear acrylic parts?

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