I tried Injection Molding using a 3D Printer!

I wanted to find out if I can use a 3D printer as an injection molding machine. I printed molds using resin and then injected the molten plastic using a hotend. But how well did it work, what are the limitations and what could this method be useful for? Let's find out more!

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*Chapters*
00:00 Introduction
01:11 Making a Mold
04:25 Sponsor
05:48 1st Attempt: PLA
07:31 High-Speed PLA
08:30 Why all of this?
09:42 Mold Pre-Heating
11:53 Switching Printers
15:25 Injection Molding with TPU
16:08 Building the Über-Extruder
17:39 Summary

#3Dprinting #DIY #injectionmolding
DISCLAIMER: Part of this video was sponsored by KiwiCo.
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[CNCKitchen]

QUESTION: Where could this method be useful?

[tominthebox]

Hello from Montreal. So what I noticed is two things. 1- you need an air hole exit to allow the hot filament to make its way instead of possibly building pressure in the mold. 2- Why not lower the gantry to push down on the mold while sitting in the hot plate? Thanks for the video.

[gydo]

Keep in mind actual injection and ISBM machines charge the barrel before injection. That is to say, they melt enough plastic to fill the mold in advance, then inject it all at once.

[LionPlush]

1. Air vent hole needed at the other side of hole for injection
2. You can inject plastic not at one end of detail, but at the middle - so plastic need just half path for fill all mold. Of couse you need air vent holes at the all end of detail.

[jaw]

I hope you make a part 2. The comments are full of great wisdom and I can't wait to see how this develops

[martindieux]

I'm an injection molding designer. Here are some tips from my point of view:
1. The air vents like everyone said. But this may not be the only cause of failure.
Since you have a parting line all around the part. The air can escape through there.
2. The mold needs clamping force so it doesn't flash, BUT the injector machine (in this case the nozzle) MUST HAVE injection pressure, and it's not a small one. We are talking about more than 2 MPa.
This is because you need to inject quickly (around 1 to 3 seconds) and the solidifing plastic will give resistance to the filling.
3. In this case in particular, the mold should be heated around 80°C to 100°C temperature so the plastic stays liquid until it gets till the end.

If you need some help, please contact me.

[optroncordian]

Couple of ideas, which come from my experience working for a molding company:
Keep the mold hot at around 10 to 20 degrees (celsius) below the melting point of the material. This will give you plenty of time to inject.
Make tiny channels at the corners and dead ends of the form to let air escape. This will reduce the needed pressure and it can serve as
an indication when the material has filled the mold.
You can make the mold outline smaller, reducing the needed resin.
Inject from center outwards, not from one end. This will spread the material more uniformly. Best is to make the input port on the larger side of the mold - that way it will be as short and as close as possible, thus reducing the heat loss before filling the form.
We are using thin motor oil as releasing agent. Sometimes petroleum jelly. Depends. These are cheaper.

[kleikPL]

10:50 injection molding operator here. You may need to optimize the mold first, like the placement of the sprue. currently, you have it at the very top of the part meaning it is quickly cooling down causing undershoots. move it more or less in the middle of the parts volume and you will be fine. I'm gonna be doing my tests soon enough as well so I'm gonna check it

[tahl]

I used to teach injection moulding theory at university and we would print a few moulds and run them with a small injection moulder, like this, as a demonstration. As most people have noted, position of the gate and airs are key. The only thing I would add is that with an injection moulding tool, you actually leave a tiny margin where between the two halves of the mould so that air can escape but plastic cannot. That's why you almost always see a tiny bit of a step along the seam where flashing eventually occurs, if the pressure becomes too great or the mould deteriorates. Hope this helps.

[fashionskiller]

injection mold design engineer here.
-First, heating up the mold before injection is crucial, as you noticed yourself. It will delay solidification of the part.
-A vent at the end of the part might be a good idea, depends how tight your splitting surfaces are.
-You should feed the part into the thickest part, like head of the screw in your last try. You always want the melt to flow from thick to thin since it tends to solidify in the thin part first.
-Pressure is not the key actually, speed is more important since melt solidifies with time. Viscosity also tends to decrease with increased speed. Normal injection of a part takes max few seconds.
-350bar of pressure is not the lower end in industry. Most of the parts I made molds for were injected with lower pressures. Machines go up to 2000 bar but it's rarely necessary. If part needs that kind of pressures then it's (mostly, not always ;) ) a badly designed part.

[nccyr]

Wow, what a ton of responses and suggestions; I believe everyone would appreciate a follow-up video on the same subject.
Thanks Stefan.

[tomashubelbauer]

I really hope you revisit this with an air escape hole, the hotend assembly down and pressing onto the mold sitting on the printer bed (potentially heating it) so you don't need to hold it and also a bigger mold. I wonder how far this technique could be pushed!

[Marco_Onyxheart]

I think you need a clamp with heating elements inside to keep the mold warm. That, and you really need airducts. It will flow way better that way.

[titom]

You need a hole on the top on the mold to get trapped air out

[Arek_R.]

I had this idea where you use few generic hotends and extruders to melt filament and inject it into larger heated cylinder, and when it's ready, a piston pushes the plastic to inject it.
Because even if you get hold of a hobby grade desktop moulder, you will struggle to buy the pellet material, and if you find it, it will probably be more expensive than filament or you will be required to buy entire euro palet at once.

[HangsFun]

Stefan, I believe you forgot a small vent hole towards the end of the mold (to let air escape) that and achieving higher temp in the mold

[LT]

A local company has done simular as you. They take all the waste plastic from milk jugs, packaging etc, and then injection mold it into 3d PRINTED(FDM) molds of combs, hair clips, cloths line clips, etc and sell them at local farmers markets. Its really cool

[JonS]

You should consider venting your mold so you aren't building up pressure by compressing air.

p.s. You don't need a draft for very short walls, as there is sufficient shrinkage to allow release.

[thenextlayer]

Suggestions: slather some two part silicone or 500C gasket sealant around the edge of the entrance hole to create a squishy seal around it. That should increase your pressure.

Additionally, the exit hole others have mentioned will help a lot.

And yeah, pushing the preheat to the limit will help. Home injection molding machines typically require that you bake the mold in the oven before injection to keep the plastic from cooling part way through.

[glics]

The first application to this that immediately comes to my mind is reusing filament waste (failed prints, calibration prints, purge waste/ams poop, etc). Would love to see some experiments in how to melt and inject those into a mold, considering your past videos on reusing waste for filament extrusion