Tell us about the injection molding process for Mini end-plates
I love the idea of using injection molding and other processes for some parts, where it makes production sense. Anything that allows you to keep your high quality, reduce waste, and shrink lead times is great. I know that some things about your process may need to be closely held, but as an aspiring "plastics nerd" I'd love to hear as much as you can tell us.
What we know so far:
1. You're recycling less-than-optimal printed parts and filament.
2. You're saving loads of printing time (about half) on the printed parts for the Mini.
3. You have two molding machines. Are they the same?
4. You're not moving away from printed parts and you're still publishing the files so we can print and/or modify these pieces ourselves.
So Questions:
1. These pieces are still PETG, but how are they different from the printed versions? Stronger or weaker? More or less shrinkage or warping? More glossy or more matte?
2. How much do you have to grind up the recycled material to get a good melt going for injection in the molds?
3. How much work did it take to CAD out the molds vs. the printed parts? What special factors did you have to work with (number of injection inlets, wall slope, release agents, etc.) Are the molds simple "sandwich molds" or are there additional mechanisms for some areas?
4. How hot do you have to get the material and how much pressure do you need to get it to flow into the molds properly?
5. Have you tried PLA? How does it mold compared to PETG?
6. What other factors have you seen influence quality when molding? Material color or age?
7. Did you find much difference between using recycled prints vs. filament vs. raw material (before being made into filament)? Is there much the prints would have been through the melting / cooling process one more time than filament or two more times than the raw material?
8. How much of your scrap black PETG are you using versus making? Do you ever run out and have to wait for more scrap or use raw material?
9. You said you have two injection molding machines, is that one for each plate? Or do the molds produce both plates on each cycle? Does the molding operation just keep up with the rest of the production for the Mini, or does it run faster so you can stock up on parts and/or not run as many hours on the machines? Have you tried making any other parts via injection molding?
10. How is maintenance of the injection molding machines and molds compared to the printers in the farm?
11. How often do you get a scrap part out of injection molding vs printing?
12. How much does injection molding these pieces improve overall production time of the Mini's?
13. Given a flat top surface on the molded part, could you 3d print on top of it and have it adhere reliably? Would you need to rough up the surface once out of the mold, or apply a texture to the mold?
14. Do you see a market for a hobbyist injection molding machine? Do you think Prusa would ever sell one? While getting molds machined would be a bit pricey, more of us are getting into CNC machining as hobbyist-level mills are increasing in quality and decreasing in price.
RE: Tell us about the injection molding process for Mini end-plates
14. Do you see a market for a hobbyist injection molding machine?
Yes i do,
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Chuck H
3D Printer Review Blog
RE: Tell us about the injection molding process for Mini end-plates
I don't have a need for this but it was fun watching the build
Having problems with bed adhesion every morning...
RE: Tell us about the injection molding process for Mini end-plates
You guys really think that a big company like Prusa with such order lead time will produce plastic parts with self-developed improvised injection molding machines??? Its not efficient and reliable, so waste of time, money.... everything. I bet they use some well known injection molding machines.
RE: Tell us about the injection molding process for Mini end-plates
@3dalhemija
You might be right, but they make their own printers.
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Chuck H
3D Printer Review Blog
RE: Tell us about the injection molding process for Mini end-plates
@3dalhemija
You might be right, but they make their own printers.
If they make their own printers, and some modified "MK printer-based" automated assembly lines, doesnt mean that they will make just about everything behind the scene (filament lines, laser cutters, CNC machines, injection molding machines etc....). They are not startup anymore, time is their/our money.
We forgot that Joseph Prusa is economist, he knows what efficiency is. They chosen injection molding to reuse waste and to skip printing bigger models (such as mini plate) that occupy several hours of farm printers. Plus, these parts will not be redesigned very often.
They actually farm inhouse parts mostly because of its production efficiency and long-term redesign sustainability, lastly because of its fancy "rEpRaP4LiFe" story that we think first off...
RE: Tell us about the injection molding process for Mini end-plates
I saw a picture of the machines being delivered on the back of a lorry prusa posted on their discord channel, but can't find it at the moment! No home build machines for sure!
RE: Tell us about the injection molding process for Mini end-plates
@3dalhemija
I think it depends on if they intend to market them. If they think it might be profitable, I am sure we will see it come to market.
I have a friend that used to buy CNC'd aluminum parts for patient lifts. He decided to start making them in house. He researched commercial machines and finally engineered a machine to make the part himself. He did that because he could make it cheaper than he could buy it and if he made it, he could fix it himself. Not everyone can do that.
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Chuck H
3D Printer Review Blog
RE: Tell us about the injection molding process for Mini end-plates
Found it! Two fanuc presses being delivered in late December.
RE: Tell us about the injection molding process for Mini end-plates
I'm working on a similar setup (small-scale) and seeing how you're blending 3D printing with injection molding has been really inspiring. I'll try to respond based on both experience and some experimentation we’ve done in a prototyping lab setting:
PETG Molded vs Printed – The injection-molded PETG parts we’ve made tend to be slightly stronger and more dimensionally stable due to better layer bonding (or lack of layers). Warping is reduced significantly, and surface finish is glossier unless you texture the mold. Some shrinkage happens but is much more predictable than FDM.
Grinding Recycled Material – We grind to pellet size using a filament shredder. It has to be fairly uniform (no long strips or chunks), or it causes feeding issues or inconsistent melt. Drying is critical with PETG—any moisture, and you’ll see bubbles or poor flow.
CAD and Mold Design – It takes a lot more CAD effort vs designing for print. You have to think about things like wall draft angles, ejector pin placement, cooling channels, and gating. We mostly use two-part molds, some are “sandwich” style, but a few have sliders for undercuts. Custom plastic fabrication sometimes complements this—we've CNC’d certain mold inserts to accommodate changes without remaking full molds.
Temp and Pressure – We run PETG around 240–260°C with pressures between 8,000–15,000 psi depending on geometry. Having precise control over the heating zone and mold temp helps a lot.
PLA vs PETG – PLA molds surprisingly well, but it’s more brittle and has a lower thermal resistance. It can be tricky to mold thin parts without cracking. PETG gives more durability.
Quality Factors – Definitely: material color (black tends to flow slightly better), moisture level, and especially residence time in the barrel affect outcomes. Older filament or reground prints sometimes discolor or degrade if not dried properly.
Recycled vs Raw – Raw pellets offer the best consistency, but filament scraps are a good second. Recycled prints are hit or miss—depends on how many thermal cycles they’ve already gone through. We sometimes mix 70% recycled with 30% virgin PETG to balance flow and strength.
Scrap Use – We use as much scrap as possible, but black PETG does run low sometimes since it's our most used color. In those cases, we supplement with raw pellets.
Two Machines – Ours are different sizes. One runs the left side plate, the other the right. We’ve experimented with multi-cavity molds, but cooling time becomes the bottleneck. The machines outpace printing, so we do stockpile parts during downtime.
Maintenance – Mold maintenance is more demanding than printers. We clean vents and polish cavities regularly to prevent buildup. Machines need less frequent, but more critical, upkeep.
Scrap Rate – Injection scrap is extremely low once dialed in—maybe 1 in 200 vs ~1 in 20 with printing due to warping or adhesion fails.
Production Speed – It’s a huge boost. What took ~90 mins to print per part now takes <3 mins per cycle in a mold. We’re making parts ~30–40% faster overall.
3D Printing on Molded Parts – Yes, with good bed leveling and a roughed-up surface. We’ve even molded textured bases to improve first-layer adhesion. It works surprisingly well.
Hobbyist Machines – Absolutely. We’ve built a benchtop unit and it's very usable. Mold cost is the main hurdle, but combining it with hobby CNC or laser cutting (like in custom plastic fabrication) makes low-volume production much more feasible. I'd love to see Prusa or another brand release a modular injection unit!
Would love to hear what others have tried—especially if anyone’s running flexible materials or doing multi-material molding.
RE: Tell us about the injection molding process for Mini end-plates
Small run injection moulding machines were available in 1986 when I was considering injection moulding custom lapel microphones,
Even small moulds were expensive in those days and there wasn't a JLCCNC option in those days...
I have seen small low volume machines are still available, both on Ali express and from local suppliers (Although the local suppliers may be badge engineering chinese devices and adding their profit on top... )
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility.Location Halifax UK