Tell us about the injection molding process for Mini end-plates  

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.