Injection Molder in Action!

I returned from The Netherlands on Sunday to find Scott hard at work on his next generation injection molding machine. This version operates in the drill press to to give better control and consistency to the injection operation, and has a much larger plastic volume.

Scott used the CNC mill (on its maiden aluminum eating operation) to generate two mold halves of a gear reduction (or multiplier), being cut in half here:

Thanks to Isthmus Engineering for their “scrap” aluminum!  You can see the 2 bosses surrounding the gears, which fit together perfectly.  The gears sit in the center, and the sprue for the injection at the left side of the large gear.

The first step is to load the heated chamber with plastic bits from laundry detergent containers (this would be called UPcycling, not REcycling, and certainly not DOWNcycling like most of your “recycled” goods end up), then to preheat the mold.  You can see the results of the first injection attempt at the near edge of the press table, everything worked perfectly but we didn’t have enough plastic loaded up:

Next is to lean hard on the press handle and hope everything stays together:

Just after this picture the single C-clamp squeezed sideways and let plastic squish out from between the mold halves, hence the flash:

Pinion gear half:

What’s great here is you can see perfectly formed edges on the teeth/gears with great surface finish.  The black/gray spots are from us being too lazy to clean out the machining chips from the mold before injecting (in a hurry).  Looking at the spur gear half you can see if we trim the flashing off the part we’ll actually have a great gear!  What else is fun is putting anything metal (or plastic) through the center of the mold, you can put a keyway in, threads, a flat, etc per application.

Using our earlier partial gear, we can see a very promising mesh:

Project is on hold until after the holiday, but look for more updates soon!

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2 comments on “Injection Molder in Action!
  1. This is awesome! I especially like the “UPcycling” part of it, which makes me think about how I can use normally discarded materials in some of my projects. I think this is an aspect of the space to talk about in promotional/PR material…

  2. Scott says:

    Unfortunately, as Chris mentioned I ran short of time and was not even able to take the ~10 minutes it would have required to double clamp the mold and make a couple workable gears. I am out of town now until Tuesday, but the great thing was that even the preliminary success we had with this gear proves out several things:

    1) It is feasible for us to machine aluminum molds and inject them with plastic using S67 equipment. I invested about 15 hours in total to design the mold, machine a prototype out of handiboard, machine the mold out of aluminum, cut the mold into pieces, finish machining it and make the first two gears. I learned a lot along the way, so this cycle could be a lot shorter effort-wise once we are fluent.

    2) There is an open source “CAD” + “CAM” (quotes used there to denote that most people would not call the tools I used for this CAD or CAM) tool chain that is workable enough for us to make parts like this. I did the design work in Inkscape and used the gcodetools plugin to generate the gcode to (ultimately, with a conversion step and some hand-editing) run the mill.

    3) The new injection molder should be able to mold parts that are reasonably large. We used less than half the capacity of the injection molder volume-wise to make the gear.

    The upcycling for this project applies to more than just the plastic. We used an old rusty 2″ diameter steel window weight for the main injection barrel, eliminating the need to buy new steel stock.

    I’m definitely looking forward to further refining our injection molding capabilities, amongst other things. The gears should help us in determining shrink rates, etc. with our (relatively) low-pressure injection process.

    Scott

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