Portable desktop injection machine
it was suppose to be an easy thing I thought but I spent then 3 full days on it at the end, lots of hours on the lathe, 1-2 hours welding and a little bit on the mill. I wanted the best result possible, tight tolerances, smooth plunge and an easy to extrude plastic with a flexible nozzle. (btw. I can’t recommend building this without lathe or mill, it really wants it accurate to get a smooth plunge).
In the next iteration I will try to have it spring loaded which is pretty difficult as I noticed.
here you go, full metal desktop injection (some part are hardened to maintain this nice blob sound in the barrel) :
Thank you, I’ve seen some of the epoxy mold approaches. Right now I’m trying to see how far one can push very low cost materials.
I’m still trying to understand what happens during the injection process and how it affects the resulting part geometry, especially when trying to fill larger volumes. While HDPE shrinks after cooldown compared to the mold dimensions. It looks a little different when it first comes out of the injection orifice. The attached image is the result of a typical ejection of residual HDPE after a mold is filled, to empty the volume. The cross section shows the orifice size with the blue ink mark. Not sure how the HDPE transitions from the high pressure in the injection volume to the final ambient pressure and when the final shape gets locked in.
nice nice, focusing on raw stock plastic opens recycled plastic to traditional handcraft, any wood tools will have it easy. I guess going for hydraulic and a heat chamber may make things even more easy, on the volume side. I still didn’t find the time to test all your precious input but things got a little relaxed on our end, so I hope I can join your work with attention soon 🙂
here’s btw. the output of 2 months messing around with the machines, mostly based on v3, just re-configured in a way that it fits on a bench top and more importantly, one the back seat of a car as we figured this stuff serves better public audience on wheels instead of a fixed workshop.. the machine on the right can be switched to ‘injection’, updates soon about this, basically enclosure and your fume extractor is missing, more or less 1m x 1m x 35 cm deep, 60 Kg but still easy to ship, 4Kw
Not sure, the shrinkage takes place on cooldown when the heater is off (I don’t ramp down the temperature control). The tube is fairly thick wall aluminum which is why I tried just one heater. The holes for the mount block go through, so there is a chance for the part to preferentially stick to one or two places. I also maintain compression during the solidification, not sure how that plays out. It is HDPE so the shrinkage is pretty high.
All good reasons to do more experimentation
The uneven shrinkage might be due to having only one cartridge heater on the side. Using 2 or three spaced evenly should give more consistent results. Adding a layer of insulation over the top of everything will also help.
So I turned the round stock to get rid of a flat spot and make it round. Ended up with a 36 mm diameter 150 mm long HDPE rod. Smooth, no pits or visible voids. Density is .85 g/cc.
Overall a useful piece of stock material.
I wanted to see if the arbor press actuated desktop injection machine could be used to compress a heated mold to make some stock material that is larger than the small injection volume. I took an aluminum tube about 41 mm ID and 184 mm long. I made a block that could be used to clamp a cartridge heater (300w) to the side. Both the tube and the block have a groove to accommodate the round heater (some aluminum tape is also used as filler). A second small block mounts the control thermocouple. The arbor press has a rod attached with piston sized to the tube. The bottom of the tube has a plug with a thread to allow attachment to the wooden base for stability. You can see all the parts in the attached pictures.
The mold heated up quickly. I filled it with large flakes from milk jugs (HDPE). To mostly fill the tube, it took a number of top-off and compaction steps. Once full I let it sit under compression and temperature for about 15 min and then let it slowly air cool. The result is a pretty solid, usable piece of round stock (though shrinkage away from the wall is not quite even and it is not quite round) . I have not cut it apart but I don’t see any voids near the surface.
The point of the exercise was to see how well locally heated compression molds would work without an oven. Thermally, the aluminum mold heated up quickly and took a long time to air cool so it is reasonably efficient (compared to heating up an entire oven). I could have used a band heater for this cylinder but I wanted to test the clamp on block approach which would be usable with flat molds. The part extraction process took a little trial and error, but given how cheap the cartridge heaters are, you could easily have a handful of molds ready to go. The arbor press was useful for all the intermediate fill/compaction steps, otherwise clamps would work as well.
Overall, while there is some process tweaking to be done, I’m happy with the results.
nice one @s2019, you’re right, anything which isn’t proven healthy is not safe (er,…this sucks at many levels). i just start researching this, indeed, there isn’t much. that’s pretty much the best i’ve found to start with : https://envirocare.org/plastic-fume-monitoring-exposure/
I started work on a fume hood for my benchtop unit. In the spirit of recycling, I used some scrap rain gutter to form the hood and a computer fan for the exhaust. Mine is set up in the garage so I’ll add some of the flexible clothes dryer vent ducting to get the fumes closer to the door. May need an extra fan to pull that distance. A match test showed that the fumes near the hot end inlet are pulled through the fan.
Unfortunately there isn’t a lot of information here on the fume topic. You can see from the photo that at 190-200 C some scorching of the HDPE takes place. You can also smell a light hot plastic odor so some extraction and exhaust should be done. This is especially true for the smaller units that are likely to be used indoors.
It would be interesting to know how the V4 team handles fumes in February.
I took another step in working with the desktop injection unit. I tried some parts that had internal features. The first one is a sort of cup bushing. The wall thickness is about 2.5 mm both radially and at the end. It shrank about .25 mm in diameter but even without a taper it was easy to tap off of the central mandrel.
The second has some internal features. A more significant step in diameter and a flat section to key onto a shaft. It took a couple of tries with small adjustments in the mandrel diameter to get the right press fit onto the shaft but otherwise all the features were well reproduced.
This was HDPE, I will try other materials as well. It is nice to be able to make usable mechanical parts besides seashells.
To better illustrate the outer skin issue i mentioned, The cylinder below was almost entirely the matte gray tone surface you can see on the bottom section and the bottom itself. The top section I turned down .1 to .2 mm and immediately some of the internal patterns are visible. Still trying to figure out what causes the skin like surface layer and how to get rid of it for complex shapes.
The second image shows the cylinder with the whole surface turned down. It shows the much more interesting coloring available under the thin outer surface.
If you take a .5mm cut off of the surface, much of the light grey color disappears and the swirls appear to be one piece with no visible voids at their boundaries. I wonder if there is a way (for more comlpex shapes) to avoid the muted glaze at the outer surface for injected multi-color parts, and get at the more vibrant colors inside.
Oh yeah, if you need to make HDPE caterpillars a low speed endmill cut is your answer.
OK, maybe I have too much time on my hands. I was trying to figure out how the cavity is filled in an injection process. I realize, mostly it is luck but there may be trends or ways to orient the inlet to affect the results.
This is an axial injection 4.7mm nozzle into a 22x22x67mm, 1.5 mm thick unheated steel form. In this case a swirl appeared to have happened in filling the form. What I was trying to understand is, if you look closely each of the layers has its own what appears to be stress rings from shrinking away from the form. The shrinkage compared to the corners ranged from .1 to .3 mm.
In the spirit of that video I remade my threaded bushing part. With a little bit more fun color mix (pill bottle, detergent, flower pot and a dash of milk jug). It is interesting that the part blank tends to have a color skin and as soon as you turn through that, all kinds of stuff pops out. In the section view, the black dot on the bottom is the sprue inlet. How the flow goes from there is probably in the video.
Now to raid the recycle bin for more colors
IMO the Gingery machine is inferior somewhat to the Precious Plastic v3. Having used both. Although that angled frame does have something going for it.
My current injection molder is the PP blueprint with a substitute of 1.5 inchx6mm angle bar stock for the 30x30mm tubing. Here in the Philippines we get a mix of metric and imperial stuff.
the thick wall tubing is not as common source as the angle bar that is used in making roof trusses.
In continuing to tinker with the desktop injector capability, I went back to seeing if a usable, internally threaded part can be injection molded. I used some 3/8″-16 rod, made some bushings to center it in the form tool, the top bushing had an off center injection hole. Using some milk bottle HDPE, first try came out well (I just cleaned up the ends to be flat). It shrinks onto the rod but is removable, Since the thread shrinks, I run a tap through it by hand to get it back to the right size but after that, it is a great threaded bushing. I actually have a use for that one.
I also injected into a square tube to make some square stock. The picture shows a 1.9×1.9×10 cm part, 32.1 gm. That is close to the limit that my 44 cc injection machine can produce. Again, for me, a usable part.
Actually, I think @cgoflyn approach of using the rack and gear is a significant difference from the Make magazine link and the PP design as well. This approach separates the leverage and the stroke length. The injection volume can be increased without increasing the injection effort or needing an increasingly long lever arm.
You do realize you are repeating the work of the Gingery injection mold machine from a few years ago?
I think the power or leverage should be the ratio of your wheel to the pitch diameter of your gear. For the arbor press I linked it is 20:1 I think my smaller one is similar. You may need a larger diameter hand wheel. The lever on my smaller one is effectively about a 23-25 cm lever length. My piston area is about 5.4 cm^2 and at times I’m pulling on it pretty good to generate pressure. I do have a fairly small diameter nozzle though. Maybe you can weld on a 1/2 inch drive interface so you can use a breaker bar https://www.harborfreight.com/12-in-drive-25-in-professional-breaker-bar-62729.html if needed. Actually it would be interesting to attach one of these https://www.harborfreight.com/12-in-drive-digital-torque-adapter-63917.html to see what torque is actually used. I may be able to cross drill a large socket to attach one to my press.
I noticed my press has two screws and a gib plate in front to control the rack and a couple of screws on the side as well. Do you have something similar?
On the assembled molds I made, having easy access to push the sprue out of the injection hole in the cap plate is useful. I usually just beltsand off what is protruding and then hand push the rest out.
The plaster mold worked well. It replicated the detail and survived a couple of injections (HDPE) without any apparent damage. The small round mark on the black shell is probably due to warm up. It was the first injection of the day and the nozzle may have still been a little cool. The metal tube frame protected the mold well.
Yes, I had a similar thought. As a follow up to the machinable wax suggestion, I wanted to see how the plaster mold would work. I wanted to make sure it was well reinforced so yesterday I cast it into a tube cut off as you describe. The plaster retained good detail. I will give it few more hours to dry and then try it. If it works well, it may make that cheap CNC engraver viable since I think it won’t have trouble carving (though slowly) the part in the machinable wax and then cast the mold in well contained plaster.
OK, I did a rev 2.0 on the wood mold approach for making a threaded bolt knob. I used some left over engineered wood floor cut-offs. Most of the cross section is homogeneous instead of grain. I drilled the 8 holes to to provide the texture and then hole-sawed out the main body. Sanded smooth and then used aluminum tape to provide the smooth surface. I used HDPE scraps (milk containers) so the color is not exciting but the surface is very smooth and usable. I did lightly sand the top to remove some light swirls. The bolt is 1/4″-20 (~6mm) for reference.
I actually need a 12mm version to replace a broken one on my miter saw. That one will get some fun colors.
In conclusion, the aluminum tape provides a smooth surface and the part releases very easily
I’m in the experiment phase. I was interested in whether it was easy to use simple available forms to mold stock shapes that could then be used for other projects (bushings, pistons, stand-offs, etc.). Right now I started with HDPE. Some parts do end up with voids, so right now I’m looking at temperatures, mold heating, and form plugs to see what works. I tried using a bolt to mold an internal thread (3/8″-16). That worked pretty well. Because of HDPE shrinkage I ran a tap through it afterwards but otherwise it worked. You can also see a small void in the bottom right corner, that I’m trying to get rid of.
Looks awesome, a bench injection machine is the next thing on my projects list 🙂
This is what the buttons look like after my wife got done with them. The funky tie dyed backgrounds are provided by various HDPE sources. The only parts that were painted were the flowers and the letters (and the black button got glitter bombed). I think they provide a fun organic look that fits well with the gardening event.
These will be given away to volunteers that contribute but I could see a potential for some workspace catering to providing interesting, low volume items for groups and events, especially if the groups are environmentally themed. I think there is a path to making these effectively, starting with a 3D printed master. The mold material development still needs work, but I think there is a low cost solution out there.
Actually, a few years back I made a small propane aluminum furnace and created my small pile of casting muffins. I plan to dust it off soon to make at least mold blanks.
For this 3D => ??? approach I was trying to start on the cheap/easy end and work my way up. For some things, just being able to have a single use path to make a PLA print into a HDPE or PP part is useful to me.
I wanted to revisit the plaster mold at a larger scale. Back in February, I posted some promising results using a plaster mold to replicate a seashell. Sticking with the ocean theme, I found a cast steel starfish that looked like it would make a good mold. I used plaster in a plywood frame for the mold and plywood/aluminum tape for the lid. The results came out pretty good. Some small amounts of plaster did stick so I’m researching ways to seal the plaster that will take the hot plastic. The second image shows the back. Other than a few wrinkles (the plywood is old and the aluminum tape does not stick as well) it shows the smooth gloss that the aluminum tape surface provides. You can see I had to inject near the end of one of the arms because the mold frame was too big for my machine, but the mold filled well. This size (125 g of HDPE) is about the limit of my machine.
I don’t plan to repopulate the oceans with my starfish, this will be one of a kind, but the results make the plaster approach promising enough to keep exploring it.
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