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Portable desktop injection machine
- This topic has 144 replies, 13 voices, and was last updated 2 years ago by
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Hey guys,
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) :
@s2019 Only one way to find out: If at first you don’t succeed, try and try again!
A hotter melt could also work, because you might not get the ‘balloon’ effect of a cool outer layer. I am worried however that raising the temperature might ‘burn’ the plastic, making the melt toxic…
Would it be possible to maybe mould vertically to encourage layering of the colours? I agree there is enough gray in the world as it is!
The typing I had in mind was not so much for repair but to identify a large piece of unmarked plastic, something like a trash bin for example. In that case the “does known plastic stick to it” criteria may be worthwhile.
I’ve tried the wooden plug approach in the past. It helped reducing voids in high aspect ratio tubes when I had less injector volume and the nozzle diameter was smaller. For the chilled tube approach, I think there is a difference between the V4 extruder based beam forming and my injector based trial. I think the injector is high pressure and relatively high speed. I’m not sure the cooling of the outer layers would be sufficient enough to separate the plastic from the wall and grow the beam from the middle/rear as opposed to from a fountain at the front. I think the extruder is much slower and lower pressure.
Even in the two different sizes I tried, the 25 mm square tube is easier to inject that the 14.5 mm tube. I think the force pushing the plastic forward goes up with the cross sectional area but the shear stress is applied at a perimeter and increases only linearly with diameter. For this specific sizing, I think the most likely way of achieving the 90 cm shaft is to raise the temperature to drop the viscosity.
One thing that is a disappointment is the exterior of the parts has that bland almost single color skin as opposed to what is happening inside. The attached image was some leftover melt that I injected into a cylindrical mold. It came out with the same dull gray skin on the outside. I then turned it a bit to square it up and the interior popped out. Part of the original motivation was to have some interesting garden stakes (score points with the gardener) as compared to the dull green ones from the store. So maybe make them square and run them through a planer afterwards to remove the outer skin.
I did try the welding approach of pressing both parts against an aluminum block at 200 C. That worked pretty well, need to experiment more with that approach.
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I tried the short forming tube followed by expansion into open air.The setup is shown in the first image. The aluminum tape was also sprayed with some mold release. Once it leaves the tube the HDPE expanded quickly and does not proceed down the v-trough very far. After the large blob formed the tube slipped in the clamps and the rest came out near the entry block.
I had tried to enhance the color selection and loaded the injector sequentially with black, yellow, and white HDPE in about 20 gm increments, repeating. During compaction there was probably some mixing but that was unavoidable. The second image shows the resulting part. Interestingly, since it was constrained at both ends during cooldown, you can see where it necked down in the middle.
The third image is the section view and provides the requested colorful flow diagram. Now would be a good time to sip some creativity enhancing liquid and let the flow theories form.
Note, I don’t see anything in the ghosting that would justify a pilgrimage.
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Yes, the ghosting presents an opportunity, but not knowing which image will show up first makes stocking the gift shop difficult.
The plastic welding is an intriguing topic. It can expand the usefulness of a limited capacity injection machine. It may also allow the use of simpler (non CNC) molds.
I also want to check the plastic typing capability of the welders (see link at the bottom of this page http://onearmy.world/community/forums/topic/v4-sheets-joinery/ )
Interesting experiment indeed.
Not just technically, but also some interestig ‘ghosting’. I wonder how many cuts it will take for Jesus to show up 🙂
It almost looks as if the ‘new melt’ is pushing through the centre like a needle, which might also explain the friction. The melt is mainly pushing outwards, not inwards.
I look forward to more colourful longitudinal cuts, including one in which the tube is cooled instead of heated…
I’m preparing some welding experiments myself.
There are actual dedicated plastic-welding-hotguns out there, incl. temperature control etc. (they are used in car/motor repair) and one should arrive next week (from China, I know).
Not much use for these shafts, but I also just happen to have a “a temperature controlled block of aluminum” aka a foil sealer that might just do the trick.
Will dig it up and try some experiments this weekend!
Interesting ideas.
At 4-5m the HDPE may be too soft at this diameter. Since I’m using my injector, I think I can only get about 90-100 cm/shot.
The short forming tube is an interesting idea. I can run the external section in some angle. I did notice a while back how much the HDPE expands after it leaves the nozzle unconstrained. Perhaps with a short tube that would be reduced.
Trying to figure out what is happening in the tube. Not sure if the HDPE is sliding along the wall or if a layer sticks to the wall and the HDPE shears in a layer. Some of the sections that @timslab showed from the larger beam extrusion looked like the material shears internally. Not sure what affect heating, polishing, releasing the tube would have on that.
This leads to the joint options, both mechanical and airgun welding. Also want to make a separate cruciform tip for loose soil.
And I thought I was just going to make a simple garden stake.
If we could get them to 4-5m they would also be ideal for using as frames for polytunnels. The short ones are cheap indeed, but the longer ones are a bit… difficult to transport, so being able to make them on the spot would be really helpful.
Would it work if you only used the tube to ‘shape’ (say 40-50cm (or maybe even less)) and would just leave the extra lenght to cool in the open (or in some kind of halftube guide rail)?
Or maybe cool the tube, as the plastic would shrink, reducing the friction?
Kind of like making filament, only somewhat thicker.
You have the setup, might be worth a test or two, if only to get tot 90cm…
Very curious about the outcome…
I tried a different experiment with the desktop injector…How far can I inject into a tube?
Specifically, I wanted to see if I could make a simple garden stake out of HDPE…Yes I know they are a couple of dollars at the store but those are plain green and are plastic over steel. I could score points at home by providing ones with a more interesting color mix (think laundry bottles).
The image shows the concept. A thin walled steel tube (14.5mm) is held in position and one end has a simple 90 degree entrance port, split for removal.
The goal was to get about 90 cm length the longest I got (not shown) was 64 cm (91gm). It really takes a lot of force to inject. I use the full leverage and a good portion of my … errr .. person weight. Each of the trials shown ended with a leak in the port to tube joint due to motion. I used simple wood tooling and minimized the port block to keep thermal mass down. I will have to enlarge that and rigidize the mount.
On the plus side, the shafts come out very nice. Nice smooth surface and a natural point on the tip. I may do a coupling that would allow using two to get longer lengths.
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Thanks @pporg I wanted to post some of the results here so people thinking of what to make broaden the options to making parts that make other things possible. In this case these pergolas are sold through a nationwide chain (Lowes) and there isn’t a good way to mount things without drilling holes and starting a rust spot.
I made a second clip in the mold and it is hard to tell the difference (first image). The wood mold held up well. I use wood screws to hold it together and if I’m careful it re-indexes pretty well on assembly (if only Legos could take the temperature). The second image shows the final install supporting the weather vane. One unplanned feature is that the bottom of the clip is just a bit tighter so it holds very nicely with no fasteners.
I’ll be making more of these…more odd stuff needs to go on top….Though we’ll stop before we reach Gaudi levels
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@pporg , Thanks.
This evolving design was never meant to be a specific design worth documenting with drawings but rather an example of a DIY process that takes the necessary off-the-shelf components and links them together using materials and techniques available to the hobbyist. As you’ve noted in the past, this forum is somewhat awkward for documenting a design. If it would be useful, I can put together a PDF with a bill of materials, some detail pictures, and rationale for why I chose that option. I would not expect anyone to duplicate my exact machine.
This design is in the DIY spirit and depends on the builder liking to tinker and hack, and also recognizes that this is hobby labor which does not cost anything. I think for anyone where these don’t apply, your desktop design that you have in the Bazar is a much better and ultimately cheaper way to go.
in case you have not seen it, here it is again. The guerrilla guide to mold making
http://lcamtuf.coredump.cx/gcnc/
Steel epoxy sprayed with silicone lube or silicone mold release spray works wonders. You can mix it with steel wool or chopped strand fiberglass to make it even stronger. I think a commercial trade epoxy is called kitty hair that has the fiber in it. Saw a youtube video of someone using it to make custom stereo speakers.
Went back to trying to see how useful wood molds could be. I have several small solar panels that run pumps for decorative fountains. The ebay pumps and panels work well but don’t have an easy mounting point. One way to grab them is with a clamping block on the small black block on the back and then drill a mounting hole in the clamping block. The first image shows the arrangement.
I need a handful of these. One option is to make wood blocks but then this is precious plastic not precious lumber. It is not worth making a proper aluminum mold so why not try a wood mold. The second image shows the mold and the resulting part before the flashing is trimmed off. Since for this part only the channel dimensions matter, I used scrap wood without machining the corners tight. Aluminum tape provides a releasable surface and wood screws hold it together. The results came out well for the application (third image). I undersized the channel because I wasn’t sure how much the HDPE would shrink so a light cut made for a light press fit on the solar panel block.
For something more precise, machine the wood to be true and fill any gaps, Should provide a well shaped part. Not intended for production, but for a handful of parts, it is a viable low cost approach. Next few will try some black PP
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I made some upgrades to increase the capacity of my desktop unit. I took the aluminum tube that I used for the compression experiment and made that my injection cylinder. Since this is a significant increase in area, I upgraded the arbor press to the next size up (1 ton). This had two advantages. The first is the obvious increase in strength, but it also has a longer stroke (150 mm). For the arbor press designs, ram stroke is a free way of increasing volume without increasing the effort needed to actuate. Of course, I could have just bought a long rack for the existing unit (like @pporg uses in his design), But I didn’t want the overall height to keep increasing and the 1 ton press was off the shelf and very low cost. The assembly is shown in the first image. Overall, the total parts cost is still around 100 USD.
Since I knew I was going to be applying a lot more force, I changed the support path to react against the arbor press instead of going through the wood frame. I just used 6mm threaded rod. The specs say that two of them should be able to handle the 1 ton load so, since I had them, I used them. The black steel tube allows me to adjust the height of the piston rod up so that I have room to load the cylinder (second image) during the fill and compact steps in the process.
The overall stroke volume is up near 200 cc, about 4x of my previous version. For me this is more usable. I definitely takes more effort to actuate the bigger piston. I have a breaker bar I’m going to sacrifice to get more leverage. I also increased the orifice size to almost 8mm.
The third image shows some of the test results, forming basic stock shapes out of HDPE. As you can see the molds are just basic wood and metal, bolted or clamped assemblies created out of the scrap bin. For me they generate usable stock material that can then be machined for other uses. The two long cylindrical parts were an experiment in constraining the part during cooldown. For both, the aluminum tube next to them was the mold. The ends were blocked with wood endcaps, clamped closed, and injected through the hole. The first try (the part next to the tube) came out well but came out bent (though it still fits in the tube). For the second (left most) part, I took the clamp off of the endcaps right after injection and let it cool down without axial constraint. The second part did come out straighter but is somewhat lumpy and the cross section is much less round. Material also bulged out of the ends. Interestingly, the square bar was constrained during cooling but stayed straight with a nice uniform cross section.
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An update to the fume hood. Last month I added the sheetmetal and fan to my desktop injection machine. Today I added the rest of the fume routing. I needed some sheetmetal to transition from the square fan to the round duct. Sheetmetal (first image) comes in many flavors, this one happens to be cocoa wafers and some other food container that fits inside the tubing. The tubing (second image) is actually RV (caravan) sewage hose. For obvious reasons I used a new one (surprisingly cheap, 6m length for less than $8). At the exit is another CPU fan to help pull the fumes out of my garage door (image 3). This fan is larger so an unused bathroom accessory got adapted to form the transition cone. I did some match smoke tests and the system seemed to pull them out nicely.
The point is, if you are working with hot plastics indoors, with a little creativity, adding a fume extraction system can be very low cost. For some machines it may take more of an enclosure and stronger fans, but is still cheap compared to the alternative. Since we have no data on the fume hazards, consider it insurance and be safe.
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Any chance of moving the posts starting on 07/03/19 someplace else so this thread is more linkable?
amazing stuff again @s2019! , indeed plastic bushings would find some use in our shop. if you don’t mind i use and reference your pictures in our blog 🙂
I am currently maxed out with work, so I will occasionally pass by. We started working recently on a smaller automatic injection, release date is in May, for max. 1000e. I have all the parts, drawings, etc… I just have no idea yet to get this work with recycled plastic chips coming from the v3 shredder (extrusion->pellets isn’t an option).
see you in a while
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.
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That looks great, love that wheel.
I think if you plug the acme dimensions into the calculator I linked, the torque required will be able to be driven with a cordless drill/driver. That way you can have a push button or toggle lever operated system.
I find it is interesting to blend the recycled colors. I think because I tend to use chunks or strips rather than fine shred I get some swirl. The surface tends to be muted but a light cut with an endmill makes it pop
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Just a follow up to the micro-lumber theme. I machined the raw stock into a more finished form. The HDPE cuts very nicely.
The threaded bushing was shaped into final form. In the process I did find a hidden cavity. It was interesting that it occurred away from the thread. For my use it is a cosmetic, not a structural flaw but I will remake it, if for no other reason than to use some more fun colors.
The square stock came out well, You can’t even see the endmill marks. The slight cavity is probably there because I used the full stroke of my machine and the pressure wasn’t sufficient at end of stroke to avoid a shrink cavity. I used some low quality thin architectural steel because that’s what I had in the junk pile in that size. You can see how the pressure deformed it. I’ll have to get an assortment of thicker wall tubing.
It was interesting, the density of the finished part is .932 g/cc, probably a reasonable number for HDPE. It would be interesting to see what other people are getting in their injected or pressed parts.
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Should work.
Found this leadscrew torque calculator https://www.amesweb.info/screws/LeadScrewCalculationsAcmeThreads.aspx . You could drive it with a cordless drill/driver
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.
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I made similar to that. Looked good but the shot size was way too small to do the kind of things I wanted to do. It also too a long time between shots because it didn’t have much plastic in it/thermal mass etc
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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.
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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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Thank you for the kind offer but I’m in small scale tinkering mode. I take perverse pleasure in hacking my way through with my very novice fabrication skills.
I do have a concept forming in my head for a Swiss Army Knife version of your injection machine. I’ll sketch (in my past career, real CAD designers would discourage me from abusing their software, usually by just shaking their heads) something up and get it to you.
hey Stan; we do another small scale – commercial desktop machine (arbor based), in hope we can provide enough molds, universal shapes (wood & aluminum, and / or plaster, epoxy) in a way that one (teens, kids) can build something useful out of it, lego like system to build a small machine,… So no worry, we make a full article, tutorial out of what you post here. that’s the best stuff i’ve seen so far and it should definitely go into the PP portfolio, our product designers are amazed 🙂
@s2019 Re: plastic typing: As long as you use pieces of the original plastic to melt, not much typing is needed, but you indeed still don’t know the right temperature. Isn’t it possible to setup a ‘heating’ needle, with some weight on top, slowly getting hotter and hotter, but switching of once it melts through/into the material.
The temperature reached before ‘switching off’ should give a pretty good idea of the kind of plastic, or at least it’s melting point.
Re: go with the flow:
Looks like this way you create ‘solid’ balloons.
Outer layer becomes solid, but the inner layer still pushes outward in all directions.
I believe the extraction of ‘beams’ with the V4 version went better with a block of wood in the mould, to add some resistance against the ‘needle effect’ .
I still think ‘cooling’ the tube, making sure the plastic is solid (or at least has a thicker outer layer) before leaving the tube (so no balloon-effect) might help.
I keep seeing a ‘heat’ problem in the flow, because the forming tube test look very much like a lit match, which makes sense if you concider every (colour) layer must have had a different temperature when formed.
This might also explain why the square test looks like a car wreck. It’s a ‘hot needle’ that’s folded in on itself, as it had nowhere else to go. The ‘voids’ are a result of this folding.
Cooled down black is reheated by the hotter yellow and white on the ‘inside’ of the needle, but as the outside remains ‘cool’ it does not mix/weld into a solid with the other black, causing voids…
Makes any sense?
Filament becomes round when it is pulled and equally cooled on all sides. The puling might not be needed, but cooling the tube (in water?) might just make the difference (as e.g. the ‘black’ won’t be reheated enough by the ‘needle’), if only to pull off your originally intended 90cm 🙂
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