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) :
Just a follow up on the simple wooden mold. I wanted to change the outer profile of the knob I had made earlier to make it more comfortable. So I took the wooden mold (3 layers of flooring) and added 8 pins (about 5mm) to form the indents. I borrowed this from a youtube guy that carefully machined it out of aluminum. Thought I would try it with wood….worked well. I think for quick prototyping, wood and or plaster can make some cheap, usable molds without the CNC or other machining.
So you spend all this time tinkering with that plastic melting gadget in the garage, your spouse looks in every once in a while and just shakes their head..What do you do to salvage some legitimacy to your activities……
Fix something of theirs! (some free gray-haired wisdom here)
This was an otherwise nice cast iron plant stand that was a bit rusty and had a busted wheel. Well, a little spray paint and that clever threaded knob made in the wooden mold in the Feb 10 post, and I achieved temporary hero status. Since we don’t take our plants for walks, the wheel function was less important.
The nice thing about using recycled plastics to make replacement/repair parts is there is no concern about plastic costs so you can make them robust. I’m guessing this solid HDPE part will hold up well, If not, I can make a bigger one.
I made some process improvements to get more interesting patterns and to control the shape better.
For the better patterns, I reduced the size of the flakes to about 1-2 sq. cm and mixed them well (see container in picture). The black and white were equal by weight.
To control the shape, I reduced the length of the mold by adding a 2 cm block on each end to make sure my shot volume would fill the mold.
I am happy with the results. The bar maintained thickness and width. The length recessed but did so after establishing a square end. The pattern mix came out much clearer and the surface is smooth and does not have the texture you get with room temperature metal molds. You can see a few wrinkles in the aluminum tape due to axial motion. The mold is from really old scrap plywood and the tape does not stick to it as well. I’ll probably switch to some flooring remnants I have.
Unfortunately this will make me start shopping for a longer rack for the arbor press to get even more stroke volume.
@pporg , not sure what you mean. When I chuck up a bar of HDPE, I can take the same cut This Old Tony takes in stainless.
I tried 210 C for the garden stake. It came out well but I could only push out about 65 cm before the nozzle end of the mold leaked under high pressure. To go further I would need to change to more positive connections. Not going to pursue that at this point, but it was a good capability test.
I need to get back to making more of the large black clips for the top of the pergola (from a week ago). There are more things that need to be attached that those will be used for.
I also tried the same approach with my square tube mold. The first image shows the configuration after injection. The tube is 15 cm long.
The second image shows the outside of the section view. There is a skin layer that is predominantly one color. The third image shows the interior of the part. Again some creativity in forming the flow theories is appropriate.
I do need to figure out how to reduce the interior voids for these later parts. Perhaps increase the temperature from 200 to something more.
In case I’m not able to generate longer HDPE shafts, I took a look at heat welding two pieces together. Nothing new here, the technique is described elsewhere on the forum. I used a simple heatgun approach. The first image shows the result after I sanded down the ridge at the joint. The second image shows a section cut through the part. The weld line is hard to detect and the joint appears strong.
The heatgun approach is a little variable. To do a number of these, it may be better to set up a temperature controlled block of aluminum and then just press each side of the joint against it until it is soft and ready to join.
It is a good technique to have available and I’ll probably go that way to assemble shafts in the .9 – 1.5 m length
I made a longitudinal cut through one of the shorter fails. To me it looks like there is a wall layer that is established and the resistance to flow is the viscosity within the HDPE (as opposed to friction with the wall), but who knows. It may be that raising the temperature from 200C may reduce the viscosity. I’m not sure that heating the tube would be a strong affect. The black/white HDPE was put into the chamber randomly. Maybe next time I’ll try a specific layering and see what that does in the tube.
This is fertile ground for making up flow theories.
“made the worms dizzy” 🙂
True, a good compost heap is better not turned, so it can properly heat up, but I’m sure they’ll find out at Project Kamp, once they start composting their Humanure!
And always aim for succes.
When V4 has gotten rid of all the plastic over 3 years (okay @pporg, probably 5), we have to start working on feeding the world!
(thanks for the links, they look delicious)
I think for a desktop/home unit the 1 ton arbor press (such as https://www.harborfreight.com/1-ton-arbor-press-3552.html )is a very convenient option. It has a decent stroke and if someone has the capability you can always fabricate a longer rack. It is very quick to actuate and has good leverage. It also provides you with feel for when the mold is full which a hydraulic cylinder may not.
Of course it all depends on the preferred configuration and capacity.
For simple molds, I made some clamp plates that can hold different shapes. Since the top and bottom plates (aluminum) handle the heavier load and temperature, the form plate in the middle can be wood or aluminum.
For the narrower forms, I just place them directly under the nozzle with a top washer or plate and then hold them in a C-clamp during cooldown.
I wanted to try making a bar using nearly the full capacity of my injection volume. I used my wood and aluminum tape mold approach. The results are shown in the images below. The resulting bar (HDPE) is about 10 x 38 x 320 mm and weigh 114g after the sprue is removed.
A few things I found interesting:
The black material was in the barrel first and then was filled with the white, and yet the ends are white, and relatively symmetrically so. Even the cross section of the sprue is black. I cut my source material into medium and large strips , not shred, so I’m not sure where the material ends up during compaction, but the result is consistent.
The shrinkage was predominantly axial and the cross section is fairly consistent until the very end. I may have run out of material but the ends are square so they probably reached the end at one point. Also the gaps on each end are very similar. I was not sure how well injecting from the middle would work but it turned out OK.
I made two cuts, each one 25mm from the center. The cross sections are shown below. Yep, it looks like a Mounds candy bar. The initial (black) plastic coats the walls and the rest squeezes through the center. Very surprised that both pieces look almost identical even though they are from different sides. Still can’t explain why the sprue is the black plastic. On future parts, I will try to really mix colors well and use smaller pieces to see if you can get that cool multi-color result without milling the surface.
Overall I’m happy with the result. My desktop machine is limited in height/stroke but I think the arbor press design that PP.org has https://precious-plastic.org/home/library/machines/arbor-injection-press-2/ could be sized up to produce parts at least twice that size, which would become interesting lumber.
I replaced the original handle that was way oversized (78 cm) for plastic to something more compact. I also angled it so it does not swing past my forehead like the original. Of course, I adopted the PP.org standard of contrasting colors for machines.
I wanted a plastic pre-processor to deal with the thicker source material (bleach bottles, plant pots, etc.). I went with using the metal shear approach suggested in this thread https://davehakkens.nl/community/forums/topic/precious-plastic-version-4-%f0%9f%98%ae/page/5/ . I got one of the 30 cm metal shears. First off, the thing is a beast. In my defense, it looks smaller on the computer monitor and the cost savings for going smaller wasn’t that great.
Well, it works great. I squish the bottle using user mass and gravity and then a few chops later it is sized to fit into the injection machine.
For those with a shredder, it is an easy and safe way to get down to single ply material for the thicker stuff.
I will be making a shorter, forward angled handle for use with plastic.
Thank you for the great link. Making a temperature resistant mold in the DIY environment/budget is a challenge. I’m planning some more trials with the plaster technique. That may be a way to bridge to 3D prints.
I think my favorite high temperature 3d print application is the guys 3d printing molds out of sand for casting engine blocks.
I have been thinking of ways to get rid of the need of cnc milling machines in the mold making process. Mold making is always the difficult of part of IM and expensive.
Look at this article: it may be helpful. https://www.3dhubs.com/knowledge-base/3d-printing-low-run-injection-molds#why
If you use conformal cooling channels connected to a water source like a tap you could get some interesting results. You should be able to cool the mold down enough to do 100 of units. If you could get a desktop extrusion printer to print molds it would be a powerful tool to increasing product development and outputs.
let me know what you think!
A few days ago I mentioned frivolous decorations. Well every patio needs to be protected. Though we like the European gargoyles as solution, these work as well.
So I needed a secure way of mounting each Tiki lamp. The first image shows the “kit”. An internal plug (HDPE – milk jugs) clamps the ceramic lamp to the base. The base (HDPE- plant pots) also adds a bottom clip that clamps it onto the pergola beam. The image also shows the simple molds that provide the geometries. The base clip itself was made in the wooden mold as previously. The mold is holding up well with repeated use
The second image shows it mounted in position. With a solar/LED cap, it is on duty day and night.
While this is successful, it does take quite a bit of time to go through the steps to get to finished parts. I think anyone planning a sustainable work space should consider the throughput that they can achieve.
Let them out of their boxes, they will each dig a really good rabbithole for any spare time (and some cash) you may have.
I’ve been thinking about having different sized piston hot ends for different types of molds. Making the large clips, I need as much volume as possible. Filling a large cavity through a large diameter nozzle requires less pressure and I can use a larger diameter piston. For small items, with smaller diameter sprue, it needs more pressure, less volume, and potentially a smaller piston. @andyn mentioned that he uses what I think was a bushing in his system to get to a smaller diameter. I’m not sure of the details of his implementation. I think in your design with a little modification, you could have the hot end and a length of the piston be a drop in replacement with the electricals connectorized appropriately. This would give the smaller user (that does not have quite the user-mass advantage I have) a chance to make some smaller items. Actually, in your desktop design, if the middle beam was replaced with a pair of back to back C-beams with a gap in between you could have both hot ends in place and just slide the one you want to use into position. That may also be a way to increase the low throughput of the injection machine.
I’m going to make a mount for my earlier smaller hot end so I can use either in my machine.
Good advise to drill the screw in and out a couple of times to melt the plastic.
Maybe a V4 version will have a bigger volume, but I’ll keep it in mind.
Thanks for all the info!
Yes, even though I’m not quite in windmill country, when it blows, it can be pretty strong, I made the clips long enough that I can put plates across the bottom to fully capture the beam. The clips are chunky with each leg about 12.5 x 38mm. I screw directly into the HDPE with sheet metal screws. I drill an undersized hole and then drive the screw in and out a few times with a cordless. The screw heats up and seems to form a thread in the HDPE.
If you go with the injector, just be aware of the size limitations on the parts. Mine has a cylinder swept volume of about 200cc, I can get maybe 130-140 g of HDPE into a part. The larger bottom clip is about the limit.
Funny how a lot of people here think alike.
I myself am looking to do a solar install in the back of my garden, as this gets a full day of southern sun as opposed to my roof which is south-east and has a tree in front of it…
Would be a bit bigger though, to help power my workshop.
In the Netherlands windpower is also an alternative, so I don’t think just a friction fit would be enough, but I guess the clips are big enough to also allow for a bolt through them.
“The wood and aluminum tape molds are holding up well” and “just making parts instead of an end item is a good use for the plastic lumber” are music to my ears, and have put an injector back on my shopping list…
I made more of the large clips in two sizes. The large size (130-140 g) is at the limit of what i can get out of my injector volume. The wood and aluminum tape molds are holding up well. The parts are very repeatable and provide a nice friction fit onto the bars they are designed for. The plan was to use them for a convenient solar panel mount and they work great. Normally I would have made those out of some wooden or aluminum assembly. Once the wooden molds were made, these were easy to make and I’ll be making more,.
The point of posting them as an example, is that sometimes just making parts instead of an end item is a good use for the plastic lumber.
I would like to claim that the solar panel will help save the planet but in truth it will just power some patio lights and frivolous decorations that i don’t feel like running line power to.
Yes, for that simple mold the next step would be to redesign the aluminum block that forms the 90 degree turn at the entrance to have a more positive seal.
One thing I’ve done both with the injector as well with some press molds is make a collection of stock material that I use on short notice to make some simple items. Yes you can buy Delrin, Nylon, or HDPE bar or rod from a plastic supplier, but it takes time, shipping costs, etc. The other option is to make it out of aluminum, but then I have to go to the metal supplier, dive into their cut-off bin, etc.
For example the test parts I made a few posts ago already got used to repair a glass/LED garden decoration where the original steel support base rusted out and a new solar panel mount was needed as well. I could have made it out of aluminum but why? And the bright yellow color matched.
I think in combination with some simple tooling, it just becomes another tool in the shop.
So in conclussion: maximum lenght seems to be 64-65cm, regardless of heat, with this setup.
Would have been nice if it had worked out-of-the-box (so to speak) at any lenghts, but longer stakes need to be welded.
Thanks so much for doing this experiment.
I’m still looking whether or not it would be interesting for my Urban Homestead project* to switch from upcycling to recycling (with machines), but so far upcycling and recycling without machines (for small objects) keeps winning.
But hey, you would not need a V4. if V3. was already perfect!
*in this case: being able to locally produce the materials needed to become self-sufficient(ish), if only through a community (or travelling) “garbage in – buildig materials out” workshop.
I think I’ll try slightly higher temperature (210-220) with the full tube to see if I can produce the .9 m, After that, this was mostly an exercise in finding the limit of pushing HDPE in narrow channels.
My setup isn’t really usable for long vertical molds.
The outer skin issue is something to work on. One of the attractive things about using recycled plastic is getting the random bright color patterns. For shaped objects, it is difficult to expose the inner color mix.
@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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