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Extrusion Moulds (v4)
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Hello!
We’ve been cranking hard at the Precious Plastic HQ with the development of v4..The focus for the beginning of the year is on exploring and developing techniques for the Extrusion machine. This topic will be focused on Moulds for the Extrusion, with all the successes, failures and set backs along the way.
Stay tuned for further topics as the development continues..
-Machine Development
-Beam Production
-Extrusion Moulds (You are here)
-Tubes and Profiles
Test: Simple corner beam mould
Objective: Test mould concept / Find a replacement for corner joints
Process:
The mould was made by cutting a 50x50mm square tube at 45°, welding tabs at the join and adding a nozzle to the tube (image 3). From there it was a matter of gathering some plastic and pressing go. For most tests I ran the machine at 200 C @ 170rpm.
Findings:
-In this case, cold moulds performed far better than warm moulds. It seems as if a cold mould forces the plastic to cool as it enters the mould and then continues to “fountain”, thus allowing it to turn the corner as hot plastic is always at the front. When the mould is warm, the plastic doesn’t cool straight away and ends up “sliding” along the mould and being too rigid to turn the corner.
-In image 2 you can see how much the forms actually shrink during cooling. What’s interesting is that the angle didn’t change at all.
-Creating corners in this manner as opposed to a traditional joint creates a far stronger result (tests will come). One can then focus on connecting the straight edges as opposed to the corners.
This is a wide topic, so feel free to shoot your ideas and suggestions!
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Great work.
A couple of questions. What does the “XX mins make” represent?
Also, are the section cuts in the background from this experiment? Are you using multi color material? Have you done a longitudinal section cut?
Very interesting, thanks again.
Hey @s2019, thanks.
XX mins make is just stating how long the machine was running to make the part. XX minutes from time of start to time of stopping the machine.
Those sections in the background are from a beam from last months tests where I changed colours at regular intervals. I’m busy working on something to illustrate the process. Planning on doing a longitudinal cut too 🙂
@timslab: so you’re using 3Kw at the end ? And are using the wood auger drill, and at which speed ? Thanks, we’ve some users asking to build extrusion machines for beams …
@timslab, thanks! Same torque sounds weird too me. I’ve got good experience with 4 Kw, unstoppable and I can recommend this. It’s enough to power the shredder at the same time. However, 170 RPM is amazing fast, wasn’t even aware it needs that much speed.
By ‘custom PP screw’ you’re referring to a standard industrial chromoly based screw ? Whilst at, how long is the barrel then 🙂
g
@timslab In some of your other tests you used a plug to apply some resistance to the plastic front. I wonder if applying this technique to the second leg of the angle to maintain pressure in the mold will help reduce internal voids. Even maintaining pressure in the mold during the initial cooling may help as well.
It will be interesting to see some of the section cuts once you make them.
@cgoflyn – yea it is quite fast.. I don’t think it needs to be that fast and it might not even be the best thing for the plastic. There are quite a few results where the plastic hasn’t spent enough time in the barrel to be fully melted. It does help with filling big moulds quickly though.
@s2019 – that’s a good idea. I’ll definitely give it a try when we’re back on that mould. I’ll cut up a long beam this week and post the results in the Beam topic ^^
I wonder if adding a preheat function to the hopper would allow the higher extrusion rates but maintain full melt. Raising the plastic to something below the melt temperature prior to entering the extruder may help.
why do you even try to do such a weird thing ? It is not better to cut straigth beam and then make a corner ?
I think it’s an interesting experiment. Sure, a straight beam is more versatile afterwards but for specific purposes, which are bit hard to think of right now because we’re not used to producing things this way, this could be a useful manufacturing technique. It’s a different way of thinking. I believe that instead of adjusting the final product to fit the production technique (in this case straight beams and joining at an angle afterwards) this might open up more possibilities of adjusting your production technique to make the final product.
Good points @s2019, @cgoflyn – will definitely give it a try. If not a warm hopper then just slightly warmer flakes.
hehe @malyboa, if we don’t try we’ll never know! I quite like this technique. I think it really opens up a lot of possibilities.. Angle joints take a bit of time making strong and pretty.. this way of doing things could create far stronger parts and with less time. In the coming months we might push this technique into different applications and designs. For now I’m just exploring 🙂
Test: Flat Wooden Guitar mould
Objective: Find simple, alternate ways of producing large objects with extrusion
Process: While @cymek was still around, he had the idea of using the extruder to make a guitar body. We used sheets of 18mm plywood and CNC cut one profile into 3 of the 5 sheets. This allowed us to change the thickness relatively easily. The aim of this was to keep it simple – so we simply screwed on a mould fitting and ran the machine as fast as we could. The mould was fastened together with screws and we used a lot of clamps to reinforce the flat areas during extrusion. I wouldn’t say the results are successful, but we did learn something.
Findings:
-Clamps aren’t enough to hold back the pressure. Some clamps bent.
-The plastic did release quite easily from the wood.
-We were not able to fill the mould completely and it was hard to monitor how much more there was to fill. However, the plastic was able to reach the very tight corners.
We’ve only brushed the surface and there is still quite a bit more we could try with this concept. If you have any suggestions, shoot!
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that’s a good reference for the more impossible, nice try though 🙂
if you really want the guitar so much :
– i’d try a heated metal mold. heat elements, or better said : heat wire can heat the flat side, up and down, pretty inexpensive on ebay
– to make the mold: a quick and dirty ring roller (easy done on the lathe, needs knurling tool) should get your bars in shape. a ring roller is also neat to make wheels btw.
– the molds upper and lower plate (heated) could ideally serve as universal system for other shapes you can set with bent bars, basically like a sandwich maker. that would be finally a cheap and universal mold system.
– you can drill a hole tapped grid pattern to mount the clamps to hold the bent bars (outside welds).
– the inside can be filled with thicker aluminum folia. @s2019 did this 🙂
keep going, you’re getting there 🙂
btw. I really urge you guys to build your own plasma table (otherwise 3k for a ready to use table but unclear how long those last). We started building one and the more i think about, things get more way more easy and cheap : better shredder, quick molds, whatever new machine, it’s just a few sheets and clicks away :). We’ve spent in total 4000 Euro, for a 2m x 1.20 meter table, Nema 23, SBR-20, height controller and the unbeatable HyperTherm – 45 XP, cuts 25 mm mild steel with ease.
Test: Larger product moulds for Extrustion.
Objective: Use simple materials and techniques to create larger product/moulds using the extrusion machine.
Material: PP
Process: A (found) wooden shape with a draft angle was used as a reference to build around. Wood and 3mm sheet was used to create both male and female halves (image 1). The mould is almost completely dis-assemblable, top and bottom can be removed and interchanged for different materials.. (more experiments to follow). For now only the metal mould has been tested with Silicon oil as release agent. The mould is not airtight and the current machine has a pressure sensor so we’re able to monitor the pressure during the run. We stop the test when plastic can be seen at the furthest edges or pressure reaches 30bar.
Conclusions:
-The extruder, used as an ‘injector’ is able to fill larger more complex shapes.
-Cold moulds (15-40 C) create an organic surface finish but parts are not completely fused. Without some pressure sensor it may be hard to know when to stop the machine.
-Hot mould (180 C) allows plastic to fill entire cavity and surface is smooth. It is also easier to monitor the state of the injection as the plastic begins to leak out the small gaps.
-The 3mm steel began to bend at 30bar. This could be fixed with reinforcment of large flat surfaces or a thicker material.
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