Low Pressure Moulding First Test: PiTrex Case Blanks ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Date: 2020-02-12 BACKGROUND: * Low-Pressure Moulding machine is Optimel 100, original Australian distributor is Tarrapath (www.lowpressuremoulding.com.au). Purchased in unknown condition but seemingly complete. * Intended moulding plastic is certain ranges of Macromelt/Technomelt branded plastic manufactured by the large German company Henkel. It is the same type of plastic as hot glue, but formulated differently. Only a small sub-set of the Macomelt/Technomelt plastic range is suitable for use (at least compared to just using ordinary hot-glue, which I'll do initial testing with). Characteristics of the different suitable types are described at the Tarapath website. * Cost and availablility of the plastic in small quantities is unknown. Helkel seem to package Technomelt in 12GK boxes, which is good. There's always a risk though that one will be required to purchase a pallet load of 12KG boxes from the Australian distributor. I'm crossing my fingers that it doesn't go this way, but to be honest it often does with this sort of thing. * There are sellers of similar plastics on Alibaba (though they take a bit of finding). They're likely to ask how many tons you want though, and expect to be directed to a shipping container to put it in. Probably not an options unless I'm making thousands. * The Henkel docs say that air pressure for moulding should be 100 - 500psi (they recommend keeping things at the lower end). Temperature should generally be around 200 - 240degC. I set 155degC for the hot glue in the book binding machine. *"Blanks" are where you test a mould without a PCB inside. Whoo! I'm learning yet another industry's lingo. STARTING CONDITION: * Chamber had some of the proper moulding plastic left in it. * Air pressure regulator has a safety valve in it that opens if the pressure reaches over 80psi (if the manual pressure adjustment is set to above this). The shed air compressor gets ubove this while running, but dips down to 40psi after it stops before cutting in again. Maybe this is adjustable? Clearly it's not designed to go up to Helkel's recommended 100psi - or maybe the safety valve is adjustable and someone was messing with it? - If I could stop the leak at the air hose connector, the compressor should stay pumped up for much longer. * Both air pressure and temperature meters tend to get stuck / go funny. A thump in the right place sometimes helps. The temperature regulation seems to work correctly regardless of how wrongly the temperature meter is reading. Probably the same case with the air pressure regulator. INITIAL TESTS * Almost 1/3rd full of left-over original plastic in the chamber, melted fine, but press the trigger and it only drips out under gravity (as it does slightly when the there's no air pressure at all). Appears to be a bloked nossle. * After extensive efforts picking out plastic, the "blockage" turned out to be a brass slug intentially installed in the aluminium part that the nossle screws onto. Appears it may be either press-fitted, or screwed in for removal using a custom tool. Very confusing. * Testing again without the nossle reveals that this brass part pops out the end when pressure is applied, allowing the plastic through, then retracts when the pressure is released. To prevent the plastic running out under gravity when not in use I suppose. When no nossle installed and plastic is low, I discovered a way to make great fake cobwebs! * This brass part needs space to pop out, and it turns out that when the nossle is screwed on all the way there isn't room for it to do so (bit of a design flaw?). With the nossle on loose, plastic now flows out through it when you pull the trigger. How far the nossle is screwed on may determine the rate of flow (in combination with air pressure), but too loose and plastic comes out through the thread as well. * I guess it's missing a spacer behind the nossle. A stack of 1/2" washers would probably do. BLANK MOULDING TEST 1 * Mixed in some hot-glue with the remainder of the original plastic (wasted most of it by this point). Temperature set to a little over 200degC - the hot glue seems alright at this temp. albeit more runny. The proper plastic doesn't melt at 155degC though, so there is a significant gap between their specs. * Nossle too loose on first attempt, stopped because too much plastic was coming up through the thread. Only moulded the bottom half (opposite side from the nossle). Came out pretty well though, the moulding apparantly works mainly under gravity, the pressaure is probably just for pushing all of the plastic in before it starts solidifying in the mould. * The bits that moulded first are mainly of the left-over proper plastic, while other bits are mainly hot-glue. The proper plastic seems harder, though the hot-glue isn't actually all that bad. A fingernail pushed against it _does_ leave a mark in either. * Picks up all of the fine details in the mould well, though unfortunately this means that the layers of the original 3D print are visible. Probably need to try Acetone smoothing on the print used to cast the production mould. Any text or a logo on the surface should come out well though (can't be sure of the repeatability of this yet though). BLANK MOULDING TEST 2 * Mostly hot-glue in the chamber by now, but still tinted a little black by the original plastic. Probably easy to add a dye to the hot-glue if I did go with that for production. * Came out very well. Fully moulded and all details reproduced fine except the surround for the edge connector. This was made solid because there wasn't a board inside for the insert to clamp onto at the right position. I'm not sure if the plastic will form a thin structure like that, or whether it would be strong enough (there are harder sorts of the proper plastic). * A single G-clamp works fine for keeping the mould halves together. Leakage between the mating surfaces isn't a problem even though there were still small gaps, not big enough for the plastic to flow through it seems. Mould alignment seems easy enough, though I'm sure I'd stuff it up eventually if I was doing a lot of them. * I think the hot-glue cools/sets a lot slower than the original plastic (much lower melting point after all). The mould heats up a lot too, as I was warned that it would in the Henkel docs. The docs recommend a water-cooled mould. I dunked the mould in a bucket of water. That works but the inside of the mould gets wet and you probably don't want steam inside the mould especially on the next run. Building water cooling pipes into the mould might be the way to go, but it would be a fiddle. I'm not sure what the best solution is here. * The solid bit that should just be the edge connector surround took ages to cool and got a bubble in it. Shouldn't be a problem with the right plastic and edge-connector insert, but worth noting for future designs. * Quite difficult to remove, but I suspect the proper plastic would be easier (not meant to be glue after all). Having a board inside to give it strength would help, though possibly at risk of flexing it (Henkel docs suggest ejector pins for large moulds, but I doubt I'll go that far). I think the draught is alright. * Seems like it wouldn't flex much with a board inside to give it strength. Should work fine mechanically. * Overall looking good, now just need to try it with a board inside.