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[casting] Aluminum melt and PLA-resin cores

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  • [casting] Aluminum melt and PLA-resin cores

    Disclaimer: I know very little about casting, watched it done, did one pour with a friend... so on so on. So here goes:

    Typically my casting-expert friend makes a pattern, uses that to make the impression in the sand then removes it prior to pouring. It's a bit more complex than that as some of you can probably tell me. :P

    The question came up "what would happen if we left the core in the box and just poured aluminum in." A bit of research shows they do this with polystyrene-foam and some other polymers... but we can't find anything on PLA plastic.

    PLA is the low-temp material that runs through 3D printers, it's very easy to print, gives good results, is inexpensive so on so on so on.

    Question before us is has anyone tried it yet? I'm asking here because you folks have a bit more practical insight than random Google results.

    Our thought process is, 3D printed cores and patterns for casting made from PLA, and if that proves to be unworkable, 3D printed polystyrene. That's a bit more difficult to run as it warps like a $&*(&!!!, worse than ABS in many regards.

  • #2
    Foam hasn't much actual material. Solid does.

    Foam burns up and disappears in vapor easily. Solid PLA or solid anything may not be so co-operative.

    When foam burns up or vaporizes, there is not much vapor etc. Solid PLA would likely make a lot more due to there being more material, so it may foul up the mold extensively.
    1601 2137 5683 1002 1437

    Keep eye on ball.
    Hashim Khan

    If you look closely at a digital signal, you find out it is really analog......

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    • #3
      Well here's the fun part -- I can vary the infill density and even 3D print hollow parts. That's what caught my casting-friend's attention.

      Starting to look like this may be one of those "going to have to try it and report back" situations.

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      • #4
        I do that fairly often. Try it and see if it works, or can be made workable. Sometimes that's the only way to know.
        Kansas City area

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        • #5
          Originally posted by Toolguy View Post
          I do that fairly often. Try it and see if it works, or can be made workable. Sometimes that's the only way to know.
          Either someone tried it and died horribly (thus it didn't get posted) or it worked so well they repressed all the information through murder and if we try it we'll get murdered too.

          Guess we'll find out next time he does a can-melt...

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          • #6
            Typically with PLA, you do an investment casting because as mentioned previously, PLA will vaporize and boil and basically blow the aluminum out of the mold. They do make filament specifically for a lost wax type of process. It is called Moldlay and is some sort of extrudable wax.
            https://www.youtube.com/channel/UCIF...7S66kX1s8rd0qA

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            • #7
              Originally posted by Joe_B View Post
              Typically with PLA, you do an investment casting because as mentioned previously, PLA will vaporize and boil and basically blow the aluminum out of the mold. They do make filament specifically for a lost wax type of process. It is called Moldlay and is some sort of extrudable wax.
              Interesting! If they invented a printable material specifically for this application that means it's been done before.

              ...not going to stop us, I want to see "aluminum blown out of the mold." YOLO.

              Based on that I am curious what would happen if I printed an entirely hollow part with minimum shells... Boiling and displacement indicates way too much plastic in my mind.... Perhaps with just enough material to hold the shape.

              Hmmm

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              • #8
                Interesting! If they invented a printable material specifically for this application that means it's been done before.
                Well.... yes and no. The "lost wax" method isn't the same as pounding sand around a lump of styrofoam. So we still are not talking about apples to apples.

                The lost wax method also does not involve molding sand. It uses plaster or similar poured in around the form and allowed to cure. Then as part of the baking process in an oven to drive out the moisture it also melts the wax original which pours out the mold. It doesn't burn and go away.

                You're talking about something else. You're talking about ram packing moist molding sand in around your printed form. This method is very much like building a sand castle where you push and pack the sand in tightly so it becomes self supporting. As such the form you put in place needs to be structurally sound or it'll simply collapse and break up. If foam plastic is being used for this sort of use the foam is so easily dented and deformed that care would be needed with the sand packing. And since it's been done apparently it is possible. But since the final finish is partly reliant on how densely the sand is packed it also suggests that the finish tends to be a bit more rough and crude as well.

                I'm thinking that for anything done with your hollow printed objects at least that much care will be required to ensure the force used in packing the sand does not just collapse the hollow form. But how well the sand is packed also determines to some extent the finish you can obtain.

                Sand cast items don't take fine details at the best of times either. If you think you're going to print a lot of fine details into your pattern and cast it in sand you may be in for a nasty shock. For a fine finish and fine details casting it is best to go with the lost wax method. And if they are already making a printable material that can be easily melted out then that's about perfect.
                Chilliwack BC, Canada

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                • #9
                  Originally posted by BCRider View Post
                  Sand cast items don't take fine details at the best of times either. If you think you're going to print a lot of fine details into your pattern and cast it in sand you may be in for a nasty shock.
                  Good point with this. I've had a few pieces cast, light duty structural shapes. Even with large flat surfaces there was still quite a bit of cleanup. It was still the best way to get the parts I needed.

                  For detailed parts in quantities I have a benchtop molding press and other means to produce parts.

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                  • #10
                    Yes, Moldlay is on my list of things to try. And, yes, it would be a lost-wax bake-out process (with plaster, etc.) rather than lost-foam. I've also thought about printing more traditional patterns, though I'm thinking even a fine texture on the plastic will make pulling it from rammed up sand difficult. I suppose spray painting with some filler-type primer might help.

                    I've read about some people getting quite fine details in lost-foam, and going to rather extraordinary lengths to get there (like pre-coating the foam). Some are using desktop CNC mills to carve the foam and then cast the results.

                    One note about lost-foam... it can be done with wet or dry sand. The dry-sand approach (which I've never tried) involves no ramming, you just pour the sand around the pattern and maybe give it a shake to settle. The sand doesn't have to hold any shape... the foam just flashes away and is replaced by aluminium faster than the sand can move... very weird to think about, but it seems people are doing it so it must work. I've seen pictures where people are getting CNC carved text (in foam) replicated in cast aluminium with poured dry sand.

                    There are weird 3D printer filaments that print hard, then you soak them in water for a few days, and they turn foam'ish rubbery and flexible, but I don't think I'd be trying to lost-foam cast those. In general, I'm thinking a quick and dirty CNC mill with a Dremel would be the best way to make foam patterns if you really wanted to go there. Considering the forces involved, you could probably convert a 3D printer to do it with a smallish motor and cutter in place of the print head.

                    Me... I'm just going to wait. Sooner or later, someone is going to figure out a 3D filament that can be printed and then soaked in a solution. That solution will do a molecule by molecule substitution that turns the plastic into something very hard and useful. I mean, if bone can turn to rock just by sitting in mineralised water, for a few million years, then there has to be a slightly quicker process Has to be a way, but then I'm no chemist.

                    David...
                    http://fixerdave.blogspot.com/

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                    • #11
                      It seems to work just fine for a lot of people with PLA
                      https://www.youtube.com/results?sear...ry=pla+casting

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                      • #13
                        Originally posted by ikdor View Post
                        It seems to work just fine for a lot of people with PLA
                        https://www.youtube.com/results?sear...ry=pla+casting
                        Plaster investment casting, aka the lost-wax process. Burning out the PLA has got to be a very messy and smoky process whereas the Moldlay filament would just melt and pour out. As well, the Moldlay doesn't appear to be that much more expensive, so it seems silly to use PLA instead. Just making more work for yourself.

                        Actually pouring aluminium right over the PLA, aka the lost-foam process, seems to be something that no one has tried... or at least successfully reported that they tried. Dry sand, super-thin wall, near zero fill... might work. I'm not going to try it first. I've had enough moments when casting aluminium that I tend to be a little careful these days.

                        David...
                        http://fixerdave.blogspot.com/

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                        • #14
                          Originally posted by BCRider View Post
                          .... But since the final finish is partly reliant on how densely the sand is packed it also suggests that the finish tends to be a bit more rough and crude as well.

                          ....
                          I have seen it where the pattern of the foam is visible in the metal. So either that wasn't done lost foam in that way, OR it does pretty good detail
                          1601 2137 5683 1002 1437

                          Keep eye on ball.
                          Hashim Khan

                          If you look closely at a digital signal, you find out it is really analog......

                          Comment


                          • #15
                            Originally posted by fixerdave View Post
                            Me... I'm just going to wait. Sooner or later, someone is going to figure out a 3D filament that can be printed and then soaked in a solution. That solution will do a molecule by molecule substitution that turns the plastic into something very hard and useful. I mean, if bone can turn to rock just by sitting in mineralised water, for a few million years, then there has to be a slightly quicker process Has to be a way, but then I'm no chemist.

                            David...
                            That's pretty much the technique used for printing metal. Here's a quote from Shapeway's site:

                            Steel is printed by depositing a liquid binder onto a bed of steel powder one layer at a time. The product is then removed from the printer and infused with bronze. While the product is being transferred from the printer to the infusion chamber, it exists in a delicate "green state" which does not support interlocking parts.

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