The Shop > Composites & Plastics
3d metalcasting test
tom osselton:
I have been playing with my 3d printer I have seen a utube video a while ago using pla plastic to cast metal. The finishes on the castings seem quite good but they say to burn out the plastic (2 - 4 hr's) then give it a shot of air to clear the residue.
I have found this molding rubber at PMS Hobby it melts in the microwave and can be used for internal or external molds it is soft and spongy and I figured if it isn’t ridged enough I could pierce it with thin brass rod or tubing that should melt into the pour it is more ridged when cold.
http://www.composimold.com/
So this is a 5 piece mold that I made, the 3 main parts are on the bottom with two glands one on each side, the top piece wasn't really necessary but I made it anyways it’s a gate connecting the two glands for pouring.
I didn't use any release agent on the first attempt and it didn‘t release very well, on the second I used pam cooking spray wiping off the excess spray making removal of the cast possible.
As you can see there is some leakage at the seams but it is quite thin and easily removed the glob on top is from the funnel I printed it in two halves (it leaked) the idea was to use it for a sprue it’s walls should have been thicker.
I could have used threaded rods to press them together as the pin holes go straight through but for coming straight from the printer (including pins) I'm impressed how well it seals.
I'm going to try casting brass and see how it goes.
Here is the rubber set in plaster /sand a 50/50 mix when it dry's out I'll melt out the rubber (200 degrees F) and open up the passage a little for the pour with a rasp I don’t think I‘ll need a riser as the brass is quite heavy.
I’ll let you know how it turns out!
vtsteam:
Very interesting Tom. Looking forward to this one.... :coffee: :coffee: :coffee:
I've done some lost foam casting in the past with aluminum, with mixed results. A couple good castings, about as many bad. The problem was the time and effort in the pattern, which goes up in smoke. I was just thinking about trying it again with constructed fanfold foam CNC routed patterns, and about lost wax/investment from molded patterns, which I've never tried. But yours looks like another option.
vtsteam:
I'll be curious to see how the sand and plaster mold goes at brass heat -- is it a special plaster?
mattinker:
--- Quote from: vtsteam on August 03, 2014, 07:39:15 AM ---I'll be curious to see how the sand and plaster mold goes at brass heat -- is it a special plaster?
--- End quote ---
Plaster is the base of "lost wax" casting, it resists the heat very well. The sand, or Grog (frequently crushed brick) gives it inert body. The thing that is critical is baking it right through over 600°C long enough for the plaster, CaSO4·2H2O + heat → CaSO4·0.5H2O + 1.5H2O to loose the the water molecules that would create steam instantly when coming into contact with the molten metal. This steam will create a gisor of molten metal, not the desired affect!. Pouring into a mold that is over 600°C slows the cooling of the metal which makes it flow better.
Regards, Matthew
awemawson:
I experimented with lost wax casting when my youngest daughter was doing an art project at school some years ago - she modelled a rather good recumbent lion in clay, from which I took a vinamold cast to make wax cores which I set in 'Investment Plaster' from a jewellery supply house.
The plaster was good for aluminium, brass and copper. I made some iron ones using sodium silicate sand round the wax core. My 'burn out furnace' is an ordinary pottery kiln.
As Matthew suggests, I poured metal straight into the moulds removed from the glowing kiln. I had bent up some steel bands to surround the block to give enough strength to handle with tongs.
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