My brother and I decided to have a go at lost-PLA aluminium casting this weekend. This is our first try, really happy with the outcome. Yes, I could have spent longer polishing the z-lines but a) I kind of like how they look and b)I’m lazy.
Polystyrene sprues glued on with contact adhesive. Model laying flat on back with sprues at thighs and neck.
Plaster of Paris/sand mould made in bottom of milk carton. Agitated the carton with electric sander for a few minutes after pouring to help remove air.
Mould burnt out first with home-made electric furnace. I’m not sure the metal would burn out quickly enough. We probably should have let the mould fully dry before baking it but we were inpatient and put it in as soon as it was set. No cracks or explosions. We repeated this process with a couple of other pieces we cast later with no problems there either so this seems safe enough.
We only had scrap metal to work with and no temperature control on the furnace so there was a bit of guesswork regarding temperatures.
I’m under no illusion this result was a bit of a fluke but we’ll still take the credit!
@Michael_Scholtz Temperature control was almost non existent. We did have a thermocouple but it had a wiring fault and was very flakey.
For burning out it is a non issue. Wait for all steam to escape first then the plastic will start burning. At these temperatures once the flames stop you can be fairly sure there is nothing left to burn…
After burning we only waited long enough to bed the plaster mould into sand to support it.
For the aluminium its pretty easy to spot the melting point. After that, its just a case of waiting for the dross to form a skin so you can scoop it off.
Cooling after pouring was only 3 or 4 minutes before removing from the sand. A quick plunge in water to make holding by hand possible and then chop the sprues off.
We did everything outside on a fairly breezy day so fumes were not really noticeable. In hindsight we should have looked into the fume issue more carefully.
I’ve been working on an extensive post on this; here is the short story:
Coal will do for melting the aluminum (if you have a fan to supply air).
PLA is the least favorable print material, I’ve yet to try HIPS but other posts suggest it probably will perform the best (currently leading is SLA (SF makerjuice)).
Plaster-sand mix depends on the sand, I recommend trying 40% to 60% sand, water mix depends on the plaster (when you add sand to the plaster/water mix, you need to add more water too).
Try to prevent the water/other-materials from turning into gasses when pouring and you should do good. PLA will stick to the insides of the mold and aluminum won’t vaporize the PLA, so you need other methods of removing the PLA.