The project that got me back into casting can only be practically made using lost wax like process. 3D printing various materials would work for the prototypes but the time is just too much for small scale production. Lost foam has the same problem unless the investment in tooling to make Styrofoam patterns from beads is justified......................pretty much things we all already know. I ran across this yesterday that may be able to change this for a lot of us once the process becomes practical for the hobby level. https://www.fabbaloo.com/2020/05/3d-printed-foam-expands-40x-for-big-prints-from-small-3d-printers I also ran across a process that extrudes a foam, more like a typical filament 3D printer, that used UV cured resins. It was/is still in the "it works in the kitchen sink stage".
It's interesting stuff for sure. It does leave one to wonder about the dimensional accuracy and strength of something that has been expanded 40x though. For printed lost foam patterns, I think the expansion is still quite the challenge to deal with because the filament would presumably need to be at/near plastic density, and contain a foaming agent or introduce a foaming agent at the printing nozzle so it could be expanded to the very low densities required for lost foam casting. Introducing a gas or foaming agent would likely require a special printer or at least nozzle, and with either, keeping the expansion within the nozzle would be difficult. With significant expansion outside the nozzle you'd be back to having poor resolution and dimensional accuracy. If you start with lower density filament, filament strength will become and issue. All the present foaming agents are not contained well and result in very short shelf lives. Lot's of problems to conquer but it sure would be great. Best, Kelly
You made me think of yet another path to very low density 3D prints, though not as fast as the expandable method. I had some trouble with PLA at one time due to water absorption. It was so bad that when viewed under magnification it had bubbles nearly half the diameter of the filament and pretty consistent. Maybe filament designed to absorb water would make for a convenient blowing agent? It wouldn't help the print speed but might cut the density down enough to go straight to sand rather than invest and burn.
Colorfabb makes a LW PLA filament that uses baking soda if I recall correctly to foam on extrusion. https://colorfabb.com/lw-pla-natural A member contacted colorfabb about lost foam casting with it. Colorfabb was testing it for that very purpose but were not successful. It is lighter than regular PLA but much denser than EPS. Density: 1.210-1.430 g·cm-3 (non activated density) 0.403 – 0,476 g·cm-3 (maximum activated density)
That is a truly inspired method. I wonder how they manage to make the filament with out having the soda out gas during production?
I could have saved them the effort on that test. That's roughly 25-30lb/ft3. The target density would be 1-1.5lb/ft3 which is an order of magnitude and factor of 2x less dense. In my searches for low cost sources of thick XPS billet, I tried DOWs dock floatation billet material but that is 8lbs/ft3 and also unviable. Large EPS billets aren't a problem as far as availability but very expensive to ship and less desirable to machine and finish. This is what I meant about the expansion challenge. Their base polymer is roughly ~60lbs/ft3 so you really do need all of the 40x expansion touted in Shoe's original post. Best, Kelly
