On 12/12/2017 14:14, Alan Braggins wrote:
On 2017-12-11, Fredxx wrote:
On 11/12/2017 23:17, Rob Morley wrote:
On Sun, 10 Dec 2017 10:31:14 +0000
Peter Parry wrote:

ABS, also available for 3D printing. Another neat trick you can do
which is used a lot by model train enthusiasts is a form of lost
plastic (rather than wax) casting. Make a positive from PLA and put
it in casting sand as you would wax. Molten metal poured in will melt
the PLA as if it was wax leaving you with a metal casting.

I thought with lost wax you baked the mould to melt/burn out the former
before pouring the metal.

Even using a sacrificial 3D print, it normal to burn out the PLA in a
firing before the pour. That process would normally use a ceramic shell,
though some plasters can be used.

Lost foam is the normal process where the sacrificial material is left
in situ in a sand mould and burnt out during the pour.

Leaving a solid plastic object in a mould, while pouring hot metal into
it, is a recipe for disaster.

There are people successfully pouring metal in to burn/melt out a sacrifical
print in place. For example:
https://www.tctmagazine.com/tctblogs...f-diy-casting/
"I knew a solid plastic print would not burn out as readily as a foam pattern,
so I thought that if a mould cavity was mostly a void (creating a fill density
roughly similar to foam - or ideally even less dense), and giving the metal a
large enough volume to fill, it should vaporize the relatively thin shell of
plastic and work about the same as the Lost Foam process.

That indeed turned out to be the case. Well mostly the case. It seems whatever
plastic doesn't immediately vaporize is more buoyant so it just floats to the
top."

That's interesting, sort of replicating the lost foam process,
minimising the amount of material needed to be burnt out.

The only issue is the time taken to print a part, obviously the smaller
the better.