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lost pla/pattern castings ?

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vtsteam:
Well unless I miss my guess here, Joules, I think the whole idea picclock wants to try at least is to take advantage of the 3D printer's promise to make complete complex shapes with details and undercuts and then cast that in plaster, for high level rendition, but if possible reduce the amount of additional material (greensand, sprue, flasks etc) and so be able to pour into an open mold. And printed traction engine wheels with treads is what he's interested in trying, for example.

Now this sounds like a tall order, and I don't own a 3D printer and not likely ever to, and am not even a lost wax/material casting fan, BUT..........

I do think what he wants is feasible. With maybe some slight modifications.
One is that it must be a baked out lost pattern process.
Second is that it be a two part plaster mold.
Third is that it not quite be an open top mold but a shallow sprue, carved like a short funnel into the plaster. And maybe some vents.

In short, think of it similar to the way a bronze statue is cast into investment. (Mattinker, where are you?)

I think that might work to do what he wants.

Is it something I'd want to do?

Nope. I like wooden patterns, greensand, and machining.

But I'm certainly willing to cheer someone else on if that's their ambition.

S. Heslop:
Myfordboy has a video on this that youtube won't stop recommending me.



I'm not 100% on the guy - from what I know he's done alot to spread a bunch of myths in the casting world. But the part in the thumbnail is an interesting shape. Shame he doesn't show what its for.

He makes it look like a fairly simple process with good results though.


I think the interesting idea with investment casting is for doing large batches of parts, assembling a tree and casting a whole bunch in one go. Maybe there's scope for making silicone moulds from the 3d printed (and ideally sealed and sanded smooth) objects for investment wax as a middle step.

S. Heslop:
Looking at that part again, it's clearly part of a 3d printer extruder.

picclock:
@vtsteam
" picclock wants to try at least is to take advantage of the 3D printer's promise to make complete complex shapes with details and undercuts and then cast that in plaster, for high level rendition,".

Spot on. I was hoping to produce the rear wheels like this using a 5% copper aluminium alloy to make the part fairly hard wearing and corrosion resistant. Definitely using lost pla if possible, as I can print this easily, possibly 2 at a time with the front wheels inside. Not sure how it will work out but worth a try.

The thing that impressed me about the myfordboy video is the extreme detail resolution which came out on the casting. You can see the 3d print lines and patterning. Two things i found a bit puzzling, when he burnt out the mold there was no smoke or mess - made me think he had done it then just placed it back in the kiln for the video. Other thing was that there was no vent pipe for the metal. Always thought it was essential yet the casting looks pretty near as good as it could be.

The other parts I thought I would have a go at pattern casting as it looks easier but I'll see how I get on.

Thanks for all the info

Best Regards

picclock

RotarySMP:
Have you checked out Alloyavenue.com? There are a number of people doing great castings with lost PLA.

I have done a couple of lost PLA castings in aluminium. so I am only a beginner at it.
I didn't have access to real investment casting shell material like Myfordboy used. I built up a shell made from 2/3 fine sand with 1/3 plaster of paris. It is difficult to get the first layer to stick. I read afterwards that using the glycol which is sold as dish washer to stop water pearling aids first layer adhesion.

The shell was built up with a brush to about 1/4" think over a couple days and then dried thoroughly.

I burnt out the PLA and fired the shell over a about two hours in my furnace with the propane burner running at low pressure. Using a 10% infill printed part, there really is not that much PLA to burn out, and it burnt quite cleanly. I was worried about ash in the corners of the mould, so tried to blow out one of the moulds with compressed air, and destroyed the shell. This is the real disadvatage of POP. By the time the PLA is burned out, you have probably exceeded the temp which dehydrates it, reducing the strength near zero. Seem like ash staying in the mould is not really an issue with PLA.

Myfordboy did an interesting twist with that casting. He left the large flat side open, with no shell, and used a normal green sand on that side, so the mould would have largely vented through the sand.

My test piece was a spoon, and had a minimum thickness of only about 1.5mm. Quite a tough test for a first attempt casting, but it worked suprising well. I can't find the photo I took sorry.

The entire work is pretty time consuming, and the risk of failure is (with POP) pretty high, but if it works, the resulting castings can have extremely high tolerances, which has been typical of investment casting methods for the last couple of thousand years.
Mark

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