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Tips/Techniques A (mostly) Successful Investment Casting.

Tips/Techniques
M

Mcgyver

Ultra Member
I thought you guys might like seeing this. I've been making a huge effort climbing the curve on resin printed patterns and then investment casting them (not quite there yet), Last weeked I diverted from that and did this this filament print casting in AL. Polycast filament, 16 hour burn out cycle, for casting, the mold at 400C, AL at 730C. It worked fairly well, that filament is awesome stuff and burned out perfectly. This would be a very difficult part to cast via the tradition two part mold with cores so it show the potential of investment casting. Its pretty neat the potential there is with this stuff.

There was some cracking of the investment, but that was my fault...hence the "mostly". It lead to a bit of flash, but 2 minutes of fettling took care of it. You are supposed to start the burnout 1-2 hours after the investment is poured, but life got in the way and it sat for a week. I did get a bit of porosity in one spot. Not sure why as I'm using an electric melter. I think the part will still work, but I need to figure out why.

what is it? I need a vertical bandsaw for job so thought to adapt my horizontal band saw....this is a bracket to mount the mini table to the bandsaw frame

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Congrats on a (mostly) good looking part. As long as the part does it's job your golden.
 
Mcgyver said:
I thought you guys might like seeing this. I've been making a huge effort climbing the curve on resin printed patterns and then investment casting them (not quite there yet),.....
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I'm very impressed! Well done!
 
Looks Good! I worked in the machine shop of a foundry (many decades ago) but have yet to get my own casting setup in place beyond collecting tools and materials. I understand that you can also carve a pattern out of Styrofoam and it will vaporize when the metal is poured into the mold, displacing it. Maybe quicker, if perhaps less precise, than 3d printing. I also read somewhere that the vaporized Styrofoam is so evil for the atmosphere that is some areas at least this is not a legal process.
 
Nice job. Demonstrates how fine sand can pick up the roughness of 3D prints. Tis a beautiful casting though.
Lost foam, never looks as nice as lost PLA and neither look as nice as a finely finished pattern.
 
jcdammeyer said:
Nice job. Demonstrates how fine sand can pick up the roughness of 3D prints. Tis a beautiful casting though.
Lost foam, never looks as nice as lost PLA and neither look as nice as a finely finished pattern.
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That is a plaster he used not sand.
 
Tom O said:
That is a plaster he used not sand.
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Yeah I realized that after I posted that. But even fine sand will show the 3D printed marks. I like making patterns I guess.
 

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It all depends on the sand you use play sand is too coarse I was using mortar sand that is way finer.
 
Thanks for all the kind remarks. Looking back, it might look like I was fishing for them with the "mostly". Not consciously anyway lol, just that its a learning process and I did one thing wrong (let the poured investment sit) and got some porosity, which I'm not 100% sure how to fix. Porosity is supposed to be more of an issue if heating by burning stuff and less with an electric melter.

The mold media is Ultravest, a gypsum based investment. Its not just gypsum or plaster and the casting is done under vacuum at 400C so the material has to have just the right properties that allow for great detail but porous enough that the vacuum works. The process is basically what a jeweller does for lost wax casting but using a 3D print instead of a wax pattern. The filament is specifically for this use, to behave like a wax, the idea being that it gives a really clean burn out at temps less than 1400F (after that the gypsum breaks down).

The surface finish was expected, it didn't matter to me for a part like this. The filament, Polycast, is also somewhat unique it that it can be
"polished" with IPA. They sell a misting chamber that (imo it is too expensive, but I haven't thought about building my own yet) that would have eliminated a lot of the 3D printed details. You can get some really neat results with it. If better is needed you can always go with an SLA print. It does however need a dry environment as it absorbs moisture; to the extent it will snap crackle and pop as it boil off in the hot end. They call for 20% RH. i put a dehumidifier in the room, set it ats its lowest setting (30%) and work just fine.

Peter, the model engineering applications are endless. I just have to get the SLA/burn out thing working smoothly. Its been extremely frustrating in that castable resins that print well need too high a burnout temp, and the one that burned out well (under 1400) are hard to print (lots of distortion). Of course there are a million variables in a multistep process in a relatively new field. The challenges could be solved with money, $300/l resin and $10/lb investment (like a dentist might use) but that isn't happening.

The other difference with resin is that it doesn't melt, it just eventually burns off. That creates a problem as it imposes an expansionary force on the mold that breaks up the surface. I just bought some R&R Plasticast investment specifically for resin casting, it supposed to be able to handle the pressure. Hope to try it the next few weeks.

Here are some the ME parts I want to try in bronze. The hand wheel is a little over 1" dia and the smallest pipe fitting is for 1/8" diameter. Amazing detail with SLA. This is with as high a resolution printer I could find (at the consumer level), an Anycubic mini 4k printer which is surprising inexpensive.

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We setup a ‘vacuum assisted investment casting‘ plant to create impeller and volute parts for centrifugal pumps about ten years ago.

The accuracy achievable with the process was amazing. Never before had I experienced producing a ’slip’ fit part from a raw casting (+/- .0001”)
Before investment casting, raw castings had to be machined to provide datum surfaces.

The part shell trees were expensive to produce because we built-up the shells with a few fine clay linings over which there were several coarse sand structural layers. These were all cast as high alloy steel parts to ensure fine grain structure and capable of high RPM operation in the pump with cavitation effects in the fluid dynamics.
 
Those are amazing. I really didn't think any 3D printer could produce that quality of print. Just looked up Anycubic mini 4k. Ah. Not a filament 3D printer. No wonder. Beautiful prints!
 
The wood grain is the printer resolution, about 700 dpi. The handwheel is for a Stuart Triple Expansion engine, if I can cast in bronze I'll hopefully be able to tumble to the point of them not showing.

The pipe fittings are just playing, but I did think it would look very prototypical on a model to use bolted flanges. The challenge will be the size of the bolts! The other idea was to make fake assemblies complete with bolts and nuts and just silver soldering tubing into them. They came from the McMaster catalogue 3d models, just scaled down.
 
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