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Plaster Extruder to 3D print metal molds.

Posted by rocket_scientist 
Plaster Extruder to 3D print metal molds.
March 03, 2010 09:48PM
One option for building more reprap structural parts, and even strong fastners, is to print a mold directly and pour liquid metal into it to cast the parts. Aluminum melts at a low enough point that something similar to the extruder head could heat up rod or wire and pour the liquid into the mold. This technique is already being done by Zcorp. It would be very useful to work on a formula similar to Zcorp's of sand, plaster, and other stuff to make molds for reprap parts. This would not only be good for structural rods and all-thread/studing, but could also make bearings and ball or roller bearings for them. Casting resolution though might limit this initially to only structural parts.


Team Open Air
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rocket scientists think LIGHTYEARS outside the box!
Re: Plaster Extruder to 3D print metal molds.
March 04, 2010 03:27AM
Hi Mike,

... i've made some experiments with paste-dispensing at room-temp and pastes mixed from ceramic dust, glass-spheres or cenospheres with waterglass (sodium silicate) - so it could be dispensed and dried in air (and/or heat-cured) to a solid and could withstand temperatures until 800 centigrades with glassspehers or over 1200 centigrades (couldn heat more) with ceramic dust or cenospheres.

With this sort of high-temp materials you can print mouds directly with the same setups/software used for reprap.

I made some test with low-temp metal alloys as Roses-metal, melting at 98 centigrades (in boiling water!) - other low-temp metals as Fields- or Woods-metal melts at 71 centigrades, but are much more toxic eye rolling smiley

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Re: Plaster Extruder to 3D print metal molds.
March 04, 2010 05:51AM
Mike, we've discussed (but not actually done) printed molds before.

I think it's a very important process, and I'm glad to see it come up again.

It may be easiest to heat the aluminum using traditional backyard foundry techniques; propane and crucible, and so on, until someone decides it makes sense to prototype and develop a semi-automated furnace-crucible thing.

Viktor, here's that recipe for investment I mentioned, basically it is generic plaster and sand. smiling smiley
We would have to play with the recipe in order to get it to work with paste extrusion, inket-powder-print**, etc.

I believe the mixture is only safe and functional after being heat-cured. The heat-curing probably helps evaporate the mechanical water.*

I need to write it up on the wiki. And try it. I just put up some raw notes at:

Also, I think it may make sense to move this thread to the casting-moldmaking thread; I may or may not do so in a few days.

*"If there is ANY chemical water left or if there is any wax residue left in the plaster there is likely to be pitting, boiling, gas released from the mold and even a violent BURP or explosion like a geyser that will blow the metal right back out the top at worst or just bubble away at less worse.

Peter will be documenting on the wiki soon.

I'm not sure how useful Roses-metal, etc are, for RepRap; they are sort of "RepRap-Trendy", but much of the time I think a generic lead-free pewter may be just as useful for many of our applications. Or a specialized paste recipe.

Economically, I think people rarely end up fabricating their own fasteners if they can possibly avoid it. Everything else you can make with your machinery is more important, like the corner blocks for your mendel, etc.

-Sebastien, RepRap.org library gnome.

Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything! grinning smiley
Re: Plaster Extruder to 3D print metal molds.
March 04, 2010 12:23PM
good catch. I always hate to find out that I was not the first to think of an idea sad smiley, but it is all-to-often true smiling smiley!

I agree that making the plaster, sand, ceramic molds on the reprap and then doing the melt and pour externally will be the limit for quite some time. But I like to get people thinking about and suggesting improvements for more distant additions so that they will be more mature a functional when the time comes. I followed the link to your wiki page and added another external link to the Gingery Books which discuss bootstraping a metal machine shop from a charcoal fired aluminum smelter and scrap parts. The section in the Lathe manual about making the cross-slide tool rest vice would be great for building X-Y stages that can easily handle the side loads and torque of heavy milling.

VDX, once I get a Mendel or better working, I would like to work with you on mold making an metal casting. I have done aluminum casting in high school ( I won't say in which centrury!), and pewter casting more recently. I would like to work with you on moving this up to masking casts of structural pieces and maybe even threaded rod/studing.

Sebastian, yes, the _only_ reason to ever make your own fasteners is either that you need something VERY custom, or that you are a few percent RP parts short of the GADA prize! But other discussions about improving the same count using plastic parts got me to thinking that I would rather cast metal than use plastic bolts or rivets.


Team Open Air
Blog Team Open Air
rocket scientists think LIGHTYEARS outside the box!
Re: Plaster Extruder to 3D print metal molds.
March 05, 2010 09:00AM
We could just use the plastic burnout process to do investment casting. Here's a guide from Stratasys on how to do it.

Though its best to burn the plastic out at very high temperatures to minimize the production of toxic gases. The PLA(PCL?) melt out process that Vik uses might be better in this regard. There's also the interesting possibility of dissolving out the PLA using a strong base.

Or we could use plastic preforms to form the plaster for 2 part molds for parts we'd make a lot of.

Though the question is, is 60 watts enough power for use to do metal casting without requiring ridiculous amounts of insulation or large amounts of time to heat the metal up? With casting it's sometimes necessary to heat treat the casting, if this turns out the be the case, it might make this impractical.

Also what metal parts do have in mind making? Bolts and screws?
Re: Plaster Extruder to 3D print metal molds.
March 05, 2010 11:44AM
The concept I am currently working with for my own next-gen entry in the Gada prize would have plastic beam trusses capped with metal strips to provide high tensile strength and low creep. They are:

1) So one thing to make right off the bat would be long thin strips of aluminum, possibly with built in pins or fasteners.

2) The next is that the moving stages, whether the bed or gantry, would be stronger sliding on metal rails rather than plastic. So the second part would be T-channels, square box channel or "C" channel, circular pipe, or circular solid bar for the stages to slide on and remain straight and true.

3) To move the stages, threaded rod/studing, the big nuts that convert threaded rod rotation to stage movement (forgot the proper name!), metal gears to speed up threaded rod or slow down belts and extruders, pulleyes for steel cables or belts, rack and pinion for direct drive, etc.

4) Metal ball or roller bearings. We might not be able to make the balls or roller for the ball bearings accurately enough, or we might need a post processing step to round them off.

5) Fasteners, bolts, screws, rivets, etc. This would only be important for getting a very high fraction of RP made parts, or for parts of the world where even fasteners are rare and expensive. However, I don't see finding enough other critical parts in such remote places to make it worth fabing fasteners even then.

Re: Plaster Extruder to 3D print metal molds.
March 30, 2010 06:30AM
After quite a while of troubleshooting on my own, I realized that when I assembled my rmb-1.2, I soldered in an atmega644 (device signature = 0x1e9609) instead of an atmega644p (device signature = 0x1e960a). Not on purpose of course - Digi-Key sent the wrong chip, the invoice did not match the package contents, and i didn't realize this until now.

mcpd questions
Re: Plaster Extruder to 3D print metal molds.
May 21, 2012 11:23AM
This is very interesting. Any updates?
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