Evaporative PLA Casting

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Jacob Longstreth

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Hey All,

I'd like to share some information on a 3D printing filament that I believe can be used in place of foam for lost foam casting. This allows you to go from a 3D print to a finished casting with basic equipment without burning out the plastic investment.

This filament is sold as "lightweight PLA", it expands during extrusion to half its original density. I coat the print in drywall mud, bury it in loose sand, and pour aluminum directly into the 3D print. To minimize the amount of material that gets vaporized I print only one outside wall and as little infill as possible. I've attached some images of the process.

Has anyone used this material for this purpose before?
 

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Hey All,

I'd like to share some information on a 3D printing filament that I believe can be used in place of foam for lost foam casting. This allows you to go from a 3D print to a finished casting with basic equipment without burning out the plastic investment.

This filament is sold as "lightweight PLA", it expands during extrusion to half its original density. I coat the print in drywall mud, bury it in loose sand, and pour aluminum directly into the 3D print. To minimize the amount of material that gets vaporized I print only one outside wall and as little infill as possible. I've attached some images of the process.

Has anyone used this material for this purpose before?
It says it the material is 80% the density of usual PLA. Did you try the method with normal PLA too? Did it make a huge impact?
 
This is fascinating! I didn't even know that lightweight PLA existed and most of the reviews mention using it for RC aircraft frames. Nothing about casting.

Can you go into further detail? That's just loose sand in a bucket, correct? No tamping green sand around molds or anything like that? What's the surface quality of the raw mold and can you still see the layer lines? Does the thinned drywall mud help with this?

You loose you 3D print in the process, but with no infill and only one wall they should print very quickly without using much filament
 
Hey All,

I'd like to share some information on a 3D printing filament that I believe can be used in place of foam for lost foam casting. This allows you to go from a 3D print to a finished casting with basic equipment without burning out the plastic investment.

This filament is sold as "lightweight PLA", it expands during extrusion to half its original density. I coat the print in drywall mud, bury it in loose sand, and pour aluminum directly into the 3D print. To minimize the amount of material that gets vaporized I print only one outside wall and as little infill as possible. I've attached some images of the process.

Has anyone used this material for this purpose before?
This is excellent. I have decades experience with lost wax and centrifugal casting and have evaluated Polymaker filament designed for casting. Unfortunately the filament is designed for really high burnout temperatures, and PLA works better at lower temperatures. So your discovery is highly useful for small component making. Given the explosion of filament types and formulations recently, please could you give us a specific description and maker of the filament you have used. Many thanks
Chris Gabel
 
Jacob:

Might I suggest that you also post this over on thehomefoundry.org in the Lost PLA forum? This is the first time I've seen anybody suggesting using the light-weight PLA in this application. 3D printed RC planes yes, casting - you're the first I know of.

Don
 
He has an Amazon link in the text as "lightweight PLA" but here it is separated for you for easy clicking.

https://www.amazon.com/OVERTURE-Filament-Cardboard-Dimensional-Probability/dp/B0BQRF32YY/?th=1
Thanks for posting this process. This is something I will want to try,
as I need to make a small cored part that I am having great dufficulty
making the core for.

I have some questions for clarifyng the details.

1)
I assume the holes on the top of your casting are core print for the part, and
sand is poured into these holes to to fill them and any cored out portion
of the actual part. THey also act as vents?
Is this correct or is there more explanation needed?

2)
Did you print this pattern as 1 print, or are there more than 1 components?

3)
how many times do you dip the mold, or how thick do you want to to be?

4)
I assume when you dip the mold, the filler goes down onto the cored
out parts of the mold and are poured out after. Is this correct?
Probably takes longer to dry inside, Any problems with cracking?

I like your gating and the dirt trap. I plan to try this on my next pour, and
will be happy to post my results. This method seems like a great way for the
folks in the hobby to get small quantities of castings.

Thanks for your contribution:
maury
Lone Star Engine Works Retired
 
It says it the material is 80% the density of usual PLA. Did you try the method with normal PLA too? Did it make a huge impact?

It looks like amazon is no longer selling the exact filament I used, I've updated the link to a material that should be equivalent. It truly does "foam" during printing to 50% density (or less).

I haven't tried this with standard PLA, but most of the posts I've read by people who have say its a mess.
 
This is excellent. I have decades experience with lost wax and centrifugal casting and have evaluated Polymaker filament designed for casting. Unfortunately the filament is designed for really high burnout temperatures, and PLA works better at lower temperatures. So your discovery is highly useful for small component making. Given the explosion of filament types and formulations recently, please could you give us a specific description and maker of the filament you have used. Many thanks
Chris Gabel

This is the exact filament I used, but its currently out of stock: link

This is a material that should be equivalent: link

It's important to note that two different materials that are sold as "LW-PLA". One type is manufactured with small amounts of gas in the filament, this only expands slightly during printing. The second type undergoes a chemical reaction during printing that causes it to "foam" by 2-3x its original volume. This is what you want for printing patterns.
 
Do you have to make allowances for the "foaming" with your printer settings for example you say you printed a 1mm thick wall, does that need to be modeled at 0.33mm to allow the mmaterial to then expand to 1mm and what about layer heights do they also increase?
 
Jasonb:

This might help: rcgroups.com This is a link to the RC Groups sub-forum on 3D printed planes. In particular, this is a "sticky" thread on CAD and Slicer techniques. You might also want to search through the 3D Printed Planes sub-forum, because I can remember several discussions on wall thickness and LW-PLA. You have to be a member to search, but joining the forum costs nothing other than some time. If you just Google RC Groups you'll need to scroll down a bit as the 3D Printed Planes sub-forum is under the Aircraft - Electric - Airplanes section. If you're into RC and haven't checked these guys out, DO IT. They've got a section and sub-forums for WHATEVER your interest is.

It might seem strange, but 3D printed planes and printing lost PLA patterns have a lot in common. The planes are usually printed with a single perimeter and require significant strength - sound familiar? Some of the people print their planes in Vase mode with a single perimeter, while other people prefer a 2 perimeter approach for more strength and will tolerate the additional weight. Some planes are printed in ABS, some use PLA, some use LW-PLA, some use PETG...

Don
 
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