nathan.b35
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Low Temp Metal Casting

Dec 28, 2018 10:36 am

3D Prints are nice.... Metal Versions are better!

With my MK3 In Tow, I'm playing with various (Low Temp) Metal Casting using 3D Prints. I have a bunch of stuff coming to play with, but so far plan to play with Low Melt Temp Metal (aka Tin / Pewter) - I'm actually using Lead Free Solder Sticks (similar to Pewter).

The techniques I am trying include:
- Plaster Of Paris using Lost-PLA Casting (Melt Out) - Done & more curing
- Caulking High Temp Silicon using 3D Printed Positive (Remove Positive) - Cast Made
- Smooth On Mold Max 60 Silicon using 3D Printed Positive (Remove Positive) - On Order
- Direct Casting into 3D Printed Negative (sand supported) - Testing Underway


Here is my first cast using Buddy. Certainly not a Hall Of Fame item (yet) but we did not suffer any burns! This was a Plaster of Paris mould made from the PLA Buddy supplied by Prusa. Plenty of defects but you can see it actual also reproduced the layer lines. No point posting my technique at this point!

Also, early tests of just trying to cast an ingot directly into a 3D Printed Box supported by sand with 1 layer walls:
- PLA: Sticks to the ingot and very hard to remove
- PETG: Sticks to the ingot and very hard to remove
- ABS: Easy to remove, just peels off
- ABS+ (eSun): TBA

The next stage will be to see what surface details can be maintained with a direct cast to a 3D Print Negative.
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nathan.b35
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Re: Low Temp Metal Casting

Jan 10, 2019 10:54 am

I've now done a few more test casts and have range of methods that don't really work. :)

Plaster Of Paris using Lost-PLA Casting (Melt Out): Tried a few more (both surface and full molds) and the results were mixed. I was using eSun PLA+ so no idea what is in it but it does not burn out cleanly, and as a result the detail can be poor. The surface mold was better at burning out as you could then (carefully) brush out what is left.

Verdict: Not really a great method, but could be fine if there was a better filament to use for burning out. So....I did get my hands on some wax filament that would be perfect but I've been unable to get it to feed though my drive gear + from what I've read, you also need to mod the firmware to let the Prusa print at 80c . It would be interesting to see how this would work if I could get it going as wax melt out is a real method.... if only I could work out how to print with it. I was also thinking about some of the soluble filaments but Plaster is water soluble as well so that is out (and who knows what Limonene would do if trying HIPS).

Direct Casting into 3D Printed Negative : From what I've found you can cast directly into a 3D Printed mold (see pic of Frog) but:
- Needs to be ABS (not ABS+) as it does not stick to the pewter
- Works best on small items where the Pewter has time to freeze before the ABS deforms to much (but you will lose detail)
- Needs 10 Perimeters (had a blow out testing with just 5 on Buddy2 - see Pic)
- If it is a full mold (not just a surface cast), dissolving that amount of ABS takes days
- Works better if you dust the inside of the molds with some Graphite as a release agent, it helps stop the formation of bubbles on the pewter surface

Verdict: It would be OK for casting small items especially if it is a flat one sided item so you can just pick the pewter out of the mold with the advantage that it is quick and easy to print such molds.

Caulking High Temp Silicon : Give this one a wide berth. There is a reason there is silicon mold material you can buy and trying to make one using the stuff from the Hardware Store (for sealing ovens etc) is just not a good idea. I could not release the 3D Part from my mix so did not even get to the pouring metal.

Verdict: Bad Bad Idea

Smooth On Mold Max 60 Silicon using 3D (Printed Positive): TBA, the silicon just arrived today but the pump that came with the vacuum chamber kit I bought is rubbish, so I'm waiting for a replacement (this stuff is expense and you don't get much so I want to give it my best shot).

Green Sand Casting (Printed Positive): TBA - yet to try but this of course should work (as that is the normal way of doing things, + you can cast higer temp metals.
Attachments
Frog.jpg
Frog
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Buddy2.jpg
Buddy#2
Buddy2.jpg (227.84 KiB) Viewed 311 times

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joan.t
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Re: Low Temp Metal Casting

Jan 10, 2019 11:50 am

My dad used to make dental models from alginate molds, then build dental plates on the models with wax and false teeth, boil our the wax and cast heat setting plastic in the remaining void... creating dentures in the process!

things I took from this.

when mixing plaster of paris, BE CAREFUL, not to 'stir in' air... the natural tendancy is to 'whip the plaster' into a slurry, to ensure good mixing and to mix for too long, this can often introduce large numbers of small air bubbles...

he found that mixing carefully, still gave a suitable slurry, which poured well and pouring early, meant that the plaster hadn't begun to harden, so it flowed well, filling all of the intricate detail. if you wash your plastic part with detergent solution (Dawn, or fairy liquid) and shake the excess solution off, the model surface is wet when you pour the plaster, and the plaster will conform better because the detergent breaks down 'surface tension'

Plaster of paris sets chemically and doesn't dissolve in water, once set...

Make sure you dry the mould completely, before pouring hot metal into the mold, failure to do so, will cause steam, which, best case, may give the appearance of air bubbles in the metal, worst case may shower you with molten metal...

regards Joan
I try to make suggestions that I believe to be well founded and safe,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions,
what you do, is YOUR responsibility.

nathan.b35
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Re: Low Temp Metal Casting

Jan 12, 2019 11:06 am

So casting directly into 3D Printed Molds is a wash.

...but I'm pretty excited as I managed to get my (no name) Wax Filament to print! :) After playing with some setting and drilling out my PTFE tube to 2.5mm (the wax filament is not very precise and is very grabby) the positives are looking good. I've now made a Plaster of Paris mold using these and I'm waiting for them to set then we will see how the melt out and casting goes tomorrow.

For this round I'm also trying TPU, as I did a bunch of burn tests on different filaments to see how much ash was left (and hence foul a mold). ABS, PLA, PETG all left ash behind, but TPU seemed to melt well first. Trying to clean up the stringing from the print was not great. We will see how that goes.

The Wax filament took a bit to get working, but I was basically using a TPU profile but with a print temp of only 105C. As you can see from the pics both Buddy and Frog printed well (these had 0 infill). Cleaning up the stringing was much easier and I played with some retraction settings for Buddy and it was pretty well perfect with no post processing required. Edit - used painters tape as it sticks way to good on the PEI sheet!

Fingers crossed!
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Frog2.jpg
Frog
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buddy3.jpg
Buddy
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randolph.l
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Re: Low Temp Metal Casting

Jan 12, 2019 8:35 pm

I don't cast anything but bullets as a regular thing and the largest ones I cast are just 570 grains (7,000 grains to 1.0 pound)

I have also cast some "Lead" solders in my youth (60 years ago) while I was learning to cast the bullets and they could be as much as 1,500 grains. these were cast into antique "tin" solder molds that were cast iron and I rather stupidly sold them for what seemed like a lot of money in my improvised college years.

I have been watching the folks printing the 28mm fantasy miniature figures and the thought came to me that using these 3d printed models to make silicone moulds and then casting them with something like Britannia Alloy such as these Pewter Ingots (2lbs - Britannia Alloy - Lead Free) to be safe for modern children ( though the $22 a pound cost of the clean metal seems very steep).

I doubt I could sell them cast in old recycled lead wheel weights.that I use for my bullets. I think that Britannia Alloy melts at about 470f or 243 C at which temperature the silicone molds are said to have good life (our hot end socks seem to be quite happy below 280C after all)

https://smile.amazon.com/Pewter-Ingot- ... 5B4DGQ68VP
Image

This seems such an obvious thing I expect lots of folks have looked into it and the trickiest part of the operation looks to be cutting the silicone mold away from the printed model. I saw more than a few videos where this system was used for making copies of movie props but most of them don't have the level of fine detail that 28mm figures have. also a vacuum chamber for pulling the air bubbles out of the silicone pour before it sets seems to be another key part of the process.

The need to also build one of these vacuum chambers and refit a refrigerator compressor into a vacuum pump to make it work is what see as the major impediment to giving this a try.

nathan.b35
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Re: Low Temp Metal Casting

Jan 13, 2019 4:45 am

Buddy was not so good, but the Frog was excellent! It's hard to take a photo of shiny metal but every layer line of details was captured but this is what it looked like straight from the mold. This method was:
- Print Positive with Wax Filament
- Make a POP mould around the wax Positive (I did use a vacuum pump to degas the POP)
- Melt out
- Cast

I've still some issue to work out with the Melt Out as there is absolutely no specs on the filament I'm using (not even a mfr). I need to do a test in an oven to see at what point it goes from liquid to burning. Apparently the idea is it hold it just below the burning point and let the mold slowly come up to that temp (takes hours). The Wax should all melt out at that point. I moved from about 150c to 260c and at that point the wax (or whatever it really is) started to burn so I ended up with crud in the mold - too bad for Buddy. Once melted out you can then heat the mold up to casting temp (but the frog was cast in a cold mold so...... I'm not sure about this last piece of advice but that is what I've read)
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