Pewter cast in ABS mold

by Terminus, published

Pewter cast in ABS mold by Terminus Apr 1, 2014
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Some metals can be directly cast into 3D printed ABS molds.


I won't talk about metal casting practices or safety because this is not the place for long, boring instructions which can so easily be found elsewhere. If you lack the necessary skills or knowledge, study and learn before attempting to cast metal. My aim here is to illustrate things specific to this technique.

While struggling to build a plaster mold a couple weeks ago, it occurred to me that an ABS printed mold might be able to contain small amounts of some lower melting point metals. I began testing things..
First attempt was with pewter M.P. 466F. Then lead (M.P. 624F) and then an unknown flavor of Zamak (the family of zinc die casting alloys, mp ~775F)

I have no idea if anyone else has already done this. Didn't see anything around here or with a short search. But if so then credit to them. There may be nothing new under the sun but this is all new to me.

A pyrometer will probably be required. Some multimeters have a "Temperature" function and include a chromel-alumel wire lead.
I also have a non-contact IR thermometer but didn't try it. It would measure the surface temperature but cannot be immersed in the melt and I think it would be less accurate. Still, some trial and error might overcome that.

Zinc pour was at 770F or slightly less. It began to solidify at about 760F. 780F was too hot and melted some of the mold in the 0.10 inch thin test-print mold (See Files). The too-hot mold got real soft and bulged outward in spots, but nothing melted through...

Generally speaking, there are numerous reasons you want the metal to cool fast but plastic is a good heat insulator. Compared to steel molds, the zinc solidifies very "slowly" on contact with the plastic mold walls, and stays pretty hot for a long while. So, zinc casts suffered significant shrinkage and were weak and brittle with the resultant large crystal formation.

Zinc permanent mold die casters can "pour" it cooler and almost slushy, like at 700-725F, because it is forced into the mold. But for gravity casting the metal must be very liquid or it won't pour at all.

Tried pouring some lead. Pure lead was poured at around 600F but this approaches the point of being difficult to work with. I used a lead caster's pot (Palmer 400W Hot-Pot) commonly used for casting fishing weights and bullets. Max temp on this pot is near 900F.

Lead is cheap, soft, dull and ugly. It doesn't pick up detail like pewter.
I don't know why anyone might waste their time casting lead. 3D printed molds deserve better than that.
Pewter might be more expensive but is far superior in every other way.

Pewter, OTOH, with its lower melting point of 466F (Formula R-92: 92% tin, 8% antimony) offered no difficulties whatsoever, even in thicker sections. Achieved excellent detail. And it can be melted on a laboratory hotplate in a stainless steel cup.

Remove mold plastic with sharp nippers but be careful not to damage your parts. I would not use fire or heat or brute force to break out the mold. Pewter bends, softens and melts too easily. I used acetone to dissolve any ABS pieces which couldn't be safely removed with nippers.

Acquisition of pewter: Thrift store hunting or buy it.
Various heavy, cast decorative items are very often pewter. Zinc predominates in mass produced items. Pewter items are often stamped somewhere on the bottom with the word "Pewter".

Metal suppliers sell ingots. My ingots weigh about 4 lbs each. Many years ago, just for kicks I walked into a local Rotometals distributor and bought some fusible alloy and a couple ingots of R-92 pewter (92% tin, 8% antimony) to make a chess set... which never happened. I recall because they didn't know me and wouldn't take a business check so I had to go out and get some cash. I didn't touch the pewter until now.
I see Amazon also sells pewter.

Having said all that, just forget about lead and zinc.. seriously. Those were just experiments to see what was possible. In the following days I plan to try aluminum and pour something at perhaps 1100 F, just to explore the limits. It might be possible to pour aluminum in very thin sections.. Ya never know.

Go get some Pewter. It's the best casting material by far. Make jewelry, rings or medallions or a million other things with the least amount of trouble and the greatest beauty and detail reproduction. It is pretty strong, easily tooled and it polishes to a bright silver shine.

Mold design:
The toughest part of all this is mold design. You are working in reverse and creating a negative. You are designing an empty cavity. Boolean operations are an indispensable tool here, imo, but they can't think for you.

The cavity cannot have ANY support inside of it. You don't want to pour metal around some hidden, stray ABS support or your finished pewter piece will contain plastic within it. And you can't get into the mold and remove the support. So, use cores and / or multiple mold parts to avoid printing any internal support.
Most people have no idea what I just said but once you try to design some fancy mold cavity it will dawn on you.. guaranteed.

A 2 piece mold for a flat plaque or pendant shouldn't pose any difficulties but a more complicated design may require significant thought and careful planning.

The two 0.10 inch thick test plate mold prints took 60 min, 35grams ABS with Afinia defaults but with minimum fill. Strength is not a factor here and a thick fill is wasted filament and takes time (and / or more acetone) to remove.

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si tu pulvérises du silicone liquide sur les surfaces de tes moules, cela devrait grandement augmenter la qualité de tes pièces couler en métal .
Ps. J'ai été joaillier sculpteur plus de 35 années . ( j'en ai coulé beaucoup des pièces dans ma vie .

if you spray liquid silicone on the surfaces of your molds, this should greatly increase the quality of your metal casting parts.
Ps. I have been a jeweler sculptor for more than 35 years. (I made a lot of metal pieces in my life

   Bye, thank you for sharing your experiences

Happy 4th of July! I hope your insurance is paid up! Metal casting in plastic is extremely dangerous with the lowest of melting points.

Casting metal is dangerous. I've tried to impress that on people throughout my projects. Your comment confirms my efforts haven't been wasted. Thank you.

The metal-casting industry has been casting tin, zinc, pewter and lead-based alloys in silicone molds since the 1960's.
Silicone is a polymer, or "plastic", if you prefer. The process is called spin-casting or centrifugal casting. Kits for the hobbyist are available.

Steel molds are extremely expensive to build. When it was realized that a new plastic could withstand moderately high temperatures, a whole new industry was created.

I won't claim 3D printed molds offer such potential, but they sure are cheap, fast, and easy to make, and if you can print something, you could just as easily print a mold for it.

do you think the aluminum could be used in such a way to make custom heat sinks? or did that not work well for you? i don't know how well pewter does for a heat sink material, as aluminum or copper is all i've ever seen.

you can use your mold to make a first casting in Styrofoam, A liver piece made in Styrofoam, you put in plaster of paris or even sand to nail
Melt your aluminum, you can cast the metal directly from this new plaster mold directly on the Styrofoam melt under the heat of the metal. To be replaced by metal

tu peux te servir de ton moule pour faire un premier coulage en Styrofoam, Pour première étape la pièce réalisée en Styrofoam, tu places dans du plâtre de paris ou même du sable de clouer
Faire fondre ton aluminium, tu peux couler le métal directement dans ce nouveau moule en plâtre directement sur le Styrofoam fondra sous la chaleur du métal. Pour être intensément remplacé par le métal

For an initial attempt, the aluminum finned thing was extremely encouraging from the metal casting point of view. I'm totally confident I could cast a functional heat sink to fit a printer-sized stepper motor, or whatever. A tubular one for an extruder could be cast, but I think those have critical internal dimensions, and would require post-casting machining? I don't have the knowledge or the need for one.... but it could be cast.

Part dimensions must be small and thin enough that the aluminum freezes very quickly. Right now I'd estimate the upper limit on thickness is about 4 mm... 0.16". There doesn't seem to be a minimum thickness. Unlike aluminum foil, very thin cast aluminum is brittle and delicate so there is a minimum practical thickness.

Generally speaking, when a mold is a one-shot affair, and is destroyed, the process is deemed expensive and time consuming. So, to justify the high cost, whatever part you're making either better be expensive, or it cannot be made any other way, or it's "art".

But how many heat sinks does a person need? Material cost is low, and printing doesn't take too long. From design to mold may be a couple hours. Other mold making processes take days to months.

I know very little about it, but pewter blows as a sink material. The important attribute is "thermal conductivity". Of the practical materials, copper is the best followed by aluminum. They somehow use diamond on IC chips.

Copper.. May be possible. That would be trick because copper heat sinks are real rare. There's a couple pipe fittings in a junk box over there, and I'm toying with the idea of trying brass/bronze. But that kinda heat kicks it up a notch and really complicates things.. It's too early to say what's possible and what's not, imo.

Aluminum heat sink cast in ABS mold

I've been working with white-metal (98%tin) and laser engraving MDF for my molds, I had pretty much considered ABS to be a foregone conclusion with this - but perhaps I'll give it a go.

Good luck with it.
Antimony is well known as a hardener, but my understanding is a significant percentage of antimony also makes the metal more fluid. I don't know what 98% tin will cast like...

There is some temperature where the metal will flow well into the mold. Much depends on the structure of the mold. Generally, thin channels and small volumes require a higher temperature, more fluidity. Large, wide channels can flow cooler, less-liquid metal.... and so forth.

I highly suggest a few trials and experiments, using a pyrometer. And keep the melt temperature as low as possible... as low as it can be while still fluid enough to fill the mold.

Recently, I was playing with vacuum casting pewter. Vacuum assist might allow the melt to be much cooler than if gravity cast.

Pewter didn't melt through. Molds survived fine. But pewter is so fluid that, when forced into the molds, it leaked through the microscopic holes and channels in the ABS prints, and ended up on the floor (actually in the catch-basin below the mold) .. It went right through it, like a sieve...

I'd be interested in any results you'd care to share... Have fun.

Was the ABS submerged in water to help prevent melting?

No. Nothing like that is required. Keep water away from molten metals. Molds must be absolutely dry.
If you pour hot, molten metal into a container (like a mold) that is even slightly wet, or has even one drop of water in it, the water instantly bursts (explodes) into steam, and that steam will push molten metal back up, out, and all over the place.... on the ceiling, the floor, and all over you.
Even if you're positive the mold is dry, always wear protective safety equipment and follow all the safety rules at all times.
There are many similar, hidden dangers. Do not cast metals unless you've studied and know what you're doing.

As for casting metals in ABS, think of it this way.

The plastic mold is extremely "cold".. perhaps several hundred degrees cooler than the molten metal.
The liquid metal is only slightly hotter than its melting point. So, if it cools even slightly, it will solidify and hold its shape. It will still be very "hot", but it has become solid.

When the molten metal hits the cold mold, the outer surface immediately cools by a few degrees and solidifies. The plastic has done its job of holding the mold-shape long enough for that solid metal shell to form.

Once that metal shell is formed, the interior also cools. It releases a lot of heat (BTUs), perhaps enough to distort or melt the plastic mold, or even set it on fire, but not enough heat remains to re-melt the metal-shell that was formed on contact.