Have you ever played with Rose’s metal? It’s a fusible alloy of bismuth, lead, and tin with a low melting point of around 100 °C. Historically, it’s been used as a solder for cast iron railings and things, and as a malleable pipe filler material to prevent crimping while a pipe is bent.
He recommends adding registration marks to multi-part molds in order to keep everything lined up, and adding a small recess in the seam for easy separation with a flat-head screwdriver. So far, the molds have held up to multiple pours, though [Ben] did print them rather thick and is glad he did.
As far as making liquid metal, [Ben] used a cast iron pot with a convenient pour spout, and a blowtorch. He added graphite powder to the molds in an effort to make them give up the goods more easily. To finish the pieces, [Ben] cut the flashing with tin snips and used sandpaper and a Dremel to smooth the edges. Copper plating didn’t work out, but [Ben] is going to try it again because he thinks he screwed something up in the process. He’s also going to try printing with TPU, which we were just about to recommend for its flexibility.
Melting aluminum is actually pretty easy to do, which is why it’s such a popular metal for beginners at metal casting. Building a foundry that can melt aluminum safely is another matter entirely, and one that benefits from some of the thoughtful touches that [Andy] built into his new propane-powered furnace. (Video, embedded below.)
The concern for safety is not at all undue, for while aluminum melts at a temperature that’s reasonable for the home shop, it’s still a liquid metal that will find a way to hurt you if you give it half a chance. [Andy]’s design minimizes this risk primarily through the hands-off design of its lid. While most furnaces have a lid that requires the user to put his or her hands close to the raging inferno inside, or that dangerously changes the center of mass of the whole thing as it opens, this one has a fantastic pedal-operated lid that both lifts and twists. Leaving both hands free to handle tongs is a nice benefit of the design, too.
The furnace follows a lot of the design cues we’ve seen before, starting as it does with an empty party balloon helium tank. The lining is a hydrid of ceramic blanket material and refractory cement; another nice safety feature is the drain channel cast into the floor of the furnace in case of a cracked crucible. The furnace is also quite large, at least compared to [Andy]’s previous DIY unit, and has a sturdy base that aids stability — another plus in the safety column.
Starting with a sufficient quantity of scrap metal, he first produced bronze ingots. Getting the actual casting right took multiples attempts. First tried a lost foam cast, which failed miserably, but provided a sample metal which was put through tensile strength testing. The second attempt was done using a wood barrel form and a split mold, and was cast horizontally which resulted in shrinkage on top of the barrel. The third attempt, arranged vertically, almost resulted in a high risk game of “the floor is lava”, with molten bronze pouring out across his garage floor after the mold split open during casting.
Attempt number four was finally successful, again using a vertical mold but with more sturdy clamping. This roughcast barrel was then drilled out and finished to a beautiful mirror with the help of a lathe and a lot of elbow grease. He then turned his attention to the carriage, which itself is a real beauty featuring custom wagon wheels with a charred wood finish and linseed oil coating.
The invention of the relatively affordable 3D printer for home use has helped bring methods used to produce parts for prototypes, samples, and even manufacturing, closer to designers. This tutorial on how to cast metal parts from 3D printed silicone molds is a perfect example of how useful a 3D printer can be when you are looking to make a custom and durable metal part at home.
After 3D printing a mold design using an Ultimaker 2 [Matt Borgatti] casts the mold using Smooth-On Mold Star 15 that can withstand heat up to 450 °F (232 °C), which he points out is ideal for the low-temp metal casting alloy tin-bismuth comprised of 58% Bismuth and 42% Tin with a melting point of 281 °F.
You may have heard of molds created from 3D printed parts before, but what makes this tutorial great is that the author, [Matt Borgatti], really sets you up to be successful. He offers up plenty of insights including mold-making techniques and terminology like why you would need a well and runners designed as part of your mold when casting with metal.
You can either reproduce his designs or use the tutorial to create your own which makes it a good start for beginners as well as another method to file away for people who already have experience 3D printing molds. This post is also really a twofer. Not only do you get detailed instructions for the method but [Matt Borgatti] uses his casted metal part for a flat-packcamera arm he designed to document projects with which you can also build using his files found on Thingiverse.
To create molds for precision parts and to learn more about using a 3D printer as a tool in the casting process, check out this method for creating higher resolution molds with a resin printer.
Casting is an exciting and very useful pastime, but it’s not exactly common these days. That’s a problem whether you’re just getting started or have been doing it for years: everyone can use the advice of another. Fear not! The US Department of Energy is here to help with the Industrial Metal’s Program’s Metal Casting cornucopia.
Although not strictly a hack, this is certainly a facilitator of hacks and any experienced user would do themselves some good by perusing the site. Click on the maps to find complex issues presented remarkably well for papers at this level of rigor. Seriously, check them out.
However, since these papers go into such depth, we can’t really say the material is beginner friendly. That’s not to say it would be bad for a newbie to read through, just that it might be a bit discouraging. But, if you need to figure out where to start in the maze of molds and sand and molten metal, we might have some articles that might help you out.
Do y’all know of any good casting resources on the interwebs? If so, leave ’em in the comments!
“I wasted a weekend learning why elemental bismuth is not commonly used for metal parts.“
It’s a fair assessment of his time spent growing unspectacular bismuth crystals, casting a bismuth cylinder that cracked, and machining bismuth only to be left with a very rough finish. But even though he admits the exercise was unsuccessful, he does provide us with a fascinating look at the physical properties of the element.
Bismuth is one of those elements you pass by in your school chemistry lessons, it has applications in machining alloys and as a lead replacement but most of us have never knowingly encountered it in the real world. It’s one of the heavy metals, below antimony and to the right of lead on the Periodic Table. Curious schoolchildren may have heard that like water it expands on solidifying or that it is diamagnetic, and most of us have probably seen spectacular pictures of its crystals coated in colourful iridescent oxides.
It was a Hackaday story about these crystals that attracted [David] to the metal. It has a low enough melting point – 271.5 °C – that it can be liquified on a domestic stove, so mindful of his marital harmony should he destroy any kitchen appliances he bought a cheap electric ring from Amazon to go with his bismuth ingot. and set to work.
His first discovery was that cheap electric rings outdoors aren’t very effective metallurgy furnaces. Relocating to the kitchen and risking spousal wrath, he did eventually melt his bismuth and pick off the top layer once it had resolidified, to reveal some crystals.
Unfortunately for him, instead of spectacular colors and huge crystals, the sight that greeted him was one of little brilliance. Small grey crystals with no iridescence. It seems the beautiful samples are made by a very slow cooling of the liquid bismuth, followed by a quick pouring off of the remaining molten metal. Future efforts, he assures us, will involve sand-insulated molds and careful temperature monitoring.
Undeterred, he continued with his stock of bismuth and embarked on the creation of a cylinder. Early efforts with a clay mold resulted in cracked cylinders, so in desperation he cast the entirety of the metal in an aluminium baking tray and cut the resulting ingot to a rough piece of stock for turning.
With the bismuth in the lathe, he then came face to face with what he alluded to in his conclusion above, why machined bismuth parts aren’t something you’ll encounter. His cylinder came out with significantly rough patches on the surface, because bismuth is both crystalline and brittle. He suggests improvements could be made if the metal could be solidified with fewer crystals, but it’s obvious that elemental bismuth on its own is not a winner in the turning stakes.
We suggest you take a look at [David]’s write-up. It may be presented as a Fail of The Week here, but in fact it’s more of a succession of experiments that didn’t work than an unmitigated disaster. The result is an interesting and well-documented read that we’re sure most Hackaday readers will gain something from.
Fail of the Week is a Hackaday column which celebrates failure as a learning tool. Help keep the fun rolling by writing about your own failures and sending us a link to the story -- or sending in links to fail write ups you find in your Internet travels.
Even though the pewter is hot enough to melt the PLA, it doesn’t appear to be a major problem if you quench the piece fast enough. According to [bms.had], a slower quench will melt some PLA although that creates a smoother surface. You can see the 0.31 mm layer lines in the cast, though, although you can use any layer height you like to control that. Creating the mold is simple (the videos use Tinkercad, although anything suitable for creating 3D models would work). You essentially attach a funnel to your part and make the entire part a hole inside an enveloping shape.