3D printing is cool, but plastic can be delicate and 3D printing with metals requires machines to expensive for the hobbyist. At the Pikes Peak Makerspace, we have found a way to make our 3D designs out of aluminum, brass, tin and zinc using the club's Lulzbot Taz 5 and a homemade used oil furnace. I hope that you find this instructable informative and more importantly inspiring. Please consider casting a vote for the 3D printing contest.
Step 1: Print Your Part
Keep in mind how you will make your mold when choosing a design. Making molds for casting is similar to resin casting molds or molds for chocolate. The important thing to keep in mind is how you will remove the original (plastic part), from the mold, without destroying the mold. If you're going to use a hollow split or open mold then it isn't important which type of plastic you use. If your part has undercut components that will prevent it from being removed from the mold, then you will want to print with PLA or Moldlay filament. PLA can be burned from the mold and Moldlay can be melted out, similar to lost wax casting. We'll discuss Moldlay in more detail later.
For more information on casting in general check out FOUNDRY 101.
Back to 3D printing, if you have a 3D printer you're ready to get started. If not, you can search for 3D printers at local libraries or Makerspaces or you can find a printer at 3Dhubs.com who will print your part for you at a competitive price. With over 10,000 printer hubs to choose from I've found 3D hubs to be an excellent resource.
Step 2: Immortalize Yourself
Using the Cubify Sense 3D Scanner we were able to make a 3D model of a members head and shoulders, which we then scaled to print on the Makerspace 3D printer. We used ABS filament, so as you will see in a later step we used a hollow split mold for casting.
Step 3: Split Mold Casting
The original inspiration for me to start casting metal was a book called The Charcoal Foundry written by David J. Gingery. His book is a great reference for anyone looking to start casting on a budget.
Split mold casting is generally done using a mold split in two halves, providing a way to remove the original part from the mold leaving an empty cavity for casting. As you can see in the photos on this step, the mold for the member bust was done in two halves. The bottom half was filled in 1" layers tamped down with a piece of wood. The bottom half was complete when the plastic bust was buried face down half way in the green sand. At this point the top surface was skimmed flat and coated with fine sawdust, to keep the two halves from bonding together.
The top half of the mold box was then installed in place and filled with green sand in 1" layers, leaving a 1" round dowel in place, to provide a sprue to fill the mold from. Once the top half of the mold was filled and packed to the top we were ready for the moment of truth, splitting the mold and removing the original. The beard had a little undercut making this step difficult, but we got lucky.
After removing the original and making sure the sprue had a good path to the mold cavity, we just needed to carefully place the top half of the mold and we were ready to cast.
Step 4: The Angry Pumpkin (Waste Oil Furnace)
I suppose now would be a good time for a safety message.
CAUTION: A furnace used in a foundry, is capable of temperatures in excess of 1000 degrees F. Proper PPE, including eye protection, gloves, boots, proper clothing and proper training and planning is critical to the safe operation of any foundry. Do Not operate a waste oil or charcoal furnace without proper training. I will not go into the details of making the waste oil or charcoal furnaces, for that there are several instructables and youtube videos available. Instead I will show you how we made metal versions of our plastic 3D prints.
The waste oil furnace we used was built by one of the members and is affectionately named The Angry Pumpkin. The photos in this step go from tuning the furnace to skimming the dross off the molten aluminum and casting multiple molds and ingots. While you can melt aluminum cans, the end result will be better if you use aluminum from cast aluminum products, such as aluminum bell housings etc.
The last picture is an example of a charcoal furnace, which requires less technical knowlege to build and operate, but is also capable of melting aluminum.
Step 5: Moldlay
MOLDLAY FILAMENT is a specialty filament for 3D printing, which prints at lower temperatures and is made to melt out of a mold at approximatley 270 degrees C. For the best results the Moldlay original would be completely melted out of the mold before introducing the molten aluminum. The example, in the photos shown here, the Moldlay Marvin original was buried in the green sand and left in the mold as the molten aluminum was poured directly over the Moldlay. As you can see, the result lacked some detail and had a couple of pit marks, but overall the plastic seemed to vaporize completely leaving behind an aluminum copy of the original. The gas bubbles formed by the vaporizing plastic created a great porous base for Marvin. We intend to try another cast when we gain access to a suitable oven for melting the Moldlay out, prior to casting. When we do, I will update this step.
Step 6: The Fails
To quote Adam Savage "failure is always an option". Here we attempted to burn out the PLA statuette directly over the furnace exhaust.
We also attempted a direct pour over a ABS Rocktopus, similar to how we cast the Moldlay Marvin. As you can see, even at >1000 degrees F the ABS hardly melted away at all.