In the process of developing a throttle body adaptor for V10 Magnum engines, I wanted to explore the possibility of offering an aluminum version. I had successfully printed the part I designed in Fusion360 in PLA on my Ender 3 V2. With this 3D printed part I had the plug I would need to create a plaster mold for casting in metal. This post is not intended to be a how to guide to metal casting, but it does document the procedure I used and the results I got.
Mold Making
3D printed prototype part prepped with the sprue and vent suspended in the mold container. The sprue was 3D printed and glued on while the vent is a piece of wax.
Pouring the plaster to create the mold. The plaster used is specifically for metal casting and was mixed at a 1 to 1 ratio as per instructions. A vacuum chamber is recommended to remove the air bubbles from the plaster but we did not have one available. Once the plaster initially set up, the plastic container was removed to aid in drying. The mold was then set in front of a space heater for 3 days to fully dry
Mold Burnout and Pouring
I used this 1950's kiln to burn the 3D printed PLA part out of the plaster mold. The same kiln was used to melt the aluminum in a crucible.
Plaster mold supported upside down in the kiln for burnout. The mold was heated for 8 hours while ramping up the temperature every 2 hours. The PLA burned out at 900F and the aluminum melted at roughly 1300F.
Pouring the aluminum into the mold. We overheated the plaster in the kiln and cracked the mold in many places. I wrapped wire around it to hold it together to attempt to get something from our efforts.
The mold right after pouring. Notice the large cracks and wire wrap. The mold was allowed to cool until the pool of aluminum on top was solid. Then the mold was dunked in water to remove the plaster.
Here is the part fresh out of the mold. With the cracks we were lucky to get something that resembled the original 3D printed part.
Results
Below are some close ups of the cast part with its many visible defects. The aluminum has a large grain structure with many stress cracks. I am not sure if they resulted from overheating the mold, cooling to quickly, or a poor alloy selection. The aluminum used was a combination of scrap that was laying around. The part also shows a high porosity with large voids and spots that did not fully cast. There are also visible lines from the cracks in the plaster mold. Since we did not have access to a vacuum chamber there is evidence of air bubbles that were trapped in the plaster leaving bumps and divots in the part. The overall part is ugly and unusable out of the mold.
Summary
My first attempt at metal casting was semi successful. Mistakes were made along the way and many lessons were learned. Setting up the mold correctly and not overheating it are critical to getting a nice casting. In addition using a known alloy vs using scrap will likely improve part quality. I am impressed that even with all the mistakes I ended up with an aluminum part that resembles the 3D printed part. I look forward to researching more into aluminum casting techniques and trying again. My goal is to reliably get a quality part and offer these to sell.