Objective
The task this week was to develop and understanding of molding and casting using Computer-Aided Manufacturing (CAM). Casts can be made either through milling and subtractive manufacturing (like sculpting with computer-aided tools), or 3D printing and additive manufacturing.
Due to limited resources in our shop, I used 3D printing.
Group Assignment
As a group, we were to review the safety data sheets for our molding and casting materials, then make and compare test casts with each of them and compare mold making processes.
As I mentioned, we didn’t have much access to a milling machine in our shop; the only one we had access to required to much training for us to use individually, so we would simply send files to our shop lead if we wanted to use negative manufacturing and mill from a wax block. We did get some test prints done to see the difference in milling vs 3D printing, but 3D printing was recommended to use for a more hands-on approach.
Next, we focused on Oomoo for making our molds, as well as other casing materials.
The big takeaway with Oomoo was that patience pays off. It’s important to thoroughly mix the two parts of the Ooomoo compund so that they are completely combined. Additionally, long periods of patient mixing will minimize the bubbles, resulting in more consistent molds.
We also talked about the material options available to use to pour into our molds. The main one was gypsum plaster, but we also discussed using metal (a tin alloy) and even soap. Making food-safe molds was not recommended, as we couldn’t really guarantee that the machines used to make our casts were food safe.
Cast Design
I’m a sucker for nostalgia, and Pokemon is still extremely dear to my heart. For this week, I decided to mold and cast a bulbasaur, my first starter Pokemon.
I was able to find a mesh design for 3D printing online, but for this project I needed to divide it in two and build the rest of the cast around it. This meant altering it in Fusion 360.
Fusion doesn’t particularly like working with meshes, so I first reduced the quality of the mesh so it could be easily converted to a solid with many planes.
Next, by selecting planes on opposite ends of the Bulbasaur, I created a midplane through the center of it.
From there I used the split body command to split the Bulbasaur through the midplane. I then moved each half and rotated them 90 degrees so the flat side was down, build boxes around each, and spaced walls off the bottom of the Bulbasaur’s feet to ensure the two halves of the cast would line up. This took longer than I expected since the Bulbasaur was such an irregular shape, but eventually had the makings of my cast. I used the mirror command to create a funnel and some aligbment ’nubs’ in each side and soon had a model that was ready to 3D print.
Cast Print
I used a Bambu 3D printer for my cast. Overall it turned out well aside from two things:
- I mistakenly did not use the high-quality options for a print, so the layers from the 3D printer were very visible
- The funnel didn’t full connect properly, meaning I’d need to manually modify it in the mold later.
Pouring the mold
Pouring the mold was overall straightforward and didn’t have many issues. I mised equal amounts of part A and part B of the Oomoo and tried to take my time. I believe I mexed for about 15min before I felt the parts were suitably mised and that most of the bubbles were gone.
I poured with as thin of a stream as I could manage, but still had a few visible bubbles in the surface. Luckily, this didn’t end up being a problem; the mold was very solid after curing for 2.5hrs, and bubbles didn’t distort it at all.
One thing I didn’t consider: the overhang of the legs for the bulbasaur made removing the mold from the cast extremely difficult, as they were essentially hooked in.
Metal Bulbasaur
Once the mold had cured, I carved out the funnel a bit more so that I could reliably pour my chosen materials in.
I decided to make a metal Bulbasaur. This involved heating a tin alloy at 400 degree fahrenheit until it was liquid and pouring it into the mold (after coating the inside in baby powder). My first attempt didn’t go according to plan. I didn’t let the mold sit for long enough and some liquid metal leaked out when I took the clamps off. When I finally removed it from the mold, it was a crumbly mess.
For round two, I elected to give the metal much more time to cure. I let it sit for about 20 min before opening the mold. To my surprise, it came out very easily ( was execting the legs to hook on like they did in the cast).
I tooke some time to sand down the layers left from the 3D print and eventually had this shiny little guy. I opted to leave the layer lines on his bulb; I thought they gave a nice floral touch.
Soap Molding
We also had the option to make a soap mold. Having already had one failed metal bulbasaur, I let the soap mold sit for a full hour before opening. Overall it worked well, but there are some indents towards the front that are most likely due to air bubbles being trapped.
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