The Snowmen Crew :) | ENGI 210: Prototyping and Fabrication

Picking our Piece:

The first step of this final project was to pick a design to mold and cast. We began with the unicorn design, and 3D printed a unicorn to see how it would look IRL. This was not approved by the TA’s because its horn was very tiny, and its ears would be considered as overhangs. We then attempted to move forward with the giraffe chess piece but this was also not a good choice because of the angle of its ossicones. The angle of the ossicones would’ve made the removal of the future casted pieces from their mold to be impractical. To move forward we decided to be more on theme with the season, and make snowmen. We thought its smooth symmetrical design would be great for casting at the end of our project. Overall, we learned to always get checked off, before moving forward because a lot of time was invested on the two previous designs. Once our design was chosen we printed a scaled version of the snowman to see how it would look in real life. To the right is the 3D printed design.

Solidworks/MeshMixing

The next step for the project was to create two positive half molds using meshmixer and solidworks. Because we both had no prior solidworks experience, we went through the beginner tutorial for creating the two positive mold halves of the snowman. Below are the results of the two molds. We then decided to 3D print the half with the snowman’s face to preserve its details, and CNC cut the second half.

3D print:

After finishing the snowman positive mold on solidworks the process was very smooth to get it 3D printed. The print came out beautifully as shown on the left.

VCarve and CNC

Creating the VCarve file was a little bit difficult. There was an issue with the amount of time the cut was going to take at first. The first rough machining cut with the ¼ end mill bit was set to take 21min, but the second cut with the ⅛ ballpoint bit was calculated to take 17hrs, which meant something was wrong or had to be changed. The solution was to change the second rough cut to a finish machining cut which lowered the time to 20min!

When it came to CNCing the now set VCarve file we began with attempting to use the Nomad. This, however, did not work because the thickness of the wood was too large, and there wasn’t enough room on the z-axis for the 1/4th bit to be calibrated. We then moved on with the ShapeokoPro. Because the thickness of the given wood was very 1.5in we drilled two lines on the edges of the wood to be able to securely clap it down.

When we finished with the CNC machine we made sure to vacuum our area. Because we didn’t do another level of finishing with the 1/16th bit, we sanded down the positive mold a bit to get smoother surfaces.

Negative Silicone Molds:

Once having the first 3D positive mold it was time to create the first negative mold of the snowman. We began with setting up our area with a strip of paper in case we spilled a solution or made a mess, and gathered the necessary materials. We got both our molds (the cnc and 3d printed molds) and made a box of indeterminate size around them (this is to box the silicone in). Then, we followed the directions for the silicone molding and used equal parts of part a and b. We needed to calculate the volume of the mold box and fill the silicone to 1cm above the highest point of the mold, and subtract out the volume of half the snowman. We calculated our necessary volume to be 242ml, so we used 121ml of part a and 121ml of part b. Above are our boxes of indeterminate size filled with silicone and the resulting negative molds!

Casting!

To begin the casting process, after the silicone molds were dried, we took them out of the molds to cast the individual snowmen. We started by combining the silicone molds using the holes we made in solidworks. To ensure that we had no spilling, we added a lot of rubber bands around the complete mold. To measure the amount of polyurethane we needed, we added the the volumes of the two snowman halves. We calculated the volume of a single snowman to be 45ml, so we added 22.5ml of part a and 22.5ml of part b.

Because we wanted to add color to our snowmen, we started with white then light pink, then dark pink, then purple (it ended up being light blue), then dark blue. We mixed these colored dyes into part a so that we had time to mix it in. Each snowman took around 8 minutes to set. This process was a lot of waiting but they came out cute. Some issues we ran into were the alignment of the molds and the nose of the snowmen. Since the nose was a very tiny piece, when we took the snowmen out of their molds none of them had a nose attached. We believe this may be due to the small size of the nose or because we removed the snowmen from the mold too quickly (since the polyurethane cures from large volume to small volume, meaning the nose would take the longest to cure).

Post Processing:

After all the snowmen were demolded, there were thin pieces of plastic lining the seam of the snowman. To remove this, we used an exacto knife. Overall, the CNC portion of the mold looked a little odd because of the large drill bit, but the 3d printed side came out very nice minus the nose. This is how the snowmen looked from the side: