MIT 2.008 Design & Mfg II

Feb - May 2019

As part of the Special Student Program at MIT, I was able to spend the 2nd semester of my senior year taking classes in Controls, Robotics, and Manufacturing. In this course, students have the opportunity to design and create yo-yos using CNC mills and the thermoforming and injection molding processes. My teammates and I decided to make a Polaroid-themed yo-yo that was complete with a removable photo. We modeled it after an early Instagram logo. My specific contributions to the team were creating toolpaths for the body piece, injection molding all of our pieces (and press fitting in our magnets), collaborating on the overall design, and cutting the thermoformed pieces down to size.

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Our inspiration was a polaroid camera (above)                                             Our first attempt in Fusion 360 (above)

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Sketches above by teammate Albert Go

Once we had completed our design, it was time to generate our tool paths. For this class, we used Fusion 360 and its CAM add-on as well. We learned the importance of entering our tool heights accurately, engaging the correct percentage of the end mill, and using optimal feeds and speeds.

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Below are our machined molds for our four injection molded pieces. One of our key features was the photo that could pop in and out of the camera. We spent a lot of time brainstorming various solutions that would allow us to have the card slide in and out. After discussion, we settled on using an embedded magnet in each piece to hold the photo inside. This required that we create two bosses in our photo mold cavity and then press fit in the magnets, so that they would be able to locate the steel piece that we wanted to be encapsulated in the plastic. Other design considerations were selecting places to put our ejector pins and adding our sprue, runner, and gate system.

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After finalizing our molds, we turned to injection molding our first pieces. We had to experimentally determine our optimal parameters for shot size, cooling time, clamping force, holding pressure, etc. As we continued into our production run, the molds took longer to cool down and we had to slightly adjust our parameters to account for this. As we grabbed our body pieces off of the injection molding machine, we press-fitted in the magnet that holds the photo in.

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We also revised our design after learning from our first results. For example, in the picture below on the right, we witnessed first-hand the negative effects that occur when you don't have uniform wall thickness. We experienced significant warpage that led us to change our design to the right picture (which still allows the photo to be supported AND allowed us to use a shrink fit for our magnet.

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The last part that we had to create was our thermoformed piece. First, we designed and 3D printed a die that would create the lens and the rainbow feature that we wanted to include on the front of the camera. Then we printed our rainbow streak onto the plastic, vacuum formed it, and cut it to size.

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Then it was time to assemble our 50 yo-yos. We are incredibly proud of the outcome!

You can learn more about the project at our website: https://yolaroid.blogspot.com/

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