The Challenge: Design and manufacture 100 yo-yos, each comprised of at least two different injection-molded components and one vacuum-formed component. Then, statistically analyze the overall manufacturing performance by measuring various critical dimensions.
Technical Approach: As a team of six, we arrived upon a design which served dual purposes: yo-yo by day, and headphones by night. We then separated into sub-teams of two, each responsible for producing a component of the final assembly. Classmate Will Bosworth and I took on the ear clip, colored red in the picture. We began by measuring the important dimensions of 10 ears on my dormitory hall. I then CNC machined a prototype ear-clip, using techniques which I learned during my internship in Apple's model shop. After validating (i.e. wearing) the geometry, we set about solid modeling a complete ear clip integrated into one half of the yo-yo casing. This geometry was then used to generate models of the required core and cavity molds. From the mold models, a CAM package called MasterCAM was used to create lathe and mill tool-paths necessary to machine the molds from solid billets of aluminum. Finally, the molds were installed in a 30 ton injection molding machine and parts were made.
Selected Design Features: One of the most challenging aspects of the yo-yo was the mouse-hole through which the audio cable passes. Because it's located on the side of the yo-yo, and our injection molding machine was not set up for side actions, we needed to create the hole as two opposing U-shaped tunnels in the red ear-clip and the white core. The mold geometry necessary to generate this feature later caused significant flash issues.
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| The prototype ear clip held within a plastic nest for two-sided machining. | The finished polypropylene ear clip. |
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| Aluminum molds CNC machined using our MasterCAM-generated G-code. | Red polypropylene was shot into our mold. Flash around the mouse-hole is visible. |
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| The MIT Laboratory for Manufacturing Productivity's 30-Ton injection molding machine. | A close-up of the danger zone. |
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| An assembled yo-yo half with a transparent vacuum-formed speaker cover. | The mouse-hole for the speaker plug required significant flash removal and deburring. |
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| The finished headphones, incognito. |