This Yo-Yo was part of my coursework at MIT for the 2.008 class, Design and Manufacturing II.  In a team of 4, we were responsible to design and manufacture 50 yo-yos using at least 2 injection molded parts and one thermoformed part.  Our design was based on the comic book character Punisher. Since our Yo-yo was not radially symmetric, we had to use our solid modelling software to determine the center of inertia to make sure we put the axle of the yo-yo in the correct place

My specific role was to create the thermoformed part (the inner white piece) that would form the skull.  Thermoforming is a process that uses vacuum pressure to pull a heated sheet of plastic over a form.  Our form was milled out of aluminum on a CNC milling machine based on the solid model and toolpaths I created on the computer.  Care must be taken to ensure the plastic can drape properly over the mold.  If the draw is too great, the plastic can become thin enough to rip or if you try to pull the plastic in very small areas, it may not draw down at all.

Once we had a formed part, we then created a die to precisely cut off the excess plastic.  The resulting cut-out would fit perfectly in our injection molded parts.

The purpose of this exercise was to become familiar with production manufacturing methods.  Plastic molding require a specific knowledge base that extends far beyond the actual engineered part.  We learned about drafting, designing runners and gates, accounting for part shrinkage, plastic flow and other factors that go into mold design.