For this deliverable, we chose to take a more in-depth look at the optimized parameters for our yo-yo's shell component. As we've talked about earlier, we knew this part of the design would be challenging, due to the raised details that surround the shell. However, after some re-machining, we finally made it ready for process optimization. Table 1 below contains all the data for our shell's process optimization, however we'd like to talk about a few key decisions regarding how we arrived at the values below. Going down the list, we kept our injection hold pressure and boost the same as the default since our part was not a special case. We set our injection hold time to 8 seconds in order to allow the gate to freeze and seal the mold. For cooling time, we originally had it set to 10 seconds, but increased it to 15 seconds since it was a larger part and needed more time to cool to avoid warpage. Our set screw feed rate, or "shot size" was set to 1.3", which gave the right amount of plastic without flash or shortshot. To rap up the list of parameters, we used six 6.042" length, 1/8" diameter ejector pins with a total shim thickness of 0.247". These sizes were determined by measuring the mold thicknesses, and an ejector counter of 2 in order to ensure that our part was removed completely from the mold. Overall, the optimizing parameters process went fairly smoothly on the whole with minimum changes needed to our designs. With that being said, we did need to slightly redesign our shell because our hole for the wings became asymmetrical across the left and right side of the shell body. To fix this error, we remachined our cavity mold, rotating the engravings by ~33°. The final shell core, cavity, and optimized part are shown in Figures 2 and 3 respectively above.
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Six SeekersGroup of six MIT students fabricating a yo-yo that looks like the golden Snitch from Harry Potter. Archives
May 2017
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