Galaxy optimization

Optimization on the galaxy piece involved solving two problems in the injection molding process while maintaining a careful minimum on the inner diameter of the rivet hole. Initially, the parts required a lot of force to be removed from the mold after injection molding due to bad sticking in the center which deformed the part (see Fig.1). This problem was solved by machining a 5 degree draft angle on the exterior of the center-most spiral arms and by manually deburring all of the center edges with a small file. Changes to the dimensions were negligible except for the inner hole diameter, discussed below. The second problem addressed arose in the cooling phase of the injection molding, when the areas of greatest thickness in the part formed large divets due to unequal cooling (see Fig.2). This problem was addressed gradually over time by shifting injection to higher injection pressures, slower injection speeds, and slightly shorter injection hold times (see Fig 3.)

Figure 1. Early round injection which shows deformation and some flash

Figure 2. Large divets in thickest regions of part

The critical dimension of the hole inner diameter on the galaxy piece was measured for 20 different galaxy parts from our optimization run. The average hole inner diameter reduced from 0.134in before optimization to a much more ideal 0.1317in after optimization. After assembling the complete yoyo, we found that the hole sizes on this latest batch of galaxy pieces spins well on the rivet and the weight distribution encourages spin as the yoyo moves.

Figure 3. Late round injection which shows much decreased deformation and crisp edges