Blowie: Yoyo

During the Fall of 2017, I worked on designing and manufacturing a yoyo toy within the context of MIT’s 2.008 Design and Manufacturing class. 2.008 is an applied engineering class that introduces students to manufacturing processes, equipment/control, systems, and design for manufacturing.

The Team

Our team was compromised of six sophomore undergraduate Mechanical Engineering students: Harriet Chiu, Pablo Muñiz, Safa Jabri, Shine Han, Wendy Ma and Zeke Long

Initial YoYo Design

When we learned we'll be making a yo-yo for this class project, we immediately knew we wanted to go with an animal design because they are such a staple of toy design. The design we settled on is one of a blue blowfish, where one half of the yo-yo will be the head of the fish and the other half of the yo-yo will be the tail of the fish. Splitting the fish this way gives us a good amount of room to have the detail that we want in the fish’s features, without having any manufacturing markings blemish the friendly face of the blowfish.

Our plan for manufacturing consisted of thermoforming the eyes and the waterbed the blowfish sits in, and injection molding the head, back and tail. The plan is to make the tail in a separate mold, so that we can customize the plastic pellet colors. The tail will then be able to be snapped into place.

Principles of Design for Manufacturing incorporated in the design

• When designing the different features of the face and back of the fish yoyo, we made sure to avoid overhang and keep (almost) constant thickness all across the shell and avoided having sharp edges to ensure good quality injection molding
• When designing snap-fit features we accounted for shrinkage when determining the part dimensions and tolerances
• When designing the body of the yo-yo, we had to account for the diameter of the shaft that will hold the nut in place when injection molding the part. We also had to make sure the shim would be easy to insert and stay in place.
• When designing the mold for the base we really had to take into consideration the process of thermoforming. We wanted the waves to look wavier at the beginning but were unable due to overhang.

Mold Design & Machining

We created our initial molds in SolidWorks by first accounting for 2% shrinkage with scaling, then defining a parting line and surface to create a tooling split for the core and cavity. The parting line was determined by choosing the largest diameter of the fillet on the edge of the part.

We suppressed the eye holes when CADing the mold to simplify our lathe tool path. The tooling split with the core and cavity molds (without ejector pins or sprue holes) for the head are shown below.

Once the initial lathe and mill work was complete, we drill holes for the eyes and inserted the 0.5” diameter eye shut-off pins, then turned them to create shut-off surfaces to be flush against the cavity.

Et voila !

Part Manufacturing - Plastics

The plastic parts were made via injection molding. An iterative process of trial and error allowed us to adjust the parameters for the injection molding process to minimize imperfections. The final parameters used were the following:

injection pressure = 1300psi

cooling time = 10s

Final Parts