2.008: Design and Manufacturing II (spring 2014)

This class focuses on design for large-scale manufacturing and assembly. We learned how altering design and process parameters affects the quality, rate, cost, and flexibility of a product. We also learned about different manufacturing processes such as injection molding, thermoforming, additive manufacturing, and metal casting.

The semester-long project for 2.008 was a group project in which we were tasked with designing a press-fit yoyo and manufacturing 50 physical products (100 identical halves). My team, which consisted of five other MechE women, went with a galaxy theme. We included a spinning "galaxy" that uses its angular momentum to continue spinning even after the yoyo is caught (see video above). We were all involved in the overall design of the yoyo, however, when it came to modeling and manufacturing the individual parts, we split up the work. Most of the parts were either injection molded or thermoformed, and all molds were machined using a CNC mill and lathe. The part that I focused on was a thermoformed protector that also functioned as a clear window. Throughout the semester we kept a rough blog to make sure that every team member was up to date on what was going on. 

​Major yoyo components:

• Injection molded body 
• Injection molded "sun" retainer ring
• Injection molded "galaxy" spinner
• Thermoformed protecting window
• Metal shim for weight and stability

(Hover over images to see captions, click to enlarge.)

Assembling the first yoyo that we made. The colors are strange because all the parts were made during test runs. These test yoyos were slightly loose, so we hd to shave a bit off the retainer ring molds for the next run to achieve a press fit

Although part production was relatively automated using the injection molding and thermoforming machines, assembly was not. We had to form an assembly line to put together and string over 100 half yoyos

Partially assembled yoyos

Fully assembled yoyo

Fully assembled yoyos

This is an example of one of the charts we used to optimize the thermoform process parameters. We made 200 test windows in batches of 5. For each bath we tweaked one parameter, slowly adjusting different parameters until we saw changes in quality

The mold for the window, which was thermoformed out of clear 0.03" ABS plastic. This was the part that I focused on, and it was made to sit flush inside the retainer ring

This is the mold core for the retainer ring, which is the top part of the yoyo. It snaps onto the body, and acts as a lid holding the shim and window to the body. In order to create a press fit, the part needed to be slightly smaller than the body

This is the mold core for the galaxy, which is the spinner attached to the middle of the body. The hole had to be dimensioned correctly to avoid both wobbling and getting stuck on its post

The mold we used for the thermoform window. It was machined using a CNC lathe. We also drilled vacuum holes near the inner circle to sharpen the corners

A window made with the optimized thermoform process parameters, and cut with a die and punch