Injection Molding: A Story (BD#2)

Injection Molded Part Breakdown

Description

For the inner silhouettes and heads within the yoyo, we planned to make them as easily recognizable as possible. In order to do that, we thought it was best for the silhouettes to be different colors but ran into the issue on how to have a single injection molded part of different colors. We decided to break down that part into several smaller parts. So the Mad Hatter and Red Queen head and silhouette we chose key colors to make them easily recognizable and separated the molds based on those colors. Both heads have white faces and red hair. The Red Queen has a red silhouette while the Mad Hatter’s hat and silhouette are purple. These decisions resulted in three molds: red, white, and purple. The featured white mold has the heads of both characters and the neck of Red Queen with press fit features that allow the assembly of the different character silhouettes so that it looks like one part.

Justification

For the Mad Hatter, the topmost pieces have pins that fit into the holes of the bottom-most parts. For the Red Queen, this is true for the head but the silhouette has the opposite setup due to the thicker neck aspect. Since the pins and holes are so small, the biggest concern for those isn’t shrinkage but short shot and flash. The critical dimensions are the positions of the pins and holes on the geometries of the parts. Since these sub parts are small, the largest being about one inch, and the the thickness is mostly uniform, the shrinkage is unlikely to cause warpage of the part. Additionally with similar parts, shrinkage was around 2-3% and it didn’t severely affect the fit of the parts. The critical dimensions like the spacing between holes and pins is within a range of 1/16” to ⅛”. With 2-3% shrinkage, the part and positioning still falls well within tolerance.

Description of Manufacturing Process with Process Plan

The Process Plan for the manufacturing of the molds is identical for all the mold colors. However, the manufacturing time for each of these molds varies based on the geometry of the intended parts.

Process Plans for Inner Silhouette (Cavity and Core)

Manufacturing Time Estimate

Heads and Inner Silhouettes take large chunks of time and though it hasn’t pushed back the team schedule, it has demanded more time than previously allotted and put more pressure and stress on planned time to complete the molds.

Photographs of Manufactured Molds