Latte yo-yo

design, course (MIT)

Overview

My Role: Designing the mold for the thermoformed “foam,” machining the mold for the coffee part (using both conversational milling and CAM) optimizing the parameters for injection molding the base, manufacturing the injection-molded base, and assisting with assembly
Tools/Skills: Design for Manufacturing, CAD (SolidWorks), CAM (MasterCAM), 3D Printing, CNC Milling, Injection Molding, Quality
Timeline: September - December 2017 (4 months)
Team: 5 (MechE)

Goal

Design a yo-yo for manufacturing at scale

Outcomes

Due to a shared love of coffee shops, my team designed a yo-yo based on a latte. The yo-yo required a base with a fitted metal shim for weighting, a snap-fit between the “coffee” and the base, a fit between an injection molded “coffee” and the thermoformed part “foam”, and a thermoformed “cup.” The yo-yos were subject to a drop test to ensure that they did not fall apart.

Final yo-yo with and without cup

Final manufactured yoyo with and without cup

Design Process

The yo-yo was first modeled using SolidWorks.

CAD model of blue yoyo with brown coffee and white foam art that looks like leaves.
CAD model of yoyo sitting within white cup.
Exploded view of yoyo parts (cup, base piece, connector, shim, foam piece, coffee piece).

This model was then used to design the molds. MasterCAM was used to create the toolpaths for creating the molds from aluminum and then the molds were made using a CNC mill and a CNC lathe. A mold was 3D printed using an SLA printer for thermoforming the “foam.”

CNC milling the mold for the yoyo base piece.

The magnets held the shim in place so that the plastic could be surround it during injection molding.

Finished yoyo base mold with magnets to hold the shim.

The fine details for the latte art required a small end mill, which broke the first time we tried to manufacture the mold using the CNC machine. Settings like the feed rate had to be adjusted to successfully create this mold.

Finished CNC milled mold for the coffee piece with a negative pattern for the latte art.

Test runs were conducted for all of the parts to optimize the process parameters and ensure the parts fit together as desired. The molds had to be modified a couple of times to improve the snap-fit. Finally, we did a production run and produced 100 of each part (50 of the cup) and assembled 50 yo-yos.

Layout of parts to assemble 50 yoyos.

The full process is shown in the video below.

Reflection

This project (developed as part of 2.008, Design & Manufacturing II) taught the lesson of keeping manufacturing in mind from the beginning of designing 3D geometry. We had to modify our molds after our initial machining since the coffee part would not fit into the base part. In our case, this involved removing some material. However, if it was the reverse, we would have had to remake the entire mold which would be costly in the real world. Understanding the material and process parameters for injection molding was key to determining if and how much the final part would shrink, something that might not be thought of when using CAD to design.