Preliminary Mold Design: Retaining Ring

This week, we've been finishing up designing our yoyo part molds in preparation for our first test run! We have one mold for the thermoformed clear plastic cover, and two each (a cavity and core) for the yoyo body, retaining ring, lettering, gold board, and entire wheel of fortune board.

One of the molds ready for its first run is the retaining ring:

Both the core (bottom) and cavity (top) molds.

The core mold features a filleted pocket around the boss extrude.

The cavity mold is stepped for the ring's ledges.

This part sits on top of the first ledge of the yoyo body, keeping the thermoformed cover in place, which will itself sit on the second ledge of the yoyo body.

The mold was created in SolidWorks using its Mold Design tools. The parting line was chosen in the middle of the ring's larger diameter to facilitate easy removal, and a shut-off surface was created at the bottom of the ring's smaller diameter.

A view of the parting line feature in SolidWorks. The body shown is our retaining ring.

The part was scaled by 1.02 based on shrinkage calculations from previous production runs of a similar retaining ring in past classes. The average outer ring diameter size was 1.9415" for this past ring, while the mold diameter itself was 1.98."

The retaining ring cavity mold we based our shrinkage calculations on.

The mold drawing was then transferred to Mastercam to add the runner and ejector pin hole placements:

CNC Lathe Mastercam for the cavity mold.

CNC Lathe Mastercam for the core mold.

ProtoTRAK Mill Mastercam for the core mold.

Since our retaining ring includes fillets which we didn't want the ejector pins to dent when removing our part, we decided to place the ejector pin holes outside of the part and create runners to the ring. (We had to use the largest radius ejector pin holes available since our yoyo body was already at the maximum size of 2.5" in diameter.)

In addition, we decided to place the ejector pin holes on the mold core instead of the cavity (where they typically are) to work around the fillet issue.

To manufacture these molds, we plan to first use the CNC Lathe, then the ProtoTRAK Mill. We chose the tools that would fit and provide the best finishes:

Retaining Ring Core:

Step	Operation	Machine	Tool	Justification
1	Rough Cut	Lathe	T0303	Used Tool 3 because we wanted to cut the outside diameter.
2	Finish Cut	Lathe	T0303	Used Tool 3 to finish to keep it consistent with the rough cut.
3	Groove	Lathe	T0909	Chose Tool 9 as a trepanning tool in order to cut a groove.
4	Center Drill	Mill	3/16” Center Drill (#2)	Chose the only appropriate tool to center drill the ejector pin holes first.
5	Peck Drill	Mill	0.120” Drill (#31)	Chose the only appropriate tool to create the ejector pin holes.
6	Contour	Mill	⅛” Ball End Mill	Chose a ball end mill tool to make one of the runners from the ejector pin holes.
7	Contour	Mill	⅛” Ball End Mill	Chose the same ball end mill tool to make the sprue runner and the other ejector pin runner.

Retaining Ring Cavity:

Step	Operation	Machine	Tool	Justification
1	Rough Cut	Lathe	T1010	Chose Tool 10 because we needed to bore out the cavity.
2	Finish Cut	Lathe	T505	Chose Tool 5 to finish because it has a smaller radius.

Here's to hoping for a successful first test run!