Update: Yo-yo Base

Process plan and Optimized parameters and Redesign

Step	Operation	Machine	Tool	Justification
Cavity Mold
1	Bore cavity mold Rough Pass	PUMA Lathe	T1010 0.03125 Large Bore	Use bore tool to make a rough pass and cut out the design for the base of the yoyo cavity
2	Bore cavity mold finish pass	PUMA Lathe	T1010 0.03125 Large Bore	Use bore tool again on final pass to smooth mold
				1m 16.94s
3	Make runner from sprue to part	Protrak Mill	#9 sphere endmill	Use the sphere endmill to create the runner from the sprue to the part
4	Widened base to add mass	PUMA Lathe	T1010	Our part is too light, so by widening the cavity mold we are adding mass to the outer rim of the yoyo base and also adding mass to the ring
Core Mold
1	Lathe rough pass core mold	PUMA Lathe	T0101 Turning Face tool	Turn down the face of the mold to match the core of the base part of the yoyo
2	Lathe finish pass core mold	PUMA Lathe	T0101 Turning Face tool	Finish pass over previous cut to smooth and clean
3	Lathe Groove rough pass	PUMA Lathe	T0909 Trepan Tool	Turn the center of the part down to match the central axis and mounting point for the earth part onto the base mold.
4	Lathe groove finish pass	PUMA Lathe	T0808 Trepan tool	Smooth out previous step using a slightly smaller radius trepan
5	Mill Peck Drill	Protrak Mill	3/16” flat endmill	Drill out the center shaft of the core mold
6	Circle Mill for center shaft	Protrak Mill	Circle mill	Fully mills out center shaft
7	Center drill for ejector pin holes	Protrak Mill	#13 drill: #2 center drill	Preps ejector pin holes to be drilled
8	Drill ejector pin holes	Protrak Mill	#17 Drill	Drills out holes for the ejector pins
9	Face off .01 on the core	PUMA lathe	T1010	By facing off a bit of the core, we are making the base of the base part thicker and adding more mass
10	Deepen the groove	PUMA lathe	T0909	By deepening the groove in the core mold we are increasing the amount of engagement the base has with the ring, hopefully this will solve the ring snap fit issue (it falls off too easily)
11	Finish the groove	PUMA lathe	T0808	Recreates a nice right angle in the groove

In general for the base mold, we increased the depth of the groove, faced off a bit of the core, and widened the cavity base mold. The first will allow for more engagement of the ring and the base to help make a secure snap fit. The later two are adding more mass to the yoyo, which should help its spin.

As for the process parameters for the injection molding machine:

Injection hold

Injection hold pressure profile
450	500	550	600	700
600	500	400	350	300
Injection hold time			10 s
Cooling time			20 s
Set screw feed stroke			2 in

Injection Boost

Injection speed profile
3.5	3.5	4	4	4.5
4.5	4	3.5	2.5	2.5
Injection boost pressure: 1399 psi

Screw Feeding

Screw Feed delay time: 5 s

Ejector counter = 2

Ejector pin length = 5.647

Total shim thickness = 0

In addition to finding these process parameters (which were optimized to give the air a chance to escape), we had to create an air vent for trapped air to escape.

The part kept looking like this without the air vent.

All parts aside from the bottom two have bubbles or  air burn!

As you can see, there appears to be a bubble/burn on the right side of these parts. No matter how we altered the parameters, the air trap wouldn’t go away and thus the air vent was necessary. Our optimized part looks like this:

The problem of air trap was solved!

However, the base mold and the ring mold weren’t fitting together well after they were optimized. We could get a snap fit, but the amount of engagement between the ring and the base was too small and the ring would easily fall off in a drop test. To solve this issue, we doubled the length of engagement and also widened the base and the ring to add mass and add strength to the ring (so it would not be as elastic). The process plan for these alterations has been added to the process plan above. I completed the alterations in lab yesterday and will reoptimize the injection molding parameters on Thursday. Hopefully then, our ring and base will fit will together and not fail during a drop test.