The Race Begins!

Hare Part

Mold Design

The hare mold was designed with a scale factor of 1.035 and is shown in the figures below. The part was designed with no draft as it is not necessary given the contours of the part. The parting line was placed at the largest outer diameter in the part. The parting surface was is on the outside of the part and it extends 0.2 inches from the part. The contours that make up the hare features are all located on the cavity. The locations of the mounting holes are based on the referenced mounting holes for the injection molding blocks that already machined. The sprue hole is placed above the part in the mold in both the cavity and core molds. The extrusion in the part, which is meant for the felt part of our design, is accounted for in the core mold, where extruded boss is placed.

Process Plans

Hare Part Core Mold

Step	Operation	Machine	Tool #
1	Rough Cut with 0.035” depth cuts	Lathe	1 (Face/Turn with Radius 0.0313”)
2	Finish Cut	Lathe	1
3	Groove Cut	Lathe	9 (Grooving Trepan with Radius 0.0385”)
4	Finish Cut	Lathe	7 (Turning Trepan with Radius 0.01”)
5	Finish Cut	Lathe	8 (Boring Trepan with Radius 0.01”)
6 (ejector pins)	Drill/Counterbore to 0.08” depth	MIll	9 (⅛” Ball Endmill)
7 (ejector pins)	Peck Drill to 1.1” depth	Mill	17 (Standard Drill - 0.12)
8 (ejector pins)	Reamed ejector pin holes	Drill Press	⅛” Reamer
9 (ejector pins)	Deburr	Hand Tool	Counterbore
10 (tail pocket)	2D Pocket to 0.100”	Mill	3 (⅛” Endmill)

Hare Part Cavity Mold

Step	Operation	Machine	Tool #
1	Rough Cut with 0.025” depths of cut	Lathe	11 (Large Bore radius 0.03125”)
2	Finish Cut	Lathe	11
3	3D Scallop	MIll	9 (⅛” Ball Endmill)
4	3D Scallop (eye of hare)	Mill	8 (1/16” Endmill)
5	3D Scallop (nose of hare)	Mill	8
6	Drill slot for runner	Mill	9 (⅛” Ball Endmill)

Photographs

 

Process Parameters

Ejector Pin Length	5.490
Shim Thickness	.074
Injection Speed	80 %
Injection Pressure	300 psi
Holding Time	6.0 sec
Holding Pressure	400 psi
Screw Drawback Speed	70.0 %
Shot Size	22.5 mm
Cooling Time	20 sec
Mold Open Position	120 mm
Clamping Pressure	123 kN

Injection molding parameter were at first kept at the default settings. The first thing we changed was the shot size. We first attempted a shot size of 20mm, but that didn’t completely fill the part (approximately ⅚ of the part filled) so we optimized it to 25 mm. At this shot size, the plastic was pushing out onto our felt tail. We were then given the suggestion to try without the felt and have the plastic completely fill the tail cavity. We optimized to 22.5mm and we found that the part looked adequate. The part was completely filled with few defects.

Summary of Learning Process

During the optimization process, the team learned how to optimize parameters for our yoyo to minimize defects and still achieve a snap fit between our parts. By decreasing the cooling time we were able to increase shrinkage which allowed for a better snap fit to our body part. We learned that if using insert molding, for a material such as felt, the compression of the material must be accounted for so that plastic does not fill the gap. To fix for this issue, the team decided to resurface the cavity mold so that the gap for the felt would be much shallower. This fixed the issue of the plastic getting into the gap that is meant for the felt piece.