Sunday, April 24, 2016

Deliverable III: Process Optimization



Dome Optimization:

Figure 1: First production of injection molded dome with clear defects.

Figure 2: Left to right: Process of optimization and noticeable disappearance of hole.

Figure 3: Optimized injection molded dome with no defects.

Process plan for Dome Cavity mold

*Positive vacuum vent holes were created on the cavity mold to prevent the defects seen in Figure 1 ie. holes. This was done after trying regular vacuum holes to no avail. Large holes were drilled on the back face of the mold then collapsed, after this the actual vacuum holes were drilled with the small 0.025" drill bit.
**Step 7 was repeated with a 60 degree rotation to create three more small runners. 

Process plan for Dome Core mold  

*Step 5 was remachined in post operation with same 3/32" flat end mill bit. This was done to ensure better snapfit, and the parameters were calculated by measuring final shrinkage factors.

To optimize the dome, the outer  
Set Up Sheet for Injection Molding of Dome (Optimized Parameters)


Injection Hold
Injection Hold Pressure Profile: P7-P16
500
500
500
500
500
500
500
500
500
500
Injection Hold Time
8.0 s
Cooling Time
10.0 s
Set Screw Feed Stroke (Shot Size)
1.7 in
Injection Boost
Injection Speed Profile: V12-V21

3.0
4.0
5.0
4.0
3.0
2.0
1.0
0.4
0.2
0.1
Injection Boost Pressure
1000 Psi
Screw Feeding
Screw Feed Delay Time
2.0 s
Ejector
Ejector Counter
2
1/8” Ejectors Pins Length
5.095
¼” Ejector Pin Length
#2
To mitigate the visible defects (Figure 1), the injection molding parameters were increased to their max in order to cause the mold to burn. This allowed us to determine the locations of the defects and machine the vacuum holes. The positive vacuum holes effectively removed the defects as seen in Figure 2. We then changed injection molding parameters to optimize the part, and the final parameters are seen in the set up sheet above. The final optimized part is seen in Figure 3.

Map Optimization:

The map was originally too large to snap into the body shell. To fix this, we remade the cavity mold to have a smaller OD in order to allow for the snap fit with the measured shrinkage tolerances taken into account. The injection molding parameters were optimized, and can be seen in the set up sheet below.

Injection Hold
Injection Hold Pressure Profile: P7-P16
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
Injection Hold Time
8.0 s
Cooling Time
25.0 s
Set Screw Feed Stroke (Shot Size)
2.2 in
Injection Boost
Injection Speed Profile: V12-V21

4.5
5.0
5.5
5.0
4.0
4.0
4.0
3.0
2.0
1.5
Injection Boost Pressure
1500 Psi
Screw Feeding
Screw Feed Delay Time
2.0 s
Ejector
Ejector Counter
2
1/8” Ejectors Pins Length
5.570
¼” Ejector Pin Length
#2
Optimized injection molded Hack Map. 

Body Shell Optimization:

There was only one iteration for the mold that makes the body of the yo-yo. Several body shells were injection molded using this mold. We inspected all of them and saw that they were consistently without blemishes of any sort (short shots, flashes, etc). The snap fits of the hack map and the dome were individually modified to fir the snap fits set in the body shell. Therefore, the original settings resulted in optimal body shells for our yo-yo.


Injection Hold
Injection Hold Pressure Profile: P7-P16
400
400
400
400
400
400
400
400
400
400
Injection Hold Time
8.0 s
Cooling Time
20.0 s
Set Screw Feed Stroke (Shot Size)
2.2 in
Injection Boost
Injection Speed Profile: V12-V21

3.5
4.0
4.5
4.0
3.0
3.0
3.0
2.0
1.0
0.5
Injection Boost Pressure
801 Psi
Intrusion Speed
100 in/s
Screw Feeding
Screw Feed Delay Time
2.0 s
Ejector
Ejector Counter
2
1/8” Ejectors Pins Length
5.460
¼” Ejector Pin Length
#2
Optimized injection molded Hack Map/Dome Shell.

Thermoform Optimization:

Optimized thermoformed Dome Cover.

The production time of the thermoformed Dome Cover was minimized reducing the form time by 5 seconds and increasing both the top oven and bottom oven temperatures by 25 degrees fahrenheit.  






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