March 19th - March 24th Body Update

I just want to make sure that everyone else is up to date with what Eddie and I have done with the body. Hope everyone had a great spring break!

Wednesday, March 19th

Eddie and I made the shaft that holds the nut that gets embedded into the body when we are injection molding. 

                         

We were given the shafts as pictured in the top left.  Using the lathe we cut the shafts to our desired dimensions. It was very important that when we placed the shaft into the center hole of the cavity mold, it was flush with the mold.  Dave advised us to make four shafts to help speed up our production rate when are are injection molding. 

                

Friday, March 21st

Friday morning we went to our first injection molding appointment. We quickly found that air was getting trapped in the plastic.  This lack of a gas vent was giving us short shots on all of our parts. 

In order to pin-point the problem, we increased the injection pressure to make the plastic burn in the problem area. 

 To fix the problem, decided to drill three 0.001" deep slots to allow the air to escape. We drew our initial design on the mold and then went into lab to do the Mastercam. We finished the Mastercam, however, it was too late for us to use the mill that day.

Even though we had a problem area, we wanted to see if our snap-fit worked with our team's rings.  We found that they fit beautifully. 

 We put together our first yo-yo and it worked!

https://www.youtube.com/watch?v=gRWsO9uzmro&feature=youtu.be

Monday, March 24th

On Monday, Eddie and I had our optimization appointment.  However, we first needed to fix our mold.  After a  minute on the mill, our air channels were on the cavity mold. 

We happily found that this fixed our problem.  There was a tiny imperfection, however the ring would be covering it, so it was perfectly fine. 

The point of this appointment was to optimize the production process of the injection molded body. We did 6 batches of 8 pieces, where each batch used different machine parameters. This process is summarized below:

Batch 3

• Injection Hold
  • Injection Hold Pressure Profile (psi):                                                                                   
    • 500     600     700     800     750                                                                                   
    • 700     600     575     575     550
  • Injection Hold Time: 8 sec
  • Cooling Time: 25 sec
  • Set Screw Feed Stroke: 2.7in
• Injection Boost
  • Injection Speed Profile                                                                                                           
    • 5.5     5.5     5     4     4                                                                                                 
    • 3.5     3        2     1     0.5
  • Injection Boost Pressure: 1600psi
• Screw Feeding
  • Screw Feed Delay Time: 2 sec
• Ejector
  • Ejector Counter: 2
• Mold
  • Ejector Pin Length: 5.695in
  • Total Shim Thickness: 0.056in

Batch 4

• Settings of Batch 3
• Injection Hold Pressure Profile (psi):
  • 700     800     900     1000   950                                                       
  • 900     800     775     775     750

Batch 5

• Settings of Batch 4
• Injection Hold Time: 12 sec

Batch 6

• Settings of Batch 4
• Injection Boost Pressure: 1400psi

Batch 7

• Settings of Batch 4
• Injection Boost Pressure: 1800psi

Batch 8

• Setting of Batch 4
• Cooling Time: 30 sec

We found it very interesting that the bodies would occasionally burn.  To us, it almost seemed independent of the parameters we were changing. The yo-yo's circled in red are the ones that burned. 

Due to the fact that the bodies were still shrinking, we could not measure them right after we were done. We will be meeting later this week to measure all of the pieces to determine which parameter settings yield the best results in the body dimensions.