Final Gantt Chart

We have finished our yoyo production and assembly! Here is the final Gantt Chart for the entire process this semester. 

Final Assembly

We all worked hard this evening and now have 58 assembled yoyos to show for it.
All the photos I took are in the dropbox.

Team Gantt Chart

Parts Team Gantt Chart - 4/9/2014

The parts team has updated their Gantt chart to reflect recent changes in our timeline.

Body Optimization Results

Xochitl and I met this weekend to measure all of the yoyos we manufactured. We decided to measure the outer diameter of the yoyo that is involved in the snap fit with the ring, as this is the most vital dimension for functionality. The target dimension was 2.3in.

We used two different calipers in order to speed up the process. However, this gave us inconclusive results as the two calipers gave different readings. One set consistently gave readings above 2.3in, and the other consistently gave readings below 2.3in. Although the two calipers gave different readings, it is important to note that the difference in readings between the two are approximately 10-thousandths of an inch, which is an incredibly small difference.

Results are tabulated here. Results to take note of are Percent Dev and Dev Length.

The most important conclusion from our measurements is that all 6 processes we tested in lab produced yoyo's within 0.3% of the target dimension of 2.3in, which is 7-thousandths of an inch. Because this dimension is involved in the snap fit, we believe that it is better to be slightly larger than 2.3in rather than smaller. Process 5 produced the largest yoyo's, as measured by both sets of calipers.

Depending on which caliper you trust, process 5 made yoyo's

• 0.14% smaller than 2.3in
• or, 0.20% larger than 2.3in

We will be discussing these results with Dave and Dave later in the week to determine which process to use in the final production run. 

Center Headed Pins

The 1/8" headed pins we ordered from McMaster-Carr arrived. They fit onto our injection molded body part. To accomplish this I used a vice to press fit the pin into the center hole. This press fit holds very sturdy.

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.