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. 

Optimization run for the ring

Sebastian and I (Delphine) ran the optimization run for the ring this afternoon. Our pieces do a nice color scheme of red to blue through some weird purples.
We played with cooling time and injection hold time.
We'll need to make measurements and decide on optimal parameters later this week.
Sad thing: we need to use fluid on the mold every 10-15 pieces or they don't fall off properly and you have to pry them off with a screwdriver, which is hard!

The acrylic, pins and a sheet of thermoform stuff (although I couldn't remember what thickness it was supposed to be, so I hope I took the right one) are in our bin now in addition to all of our 50 optimization run rings.

I forgot to take a picture, sorry :(

Body Molds Are Finished!

On Friday Eddie and I completed the the mill and lathe work for the molds.  I've attached pictures below. We are setting an appointment during our lab on Wednesday to make the shafts.

The lathe at work!

 The Cavity

The Core

Ring molds done

No pictures because I forgot, but they're all set.

Also - FYI, we shouldn't be using lab time to actually make parts until all teams have their molds machined. So if we want to mold/thermo form we have to make an appointment.

Bubble Thermoform Mold Complete!

Here is the finished core for the thermoformed bubble. There are 8 vacuum holes in the mold.

 

Updated Gantt Chart

We're on track with the project, keep up the good work team!

Completed Bubble Core Mold

Hello all. I made a mold for thermoforming the "Bubble", that is, the clear outer casing of the yo-yo that covers the clock face features.

The pertinent files are in the Dropbox>Timeturner>Bubble. Revision 3 is the up-to-date model, which fixed the trench in the face of the Revision 2 core.

Machining appointment with Rashed during lab time Wed. March 12, 2014.
Great progress, everyone.

Completed Body Cavity Mold

Today I finished making the cavity mold!

I will make sure to go into lab to put everything in the dropbox folder.  Right now the G-Code and Mastercam toolpaths for the lathe and mill are saved on my Z-Drive.

What is shared with you guys:

• The Solidworks model and dimensioned drawing (dropbox folder)
• Process plan for lathe and mill (google drive)
• The finished deliverable report (google drive)

I've printed out our deliverable and I will be submitting it in class tomorrow.

Good work team!

Finished Body Core Mold

Today I was able to finish the Body Core mold:

• the Solidworks model and dimensioned drawing (see below)
• Mastercam lathe and mill tool paths (in the dropbox folder)
• G-Code the two machines (in dropbox folder)
• Process plan for two machines (in google drive)
• began the deliverable 2 report (in google drive)

Things to finish for this week:

• Do tool paths for cavity mold
• Process plan for cavity mold
• Make dimensioned drawing for cavity mold
• Update google doc with dimensions used to determine shrinkage
• Analyze G-code for deliverable
• Update the Gantt chart in the blog

First Molds Made! Parts Update - 3/8/2014

Hi!


Delphine, Sebastian and I met today to discuss changes to our design, and


We were worried about the hands of our clock for a while, with two major concerns:

1. That, given enough clearance, a hand could snag on another.
2. That the hands would sag and be overlapping at all times.

After some back-of-the-envelope calculations, the first concern turned out to be dismissible as unlikely. The second concern was solved by deciding to change the hand design to be one piece of 1/8" acrylic that included both hands, instead of two 1/16" pieces that were two individual hands.


We also designed and wrote the tool paths/Gcode for both the cavity and core molds.



Here's an image of the cavity mold:

Here's the core mold

A cross-sectional view of the two of them together:

We ended up having to change the ring's design due to complications with the mold. A fillet was added in one location, and removed in another.

 

A sketch of the ring's cross-section, denoting the changes:

The ring itself is black, which makes it difficult to see the dimensions on it.



Glad to see some results after a long day of work!

Body Mold Update

Xochitl and I met today to make revisions on the yo-yo body. Several changes were made to the design:

• Re-dimensioned the center hole for the nut: 0.5" diameter, and made the hole slightly longer
• Re-dimensioned the center hole for the press fit, such that there is 0.005" clearance for the pin to be press fit
• Removed some of the center material to keep uniform thickness

        

 

With the design revised, we made the molds. Xochitl determined the percent shrinkage we expect to see based on taking measurements from previous yo-yos with similar features. We determined a shrinkage of about 2.3%. To make the molds on Solidworks we followed a tutorial:

Here are our molds:

 

 


The next steps to take are to make dimensioned drawings of the two molds, and to Mastercam the tool paths to manufacture the molds.

Initial Yo-Yo Design

We have designed our yo-yo to resemble a clock. When the yo-yo is in motion the two clock hands will spin about a pin.

The yo-yo components are as follows (from front to back on the picture below):

• Injection molded body using black polypropylene
• Laser cut plastic clock face from 0.02" white High Impact Polystyrene
• Laser cut clock hands from 1/8" black acrylic
• 1/8" stainless steel captive pins
• Thermoformed cover from clear High Impact Polystyrene
• Injection molded ring that snap fits entire assembly

Yo-yo halves will be assembled together using nuts, screw, and metallic sleeve. In total, 50 fully functional yo-yo's will be produced.