Group Meeting Minutes 4/1

No meeting occurred the week of Spring Break because of group members traveling. Hannah, Joanna, and Kelsey got together to ensure the fit of the IJ2 and TF pieces.

This week's meeting was moved from Friday (typical time) to Tuesday due to group member conflicts.

Agenda

1. Progress
2. Team successes/needs
3. Timing planning
4. Blog post, Gantt chart update reminders
5. Future goals

Progress in past week:

• IJ2 Process Optimization
• TF Process Optimization (mold remachining required to fix webbing)
• IJ1 Process Optimization started - molds may need remachining due to issues encountered (too much shrinking)
• IJ3 molds made - process optimization to occur this week

Summary of team accomplishments:

Team	Accomplished	To do this week	Issues Foreseen
IJ1	Original molds machined          Process optimization begun (shrinkage encountered)	Measure 5 injection molded parts          Rescale molds in Mastercam, export GCode         Next week: make new molds, new process optimization	Shrinkage (being dealt with)
IJ2	Original molds machined (mold issue fixed with quick remachining of cavity)          Process optimization completed	Finish report	None unless changes need to be made to accommodate other parts
IJ3	Original molds machined	Complete process optimization          Fix any issues with the molds to fit IJ2 and TF, snap fit	Molds may need changes to fit other parts
TF	Original molds machined          New mold machined to fix webbing          Process optimization completed	Drill out alignment holes for better center punching (making parts concentric)          Finish report	None unless changes need to be made to accommodate other parts

Goals:

• Complete prototype and Report 3 components by next Friday (4/11) in case any other issues need to be dealt with
• "Assembly Party" 4/27 (very tentative) or in Tuesday lab

Group Meeting Minutes 3/21 (delayed post)

Our group meeting this week happened remotely due to Spring Break travel plans.

Molds machined:

• IJ1
• IJ2
• TF

To be machined after break:

• IJ3

To do over break:

• IJ2 Process Optimization
• TF Process Optimization
• Check fit of the two parts

All other team members will be out of town and will finish machining and begin process optimization in the first lab after break (4/1).

Easiest molds to remachine if there are problems:

• IJ1 (body)

Problems we foresee: IJ3 (cap) may need mold adjustments to fit with other pieces.

We will prioritize not changing IJ2 because of the difficulty of machining.

IJ2 Process Optimization

Justification and Discussion of Process Optimization

At the start of our process optimization, we realized that the 6 trapezoid voids were filled by the mold rather than being hollow as we had expected. This was an error in our original GCode: we mistakenly milled down the cavity too little. However, our original SolidWorks drawings were correct, so this issue did not require a full mold redesign. We fixed the problem by removing an additional 0.02” everywhere on the original cavity but the protruding trapezoids. The new GCode file name is listed below and reflects our finalized mold design.

For the first half of the iterations of injection molding process optimization, machine alignment caused in issue because our part is so thin. The core and cavity did not line up perfectly, resulting in unfilled gaps at the corners of the center triangles. We fixed this by using looser pins to hold the molds in the machine (0.230” brass pins), as suggested by Dave, and manually aligning the core mold slightly back and down in the machine to fix the alignment problem. When we actually run the process to mass-produce parts, we will do several trial runs at the start to ensure correct alignment of the machine. Additionally, we increased the injection hold pressure profile to ensure the whole part would properly fill—the first 5 pressures were changed to 600 psi as shown in our parameter chart below.

Furthermore, the parts from the early runs of our injection molding suffered from flash. The increase in the pressure profile to compensate for voids worsened the initial flash. To fix this, we both decreased the cooling time, cutting it from 12 to 6 seconds, and the feed stroke, decreasing it from 1 to 0.7 inches.  This resulted in a part that met our design specifications in terms of overall appearance and dimensions. 

The original part, with voids and flash, is shown below.

Finally, because our part is so thin, we concluded that we would need to intermittently spray the molds with mold release during the production cycle. Based on our trials, we determined that we should spray the molds every 5 parts.

Once Kelsey, our team member in charge of the thermoformed part that needs to poke through our trapezoid holes, also finished her process optimization, we tested that our parts fit together as designed. The photo below shows our two optimized parts oriented as planned, confirming that both parts are up to specifications.

Component’s Set-up Sheet

INJECTION HOLD

INJECTION HOLD PRESSURE PROFILE: P7-P16
600	600	600	600	600
400	400	350	350	350
INJECTION HOLD TIME			Z2 = 6
COOLING TIME			Z4 = 6
SET SCREW FEED STROKE			C1 = 0.70

INJECTION BOOST

INJECTION SPEED PROFILE: V12 –V21
2	2.5	3	3.5	4
3.5	3	2	1	0.5
INJECTION BOOST PRESSURE			P6 = 1600

SCREW FEEDING

SCREW FEED DELAY TIME

Z3 = 1

EJECTOR

EJECTOR COUNTER

AZ = 2

EJECTOR PIN LENGTH = 5.695”

TOTAL SHIM THICKNESS = 0.037” + 0.007” + 0.010” = 0.054”

- Hannah and Joanna

Machining IJ2 Molds

Joanna and I machined the core and cavity molds for the IJ2 piece during lab today. Everything turned out nicely.

First we milled the cavity:

 Then we turned the core (leaving the center section for milling):

 And finally, we milled the core with ejector pin holes:

Our finalized molds fit together well.

 We had a lot of fun machining (and wearing goofy, colorful safely glasses):

We expect to test the injection molding on Monday 3/24.

Thank you to both Daves for their help!

Determining Thermoform Plastic Stretch

We are using 0.03” thick white thermoform plastic to make our piece. There are 6 pinwheel sections that will be raised during thermoforming, and each of these sections has a projected area of 0.964in². The total surface area of each raised segment will be 1.2218in² which means that the thickness of the thermoform plastic will decrease on average 21.1%. This means that the average thickness of the stretched plastic is expected to be 0.0237in.

The plastic does not stretch evenly and is expected to be somewhat thick on the top of the extrusion than on the sides. With this in mind, the mold has been constructed with a 0.0225in margin between the mold and expected edge of the extruded part. This is an upper estimate of the ultimate thickness of the plastic along the edges to allow re-machining if necessary once the prototype has been produced and measured.

The extrusions are 0.205in tall as the final height of the extrusions is expected to be 0.23in above the top surface of the mold. The thickness of the plastic on the top surface is expected to come out to about 0.027in and an estimated eventual 1% shrinkage from the initial molded height, the part should be meet the required dimensions at 0.23in.

Goal Maximum Height: 0.23”

Height of mold: 0.205”

Original Thickness of Plastic: 0.03”

Stretched Thickness of Plastic (top surface): 0.027”

Maximum Height (prior to cooling and shrinking): 0.232”

Maximum Height (after cooling and shrinkage): ~0.2296”

-> Expected part dimensions are within the 0.005” tolerance of the designed part dimensions