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 PIN LENGTH = 5.695”
TOTAL SHIM THICKNESS = 0.037” + 0.007” + 0.010” = 0.054”
- Hannah and Joanna
