Injected Molded Part Presentation
These are the core (left half) and cavity (right half) mold
of our ‘triangle insert’ piece. This piece is going to be snap fit into the
main body and will make up the main triangle shape of the Aperture Science
logo. The large triangles in the core mold on the left will be the triangles in
the logo while the small triangles on the cavity mold on the right are meant to
thin the part so that it cools more evenly. The small indents around the
outside of the cavity mold are to make runners for our ejector pins to push off
of.
To calculate our mold dimensions our first reference was the
inner diameter of the body piece. We needed to make sure this would be able to
snap fit in so we sized this piece’s outer diameter to be 0.01” larger than the
inner diameter of the body. Then we had to scale the mold to allow for
shrinkage. We measured the size of dimensions on a mold from a past year for a
part of similar volume and thickness. We found a part with a mold diameter of
2.4” and an average part diameter of around 2.36. After measuring a few other
dimensions on the mold and on the injection molded parts we determined that the
parts shrank by about 1.5%. We scaled our mold up by this amount accordingly
before creating the tool paths in Mastercam.
All of the work for this mold was done on the mill. The core
took about 1 hour and 20 minutes to machine including tool switching time and
the cavity took around 45 minutes. The longest process on the core mold was
machining the triangle holes. Each has a 1/16” radius in each corner which was
first drilled with a 1/16” end mill, then the pocket was machined with a 1/8”
end mill and remachined with the 1/16” end mill to clean up anything that had
been left.
Manufacturing Time
The machining time require to produce our yo-yos includes
the manufacturing time for the molds, each injection molded and thermoforming
piece in the final production run and time due to process optimization. We
assumed that the time to change tools is zero in the machining process. Also,
we assumed that the process optimization for thermoforming parts is less than
that of injection molding parts. The time to produce each mold was taken from
Mastercam’s toolpath times. The spider cavity mold will take 6 minutes while
the core will take 154 minutes for a total of 160 minutes or 2 hours and 40
minutes. The triangle insert cavity will take 46 minutes while the core will
take 105 minutes for a total of 151 minutes or 2 hours and 31 minutes. The body
cavity mold will take 4 minutes while the core will take 8 minutes for a total
of 12 minutes.
To find
the cycle time for each injection molded piece, we used the typical cycle of
injection molding from lecture with incorporating each pieces individual
estimated cooling time. In order for a piece to be cool enough to inject, the
thickest part of the piece must be at a temperature where there is no viscous
rubbery flow of material and the polypropylene exhibits plastic material
behavior. We used AutoDesk Simulation Mold Flow Advisor to estimate the cooling
time of each part made for our yo-yo assembly. The
simulation provided us with cooling times that we added into our cycle time for
each piece. The body piece will take 45 seconds, the spider 16 seconds, while
the triangle insert will take 40 seconds to produce one of. Multiplying these
out to produce 50 yo-yos, 100 of each component will need to be produced.
Assuming no time lost to change tools, the production run will take 75 minutes,
27 minutes, and 67 minutes respectively for the pieces above. For the
thermoforming Portal insert, we expect a time to complete one piece in the
range of 15-60 seconds. For 100 of them, the estimated time is between 25-100
minutes.
The
total time estimated to complete the yo-yos is the mold fabrication, total
production run for the injection molded pieces plus the estimated time for
thermoforming and the time to assemble the yo-yos. Our total time estimated is between 11 hours 7
minutes to 12 hours 22 minutes depending on thermoforming time.
Process
|
Time to Manufacture
|
Final Production Run (time x 100) Makes 50
yo-yos
|
Process Optimization
|
Body
Mold Fabrication
|
12 minutes
|
||
Spider Mold Fabrication (cavity + core)
|
160 minutes
|
||
Triangle Insert Mold Fabrication (core +
cavity)
|
151 minutes
|
||
Portal Insert Thermoforming Mold
|
|||
Body Injection Molding
|
45 seconds
|
75 minutes
|
60 Minutes
|
Spider Injection Molding
|
16 seconds
|
27 minutes
|
60 Minutes
|
Triangle Insert Molding
|
40 seconds
|
67 Minutes
|
60 Minutes
|
Portal Insert Thermoforming
|
25-100 minutes
|
30 Minutes
|
|
Assembly
|
180 seconds
|
150 minutes
|
120 Minutes
|
Total Time (Mold manufacturing time + Final Production
Run+Assembly)
|
642 minutes
|
Manufactured Molds
Triangle Insert
Triangle Insert Mold
Triangle Insert Core Mold Being Machined
Potential rework machining for the triangle insert mold may be needed in order to get the snap fit to work correctly between pieces.
Below is a movie of the mold being machined
Body
Body Cavity Mold, Body Core Mold, Body Molds
Potential rework machining may be needed on the body core mold in order to get the snap fit to work between pieces. The size of the core diameter may need to be smaller due to shrinking of other pieces.
