MAS 863
Dodecahedra
So this was a very fun assignment, but a difficult one. Our goal
was to create an injection molded "construction-kit", a set of LEGO-like
pieces which could be assembled in interesting ways.
When injection molding, the work is in the design of the mold --
once the mold is made, it can be used over and over again to create
hundreds of the same kind of part; thus injection molding (which is,
of course, how LEGO's are actually made) is very appropriate for
making this kind of toy.
I chose to make a "Dodecahedron construction kit" -- a set of plastic pieces
which were capable of linking together to assemble into a dodecahedron --
which looks kind of pretty and you can put it on a shelf.
The work of injection molding, again, lies in the construction of the mold, and
the suggested method for creating molds was the NC mill, which is controlled by
files output from I-DEAS, a massive program of infinite power and complexity.
So the first (and arguably, most difficult) part of this project was to construct
a model of the mold in I-DEAS -- Anyone not experienced with using I-DEAS before
this project quickly became experienced at it!
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1. |
First a dodecahedron is made in I-DEAS and shattered
into 60 identical pieces. |
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2. |
Flanges are added to the object to make it able to connect
correctly to others like it. |
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3. |
Finally the molds are made, depressions in each mold
shaping out the object. |
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With the model complete, I-DEAS can output a control file to direct the mill, and
thus the second part of the project takes place in the machine shop.
One takes a rectangular slab of aluminum, smoothes it, and then runs the
I-DEAS control file through the mill, watching it magically carve the right shape
out of the material.
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4. |
The mill in the process of slowly milling out the first mold.
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5. |
Both sides of the mold are completed, and placement holes
drilled in precise alignment. |
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6. |
Smoothed and faced, the two halves snap together
and the mold is finally done. |
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If done right (which for me involved several attempts!) the two mold-halves
snap together and the channel is perfectly aligned. The injection machine
can now inject high-pressure molten plastic into the mold hole. Inside,
the plastic fills the mold and quickly solidifies, and when the mold is
pulled apart a perfectly shaped little plastic piece falls out.
This is the fun part of injection molding. Over and over again,
you stick the mold into the "Mini-Jector" injection mold machine, push the button,
and hear that satisfying Thunk as another
load of plastic fills the mold.
Pull the piece out, toss it in a box, and repeat.
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7. |
A close-up of a single plastic piece from my injection mold.
In the background, an assembled dodecahedron can be seen.
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8. |
Two assembled dodecahedra, next to the mold that created them. Each
dodecahedron is made of 30 of the little plastic pieces.
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While I had to run the mill several times before it finally made my mold
correctly, I had the lucky experience that, once my mold was completed,
my pieces worked right away! They assembled into dodecahdra with no trouble!
Many people told me they were impressed,
and seemed to enjoy snapping my pieces together.
:)
The one thing that could be better is that the pegs holding the pieces together
were a little tight -- one of these days, I should remill
the mold with slightly larger spaces for the pegs to go into....
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