Plastics Exercises

As part of my Materials Molding and Forming Course (TEL 204), a course with a focus on plastics work, I molded and formed many different plastic materials in various ways. My artifacts from this class are shown and described below.

The the artifacts shown on this page are:

Rotationally Molded Elephant
Expanded Polystyrene Bead Elephant
Blow Molded Coin Container
Plastisol Coaster and Coin Purse
Injection Molded Artifacts
Fiberglass Candy Dish and Soap Dish
Vinyl Heat-Sealed Pouch
Plastics Repair Artifact

Rotationally Molded Elephant

This low-density polyethylene (LDPE) elephant was created using rotational molding. This is where a mold, charged with LDPE powder and pigment is rotated constantly while it is heated and then cooled in a special oven. The powder coats the inside of the mold and then cools in-place.

Expanded Polystyrene Bead Elephant

This elephant was created using the same mold as above, but using hot-water-expanded polystyrene (PS) beads. When the beads are heated, they soften and the pentane stored inside of them during their manufacture expands. The soft beads then cohere and hold their shape when cool.

Blow Molded Coin Container

This coin container was produced using blow molding. In blow molding, a tube of hot plastic (in this case LDPE) called a "parison" is extruded downward. A mold is then clamped around the parison, and air is blown into the top of the parison, pressing the plastic against the mold and cooling the plastic simultaneously.

Plastisol Coaster and Coin Purse

The coaster to the right was created using conventional plastisol casting. This is where plastisol (a slurry of plastic particles and some volatile solvent) is poured into a mold and baked. In the process of baking, the solvent dissipates leaving the plastic (in this case polyvinyl chloride, or PVC) behind.

The below money pouch is an example of plastisol dip casting. This is where a mold is pre-heated, dipped into liquid plastisol, and then placed back into an oven to cure. In this case the final product was cut off of the mold, producing the desired slit, but in some cases the product may be peeled from the mold or left on—such as in the case of tool handles.

Injection Molded Artifacts

These items were created using small injection molders. A charge of molten plastic is injected under pressure into a clamped mold. Note that the screw driver has a metal insert which is placed into the mold before it is clamped.

Fiberglass Candy Dish and Soap Dish

This glass-reinforced polyester matrix in the shape of a "candy dish", was created by laying up woven fiber-glass and polyester resin in a waxed cardboard mold.

To the right is shown a "soap dish". This was my first significant foray into modeling using Fusion 360 with the intent of ultimately producing a part. I modeled the dish first, and then used the model of the dish to produce a negative model which I used to create tool-paths. I then used a Techno Router to cut a form out of medium-density fiberboard (MDF), which I then used to layup a fiberglass composite.

The actual artifact has some flaws which I believe stemmed primarily from mold-design problems and rookie layup errors—problems which could be solved with more prototypes and more production runs.

Finally, I acknowledge that a fiberglass soap dish is not really a product anyone might want, but it was an excellent design-build experience for me nonetheless.

Vinyl Heat-Sealed Pouch

This heat-sealed vinyl safety glass pouch was created using clear vinyl sheet and a heat sealing machine. The pattern was laid out ahead of time on card stock.

Plastics Repair Artifact

This piece of high density polyethylene (HDPE) was hot-air welded back together.

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