Your Guide to Plastic Molding

By Mark Jansen

Plastics are synthetically produced non-metallic compounds. It
can be molded into various forms and hardened for commercial
use. Plastic molding products can be seen everywhere. Examples
are jars, protective caps, plastic tubes, grips, toys, bottles,
cases, accessories, kitchen utensils and a lot more.

Even the keyboard and the mouse that you use are made through
plastic molding. Even the plastic parts of the chair that you
are sitting on are created this way.

The basic idea in plastic molding is inserting molten liquid
plastic into a ready shaped mold, for example the mold of a
bottle. It will then be allowed to cool, then the mold will be
removed to reveal the plastic bottle.

Plastic molding can also custom-mold a wide variety of plastic
products including: garden pots, cabinets, office trays and
boxes, barriers, barricades and traffic signage and displays for
product and marketing promotions.

If you are planning to go into a plastic molding business, you
should first know the different processes. Choose from a plastic
molding process that fits your budget, your expertise, and your
resources. Here are basic definitions of various methods of
plastic molding.

The Plastic Molding Processes:

1. Injection Molding

In Injection Molding, melted plastic is forced into a mold
cavity. Once cooled, the mold can be removed. This plastic
molding process is commonly used in mass-production or
prototyping of a product. Injection molding machines were made
in the 1930's. This can be used to mass produce toys, kitchen
utensils, bottle caps, and cell phone stands to name a few.

2. Blow Molding

Blow molding is like injection molding except that hot liquid
plastic pours out of a barrel vertically in a molten tube. The
mold closes on it and forces it outward to conform to the inside
shape of the mold. When it is cooled, the hollow part is formed.
Examples of blow molding products are bottles, tubes and
containers.

Equipments needed in setting-up a blow molding business are
relatively higher than injection molding.

3. Compression Molding

In this type of plastic molding, a slug of hard plastic is
pressed between two heated mold halves. Compression molding
usually uses vertical presses instead of the horizontal presses
used for injection and blow molding. The parts formed are then
air-cooled. Prices of equipments used for compression molding
are moderate.

4. Film Insert Molding

This plastic molding technique imbeds an image beneath the
surface of a molded part. A material like film or fabric is
inserted into a mold. Plastic is then injected.

5. Gas Assist Molding

Also called gas injection molding is used to create plastic
parts with hollow interiors. Partial shot of plastic is then
followed by high-pressure gas to fill the mold cavity with
plastic.

6. Rotational Molding

Hollow molds packed with powdered plastic are secured to
pipe-like spokes that extend from a central hub. The molds
rotate on separate axes at once. The hub swings the whole mold
to a closed furnace room causing the powder to melt and stick to
the insides of the tools. As the molds turn slowly, the tools
move into a cooling room. Here, sprayed water causes the plastic
to harden into a hollow part. In this type of plastic molding,
tooling costs are low and piece prices are high. Cycle time
takes about 40-45 minutes.

7. Structural Foam Molding

Structural foam molding is a process of plastic molding usually
used for parts that require thicker walls than standard
injection molding. Inserting a small amount of nitrogen or
chemical blow agent into the plastic material makes the walls
thicker. Foaming happens as the melted plastic material enters
the mold cavity. A thin plastic skin forms and solidifies in the
mold wall. This type of plastic molding can be used with any
thermoplastic that can be injection molded.

8. Thermoforming

In this plastic molding process, sheets of pre-extruded rigid
plastics are horizontally heated and sucked down into hollow
one-piece tools. When the hot plastic solidifies, its shape
conforms to that of the mold.

Tooling costs are usually low and piece prices vary on the
machinery.

Plastic molding is a very technical process. It needs experts in
this type of manufacturing business for it to be competitive in
the market. Therefore, a very scientific and systematic study
should be first made before going into this endeavor.

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