In 1868, John Wesley Hyatt developed
the first plastic injection mold, and the plastic injection moulding process. He
used the plunger method to successfully inject hot, liquid celluloid, often
called the first thermoplastic, into a split-die mold. This process was little changed until James Hendry built the first
screw plastic injection mold in 1946. Today, nearly all industrial and medical plastic
injection
moulding processes use the screw method.
Plastic moulding is a very methodological and technical
process. Thus it needs experts in this type of manufacturing business for it to
meet the safety terms and to be competitive in the market. A very scientific
and systematic mechanical study is first made before going into this endeavor.
Here I have discussed some known plastic injection moulding process that can
help you to understand the various ways it is done for industry specific
plastic products.
1. Injection Moulding.
Examples of
applications: Medical plastic laryngeal mask
components, laboratory products, extraction systems,
toys, aircraft undercarriage components, kitchen
utensils, bottle caps, and cell phone stands.
In Injection Moulding, melted plastic is forced into a mold cavity. Once
cooled, the mold can be removed. This plastic injection moulding process is
commonly used in mass-production or prototyping of a product. Typically this
process is used to produce plastic mouldings where the relatively high tooling
cost can be justified by low unit costs and tolerances which cannot be achieved
by other moulding processes.
2. Blow Moulding.
Examples of
applications: Automotive, Toys, Recreational, tubes and containers,
Medical, Housework Appliances
The process is divided into three steps: injection, blowing
and ejection. Blow moulding is like plastic
injection moulding 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. Equipments needed in setting-up a blow moulding business are relatively
higher than injection moulding.
3. Compression Moulding.
Examples of
applications: Automotive exterior panels especially for commercial
vehicles, Radio & appliance knobs, ash trays & electrical parts.
In this type of plastic moulding, a slug of hard plastic is pressed between
two heated mold halves. Compression moulding usually uses vertical presses
instead of the horizontal presses used for injection and blow moulding. The
parts formed are then air-cooled. Prices of equipments used for compression moulding
are moderate.
4. Film Insert Moulding.
Examples of applications: FIM can be
used to apply clear scratch-resistant hard coats, logos, text and graphics in
any color or combination of colors to plastic parts prior to injection molding.
This plastic moulding 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 Moulding.
Examples of
applications: Flat panels for office equipment, Computer enclosures,
Furniture, i.e. tabletops, Automotive panels, Domestic appliances - e.g.
fridges.
Also called gas injection moulding 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 Moulding.
Examples of
applications: All kinds of plastics mostly hollow Plastic Parts.
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 moulding, tooling
costs are low and piece prices are high. Cycle time takes about 40-45 minutes.
7. Structural Foam Moulding.
Examples of
applications: Typical products are large trash containers, freeway sand
safety containers and in-ground housing for water systems.
Structural foam moulding is a process of plastic injection moulding usually used
for parts that require thicker walls than standard injection moulding.
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 moulding can be used with any thermoplastic
that can be injection molded.
8. Thermoforming.
Examples of
applications: Clamshells, Trays, Blisters, Displays, Guards, Covers, Totes,
Shields, medical plastics
