Types of Plastic Molding Processes

Plastic molding makes this product.

Plastic molding is the process of shaping plastic using a mold. It started in the late 1800s, making products like combs and buttons. There are many different type of molding techniques to use for making plastic products. The methods range from simple molding for common house products to complex molding designs and flexibility for surgical or cosmetic products. Cost is also a factor in deciding what type to use.

Blow Molding

Blow molding is used to make items such as plastic bottles for beverages and cosmetic product containers. The plastics are produced at high rates with this molding method. The process combines extrusion and thermoforming techniques. The machines heat plastic resin, made with a high or low density polyethylene, in closed molds to make the desired shape of the mold cavity.

Injection Molding

The most common form of molding plastic is injection molding. It produces three-dimensional, solid parts with a moderate to high strength. Complex shapes can be produced with this type of molding. The advanced molding techniques are insert molding and reaction molding. Plastic is melted and injected into a mold cavity. The plastic is cooled down. After cooling, the mold is ready to be opened and the plastic form removed.

Dip Molding

The process is the simplest means of molding plastic. It produces a large quantity of parts and product at a low cost. Some examples are surgical gloves, condoms and handles for tools. First, the metal molds are surface prepped to make the part easier to be stripped from the mold when it is dry. The part is dipped into a polymer vat for a dip coating or a molding. Flexible products get a fabric layer applied between the polymer coats. Objects are then buffed and prepped so the plastic coating stays firmly in place.

Rational Molding

Rational Molding is a product formed from a fine powder consisting of a molten polymer inside a three dimensional mold. It rotates in a heated chamber. When the mold is turning, the polymer sticks to the sides of the mold and becomes a hollow part. The parts are uniform in shape and very high strength quality.

Structural Foam Molding

This process is used for parts that need thicker walls than the standard molding processes. A chemical or nitrogen agent is added to the plastic material. This allows the walls to become thicker. When the melted plastic enters the mold the foaming occurs.

References

• PlasticsTech: Processes, Molding
• IQS Directory: Plastics, Plastic Molding & Plastic Suppliers