5 Common Plastic Molding Processes

5 Common Plastic Molding Processes

Plastics are being used to make everything from human body parts to automotive parts. Each application requires a special manufacturing process that can mold the part based on specifications. To help understand the different requirements, here is a brief overview of the different types of molding along with their advantages and applications.

5 Common Plastic Molding Processes

Blow Molding – Perfectly suited for hollow objects, like bottles.
The basic steps used in glass blowing are also found in blow molding. A heated plastic mass is inflated by air. The air pushes the plastic against the mold to form the desired shape. Once it’s cooled, the plastic is ejected.

The blow molding process is designed to manufacture high volume, one-piece hollow objects. If you need to make a lot of bottles, this process is perfect for you. Blow molding creates very uniform, thin walled containers and in an economically way.

Injection Molding – Suited for high-quality, high-volume part manufacturing.

Injection molding is one of the most versatile of all molding techniques. The presses used in the process vary in size and are rated based on tonnage or pressure. Larger machines can injection mold car parts, while smaller machines can produce very precise plastic parts for surgical applications. In addition, there are many types of plastic resins and additives that can be used in the injection molding process, increasing its flexibility for designers and engineers.

Extrusion Molding – Well suited for long hollow formed applications like tubing, pipes and straws.

While other forms of molding uses extrusion to get the plastic resins into a mold, this process extrudes the melted plastic directly into a die. The die shape, not a mold, determines the shape of the final product. The extruded “tubing” is cooled and can be cut or rolled for shipment.

Compression Molding – Suited for larger objects like auto parts.

Compression molding says it all. A heated plastic material is placed in a heated mold and is then compressed into shape. The plastic can be in bulk, but often comes in sheets. The heating process, called curing, insures the final part will maintain it integrity. As with other molding methods, once the part has been shaped, it is then removed from the mold. If sheeting plastic material is used, the material is first trimmed in the mold before the part is removed.

The method of molding is very suitable to high-strength compounds like thermosetting resins as well as fiberglass and reinforced plastics. The superior strength properties of the materials used in compression molding make it an invaluable process for the automotive industry.

Rotational Molding – Suited for large, hollow, one-piece parts.

This process uses high temperatures and rotational movement to coat the inside of the mold and form the part. The constant rotation of the mold creates centrifugal force forming even-walled products. Because it is ideally suited to large hollow containers, such as tanks, it’s not a fast moving process. However, it is a very economical process for particular applications and can be cheaper than other types of molding. Very little material is wasted using this process, and excess material can often be re-used, making it an economical and environmentally viable manufacturing process.

Each type of molding has its strengths and weaknesses. Designers and engineers need to understand these differences and the production options available. Design-Tek will consult with you on what a specific project should be able to provide as well as additional insights into the applications and materials that are best suited to an individual project.