Blow Molding And Injection Molding: What Is The Difference?

What is injection molding?

The injection molding process employs precision molds and tooling to produce solid plastic parts.

The key to this molding process is in the mold. The custom-designed components are made with great detail from stainless steel or aluminum and built to withstand high temperatures and extreme pressures. Additionally, the two halves of the mold require a high precision match to allow for controlled operation and proper part production.

Once the mold is designed and produced, it can be used for manufacturing operations. The injection molding process begins with the melting of resins or polymers at very high temperatures. The liquid plastic is then injected into the completed mold using high pressure, ensuring that the material reaches all the cavities of the mold. Following the injection stage, the mold is cooled, allowing the plastic to set or harden. When sufficiently cooled, the mold releases the completed plastic part.

What is blow molding?

In contrast to injection molding, the blow molding process employs principles similar to that of glassblowing to create hollow parts. Compared to injection molding, the blow molding’s tooling formation stage is not as critical. However, careful monitoring of the molding process is essential due to the increased potential for the development of wall thinning, air leaks, flash, and streaks.

The blow molding process begins by heating raw plastics materials to temperatures of 350-420 degrees F.  The material is then extruded from the head of the machine as a hollow tube aka parison.  The mold closes around the parison and roughly 80psi is blown into the parison causing it to balloon and take the shape of the mold.  The mold is then cooled, allowing the plastic to “set.”  Once the set time has been reached, the mold opens, and produces the product to the operation.  The part then goes through a degating process which allows inside of the part to be accessible.

The process is different

Blow molding: Blow molding uses gas pressure to inflate the hot parison closed in the mold into a hollow product, or the tube parison is inflated into a tube film without a mold.

Injection molding: injection molding is to melt plastic materials, and then inject them into the film cavity to form.

Raw material is different

Blow molding: The raw materials for blow molding are usually polyethylene, polyvinyl chloride, polypropylene, polystyrene, thermoplastic polyester, polycarbonate, polyamide, cellulose acetate, and polyacetal resin, among which polyethylene is used most.

Injection molding: The raw materials for injection molding are usually thermoplastics or thermosets.

The application is different

Blow molding: Blow molding is widely used in industries such as bottles, jars, baby products, and sporting goods.

Injection molding: injection molding is widely used in mobile phones, laptop computers, a variety of plastic shells, communications, micro-motors, computers, electrical appliances, electronics, toys, watches, lighting, locomotives and other industries.

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