About Injection Plastic Molding

Plastic Injection molding (Plastic injection moulding) is a manufacturing technique that involves forcing melted plastic into a predefined mold to create a part with the desired features. This process enables high volume production of parts while maintaining a tight tolerance. The type of material being molded affects the tolerance able to maintain as well as the surface finish of the final component. When using plastic injection molding for manufacturing, the part must be designed to be compatible with the process. Some features can greatly increase the cost of the mold / parts or make the part unable to be molded. Some of these features include overhangs and undercuts. In addition, to facilitate removal for the mold, vertical walls will typically require a draft.

 

Injection Molding Process

The actual process of injection molding is quite simple. In a “liquid” form is injected into a metal mold under high pressure where it is allowed to solidify. Once it hardens enough it is ejected from the mold and the mold is refilled for the next part. Most common types of plastics used are thermoplastics and thermosets. In general, the process of both is the same. The major difference is that thermoplastics molding typically uses raw plastic pellets which are melted prior to injection where as the thermosets use two different chemical compounds which when mixed, harden into the final product.

 

Injection Molds

The molds and part design are one of the most critical components of successful injection molding. They are expensive to manufacture and add substantial upfront cost. When using a thermoplastic, the mold size must compensate for the shrinkage that occurs during the cooling process. It is not unusual for several modifications to be made to the mold to get the dimensions of the final part to be within specifications.

Molds can be made from many materials but most common are aluminum (soft molds) and Stainless Steel. Which material to use mainly depends on how many parts the mold is to produce before being scrapped and the material being molded.

Other factures to consider when designing a mold is where the material will be injected, runners and spacing between parts if a multi cavity mold, air vents to allow gas to escape, ejector pin placement.

You can read reviews for the best plastic injection molding companies to help find the best injection molder for your project. 

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