How do you determine what type of plastics manufacturer you should work with to design your custom plastic part? Forming plastic parts for industrial, commercial or medical uses requires different processes depending on the shape required and application of the product. Here’s the difference between plastic extrusion and injection molding.

Extrusion and Injection Molding Basics

Simply put, the EXTRUSION process is required to create continuous linear, two-dimensional shapes.

INJECTION MOLDING produces three-dimensional shapes that do not remain constant in a parallel line.

Injection Molding Process

This production method is basically based on the molten die-casting method. Heated liquid fills a mold followed by cooling to set and eject a piece as a solid shape. Examples: chess piece, plastic comb, plastic plate or cup, or a three-dimensional shape with openings such as a plastic basket or crate.

Extrusion Process

During the plastic extrusion process, the material is heated and is forced through a shaped cut in a metal plate creating a continuous form that can be stretched and then cooled to set. These linear products can also be cut to length into plastic parts once cooled. Examples include industrial piping, medical device tubing, synthetic filaments, plastic rails, plastic sheeting and plastic drinking straws (coextrusion). Check out “What is Extrusion” for more details.

End Product Differences and Advantages

While the final shape required for a part often dictates the process used, both extrusion and injection molding have their own advantages.

INJECTION MOLDING typically has a higher, initial design cost due to the complexity of the mold structure. Its cyclical production, however, typically creates a finished piece that often does not require further assembly or secondary processing.

The EXTRUSION method can create complex cross-sections such as multi-lumen tubing used in medical devices or food processing. The surfaces of extruded materials are smooth and do not require post-production “clean-up.” Extrusion is ideal when a variety of lengths of the same profile shape is required. By producing a stock product with a continuous production process and cutting to length post-process per demand, setup and die/design costs are reduced for similar items.

Need help?

While the information above provides basic guidelines, the experts at PBS Plastics can assist you in determining the most efficient and cost-effective process for your plastic part supply needs.