Extrusion Vs Injection Molding

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Injection molding and extrusion molding are two prominent plastic molding processes used throughout the industrial and manufacturing sectors to create items of various shapes and sizes. Both approaches offer distinct advantages based on the products and the consumer. Let’s look at the distinctions between injection molding and extrusion molding to help you decide which is ideal for your manufacturing needs.

Injection Molding

Micro-injection molding machine
Source: Pinterest

Plastic molding is generally accomplished through two processes used by plastic producers. Plastic injection molding is the first method, in which producers “inject” molten polymer material into a mold and allow it to settle and cool into a specified form. Manufacturers push molten plastic through a die to generate the required form in the second process, plastic extrusion.

This is among the most used ways of molding polymers into 3D forms. It is founded on the molten die casting process and comprises a clamping unit and an injection unit.

The plastic resin is placed in the hopper, which causes the plastic out from the feed portion to be released into the compressing area, where friction heat is applied. A reciprocating screw pushes the plastic through a long chamber. Melting, or molten plastic, is pushed via the injector into a sealed, cooled/hot mold. The melt may be readily shaped into the mold’s desired form and size.

Injection Molding Steps

  • Plastic pellets or granules are initially loaded into a feed section through a hopper.
  • Inside the feed portion, these loaded plastic grains are crushed. The granules melt due to frictional heat, creating a viscous liquid known as melt.
  • The meld is routed from the feed part to an injector. This injector might be of several sorts.
  • When the injector is turned on, molten material is injected into the die cavities. While consuming the form, the liquid substance grows inside the die. During the cooling process, the material in the mold hardens.
  • When the die has cooled, die ejectors open it and a product of the required form is produced.


The following are the benefits of this procedure:

  • Used in the creation of three-dimensional things.
  • Waste was reduced and the material was recycled.
  • Capable of producing fine details and complicated geometry.
  • Improves the part’s strength once it has been molded.
  • The ability to employ various varieties of plastic at the same time.

Extrusion Molding

High-grade t-slot extrusion profile
Source: Pinterest

This method drives things through a die to form shapes with consistent cross-sections such as window parts, drinking straws, pipelines, and seals. This approach is used to create two-dimensional shapes. The extrusion machine’s motor spins a screw that pushes plastic via a heater.

The polymer granules melt into fluid, which is then forced through a 2D die open tool. This pushes the materials into a hollow tube based on the die’s particular geometry. After chilling, the material solidifies into a tube shape. This item is now waiting to be cut into the desired sizes.

Steps Involved in Extrusion Molding

  • First, granular plastic or granules of plastic are introduced into the feeder.
  • For uniform distribution, these granules pass through a screw-thread design from the feeder to the die. The intake is headed by putting heat jackets on the outside of the casing. These grains melt into a thick, uniform liquid as a result of the produced heat.
  • A die with a tiny cavity of the desired form is connected to the feeder’s end. The molten material is forced through the die cavity and expelled from the other end.
  • The result takes on the required form when the extruded portion cools.


The following are some of the benefits of the extrusion process:

  • Hard and fragile materials are shaped.
  • It is advantageous for the production of unusual cross-sections.
  • Ensures a smooth finish to the finished product.
  • Changes are made to the item after it has been taken from the extruder.
  • Complex forms with various thicknesses, textures, and colors may be created.

Key Differences Between Extrusion and Injection Molding

Historic Differences

an old industrial machine
Source: Unsplash

Among industrial producers, injection molding and/or extrusion processes are defined to create items of various forms and sizes. The injection molding technique is built on the melted die-casting technology. The clamp and the injection unit comprise the injection-molding unit. Injection molding, as opposed to extrusion, produces three-dimensional structures.

In 1795, Joseph Brahman patented the first hydraulic press. However, the method was more thoroughly refined in 1820, when Thomas Burr invented the first hydraulically driven press for manufacturing firms. The method was not developed until 1894 to incorporate brass and metal alloys for non-continuous extrusion of final components. The injection molding method as we recognize it now would be eventually created in the 1930s.

In terms of plastic extrusion, this method was first used to process rubber in 1836. This is a technique in which molten plastic or a variety of alternative materials are constantly forced into a two-dimensional die aperture by feed screws. The molten form is then passed through a succession of templates or blocks, where it preserves the correct shape as it cools. 

The completed result from the extrusion process has a two-dimensional shape that is continuous in length. Extrusion creates linear forms that may be cut to different lengths and/or notched, punched, or otherwise produced, frequently while the process is running.
Extrusion and injection molding both have benefits. The capacity to generate complicated cross-sections is one advantage of employing the extrusion technique over other approaches. Furthermore, as compared to other techniques, both rigid and soft materials may be molded into any shape, and the final products have a flawless surface finish. There is little waste in both the injection molding and extrusion operations since the debris may be recycled again.

End Product Differences

Plastic molded products
Source: Unsplash

Because of the intricacy of the mold construction, injection molding generally has a higher initial design cost. Its cyclical manufacturing, on the other hand, usually results in a completed component that does not require additional assembly or secondary processing.

Extrusion is capable of producing complicated cross-sections, including such multi-lumen tubing used in medical equipment or food processing. Extruded materials have flat surfaces that do not necessitate post-production “clean-up.” 

When a range of lengths of the same profile shape is required, extrusion is appropriate. Setup and design expenses for comparable products are minimized by creating a stock product with a continual production chain and cutting to length post-process per order.

In a nutshell;

  • Injection molding is best suited for three-dimensional product development, whilst extrusion molding is best suited for two-dimensional product development.
  • Injection molding is the oldest method of plastic manufacture, whereas extrusion is relatively recent.
  • Extrusion can produce irregular cross-sections. Injection molding, on the other hand, may necessitate the use of complex dies to accomplish the same result.
  • Injection molding gives items strength, but extruded products are weaker.
  • Because of the high cost of dies, injection molding is deemed pricey. Nonetheless, due to its efficiency, this technique is the most commonly used.

The Bottom Line

The choice between plastic extrusion and injection molding does not have to be a contest. Both of these technologies serve distinct functions and have distinct advantages, and both are beneficial to plastic producers. Extrusion cannot generate the intricate 3D forms that injection molding can, nor can injection molding produce the unusual cross-sections that extrusion can. Each technique has a distinct position in the plastic production process.
With that knowledge, we believe you’re well off on your journey to understanding the plastic molding process and can choose a molding form or manufacturer wisely. If not, do remember to read again, for valuable insights into the issue.

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