What Is the Difference Between Plastic Injection Molding and Extrusion?

Plastic injection molding and extrusion processes are both used to create a wide range of products, from consumer goods to industrial components. There are differences between the two processes that can make one preferable over the other depending on the end-use application. Below is an in-depth comparison of plastic injection molding and extrusion:

What Is Plastic Injection Molding?

Plastic injection molding involves creating plastic parts by injecting heated plastic material into a mold to shape and solidify it. This process can be used across many industries to create consumer and industrial products. They include toy blocks, medical devices, automotive parts, and electronics.

The process begins with creating the desired molds from metal alloys such as stainless steel or aluminum. Once the molds are ready, they are loaded into the injection molding machine. A hopper feeds granulated plastic material into the heated barrel.

The manufacturer mixes the material and then heats it until it is malleable. Engineers inject the material under pressure into the mold cavity through an actuating ram or screw-type plunger at high speed, forming the part in the desired shape and design.

When the part cools down, it becomes solid again. The manufacturer can enject plastic material from the machine before post-processing steps such as painting, trimming, or assembly.

What Is Extrusion?

The plastic manufacturer can use extrusion to create uniform, continuous profiles and shapes out of different types of thermoplastics. They place plastic pellets or granules into the extruder and heat them until they become malleable.

The molten plastic is then squeezed through the die. This is to form a desired shape or profile, which then goes onto a cooling conveyor. After cooling the plastic, they are cut into lengths.

The manufacturers use an extrusion process to create products such as pipes, straws, and window frames. They can also create door frames, tubing for automotive drive train components, and plastic signage.

Key Differences Between the Processes

Complexity

Injection molding can be more complex than extrusion. The production process may require creating an intricate metal tool with a cavity that matches the shape of the desired product. The tool should be able to withstand high pressure, temperature, and repeated use throughout the production cycle.

Extrusion often only requires a single screw that melts the plastic pellets and pushes them through a die with the desired shape. Injection molding can be suitable for producing more complex parts with multi-level designs. Extrusion can be better suited for simpler, continuous shapes.

Production Speed

Injection molding often has a higher production speed than the extrusion process. Injection molding can produce up to thousands of parts in a single cycle. Extrusion can only produce one part at a time. The injection molding machines are also more automated with robotic arms, allowing for increased speed and efficiency.

Injection molding may require shorter cooling times between cycles, leading to faster completion times. Extrusion can have a longer lead time, especially if the processes include extruded tubing or complex profiles.

Product Size

Injection molding can be more suited for producing small and complex products, such as gears and housing parts. Extrusion can produce longer and wider products much faster than injection molding. With injection molding, the production of larger products could be slower and has a higher risk of defects.

Plastic Manufacturing Processes

Plastic injection molding and extrusion differ in material utilization, product size, and equipment. You should consider these differences when choosing the manufacturing process that best suits your product.

Injection molding may offer better material efficiency and can be more suited for producing small and complex products. Extrusion could be more efficient for large-scale, continuous production runs of wider and longer products.

By choosing the correct process, you can take advantage of the best pricing and manufacturing options while maximizing efficiency and meeting customer needs.

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