There are a wide range of plastic manufacturing services you might be considering for your needs, and these are so diverse that they’re often split into specific sub-categories. Two of the most popular such processes used today, but which have some significant differences that separate them in several ways, are plastic injection molding and plastic extrusion molding.
At EnviroTech Custom Injection Molders, we’re here to provide our clients with the very best custom injection molding programs in the country, producing components for dozens of completely unique industries. How do our injection molding processes compare to extrusion, and which is right for your needs? Here’s a basic primer.
Injection Molding Basics and Processes
Plastic injection molding refers to a process where molten plastic material is injected into a mold, and then cooled to produce the desired part. This method of manufacturing is known for creating high-quality parts due to its ability to create parts with extremely precise tolerances, tight dimensional accuracy, and scale compatibility.
This process generally requires several steps in order to complete successfully:
- The design of the plastic component itself: This is where you’ll need to determine the size, shape, and features of the desired part. The molding company you work with will also be able to help you with the design process if needed.
- Creating the mold: In order for injection molding to take place, a custom mold must first be created. This is generally done using CNC machining or cast aluminum.
- Loading the mold with plastic: The next step is to load the mold with liquid polymer resin, which will then be injected into the space between two halves of the custom mold and cooled. Once it cools, it’s removed from the mold and can be used as needed.
That’s just a simple explanation of the injection molding process. As you can see, it’s a fairly involved process that requires quite a bit of precision and attention to detail in order to be successful.
Extrusion Molding Basics and Processes
Extrusion molding, on the other hand, also involves transferring molten plastic through a cavity — but rather than being injected, the plastic is simply pushed through the mold using a ram or screw. This type of manufacturing process generally produces less precise parts than injection, though it can be used to create shapes that would otherwise be difficult to achieve with other processes.
To perform extrusion, there are several steps involved:
- The design of the component being created: Extrusion molding can be used to create parts with a wide variety of shapes and sizes, so it’s important to have a clear idea of what you need before getting started.
- Creating the die: A custom die must be created in order for extrusion to take place. This is generally done using CNC machining or cast aluminum.
- Feeding plastic: Powdered plastic or plastic granules will be fed into the die, travelling through a screw-thread pattern and into the cavity of the die.
- At the end of the feeder is the die, which has a small cavity in the desired shape. The molten plastic is pushed through this die cavity and extracted from the end.
- The part is cooled and can then be removed from the die.
What They’re Known and Used For
Among these two processes, injection molding has a far wider range of uses and applications than extrusion. Injection molding can be applied to virtually any kind of plastic product manufacturing, from small, precise parts like medical components to larger items like car fenders.
Extrusion, on the other hand, is limited to products that can be created by pushing molten plastic through a die — meaning that it’s not well-suited for products with intricate designs or many small features. It’s more commonly used for creating items like pipes, tubes, T-sections, and other more-or-less rectangular products.
Another key difference here: While injection molding can produce three-dimensional parts that have incredible detail, extrusion molding is generally limited to two-dimensional parts. It’s more typically used for creating flat, rectangular products like pipes and tubing, rather than complex three-dimensional shapes.
This is a big part of what limits extrusion to products that can be created by pushing plastic through a die — it’s simply not capable of creating the small, intricate recesses and designs required for many finished plastic products.
One small area where extrusion may be a more desirable process for you: If you require atypical cross-sections for your finished product, extrusion may be the better fit. For example, you may need a pipe or tube with an oval shape rather than the standard circle shape that most such products have. Extrusion can produce this kind of variation while injection molding is limited in what it can do here — to be specific, injection molding may require such an intricate die for this process that it’s simply not worth doing.
Strength of Products
Another realm where injection molding is clearly superior: Strength of the finished product. Injection-molded products have greater tensile and compressive strength than extrusion molded ones, due to the nature of the manufacturing process.
This is particularly important if you’re considering extrusion molding for use in a high-stress or safety-critical application, as these types of parts may be required to withstand significant amounts of force or pressure. You’ll want to make sure that your finished product is as durable and resilient as possible, which means using injection molding instead of extrusion if you can.
The cost comparison between plastic injection molding and extrusion can be a bit tricky to pin down, since the factors involved are so significant. Injection molding tends to be more expensive up-front, but it’s vital to consider the value of the finished product when making your decision.
In many cases, injection molding is simply a better process that results in a higher-quality product — and this can be worth the extra cost, particularly if you’re selling that product to customers who value quality over all else.
For more on plastic injection molding compared to a process like extrusion molding, or to learn about any of our injection molding products or company policies, speak to our team at EnviroTech Custom Injection Molders today.