Thermoplastic Molding: An Overview

Home Thermoplastic Molding: An Overview

You might have heard of the term thermoplastic molding and are wondering what it’s about. Or maybe you’ve not heard of it before, but are curious about the various forms of molding that are relevant to the manufacture of the products you deal with. This guide walks through the details of thermoplastic molding, giving information on the very details that make the process efficient.

Definition of Thermoplastic Molding

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Thermoplastic injection molding is a production method that uses plastic resin to insert into a pre-made mold to generate completely functional parts. Rapid injection molding is a subcategory of thermoplastic injection molding that is best used for fine-tuning prototypes before a product is approved for manufacturing. Another subgroup, production injection molding, is best suited for large quantities of goods.

How the Process Works

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As previously said, thermoplastic injection molding entails injecting a resin into an already constructed mold to manufacture pieces in the mold’s shape. But first, let’s take a deeper look at how the system works:

  • A CAD file is used to create a mold. It takes time to produce the mold, thus this is the time-consuming phase of the procedure. Molds of this type are generally constructed of aluminum or steel.
  • The thermoplastic resin is poured into the mold once it has been produced, and the component is then allowed to cure and solidify. Before being released into the mold to cool and cure, the material would be first fed into a heated nozzle.
  • After curing, the component is taken from the mold, and the procedure is repeated until the part run is finished.

This method, also known as “thermoplastic molding” or “thermoplastic injection molding,” involves the injection of molten polymer (thermoplastic substance) into a mold at increased pressure. The injection tools are created using a highly particular approach. Aluminum (rather than the more typically utilized steel) provides for lower investment costs since it can be produced more quickly. 

The cost of the mold is determined by the number of cavities and the intricacy of the forms of the molded item. Following the creation of the mold, the plastic material is added under constant pressure by the injection molding machine.


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Every manufacturing method has advantages and disadvantages. Before we get into the drawbacks, here are a few of the benefits of thermoplastic injection molding:

  • Accuracy: Thermoplastic injection molded parts may be manufactured with pinpoint accuracy, giving them a significant edge over alternative prototyping techniques such as 3D printing. (Further on this later, when we examine design issues.)
  • Surface Finish: Thermoplastic injection molding may be performed using a wide variety of every day and engineering-grade materials. The method may also produce components with immaculate surface finishes, allowing the manufacturing process to produce not just prototypes but also small- and large-scale production runs. The manufacturing method can also provide rough or pebble-grained surface finishes.
  • Speed: Thermoplastic injection molded parts are generally turned around in a matter of days. When used for prototypes, it helps developers to make design modifications rapidly, allowing it to reach the market sooner. If the technique is utilized for production, runs can be finished in days, allowing products to be on shop shelves sooner. The time required to create the mold is the most time-consuming element of the injection molding process. Molds, on the other hand, maybe made to fine-tune samples and then utilized again for a production run.
  • Manufacturability predictor: We’ve already explored how thermoplastic injection molding may be used for prototyping. And here’s why: not only can components be finished and switched around in days, but the two advantages of the technology described above, precision and exterior finish quality, make the process a fantastic forecast of manufacturability. Often, developers would buy multiple early prototype runs using alternative technologies, then utilize thermoplastic injection molding to confirm product design before moving forward with manufacture. Because pieces may be made from a variety of resins, designers will also experiment with surface treatments and materials.


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As previously said, every manufacturing method has advantages and disadvantages. Here are some of the disadvantages of thermoplastic injection molding:

  • Cost: The most significant disadvantage of the procedure is undoubtedly its expense. This is due to the high cost of the tooling and the time required to make the mold, which means that developers will be responsible for these initial tooling expenses.
  • Speed: We also cited “speed” as a benefit of thermoplastic injection molding; however, if speed is a benefit or a disadvantage depends on what thermoplastic injection molding is utilized for. For example, if it is used for initial designs, speed is a disadvantage. Why? Because it is a considerably slower and far more expensive procedure when compared to alternative prototype technologies such as 3D printing. 3D printing, on the other hand, takes hours to manufacture one-off items, whereas thermoplastic injection molding could do so in days due to tooling.
  • Flaws: As with any manufacturing process, thermoplastic injection molding can result in defective components. These can be caused by several causes, such as tooling flaws, poor product architecture, thermoplastic resin substance which is too hot, injection rates were either too fast or slow, a shortage of ventilation in the tooling, garbage on the tool surface, and a lack of appropriate cooling surrounding the tool.


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With the proper material, this method enables the manufacture of tiny series. The applications of thermoplastic injection in the plastics sector are quite diverse, encompassing the automotive, package, medical, and electronics industries in particular. A thermoplastic injection can meet regulatory standards and restrictions in an area that requires several tests and certifications, such as the medical sector. 

The pieces produced are functionally equivalent to those manufactured in series. Furthermore, the thermoplastic injection manufacturing process is utilized to create parts that are either very small, like electrical components, or very big, like vehicle body pieces.

Design Considerations

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We’ve already discussed how thermoplastic injection molding can manufacture parts with high precision, making it excellent for both prototype and production runs. However, to create the finest possible components, product design must fulfill minimum and maximum thickness criteria. 

The thermoplastic injection molding method, in particular, can produce parts with a tolerance of 0.2 mm. Furthermore, the technique is capable of producing more sophisticated components with tolerances as close to 5 micrometers in diameter and longitudinal characteristics. Surface finish accuracy generally ranges between 0.5 and 1 micrometer.


A mold
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Almost any engineering-grade plastic resin may be used for thermoplastic injection molding. But that doesn’t even take into account more generic resins. Engineer-grade resins are generally used to build final prototypes before manufacturing, whereas generic resins are used to produce early iterations or less important elements of a product. 

As previously stated, the wide range of plastic resins that may be produced by thermoplastic injection molding enables product creators to experiment with diverse components and surface treatments for their goods.

The Bottom Line

To summarize, thermoplastic injection molding may be used for prototype, short and long-run production owing to its speed, completed component quality, and wide range of basic and engineering-grade materials that can be used. However, like with any manufacturing process, errors might occur, potentially delaying your product delivery. That is why it is critical to work with a reputable, experienced firm for your part production requirements.

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