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Thermoforming vs. injection molding: Guidelines for product teams

Plastics are the most commonly-used materials in manufacturing today, offering impressive versatility and cost-effectiveness. Accordingly, there are numerous methods by which to manufacture plastic parts, including 3D printing, CNC machining, polymer casting, and extrusion.

Among the most popular are injection molding and thermoforming, which share some common characteristics. However, it’s important that product teams understand the differences between these two processes, including their respective benefits and drawbacks, to make an informed decision on how to best manufacture their plastic parts.

Breaking down plastic injection molding

Injection molding is a highly-engineered manufacturing process that requires a lot of upfront investment and engineering to perform successfully. Split-die molds are injected with hot liquid polymers that are then cooled and released to form solid parts.

Because of the high upfront investment, injection molding is ideal for high-volume production runs. Injection molding produces parts as finished pieces, offering highly efficient material use and a low scrap rate, which reduces the price-per-part in high volumes.

In general, injection molding is well-suited for manufacturing smaller, more intricate parts, because it can accommodate complex geometries and tight tolerances. What’s more, it is compatible with a wide variety of plastics.

Overall, injection molding is a good option for projects requiring complex or detailed designs, high volumes, or short lead times. The process is also notably cost-effective after the initial tooling investment — for high-volume product runs, it’s often a highly efficient and economical choice.

Understanding thermoforming

Thermoforming is the process of forming a heated plastic sheet to the surface of a mold. Unlike injection molding, it’s single-sided; only one side of the plastic conforms to the mold. As a result, it does require secondary finishing processes, unlike injection molding. Vacuum forming and pressure forming are two of the most popular styles of thermoforming.

Thermoforming process
Thermoforming does require secondary finishing processes, unlike injection molding.

Thermoforming tends to be a good option for smaller production runs, defined as about 250 to 3000 parts per year. It’s also better suited for parts with simpler geometries and larger tolerances, which tends to include large parts with basic designs.

However, thermoforming can only be performed with certain kinds of plastics, so it’s somewhat less versatile than injection molding in that respect. Generally speaking, thermoforming is a good choice for projects with lower tooling budgets or limited production volumes.

Choosing the right plastic manufacturing method

While injection molding tends to offer great versatility and little waste, the upfront cost can be prohibitive, particularly for low-volume production. Thermoforming, on the other hand, demands less startup cost and time; however, it requires secondary finishing, and it is ill-suited for parts with complex geometries.

It’s undeniably challenging to determine the best manufacturing method for any given part, but it’s also of paramount importance. Every project comes with different requirements and unique challenges — there’s no one-size-fits-all solution, and often no easy answer. That’s why a full-service, on-demand manufacturing partner like Fast Radius can make all the difference.

At Fast Radius, we’re committed to helping our customers choose the manufacturing method that’s right for their project, working closely with our clients from design to delivery to guarantee satisfaction when it comes to price, timeline, and quality. If you’re ready to get started with your next plastic manufacturing project, contact us today.

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