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How Does Structural Foam Molding Differ From Injection Molding

For successfully producing parts, it’s important to understand structural foam molding as another manufacturing process. Read further to learn about how it differs from the injection molding process.

How Structural Foam Molding Differs From Injection Molding - KB Delta

Over the years, injection molding has become an important manufacturing process used in the production of parts and products.

The numerous benefits of plastic injection molding can be attributed to the high adoption of this process by manufacturers.

Some of these benefits include the development of a variety of parts rapidly and in bulk.

Nonetheless, there are different types of injection molding, even though it could be a bit challenging for manufacturers or product developers to make a choice on which will be the best to design their products.

The latter won’t be the case when you rely on the differences between structural foam molding and injection molding. We’ve outlined this below.

You get to know how structural foam molding differs from conventional injection molding, thereby helping you to make an informed decision on the ideal manufacturing process to use for designing your parts and products.

What is Structural Foam Molding?

Structural foam molding is a low-pressure injection molding process.

This process involves the application of inert gas (nitrogen gas or a chemical blowing agent) to a melted polymer before the mixture is injected into the mold.

The gas forces the polymer into the mold, and spreads its thickness uniformly throughout the mold, thereby helping it to take the shape of the equipment.

Also, the purpose of the gas is to reduce the density and weight of the finished product and at the same time, increase its strength.

When the polymer cools within the mold, solid skin is created against the walls of the mold while a honeycomb structure becomes the interior structure.

This honeycomb structure makes it possible to reduce product weight without compromising its structural integrity. And it helps to prevent shrinkage.

Benefits of Structural Foam Molding Over Injection Molding

There are several benefits of structural foam molding over conventional injection molding, which makes it a good choice for manufacturers.

Some of these benefits include:

1. Improved Aesthetics

The use of structural foam molding has helped in the creation of thick and intricate parts and products that lack depressions or sink marks.

Likewise, parts manufactured with structural foam molding have a much more polished, consistent surface finish, and as such, they can have your desired texture.

Given that this is a low-pressure molding process, it also helps to reduce stress and warpage issues.

That being so, this is a process that can be used in the creation of products with higher quality than traditional injection molding in certain cases.

There’s also the excellent acoustic and thermal insulation properties of products produced using this process than other methods.

2. Improved Strength

The honeycomb structure that is formed during structural foam molding has shown renewed strength.

Therefore, structural foam molding results in the production of parts and products with a high strength-to-weight ratio, even higher than those formed during traditional injection molding.

These parts are larger and sturdier compared to those that are created in regular injection molding.

On the same note, parts with structural foam molding are more resistant to impact.

They can be used in a wide variety of applications, and products made through this process can serve as a replacement to sheet metal, concrete, fiberglass, or wood.

It is, however, worth noting that the end product formed with structural foam molding tends to be lightweight and rigid, but with a relatively hard surface.

3. Variety of Mold Options

Structural foam molding is a lower pressure process, unlike the traditional injection molding.

The low pressure and forces allow economical molding equipment and tool to be used, which results in the mass production of very large or multiple parts from the same machine.

The production is also carried out in a single cycle, and at a cost that is lower than conventional injection molding.

For instance, aluminum molds can be used during the process whereas, the same type of molds will not be suitable for use in traditional injection molding.

Aluminum molds, on the other hand, can last longer since they are not susceptible to the high pressure during the molding process.

Also, these molds are less expensive to use.

4. Low Startup Costs

Another advantage of structural foam molding is the fact that a steel mold is unnecessary in the process.

What this means, is that lighter and less expensive materials can be used for molding.

As a result, it has a lower startup cost compared to conventional injection molding, therefore, making it a good alternative when it comes to lower volume applications.

On the same note, structural foam molding has production, design, and cost advantages.

Let’s take a quick look at each:

Production Advantages

  • Better heat transfer of aluminum resulting in faster cycles
  • High dimensional stability over the entire production run
  • Multiple molds can be run simultaneously
  • Different material or colors can be molded simultaneously
  • Works as an excellent substrate for high quality painted finish applications

Design Advantages

  • Part weight reduced by 10% to 30%
  • Molding of parts that weigh up to several hundred pounds
  • Honeycomb structure gives increased strength and stiffness
  • Molding of large, complex parts without sink marks
  • Molding of parts .500 inches thick or greater

Cost Advantages

  • Reduced cost and increased productivity
  • Recycled post-consumer plastics can be used
  • Lower cost of raw material due to the use of commodity resins
  • Low injection pressure allows for use of lower-cost aluminum molds
  • Recyclable parts that are also returnable for supply chain cost-effectiveness


Structural foam molding differs from injection molding, attested by the higher quality of products and large structural parts produced.

These are sturdier products with a very high strength-to-weight ratio and excellent thermal properties.

What’s more, this low-pressure molding process helps to produce parts that are structurally sound. In addition to thicker wall sections, almost stress-free, and with minimal warpage.

And remarkably, these benefits are offered at lower production costs since expensive materials like steel are unnecessary.

How Structural Foam Molding Differs From Injection Molding - KB Delta

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