What Is Structural Foam Molding?

Roto Dynamics

3 years ago

Structural foam molding (SFM) is an injection molding process that is used to make strong, durable, and lightweight molded plastic products. Since it consumes fewer resources, structural foam molding is more efficient and less expensive than other injection molding processes while delivering similar results. SFM is used to produce a wide variety of components and parts.

Table of Contents

What is structural foam?

Structural foam is a combination of a base polymer resin and a foaming agent. The process is able to use quite a few different types of base polymer resins to produce finished structural foam products.

Since it is less dense than conventional types of injection-molded polymers, it would be natural to assume that structural foam is also less durable. However, foam molding results in plastics that are significantly more rigid than other solid materials.

Structural foam is a great alternative to wood, fiberglass, metal, or even concrete. Parts can be foamed that have features which thermoforming is not capable of molding.

How is structural foam part made?

Structural foam parts are made using a process that’s very similar to the process used to make other injection-molded plastics. However, a blowing agent is used to expand the material outwards. As a result, less pressure is involved which therefore requires less expensive tooling than injection molding.

This reduced pressure allows us to make foam molds that are much larger than parts we make with conventional polymer resins for a lower price. In fact, parts made with foam molding can weigh hundreds of pounds. Structural foam molding can also be used to produce multiple parts during a single production cycle.

How does structural foam molding work?

Let’s run through a step-by-step list of how the foam molding process works:

1. Combination of polymer resin with foaming agent

First, a structural foam molding machine is used to combine a polymer resin with a gaseous foaming agent. The resulting mixture is a polymer-gas melt.

2. Injection of foaming polymer into mold

The combined structural foam materials are then injected into a mold at low-pressure. The cells on the surface of the mixture burst and form a skin along the wall of the mold. At the same time, the inner section of the mixture forms a lattice structure that has impressive dimensional stability.

3. Removal from mold and tooling

Once the foam cools and takes the form of the internal mold features, it is removed from the mold. From there, efficient tooling processes are used to make any desired changes to the shape or structure of the molded part.

What is gas-assist molding?

Gas-assist molding is an alternative type of foam molding. Structural foam molding companies use gas-assist molding send a charge a of high pressure gas through channels that have been machined into the mold.
Instead of mixing it with the foam, the nitrogen gas maximizes resin flow the farthest extremes of the mold. Gas-assist molding provides better control over the wall thickness and flatness of the part.

What are the benefits of structural foam molding?

There are benefits in using structural foam molding. Here are a few examples of why this plastic part production process can be desirable:

Reduced resource use

Structural foam molding companies use less energy to produce foam-molded plastics than they use to produce solid plastics. Since structural foam molding also uses decreased quantities of polymer resin, this practice is highly sustainable. Foam molding is also more efficient since it’s possible to run multiple molds simultaneously.

Decreased costs

Since it is less resource-intensive, foam molding is also cheaper than conventional injection molding. At the same time, structural foam molding provides greater value than conventional injection molding.

Better dimensional stability

In plastics manufacturing, dimensional stability is the measurement of how well a plastic maintains its size during shifts in temperature and humidity. Structural foam molding results in plastics that have remarkably high dimensional stability. As a result, the plastics we make with foam molding are ideal for outdoor environments or other environments where fluctuations in temperature and humidity are common.

Lightweight results

The low-pressures used in foam molding make the plastic parts around 20 percent lighter than the solid plastics that used in injection molding’s high-pressure process. At the same time, foam molding results in plastics that have remarkably high stiffness-to-weight ratios.

The rigidity of the plastics used in structural foam molding are much higher than the rigidity of conventional plastics. As a result, foam molding results in strong, durable plastics that are simultaneously durable and affordable.

Wide variety of usable materials

A thermoplastic is a type of plastic that becomes molten when exposed to heat. We can combine practically any type of thermoplastic with a foaming agent during the foam molding process. As a result, you can use foam molding to make lightweight, durable forms of almost any type of conventional plastic.

Impressive part diversity

You can use structural foam molding to produce thin parts that feature remarkable structural integrity. At the same time, you can use similar structural foam molding processes to produce huge, thick parts.

Regardless of the types of parts you’d like us to make using structural foam molding, the finished parts will be strong, rigid, dimensionally stable, and lightweight.