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The Basics of Structural Foam Molding

structural foam molding

Structural foam, like gas assist, is another manufacturing process in the plastic injection molding family. The process can create large and complex parts that would normally need to be made up of many components. Find out if structural foam molding can simplify your part assembly in this introductory guide. 


What is structural foam molding?

Structural foam molding is an alternative molding process for parts that require geometries and flow lengths that cannot be effectively molded using traditional plastic injection molding. The process is similar to injection molding except a chemical blowing agent is used during the molding process. The chemical agent combines with the resin fed into the mold press creating a chemical reaction. The chemical reaction forms gas bubbles inside the now-melted resin. When the gas bubbles expand, they form a cellular matrix, or “foam”, that packs out the tool cavity and creates the part.


Benefits of structural foam

There are several benefits that come from using structural foam molding to manufacture parts. The gas bubbles within the plastic part help fill in mold walls and cavities more effectively than traditional molding. The molding pressures are also decreased due to the presence of expanding gas. Molding pressure is lowered to about 1 ton per square inch of the part area when compared with around 4 tons for traditional molding. The decrease in molding pressure means that the parts can be formed using smaller injection molding machines, driving costs down.

Structural foam is better suited for thicker-walled parts due to the lowered pressures. The molding process can help product designers achieve over 100% rib to wall ratios for thick parts. The presence of gas within the plastic also decreases the weight and lowers resin costs.

One of the largest benefits is that multiple components can be redesigned into a single moldable piece. Reducing the number of manufacturing processes needed for a part can easily offset tooling prices leading to a more cost-effective process. 


Design considerations for structural foam molding

Designing parts for manufacturing using structural foam requires a few more considerations when compared to traditional plastic injection molding. It is important to consider the design criteria early on, rather than switching molding techniques later in the product development process. The part walls must be thicker than ¼ inch because thin walls deter the necessary chemical reaction. This increase in part size will increase part cost, but this can be offset by the lower weight of the foam.

The finished surfaces of a structural foam part are inherently rough due to the foam texture. Due to the rough aesthetics, unfinished structural foam surfaces should be limited to the interior of a part if possible. In order to create a more aesthetically pleasing part, it will need to be sanded down and finished with some type of paint. The added finishing processes will also add to costs and completion time.


How to finish structural foam parts

Structural foam can be finished through sanding and a multistep painting process. The sanding will reduce the roughness of the part and help achieve a smoother finish. However, this still will not be comparable to a traditional molding finish. A multi-step paint process of priming, finishing, and spatter coating is recommended to achieve the best aesthetic possible for a structural foam molded part.


About Synectic Product Development: Synectic Product Development is an ISO 13485 compliant, full-scale product development company. Vertically integrated within the Mack Group, our capabilities allow us to take your design from concept all the way to production. With over 40 years of experience in design, development, and manufacturing, we strive for ingenuity, cost-effectiveness, and aesthetics in our designs.  Learn more about our contract manufacturing services and see how we can help your next project.

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