Advantages of Structural Foam Injection Molded Parts - Ferriot Inc.

To properly benefit from the advantages of using structural foam parts in your product’s design, first, you need to understand the process.

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Here’s how it works. The structural foam injection molding process uses a foaming agent (typically nitrogen gas or chemical blowing agent) added to a resin polymer as it melts, then injected into the standard injection molding tool (or die). In this process, the injection molding blowing agent activates and pushes resin uniformly into the cavity pockets; as the part cools, a solid skin forms against the mold. Inside the mold, the resulting foaming action produces a honeycomb-like structure behind the solid skin while reducing post-mold shrinking.

The resulting structural foam part is significantly lighter than other parts produced using other standard injection molding processes. The majority of structural foam parts utilize this injection molding method to reduce the overall weight of the part by up to 30%. However, lower weight isn’t the only advantage. Structural foam molding can provide several benefits you may want to consider as you plan your next project.

1. Can replace many types of materials
   Structural foam is increasingly replacing metal, wood, concrete, and fiberglass, primarily due to its ability to reduce a product’s overall weight while providing a high stiffness-to-weight ratio. 
2. Lighter in weight
   Due to the honeycomb, cellular composition resulting from the structural foam injection molding process, the finished parts have a high stiffness-to-weight and strength-to-weight ratio, enabling parts to be larger while weighing 10 to 30% less without sacrificing rigidity and strength.  
3. Many available resins
   Many resin polymers are available for manufacturing structural foam molded parts, including nylon, polycarbonate, ABS, PC/ABS, TPE, acrylic, acetol, polypropylene, polyethylene polystyrene, and PVC. To learn more about the various types of resins, view the resin selection webinar. 
4. High dimensional stability
   Controlling dimensional stability is important for all injection molded parts. Slight changes in dimensions can occur in all injection mold tools. However, due to the low mold cavity pressure and the resulting honeycomb-like structure, parts that use structural foam are typically more dimensionally stable as well as highly impact resistant.
5. Environmentally friendly
   If available, it is possible to utilize recycled post-consumer resin materials in the structural foam injection molding process. The resulting parts that are produced are also able to be recycled at the end of the product’s lifecycle. Together, this helps reduce the overall carbon footprint of products. 
6. Saves production costs
   Using structural foam injection molded parts can reduce the cost of materials, tooling, and the overall production run. Tooling for structural foam molding can have the same level of detail as other injection mold tooling. Additionally, because the pressure is lower, it is possible to use aluminum tooling for the injection mold. The aluminum mold can last as long as steel molds because of the lower pressure being used.

The key to using structural foam parts successfully is in the ability to incorporate them into today’s complex custom mold designs. To learn more, download our whitepaper, Structural Foam Injection Molding Resources Guide.

To learn more, download the Structural Foam Injection Molding Resources Guide

Structural foam molding is an alternative molding process for parts requiring geometries and flow lengths outside the parameters for 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, causing 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.

There are several benefits that come from manufacturing parts using structural foam molding. The gas bubbles within the plastic part help fill in mold walls and cavities more effectively than traditional molding. Additionally, the molding pressure decreases due to the presence of expanding gas. Gas expansion lowers the pressure to about 1 ton per square inch of the part area, compared with 4 tons for traditional molding. Lower pressure means that the parts are formed using smaller injection molding machines, driving costs down.

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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. Gas present within the plastic decreases plastic weight and lowers resin costs.

One of the most important benefits is that structural foam allows combining multiple components into a single moldable piece. Fewer manufacturing processes needed to produce a part can easily offset higher tooling costs.

Designing parts for manufacturing using structural foam requires a few more considerations when compared to traditional plastic injection molding. Engineers must consider the design criteria early in the process, rather than switching molding techniques. The part walls must be thicker than ¼ inch because thin walls deter the necessary chemical reaction. The increased part size will increase cost, but the lower foam weight offsets this.

The finished surfaces of a structural foam part are inherently rough from 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 the surface requires sanding and painting. The added finishing processes add to costs and completion time.

To recap, structural foam molding reduces part weight, lowers press tonnage requirements, and produces parts that are very large, thick, or hard to fill. Structural foam is just one method of plastic injection molding that Synectic has extensive experience in developing. If you are unsure if structural foam molding would be the correct process for your project or would like some expert manufacturing advice, contact us below and we would be happy to help.

About Synectic Product Development: Synectic Product Development is an ISO 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.