What is Structural Foam Molding?
Structural foam is a composite material that is produced when a polymer (usually thermoset (but also thermoplastic)) is mixed with an inert physical gas (such as nitrogen) or a chemical blowing agent during the molding process. The result is not a solid material, but a combination of a low-density microporous “core” and a high-density external “skin”. The core reduces the overall weight of the material, while the strong skin keeps it strong and impact resistant.
Why use Structural Foam Molding?
The foam injection molding process can be used for parts of many different sizes to produce lighter, high-strength molded parts. Many large parts require wall thicknesses that can be efficiently produced by standard injection molding. Structural foam can achieve faster processing and cycle times on thicker parts. This low-cost molding process produces parts with reasonable structure, almost stress-free, and minimal warpage. Lomont’s structural molded parts are thicker and stronger than those made by other processes.
Structural Foam Molding features
The structure of this material is like a sandwich, the low-density core is completely surrounded by the high-density skin. The texture of the core is often described as resembling a “sponge” or “honeycomb”. Due to its unique core texture, structural foams are generally 20% to 40% lighter than solid polymers, aluminum, steel, sheet molding compounds, or other commonly used materials.
Due to its less robust nature, the base material used to make structural foams is usually a thermoplastic polymer rather than a thermoset polymer. Commonly used thermoplastics include, but are not limited to: polyurethane, polycarbonate, polyphenylene ether (Noryl), polybutylene terephthalate (Valox), and acrylonitrile butadiene styrene.
Structural Foam Molding process
Structural foam molding is a low-pressure injection molding process that can produce very large structural parts. The molten plastic is mixed with the foaming agent and injected into the mold to “foam” the plastic. The structural foam injection molding process is very suitable for large plastic parts, because the foam bubbles in the resin matrix squeeze out the resin and reduce the incidence of plastic parts showing side sinking. Structural foam molded parts are usually very thick, with wall thicknesses close to 0.250 inches, making them ideal for making invisible plastic structural elements. Visible parts require sanding, painting and finishing.
The process of forming structural foam parts is very similar to the traditional reaction injection molding method. The two components, such as polyol and isocyanate (which combine to form polyurethane) are stored in liquid form in separate containers. They are mixed together to form a resin, which is injected into a pre-prepared mold and cured by a chemical reaction.
In addition to polyols and isocyanates, inert gases or chemical blowing agents are added to the mixture during the injection process. This changes the nature of the chemical reaction that ultimately occurs.
Compared with standard solid polyurethane reaction injection molding, fewer polyols and isocyanates are used, so the resin will not completely fill the mold. Instead, the gas or blowing agent is activated by the reaction between the two components. It expands and fills the empty space of the mold with foam. This creates the “honeycomb” texture known as the inner core of the structural foam. The surface cells collapse when in contact with the mold wall, forming a solid surface layer around the outside of the material.
Structural Foam Molding material
Polyphenylene ether-PPO (Noryl)
Polybutylene terephthalate-PBT (Valox)
Acrylonitrile Butadiene Styrene – ABS
Benefits of Structural Foam Molding
The use of structural foam as a manufacturing material has many advantages. Of course, structural foam was initially known for its ability to produce components of unparalleled size, such as vehicle roofs or body panels. However, it was soon discovered that structural foam brought many additional benefits.
Structural foam components are very light. With typical weights ranging from 55 pounds per cubic foot to only 2 pounds per cubic foot. In addition to weight reduction, structural foam is strong, durable, and very rigid—in fact, it is eight times harder than similar materials such as solid polymers. The modulus of the material increases as its density increases, reaching an astonishing 250,000 psi. In addition, this foam material is a good heat and sound insulation material.
Structural foam is also highly plastic, and it can produce different wall thicknesses on a single part. In some cases, structural foam can even produce wall thicknesses greater than the previous largest 1/2 inch (13 mm). It also allows the use of thicker ribs and bosses and reduces the risk of “sinking” on ribs or large sections due to the low viscosity of the mixture. Structural foam products bear less overall stress during the molding process and have strong resistance to warping or deformation.
Structural Foam Molding retains the common impact resistance, impact resistance and temperature resistance of thermoplastic and thermoset polymers. It has almost no thermal expansion, so it is very suitable for products used in various climates or temperatures. The acoustic and sound-damping properties of structural foam are also superior to standard solid polymers.
Structural Foam Molding is also a very cost-effective process. Lower pressure and clamping force are required during injection and curing, allowing tools and molds to be made of lower cost materials such as aluminum. The cycle time is competitive with injection molding and reaction injection molding, which makes it a time-saving and cost-saving process.
The risk of damage to Structural Foam Molding products in the mold or during removal is below average, making it an efficient and easily repeatable method. In addition, structural foam does not produce potentially harmful styrene fumes, reducing the health risks of workers involved in the molding process.
Finally, Structural Foam Molding also has a highly paintable and beautiful surface. All Structural Foam Molding products can be sprayed in the mold (IMP), which further saves time and money. It is also possible to apply multiple colors to a single part in the mold. The surface is easy to clean and can be sawed, screwed, stapled or bound without any problems.
If you need to manufacture large parts without sacrificing quality, Structural Foam Molding is your best choice.
Suggestions for Structural Foam Molding
Use low pressure injection molding (LPIM) machines to inject large Structural Foam Molding products, such as material handling bulk boxes, pallets, tool boxes, construction products, pool panels and ladders, fences, retail display stands, suitcases, storage sheds, shelves, cargo systems , Ground fences, leisure slides and toys, outdoor furniture, water storage tanks and drainage systems, tombs, garden trellis, dog houses, dock systems, cleaning and restaurant products, and industrial carts.
WIT MOLD To ensure that all products always meet your expectations, our highly skilled team is trained to use the most modern quality assurance methods:
Statistical process control
Team-oriented problem solving
Gage R&R Research
Gage measuring system
Advanced Quality Plan (AQP)
Color measurement system