Structural Foam

SUMMARY
Advantages:
Large part availability
Low tooling cost
High strength to weight ratio
Very good durability and impact strength
Disadvantages
Thicker walls vs. injection molding
Slow cycle times (lower production yield vs. injection molding)
Finished part has “swirl” marks on exterior requiring secondary finishing if the exterior
appearance is important
TYPICAL APPLICATIONS
Material handling applications
Toys
Automotive parts
Boating products
Sporting goods
Furniture
Custom Products

Structural foam molding is typically used in load bearing or large part applications in which a high degree of rigidity and lower weight is desired vs. injection molding. Structural foam is not to be confused with expanded polystyrene, which is associated with disposable foam blocks that package and protect new appliances and electronics. Instead, structural foam is an extension of the injection molding process with the exception that it has the advantage of producing very large parts with thick walls, up to 3/8” thick. The finished product exhibits a superior strength to weight ratio and a very durable part, useful in industrial applications.

The tooling used for structural foam molding is also lower in cost than injection molding, lending the process to custom product applications. Injection molding requires very high internal pressure within the mold necessitating the usage of high strength steel to withstand the stress when the material is injected into the cavity. Structural foam molding differs in that a chemical blowing agent is injected with the material and expands the material within the cavity of the mold, greatly reducing the internal pressure inside the mold. The finished part has a solid skin on the exterior and a cellular cross-section internally due to the foaming action of the blowing agent. As a result of the low molding pressure, structural foam tooling is typically made of aluminum, which can be machined up to three times faster than steel molds and weighs approximately one third less than equivalent steel molds. The shortcoming of structural foam is that the wall thickness must be fairly thick, usually no less than 1/4”, as the thick walls act as channels for the material to flow under low pressure and for the chemical blowing agent to provide the cellular coring of the part.. Additionally, structural foam molding has a drawback with production yield (parts per hour) vs. injection molding as the thick walls require longer cooling times before the part can be removed from the mold.

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