The structural foam molding process requires an inert gas (such as nitrogen) to be mixed with the chosen plastic material inside an extruder barrel. This mixture is then injected into a mold using less pressure than what is common in injection molding.
Once injected, the gas expands, filling the mold cavity. Alternatively, a chemical reaction within the blend itself may lead to the desired foaming action. When the foaming plastic touches the cold mold wall it solidifies, producing a thin layer of skin. This skin is supported by a cellular structure that is not dissimilar to wood products. Unlike injection molding, high pressures are not needed. The foaming action caused by the gas is sufficient to create the part.
One of the advantages of structural foam molding is that it does not require a steel mold. Instead, lighter and less expensive materials such as aluminum are acceptable. It is also associated with lower startup costs than what is required to pursue injection molding, making it a worthwhile alternative for lower volume applications.
The products this method produces tend to have excellent strength-to-weight ratios and better acoustic and thermal insulation properties than similar products made with other methods.
