Advantages provided by automotive structural foam
Automotive foam packaging is engineered to perform as a barrier against noise, vibration and harshness (NVH) in order to enhance driving comfort. It can also be configured to be crash-active so that the surrounding metal can be forced to behave in a certain way during a crash. Design flexibility is also achieved because foam can fill any cavity shape and contour with no redesign required. The lightweight construction potential of foam is more than 40% more mass efficient if compared to steel with an equivalent weight. Polyurethane foam that is widely used as automotive structural foam can be applied whenever cavity sealing and stiffening are required particularly in the body-side joints, sills, pillars, underbody cross-car structure, frame rails, longitudinal structure, door panels, engine cradles, lateral rails and hydro-formed replacements. Foam is relatively lower material cost compared to metal yet it improves performance with net body structure mass.
How is structural foam integrated into the car?
Automotive structural foam must be integrated into the car body during the manufacturing process. This can be achieved if the injection-molded plastic insert is surrounded by the expandable structural foam with an adhesive. One important consideration is to ensure that automotive structural foam has not expanded or hardened. The prepared plastic insert is placed in the car body frame with the usual finishing process but during the cathodic dip coating the foam system should not yet react. It should only be in the downstream drying booth with temperatures of about 180oC to 200oC (356oF to 392oF) that foam should harden, a process wherein it expands in a controlled manner to securely join the plastic insert to the metal structure from the inside.
During the design of the plastic inserts, it is important to consider the overall system that consists of plastic, structural foam and metal. The design process is not actually easy or simple because it involves carrying out numerous crash simulations; however, this is carried out through the computer. The challenge here is not the analysis of the simulation because there is a computer that does the job but how to consider the markedly non-linear behavior of various structural foams and adhesives including simulating their failure or the peeling of the joined structures in the event of an actual crash. It is therefore important to consider the types of adhesive used, gluing technique, gluing surface, material of the plastic insert and type of automotive structural foam. Various measurements need to be carried out on the structural foam samples as well as the adhesives in order to determine their load properties under various types of loads.