Advancements in Expanded Polypropylene (EPP) foam processing techniques permit a more targeted response to automotive industry requirements including increased energy management efficiency, parts consolidation, reduced offset tolerances, and lower prices. This paper will describe these advanced processing techniques and the advantages they provide for energy management applications such as FMVSS 201, FMVSS 581, pedestrian impact safety, and IIHS 8 kph bumper impact testing requirements. Some quasi-static and dynamic stress-strain information, as well as some cellular (bead foam) modeling information is included.
The energy management capability of a molded EPP part is a direct function of its molded density. Multiple densities can be strategically located within a given molded part in a one-step or multi-step process in order to meet specific customer requirements. These techniques include: ‘traditional’ dual density molding, fore-aft (in die-draw) dual density molding, non-moving slide dual density molding, and tri-density molding. Of particular interest, is the fact that these various molding techniques and the multi-density parts they produce are currently in production, and can be created with commercially available equipment.
The energy management capability of a molded EPP part has also improved as a result of recent developments and improvements in EPP foam bead technology. These developments have led to the creation and recent commercialization of Ultra Low Density EPP (Below 16 g/l) and Ultra High Density EPP (above 225 g/l). It is important to note that another EPP material has been developed, and is being commercialized that will mold up to 300 g/l using commercially available equipment. EPP foam bead technology is constantly evolving to meet the ever changing needs of the automotive industry.