A Steel-Plastic Hood Concept for Passenger Cars

A novel hood of steel and plastic has been designed to achieve an effective balance between weight and cost. The design concept uses a thinner (lighter weight) 0.024-inch-thick steel sheet for the outer component and a compression molded SMC inner component combined with an inner very thin (0.015-inch-thick) steel sag pan. Cost estimates of the hybrid hood were made using a mathematical cost model developed by MIT and indicated costs similar to an all-steel hood, but significantly lower than for an all-SMC hood. In addition, the weight of the hood is less than the all-steel hood.

The steel outer optimizes the surface characteristics of the hood and maintains appearance compatibility with other exposed steel body panels. The inner steel sag pan is used in membrane tension to work with and complement a minimal weight SMC panel. The inner SMC portion also acts in compression and bending to significantly limit panel deflections and greatly increase the assembly's stiffness. Key adhesive bonding tests were successfully conducted with bare and coated steel substrates selectively bonded to SMC during the SMC molding cycle.

The encouraging engineering analysis of the novel hood and the attractive combination of low weight and cost suggest that similar benefits could be derived from combining steel and plastic in other two-piece assemblies (deck lids and doors).