Vertical Body Panels: Flexible Class A Surface Composites Via Compression or Injection Molding

Low Profile Class A sheet molding compound (SMC) is recognized as the composite material of choice for horizontal automotive body panels. The excellent surface, dimensional stability, stiffness and coefficient of thermal expansion have made it preferred for hoods, deck lids and roofs. softer thermoplastic and thermosetting (RIM) materials have been more considered for fenders and occasionally doors. recent studies have shown performance problems with these materials and SMC composites are being considered as an alternative.

Increased flexibility over standard rigidity SMC is considered desirable for vertical body panels, particularly fenders. This flexibility can be achieved but normally at a major price in surface smoothness. This paper reports on research and development work done to achieve Class A surface flexible SMC/BMC composites that can be either compression or injection molded. these advancements have been made by a combination of shrinkage control agent (low profile additive) chemistry, unsaturated polyester structure, fiber wetting agent and fiberglass size technology. A comparison is made of surface characteristics, flexibility and physical properties which can be obtained via these two processing/molding techniques.