Manufacturing Demonstration of Automotive Seat Backrest Using Sheet Molding Compound and Overmolding with Continuous Reinforcement

Sheet molding compounds (SMCs) are increasingly used in high-volume automotive applications for lightweighting and as a cost-neutral or low-cost solution to incumbent metal parts. Only a limited number of studies exist on SMC-based structural automotive parts. In this work, the SMCs formulated with vinyl ester resin were considered as they represent cost-efficient and durable automotive composite materials. The concept of manufacturing process with overmolding of continuous fiber at select areas enhancing local strength and stiffness with the bulk SMC domain is also introduced. The studies were extended from the coupon level to the production of an automotive SMC composite seat backrest. Both test coupons and seat backrest parts were compression molded using structural SMCs. These were also evaluated with continuous glass fiber-overmolded SMCs for enhanced performance and damage tolerance. Flexural, interlaminar shear, and Izod impact tests were conducted for SMC and SMC-overmolded (OM) specimens to evaluate their structural integrity. Scanning electron microscopy was conducted to analyze failure modes, fiber wet-out, and interfacial bonds. Mechanical evaluation of SMC-OM across and along the flow direction of the seat was conducted. The flexure, impact, and interlaminar shear strength of SMC-OM was 6% to 27% higher than SMCs. High-resolution X-ray computed tomography was used to study the microstructure and the effect of SMCs on local fiber orientations of continuous glass fiber format after compression molding and the interface of two formats of fiber reinforcement. Vibration-based nondestructive evaluation showed distinct frequency shifts to higher values, indicating higher local stiffness of the overmolded SMC component.