A panoramic sunroof is larger than a normal sunroof, offering a wide view and ventilation by opening a large glass window. Therefore, a frame of panoramic sunroof must have high physical properties and dimensional stability because it has a massive window and a heavy electric motor. To this end, the panoramic sunroof frame worldwide utilizes steel, with high physical properties and dimensional stability. However, the high-weight steel adversely affects fuel efficiency and increases the center of gravity of a vehicle, thereby reducing driving stability. Therefore, glass fiber-reinforced plastic (GFRP) with a low specific gravity was considered as the sunroof frame material to replace the steel. However, GFRP couldn’t secure dimensional stability due to increased fiber content to fulfill the required physical properties. Although it was possible to replace the steel with carbon fiber (CF)-reinforced plastic having high physical properties and dimensional stability, sustainable mass production was not secured due to the high price of the CF. Herein, we report a highly designed panoramic sunroof frame made of long and flat glass fiber (LFGF)-reinforced plastic. Initially, we screened fiber-reinforced plastic based on PA6-CF20 which satisfied the required lightweight and physical properties. By changing the carbon fiber to long glass fiber, we could achieve the required physical properties at a low price. To improve the dimensional stability, the general cylindrical GF was changed to the flat GF. As a result, the PA6-LFGF40 was prepared with excellent physical performance, reasonable price, and good dimensional stability. Detailed mechanistic investigation using material property test and injection molding simulation revealed that the cause of the high dimensional stability of the PA6-LFGF40 was a low unequal contraction and residual stress depending on the flat shape of the fiber. Based on these studies, the K5 (Kia midsize sedan) panoramic sunroof frame made of PA6-LFGF40 was tested to check the product reliability and proved its better performance than the existing PA6-CF20 frame.
Hyundai Motor Company: Kyeong-Bae Seo, Sang Sun Park