Light as a feather — stiff as a board

Glass-mat thermoplastics give automotive parts a svelte new look. The modular design lets the LD-GMT headliner system mount to the Nissan Xterra in a single assembly. The LD-GMT composite can be laminated using direct molding. This eliminates several production steps common of traditional materials. Glass-mat thermoplastics (GMTs) are becoming the material of choice for automotive engineers designing high-impact, structural parts. Compared to metals, GMTs have higher strength-to-weight ratios and impact resistance, offer greater design flexibility, and better resistance to chemicals and corrosion. They are also electrically insulating and have relatively high stiffness and good dimensional stability. GMTs are challenging traditional sheet-molding compounds (SMCs) as well. GMTs have shorter molding cycle times and an infinite shelf life — thermoset (TS) SMCs need controlled storage and have a limited life. GMTs are also lighter and more ductile than their SMC counterparts and better resist impact at both high and low temperatures. Composite maker Azdel Inc., Shelby, N.C., recently added two new GMT systems for automotive use. One is a low-density, long-fiber blend that is 50 to 85% lighter than conventional GMTs. Called Superlight, it is currently geared toward nonstructural interior parts such as headliners, load floors, sunshades, and trunk liners. Superlight is also a more environ-mentally friendly, recyclable alternative to conventional PVC under-body corrosion barriers. The other GMT from Azdel is a first-generation, mineral-filled reinforced composite that can replace SMCs in nonappearance structural applications. Traditional GMT composites are generally flow molded in a compression press and weigh 4,000 to 4,900 gm/m for thicknesses on the order of 2.5 mm. According to Enamul Haque, global technology manager at Azdel, the new lowdensity (LD) GMT offers the same advantages as conventional GMTs but weighs in at only 600 to 2,000 gm/m for the same composite thickness. LD-GMT is made in a process similar to that