“We don’t use traditional chemistries you often see in BMC,” says Landis. “And we’ve developed methodologies that allow us to use a variety of resins, fiberglass and carbon.” He adds that traditional materials in the BMC field are highly loaded with filler, while IDI’s formulation has very low amounts of filler. Most of IDI’s customers for structural thermoset BMCs are in the automotive market and use the materials for inner structural car parts because they provide lower density and good strength, plus they can mold thinner gauge parts.
The driver behind advancements has traditionally been the aerospace industry’s need for lighter, stronger, stiffer materials. Automotive has followed closely on aerospace’s heels. One of the more innovative high-performance applications is the battery pack enclosure for General Motors’ 2014 Chevrolet Spark. This year, Continental Structural Plastics (CSP) in Auburn Hills, Mich., will produce 2,600 compression-molded battery enclosures for the Spark. They include a 1 x 1.4 meter tray and cover that are joined together at the automaker’s plant once the battery module is installed. The enclosure sits fore and aft of the rear axle between the wheels.
The battery enclosure had to meet stringent performance requirements and pass rigorous testing, including crash, mechanical shock, post-crash integrity, fire-resistance, drop, water immersion and vibration/shock tests. CSP partnered with Cytec Industrial Materials for a materials solution. Cytec created MTM® 23, a volatile organic compound (VOC)-free thermoset vinyl hybrid resin woven glass reinforced prepreg. The material, used in conjunction with a chopped fiber material in an SMC, allowed CSP to form a complex-shaped enclosure that protects the battery in a catastrophic event. The composite is 40 percent lighter than a metal counterpart, according to CSP.
One of the biggest challenges for CSP was that it had not worked with prepreg material in a laminate-type structure before. “The design was adapted to existing space in the vehicle, which made the geometry very challenging to work with as a laminate-based design,” says Chris Johnston, director of technology and processes at CSP. “We had to do a lot of work on ply pattern development using draping simulations to see how the fabric would lay across 3D surfaces.”