Improving Sheet Molding Compound

Zebulon McReynolds

An important attribute of the compression molding process is the requirement of (Sheet Molding Compound) SMC. The fibers, commonly glass or carbon fibers, are impregnated with thermoset resin and collected in continuous form on a conveyor belt. The SMC charge is rolled between rollers to wet out the fibers with resin. The SMC charge is then compression molded to a desired part reflecting the designed mold. The part could be an automotive part or any other industrial applicable part. Compression molding with fibers and polymers is the largest component of most of the manufacturing industries in the world. Whether it is the components of the interior of a car, a tooth brush, or a plastic chair, a compression molded part is used in most of the day-to-day use objects.

With development in this field, stronger molded fiber parts are cheaper to manufacture. With increase in demand, the time of production can be cut down as well as cost. My research, along with my cell group at the Fibers and Composites Manufacturing Facility, focuses on the use of SMC production line, while perfecting the use of randomly oriented fibers, compression molded parts are characterized for mechanical properties. Various check points need to be addressed for smooth functioning of the SMC line, such as SMC conveyor belt motion, jamming of the fiber cutter, random fiber lengths, and uneven fiber distribution. Due to the randomness of the fiber lengths and distribution, compression molded parts lack consistent mechanical properties. Mats contain high degree of flaws and could not be used for compression molding. By researching methods to minimize the flaws in the SMC charge we can help companies to manufacture cheaper and more effective SMC material in a smaller amount of time, boosting the mass production of products.

Glass fibers (GF) and carbon fibers (CF) are used to make SMC charge and characterized for various fiber length and fiber weight fraction. The automobile industry is cost sensitive and SMC is used to reduce the weight and enhance the efficiency of the vehicle. Though CF is more expensive than GF, it is used to increase the stiffness and reduce the weight of the final part. In commercial SMC manufacturing, it is not easy to combine GF and CF as the fiber surface properties are different for a given resin system. Hence in this trial both GF and CF are combined with polyester resin using slow compaction technique and post cure at 90 °F for 24 hours.