COMPRESSION MOLDING OF LONG CHOPPED FIBER THERMOPLASTIC COMPOSITES

When it comes to fabricating advanced composite structures, there is an array of fabrication processes available. However, when part complexity increases, performance is demanding and higher volume production rates are required the field begins to narrow. One such method that meets these criteria is compression molding with long chopped fiber thermoplastics. Compression molding is the process by which a charge of fiber reinforced prepreg bulk molding compound (BMC) is molded under heat and high pressures to form complex shaped parts. The BMCs under discussion are created by chopping existing unidirectional fiber reinforced thermoplastic tape into long lengths [6.4mm to 50.8mm (0.25 inch to 2.0 inch)]. These loose chips or strands are then weighed out to the exact amount required to fill the volume of a given tool, placed in a matched metal mold and heated and compressed to pressures that force the fibers to flow into the mold cavity, filling in every complex feature before cooling. Thermoplastic BMC compression molding requires a degree of mold temperature control not normally required by thermoset compression molding. TenCate/CCS uses a tooling concept called XPress to tightly control the mold temperature in zones over the surface of the part. Flat plates and a carbon fiber/thermoplastic bracket with complex features has been molded using this process. Structural test coupons have been molded and tested for stiffness and strength characterization. State-of-the-art design and analysis routines are now available to aid in the design of parts using these BMC materials.