Continuous fibre reinforced thermoset composite materials have become established in aerospace, sporting goods, and industrial markets due to their acknowledged benefits vs. metals; including reduced weight, corrosion resistance, and design freedom. There are an increasing number of applications in the auto industry, says Hexcel’s business development manager for Thermoplastics, Tim Greene.
Continuous fibre reinforced thermoplastic (CFRTP) materials offer several additional benefits compared to thermosets, including improved impact resistance or toughness, rapid moulding, unlimited shelf life, recycleability, and no hazardous solvent emissions during processing. However, CFRTP commercial applications have been limited due to a lack of easily processed material forms and associated moulding process technology. Hexcel has developed a range of highly drapeable, conformable TowFlex CFRTP products to enable cost-effective compression moulding of complex shaped structural parts, he says.
TowFlex materials are produced in a solvent-free process by passing a “tow” of continuous carbon, glass, or aramid reinforcement fibres through an electrostatically charged cloud of powdered thermoplastic resin. The charged resin is uniformly distributed on the reinforcement fibres, which then pass through an oven to melt-fuse the powder particles to the surface of the fibres. The resulting “towpreg” is partially impregnated with the desired thermoplastic resin and remains very flexible. This flexible towpreg can be woven into drapeable fabrics or braided into tubular sleeving for further processing.
The TowFlex powder coating process has been demonstrated with a variety of thermoplastic polymers with fibre volumes from 30%-70%. Products are available with fibre/resin combinations to suit a wide range of application requirements. Standard fabric products currently in production include polypropylene, nylon, PPS, PEI, and PEEK resins combined with carbon or glass reinforcement fibres. These materials are well suited for medium-high volumes (1000-50,000+ parts/year), and are currently in commercial use for various compression moulded structural products.
TowFlex products are available in several product forms for use in moulding processes such as compression moulding, bladder moulding, thermoforming, and pultrusion, according to Greene.