Adhesive bonding of composite ribbon during automated tow placement

Manufacture of thermoplastic composites by automated tow placement (ATP) currently relies on heating composite ribbons well above the softening temperature of the matrix resin. High temperature causes the ribbon to deform and deconsolidate, which then requires the application of high pressure to re-consolidate and bend the ribbon to the composite substrate. A significant degree of fiber waviness in the composite components results from ribbon distortion. High placement temperatures and pressures require heavy, expensive tooling and slow placement speeds. To lower required placement temperatures, the addition of a thin adhesive layer to the ribbon prior to placement was evaluated. Adhesive coated thermoplastic ribbons were tow placed using gas torch temperatures 400 degrees C below typical settings. Interfacial bond strength of two ply composite laminates made from these ribbons was measured. It was found that current ribbon dimensional variations and placement accuracy limitations require that the matrix resin be softened to permit establishment of full interfacial contact. However, the presence of the adhesive layer was shown to increase interlaminar bond strength at law placement temperatures. With reductions in ribbon dimensional variability, surface roughness, and void and volatile content low temperature placement may become possible.