Study of Processing Conditions on the Forming of Ribbed Features Using Randomly-Oriented Strands Thermoplastic Composites

Compression moulding of randomly-oriented strands composites offer the possibility to manufacture complex parts with fast processing cycle. In this paper, effects of pressure, strand size, temperature and material placement in the mould cavity on the quality of a T-shape part were studied experimentally. Low pressure results showed both strand size and temperature effects on the filling of a 25 mm rib deep cavity. Critical filling pressures for three strand sizes were obtained. A pressure of 10 bar was enough to fully consolidate parts with smaller strand (3.17 mm × 6.35 mm) at 400 °C. Parts processed at filling pressure showed a void content no greater than 1.2 %. Increasing pressure to 70 bar resulted in decreased void content between 0.44 % and 0.03 %. The lowest void content was obtained for parts processed at lower temperature. Short-beam shear (ASTM D2344) showed similar strength for ribs processed at filling pressure and high pressure (70 bar). This same trend was observed for component testing of the T-shape. At the component level, initial strand placement greatly affected mechanical performance as merging flow fronts caused a knit line and a reduction of at most 40 % in strength. The main findings show that processing a complex feature at filling pressure Pfill was sufficient to reach nominal mechanical properties. This suggested that moderate porosity was not detrimental to the mechanical performance for the given tests.