Exploiting melt compressibility to achieve improved weld line strengths

The structural integrity of thermoplastic composite parts varies significan tly with the local polymer morphology, fibre distribution, and fibre orient ation. Reductions of 30% in the ultimate stress and impact properties of kn it lines in composite filled parts are common, with much greater losses bei ng reported for many material systems.(1-3) A method is presented for incre asing the knit line strength to or beyond the nominal strength of the part without requiring additional investment in tooling or processing. In additi on, the fundamental concept of this technique should lead to additional str ategies for dynamically controlling the polymer flow and fibre orientation to deliver optimum part properties for composite material systems. PRCPA/14 17 (C) 1998 The Institute of Materials.