OPTIMIZATION OF THE ULTRASONIC WELDING OF PEEK-CARBON COMPOSITES

The ultrasonic welding of PEEK-carbon composites was studied in order to better understand the process and determine the optimum welding con ditions. The parameters varied were the applied pressure and the weldi ng time. The optimum applied pressure at the hem-sample interface was found to be 3.8 MPa. The joint properties were evaluated through fract ure tests in both Mode I (opening) and Mode II (shear). It was found t hat the optimum welding time depends very much on the physical configu ration of the specimen being welded; this affects the efficiency of co nversion of the ultrasound into thermal energy in the composite. Howev er, for both types of specimen tested (Mode I and Mode II) the optimum joint strength was found to correspond to a specific value of total e nergy input, namely 6.8 J/mm(2). This gave critical strain energy rele ase rates of G(Ic) = 3.2 kJ/m(2) and G(IIc) = 4.6 kJ/m(2). A variation of the energy by 10% in either direction resulted in a decrease in pr operties by about half. Hence the weld energy can be used as a reliabl e control parameter to produce joints with strengths equivalent to tho se of molded composite.