Our aim with this work was to evaluate how the thermoplastic resin used in the composite adherends and on the energy director affected the static ultrasonic welding process in both parallel and misaligned configurations. Polyetheretherketone (PEEK) and low-melt polyaryletherketone (LMPAEK) were the resins used and their thermomechanical properties were characterized via dynamic-mechanical analysis and modulated differential scanning calorimetry. With parallel adherends, neither the welding time nor the through-thickness heating in the adherends vary significantly. This similarity was attributed to a larger heat capacity of the PEEK energy director counterbalancing its higher viscoelastic heating rate. With misaligned adherends, the welding time was larger for PEEK welds than for LMPAEK welds and LMPAEK adherends presented a larger though-thickness heating. These effects were attributed to the larger bulk viscoelastic heating rate of carbon fibre reinforced/LMPAEK adherends adding up to the lower heat capacity of LMPAEK.

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This paper evaluates the potential of changing the welding force and the compliance of the energy director (ED) to reduce the effects caused by misaligned adherends, which were: increased through-thickness heating, reduced size of welded area and increased heating time. In the methodology that was followed, we welded adherends misaligned by approximately 4.5° in different scenarios: with higher welding force; with increased ED compliance by the use of a thicker ED and; with increased ED compliance by the use of a discontinuous ED. The most significant reduction of the effects caused by misaligned adherends was obtained when combining the use of both increased welding force and discontinuous ED. Such improvement derives from the imposed parallelism caused by the use of a higher welding force and from a more efficient concentration of heat generation at the weld line that occurs when a discontinuous ED is used.

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Research on ultrasonic welding of composites has focused mostly on studying parameters that are inputs for the process or material-related parameters, but almost no attention has been given on the effect of manufacturing tolerances. In this work, we investigated how an angle between adherends impacts the welding process and the weld quality. By increasing the angle between top and bottom adherends, it was found that the duration of the process increased while the power consumed, the weld uniformity and the weld strength decreased. However, by increasing the clamping distance, which increased the compliance of the adherends and hence their ability to deform under the applied welding force, the effect of the misalignment on both the welding process and weld quality could be substantially reduced.@en