Characterisation of thermoplastic sandwich panels manufactured by continuous ultrasonic welding of skins to the core

Continuous ultrasonic welding is an emerging, fast, and energy-efficient technique for joining thermoplastic composite structures. This research emphasises its potential as an innovative approach for achieving continuous skin/core bonding in manufacturing mono-polymer thermoplastic sandwich structures. Therefore, this study aims to develop a continuous ultrasonic skin/core welding setup equipped with a horn and a compaction roller. A single cantilever beam (SCB) fracture toughness test was conducted on sandwich panels, manufactured using commingled E-glass/polypropylene (PP) skins and a PP foam core, to assess the quality of skin/core welding under different welding conditions. Mode I fracture toughness was measured at various welding speeds (e.g., 4-, 5- and 6 mm/s) and horn pressures (e.g., 0.17-, 0.28- and 0.39 MPa) using two data reduction methods, accounting for assumptions related to compliant skin specimens. Variations in processing parameters significantly impact heat generation and its distribution at the skin/core interface, thereby affecting the weld quality. Hence, careful optimisation of processing conditions ensures a sustainable manufacturing route for sandwich panels, enabling efficient assembly, rapid processing times, and the manufacturing of thermoplastic sandwich structures.