Induction welding of thermoplastic composites with lightning strike protection

Abstract

Induction welding nowadays is one of several welding techniques suitable for joining thermoplastic composites. Currently, induction welding at an industrial level is used to weld secondary aircraft structures like tail movables and rudders. One of the challenges when progressing induction welding towards primary aircraft structures is more extensive use of lightning strike protection (LSP) in these parts.

In this work, tests were carried out on flat quasi-isotropic (QI) single lap shear specimens made by AFP from Toray Cetex® TC1225 T700/LM-PAEK unidirectional (UD) tapes. LSP material was applied single or double sided by hand in case of the continuous LSP. For the AFP LSP tape, slitted to a width of ¼”, direct AFP placement onto the laminates was done in three different patterns being in 0°, 90° and a 0/90° orientation (gingham pattern). In the gingham pattern the LSP tapes are placed with a ¼” gap and overlap at certain sections. By optimising the welding parameters and the tooling it was possible to weld all types of LSP, in which the gingham pattern proved the best variant and the continuous LSP mesh the most difficult option to weld. Mechanical testing showed good performance of all the welds.