Abstract

Rib-AM project aims to contribute to the development of novel in-situ manufacturing technologies applied to large size components of primary structure of aircrafts. Framed in Clean Sky 2, the activities within Rib-AM are set out to develop a leading-edge (LE) concept based on reinforced thermoplastic materials avoiding mechanical joints between the skin and the ribs. Induction Welding (IW) process has been selected for the integration of the ribs into the leading-edge structure. The development of an appropriate IW process methodology, including the introduction of magnetic flux concentrators and new coil designs, are key to assure the quality and structural integrity of the produced joints.

In this research, the mechanical strength of induction welded thermoplastic composites have been evaluated at sample level. Characterization specimens have been obtained by welding: (i) short carbon fiber reinforced polyether ether ketone (SCFR/PEEK), with 10 % carbon content, processed by additive manufacturing – fused deposition modeling; and (ii) multidirectional carbon fiber reinforced polyether ether ketone (CFR/PEEK) laminates processed by oven consolidation. The mechanical characterization of the strength has been carried out by means of the block shear test method. In addition, light optical microscopy has been performed to analyse the SCFR/PEEK - CFR/PEEK interface. Infrared thermography (IRT) has been considered for the non-destructive characterization of the welded joints to evaluate the feasibility of being applied as an inspection method for induction welded structures. IRT results have been validated by X-ray computed tomography.

Abstract

Future aircraft manufacturing factories are moving towards more flexible and adaptable manufacturing systems that enable shorter manufacturing cycles, environmental friendliness, energy efficiency, and higher productivity. A global aeronautic trend to face this challenge includes the replacement of metal parts with composite counterparts with emphasis on thermoplastic composites (TPCs) for their unique ability to be recycled, reprocessed, and welded. Aiming to commit to the drastic projected increase in aircraft production rates, WELDER project, focused on the next-generation MultiFunctional Fuselage Demonstrator (MFFD), has promoted the development and investigation of highly integrated and robotized manufacturing technologies that needed to be scaled up from a laboratory to an industrial environment. To contribute to such an advance, resistance welding was investigated in this work and successfully automatized for fuselage components assembly.

Welding investigation, including process maturation, parameter optimization, and scale-up analysis was performed at laboratory using LM-PAEK/CF composites. A resistance welding Heating Element (HE), made of stainless steel metal mesh and embedded in glass fiber scrims, was first designed and manufactured using a hot press. The HE, priorly characterized by electrical analysis, was adopted, in conjunction with a lab-scale welding head, to optimize and define appropriate processing times (welding and cooling), welding power, and pressures for the welding of the composite parts. The welds were characterized by visual inspection, microscopy analysis, and mechanical tests (SLSS tests - AITM 1-0019). Once materials and processes were optimized, they were scaled up to finally perform the welding of the frame couplings into MFFD.