Nowadays, composite materials are gradually gaining relevance in the aeronautic sector. Their excellent mechanical properties, as well as their reduced density make them a suitable material to reduce the aircraft weight while respecting the mechanical requirements of the metallic materials they are replacing. Nevertheless, as these materials continue to develop and gradually increasing their presence in the aircraft industry, preventive measures should be taken for the treatment of such materials after the end of their useful life.
With a view to solving this future problem, HELACS project is conceived as a solution for the dismantling of not only the aforementioned composite parts, but parts of different materials throughout the aircraft. HELACS combine 2 dismantling technologies: resistance welding debonding and abrasive water jet cutting (AWJ cutting).
Resistance welding is a joining method in which two thermoplastic materials, based on the placement of a metallic mesh between the mentioned CFRP plates. When an electric current pass through it, this plate acts as a heating element, creating a homogeneous temperature distribution along bonding surface. Also, at the same time a glass fibre fabric reinforced PEI (GF/PEI) is used as an electrical insulator between the heating element and adherend laminates. In this process, electric power, process time and applied pressure are key parameters. This bounding method creates a joining surface between thermoplastic parts. At this point, HELACS studies the reversibility of the process, applying an electric current on the welding mesh, increasing its temperature above its glass transition temperature (Tg) and applying a stress in opposite directions for each plate. The result is a reverse welding process, named debonding, in which both thermoplastic parts can be separated. This dismantling process should be thoroughly investigated, so that the optimisation of its parameters allows a clean separation of both parts, without damaging the weld zone. Nevertheless, the operability of this process has been tested and verified during the project.
Furthermore, second dismantling technology proposed is Abrasive Water Jet cutting. This technology is defined as a chopping technology available for plenty of materials, common at industrial environments. It combines high pressure water with an abrasive agent to perform high speed cuts. The aim of HELACS project is the verification of the feasibility of this process for the cutting and dismantling of composite parts of various thicknesses or configurations (parts of varying thicknesses or parts separated by a gap), optimising its parameters to obtain straight cuts, which avoid the delamination of the material. The ultimate aim should be not only to cut aircraft parts from any material in situ, but also to optimise the process for the removal of rivets between parts.