HELACS has developed a reversible resistive welding methodology, which will be used to "take off" and reuse carbon fiber reinforced thermoplastic panels, which will be part of the new generation of aircraft.
The aim of the project, led by Aitiip and funded with almost 2 million euros by the European Union's Clean Sky 2 JU program, is to reduce CO2 emissions from aircraft by 50% and improve the recyclability of parts for the aeronautical industry of the future by 40%.
The European HELACS project, coordinated by Aitiip Centro Tecnológico, aims to develop a dual methodology of controlled integral dismantling, to enable the classification, recycling and reuse of aircraft parts made of thermosetting and thermoplastic composite materials, which have reached the end of their useful life. Annually, the aircraft industry generates more than 40,000 tons of composite waste. With the recovery of materials, the technology proposed by HELACS will support the transition of the next generation of aircraft to an energy-efficient model.
In this sense, HELACS is conceived as a solution to future aircraft dismantling problems arising from the recent introduction of the innovative carbon fiber reinforced polymer (CFRP) material. These materials are fully introduced in strategic industries due to their interesting mechanical properties combined with their low density. They are also suitable for replicating joining processes used in conventional metallic materials, such as riveting and welding. However, their recycling and reuse still present an operational and environmental challenge.
Thus, the HELACS project consortium has spent two years developing and validating a set of highly novel disassembly technologies capable of separating these new CFRP parts quickly, safely for operators, and with a high level of automation. The HELACS solution, in fact, goes further, anticipating upcoming aircraft structural implementations, as its recovery methodologies can be used to recover CFRP materials that are not even in circulation yet.
The objective of the HELACS project, funded with almost 2 million euros by the European Union's Clean Sky 2 Joint Undertaken program, is to reduce CO2 emissions from aircraft by 50% and to improve the recyclability of parts for the aeronautical industry of the future by 40%. The HELACS consortium is made up of four partners from Spain, Belgium and the United Kingdom: Aitiip, PLATA, Centexbel and Gen 2 Carbon.
Reversible resistance welding and machine learning for waterjet cutting
The project focuses its research on the development of a reuse model that combines a water cutting system (which allows to selectively cut the thermosetting part in a dimension suitable for recycling) and a pyrolysis process (carbonization of the thermosetting matrix, to reuse the carbon fibers that survive this chemical decomposition). To perform the waterjet cutting, a robotic technology based on machine learning is being developed. That is, the "human", using the so-called dummy tool, will mark the cutting route with his movements and the robot will clone the path to perform the cut with high-pressure water.
Another of the technologies developed as part of the project is resistance welding joining and debonding, an assembly process adapted to thermoplastic materials (which fall into the family of CFRP materials). This process, which is expected to be one of the main assembly methods for thermoplastic materials in the future, is based on the placement of a metal mesh between the parts to be welded. Once the parts have been placed, electric current is applied to the mesh, generating a high temperature zone due to the Joule effect. This zone reaches the glass transition temperature of thermoplastics (Tg), which, combined with an applied pressure, creates a bonding zone upon cooling.
The HELACS project has carried out a significant number of resistance welding tests, focusing not only on assembly, but also on the reversibility of the process, i.e. resistance to debonding. For this purpose, a specific tooling was developed to apply the above-mentioned pressure and electric current to the weld zone. This joint has significant advantages over bolted and riveted joints, creating a bonding surface, rather than spot joining areas, which are weakened by the necessary drilling. It should be noted that the welding process does not only affect the CFRP plate on the welded side. The opposite side of the plate shows an affected area of the thermoplastic.
Moreover, HELACS has succeeded in demonstrating the reversibility of this process. Once the welding is completed, the application of a second electric current, equal to the welding current, returns the material to its Tg. This process, linked to a force in the opposite direction to that of the welding, is capable of creating the optimum conditions for the peeling operation. As can be seen in the image, the weld zone is affected by the process.
The conclusions drawn from the experiments carried out are very positive. This process, when integrated into the aeronautical industry, could allow the disassembly of complete assemblies and their subsequent welding without the need for intermediate processes, allowing an improvement in terms of logistics and process times.
Thanks to the revolutionary methodologies that come with the HELACS project, the aeronautical industry will be able to find an innovative technological system of dismantling and maintenance of aircraft to give a new life to materials, developments and innovations that will be transferable to other industries as well.