Tue, 29 September, 2020
Composite materials offer excellent strength to weight ratios, providing great benefits for aerospace manufacturers who are seeking new, lighter solutions across the industry.
However, for all of the advantages, there are still challenges associated with the use of composites in aircraft manufacture. Performing differently to the metals that are traditionally used, carbon fibre parts are anisotropic, with laminar construction and can fail without showing signs of visible deterioration. Furthermore, manufacturing defects, such as damaged or misaligned fibres, voids and delamination, can lead to reduced material performance.
It is therefore important to use non-destructive evaluation (NDE) techniques to ensure components meet the required mechanical properties. These NDE requirements currently account for 10% of manufacturing time and 5% of manufacturing costs, meaning that there is plenty of scope to improve and accelerate these processes.
Current techniques have drawbacks, with ultrasonic inspection requiring the use of a couplant that adds moisture to the manufacturing environment, while X-ray can be dangerous and expensive for shop floor use.
While ultrasonic inspection is the most commonly used technique, with top speeds of around 1m2/h, there have been attempts to introduce automation to the process. However, this has proven difficult due to the sensitivity of the process.
As a result, TWI has been working alongside a consortium of project partners on the CFLUX project to develop an inspection system that has the potential to work at 30m2/h, which is 30 times faster than manual ultrasonic NDE and eight times faster than an ultrasonic gantry system.
The project partners, M Wright & Sons, ETherNDE, Advanced Hall Sensors, Far UK and TWI are developing two non-contact, dry NDE techniques for carbon fibre. These techniques will allow thorough quality assurance of raw materials, using automation and advanced eddy current technologies to identify subsurface defects in larger manufactured components.
The project involves the design of demonstrator parts, which will be subjected to finite element analysis and mechanical testing with the NDE technologies integrated with automation via a 'cobot' and viewing / interrogation software.
TWI Technology Centre (Wales) has been using industrial robots for automated non-destructive testing (NDT) since 2012 and is continually working towards improving the existing setup. While research until now has focused on integrating NDT into the manufacturing process, TWI is also developing a more flexible automated inspection solution for smaller component inspection that can be used alongside a human operator.
A cooperative robot (also referred to as a cobot) has been purchased as part of the AEMRI (Advanced Engineering Materials Research Institute) initiative, which is part funded by the European Regional Development Fund through the Welsh Government. These robots are specifically designed to work alongside humans in a shared workspace by monitoring the forces applied to each joint to avoid injury during collision. Furthermore, cobots are easily programmable, can interface with external equipment and can position NDT sensors with six degrees of freedom. The cobot has a high-resolution force-torque sensor, which allows it to “feel” and follow a surface while exerting a controlled force onto the surface. This is especially relevant for ultrasonic and potentially eddy-current inspections. A cobot is also useful from an R&D perspective; When developing a new NDT technique employing a robot, there is inevitably a lot of initial physical interaction required between robot and operator. With a cobot this can be done safely and more efficiently compared to a traditional robot cell setup
The Innovate UK-funded project has recently reached a milestone with a 3D sample designed by FAR and printed by Wright & Sons being used for scanning tests. A plastic dummy part, enhanced with metal washers was used to produce positive signals that could be used to tune the eddy current response. This offline path planning was performed by TWI on RoboDK software before the system signals were integrated on TWI CFLUX software. The amplitude signals from the bespoke EtherNDE eddy current probes were plotted on a 3D mesh to create a CAD type model result on the screen.
You can see the CFLUX eddy current and Quantum Well Eddy Current Field Measurement (QW-ECFM) NDT of carbon fibre composite materials in operation in this video.
This first breakthrough is a large step in creating a final system that will allow for the inspection of composite parts for the aerospace industry.
This project is funded by Innovate UK under grant agreement 113229