Economical and non-destructive inspection of thick-walled CFRP components

The more complex carbon fibre reinforced plastics (CFRP) components are, the more difficult they are to examine. As a rule, the robot-assisted examination systems required for this are therefore designed for a limited range of components, which can hardly be used for examining other components.

In the SonicScan project, research was conducted into how thick-walled CFRP components can be automatically inspected using phase array technology. In this interview with K-MAG, Dr Christian Eitzinger explains how this technology works and what advantages it has for users.

Dr. Eitzinger, what was the previous way of testing thick-walled components made of fibre composites?

Dr Christian Eitzinger: There are few alternatives for testing thick-walled and intricately shaped components. The usual testing so far has been done manually by an expert who guides the probe over the surface and interprets the signals. However, this approach is not economically feasible for series production in aviation. The only alternative is X-ray methods that inspect the entire volume of the component.

In general, for innovative aeronautical components, such as the carbon fibre composite landing gear component dealt with in the project, the subsequent testability of the component must be taken into account in addition to the component design.

What new approach did you pursue with your research?

Eitzinger: The project has set itself the goal of making the testing of such components possible with ultrasound on the one hand, and increasing the degree of automation on the other.

How does your phased array technology work?

Eitzinger: In contrast to conventional testing with a single sound source, phased array technology uses several small probes arranged next to each other. By controlling these probes in a targeted manner, a cross-section of the component can be inspected without moving and the beam can be focused on a specific area. In general, phased array technology can produce higher quality measurement data in less time.

What advantages does your technology have for users?

Eitzinger: In order to be able to inspect an entire component, the ultrasonic sensor must be guided over the component. In the SonicScan project, in addition to the inspection technology itself, the automation of the inspection with the help of robots was also investigated. The focus of the developments was on automatic motion planning, which ensures that the entire volume can be inspected without collision. For the users, this reduces the manual effort required for component testing in series production. The higher flexibility of a robot-based inspection and the possibility to automatically plan the movement also allow a faster changeover of the inspection system to new component geometries.

What challenges did you encounter during development? How did you overcome them?

Eitzinger: Basically, ultrasound - just like any other testing technology - has certain physical limits. In thick-walled composite components, the attenuation of the signal is particularly pronounced and the complicated shape of the component with tapers, radii and a generally anisotropic structure further reduces the quality of the signals. In the project, the physical properties of the test technology were therefore considered in detail for the motion planning of the robot. This allows the planning to keep the quality of the signals as high as possible and to extend the limits of what is physically possible a little further. In addition, we used the latest machine learning methods ("deep learning") to analyse the signals and achieved very good detection performance despite limited training data.

The research has been completed since mid-2021 - what are the next steps in this project?

Eitzinger: At the end of the project, there was a laboratory demonstrator on which the essential functions could be proven. Together with our project partner ACS Solutions GmbH from Saarbrücken, who contributed expertise in the field of ultrasound, Profactor is currently further developing the robot-based testing technology to increase its level of maturity and bring it to industrial implementation.

To what extent are you taking a step towards the future of the plastics industry with this technology?

Eitzinger: Modern production methods, especially also for carbon and glass-fibre composite components, open up completely new possibilities for designers to design components. Additive manufacturing has also significantly increased the range of economically producible components. In areas with high safety and quality requirements, however, testing technologies are also needed so that such components can be manufactured in series production with quality assurance. The SonicScan project has made a significant contribution to this.

In your opinion, what is the general potential of robotics in the plastics industry?

Eitzinger: The potential of robotics is far from exhausted. Starting with simple "pick & place" tasks, for example in the loading and unloading of injection moulding machines, a number of other applications are in development or at the transition to industrialisation. These include, for example, the automatic draping of fibre composite components, the polishing of surfaces or the application of adhesive and sealing traces. In the medium term, human-robot collaboration will also gain in importance because it combines "the best of both worlds" for a number of tasks.