Sound waves can reveal properties on surfaces. Parameters such as coating quality or the surface quality of components can be analyzed non-destructively using lasers and sensors. This laser-induced surface wave spectroscopy is already a tried and tested measurement technology in research and in some industrial laboratories.
With "LAwave", the Fraunhofer Institute for Material and Beam Technology (IWS) in Dresden has now presented the second generation of a user-friendly measuring device at the Control quality assurance trade fair, which enables the breakthrough into industrial practice. "This technology enables us to examine coatings and surfaces non-destructively, quickly and very precisely," explains project manager Dr. Stefan Makowski, who heads the coating characterization group at the Fraunhofer IWS. "With LAwave, we are now taking the step towards application in industry."
Specific fields can be found, for example, in automotive engineering, surface coating and microelectronics. For example, surface acoustic wave spectroscopy can evaluate cracks and pores on thermally sprayed surfaces without destroying the component, as is the case with conventional cross-sectional examination. In the semiconductor industry, the removal of impurity layers on silicon surfaces can be examined. LAwave technology is also suitable for the quality control of PVD coatings, such as wear-resistant and friction-reducing coatings made of diamond-like carbon on motorcycle chains and engine components.
"This technology enables us to examine coatings and surfaces non-destructively, quickly and very accurately"
LAwave-based analysis of the latest generation of brake discs offers great potential for protecting the environment and health: The vehicle industry is increasingly coating steel discs with special layers of hard metal, ceramic or other materials to reduce abrasion and corrosion. On the one hand, this is intended to ensure that cars and motorcycles meet the increasingly stringent particulate matter limits in the EU. On the other hand, manufacturers are preventing an unwanted side effect of the switch to electric drives: Electric vehicles often only use the engine brake to recharge their batteries via recuperation. They use the conventional wheel brakes less often - and these rust more quickly as a result. Both problems can be greatly reduced by the aforementioned additional layers, although they cannot yet be tested non-destructively.
The Fraunhofer IWS has continuously developed and improved the decades-old technology and software and made the design more user-friendly together with partners. A cooperation between the Fraunhofer IWS and the Chair of Technical Design at the Technical University of Dresden (TUD) contributed to this. Further technological improvements are currently being developed that will open up new fields of application for LAwave. For example, artificial intelligence can significantly improve the quality of the analysis. A mobile LAwave measuring head is also on the agenda. It is intended to enable the surface analysis of internally coated tubes or rollers as well as other particularly heavy, large or complex-shaped machine components that cannot be clamped in a stationary device.
LAwave at a glance
Researchers in Dresden have developed a sophisticated principle over decades: they use a special laser to generate inaudible sound waves on the surface of a component. By transmitting frequencies with a high bandwidth across the workpiece, the waves propagate at different speeds at different depths in the material. Sensors on the surface record how fast the waves arrive, and special software evaluates the collected measurements. The resulting signature provides information about the mechanical properties and defects of the workpiece, such as cracks, pores or foreign atoms.
