Surfaces are important quality features, as they have a decisive influence on the further processing of components and their reliable function. Laser-induced plasma spectroscopy can specifically analyze the elemental composition of a surface and provide information about contamination. Digitized inline measurement is the key to highly efficient process control in order to detect contaminants during the manufacturing process. Within the BMWi-funded "Alaska" project, this technology was used and transferred into a fully automated unit for complex process chains.
If particulate, chemical or filmic impurities are present on material surfaces, they have a significant impact on subsequent production steps, such as bonding, painting or electroplating. The detection of surface contamination is particularly important in adhesive bonding production processes, as only clean surfaces can be reliably bonded. In this case, process-securing, accompanying quality assurance is of great importance. Fraunhofer IFAM uses laser-induced plasma spectroscopy - LIPS or LIBS for short - for this purpose. LIBS is a laser spectroscopic method that can be used to determine the element-specific composition of a sample. The high energy density of the laser - with a standard wavelength of1064 nm - generates extreme excitation of the atoms, creating a plasma on the surface, which emits light radiation when it cools down - when the atoms return to their ground state. This radiation is specific and unique for each element. The radiation is then picked up by a special light guide and directed into a spectrometer, which evaluates the element distribution in real time. With the help of the LIBS system, the majority of elements in and on surfaces can be analyzed qualitatively and quantitatively without the samples requiring special preparation.
LIBS measuring head for integration into a robot-guided production environment
Compact LIBS measuring head on a robot system for the automated measurement of components
According to the current state of the art, setups for surface analysis using LIBS technology consist of a stationary, permanently installed measuring head for material analysis, in front of which the samples must be moved precisely. Flexible and robot-guided inline surface analysis has not yet been possible for this system, as the measuring heads cannot be mounted on existing robot systems due to their heavy weight and design. In order to integrate the LIBS technology into existing production processes, a compact LIBS measuring head for mounting on existing robot systems was developed in collaboration with LTB Lasertechnik Berlin. An important goal within the project was to design a small and lightweight system that is also equipped with robust components in order to withstand the movement on the robot and thus not cause any changes to the measurement quality. A laser with a wavelength of 1064 nm was used for this purpose. As a result of this development, LIBS measurements can now be fully automated and integrated into complex process chains. Concrete application scenarios are conceivable, for example, in the production of fiber-reinforced plastics or in the prevention of paint wetting defects. If the measured values are outside the tolerance range, the process can be readjusted directly and easily.
Material and application-specific further development of LIBS technology
With its extremely low material removal in the nanogram range or less, LIBS technology with a 1064 nm laser can be used in many applications. The microdefects generally do not interfere with the subsequent treatment of the components or the measurements are carried out at non-critical points. However, it is not only the subsequent processes, but also the surface condition and the material to be tested that are decisive for the use of this technology. For example, minimally invasive surface analysis of fiber composites requires a different wavelength and a different amount of energy compared to metals, glass or plastics. In order to minimize damage to the material, it may be necessary to use a laser with a wavelength of only 532 nm or 266 nm with an adapted amount of energy in certain applications. Laboratory tests at the Fraunhofer IFAM have shown that LIBS technology with 266 nm reduces material damage in diameter and depth by 95 % compared to 1064 nm, while maintaining the same quality of measurement data. This means that the LIBS system can be individually adapted and used in any production area in which surface and material properties play an important role. The analysis is not limited to solids; pasty or liquid substances can also be analyzed for their elemental composition.
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LIBS
Video about the analysis of the elemental composition of surfaces.
www.youtube.com/watch?v=IAUsKTThJjYwww.youtube.com/watch?v=IAUsKTThJjY
