Holographic high-speed interferometry for keyhole evaluation in laser material processing

• Applicant: Professor Dr.-Ing. Jürgen W. Czarske
• Subject Area: Measurement Systems
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 558702699

Laser material processing is becoming increasingly important in industrial manufacturing as a highly effective and precise technology. For example, laser welding processes are increasingly being used for vehicle transmission and structural components as well as in electromobility and are a key factor in determining the quality and durability of components as well as productivity and cost-effectiveness in manufacturing. During deep penetration welding using a high-power laser, the interaction of the high-energy laser beam with the material creates a vapor capillary (keyhole), which is moved along the welding contour and at the end of which the weld seam is formed as a result of the solidification of the enveloping melt. The stability of the keyhole is crucial for high weld seam quality. However, the systems currently in use, such as OCT, are not yet suitable for detecting the keyhole condition reliably and quickly enough to realize real-time control and avoid typical weld seam defects such as large pores or seam ejections. In order to circumvent the current limitations of scanning OCT in terms of data rate and field of view, digital holographic interferometry is to be used, which enables inherently planar or spatial recording of the keyhole using high-speed cameras. A corresponding holographic interferometric high-speed measurement system and algorithms for data acquisition and evaluation were developed and applied as part of the previous project, whereby a high spatial resolution (140 µm) and time resolution (17 µs) were achieved. In the “KEEN” project, holographic 2-wavelength interferometry is to be used for the first time for in-situ 3D analysis of a keyhole during laser welding in order to obtain information on process stability. To this end, advances in laser and camera technology as well as Deep Learning-based signal processing will be used and measuring equipment and data evaluation will be developed for the specific conditions of laser welding in terms of robustness as well as spatial and temporal resolution. The spatially resolved analysis of the weld seam quality and the linking with the process parameters and additional sensor data will be used to develop control algorithms with the inclusion of deep learning. Through cooperation with application partners in the field of laser optics and sensor technology as well as in process engineering applications, the method and system technology will be tested, optimized and prepared for industrial applications.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: Lessmüller Lasertechnik GmbH; ZF Friedrichshafen AG
• Cooperation Partner: Dr.-Ing. Andreas Wetzig