Process Monitoring

One of the many important research areas in which the LZH is active is the monitoring of laser material processes. Although these projects mainly focus on laser welding, cutting processes are also being considered.

The increasing demand for automated quality control in industry calls for extensive research in this field. The automotive industry, for example, having discovered the laser as a versatile tool, is highly interested in such systems.

The LZH has developed a system for process monitoring, known as ProWatcher, which has proved its reliability in several industrial laser welding applications. The system was designed for Nd:YAG lasers, and uses an optical sensor that monitors and evaluates the process radiation which is guided back through the optical fiber of the laser. Further developments concentrate on extending the system to a multiple sensor system, making it possible not only to identify, but also classify a multitude of typical process faults.

The sensors of the modified system measure different wavelengths not only of the optical emission, but also of the acoustic emission. Moreover, they measure the temperature distribution on the surface of the workpiece, the beam position, the condition of the cover slide, and the pressure of the process gas. Since the goal is to obtain a realtime evaluation of the acquired data, fast sensors and algorithms must be developed and implemented.

Linking the acquired data in an intelligent way, and evaluating them makes it possible to identify the different types of faults. Conventional systems are limited to mere fault detection, whereas a smart combination of characteristic signal patterns from different sources clearly increases the certainty with which the type of fault can be determined. This additional information allows a systematic problem detection in the process chain.

In addition, image processing systems for the measurement of seam surfaces are under development. Using a light section technique and a camera, the geometry of the seam surface is measured. This provides a reliable detection of top bead depressions or edge displacements in sheet metal.

Furthermore, image processing systems for the spatially resolved measurement of process radiation are being developed. Such systems can be used to detect joining gaps, e.g. during the welding of tailored blanks.

The requirements to be met by process monitoring techniques are defined in close cooperation with industrial users.