The independent research company blz (Bayerisches Laserzentrum) based in Erlangen, Bavaria, helps users to make the laser tool more usable for production processes. The realisation of the goals is based on the cross-technology competence in the field of applied laser technology: Laser material processing and process analysis, additive manufacturing, laser system technology, optical simulation, laser protection and knowledge transfer.

Requirements for Processing Quality

The processing quality in research and industry must meet high standards. Many factors play a role in achieving the desired result. Thus, a constant control in the different processes is necessary. A camera can be a part of the analysis.

Therefore the blz purchased a MotionBLITZ EoSens® mini2 at the beginning of 2020. This camera is a high speed memory camera and with its compact design ideally suited for confined spaces.

The camera was quickly ready for use, as the blz had been using an identical test system since autumn last year. Therefore the camera could be used immediately for more comprehensive studies.

Schematic experimental setup for process observation during laser beam welding of copper materials

 

The memory camera is used in the laser center for process observation during various laser material processing operations. These are processes such as welding, cutting, soldering and generative manufacturing processes. The system is used in particular for welding aluminium and copper materials, remote welding of ferrous and non-ferrous metals, laser material processing with wavelengths in the visible range and soldering of microelectronic components.

Withstand extreme process conditions

All these processes can result in defects, so-called seam inhomogeneities: weld spatter, pores and blowholes. By knowing the origin, countermeasures can be developed to avoid them. With the help of the high-speed camera, such defects can be identified and the weak points can then be eliminated. For example, spatter occurring in the powder bed can be detected and the process can be adjusted accordingly. Furthermore, the characteristics of the weld seams, the melting dynamics and the material evaporation, which occurs in the form of a steam flare above the keyhole, can be observed during the process.

Macroscopic view of a weld specimen to assess the weld appearance (weld bead in copper ETP)

Observation of the process zone during the deep welding process in copper; comparison between the high-speed images and the process result (previous figure)

 

"We work closely with industrial partners and the Chair of Photonic Technologies (LPT) at FAU Erlangen-Nuremberg in application-oriented research. These can be the most diverse research topics or even direct industrial assignments. At the moment, our application-oriented research is mainly focused on laser processes for material processing of copper and aluminium materials. Especially in the field of e-mobility, there is a lot of research, as welding processes are required there to a high degree, be it for the contacting of battery cells or in the production of the power electronics of battery electric vehicles", reports Florian Kaufmann, who works in the field of "Process Technology Metals" in the application-related research at the blz.

Test setup for remote laser beam welding of metallic materials

 

Flexible camera use

The camera can be used as a mobile device for various applications as required. Thanks to its compact design with dimensions of 63 x 63 x 64.5 mm, it can be used flexibly and can also be taken away from home. The EoSens® mini2 is installed either directly in the beam path or from outside the machine. Depending on the application or system technology, the camera and lighting can also be suitably positioned using a tripod or robot arm to document what is happening.

"The camera images are used for the analysis of the process stability. We want to understand how the errors occur in the various applications and then use this knowledge to avoid them. For example, spattering is increasingly common in copper welding, especially in laser beam welding with conventional laser beam sources, which emit around 1 µm in the infrared spectrum. This must be recognized in time, because in the worst case this can lead to rejects or damage to the component," says Florian Kaufmann.

Great potential is seen in laser beam sources of visible wavelengths, which are currently taking the development step towards the high-power class. The blz has at its disposal a laser system from Trumpf GmbH, which is unique in Europe and offers 3 kW output power at 515 nm wavelength. "The investigation of the influence of the changed processing wavelength on the process result during laser beam welding of copper is an essential field of application in which we want to use the camera system".

Processing cabin for scanner-based laser beam welding of highly reflective materials with visible wavelength - process observation during welding of copper materials

 

The system limits the duration of a camera recording to 1.5 seconds. Depending on the image section and the laser process, longer observation times can also be selected. For example, during soldering, the system records in the range of up to 10 seconds, but this is accompanied by a smaller image section.
Depending on customer requirements and the problem at hand, the camera images are evaluated either optically subjectively or by means of an algorithm.

Since the camera is almost self-explanatory with the software supplied, there were hardly any questions to the support team. When there were questions about the camera's internal ring buffer, the support team was able to provide quick assistance. "Overall, we are very satisfied with the system," says Florian Kaufmann.

Laser beam deep welding of copper with green wavelength (λ = 515 nm)