ReLaTiS – Transient Spatial Reflection of Laser Radiation during Laser Deep Penetration Welding

Motivation

The advantages of laser beam welding, such as its high flexibility, its high local energy input, and its fast processing speed, led to a substantial in-crease of industrial applications using this technology. However, only a portion of the laser energy is absorbed during welding due to reflections. These reflections can damage the system components and lead to a reduced process efficiency. Especially during the formation of the keyhole high intensities occurs. For this reason, the main focus in this research project was the investigation of the dynamic behavior of the reflected laser radiation.

Project Goal

The aim of the research project was the development of a process model to calculate the radiation intensity in the surrounding area of the process zone. In addition, an experimental investigation of the reflections should be carried out. Therefore, necessary laser safety measures could be designed as a function of the actual radiation load.

Description of the work carried out

For the experimental measurement of the reflections, a measurement technique was developed, which allows the measurement of the reflections on the entire hemisphere during a deep penetration welding process. In addition to the experimental investigations, a process model was developed to calculate the reflections during the formation of the vapor capillary. Different phases had to be taken into account. In the first phase, the laser radiation is reflected on the solid material before it melts and then evaporates, resulting in the formation of a vapor capillary. To calculate the reflection on the solid material, the surface roughness of the material had to be considered. This was implemented in the form of a Gaussian random interface. In order to consider the beam propagation, a raytracer was programmed, in which a beam is split into many individual beams. For each single beam, the beam propagation is calculated according to the laws of geometrical optics. In order to simulate the deformation of the surface by evaporation, a numerical CFD model was developed in this research project which takes into account the temperature as well as the flows in the liquid and vapor phase. Through the coupling of the numerical model with the raytracer, the influence of the beam propagation on the absorption in the material as well as on the reflection during this process could be investigated.

Acknowledgment

„ReLaTis“ was funded by the Deutsche Forschungsgemeinschaft (DFG).

Duration 01.08.2013-29.02.2016
Funded by DFG