Methodology for the identification and implementation of application specific intensity distributions for material processing with laser radiation

Fraunhofer-Publica (Fraunhofer-Gesellschaft)

Abstract

The presently ongoing digitalization in industry and society increasingly enables a detailed analysis as well as a simulative representation of manufacturing processes. This especially holds for laser-based material processing for which appropriate processing parameters can be identified through an accurate modelling of the basic physical principles. One relevant parameter in these processes is the laser beam’s intensity distribution, which strongly influences the temporal and spatial temperature profile within the treated workpiece and subsequently defines the resulting processing quality as well as efficiency. Thus, in this work, application specific intensity distributions that induce previously defined temporal and spatial temperature profiles within the workpiece are numerically derived and realized. In a first step, the needed intensity distribution is computed by formulating the situation as an inverse heat conduction problem which is solved numerically. Here, the approach is restricted to processes where only a heating of the material without change in state of aggregation takes place. Examples for those processes are laser hardening, laser softening of high-strength steels, the laser assisted tape placement or – making certain assumptions – the laser based thin film functionalization. The implemented method then accounts for temperature dependent thermophysical and optical material properties, complex 3D-geometries, surface or volume absorption of the laser beam energy, as well as quasi-stationary or time-dependent distributions. Afterwards, beam shaping methods are presented within this work which are applicable for the realization of the obtained, strongly inhomogeneous intensity distributions. On one hand, the use of freeform optics that enable the generation of almost any stationary intensity distribution through a specific shaping of their optical surfaces is suggested. For the implementation of freeform optics in laser material processing, design strategies are presented that - for the first time – rigorously take into account the comparably low beam quality of the used laser radiation. Alternatively, as it is impossible to use freeform optics for a timedependent adaptation of an intensity distribution, methods for the application specific beam shaping with VCSELs are presented. These are specially designed high-power lasers that exhibit the potential of a plane arrangement with different zones which are independently addressable for a flexible beam shaping. In this work, new strategies are described to calculate the necessary VCSEL control and arrangement for the realization of application specific intensity distributions in materials processing. Finally, validations of the simulative approaches are presented by means of experimental results.

Authors 1

1. Annika Bonhoff corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen