Influence of the opto-mechanical chain on the energy provided by the laser spot to the material in laser powder bed fusion processes

The additive manufacturing machines used in laser powder bed fusion processes are composed of an opto-mechanical chain whose purpose is to focus the laser in the work plane to locally fuse the material with the required energy. The opto-mechanical chain does not only position the laser spot, it also induces a modification of its shape and thus the distribution of energy brought to the material. As a result, the shape of the laser spot is not the same at every point on the machine, which can have an influence on the characteristics of the produced parts. This aspect related to opto-mechanical chain technology is very often ignored, particularly in thermal modelling. In this work, we study the impact of opto-mechanical chains composed of post-objective focusing systems on the energy distribution of the laser spot in the entire achievable space by the system. For this purpose, mathematical models are used to evaluate the position of the laser spot in the work plane as well as the orientation of the laser beam. An energy model of Gaussian laser beams is then used and applied to these geometric models. The coupling of these two models makes it possible to study the energy distribution of the laser spot at any point in the workspace of an additive manufacturing machine. The work is confirmed with experimental measurements made on a test bench representative of an industrial additive manufacturing machine.