Investigation of the Process Windows of PBF-LB/Ti6Al4V for Variable Laser Spot Diameters

Abstract

The layer-by-layer component generation, which is characteristic for additive manufacturing processes, makes it comparatively easy to produce complex structures. Since no component specific tools or devices are required, a production of highly individualized components is possible. The most widespread additive manufacturing technology of metals in industry is laser-based powder bed fusion (PBF-LB). In this process, commonly a laser with a fixed spot diameter is used to selectively melt the metallic powders in the powder bed. However, the laser spot diameters used are usually smaller than 100 µm and thus adapted to the production of fine structural details. This leads to the disadvantage of low build-up rates of the PBF-LB processes. To overcome this conflict, a defocusing of the laser beam can be used, which allows a variation of the laser spot diameter within the process. In this work, the process windows for variable laser spot diameters are determined based on a design of experiments (DOE) approach in which laser power, scanning speed and hatch distance are varied. The criteria used to define the process windows are the relative density of the samples as well as the process stability. Based on the experimental results, the potential of defocusing to increase the build-up rates is derived for the titanium alloy Ti6Al4V. Furthermore, a machine learning based anomaly detection model is used to support the investigations presented in this work.

Keywords: additive manufacturing, process windows, laser-based powder bed fusion, anomaly detection