Concentric Scanning Strategies for Laser Powder Bed Fusion: Porosity Distribution in Practical Geometries

Abstract

Besides the optimisation of process parameters such as laser power or scan speed, the choice of the scan path represents a possibility to optimise the laser powder bed fusion process even further. The usual hatching strategy creates a homogeneous microstructure but makes it necessary to switch the laser off and on after each scan vector, which can slow down the fabrication. Moreover, the end of each scan vector is a location susceptible to the creation of keyhole pores. In this work, these disadvantages were meant to be avoided by using scan strategies that consist of longer paths and thus less end of track points. To this end, an open-source tool to tailor the LPBF G-code to geometric part features and advanced path configurations was developed and embedded into a co-visualization platform. With this tool, specimens built with four different types of paths were fabricated and the effect of these alternative scan strategies on pore distributions and path neighbourhood was investigated using micro-computed tomography. In the examined example geometry, a spiral scan pattern reduced the distance the laser had to jump between scanning by 78%. However, with the alternative path patterns, the defect architecture was strongly dependant on the part geometry and increased the overall porosity to 0.42%. Respective alleviation approaches are therefore necessary and are discussed in the remainder of this work.

Influence of laser powder bed fusion scanning pattern on residual stress and microstructure of alloy 718

“…10b. In both images, slightly increased number of defects around the center is observed which was observed for con-centric scanning [45]. In the BSD image, concentric circles are observed related to the phase contrast.…”

Process-Specific Topology Optimization Method Based on Laser-Based Additive Manufacturing of AlSi10Mg Components: Material Characterization and Evaluation

“…A typical region with higher porosity in PBF-LB components is, for example, the interface between the contour and hatching area. Typically, this region has a small thickness of about 100 µm, thereby, making it difficult to experimentally characterize [23]. Therefore, an approach was used in this study in which the 3D microstructure was reconstructed from binarized µCTdata to determine effective elastic constants with the use of finite element analysis (FEA).…”

“…Afterwards, the hatching of the inner areas (hatching area) takes place. Therefore, an increase in keyhole-porosity can be found in the interface between the contour and hatching area leading to an inhomogeneous distribution of pores in PBF-LB components [23,24]. During a cyclic load, pores can lead to crack initiation and have therefore a major impact on the fatigue performance of a component [25].…”

“…The minimum wall thickness results from the fact that, in each layer plane, all three characteristic regions must be present in the following order: Contour-Interface-Hatching-Interface-Contour. Thin-walled component areas can often be scanned without the use of a hatching scan, which can lead to deviations regarding the assumed porosity distributions [23]. The averaged material properties resulting from the characterization in Section 3.1 are assigned to the three characteristic regions with the use of the material database as shown before.…”