A major factor slowing down the establishment of additive manufacturing processes as production processes is insufficient reproducibility and productivity. Therefore, this work investigates the influence of ring-shaped beam profiles on process stability and productivity in laser-based powder bed fusion of AISI 316L. For this purpose, the weld track geometries of single tracks and multi-track segments with varying laser power, scan speed, hatch distance, and beam profile (Gaussian profile and three different ring-shaped profiles) are analyzed. To evaluate the process robustness, process windows are identified by classifying the generated single tracks into different process categories. The influence of the beam profiles on productivity is studied by analyzing the molten cross-sectional areas and volumes per time. When using ring-shaped beam profiles, the process windows are significantly larger (up to a laser power of 1050 W and a scanning speed of 1700 mm/s) than those of Gaussian beams (laser power up to 450 W and scanning speed up to 1100 mm/s), which suggests a higher process robustness and stability. With ring-shaped beam profiles, larger volumes can be stably melted per track and time. The weld tracks created with ring-shaped profiles are significantly wider than those generated with Gaussian profiles (up to factor 2 within the process window), allowing enlargement of the hatch distances. Due to the higher scanning speeds and the enlarged hatch distances for ring-shaped beam profiles, the process can be accelerated by a factor of approximately 2 in the parameter range investigated.

Despite the maturity of laser-based powder bed fusion of metals (PBF-LB/M), some barriers prevent the manufacturing process from fully being established in the industry. One drawback is spatter formation, which is disadvantageous to PBF-LB/M for three main reasons. First, adhering spatter can initiate coater collision, resulting in process failure. Second, large adhering spatter may cause lack-of-fusion defects as they require more energy to remelt sufficiently compared to unprocessed powder. Furthermore, big nonadhering spatter cannot be recycled as powder. The recycling of small spatter particles potentially results in degraded material properties. Ring-shaped beam profiles have been established for deep penetration welding to reduce spatter formation. Investigations on ring-shaped beam profiles in PBF-LB/M focus on improving productivity and process robustness. Qualitative spatter reduction in PBF-LB/M using ring-shaped beam profiles has also been reported. This publication quantitatively examines the influence of ring-shaped beam profiles on spatter formation in PBF-LB/M. Image processing algorithms of on-axis high-speed images are utilized for spatter detection and tracking. A self-developed spatter segmentation is used to determine the spatter size. A Laplacian of Gaussian filter is combined with a Kalman tracker to count and track the spatter. The results show that spatter formation is highly influenced by the beam profile and the chosen process parameters. Considering the melt track width, ring-shaped beam profiles could reduce the number of spatter per fused area. High numbers of spatter are generated when parameter sets result in balling. Moreover, spatter velocity is primarily dependent on the introduced dimensionless enthalpy.

Manufacturing structures with low overhang angles without support structures is a major challenge in powder bed fusion of metals using laser beam (PBF-LB/M). In the present work, various test specimens and parameter sets with continuous wave (cw) and pulsed exposure are used to investigate whether a reduction of downskin roughness and overhang angle can be achieved in PBF-LB/M of Ti6Al4V. Starting from cw exposure, the limits of overhang angle and surface roughness at the downskin surface are investigated as a reference. Subsequently, the influence of laser power, scanning speed, and hatch distance with fixed pulse duration (τ_pulse = 25 µs) and repetition rate (υ_rep = 20 kHz) on surface roughness R_a is investigated. Pulsed exposure strategies enable the manufacturing of flatter overhang angles (≤20° instead of ≥25°). Furthermore, a correlation between the introduced volume energy density and the downskin roughness can be observed for pulsed exposure. As the reduction in volume energy density causes an increase in porosity, the combination of pulsed downskin exposure and commercial cw infill exposure is investigated. The larger the gap in volume energy density between the infill area and downskin area, the more challenging it is combining the two parameter sets. By combining cw infill and pulsed downskin exposure, flatter overhang structures cannot be manufactured, and a reduction in roughness can be achieved.

Several studies demonstrate the potential of pulsed exposure strategies for improving spatial accuracy, surface quality, and manufacturability of low-angle overhangs in laser-based powder bed fusion of metals. In this paper, those fundamental potentials are transferred to the support-free manufacturing of heat exchanger structures with partial horizontal overhangs made of Ti6Al4V. The pulsed exposure with pulse repetition rates of 20 kHz and pulse duration of 25 µs enabled the support-free manufacturing of these complex structures with densities of more than 99%. A comparison of the Archimedean density determination with optical density determination using micrographs indicate permeability of the specimens below an applied volume energy density of 30 J/mm³ due to open porosity. Furthermore, the pulsed manufactured structures show an improved flow behavior within the heat exchanger compared to specimens manufactured with continuous exposure strategies.

Computational models that predict melt pool shapes and temperature evolution in laser-based powder bed fusion of metals (PBF-LB/M) can range from simple thermal simulation models to more advanced models that incorporate more detailed physics of the process. While advanced models can accurately predict thermal fields and melt pool fluid dynamics, they are computationally more expensive and, thus, less suited for part-scale simulations or numerical optimization, where repeated model evaluations are necessary. On the other hand, thermal simulations are computationally efficient and attractive for their simplicity, but their accuracy is mainly limited to conduction-dominated processes. Moreover, the conduction model’s validity range is not fully understood for non-Gaussian laser beam shapes. This paper demonstrates that predictions of melt pool depth and width carried out by a heat conduction model are accurate to within 20 % for all investigated laser profiles, provided that the simulated maximum temperature does not exceed a certain threshold value for stainless steel 316L. This is established by thoroughly investigating the validity range of the heat conduction model through comparisons with over 200 single-track experiments on bare plates. The temperature predictions from the model are compared with multi-physics simulations using smoothed particle hydrodynamics (SPH). Through detailed analysis and validation for three laser beam shapes, this contribution provides valuable insights into the accuracy and applicability of heat conduction models in bead-on-plate melting simulations and offers a path to optimize process parameters, such as laser beam shape, scanning strategy, and other processes for diverse applications aimed at PBF-LB/M.