2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Process Development: Powder Bed Fusion Monitoring and Imaging II
Program Organizers: Joseph Beaman, University of Texas at Austin

Tuesday 1:40 PM
August 15, 2023
Room: 410
Location: Hilton Austin

Session Chair: Toshiki Niino, University of Tokyo

1:40 PM
Comparative Analysis of Process Stability in PBF-LB/M: (Thermal) Highspeed Imaging vs. Melt Pool Monitoring using Novel Gas Mixtures: Tobias Deckers¹; Pierre Forêt¹; Franz Wolf¹; Stefan Kleszczynski²; Gerd Witt²; ¹Linde GmbH; ²University Duisburg-Essen
    The powder bed fusion of metals using a laser beam (PBF-LB/M) is increasingly gaining popularity in the industry. However, to compete with established manufacturing processes, ensuring a consistent quality of parts processed by PBF-LB/M is crucial. In-situ process monitoring systems, such as coaxial melt pool monitoring (MPM), can contribute to this goal by minimizing post-process quality control. To identify the relevant phenomena to be monitored, firstly, two monitoring systems, a commercially available MPM system and a thermal high-speed camera, were compared. Secondly, the suitability of the MPM system for in-situ quality control was tested by employing novel gas mixtures to the process. The mixtures include argon with hydrogen, helium, and carbon dioxide. The first results showed the capabilities of the MPM system to monitor relevant process anomalies. Also, the addition of helium and hydrogen to the process gas resulted in an improvement in the melt pool stability compared to argon.

2:00 PM
Application of In-situ Process Monitoring to Optimise Laser Parameters during the L-PBF Printing of Ti-6Al-4V Parts with Overhang Structures: John Power¹; Owen Humphreys¹; Mark Hartnett²; Darragh Egan¹; Denis Dowling¹; ¹I-Form; ²Irish Manufacturing Research
    The development of laser powder bed fusion (L-PBF) has allowed for increased flexibility and complexity of designs over other manufacturing methods. Overhang structures are a common challenge in L-PBF, as they can lead to print defects, e.g. porosity, due to the decreased thermal conductivity of the powder below the print layer, which causes overheating in the overhang meltpool. In-situ process monitoring, which involves real-time monitoring of the printing process, has been shown to be effective in detecting and correcting overhang defects. By controlling the laser energy during the printing of L-PBF overhang structures, the level of porosity and roughness can be significantly reduced (an 88% reduction in Ra roughness was achieved), while the microstructure can be optimised. This result was achieved by monitoring the meltpool temperature (based on photodiode IR measurements). Informed by these measurements, the laser treatment energy is closely controlled to prevent overheating the overhang print layer’s meltpool.

2:20 PM
Coaxial Photodiode Signal Trends and Predictions: Power, Speed, Spot Size, Material and Time: Gabe Guss¹; Aiden Martin¹; Nick Calta¹; ¹Lawrence Livermore National Laboratory
    The coaxial photodiode signal collected during laser powder bed fusion printing on our GE M2 series 4+ machine, has become important for multiple projects related to building feed forward models, predicting defects and optimizing parameters. To help justify our heavy use of this sensor data, more than a thousand single tracks were generated on titanium, stainless steel and aluminum, while varying power, speed and spot size. The experiment was then repeated after a year of time. We will report the trends in sensor data observed across these parameters, like increasing signal with laser power, decreasing signal with scan speed, and an unexpected, peaked signal with spot size, and the variation from the two, time separated experiments. Prepared by LLNL under Contract DE-AC52-07NA27344

2:40 PM
Enabling Advances in Laser Powder Bed Fusion with In Situ Monitoring: Steven Storck¹; vince pagan¹; Brendan Croom¹; Mary Daffron¹; Ari Lax¹; Robert Mueller¹; Mark Foster²; Colin Goodman²; ¹Johns Hopkins Applied Physics Laboratory; ²Johns Hopkins University
    The potential of additive manufacturing to disrupt production of components from aerospace to medical devices has been demonstrated over the last 2 decades. The application of these innovative technologies has, however, been limited by the ability to qualify critical hardware which often exceeds 60% of the final part cost. In addition to process quality, novel ways to apply in situ monitoring for alloy development will be discussed aiding in the accelerated implementation of classical or novel alloys currently unattainable with the technology. The JHU/APL team has developed two novel on-axis sensors capable of measuring at between 500,000 and 11,000,000 Hz in hyperspectral ranges enabling direct measurement of real time temperature and spectral information. This technology paired with advanced calibration enables decoupling of wavelength and thermally dependent emissivity. The sensor paired with a FPGA enables real-time control of the laser parameters at high rates unlocking prescribed processing temperature set point.

3:00 PM
High-precision Measurement of Melt Pool Properties during Laser-based Powder Bed Fusion of Metals by High-speed Imaging: Arno Elspass¹; Jan Wegner¹; Hanna Schönrath¹; Niklas Horstjann¹; Stefan Kleszczynski¹; ¹University Duisburg-Essen
    Laser-based powder bed fusion of metals is used to produce complex and high performance components for different industrial applications. Due to the high complexity of the underlying physical mechanisms during the process, its control is still challenging. To avoid process-specific defects, which affect mechanical properties, a huge amount of specific knowhow is crucial. Especially for regulated industries, such as medical or aerospace, this is a limiting factor for the widespread use of this technology. In this work high speed imaging in combination with a high magnification optic, resulting in a resolution of 1.44 µm/pixel is used to gain a deeper insight in the property-determining mechanism and boundary conditions during the process. Thereby, the intensity distribution of the melt pool is measured and analyzed with an imaging script to determine width, length and cooling rate by means of intensity. The potential of this data for predicting resulting material properties is demonstrated.

3:20 PM
High-speed Observations and Quantification of Spatter Counts and Trajectories in Laser Powder Bed Fusion : Christian Gobert¹; Jack Beuth¹; ¹Carnegie Mellon University
    In laser powder bed fusion additive (L-PBF) manufacturing, key process variables such as laser power, scan speed and hatch distance are varied and the respective impact on porosity content for coupon specimens is observed and reported in process maps. The resulting process maps help end-users identify key process regimes such as keyholing, fully dense, and lack of fusion in parameter space. One potential cause of porosity in L-PBF is spatter, which encompasses ejected material from laser-material interaction. In this work, spatter generation quantified through high-speed video observations of the printing process is correlated to the porosity content in cross-sectioned coupons across process space. Trained machine learning models are used to identify and track spatter in high-speed observations of the printing process. Spatter generation related to key process variables and materials is studied in the aim of identifying optimal process settings to minimize spatter emissions.

3:40 PM
High Speed Video Imaging of overhang surfaces in Beam Shaped Laser Powder Bed Fusion of 316L stainless steel: Lars Vanmunster¹; Arnout Dejans¹; Brecht Van Hooreweder¹; Bey Vrancken¹; ¹KU Leuven
    One of the novel strategies under investigation increase the build rate of laser powder bed fusion (LPBF) additive manufacturing is shaping the beam intensity profile to something other than a Gaussian distribution. Ring-like spot shapes are thought to allow for faster scan speeds and increased hatch spacing compared to defocused Gaussian beams. In this talk we will present our work on LPBF of 316L stainless steel with a variable beam profile laser switching between single mode and ring-like multimode spot shapes, implemented in a system allowing for in-layer beam switching. A high speed camera with fixed reference frame and a top down view is used to compare the difference in evaporation, denudation and spatter behavior between the different beam shapes for single tracks and full layers. The results improve our understanding of the potential to increase productivity with different beam shapes, and in-layer switching thereof.