2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Process Development: Powder Bed Fusion Monitoring and Imaging III
Program Organizers: Joseph Beaman, University of Texas at Austin
Wednesday 8:00 AM
August 16, 2023
Room: 410
Location: Hilton Austin
Session Chair: David Deisenroth, National Institute of Standards and Technology
8:20 AM
Laser Induced Breakdown Spectroscopy for In-situ Monitoring of Laser Powder Bed Fusion Processing: Justin Krantz1; Cody Lough2; Ben Brown2; Jinyu Yang1; David Go1; Robert Landers1; Edward Kinzel1; 1Univ. of Notre Dame; 2Kansas City National Security Campus
Laser powder bed fusion is the most widely used powder-based additive manufacturing process. A major hurdle for laser powder bed fusion processes is identification and addressing of flaws in the as-built part. In-situ monitoring of laser powder bed fusion processes allows for identification of flaws and the potential to address them during the build. A particular emphasis is placed on the ability to capture information about the material composition through laser-induced breakdown spectroscopy. An ultrafast pulsed laser is coaligned with a continuous wave process laser for simultaneous application. The ultrafast laser is used to probe the melt pool of in-process laser powder bed fusion build, creating a plasma from which signals are collected. The use of the ultrafast laser minimizes adverse effects on the melt pool during processing. This process allows for superior emission collection capabilities compared to techniques such as optical emission spectroscopy.
8:00 AM
Infrared Camera (IR) Feature Extraction for Defect Detection in Laser Powder Bed Fusion: Shawn Hinnebusch1; Berkay Bostan1; David Anderson1; Albert To1; 1University of Pittsburgh
Part qualification is a critical step in advancing additive manufacturing. This work uses an infrared (IR) camera to construct features for a machine learning algorithm to predict defects with +90% accuracy. A custom heating module with thermocouples was employed to calibrate the IR camera with various scanning strategies from room temperature up to 500 ℃. Another custom plate enables angle perspective corrections accounting for distortion caused by the rotation or angle effects of the camera. After image correction, a voxel mesh is superimposed on top of the IR data to distinguish between the powder and the part. The images are separated by layer to analyze layerwise heat accumulation, cooling rates, heat intensities, melt pool spatter, spatter landing location, and scanning strategy. A machine learning algorithm uses the 3D reconstruction as the input to predict defects in a lack of fusion part.
8:40 AM
Layer-wise In-process Monitoring-and-Feedback System Based on Surface Characteristics Evaluated by Machine-Learning-Generated Criteria: Toshi-Taka Ikeshoji1; Makiko Yonehara2; Kenta Aoyagi3; Kenta Yamanaka3; Akihiko Chiba3; Hideki Kyogoku1; Michiaki Hashitanani2; 1Kinki University K.U.RING; 2TRAFAM; 3Tohoku University
In the laser powder bed fusion (PBF-LB) process, a set of parameters that are considered optimal are selected. Still, a set of parameters cannot accommodate complex model geometries, model placement in the build chamber, and unforeseen circumstances, leading to internal defects. Therefore, a new in-situ monitoring and feedback system has been developed to suppress the occurrence of lack-of-fusion (LOF) defects in the PBF-LB process. This system measures surface properties after each laser irradiation to predict whether LOF defects occur. Then, if necessary, a feedback process is performed to re-melt the same surface. Evaluation thresholds are defined by a combination of aerial surface texture parameters created in advance by machine learning of surface properties and defect occurrence. For example, a square pillar of Inconel 718 alloy built with feedback had a higher relative density than one without feedback.
9:00 AM
Multi-laser Diode Area Melting of Ti6Al4V: A Novel Alternative Approach to Traditional Laser Powder Bed Fusion: Mohammed Alsaddah1; Kristian Groom1; Kamran Mumtaz1; 1The University of Sheffield
Laser Powder Bed Fusion (LPBF) selectively melts thin layers of metallic powder. The process depends on a high-power fibre laser at a wavelength of 1060nm using a galvo scanning system to create 3D complex parts. However, this method presents related challenges, such as scalability, processing efficiency (due to poor radiation absorption and wall-plug efficiency), and high thermal gradient due to rapid solidification. An alternative approach has been developed called Diode Area Melting (DAM) offers better process efficiency, scalability and controllable thermal gradient (lower cooling rate) during the process by incorporating several individually controllable, low-power (4.5W) with a short wavelength (808nm) using fibre-coupled diodes lasers into a single laser head traversing over the powder bed. This work demonstrates the potential of using DAM to process Ti6Al4V material by employing multiple lasers with different beam profiles to improve the process efficiency, mechanical properties, and microstructure of the final parts.
9:20 AM
Multimodal Process Monitoring to Predict Outcomes during Laser Powder Bed Fusion: Nicholas Calta1; Sanam Gorgannejad1; Yuchen Sun1; Maria Strantza1; Aiden Martin1; Gabe Guss1; Michael Juhasz1; Jenny Nicolino1; 1Lawrence Livermore National Laboratory
Process monitoring is a significant area of ongoing research in the laser powder bed fusion (LPBF) community because of its potential to accelerate part certification and qualification. A variety of different monitoring modalities have been applied to LPBF including approaches based on thermal emission, plasma emission, acoustic emission, optical and infrared imaging, and others. These disparate monitoring approaches provide different and often complimentary information about process stability. This talk will give an overview of how multiple monitoring approaches can be used in a complimentary fashion to identify both process stability and defect formation events. This is accomplished by selecting monitoring modalities that probe orthogonal aspects of the physical process. The primary focus will be on optical and acoustic emission monitoring in concert with high speed X-ray imaging, but other modalities will also be discussed. Prepared by LLNL under Contract DE-AC52-07NA27344.
9:40 AM Break
10:10 AM
Optical Metrology for Laser-matter Interaction in LPBF: Challenges and Opportunities: David Deisenroth1; 1National Institute of Standards and Technology
Recent studies in optical metrology of laser powder bed fusion (LPBF) indicate that there remains insufficient understanding of the optical phenomena that occur during laser-matter interaction, which limits the accuracy of non-contact measurements for multiphysics model validation applications. One of the first challenges is accurate measurement of the power density distribution (often a two-dimensional gaussian profile) of high-power lasers under conditions of interest for LPBF. Furthermore, process byproducts (including metal vapor, condensate, and ejecta) can interact with the light propagating to (and from) the melt pool, which can attenuate, scatter, or otherwise distort the power density distribution that is delivered to the melting surface; preliminary results of measuring the effects of process byproducts are discussed. Finally, metrology for quantifying the total laser power reflected from the laser-matter interaction (used to approximate laser absorption), as well as for visualizing the directional distribution of reflected laser power, will be discussed.
10:30 AM
The Detection of Defects Caused by Reduced or Interrupted Shield Gas Flow in Laser Powder Bed Fusion: James Bell1; 1Imperial College London
Without proper shield gas flow in laser powder bed fusion (LPBF), soot and condensate in the plume escaping the melt pool will interfere with the laser causing porosity. In this study gas flow was varied for several layers while building columnar parts located across the build plate, and the effect of blocking sections of the outlet while building was also investigated. Co-axial monitoring with a high-speed camera was used to determine whether the reduction in, and interruption of gas flow could be detected by changes in the melt pool geometry and other features indicative of suboptimal melting conditions. The flow speed was measured across the build chamber. Results showing the changes in monitoring signal due to reduced and interrupted gas flow are presented, as well as the induced differences in part quality. Transferability of the findings to a production system using a photodiode for melt pool monitoring will be discussed.
10:50 AM
Time-resolved Optical Spectroscopy in Metal Powder Bed Fusion: Matthias Beuting1; Luis Escano1; Alex Fairhall1; Randall Goldsmith1; Lianyi Chen1; Scott Sanders1; 1University of Wisconsin-Madison
Our work addresses the challenge of understanding the dynamics of the interaction between partially evaporated metal and the melt pool in powder bed fusion. So far, few contactless sensing strategies have been developed for measuring metal vapor temperature, density, and composition - information crucial for modeling the influence of plume recoil pressure on the microstructure of the part being built. We used optical emission spectroscopy (OES) and tuned diode-laser absorption spectroscopy (TDLAS) to study the vapor plume during the processing of Ti-6Al-4V. The use of novel blue diode lasers allowed for time-resolved measurement of the temperature of gaseous vanadium using TDLAS in selective laser melting (SLM) and electron beam melting (EBM). The fast repetition rate of 20 kHz provided further insights into the transient plume conditions in EBM, revealing a roughly symmetrical shape with uniform temperature.
11:10 AM
Using In-situ Two-color Thermal Imaging to Validate Multi-physics CFD Melt Pool Models for LPBF: Alexander Myers1; Guadalupe Quirarte1; Francis Ogoke1; Amir Barati Farimani1; Jack Beuth1; Jonathan Malen1; 1Carnegie Mellon University
An experimental method to image melt pool temperature with a single color camera was developed, and the in-situ measurements were used to better understand melt pool physics. The experimental approach leverages the principle of two-color thermal imaging, which negates the need for a priori knowledge of melt pool emissivity. The high-speed color camera's ability to accurately measure temperature was validated with a NIST blackbody source. It was then used to image 316L stainless steel single beads off-axis on the TRUMPF TruPrint3000 laser powder bed fusion machine. Multi-physics computational fluid dynamics models (CFD) are used to simulate metal melt pools, but some parameters are not well characterized for metals. Fitting a FLOW-3D model to ex-situ measurements of the melt pool cross-sectional geometry identifies multiple combinations of model parameters. Comparing the simulated temperatures to the in-situ measurements narrows the parameter selection, motivating the need for thermal imaging to advance CFD model validation.
11:30 AM
Two-color Thermal Imaging of WC-Ni Cermet Melt Pools in Laser Powder Bed Fusion: Guadalupe Quirarte1; Alex Gourley1; Alexander Myers1; B. Jayan1; Jack Beuth1; Jonathan Malen1; 1Carnegie Mellon University
Resolving the melt pool temperature distribution in additive manufacturing processes is key to understanding the underlying physics and developing improved process monitoring tools. This project applies a new method to measure dense tungsten carbide (WC)-17 wt.% nickel (Ni) composite melt pool temperatures in laser powder bed fusion (L-PBF) using a high-speed color camera two-color technique. Conventional manufacturing of cermets like WC-Ni is difficult compared to metal alloys, but these materials can have advanced performance and can be made by additive processes. One of the major challenges associated with experimental temperature measurement methods in L-PBF is the accelerated and localized heating and cooling of the process. Measuring the melt pool temperature using conventional infrared imaging techniques or pyrometry lack the temporal and spatial resolution needed for measuring LPBF melt pool temperature profiles. Separate measurements of WC-Ni cermet thermal conductivity enables improved thermal models that are compared with the experimental temperature measurements.