2024 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2024): Process Development: Powder Bed Fusion V
Program Organizers: Joseph Beaman, University of Texas at Austin
Wednesday 8:00 AM
August 14, 2024
Room: 416 AB
Location: Hilton Austin
Session Chair: Emmanuel Ekoi, University of Texas at Austin
8:00 AM
Optical Tomography based on Near Infrared Imaging for Spatter and Distortion Detection in LPBF: Eduardo Miramontes1; Caleb Campbell1; Brett Eugene2; Shuchi Khurana2; Bradley Jared1; 1University of Tennessee; 2Addiguru, LLC
Laser Powder Bed Fusion(LPBF) has made significant strides, especially in the Aerospace, Defense and bio-medical industries. However, the process continues to be hampered by flaws such as distortion and spatter caused by process instability and cyclical thermal loading. To address the continued necessity for a system capable of detecting such flaws in-situ, in real time, an imaging technique known as Optical Tomography(OT) is being developed. By employing a near-infrared sensor, long exposure image capture, band-pass and neutral density filters, partial laser path images are obtained, which are combined into a cumulative image showing the pathway of the laser across a layer and variations in laser energy. Useful features are extracted from the images using Computer Vision(CV) and utilized to create a predictive model for pre and post-build distortion, and spatter. CT scanning and metallography supplied the ground truth for predictive models. Model predictions were tested on a validation build.
8:20 AM
Low-Cost Calibration Plate for Enhanced In-Situ Monitoring in Laser-Powder Bed Fusion (L-PBF): Brett Brady1; Caleb Campbell1; Shuchi Khurana2; Bradley Jared1; 1University of Tennessee, Knoxville; 2Addiguru
Laser-Powder Bed Fusion (L-PBF) additive manufacturing relies on precise control for quality assurance and reproducibility. In-situ monitoring is crucial for achieving these goals. We introduce a multi-modal calibration plate to enhance monitoring in L-PBF machines. Designed with materials of varying emissivity, it accommodates Near-Infrared (NIR) and infrared (IR) cameras. This plate facilitates the acquisition of multi-angle perspectives, allowing for camera mounting to differ between or within machines. By integrating different modalities and angles, calibrated overlays provide real-time insight into the printing process. Work demonstrated here involves a Pixelink NIR camera (visible wavelengths) and a FLIR A-50 IR camera (infrared wavelengths). Using a homography matrix, computed via the least squares method, perspective transformations ensure accurate imaging during printing. Work is currently ongoing to quantify the accuracy of the method, its repeatability, and its reproducibility. The error is expected not to exceed 3mm in any direction.
8:40 AM
Capturing 3D Temperature and Strain Fields using OBR Based Sensing in Additively Manufactured Parts: Brian Hlifka1; Gautum Parthasarathy2; Glen Koste2; Victor Ostroverkhov2; Claire Henderson2; Thomas Adcock2; Thomas Dyson2; Julin Wan2; Robert Landers1; Edward Kinzel1; 1University of Notre Dame; 2GE Aerospace Research
In-situ temperature and stress monitoring is critical for preventing part failure and enables the collection of performance data for future designs. Single-mode (SM) optical fiber sensors are a viable option given their dimensions and high sensitivity. Distributed measurements along the length of the SM fiber are captured using optical backscattering reflectometry (OBR), where fluctuations in the density of the optical fiber core cause Rayleigh scattering. The fiber is integrated into both plastic and LPBF-manufactured parts. A discrete thermal or stress load generates a response along the fiber and the responses from a series of loads can be assembled to form the signature space for the part. A new unknown load can be measured by projecting the OBR response into this space, with locally variable coupling allowing the stress and temperature to be differentiated. The paper presents the approach along with several demonstrations.
9:00 AM
The Effects of Multi-laser Process Parameters in LPBF Manufactured Inconel 718: Luis Marquez1; Diego Ariza1; Javier Lares1; Edel Arrieta1; Francisco Medina1; 1University of Texas at El Paso
This study investigates the influence of multi-laser process parameters on the porosity and alignment of Laser Powder Bed Fusion (LPBF) manufactured Inconel 718. The LPBF process, allows for the fabrication of complex geometries with high material efficiency. However, the quality of the manufactured parts, particularly porosity and alignment, are significantly affected by the process parameters used during printing. In this study, we focus on multi-laser stitching, a technique that involves the use of multiple lasers to manufacture a single part. Process parameters were systematically varied during the printing of jailhouse type specimens, including build direction, laser power, scanning speed, and alignment, to analyze their effects on the resulting porosity. We observed that certain combinations of process parameters can significantly reduce porosity, leading to improved mechanical properties. This research provides insights for optimizing the LPBF process for the manufacturing of Inconel 718, by presenting a correlation between process parameters and resulting porosity.
9:20 AM
Effect of Processing Conditions on the Background Signal in Acoustic Monitoring in Laser Powder Bed Fusion: Shivam Shukla1; Milad Nasab1; Bey Vrancken1; 1Department of Mechanical Engineering, KU Leuven, Celestijnenlaan 300, 3001 Leuven, Belgium & Flanders Make@KU Leuven, 3001 Leuven, Belgium;
Due to its high temporal resolution acoustic emission-based monitoring has shown great potential for laser powder bed fusion, as it enables to capture events in 10-100 μs time scale along with sub-surface information. However, being highly sensitive in nature, the obtained results are influenced by several non-process related factors other than the laser settings. In this study, a microphone and a vibro-acoustic sensor below the base plate are used to determine the effect of sample positioning, scan vector orientation, gas flow, and other background variables on the acoustic signals at a 1.25 MHz sampling rate. Results show that the microphone’s response is more susceptible to variations in these background processing conditions than for changes in the laser power and the scan speed, especially compared to the structure-borne acoustic emission sensor. The results can be leveraged to more comprehensively determine the acoustic background signals during LPBF, to improve the signal-to-noise ratio.
9:40 AM
Gradient Segmentation of In-Situ Infrared Images for Porosity Detection in Electron Beam Powder Bed Fusion: Brian Johnstone1; Christopher Saldana1; 1Georgia Institute of Technology
For metal additive manufacturing to be more effectively and widely used, greater process control is needed. One way to achieve this is through in-situ process monitoring, such as using layer-wise infrared imaging to detect porosity in electron beam powder bed fusion. Due to the pores having more emissivity than the solid part, they appear brighter in infrared images and can therefore be detected via image processing techniques. This work compares how applying different image filtering and gradient types can detect these brighter spots correlating to developing pores. Results were assessed both qualitatively via image appearance and histogram distributions and quantitatively via X-ray computed tomography scans. Gradients that use larger kernel sizes (specifically three-by-three) were more accurate in detecting porosity, and this was further aided by an anisotropic diffusion filter. This work provides objective insight into using gradient-based segmentation for academic and industry defect detection for greater process control.
10:00 AM
Quantitative Analysis of In-situ Pore Removal in Porous L-PBF Substrates: Garrett Mathesen1; Conor Porter1; Fred Carter1; Jian Cao1; 1Northwestern University
While laser powder bed fusion (L-PBF) is a popular method of metal additive manufacturing, it is still limited in adoption by certain industries due to porosity created during the manufacturing process. Post-processing methods of porosity removal or closure exist, such as hot isostatic pressing, but may have limited effectiveness. This work details quantitative analysis of the in-situ porosity removal process in AlSi10Mg for L-PBF utilizing high speed operando X-ray imaging. The pore removal process was observed through laser scanning of porous substrates both with and without powder with variations in the scan speed and laser power. Image processing techniques were used to classify and calculate pore metrics to determine the count, size, and depth of the removed pores in the X-ray images and the change in the relative density of the part for different parameter sets. These observations show the possibility of utilizing these removal processes during successive layer scanning.
10:20 AM Break
10:40 AM
In-Situ Powder Assessment by Frequency-Domain Thermal Response
: Sina Ghadi1; Xiaobo Chen1; Nicholas Tomasello1; Srikanth Rangarajan1; Guangwen Zhou1; Scott Schiffres1; 1State University of New York
In powder-bed additive manufacturing, metal powder defects can compromise product quality. We introduce a non-destructive evaluation method sensitive to thermal properties at adjustable depths. This method modulates the energy source and analyzes temperature responses in the frequency domain, enabling us to assess thermal properties and detect defects in metal powders and printed materials while providing clearer melt pool temperature measurements.Our experimental setup, revealing distinct responses tied to material features such as core detection, age, oxygen content, and particle size distribution. This real-time detection process works seamlessly with existing powder bed fusion lasers and demonstrates sensitivity across materials like Cu, AlSi10Mg, In718, SS316L, Ti64 G23, and G5. Frequency-domain measurements are less noisy and more robust than traditional thermography methods. By applying machine learning techniques, we successfully identify powder core, age, oxidation, deposition thickness, and size distribution. This innovative approach has promising potential to enhance quality control and process monitoring.
11:00 AM
Process Parameter Development for SS316L on the Freemelt-ONE Open Architecture Electron Beam Powder Bed Fusion Machine: Berkay Bostan1; Dylan Treaster2; Daniel Ju2; Diederik Schlingemann2; Yanen Huang2; Shlok Desai2; William Templeton2; Sneha Narra2; 1University of Pittsburgh; 2Carnegie Mellon University
This study was conducted by graduate students in a semester-long additive manufacturing laboratory class as part of the term project. The goal is to develop deposition parameters for SS316L on the Freemelt-ONE Electron Beam Powder Bed Fusion machine in a span of four weeks and using only one build. Due to the lack of established parameters for SS316L particularly for Freemelt-ONE, a simple analytical model was used in conjunction with defect criteria and established process conditions for the laser powder bed fusion (LPBF) process to quickly develop an initial set of process parameters - power, velocity, and hatch spacing. Results will focus on defects and overall process viability. This work highlights the effectiveness of a simplified strategy in determining preliminary process parameters by leveraging the established knowledge in the LPBF process. It paves the way for subsequent fine-tuning and optimization through comprehensive experimental characterization or high-fidelity modeling for SS316L.