2024 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2024): Process Development: Powder Bed Fusion II
Program Organizers: Joseph Beaman, University of Texas at Austin
Tuesday 8:00 AM
August 13, 2024
Room: 415 AB
Location: Hilton Austin
Session Chair: Frank Liou, Missouri University of Science and Technology; Sivasubramanian Chandramouli, Purdue University
8:00 AM
A Mechanical Test Artifact for Determining Relative As-built Fracture Toughness in Laser Powder Bed Fusion: Dinh Son Nguyen1; Soumya Sridar1; Wei Xiong1; Albert To1; 1University of Pittsburgh
This work proposes a mechanical test artifact that provides a quick assessment of the relative as-built fracture toughness of PBF-processed materials. The proposed artifact consists of a cantilever beam attached to a rectangular bar to form a sharp interface. Due to an increasing amount of residual stress with build height, the interface will eventually crack at the interface on the free end of the cantilever beam. Since fracture toughness is highly sensitive to defects, the extent of cracking provides an indication of the relative fracture toughness among different processing conditions. To demonstrate its capability, the proposed test artifact is utilized to optimize the process parameters for Inconel 718 using a process mapping approach. The process map obtained reveals that the measured crack length on the printed artifact has a higher sensitivity than the measured density with varying process parameters, allowing the optimal parameters to be identified easily.
8:20 AM
Influence of Layer Pitch Expansion for PBF-LB/P Efficiency Improvement on Part Strength: Yuki Yamauchi1; Koichi Fujii1; Takashi Kigure1; Toshiki Niino2; Hirofumi Nonaka3; Mitsuhiro Kumasaka3; 1Tokyo Metro Ind Tech Research Institute; 2Institute of Industrial Science, the University of Tokyo; 3ASPECT Inc.
Although PBF-LB/P is one of the most promising additive manufacturing technologies for part production, the industries that use it are limited. One reason for this limitation is the production cost of PBF-LB/P, which can be reduced by increasing process efficiency, such as production speed. In this study, to improve the production speed of PBF-LB/P, we attempted to expand the layer pitch, which is called the layer thickness, that is, the distance of platform movement per layer. The layer pitch can affect the interlayer adhesion or part strength. Herein, the relationship between layer pitch and tensile strength in the z-direction was investigated. Because the energy required to melt the supplied powder per layer also varies with the layer pitch, process parameters such as the energy density of laser exposure per layer were adjusted when the specimens were built.
8:40 AM
Process Limitation for Powder Bed Fusion with Laser Beam Multiplication: Florian Spieth1; Thorsten Heeling1; Hans-Christian Moehring2; 1Robert Bosch Manufacturing Solutions GmbH; 2Institute for Machine Tools University Stuttgart
The necessity to improve the productivity per laser in powder bed fusion is driven by demands for increasing build rates, combined with high resolution and process requirements. One promising solution is the use of a beam splitter to build multiple parts with a single laser scanner system at once, utilising the full available laser power available in today’s single mode laser systems. However, due to its specific characteristics, this approach leads to limitations regarding part size, process window, build job layout, geometric tolerances, and machine specifications. This publication aims to investigate the influence of process boundaries on viable applications. In particular, the effect of beam splitting-related optical errors and the effect of shielding gas flow direction are analysed. The position dependent intensity and the superposition of effects are evaluated in terms of future boundaries on the technical implementation. Additionally, potential compensation methods for mitigating the detected limitations are discussed.
9:00 AM
Development of an In-situ Laser Calibration Method for Multi-laser Powder Bed fusion Additive Manufacturing System: Ho Yeung1; David Deisenroth1; Sergey Mekhontsev1; 1National Institute of Standards and Technology
A new in-situ laser calibration method for multi-laser powder bed fusion (LPBF) systems has been developed to address the prevalent challenges of part quality at the stitched regions due to misalignments of different lasers. In the proposed method, cameras coaxially aligned with the processing lasers are utilized, capturing images of a dimensional reference artifact during scanning and reconstructing the scan path from these images in the artifact’s coordinates. This enables an automated and precise calibration of each laser to a unified global coordinate system without the necessity of external measurements. Preliminary tests show that the patterns scanned by two different laser systems are highly superimposed, with errors less than 20 micrometers. This method is expected to enhance the efficiency and quality of multi-laser LPBF systems by ensuring precise alignment and synchronization of laser beams.
9:20 AM
Multi-Laser Powder Bed Fusion of Cu10Sn Using Low-Power 450nm Diode Lasers: Erhan Cetin1; Alkim Aydin1; S. Can Erman1; Kamran Mumtaz1; 1University of Sheffield
Due to its inherent high reflectivity, the processing of copper and its alloys is challenging using low power lasers. Literature reviews indicate that using a 450 nm blue laser for processing copper increases absorptivity dramatically from 5% to 65% (x13 higher) compared to traditional laser powder bed fusion (LPBF). Therefore, this study aims to demonstrate that diode lasers with a wavelength of 450 nm are suitable for producing Cu10Sn samples. In this work, diode point melting additive manufacturing technique was used and single layers were produced using diode lasers connected to the X-Y portal to scan on the copper substrate. Various hatch distances (i.e., 50, 75, 100, and 125 μm), scanning speeds (ranging from 150 to 2100 mm/min), and laser powers (20 and 40 W) were selected as process parameters. To determine the mechanical and physical properties of the sample, surface roughness, relative density and melt pool characterization were examined. The results showed that the surface roughness value of samples produced with low hatch distance and low scanning speeds (i.e., in high surface energy values) for 20 W laser power is approximately up to 3.5 times lower than that of 40 W laser power. Additionally, optical analysis of the top surface images revealed that the surface energy density values of Cu10Sn samples with a relative density of 85% or higher ranged between 22 and 30 J/mm². Furthermore, the highest relative density value was found to be 87.84% with laser power of 40 W, hatch distance of 50 μm, and scanning speed of 2100 mm/min.
9:40 AM Break
10:00 AM
Parametric Investigation of Single-Layer Stainless Steel 316L with Novel Laser Powder Bed Fusion
Technology: Diode Area Melting with 450 nm Blue Lasers
: S. Can Erman1; Alkim Aydin1; Anqi Liang1; Kamran Mumtaz1; 1University of Sheffield
Diode Area Melting (DAM) is a new additive manufacturing technology which contains low optical power (~3.5W) output and lower wavelength (450 nm) lasers compared to traditional laser powder bed fusion (LPBF) with 1064 nm. DAM enables processing with independently addressable 450 nm blue diode lasers via connects to multiple fiber-coupled outputs in a single head which contains multiple spots. DAM helps to increase power absorptivity of metals in additive manufacturing process by using a shorter wavelength laser. In previous, DAM studies were held with 450 and 808 nm lasers with Ti-6Al-4V. This paper proposes a particular data set to literature as a combination of DAM and stainless steel 316L (SS316L). Besides, this work demonstrates an optimum process parameter window for single layer SS316L structures. Different laser process parameters such as scanning speed (from 50 to 500 mm/min), and hatch distance (0.2, 0.3, and 0.4 mm) are successfully optimized to obtain fully melt single track and single layer samples.
10:20 AM
Identification and Reduction of Disturbance Factors in the Acoustic Process Monitoring of the PBF-LB for Quality Assurance: Peter Gross1; Holger Merschroth1; Italo Balestra2; Cristiano De Boni2; Alexander Fritz2; Johannes Schötz2; Yaxiong Ren3; Tobias Melz3; Matthias Weigold1; 1Institute for Production Management, Technology and Machine Tools; 2OmegaLambdaTec GmbH; 3Institute for System Reliability, Adaptive Structures, and Machine Acoustics
Powder bed fusion with laser beam for metals (PBF-LB/M) is widely used to produce complex parts for lightweight applications. Although there have been many investigations to set up an in-situ process monitoring for the PBF-LB/M, cost-intensive quality assurance is necessary. Acoustic process monitoring is a promising approach due to high data rates with small memory requirements, a simple implementation and the possibility to detect subsurface defects. However, disturbance factors during the acoustic measurements affected the quality of defect detection. In this paper, we present an approach to identify and minimize disturbance factors by varying the process boundary conditions such as the reflection behavior of the build chamber while monitoring single track experiments. Subsequently the impact of the build chamber reflection on the data quality is evaluated by a comparative analysis. This work shows that a careful consideration of the boundary conditions plays a crucial role to ensure reliable defect detection.
10:40 AM
In-Situ Sensor Monitoring for Defect Prediction During Metal 3D-Printing of Aluminum Alloy Using Convolutional Neural Networks: Sandesh Giri1; Sen Liu1; Sanam Gorgannejad2; Peiyu Quan3; Vivek Thampy3; Nicholas Calta2; Christopher Tassone3; 1University of Louisiana at Lafayette; 2Lawrence Livermore National Laboratory; 3SLAC National Accelerator Laboratory
Laser powder bed fusion (LPBF) 3D printing of alloy materials shows the potential for advanced manufacturing and environmental sustainability in the future. However, LPBF alloying process is prone to defects which may affect the structural integrity and mechanical properties of manufactured components. This research presents an approach for detecting and classifying porosity defects of Al6061 alloy through in-situ photodiode sensor monitoring and advanced in-situ synchrotron X-ray characterization. Continuous Wavelet Transforms (CWT) were applied to the photodiode sensor signals collected during LPBF process to create time-frequency scalogram representations. These CWT plots were then analyzed using Convolutional Neural Networks to identify and classify different types of pore regions, “No Pore”, “Gas Pore” and “Keyhole Pores”. This method demonstrated high reliability across various defect classifications, effectively detecting and providing valuable insights into the mechanisms of pore formation. This research shows the potential for cost-effective, scalable flaw detection and process monitoring in additive manufacturing.
11:00 AM
High Precision In-Situ Alignment Procedure in Dual Laser Powder Bed Fusion for Congruent Laser Operation: Samuel Searle1; Bey Vrancken1; 1Belgium & Flanders Make@KU Leuven
Congruent operation of multiple lasers on a single part in powder bed fusion necessitates the introduction of a hatching overlap to overcome potential mis-alignments between the laser scan-fields. These have previously shown to grow during long prints, creating the possibility for lack of fusion, poor geometrical tolerance and surface finish. In this work an in-situ alignment procedure that leverages a normal off-axis powder bed camera (Basler ace 2) is proposed. It can determine laser position down to less than 20 μm MSE by taking concepts from astronomical star centroiding. Prints were performed with the alignment process integrated directly into a Print Genius 150 dual laser printer, showing firsthand the simplicity and necessity of the proposed procedure. Furthermore, the procedure can also be adapted to accurately determine the perspective transform for monitoring cameras, removing the need for tedious checkerboard calibration and enabling a direct link to the laser coordinate system.
11:20 AM
In-Situ Melt Pool Monitoring to Optimize Laser Powder Bed Fusion of Scalmalloy®: Arun Prasanth Nagalingam1; Jim Warren2; Ozgur Poyraz2; Muhammad Shamir2; Evren Yasa2; James Hughes2; Erkan Bugra Tureyen2; 1University of Sheffield; 2AMRC North West
In-situ monitoring techniques are gaining importance for metallic additive manufacturing methods to reduce the time spent in subsequent quality control stages by using the data obtained from process monitoring. Although different systems based on thermal imaging or emission detection have been developed mainly for process monitoring, there is a need to better understand the relationship between the monitored data and the final part quality. Thus, this study focuses on correlating the melt pool monitoring (MPM) data to material attributes and further optimize laser-based powder bed fusion (PBF-LB) process parameters for a high strength Al alloy (Scalmalloy®). A systematic approach modifying the laser power, hatch distance, exposure time, and scan speed was used for process parameter optimization. The outcomes of the MPM were compared with optical density measurements and surface texture analysis. The findings highlight the efficacy of melt pool monitoring in guiding process optimization efforts for PBF-LB.
11:40 AM
On the Nature of Recoater Damage Powder Spreading Mechanics: Caroline Massey1; Christopher Saldaña1; 1Georgia Institute of Technology
Laser powder bed fusion (PBF-LB) additive manufacturing gained popularity for the creation of low volume parts for defense and commercial applications. Parts made via PBF-LB can be difficult to qualify due to their variation in performance, even within the same build. During the build process, regions of the PBF-LB recoater blade could be subject to damage by spatter or superelevation in the powder bed. As a result, the worn recoater can potentially cause spreading defects in the localized topology profile, which could in turn cause porosity or form deviations. These process concerns are not well understood for their criticality and subsequent impact on part quality. This study will investigate the mechanics of recoater damage through discrete element method simulations and experimental methods.