2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Applications: Residual Stress
Program Organizers: Joseph Beaman, University of Texas at Austin
Tuesday 8:15 AM
August 15, 2023
Room: 615 AB
Location: Hilton Austin
Session Chair: Ming Leu, Missouri University of Science and Technology
8:15 AM
Distortion and Residual Stress Mitigation of Large Parts for Wire-arc Additive Manufacturing: Wen Dong1; Xavier Jimenez1; Carter Gassler1; Albert To1; 1University of Pittsburgh
Wire arc additive manufacturing (WAAM) has drawn increasing attention due to its ability to print large metal parts. However, thermal gradients during the process can result in significant residual stress and distortion, negatively affecting product quality and making post-processing more difficult. In the present work, we have implemented several strategies when printing a part ~900 mm long to mitigate these issues. Firstly, a fixture designed based on topology optimization is attached to the baseplate to reduce distortion. However, cracks were observed in the baseplate near the deposit ends after the first trial. Then, we carefully examined and modified the deposit and baseplate shapes to further reduce the residual stress. The second trial successfully printed a part that met the required specifications. Due to its high accuracy and low cost, the modified inherent strain (MIS) method is employed to predict the distortion and residual stress for fixture design and shape modification.
8:35 AM
Effect Of Inter-Layer Dwell Time on Residual Stresses in Directed Energy Deposition of High Strength Steel Alloy: Ranjit Joy1; Sung-Heng Wu1; Usman Tariq1; Muhammad Arif Mahmood1; Frank Liou1; 1Missouri University of Science and Technology
Adoption of metal additive manufacturing by various industries is being hindered by the presence of residual stresses and distortion in the deposited parts. Large thermal gradients during directed energy deposition often led to residual stresses in the final deposit. Parameter optimization is predominantly used for residual stress mitigation. However, the effect of process parameters is material specific. Current research aims to study the effect of inter-layer dwell time on residual stresses in directed energy deposition of high strength steel alloy. Specimens were deposited at three levels of inter-layer dwell time. Surface as well as bulk residual stresses were measured using X-ray diffraction. Both surface as well as bulk residual stresses were found to increase with an increase in the inter-layer dwell time.
8:55 AM
Quantification of Residual Stress in Directed Energy Deposition Additive Manufacturing via Bridge Method: Joshua Taggart-Scarff1; Stephen Cluff2; Clara Mock2; Brandon McWilliams2; 1Survice Engineering Company; 2DEVCOM Army Research Laboratory
Residual stress buildup in additively manufactured parts can result in cracks, part delamination, and other warpage in the final part. Current methods of evaluating residual stress in directed energy deposition (DED) additively manufactured parts are either non-quantitative or are complex, expensive, and time consuming. Quantification of residual stress in additively manufactured parts is key to validating models that accurately predict the effects of processing parameters on mechanical properties and part geometry. Bridge structures were built via DED using three different hatch-fill strategies. After completion of the build, a section of the bridge feet was removed creating a cantilever beam section. The deflection of the cantilever beam section was measured using a coordinate measuring machine and compared to the predictions of a fast part-scale residual stress model. The method developed can lead to more efficient predictions of residual stress formation for DED additively manufactured parts.
9:15 AM
Residual Stress Analysis of Laser Powder Blown Inconel 718 Across Different Overhang Angles and Laser Outputs: Alejandro Hernandez1; Kurtis Watanbe1; Dajalma Garcia1; Kevin Wheeler2; Francisco Medina1; Ryan Wicker1; 1W.M. Keck Center for 3D Innovation; 2National Aeronautics and Space Administration
Directed Energy Deposition (DED) is an increasingly utilized additive manufacturing (AM) method to reproduce tough and utilitarian components for fields such as Aerospace. These components, however, are subject to a unique thermal process that impacts their mechanical properties. Such properties include the residual stress concentration and its direction, deformation, and microstructural composition of a component. Since the thermal fluctuations derive from the printing process itself, it is possible that the mechanical properties are impacted by other DED printing parameters. By using an Inconel 718 powder feedstock in Laser Powder blown Directed Energy Deposition (LPF-DED), a series of coupons with four different overhang angles of 0-, 20-, 30-, and 35° printed with different laser power outputs (1070W and 2000W) to observe these properties. These coupons will be analyzed using both non-destructive and destructive methods to record how these parameters mechanically affect the prints.
9:35 AM
A Data Driven-based Geometric Compensation Method for Laser Powder Bed Fusion: Wen Dong1; Basil Paudel1; Albert To1; 1University of Pittsburgh
The residual stress and deformation induced during the laser powder bed fusion (L-PBF) process can degrade the performance and quality of the products and increase the difficulty of post-processing like machining and cutting. The present work develops a data driven-based geometric compensation method to reduce the part distortion in L-PBF processes. The method includes four steps: (1) collect distortion data based on both numerical simulations and experimental measurement; (2) implement principal component analysis to reduce the data size and extract features that account for 99.99% of the total energy; (3) train the Gaussian process model for each feature to establish relationships between the initial and as-built shape of a part; (4) apply the trained model to generate the compensated geometry so that the as-built shape is the desired one. The experimental validation shows that the proposed approach is able to effectively improve the geometric accuracy of the as-built part.
9:55 AM Break
10:25 AM
Thermal Stress Prediction in in Laser Powder Bed Fusion: Tao Liu1; Edward Kinzel2; Ming Leu1; 1Missouri University of Science and Technology; 2University of Notre Dame
Residual stresses, caused by non-uniform heating, in the parts produced by laser powder bed fusion (LPBF) can lead to geometric errors as well as mechanical defects such as cracks. This paper presents the potential for predicting residual stresses in-process using data obtained from in-situ infrared thermography. The measured surface temperature is used to rapidly predict the part’s interior temperature field using a Green’s function approach. The stress field is then predicted from the temperature field and the residual stresses are estimated from an elastic-plastic analysis. The predicted residual stress is compared to experiments LPBF printed cantilevers by measuring the deflection after the parts are removed from the build plate. This method can be used to select process parameters that minimize residual stress, as well as detecting and correcting defects as they occur.
10:45 AM
The Effect of LaserSscan Strategy on Residual Stress of Titanium Alloys Using Laser Foil Printing Additive Manufacturing Processes: Ting-Chun Huang1; Chia-Hung Hung1; 1National Cheng Kung University
In this study, we investigated the effect of two different scan strategies, line pattern scanning (LPS) and spot pattern scanning (SPS) strategies, on the residual stress for the fabrication of Ti-6Al-4V parts by using the laser-foil-printing (LFP) process. The residual stress of LFP-fabricated parts was measured through X-ray diffraction (XRD). The XRD and simulated results indicate the residual stress of part made by SPS can be significantly reduced by 55% compared part made by LPS because LPS scanning length is clearly larger than SPS scanning length. No accumulation of residual stress occurs when using SPS in LFP. Besides, SEM images and XRD patterns show the cross section of LPS is dominated by α' phase while the cross section of SPS is consisted of α phase and β phase. Thus, the residual stress of Ti-6Al-4V parts can be reduced effectively in LFP by using a SPS strategy.
11:05 AM Cancelled
Resonant Ultrasound Spectroscopy Modeling of Hybrid Metal Additive Manufacturing Samples with Residual Stresses: Jazmin Ley1; Cristian Pantea2; John Greenhall2; Joseph Turner1; 1University of Nebraska - Lincoln (UNL); 2Los Alamos National Laboratory
Hybrid additive manufacturing (AM) involves secondary processes or energy sources to alter specified locations within the build. Each hybrid step can refine the grain size, increase dislocation density, or modify residual stresses. Typically, the changes in mechanical properties are not confined within a single layer but have a compounding effect on preceding layers. Control of properties within a build can enhance component performance but unique challenges remain for nondestructive validation of such samples. Traditional ultrasonic methods on hybrid-AM components have successfully mapped material variations with sufficient spatial resolution. However, the use of resonance ultrasound spectroscopy (RUS) for hybrid-AM is less developed. In this presentation, finite element models are used to examine the sensitivity of RUS measurements in terms of frequency shifts and mode shapes with respect to specific layers of residual stress. The RUS model provides new insights for experimental results from hybrid-AM samples of stainless steel with milled layers.