2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Modeling: Deposition of Particles and Fibers
Program Organizers: Joseph Beaman, University of Texas at Austin
Tuesday 8:15 AM
August 15, 2023
Room: 416 AB
Location: Hilton Austin
Session Chair: Alaa Elwany, Texas A&M
8:15 AM
Part Scale Simulation of Heat Affected Zones for Parameter Optimization in a Microscale Selective Laser Sintering System: Joshua Grose1; Farzana Tasnim1; Michael Cullinan1; 1The University of Texas at Austin
The Microscale Selective Laser Sintering (μ-SLS) system can produce feature sizes on the order of a single micrometer, far smaller than existing additive technologies. Despite this advantage, there are challenges in producing reliable small-scale parts due to unwanted heat transfer in the nanoparticle particle bed. To address this issue, a multiscale Finite Element thermal model has been developed to predict the temperature changes that occur during sintering within the particle bed. Nanoscale particle models are used to quantify material property changes experience by particle groups that undergo laser sintering. This work processes the property relationships developed by the particle models and integrates a comprehensive property function into the part-scale model to capture the nuanced thermal evolution that occurs during sintering. The multiscale model predicts the extent of heat spread during sintering to optimize input laser parameters, reduce unwanted heat spread, and improve the minimum feature resolution of printable parts.
8:35 AM
On the Effect of Recoater Damage on Spreading Behavior: Caroline Massey1; Christopher Saldaņa1; 1Georgia Institute of Technology
Laser powder bed fusion (LPBF) additive manufacturing allows for the opportunity to customize parts, manufacture low lot size items, and revolutionize supply chain logistics. One key challenge to the adaptation of LPBF technology is that the process needs to be optimized to achieve consistency between builds and lots. Recoater spreading can affect the topology of the powder bed, which could lead to variability in porosity and surface roughness if the recoater blade is damaged. The present study will investigate the effect of damage to the recoater on the powder bed using the discrete element method (DEM). Intentional notches will be introduced to the recoater to simulate damage. Interactions between the damaged recoater and the topology and spread quality of the powder bed will be investigated.
8:55 AM
Modeling Carbon Fiber Suspension Dynamics for Additive Manufacturing Polymer Melt Flows: Jason Pierce1; Douglas Smith1; 1Baylor University
The addition of short carbon fibers to the feedstock of large-scale polymer extrusion/deposition additive manufacturing results in significant increases in mechanical properties dependent on the fibers’ distribution and orientation in the beads. In order to analyze those factors, a coupled computational fluid dynamics (CFD) and discrete element modeling (DEM) simulation system is utilized to model the behavior of fibers in nozzle geometries after calibrations in simple shear flows. The DEM model uses bonded discrete particles to make up flexible and breakable fibers that interact with each other in alignment with established literature as well as with the variable flow and geometries present in nozzles. Results enable determination of proper Coefficient of Interaction values as well as provide enhanced insight into the evolution of fiber orientation during deposition over existing models through individual fiber tracking over time and space on multiple parameters of interest such as orientation, flexure, and contact forces.
9:15 AM
Understand Powder Deposition Behaviors of a Novel Electrostatic Powder Spreading Technique Using Particle Dynamics Simulation: Ziheng Wu1; Michael Troksa1; Eric Elton1; 1Lawrence Livermore National Laboratory
Powder bed fusion is gaining more industrial presence across many sectors due to its increasing productivity. Most of the current process improvements focus on beam optimization while limited attention has been paid to modifying the spreading technique. Many industries show interest in multi-material printing as their applications can leverage the beneficial properties of several materials. However, almost all the existing spreading methods are mechanical based which prevents the deposition of different feedstocks selectively. We are developing a contact free electrostatic powder spreader that can perform multi-material powder patterning and in-situ mixing. This study focuses on developing custom modules in Ansys Rocky to perform powder dynamics simulations which have been validated against the deposition rate experiments using the electrostatic spreader. The simulations are used to study the different powder responses at various spreader geometries, electric fields, and materials. The results provide us with essential insights and guidelines for spreader prototyping.
9:35 AM
Predicting the Printable Parameter Space for Laser Directed Energy Deposition Using a Data Augmented Thermal Model: Peter Morcos1; Matthew Vaughan1; Brent Vela1; Jiahui Ye1; Alaa Elwany1; Ibrahim Karaman1; Raymundo Arroyave1; 1Texas A&M University
Laser Directed Energy Deposition (DED) is an additive manufacturing technique used to produce large and complex metal parts through the deposition of metal powder. However, the complexity of the process due to the presence of multiple processing parameters makes it very challenging to fabricate high-density parts without extensive experimental work. Therefore, the urge of having a reliable and efficient tool for predicting the printable space of parameters is crucial. In this work, a computationally inexpensive model is used to predict the clad geometry using the primary processing parameters in DED, including laser power, scanning speed, and mass flow rate. Single tack experiments were printed and characterized. The measured clad dimensions were used to augment the thermal model and generate 2D process maps at each powder flow rate.
9:55 AM Break
10:25 AM
Investigating the Effect of Generalized Newtonian Fluid on the Micro-void Development within Large Scale Polymer Composite Deposition Beads: Aigbe Awenlimobor1; Douglas Smith1; Zhaogui Wang2; 1Baylor University; 2Dalian Maritime University
Continuous research on the formation and development of micro-voids within the bead microstructure of polymer composite during extrusion/deposition process is currently ongoing, considering the adverse effect these features have on part quality. A computational method is employed to investigate potential volatile-induced micro-void nucleation mechanism by simulating the evolution of a single rigid ellipsoidal fiber in purely viscous polymer extrusion/deposition flow through a BAAM nozzle. While previous studies on potential micro-void nucleation mechanisms have assumed a Newtonian fluid property definition for the polymer melt flow, the current study assesses the impact of a generalized Newtonian fluid (GNF) model on the fiber’s response. Preliminary findings based on Jeffery’s flow assumption reveal a decrease in the fiber’s orientation kinetics due to the shear-thinning fluid behavior with an accompanying reduction in the pressure distribution around the fiber’s surface for a power-law fluid with low flow behavior index which increases the likelihood for micro-void nucleation.
10:45 AM
Multi-physics Modeling of Low-temperature Directed Energy Deposition of Stainless Steel 316L: Kishore Mysore Nagaraja1; Dong Qian1; Wei Li1; 1The University of Texas
The Directed energy deposition (DED) process is greatly influenced by the ambient temperature at on-site repair. In Northern hemisphere locations, DED is particularly influenced by sub-freezing temperatures. However, its influence on the process is not yet studied. This critical gap is fulfilled in this research through a multi-physics computational fluid dynamics (CFD) modeling of the low-temperature DED of the SS316L powders. The model is validated with test cases: -3°C for sub-freezing and 20°C for room temperature cases using a cryogenic DED platform. The modeling involves powder spray, local melting, rapid cooling, solidification, evaporation, and fluid-gas interactions. The results show, at sub-freezing, the molten pool is ~63% bigger with the maximum temperature reduced by ~9.5%. The deposition saw an increase in width by ~8.6% and height by ~26% than the room temperature case. Overall, the versatile modeling-experimental platform helps study cryogenic DED cases for in-space additive manufacturing.
11:05 AM
Real Time Quantification of Shear-induced Molecular Ordering in Direct Write Printing of Bottlebrush Based Polymer Networks: Daniel Rau1; Baiqiang Huang1; Liheng Cai1; 1University of Virginia
Bottlebrush polymer networks provide a new class of inks with extreme softness for Direct Ink Write. However, it remains a challenge to understand the effects of the extrusion process on the molecular ordering of bottlebrush polymers, which have a long linear backbone densely grafted by many relatively short linear side chains. Here, we leverage a customized extrusion system and use small and wide-angle x-ray scattering to quantify the molecular ordering of linear-bottlebrush-linear triblock copolymers in-situ. We discover that higher shear rates promote the alignment of the self-assembled microstructures resulting in much larger characteristic length scales. Moreover, the ordering profile across the nozzle diameter is highly correlated to the flow profile of the viscoelastic triblock copolymer inks. Our results provide insights into the previously unexplored processing-microstructure-mechanical property relationships of bottlebrush-based polymer networks and may provide a new avenue for printing single material structures with functionally graded mechanical properties.
11:25 AM
Optimization of Computational Time for Digital Twin Database in Directed Energy Depostion for Residual Stresses: Usman Tariq1; Ranjit Joy1; Sung-Heng Wu1; Muhammad Arif Mahmood2; Michael Woodworth3; Frank Liou1; 1Missouri University of Science and Technology; 2Intelligent Systems Center; 3The Boeing Company
Metal Additive Manufacturing has grown rapidly and proven to be a cost-effective way to produce high-quality products. As metal additive manufacturing involves large thermal gradients which incorporate residual stresses and distortion at the end part hence having knowledge of these properties is essential for quality control. Finite Element Analysis (FEA) is one of the methods to predict for residual stresses to improve part quality and strength at the cost of high computational power. The aim of this study is to decrease computational time by incorporating thermo-mechanical model for Directed Energy Deposition (DED) process using Ti-6V-4Al which would predict thermal history and consequent residual stresses. Different methods of FEA models are included which use simple assumptions and gives a comparison between computational cost and numerical accuracy which can help move towards the realization of digital twin.
11:45 AM
Experimental and Finite Element Comparison of 3-axis and 5-axis Wire Arc Directed Energy Deposition: Matthew Register1; Ryan Stokes1; J Betts1; Liv Russell1; Matthew Priddy1; 1Mississippi State University
Wire arc directed energy deposition (WA-DED) is a metal additive manufacturing (AM) process that utilizes an electric arc heat source to melt wire in a layer-by-layer fashion. Unlike traditional AM, the WA-DED process has six axes of rotation, allowing geometrically complex parts to be built without the need of support structures. However, it is not well understood how the thermal history may change as an effect of multi-axis toolpaths, thus also affecting the resultant mechanical properties. This work examines the variation in temperature history, residual stress, and distortion between 3- and 5-axis toolpaths for the same geometry using an experimental and computational approach. Using finite element (FE) thermo-mechanical modeling, the nodal temperature history was compared with thermocouples on the substrate and infrared camera data near the melt pool to validate the FE thermal response. Deflection experimental measurements were collected with a laser profilometer for FE mechanical model validation.
12:05 PM
Adapting a Conventional Design for Additive Manufacturing Workflow to Account for Continuous Carbon Fiber Reinforced Parts: Gavin Adams1; Nicholas Meisel1; 1Pennsylvania State University
The use of continuous carbon fiber (CCF) reinforcement has the potential to revolutionize the material extrusion field of additive manufacturing. For example, the Markforged X7 system utilizes CCF reinforcement with the aim to produce parts with mechanical results rivaling those of aluminum. However, due to certain constraints with the deposition of CCF in material extrusion, traditional design for additive manufacturing (DfAM) techniques must be reevaluated. This paper explores the application of DfAM principles in CCF and include the development of a new DfAM workflow for this technology. The research is demonstrated through a case study, which highlights the importance of considering fiber orientation in the design stage to achieve ideal mechanical results relative to the loads associated with the part. Overall, this paper provides an initial, potentially valuable workflow for designing and manufacturing CCF parts using AM and highlights the importance of DfAM principles in achieving desirable mechanical results.