2026 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2026): Friction Stir, Binder Jetting, and Viscous Thread Printing
Program Organizers: David Leigh, University of Texas at Austin
Tuesday 1:30 PM
August 4, 2026
Room: Zlotnick Ballroom 6
Location: AT&T Center
1:30 PM
Characterization of Processing Defects in an AFSD Deposited 5xxx Aluminum Alloy: Mason Smith1; Bradley Jared1; Dayakar Penumadu1; Sirirut Akawut1; Zach Arwood1; 1University of Tennessee Knoxville
Additive Friction Stir Deposition (AFSD), a new solid-state AM technology based on friction stir welding, stands apart from established methods via unprecedented build rates and print volumes. However, there is a notable gap in the literature on AFSD defect detection and characterization. In this work, the causes and effects of various heterogeneities are explored through an unrepresented alloy system: 5xxx aluminum. Due to its corrosion resistance and AFSD’s potential in fabricating large components for marine applications, the intersection of material and process is prudent. Three distinct feedstock forms were deposited by AFSD, and subsequently interrogated using non-destructive evaluation (NDE), various microscopy techniques, and targeted sample extraction. Both before and after heat treatment, ultrasonic testing highlights potential tunnel defects and kissing bonds within all printed material. Sectioning was then performed to isolate and quantify the nature of these features, as well as their effects on mechanical properties.
1:50 PM
In-Situ Thermal Measurements of Multi-Pass and Multi-Layer Additive Friction Stir Deposition Builds: Henry Claesson1; Mark Pandol2; Hang Yu2; Chris Williams1; 1Department of Mechanical Engineering, Virginia Tech; 2Department of Material Science and Engineering, Virginia Tech
As a solid-state metal AM process, AFSD relies on friction and pressure to deposit metal below the material's melting point. AFSD parts feature a refined microstructure and mechanical performance comparable to that of wrought parts. A thorough understanding of the thermal history of an AFSD build is a critical step towards prediction, qualification, and process control. However, characterizing this thermal history presents a unique challenge, as AFSD processing employs a PID control loop to regulate processing conditions and maintain successful deposition, making thermal modeling of the AFSD process non-trivial. To develop a more holistic understanding of the thermal history of AFSD builds, this work investigates multi-pass and multi-layer AFSD depositions through in-situ point thermocouple measurements to characterize a complete thermal profile of a multi-pass and multi-layer AFSD build. The thermal data gathered provides critical insight into the process-structure relationships governed by the thermal history of as-deposited Al6061 AFSD material.
2:10 PM
Joining Additive Manufactured 316L via Friction Welding: An In‑Situ Microtensile and Microstructural Evaluation: Loïc Jegou1; Fatma Depboylu2; Andrei-Alexandru Popa2; 1European Synchrotron Radiation Facility ESRF; 2University of Southern Denmark
Integrating Laser Powder Bed Fusion (LPBF) with Rotational Friction Welding (RFW) enables large-scale fabrication of complex 316L stainless steel components. While our previous macro-mechanical studies confirmed joint integrity, fractures consistently occurred in the base metal (BM), masking intrinsic weld zone (WZ) properties. To overcome this, this study utilizes in-situ micro-tensile testing coupled with high-energy synchrotron X-ray diffraction (HE-XRD). Longitudinal and transverse specimens were analyzed under real-time loading to isolate interface behavior. Preliminary results demonstrate significant grain refinement (10.2 µm vs. 25.4 µm in BM) and increased hardness (290 HV vs. 268 HV) within the WZ, directly influencing local strain localization. Ongoing analysis of specific {hkl} lattice strains, dislocation evolution, and Orientation Distribution Functions (ODF) characterizes the deformation stability of the WZ fiber texture. This work establishes a new reliability standard for hybrid additive-joining technologies.
2:30 PM
Effect of Peak Temperature on Porosity in Architected Infill Binder Jet Additive Manufacturing: Sarita Sepulveda1; Christopher Williams1; 1Virginia Tech
Prior research has focused on reducing porosity and improving densification in binder jetted parts, as porosity is often considered a limitation to achieving desired mechanical properties. However, controlled porosity can be advantageous for tailoring functional architectures. This study presents an architected infill binder jetted structure with tailored porosity that distinguishes between bound (powder with binder) and unbound (powder without binder) regions to investigate pore evolution and enable spatial control of porosity. X-ray CT scanning and optical microscopy are used to characterize pore evolution and morphology as a function of peak sintering temperature.
2:50 PM
Effect of Powder Spreading Strategy on the Densification of Binder-Jetted Copper Components: Zakki Emzain1; Alkim Aydin2; S. Can Erman1; Ahmet Kus1; Kamran Mumtaz1; 1University of Sheffield; 2Gazi University
Binder jetting additive manufacturing offers a promising alternative route for processing copper components, particularly where LPBF faces challenges associated with the high reflectivity and thermal conductivity of copper. However, achieving high sintered density in binder-jetted copper remains challenging and is strongly influenced by powder bed quality during layer deposition. This study investigates the effect of powder spreading strategy on the green and sintered properties of binder-jetted copper fabricated using a customised binder jetting system with an aqueous PVA binder. Layer thickness (80 μm) and sintering temperature (1075°C) were maintained constant while three spreading strategies were evaluated: single spreading, double spreading in the same direction, and bidirectional double spreading. Double spreading in the same direction achieved the highest green density (51.3 ± 0.81%) and sintered relative density (95.61 ± 0.77%). The results demonstrate the significant influence of powder spreading strategy on powder bed packing and densification behaviour in copper binder jetting.
3:10 PM
Metal Viscous Thread Printing: Brett Emery1; Jacob Miske1; Cole Carson1; Keith Brown2; Jeff Lipton1; 1Northeastern University; 2Boston University
Metal foams are valued for their thermal, electrical, and mechanical properties, but conventional production limits gradient structures and requires costly infrastructure. Viscous Thread Printing (VTP) exploits mechanical instabilities during Fused Filament Fabrication (FFF) to produce gradated, stochastic foams at the desktop scale. Previously limited to polymers, here we demonstrate metal foams with programmable porosity gradients in copper, bronze, and steel. We combine VTP with a metal-polymer process, termed metal viscous thread printing (M-VTP), reaching relative densities from 0.18 to 0.63. Copper foams exhibited a 10x range in stiffness and half the thermal conductivity of rectilinear copper lattices, while maintaining similar electrical conductivity. They demonstrated mechanical densification behavior for energy absorption and over 10x increase in specific toughness compared to conventionally printed copper. M-VTP specimens showed six times fewer post-processing cracks than rectilinear lattices suggesting greater robustness. M-VTP enables desktop-scale production of stochastic metal foams with programmable properties across alloy systems.
3:30 PM
Direct Measurement of High-Power Laser Spot Deformations under Thermal Lensing Conditions in Laser Powder Bed Fusion: Zhuo Yang1; Ho Yeung1; 1NIST
Thermal lensing of laser powder bed fusion machines can induce inconsistent energy input during the melting process, ultimately compromising part quality. This study presents a series of experiments designed to directly measure high energy laser spots using a high-speed camera. The experiment utilized realistic scanning conditions 10 by 10 mm patch on a SS316 substrate. This region was scanned repeatedly to heat specific sections of lenses and mirrors, thereby simulating multilayer fabrication conditions. The investigation evaluated various optical assemblies, including F theta lenses and diverse protective window configurations. Furthermore, the impact of different scanning strategies, specifically varying hatch distances and laser idling times, was assessed. The results indicate an observed 5% to 10% change in laser spot size under standard air-cooling conditions. Additionally, the thermal lensing effect was found to be highly sensitive to the thickness, coating, and relative position of the protective glass within the optical path.
3:50 PM
Flash Thermography for Thermal Diffusivity and Density Measurement of Cured Binder-Jet Samples in the Presence of Thermal Contact Resistance: Shu Wang1; Nathan Crane1; 1Brigham Young University
Density is a key indicator of part quality in binder jetting, but density measuremetns remain difficult. This work considers ex-situ measurement of cured SS316L samples as a possible enhancement of traditional witness parts and a step towards in-situ monitoring. A thermal contact resistance (FT-RTc) was added to a typical 1D Flash thermography (FT) model to measure thermal diffusivity and density in cured samples printed at 40%, 70%, and 100% binder saturation . The results show that FT can be extended from unbound powder to cured printed samples. Thermal diffusivity and density were both retrieved, although density uncertainty in cured samples was much larger than in previous unbound-powder measurements. An absorptivity-based correction substantially reduced the sample-level density error, indicating that absorptivity variation is a major source of cured-sample density uncertainty. The FT-Rtc model also remained effective under substantially different contact conditions.
4:10 PM
Active Thermography of Laser-Powder Bed Fusion Additive Manufacturing 316 Stainless Steel: Chase Joslin1; 1ORNL
Laser-powder bed fusion additive manufacturing (L-PBF AM) continues to be a reliable tool for creating complex geometries. However, evaluation techniques do not yet fully certify and qualify L-PBF AM components. This study used flash thermography to investigate the viability of detecting subsurface porosity ex-situ. Then, in-situ active thermography was utilized to observe changes in layer-wise thermal signatures on 316 stainless steel (SS) L-PBF AM parts. Imaging the surface of printed SS with a near-infrared camera and an on-axis photodiode identified sub-surface pores in-situ. A dynamic multiscale convolutional neural network (DMSCNN) was trained to classify 2-dimensional (2D) visible-light, near-infrared, and photodiode images. A regression model was fit to predict percent porosity using DMSCNN results. Parts printed with surrogate pores had a correlation coefficient of 0.795. Although the regression model did not accurately predict porosity within control parts, the experiment shows viability to detect large scale lack-of-fusion porosity in L-PBF AM in-situ.