2024 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2024): Process Development: Binder Jetting and Polymer/Ceramic Powder Bed
Program Organizers: Joseph Beaman, University of Texas at Austin

Wednesday 8:00 AM
August 14, 2024
Room: Salon G
Location: Hilton Austin

Session Chair: Desiderio Kovar, University of Texas at Austin

8:00 AM
Rapid Curing of Ceramic Binder Mixtures Using Microwave Radiation: Saptarshi Mukherjee¹; Ethan Rosenberg¹; Johanna Vandenbrande¹; Johanna Schwartz¹; Emeraldo Baluyot¹; Maxim Shusteff¹; James Kelly¹; Joseph Tringe¹; ¹Lawrence Livermore National Laboratory
    Advanced manufacturing methods for ceramics rely on a layer-by-layer construction that are time consuming and costly. Recent development of an optical volumetric additive manufacturing (VAM) technology has enabled rapid 3D printing in a singular step. However, optical VAM is limited to transparent photo resins. Here we propose to develop a fast, scalable VAM system for ceramic materials utilizing microwave radiation. The concept relies on developing a high-power microwave antenna array coupled to a beamforming algorithm to superimpose multiple microwave beams and deliver localized energy to arbitrary 3-D volumes. While current stereolithography techniques require large polymer binder volumes (>50 vol.%) that can lead to sub-surface voids after post-processing and long processing times, we design microwave absorptive polymers that can be used in low volume fractions (<40 vol.%) to control microwave energy and achieve rapid, focused green body curing. Results from preliminary experiments and a coupled electromagnetic thermal model will be presented.

8:20 AM
Prewetting of Binder Jet Print Beds to Improve Line Quality and Expand Print Windows: Madilyn Lawrence¹; Jacob Lawrence¹; Nathan Crane¹; ¹Brigham Young University
    Binder Jetting (BJ) is an additive manufacturing process that creates parts in a layer-wise process from a powder feedstock using inkjet droplets of binder. Binder Jetting shows promise as an industrial process. However, limited understanding of printing process parameters leads to defects in the printed parts and may limit build rates. In this study, lines were printed with a range of print parameters, extracted using an adhesive film, and imaged to quantify line size and quality. Print parameters included droplet spacing, inter-arrival time, amount of moisture in the powder bed, droplet size, and droplet velocity. Results from this study show that pre-treating the bed with moisture combined with low velocity droplets increases the range of print parameters that result in successful line formation and the potential for faster build rates.

8:40 AM
Toward In-Situ Sensing of Powder Packing Density In metal Binder Jetting Using Recoating Force: Chen Qian¹; Chinedum Okwudire¹; ¹University of Michigan
    Powder packing density is an important parameter in metal binder jetting (BJ) 3D printing. Research shows that this parameter is closely related to the quality of the final printed parts, affecting its strength, shape distortion, and surface finish. However, it is challenging to measure packing density in-situ. To address this challenge, we propose a novel method for estimating packing density where the force exerted on the powder recoater by the powder bed is measured and used to estimate the local packing density during the printing process. The proposed method enables real-time measurement of packing density, broadens the scope of BJ by offering the possibility of implementing closed-loop feedback control of packing density during the printing process. Closed loop control of packing density holds promise to enable high quality BJ parts to be produced using low-cost water atomized powder instead of high-cost gas atomized powder.

9:00 AM
Machine Design and Process Development of Volumetric Polymer Powder Bed Fusion by Radio Frequency Additive Manufacturing (RFAM): Matthew McCoy¹; Carolyn Seepersad¹; Christopher Saldaña¹; ¹Georgia Institute of Technology
    Selective laser sintering (SLS), along with related processes like high speed sintering, are widely adopted additive manufacturing technologies in service bureaus and small-to-medium production lines, facilitating product development and fabrication of injection molded part proxies. Recent market trends show increased demand for lower-cost SLS printers, and OEMs are simultaneously focused on increasing production rates and material libraries. Radio Frequency Additive Manufacturing (RFAM) intends to address cost, speed, and materials compatibility, demonstrating the potential for volumetric fabrication of thermoplastic parts by selectively doping a powder bed with an RF absorptive material and subjecting the entire volume to RF radiation for simultaneous melting and densification. However, achieving user-ready parts with precise definition, accuracy, and repeatability requires further exploration. Key objectives include understanding and improving geometric performance, mechanical properties, recyclability, energy consumption, and cost-effectiveness. Our work concentrates on advancing RFAM through an open-system design, aiming for faster and more economical production.

9:20 AM
Research on Influence of Scan Strategy on Part Shrinkage in Low Temperature Laser Sintering of Polymer: Takashi Kigure¹; Yuki Yamauchi¹; Toshiki Niino²; ¹Tokyo Metropolitan Industrial Tech Rsch Inst; ²Institute of Industrial Science, the University of Tokyo
     In the previous study, the low temperature laser sintering, which allows the powder bed temperature during process to be lower than the recrystallization temperature, has achieved improvement of material recycle rate and processing of high-performance plastics using non-high temperature resistant machine.To obtain the desired shape, it is necessary to correct the input shape data, but since the shrinkage process in low temperature laser sintering is different from normal laser sintering, the shape correction method used in normal laser sintering is not applicable. The goal of this study is construction of shape correction method for low temperature laser sintering. As the first step, fundamental phenomenon of shrinkage in low temperature process was investigated. As a result, it was indicated that scan direction, scan length, and build height affected shape, due to differences in shrinkage units and accumulation of deformation. These results are basic information for understanding the shrinkage mechanism.

9:40 AM
Powder Packing and Part Removal in Compressed Powder Beds: David Khanan¹; Joseph Beaman¹; Desiderio Kovar¹; Matthew Cassoli¹; ¹University of Texas Austin
    The final density of fired ceramics can be enhanced by increasing the relative density of ceramic powders prior to sintering. For selective laser flash sintering (SLFS), higher powder bed density is attained by applying a pressure to increase the relative density of the powder prior to laser scanning and post-process firing. In this study, the consistency of packing layers of 8YSZ onto an existing 8YSZ substrate was studied by first uniaxially pressing 8YSZ powders into a pellet. Additional powder was then spread over the existing sample and uniaxially pressed again. Metrics for characterizing the powder compaction and repeatability of adding additional layers, as required for additive manufacturing, were studied. After laser scanning, the part must be removed from the compressed, but unscanned regions. Methods were studied to separate the scanned regions including sonication, abrasion, and dispersion.

10:00 AM
Spatiotemporal Modulation of Light in Microscale Selective Laser Sintering for Enhanced Process Resolution Using a Digital Micromirror Device: Aaron Liao¹; Joshua Grose¹; Heejin Kim²; Michael Cullinan¹; Chinedum Okwudire²; ¹University of Texas at Austin; ²University of Michigan
    Microscale selective laser sintering (μ-SLS) aims to fabricate sub-5 μm features with a high throughput for the advanced semiconductor packaging industry, where fine resolution features are required. In μ-SLS, a metal nanoparticle bed is heated with laser projection masks from a digital micromirror device (DMD). As sintering progresses, unwanted heat conduction to areas outside of the mask occurs, reducing process resolution. Additionally, optical vignetting and DMD defects produce nonuniform intensity across the frame. A beam profiler was used to determine a field correction for spatial nonuniformity across the projected area. This was combined with a control framework based on a finite difference model to optimize a series of masks. A Python script was used to display these masks in sequence, leveraging the full spatiotemporal modulation capabilities of the DMD and enhancing process resolution across the exposure area.

10:20 AM Break

10:40 AM
Control of Selective Laser Flash Sintering of Ceramics Using an AC Electric Field: David Khanan¹; Desiderio Kovar¹; Joseph Beaman¹; ¹University of Texas Austin
    Selective laser flash sintering (SLFS) allows for the production of ceramic parts with complex shapes and quick post-processing times as pyrolysis is not required. During the SLFS process, an AC electric field is passed across the build surface while a laser scans at high speeds to heat the powder and afterwards a new layer can be applied. The effect of the large electric field strengths and localized heating from the laser combine to activate carriers in the scanned region. The resulting Joule heating produces further heating of the powder that bonds the particles at the contact points via necking. The effects of processing parameters were studied by passively and actively varying the AC electric field while measuring and controlling the local temperature in the laser scanned regions.

11:00 AM
Photocurable Resin Formulation for Reduced Thermal Expansion: Muhammad Sufian¹; Rahul Sheley¹; Jitendra Tate¹; ¹Texas State University
    Despite its commendable resolution capabilities, Stereolithography 3D Printing (SLA) often falls short in achieving desired material properties compared to alternative additive manufacturing techniques. To address this limitation, one strategy involves nickel electroplating of printed parts, thereby enhancing mechanical strength, heat resistance, and chemical durability. However, this approach introduces a discrepancy in the coefficient of thermal expansion (CTE) between the resin and the nickel coating, leading to internal stresses and potential part failure when subjected to high temperature fluctuations. In this work, we report the successful development of a noble SLA resin using pre-dispersed amorphous silicon dioxide in cyclo aliphatic epoxy resin that offers high modulus, high strength, low density, and low Coefficient of Thermal Expansion (CTE). Tensile, flexural, and impact properties have been evaluated. Dispersion of nanomaterials has been studied using Scanning Electron Microscopy(SEM) and thermal properties were analyzed using Thermo Mechanical Analysis (TMA).

11:20 AM
Predictability of Drag force Towards Optimizing Fingers to Aid Automation in the Depowdering Stage of Binder Jet AM & Granular Physics: Sarita Sepulveda¹; Amy Elliott²; Sun Yi¹; ¹North Carolina A&T State University; ²Oak Ridge National Laboratory
    Currently, manual depowdering of BJAM parts is labor intensive and prohibits the technology’s wide-spread use in the industry. Automation of binder jet depowdering consists of controlling a robot to grip and lift a part. In this study, the drag of the end effectors, or fingers, utilized in the automation of binder jet depowdering when moving through a bed of powder will be evaluated. Findings in the literature will be discussed which includes a range of analysis understanding powder flowability and drag through granular mediums. The objective of this presentation is to correlate drag forces from experimental data and theoretical data with three fingers of varying diameters while the cross-sectional area is controlled. These new findings from experimental and theoretical drag forces are explored to develop predictability on optimizing future finger designs for various powders and preventing part deformation to aid in the automation process in BJAM and understand granular physics.