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1. Tuning Process Parameters for Multi-Material Extrusion Through In-house Nozzle System for 3D Bio-printing Process

   Quigley, C. ; Hurd, W. ; Clark, S. ; Sarah, R. ; & Habib, M. A. ( May 2023 , Proceedings of the IISE Annual Conference & Expo 2023)

   Eds: Babski-Reeves, K ; Eksioglu, B ; Hampton, D. (Ed.)

   The emerging field of three-dimensional bio-printing seeks to recreate functional tissues for medical and pharmaceutical purposes. With the ability to print diverse materials containing different living cells, this growing area may bring us closer to achieving tissue regeneration. In previous research, we developed a Y-shaped nozzle connection device that facilitated the continuous deposition of materials across multiple filaments. This plastic device had a fixed switching angle and was intended for single use. In this study, we present an extension of our previous nozzle system. To fabricate the nozzle connectors, we chose stainless steel and considered angles of 300, 450, and 900 (both vertical and tilted) between the two materials. The total material switching time was recorded and compared to analyze the effects of these angles. We used our previously developed hybrid hydrogel (4% Alginate and 4% Carboxymethyl Cellulose, CMC) as a test material to flow through the nozzle system. These in-house fabricated nozzle connectors are reusable, and sterile and enable smooth material transition and flow. 

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2. Continuous multi-filament 3D printing for tension-compression structure components

   Teng TENG, Yefan ZHI ( July 2023 , Proceedings of the IASS Annual Symposium 2023)

   In this research, we propose a Multi-Filament Fused Deposit Modelling (MFFMD) printer and a respective generator that can be used to produce structural parts with locally tailored functional properties. 3D-printed structural components can highly benefit from multi-material printing with tuneable functional properties. Currently, multi-material printing is mainly achieved using multiple separate nozzles, leading to discontinuous flow in switching materials. This limitation results in material interface delamination, minimal control in the continuous transition of material properties, and longer production time.To address this, we first design and build an MFFMD printer with a single customized nozzle allowing seamless switching between multiple filaments. We then develop a method that generates a continuous toolpath of a given geometry and differentiates materials based on various stress conditions at particular regions. To illustrate, we fabricate a Pratt truss as an example of a tension-compression structure as a case study. In one go, the MFFMD printer deposits resistant filament, respectively, at tension- or compression-concentrated regions based on local stress conditions. Comparative load tests are conducted to validate the performance enhancement of multi-filament prints against single-filament prints. Our proposed method is a prototypical study conducted on a small scale. While it mainly uses thermal plastic filaments, it can be expanded to other construction materials and scales in the future. 

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3. Designing an Interchangeable Multi-Material Nozzle System for 3D Bioprinting Process

   https://doi.org/10.1115/msec2021-63471  

   Nelson, Cartwright ; Tuladhar, Slesha ; Habib, Md Ahasan ( June 2021 , Proceedings of the ASME 2021 16th International Manufacturing Science and Engineering Conference)

   null (Ed.)

   Three-dimensional bioprinting is a rapidly growing field attempting to recreate functional tissues for medical and pharmaceutical purposes. Development of functional tissue requires deposition of multiple biomaterials encapsulating multiple cell types i.e. bio-ink necessitating switching ability between bio-inks. Existing systems use more than one print head to achieve this complex interchangeable deposition, which decreases efficiency, structural integrity, and accuracy. In this research, we developed a nozzle system capable of switching between multiple bio-inks with continuous deposition ensuring the minimum transition distance so that precise deposition transitioning can be achieved. Finally, the effect of rheological properties of different bio-material compositions on the transition distance is investigated by fabricating the sample scaffolds.

    

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4. Effects of Needle Lift and Fuel Type on Cavitation Formation and Heat Transfer Inside Diesel Fuel Injector Nozzle

   Zeidi, Javad SM ; Dulikravich, George S ; Reddy, Sohail R ; Darvish, Shadi ( May 2017 , International Symposium on Advances in Computational Heat Transfer, paper CHT-17-102, Naples, Italy, May 28-June 1, 2017)

   In the present study, the flow inside a real size Diesel fuel injector nozzle was modeled and analyzed under different boundary conditions using ANSYS-Fluent software. A validation was performed by comparing our numerical results with previous experimental data for a rectangular shape nozzle. Schnerr-Sauer cavitation model, which was selected for this study, was also validated. Two-equation k-ε turbulence model was selected since it had good agreement with experimental data. To reduce the computing time, due to symmetry of this nozzle, only one-sixth of this nozzle was modeled. Our present six-hole Diesel injector nozzle was modeled with different needle lifts including 30 μm, 100 μm and 250 μm. Effects of different needle lifts on mass flow rate, discharge coefficient and length of cavitation were evaluated comprehensively. Three different fuels including one Diesel fuel and two bio-Diesel fuels were also included in these numerical simulations. Behavior of these fuels was investigated for different needle lifts and pressure differences. For comparing the results, discharge coefficient, mass flow rate and length of cavitation region were compared under different boundary conditions and for several fuel types. The extreme temperature spike at the center of an imploding cavitation bubble was also analyzed as a function of time and initial bubble size. 

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5. Concurrent characterization of compressibility and viscosity in extrusion-based additive manufacturing of acrylonitrile butadiene styrene with fault diagnoses

   https://doi.org/https://doi.org/10.1016/j.addma.2021.102106  

   Kazmer, David O ; Colon, Austin R ; Peterson, Amy M ; Kim, Sun K ( June 2021 , Additive manufacturing)

   null (Ed.)

   Compressibility and viscosity of polymer feedstock are critical to their volumetric flow rate, weld strength, and dimensional accuracy in material extrusion additive manufacturing. In this work, the compressibility and viscosity of an acrylonitrile butadiene styrene (ABS) material is characterized with an instrumented hot end design. Experiments are first performed with a blocked nozzle to characterize the compressibility behavior. The results closely emulate the pressure-volume-temperature (PVT) behavior of a characterized generic ABS. Experiments are then performed with an open nozzle over a range of volumetric flow rates and temperatures. The static pressure data is fit to power-law, Ellis, and Cross viscosity models and the dynamic melt pressure data is then used to jointly fit material constitutive models for compressibility and viscosity. The results suggest that the joint fitting substantially improves the fidelity relative to the separately characterized viscosity and compressibility. The implemented methods support material extrusion process simulation and control including real-time identification of process faults such as (1) limited melting capacity of the hot end, (2) skipping (grinding) of the extruder drive gears, (3) low initial nozzle temperature, (4) varying flow rates associated with the intermeshing gear tooth velocity profile, and (5) delays and reduced melt pressures due to drool prior to extrusion. The ability to monitor the printing process for faults in real time, such as that presented in this work, is critical to born qualified parts. Additionally, these approaches can be used to screen new materials and identify optimal processing conditions that avoid these process faults. 

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