More Like this

1. Increasing Throughput in Fused Deposition Modeling by Modulating Bed Temperature

   https://doi.org/10.1115/1.4050177  

   Snapp, Kelsey L. ; Gongora, Aldair E. ; Brown, Keith A. ( September 2021 , Journal of Manufacturing Science and Engineering)

   null (Ed.)

   Abstract Additive manufacturing (AM) techniques, such as fused deposition modeling (FDM), are able to fabricate physical components from three-dimensional (3D) digital models through the sequential deposition of material onto a print bed in a layer-by-layer fashion. In FDM and many other AM techniques, it is critical that the part adheres to the bed during printing. After printing, however, excessive bed adhesion can lead to part damage or prevent automated part removal. In this work, we validate a novel testing method that quickly and cheaply evaluates bed adhesion without constraints on part geometry. Using this method, we study the effect of bed temperature on the peak removal force for polylactic acid (PLA) parts printed on bare borosilicate glass and polyimide (PI)-coated beds. In addition to validating conventional wisdom that bed adhesion is maximized between 60 and 70 °C (140 and 158 °F), we observe that cooling the bed below 40 °C (104 °F), as is commonly done to facilitate part removal, has minimal additional benefit. Counterintuitively, we find that heating the bed after printing is often a more efficient process for facile part removal. In addition to introducing a general method for measuring and optimizing bed adhesion via bed temperature modulation, these results can be used to accelerate the production and testing of AM components in printer farms and autonomous research systems. 

   more » « less
2. Effects of Environmental Temperature and Humidity on the Geometry and Strength of Polycarbonate Specimens Prepared by Fused Filament Fabrication

   https://doi.org/10.3390/ma13194414  

   Fang, Lichen ; Yan, Yishu ; Agarwal, Ojaswi ; Yao, Shengyu ; Seppala, Jonathan E. ; Kang, Sung Hoon ( October 2020 , Materials)

   null (Ed.)

   It is widely known that the printing quality of fused filament fabrication (FFF) is heavily affected by environmental temperature and humidity, taking the form of warping and porosity. However, there is little understanding about the quantitative relations between environmental conditions, geometry, and the mechanical properties of printed parts. In this study, we systematically investigated those relations using bisphenol A polycarbonate as a model material system. For the environmental temperature, an in-situ infrared imaging analysis revealed the presence of an up to 5.4 °C/mm thermal gradient when printing using an open-chamber printer and a heated build plate. For the environmental humidity, an analysis of X-ray micro-computed tomography (micro-CT) scans showed an up to 11.7% porosity that was brought by polymer water content absorbed from environmental moisture. Meanwhile, tensile tests showed a mechanical performance loss associated with those defects, but, surprisingly, the transverse direction ductility had the potential to increase at a higher porosity. Furthermore, the experimental results were combined with analytical and parametrical studies to elucidate quantitative relations between environmental conditions and printing quality. Based on the results, quantitative guidelines for the estimation of printing quality based on environmental conditions are provided that would also help users to obtain desired printing results with a better understanding of the effects of environmental conditions. 

   more » « less
3. 3D printing using powder melt extrusion

   https://doi.org/10.1016/j.addma.2019.100811  

   Boyle, B. M. ( August 2019 , Additive manufacturing)

   Additive manufacturing promises to revolutionize manufacturing industries. However, 3D printing of novel build materials is currently limited by constraints inherent to printer designs. In this work, a bench-top powder melt extrusion (PME) 3D printer head was designed and fabricated to print parts directly from powder-based materials rather than filament. The final design of the PME printer head evolved from the Rich Rap Universal Pellet Extruder (RRUPE) design and was realized through an iterative approach. The PME printer was made possible by modifications to the funnel shape, pressure applied to the extrudate by the auger, and hot end structure. Through comparison of parts printed with the PME printer with those from a commercially available fused filament fabrication (FFF) 3D printer using common thermoplastics poly(lactide) (PLA), high impact poly(styrene) (HIPS), and acrylonitrile butadiene styrene (ABS) powders (< 1 mm in diameter), evaluation of the printer performance was performed. For each build material, the PME printed objects show comparable viscoelastic properties by dynamic mechanical analysis (DMA) to those of the FFF objects. However, due to a significant difference in printer resolution between PME (X–Y resolution of 0.8 mm and a Z-layer height calibrated to 0.1 mm) and FFF (X–Y resolution of 0.4 mm and a Z-layer height of 0.18 mm), as well as, an inherently more inconsistent feed of build material for PME than FFF, the resulting print quality, determined by a dimensional analysis and surface roughness comparisons, of the PME printed objects was lower than that of the FFF printed parts based on the print layer uniformity and structure. Further, due to the poorer print resolution and inherent inconsistent build material feed of the PME, the bulk tensile strength and Young’s moduli of the objects printed by PME were lower and more inconsistent (49.2 ± 10.7 MPa and 1620 ± 375 MPa, respectively) than those of FFF printed objects (57.7 ± 2.31 MPa and 2160 ± 179 MPa, respectively). Nevertheless, PME print methods promise an opportunity to provide a platform on which it is possible to rapidly prototype a myriad of thermoplastic materials for 3D printing. 

   more » « less
4. 3D Printed Stress Sensors for Non-Destructive Evaluation of Space Structures

   Perla Latorre-Suraez, Rohan Madathil ( April 2021 , AIAA 2021 Regional Student Conference, April 2021.)

   Self-sufficient and non-contact sensors play multiple roles in lunar, planetary exploration, and Earth structures. These sensors allow engineers to accurately examine structural integrity and defects on mechanical components for optimal operations. Structural integrity allows the industry to ensure the safety and capacity of key structures. Materials like α-alumina can be employed as sensors due to the photoluminescent properties that they possess. Piezospectroscopy is a non-destructive evaluation (NDE) method capable of capturing in-situ stress using α-alumina due to the chromium ion impurities that it contains. The chromium ion impurities carry spectral characteristics, that when excited with an Nd: YAG laser (532 nm), demonstrate capabilities for structural integrity monitoring. In this work, a 3D printing method is developed to autonomously create sensors that are compatible with use in space environments. The 3D printing method intends to provide the industry flexible and adaptive solutions for structural integrity monitoring. This method includes a modified Fused Deposition Method printer by exchanging its original nozzle with a syringe base nozzle. The printing parameters such as printing speed, printing bed temperature, coating thickness, and syringe volume are determined during the testing process. Challenges include achieving uniform integration and nanoparticle dispersion as well as adhesion between the matrix and the substrates. The parameters to encounter these challenges will depend on the materials used. Experiments with three different volume fractions (VF) of α-alumina within an epoxy were performed to address the printing challenges. The sensors were applied to nine specimens, three of each VF but with varying deposition rates after the mixture process. These experiments considered the mixing and deposition method while testing the dispersion within the α-alumina and the epoxy matrix. The substrates, on which the epoxy matrix was deposited, underwent a surface treatment to ensure adhesion between the substrate and the sensor matrix. During this experiment, the epoxy matrix was deposited with a syringe onto a substrate and cured at room temperature. The specimens were tested with a tensile load using an electromechanical MTS. While the samples are tensile loaded, the sensors were characterized via photoluminescent piezo spectroscopy to determine which VF demonstrates the best stress sensing capabilities, along with the adhesion between the matrix and the substrate. The data collected allows the optimal VF to be established for future applications. 

   more » « less
5. Recent advances in printable thermoelectric devices: materials, printing techniques, and applications

   https://doi.org/10.1039/C9RA09801A  

   Hossain, Md Sharafat ; Li, Tianzhi ; Yu, Yang ; Yong, Jason ; Bahk, Je-Hyeong ; Skafidas, Efstratios ( February 2020 , RSC Advances)

   Thermoelectric devices have great potential as a sustainable energy conversion technology to harvest waste heat and perform spot cooling with high reliability. However, most of the thermoelectric devices use toxic and expensive materials, which limits their application. These materials also require high-temperature fabrication processes, limiting their compatibility with flexible, bio-compatible substrate. Printing electronics is an exciting new technique for fabrication that has enabled a wide array of biocompatible and conformable systems. Being able to print thermoelectric devices allows them to be custom made with much lower cost for their specific application. Significant effort has been directed toward utilizing polymers and other bio-friendly materials for low-cost, lightweight, and flexible thermoelectric devices. Fortunately, many of these materials can be printed using low-temperature printing processes, enabling their fabrication on biocompatible substrates. This review aims to report the recent progress in developing high performance thermoelectric inks for various printing techniques. In addition to the usual thermoelectric performance measures, we also consider the attributes of flexibility and the processing temperatures. Finally, recent advancement of printed device structures is discussed which aims to maximize the temperature difference across the junctions. 

   more » « less