Conference Programme

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M-02: Symp M
Monday, 19/Jun/2017:
4:00pm - 6:15pm

Session Chair: Xiaochun Li, University of California Los Angeles
Session Chair: Shih-Chi Chen, The Chinese University of Hong Kong
Location: Rm 327

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4:00pm - 4:30pm

3D Printing of Ultra-Tough Polyion Complex Hydrogels


College of Mechanical Engineering, Zhejiang University, China

Polyion complex (PIC) hydrogels have been proposed as promising engineered soft materials due to their high toughness and good processibility. In this work, we reported manufacturing of complex structures with tough PIC hydrogels based on three-dimensional (3D) printing technology. In concentrated saline solution, PIC forms viscous solution, which can be directly extruded out of a nozzle into water, where dialyzing out of salt and counterions results in sol-gel transition to form tough physical PIC gel with intricate structures. The printability of PIC solutions was systematically investigated by adjusting the PIC material formula and printing parameters, in which proper viscosity and gelation rate were found to be key factors for successful 3D printing. Uniaxial tensile tests were performed to printed single fibers and multi-layer grids, both exhibiting distinct yet controllable strength and toughness. More complex 3D structures with negative Poisson's ratio, gradient grid and material anisotropy were constructed as well, demonstrating the flexible printability of PIC hydrogels. We also design and manufactured macroscopic ultra-tough hydrogel constructs with titin-like domains by heterogeneous 3D printing with multiple nozzles, which shows significantly enhanced extensibility and toughness compared to the counterpart without folded domains. The methodology and capability here provide a versatile platform to fabricate complex structures with tough PIC hydrogels, which should broaden the use of such materials in applications such as biomedical devices and artificial tissues.

4:30pm - 5:00pm

Controllable Microstructure and Mechanical Properties of Electron Beam Melted Ti-6Al-4V

Pan WANG1, Beng Loon AW1, Mui Ling Sharon NAI1, Xipeng TAN2, Shu Beng TOR2, Jun WEI1

1Singapore Institute of Manufacturing Technology, Agency for Science, Technology and Research (A*STAR), Singapore; 2Singapore Centre for 3D Printing, School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore

Electron beam melting (EBM) is a powder bed additive manufacturing technology and suitable for producing near-net-shape metallic parts with complex geometry and high quality. However, the EBM-built components exhibit spatially and geometrically based microstructure and mechanical properties. Therefore, further study to design processing parameters in turn to control the microstructure in EBM-built component is critical. The present effort is focused on the effects of processing parameters on the mechanical properties of Ti-6Al-4V components fabricated by selective electron beam melting additive manufacturing. The variations of microstructure and their related mechanical properties were reported. Moreover, the pore formation mechanism in EBM-built component was discussed and a new method to fabricate fully dense component was proposed. Furthermore, a process map resulting in specimens without a lack of fusion and a good geometrical accuracy was developed. These findings are valuable for the control of desired microstructures for specific applications, which further propel the practical applications of EBM-built industrial parts in the near future.

5:00pm - 5:15pm

3D Printing of Silver Microarchitectures with Newtonian-Fluid Silver Nanoparticle Ink

Sanghyeon LEE1,3, Jung Hyun KIM1, Muhammad WAJAHAT1,2, Hwakyung JEONG1, Won Suk CHANG1,3, Seung Kwon SEOL1,2

1Nano Hybrid Technology Research Center, Korea Electrotechnology Research Institute (KERI), South Korea; 2Electrical Functional Material Engineering, Korea University of Science and Technology (UST), South Korea; 3Department of Electronics and Computer Engineering, Hanyang University, South Korea

Recent interest in 3D printing technology has led to a new concept of printed devices – known as 3D printed electronics. The 3D printed electronics involves the fabrication of 3D functionalized structures on the substrate and pattering of materials on 3D printed or non-flat substrate for producing electronic devices. So far, most efforts in 3D printing technology have been devoted to materials design and printing approaches for the production of 3D structures with high mechanical strength. As a result, it is difficult to obtain functional 3D structures for electronics, though we can easily produce plastic or metallic 3D objects with coarse resolution by different types of commercial 3D printing methods such as stereolithography (SLA), fused deposition modeling (FDM) or selective laser sintering (SLS). It requires the development of printing approaches to achieve functional 3D structures with high spatial resolution.

In this work, we report on a simple and inexpensive meniscus-guided metallic 3D micro-printing method using a low-viscosity silver nanoparticle (AgNP) ink. The method uses a localized deposition of AgNPs in an ink meniscus to print 3D microarchitectures. The printed structures was obtained by horizontally (or vertically) pulling the ink-filled micronozzle without applying any pressure for ink extrusion. During the printing process, rapid solidification induced by evaporation of solvents in the low- viscosity ink meniscus retained freestanding structures without the need for additional energy. Poly(acrylic acid)-capped silver nanoparticle (PAA-AgNP) ink with Newtonian fluid behavior and a viscosity of ~ 7 mPa∙s was synthesized by microwave rapid heating to achieve continuous ink flow through a confined nozzle geometry without aggregation and nozzle clogging. The meniscus-guided method could lead us to produce highly conductive 3D microstructures up to 104 S/cm obtained via post-thermal treatment, such as freestanding pillar arrays, arched bridges, pyramids, and colosseums.

5:15pm - 5:30pm

A Roll-to-Roll Processing System for Coating and Printing

Xuechuan SHAN, Budiman SALAM, Vasudivan SUNAPPAN, Yicai Adrian ZHANG, Jun WEI

Singapore Institute of Manufacturing Technology, Agency for Science, Technology and Research (A*STAR), Singapore

In this paper, a novel roll-to-roll processing system for manufacturing flexible printed electronics and its applications are presented. The roll-to-roll system has coating, printing and lamination modules for manufacturing multi-layer devices, changing between roll-to-roll coating and printing processes can be realized easily with only a short interval. In addition to unwinder, rewinder and precisely controlled drying ovens, the roll-to-roll system also consists of web aligners, load cells, web tension controllers for precise film handling. As one example of using the developed system for roll-to-roll processing, we have demonstrated electroluminescent lighting devices manufactured through roll-to-roll coating and printing.

5:30pm - 5:45pm

Active Control of Microstructure in Electron Beam Melting of Ti6Al4V

Guglielmo VASTOLA, Gang ZHANG, Qing Xiang PEI, Yong-Wei ZHANG

Institute of High Performance Computing, Agency for Science, Technology and Research (A*STAR), Singapore

Electron beam melting (EBM) is a powder-bed fusion technique for production of net-shape metallic components. Because of the complex interaction among the energy beam, the powder bed, and material phase transformations, EBM is very sensitive to process parameters such as beam power and scan speed. As a result, the process window to produce fully-dense parts with ASTM-grade mechanical properties is very narrow. In such scenario, envisioning further control of mechanical properties is very challenging. In fact, while a coarser, milder microstructure would be more attractive compared to that of as-built parts, the actual cooling rates and thermal gradients are simply incompatible with such microstructures, without compromising on part density and surface roughness. In this context, computer simulations can prove useful to precisely quantify the effect of process parameters on solidification and on solid-to-solid phase transformations such as the martensitic transformation in Ti6Al4V. As a departure from traditional attempts to control microstructure by changing the process parameters, in this work we propose the introduction of a thermoelectric module (TEM) as an active device inside the build chamber. We show that by injecting or extracting heat through the TEM device, the volume fraction of martensite can be controlled in its entire range. In particular, we show that commercial TEM modules can deliver sufficient thermal power to completely block the formation of martensite. As a result, microstructure can be controlled locally while retaining the beam power and scan speed optimal for part density and surface finish. This work is now a Singapore patent and further work towards commercial application is being investigated.

5:45pm - 6:00pm

Compressive Strength of Porous 3D Printed Spodumene

Ming Xuan GAN1,2, Chee How WONG1

1School of Mechanical and Aerospace Engineering, Singapore Centre for 3D Printing, Nanyang Technological University, Singapore; 2SLM Solutions Singapore Pte Ltd, Singapore

Materials used in the selective laser melting (SLM) technique are currently limited to metals. As a result, this limitation has restricted the full potential of SLM. Being a powder bed-based additive manufacturing (AM) method, it is able to manufacture geometrically complex components not possible with conventional subtractive methods. In addition, it is also possible to manufacture interlocking parts, which enables the user to bypass part assembly stage in the production line. However, the many potentials of this AM method are being limited to the types of materials it can process. Overcoming materials limitation is an important step to wider usage of SLM AM. In order to overcome this issue, we have previously studied the effect of processing parameters in the manufacturing of a glass-ceramic article using SLM. The material used belongs to a naturally occurring mineral – spodumene. The advantage of this material is its low coefficient of thermal expansion, if added as an additive, can improve the thermal shock resistance of a part. By optimising the processing conditions, we were able to print three-dimensional glass-ceramic parts for various characterisation. Some properties we have studied on includes the relative density and phases form after heat-treatment. In this study, we focus on the compressive strength of cylindrical SLM manufactured glass-ceramic articles with respect to the post-heat-treatment temperatures. In addition, this study aims to show that the direct laser melting of ceramics, without binders, is still possible with appropriate processing conditions.

6:00pm - 6:15pm

Direct-Write 3D Electrospinning of High-Aspect Ratio Microstructures

Kwok Siong TEH

San Francisco State University, United States

During a conventional electrospinning process, a polymer solution is charged to a high voltage, creating electrostatic repulsion between molecular chains with like charges. Above a certain threshold voltage, the repulsive force overcomes the surface tension of the solution, leading to jets of polymer fiber being expelled from solution surface and accelerated toward a ground collector. This often results in a random mesh of non-woven fibers on the collector due to strong repulsion between the as-deposited fibers and the incoming fibers. In order to construct 3D monolithic micro/mesoscale structures, it was necessary that the incoming fibers be able to deposit on top of as-deposited fibers in an orderly, controlled manner. To achieve spatial control of such deposition, there exists a need for a dissipative pathway for the residual charges. To this end, we successfully demonstrated the fabrication of high-aspect-ratio, free-standing three dimensional polymeric mesoscale structures based on a solution-based, direct-write near-field electrospinning process. We discovered and demonstrated the key to mitigating the buildup of residual charges lies in the use of a semiporous substrate as the collector. Using this technique, we were able to directly electrospin high-aspect-ratio 3D microstructures—3D walls, grids, and tubes—on a semiporous substrate in a controllable manner. This technique expands the current repertoire of direct-write polymer fabrication processes and augments the capability of electrospinning to construct 3D microstructures—hitherto a near-impossible feat—for various applications. In this work, we will demonstrate the fabrication of a 2 × 2 cm2, 100 μm-thick (20 layers of stacked fibers), 3D conductive polymer-carbon nanotube grid as a flexible electrode for a solid-state micro-supercapacitor.

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