• Korean Journal of Materials Research
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• v.34 no.10
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• pp.457-463
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• 2024

3D printing using ceramic powder to produce precision ceramic parts has been studied with various additive manufacturing methods. This study analyzed problems occurring in alumina additive manufacturing that uses digital light processing (DLP) as well as methods to address such problems. For efficient analysis, we have classified alumina additive manufacturing into three types according to the driving method of the build platform - lifting type (LT), tilting type (TT) of the vat, and blade movement type (BT). LT had a problem with detachment and cracking of the alumina green body. However, this could be prevented by carefully controlling the cure depth of the suspension slurry and the bonding force between layers and improving the material used for coating the vat. TT, which resulted in non-uniform alumina additive manufacturing, could be improved by modifying the bidirectionality of the axis and the fluidity of the highly viscous alumina suspension slurry. BT resulted in detachment of the specimen as well as non-uniform results, but this could be avoided by shortening the shifting distance of the alumina suspension when it is introduced to the build platform, and enabling effective spreading.

• Journal of Powder Materials
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• v.26 no.6
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• pp.508-514
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• 2019

In the development of advanced ceramic tools, material improvements and design freedom are critical in improving tool performance. However, in the die press molding method, many factors limit tool design and make it difficult to develop innovative advanced tools. Ceramic 3D printing facilitates the production of prototype samples for advanced tool development and the creation of complex tooling products. Furthermore, it is possible to respond to mass production requirements by reflecting the needs of the tool industry, which can be characterized by small quantities of various products. However, many problems remain in ensuring the reliability of ceramic tools for industrial use. In this study, alumina inserts, a representative ceramic tool, was manufactured using the digital light process (DLP), a 3D printing method. Alumina inserts prepared by 3D printing are pressurelessly sintered under the same conditions as coupon-type specimens prepared by press molding. After sintering, a hot isostatic pressing (HIP) treatment is performed to investigate the effects of relative density and microstructure changes on hardness and fracture toughness. Alumina inserts prepared by 3D printing show lower relative densities than coupon specimens prepared by powder molding but indicate similar hardness and higher fracture toughness values.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.247-253
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• 2019

3D printing technology has attracted considerable attention because of its potential to fabricate the intricate design of ceramic products. In this study, ceramic 3D nozzle printing was introduced to manufacture complex alumina products with a ceramic pigment. The alumina paste was formulated by incorporating an elastomer to impart viscoelastic properties. Viscoelastic pastes play an essential role in ceramic 3D nozzle printing. The effects of the viscoelastic properties of the ceramic pastes on their printability were assessed using comprehensive rheological analysis, and various shapes were printed. As a result, the paste with a high yield stress showed better printability. In addition, a ceramic pigment was added to the developed pastes to increase the aesthetics of the printed ceramic structure. The printed ceramic parts were sintered in air at 1300 ℃. The stability of the ceramic pigment was confirmed even after high-temperature sintering.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.81-81
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• 2009

Non-sintered Alumina films were fabricated via inkjet printing processes without a high temperature sintering process. The packing density of these inkjet-printed alumina films measured around 60%. Polymer resin was infiltrated thru these non-sintered films in order to fill out the 40% of voids constituting the rest of the inkjet-printed films. The concept of inkjet-printed Alumina-Resin hybrid materials was designed in order to be applicable to the ceramic package substrates for 3D-system module integration which may possibly substitute LTCC-based 3D module integration. So, the dielectric properties of these inkjet-printed $Al_2O_3$ hybridmaterialsareofourgreatinterest. We have measured dielectric constant and dissipation factor of the inkjet-printed $Al_2O_3$-resinhybridfilmsbyvaryingtheamountofresininfiltratedthruthe$Al_2O_3$films.

• Journal of Powder Materials
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• v.26 no.4
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• pp.327-333
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• 2019

In this study, a process is developed for 3D printing with alumina ($Al_2O_3$). First, a photocurable slurry made from nanoparticle $Al_2O_3$ powder is mixed with hexanediol diacrylate binder and phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide photoinitiator. The optimum solid content of $Al_2O_3$ is determined by measuring the rheological properties of the slurry. Then, green bodies of $Al_2O_3$ with different photoinitiator contents and UV exposure times are fabricated with a digital light processing (DLP) 3D printer. The dimensional accuracy of the printed $Al_2O_3$ green bodies and the number of defects are evaluated by carefully measuring the samples and imaging them with a scanning electron microscope. The optimum photoinitiator content and exposure time are 0.5 wt% and 0.8 s, respectively. These results show that $Al_2O_3$ products of various sizes and shapes can be fabricated by DLP 3D printing.

• Journal of Powder Materials
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• v.27 no.6
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• pp.490-497
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• 2020

The 3D printing process provides a higher degree of freedom when designing ceramic parts than the conventional press forming process. However, the generation and growth of the microcracks induced during heat treatment is thought to be due to the occurrence of local tensile stress caused by the thermal decomposition of the binder inside the green body. In this study, an alumina columnar specimen, which is a representative ceramic material, is fabricated using the digital light process (DLP) 3D printing method. DTG analysis is performed to investigate the cause of the occurrence of microcracks by analyzing the debinding process in which microcracks are mainly generated. HDDA of epoxy acrylates, which is the main binder, rapidly debinded in the range of 200 to 500℃, and microcracks are observed because of real-time microscopic image observation. For mitigating the rapid debinding process of HDDA, other types of acrylates PETA, PUA, and MMA are added, and the effect of these additives on the debinding rate is investigated. By analyzing the DTG in the 25 to 300℃ region, it is confirmed that the PETA monomer and the PUA monomer can suppress the rapid decomposition rate of HDDA in this temperature range.

• BioChip Journal
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• v.16
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• pp.82-98
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• 2020

We report a quantitative and systematic method for determining 3D-printing and surface-treatment conditions that can help improve the optical quality of direct-printed microfluidic devices. Digital light processing (DLP)-stereolithography (SLA) printing was extensively studied in microfluidics owing to the rapid, one-step, cleanroom-free, maskless, and high-definition microfabrication of 3D-microfluidic devices. However, optical imaging or detection for bioassays in DLP-SLA-printed microfluidic devices are limited by the translucence of photopolymerized resins. Various approaches, including mechanical abrasions, chemical etching, polymer coatings, and printing on transparent glass/plastic slides, were proposed to address this limitation. However, the effects of these methods have not been analyzed quantitatively or systematically. For the first time, we propose quantitative and methodological determination of 3D-printing and surface-treatment conditions, based on optical-resolution analysis using USAF 1951 resolution test targets and a fluorescence microbead slide through 3D-printed coverslip chips. The key printing parameters (resin type, build orientation, layer thickness, and layer offset) and surface-treatment parameters (grit number for sanding, polishing time with alumina slurry, and type of refractive-index-matching coatings) were determined in a step-wise manner. As a result, we achieved marked improvements in resolution (from 80.6 to 645.1 lp/mm) and contrast (from 3.30 to 27.63% for 645.1 lp/mm resolution). Furthermore, images of the fluorescence microbeads were qualitatively analyzed to evaluate the proposed 3D-printing and surface-treatment approach for fluorescence imaging applications. Finally, the proposed method was validated by fabricating an acoustic micromixer chip and fluorescently visualizing cavitation microstreaming that emanated from an oscillating bubble captured inside the chip. We expect that our approach for enhancing optical quality will be widely used in the rapid manufacturing of 3D-microfluidic chips for optical assays.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.7
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• pp.89-96
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• 2021

In this study, a mini hydro cyclone was designed and manufactured to achieve an inlet flow rate of 2 L/min in the experiment, which was conducted using alumina powder with a specific gravity of 3.97. This hydro cyclone was studied for using in steam and water analysis system (SWAS) of thermal power plant and was manufactured by 3D printing. Numerical analysis was performed with Solidworks Flow Simulation, utilizing the reynolds stress method (RSM) of fluid multiphase flow analysis models. Experimental and numerical analysis were performed under the three conditions of inlet velocity 2.0, 4.0, and 6.0 m/s. The separation efficiency was over 80% at all inlet velocity conditions. At the inlet velocity 4m/s, the separation efficiency was the best, and it was confirmed that the efficiency was more than 90%.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.11
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• pp.17-23
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• 2021

A cyclone is a dust-separating mechanism that works on the principle of centrifugal force. The performance of a cyclone is evaluated using pressure loss and collection efficiency. A multi-cyclone arrangement is used to improve the collection efficiency within a limited area. In this study, experiments and numerical analyses were conducted on a dual arrangement of mini-hydrocyclone separators, which was fabricated using 3D printing. The experiment was performed at an inlet flow rate of 0.7 m/s, and alumina powder with a particle size of 0.5, 15, and 50 ㎛. ANSYS FLUENT, was used for the numerical analysis. The reliability of the numerical analysis was verified through a comparison with the experimental results. The errors in the experiment and numerical analysis were confirmed to be 2% at the outlet flow rate.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.721-724
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• 2001

In this paper, we present the effect the length the MSL(Microstrip Line) on the oscillation characteristic of the fabricated VCOs(Voltage Controlled Oscillator) designed and analyzed by RF circuit simulator Serenade(ANSOFT Co.) and fabricated by screen printing method on the alumina substrate. We have fabricated VCOs with 3 different MSL length and each MSL length of the VCO is 140mi1, 280mil and 560mi1. The oscillation frequency of each sample(VCO) was tuned to UHF band(750MHz∼900MHz) varying the capacitance. The experimental result shows the phase noise -82∼-97[dBc/Hz] at a 50 [kHz] offset frequency, the pushing figure 94∼318[kHz] at 3${\pm}$0.15[V] and the harmonics 13∼21 [dBc] between MSL length 140mi1s and 560mi1. The frequency and output variation width are 779∼898[MHz], -36∼-33[dBm] at MSL length 140mi1; 818∼836[MHz], -27.19∼-27.06[dBm] at 280mi1;751.54∼751.198[MHz],-33.44∼ -33.31[dBm] at 560mi1. we examined 3 VCOs oscillation characteristic difference through comparison with phase noise, oscillation power and frequency by control voltage change, harmonics and pushing figure for each sample.