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SLM 공정으로 제작된 SKD61 공구강의 조형 특성에 관한 연구
윤재철,최중호,김기봉,양상선,양동열,김용진,이창우,유지훈,Yun, Jaecheol,Choe, Jungho,Kim, Ki-Bong,Yang, Sangsun,Yang, Dong-Yeol,Kim, Yong-Jin,Lee, Chang-Woo,Yu, Ji-Hun 한국분말야금학회 2018 한국분말재료학회지 (KPMI) Vol.25 No.2
In this study, two types of SKD61 tool-steel samples are built by a selective laser melting (SLM) process using the different laser scan speeds. The characteristics of two kinds of SKD61 tool-steel powders used in the SLM process are evaluated. Commercial SKD61 tool-steel power has a flowability of 16.68 sec/50 g and its Hausner ratio is calculated to be 1.25 by apparent and tapped density. Also, the fabricated SKD61 tool steel powder fabricated by a gas atomization process has a flowability of 21.3 sec/50 g and its Hausner ratio is calculated to be 1.18. Therefore, we confirmed that the two powders used in this study have excellent flowability. Samples are fabricated to measure mechanical properties. The highest densities of the SKD61 tool-steel samples, fabricated under the same conditions, are $7.734g/cm^3$ (using commercial SKD61 powder) and $7.652g/cm^3$ (using fabricated SKD61 powder), measured with Archimedes method. Hardness is measured by Rockwell hardness testing equipment 5 times and the highest hardnesses of the samples are 54.56 HRC (commercial powder) and 52.62 HRC (fabricated powder). Also, the measured tensile strengths are approximately 1,721 MPa (commercial SKD61 powder) and 1,552 MPa (fabricated SKD61 powder), respectively.
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A Return-to-zero DAC with Tri-state Switching Scheme for Multiple Nyquist Operations
윤재철,정윤환,유태근,홍요한,김주언,윤동현,이성민,조영권,김용신,백광현 대한전자공학회 2017 Journal of semiconductor technology and science Vol.17 No.3
A return-to-zero (RZ) digital-to-analog converter (DAC) with a tri-state switching scheme is proposed in this paper. The proposed scheme provides a triple weight output for RZ operation by using a conventional differential current switch and simple pseudo-differential F/Fs. The RZ function is realized with only two additional transistors in each F/F cell, which results in a power dissipation increase of less than 5%. To verify the performance of the proposed method, a 10-bit RZ DAC is fabricated using standard 180-nm CMOS technology. Measured results show that the worst SFDR performances are 60 dBc and 55 dBc in the 1st and 2nd Nyquist bands, respectively, when operating at 650 MHz clock frequency. The total power consumption is 64 mW, and the active area occupies 0.25 mm².
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윤재철,김양도,박대희,윤정열 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.10
Iron aluminate (FeAl2O4) hollow particles with a spinel structure were synthesized by using a spray pyrolysis process. FeAl2O4 hollow particles were formed at a reaction temperature of 900 C at a flow rate of 40 L/min as a result of the rapid solvent evaporation and decomposition gases from the droplets in the spray solution prepared from metal salts and organic reagents. FeAl2O4 hollow particles were fabricated at a reaction temperature of 900 C with a flow rate of 40 L/min. The FeAl2O4 hollow particles were heat treated for 3 hours at 600 C in a 5% H2/Ar atmosphere to form the crystal particles. Subsequently, FeAl2O4 nanoparticles were fabricated from the FeAl2O4 hollow particles by using the wet milling process. After milling for 60 minutes, transmission electron microscopy revealed the FeAl2O4 particles to have a mean size of approximately 50 nm. The FeAl2O4 nanoparticles were fabricated successfully by using a two-step process, spray pyrolysis and wet milling.
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혈관중재술 후 경피적 혈관봉합기구에 의한 넙다리동맥 급성폐색증의 외과적 치료 1예
윤재철,권준성,김한영,강희준,윤대근,전성은,이재정,이정훈,이삼열,박성길 대한혈관외과학회 2011 Vascular Specialist International Vol.27 No.1
Vascular intervention via the femoral artery can cause vascular access complications and complications from closure of the arteriotomic incision site such as bleeding, thrombotic complications and vascular trauma. These types of complications occur in about 2% to 10% of the cases. After removal of the catheter, hemostasis is traditionally achieved by manual compression as a standard method. Many vascular closure devices have been developed in an attempt to improve the patient’s comfort and to decrease the time to ambulation. Yet the safety and effectiveness of these vascular closure devices as compared to that of manual compression remains unclear. Herein we report on a case of femoral arterial occlusion due to vascular closure devices and the operative management.
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금속 3D 프린팅 공정 최적화를 통한 H13 공구강 조형체의 기계적 특성 향상
윤재철,최중호,이행나,김기봉,양상선,양동열,김용진,이창우,유지훈,Yun, Jaecheol,Choe, Jungho,Lee, Haengna,Kim, Ki-Bong,Yang, Sangsun,Yang, Dong-Yeol,Kim, Yong-Jin,Lee, Chang-Woo,Yu, Ji-Hun 한국분말야금학회 2017 한국분말재료학회지 (KPMI) Vol.24 No.3
In this study, H13 tool steel sculptures are built by a metal 3D printing process at various laser scan speeds. The properties of commercial H13 tool steel powders are confirmed for the metal 3D printing process used: powder bed fusion (PBF), which is a selective laser melting (SLM) process. Commercial H13 powder has an excellent flowability of 16.68 s/50 g with a Hausner ratio of 1.25 and a density of $7.68g/cm^3$. The sculptures are built with dimensions of $10{\times}10{\times}10mm^3$ in size using commercial H13 tool steel powder. The density measured by the Archimedes method is $7.64g/cm^3$, similar to the powder density of $7.68g/cm^3$. The hardness is measured by Rockwell hardness equipment 5 times to obtain a mean value of 54.28 HRC. The optimum process conditions in order to build the sculptures are a laser power of 90 W, a layer thickness of $25{\mu}m$, an overlap of 30%, and a laser scan speed of 200 mm/s.
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