• 한국산학기술학회논문지
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• 제11권1호
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• pp.73-78
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• 2010

본 연구에서는 분산전원이 연계된 배전계통에서 발생하는 고조파를 평가하고자 PSCAD/EMTDC를 이용하여 분산전원 배전계통 연계 시의 시뮬레이션을 수행하였다. 실계통과 유사한 배전계통 및 태양광발전 시스템을 모델링하여 연계지점을 구간마다 시뮬레이션을 수행하였다. 고조파 연계기준(IEEE Std 1547과 IEEE Std 519)을 적용하여 알고리즘을 작성하고, 시뮬레이션 데이터는 FFT로 변환하여 THD와 TDD로 구분하여 평가하였다. 구간별로 구분하여 평가한 고조파 함유량은 분산전원을 연계하지 않은 상태와 각 구간과 Case 별로 구분하여 평가하여 연계하기 전과 비교하여 고조파를 파악한 결과 모든 배전계통의 구간에서 고조파 분포가 적합하다는 평가를 할 수 있었으며, 부하로 선정한 50kW 유도모터의 특성으로 인해 구간 2에서의 고조파 분포가 증가함으로서 연구 결과의 효용성을 입증할 수 있었다.

• 열처리공학회지
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• 제22권5호
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• pp.282-289
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• 2009

The effects of the high temperature gas nitriding (HTGN), tempering and subzero treatment of STD11 steel have been investigated. HTGN treatment was carried out at $1050^{\circ}C$, $1100^{\circ}C$ and $1150^{\circ}C$ for 1 hr. in an atmosphere of $1\;kg/cm^2$ nitrogen gas. Tempering and double-tempering were performed at $550^{\circ}C$ for 1 hr. The surface layer of HTGN-treated steel appeared the precipitates of $M_2N$, $M_7C_3$ and $M_{23}C_6$ in the matrix of austenite. However, the interior region exhibited martensite with the precipitation of carbides. The nitrogen content of the surface layer appeared ~1.35 wt.%, ~0.83 wt.% and ~0.56 wt.% at the HTGN treatment temperature of $1050^{\circ}C$, $1100^{\circ}C$ and $1150^{\circ}C$, respectively. The surface hardness of double-tempered and subzero-treated steel measured the maximum value of 828 Hv, 960 Hv, 750 HV after HTGN treatment at the $1050^{\circ}C$, $1100^{\circ}C$ and $1150^{\circ}C$, respectively. These hardness value increased above 230~420 Hv compared with the HTGN-treated steel due to the decrease in retained austenite and existence of fine precipitates.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.903-906
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• 1997

For the net shape manufacturing, grinding is a important process that influences directly the accuracy and the integrity of products. We studied and researched the grinding force, surface roughness, and grinding wheel durability, according to the change of a feed speed of the table and a depth of the cut step by step with experiment that it is used to WA wheel. Workpiece materials were used STDII. The purpose of this study proposes the basic data for design of the machine tool and for controlling the machining parameters to obtain optimum performance of plunge grinding system during operation.

• 한국공작기계학회논문집
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• 제13권5호
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• pp.7-15
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• 2004

The purpose of this study was to present the method to choose the optimum machining condition for the wire EDM. This was completed by examining the ever-changing quality of the material and by improving the function of the wire electric discharge machine. Precision metal mold products and the unmanned wire electric discharge machining system were used and then applied in industrial fields. This experiment uses the wire electric discharge machine with brass wire electrode of 0.25mm. To measure the precision of the machining surface, average values are obtained from 3 samples of measures of center-line average roughness by using a third dimension gauge and a stylus surface roughness gauge.

• 한국공작기계학회논문집
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• 제16권4호
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• pp.119-126
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• 2007

Generally, the machinability of materials that have a good mechanical properties is poor. The material having a high strength, high toughness in high temperature and wear resistance, it is difficult to remove a chip from workpiece. STD11 and NAK80 are kinds of these materials and these materials can be used in many industrial fields. But it is limited in use because of high cost and poor machinability. In this experimental study, the cutting of STD11 and NAK80 were used to decide the machinability and the tool shape of CBN ball end mill. From the results, the CBN ball end mill is verified that the estimated cutting edge shape of rake angle 30 degree has consistent effect on the tool wear and cutting force.

• 한국공작기계학회논문집
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• 제17권6호
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• pp.104-110
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• 2008

A lot of straight bevel gears have been manufactured by the cold forging process in order to improve the productivity and mechanical property of the product. The die for the cold forging of the gear needs high precision and reproducibility. In the study, cold forging die has been modeled by CAD/CAM and manufactured by machining center using ball end mill coated by (Al, Ti)N for heat-treated alloy steel(STD11, HRC 60). Through the measurement of the machined die, satisfactory dimensional accuracy and surface roughness were obtained. In the future, many 3-d cold forging dies will be directly machined instead of electric discharge machining.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1992년도 춘계학술대회 논문집
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• pp.99-103
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• 1992

The EDM characteristics of STD11 steel with copper and graphite as electrode have been investigated by using Hansvedt SE-155B electro-discharge machine. The effects of parameters such as duty factor and frequency on electro-discharge machining were discussed. It was found that those parameters have significant influences on the relative electrode wear(REW), metal removalrate(MRR) surface integrity. When the duty factor was increased under the constant frequency of 2 KHz, the MRR was also increased and the REW was decreased. But REW was constant with higher duty factor of 50%. In the case of the smaller duty factor and the higher frequency, the surface roughness has become better. When the graphite was used as electrode at thes same condition, the tool electrode built-up phenomenon has been obsdrved.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 춘계학술대회 논문집
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• pp.862-865
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• 2000

The surface grinding of STD-11 was attempted on the machining center. Grinding experiments were performed at the various grinding conditions and the grinding force, machining error, grinding ratio, and surface roughness were measured. The experimental results indicate that the grinding ratio decreases as the table speed and depth of cut increase. The surface roughness of ground surface was not affected by the change of depth of cut. The surface roughness values obtained on the experiments were 0.02 ～ 0.03${\mu}{\textrm}{m}$ which are fairy good and acceptable for ground surface.

• 한국생산제조학회지
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• 제8권6호
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• pp.16-25
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• 1999

In recent years, grinding techniques for precision machining of brittle materials used in die, model and optical parts have been improved by using superfine abrasive wheel and precision grinding machine. The completion of optimum dressing of superfine abrasive wheel makes possible the effective precision grinding of die steel(STD-11). In this study, a new system and the grinding mechanism of optimum in-process electrolytic dressing were proposed. This method can carry out optimum in-process electrolytic dressing of superfine abrasive wheel. Therefore, the optimum in-process electrolytic dressing is a good method to obtain the efficiency and mirror-like grinding of STD-11.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.266-269
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• 2002

Research during the past several years has established the effectiveness of acoustic emission (AE)-based sensing methodologies for machine condition analysis and process. AE has been proposed and evaluated for a variety of sensing tasks as well as for use as a technique for quantitative studies of manufacturing process. STD11 has been known as difficult-to-cut materials. For this study, the micro-grooving machine was developed. The experiments were performed using diamond blade and CBN blade f3r machining STD11. Evaluating the machining conditions, frequency spectrum analysis of acoustic emission (AE) signals according to each conditions were applied.