• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.679-682
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• 2002

Resistance spot welding using air gun has been used for joining the sheet metal in automotive manufacturing process. Although air gun has many advantages, it also has the limitation to control the pressure as a factor to improve weld quality. In this study, we apply servo gun using servo motor to resistance spot welding and find the relationship between welding pressure and welding quality. Trough the experiment to change welding pressure during the welding cycle, we can make it clear that the change of welding pressure is greatly influence on the welding quality. To get in a. using response surface methodology, drew out the optimal welding pressure profile for welding quality progresses. We made an optimal profile of welding pressure which improves welding quality using response surface methodology.

• Journal of the Korea Safety Management & Science
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• v.17 no.4
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• pp.67-75
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• 2015

This paper reviewed the relationship between emotional labor and service quality, and the moderating effect of superior and coworker support. Based on the responses from 520 hotel employees, the results of multiple regression analysis appeared as follow; 1) deep acting affected positively on all service quality factors(responsiveness, empathy, reliability). 2) surface acting didn't affect significantly on all service quality factors(responsiveness, empathy, reliability). 3) coworker support affected positively on the relationship between deep acting and responsiveness. 4) superior support affected positively on the relationship between deep acting and responsiveness, and on the relationship between surface acting and responsiveness.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.12
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• pp.21-28
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• 2004

In modem manufacturing industries such as the airplane and automobile, aluminum alloys which are remarkable in durability have been utilized effectively. High-speed machining technology for surface roughness quality of workpiece has been applied in these fields. Higher cutting speed and feedrates lead to a reduction of machining time and increase of surface quality. Furthermore, the reduction of time required for polishing or lapping of machined surfaces improves the production rate. Traditional milling process for high speed cutting can be machined with end mill tool. However, such processes are generally cost-expensive and have low material removal rate. Thus, in this paper, face milling cutter which gives high MRR has developed face milling cutter body for the high speed machining of light alloy to overcome the problems. Also vibration experiment to detect natural frequency in free state and frequency characteristics during machining are performed to escape resonance.

• International Journal of Highway Engineering
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• v.20 no.1
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• pp.69-76
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• 2018

PURPOSES : This study determined the optimal usage rate of RAP (reclaimed asphalt pavement) using cold central-plant recycling (CCPR) on a road-surface layer. In addition, a mixture-aggregate gradation design and a curing method based on the proposed rate for the surface-layer mix design were proposed. METHODS : First, current research trends were investigated by analyzing the optimum moisture content, mix design, and quality standards for surface layers in Korea and abroad. To analyze the aggregate characteristics of the RAP, its aggregate-size characteristics were analyzed through the combustion asphalt content test and the aggregate sieve analysis test. Moreover, aggregate-segregation experiments were performed to examine the possibility of RAP aggregate segregation from field compaction and vehicle traffic. After confirming the RAP quality standards, coarse aggregate and fine aggregate, aggregate-gradation design and quality tests were conducted for mixtures with 40% and 50% RAP usage. The optimum moisture content of the surface-layer mixture containing RAP was tested, as was the evapotranspiration effect on the surface-layer mixture of the optimum moisture content. RESULTS : After analyzing the RAP recycled aggregate size and extraction aggregate size, 13-8mm aggregate was found to be mostly 8mm aggregate after combustion. After using surface-chipping and mixing methods to examine the possibility of RAP aggregate segregation, it was found that the mixing method contributed very little for 3.32%, and because the surface-chipping method applied compaction energy directly as the maximum assumption the separation ratio was 15.46%. However, the composite aggregate gradation did not change. Using a 40% RAP aggregate rate on the surface-layer mixture for cold central-plant recycling satisfied the Abroad quality standard. The optimum moisture content of the surface-layer mixture was found to be 7.9% using the modified Marshall compaction test. It was found that the mixture was over 90% cured after curing at $60^{\circ}C$ for two days. CONCLUSIONS : To use the cold central-plant recycling mixture on a road-surface layer, a mixture-aggregate gradation design was proposed as the RAP recycled aggregate size without considering aggregate segregation, and the RAP optimal usage rate was 40%. In addition, the modified Marshall compaction test was used to determine the optimum moisture content as a mix-design parameter, and the curing method was adapted using the method recommended by Asphalt Recycling & Reclaiming Association (ARRA).

• Food Science and Preservation
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• v.4 no.3
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• pp.265-270
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• 1997

Effect of modified atmosphere packaging conditions on quality changes of dry jujube was investigated. Dry jujubes with moisture content of 26.7% were packaged in PET/Al/PE film pouches with modified atmospheres. The tested packages include those with normal air, vacuum, CO2 flushing, N2 flushing and O2 scavenger. Packages were stored at 25$^{\circ}C$ for 6 months, during which ascorbic acid concentration, browning level, titratable acidity and surface color were measured. Generally modified atmosphere packages could improve quality retention of dry jujubes except that vacuum package resulted in large surface color change. CO2-flushed package showed the best quality retention of high ascorbic acid content and low browning during 112 days, but caused high amounts of ascorbic acid destruction and browning in longer storage. In all the modified atmosphere packages titratable acidity reached a maximum followed by decline and subsequent rise, while it increased linearly with time in normal air package. Considering ascorbic acid retention browning level and surface color changes during 112 days, the packages of CO2 flushing and N2 flushing were better than others.

• Journal of Korean Society for Quality Management
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• v.30 no.4
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• pp.58-67
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• 2002

Since the inception of off-line quality control, it has drawn a particular attention from research community and it has been implemented in a wide variety of industries mainly due to its extensive applicability to numerous real situations. Emphasizing design issues rather than control issues related to manufacturing processes, off-line quality control has been recognized as a cost-effective approach to quality improvement. It mainly consists of three design stages: system design, parameter design, and tolerance design which are implemented in a sequential manner. Utilizing experimental designs and optimization techniques, off-line quality control is aimed at achieving product performance insensitive to external noises by reducing process variability. In spite of its conceptual soundness and practical significance, however, off-line quality control has also been criticized to a great extent due to its heuristic nature of investigation. In addition, it has also been pointed out that the process optimization procedures are inefficient. To enhance the current practice of off-line quality control, this study proposes an integrated optimization model by utilizing a well-established statistical tool, so called response surface methodology (RSM), and a tolerance - cost relationship.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.1
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• pp.75-81
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• 2004

In this study surface modeling .method with 3D curve net is proposed. For surface modeling, ship hull was divided into several parts, Generated surface was loaded general purpose CAD program through IGES file format, and the quality of generated surface model was checked by CATIA's internal function. Lastly it is tried to find a method for improving the accuracy of surface connection by using the blending method in CATIA and the result was discussed.

• Korean Journal of Environmental Agriculture
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• v.16 no.4
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• pp.356-364
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• 1997

To investigate the water quality status of agricultural water source for greenhouse area in Gyeongnam, the surface water quality was examined six times from October in 1995 to March in 1996 at five areas in Gyeongnam. The pH values of surface water were in the range of 6.6${\sim}$9.1 pH in Kimhae and Changnyong areas were out of range in 6.0${\sim}$8.5 which was water quality standard for agriculture. The DO values of surface water were relatively high with average 10.0mg/l in Kimhae, Changnyong, Sacheon and Chinju areas except for Haman area. The BOD values of surface water exceeded water quality standard for agriculture(8.0mg/l) in three sites and one site in Haman and Sacheon, respectively. The COD values of surface water exceeded water quality standard for agriculture(8.0mg/l) in Kimhae, Changnyong and Haman. The ${NH_4}^+-N$ values in surface water of Changnyong and Haman areas were 1.21mg/l and 2.75mg/l, respectively. The average values of $NO_3\;^--N$ in surface water was appropriate for agriculture. The values of $K^+,\;Na^+,\;Mg^{2+},\;Ca^{2+},\;{PO_4}^{3-}$ and $SO_4^{2-}$ in Haman were the highest of those of the others. And Pb was below 0.1mg/l which was water quality standard for agriculture. The average values of Cu, Cd and Zn were below water quality standard for agriculture. Between COD and SS in surface water was positively correlated with r$=0.799^{{\ast}{\ast}}$. BOD in surface water was positively correlated with $NH_4\;^+-N,\;PO_4\;^{3-},\;SS,\;K^+,\;Na^+$ and $Cl^-$. Surface water pollution status of agricultural water source of greenhouse areas in Gyeongnam was in order of Chinju< Sacheon< Kimhae< Changnyong< Haman area.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1768-1771
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• 2003

Hard turning replaces grinding for finishing process with expectations of higher productivity and demanded surface quality. Especially for the surface roughness as surface quality demanded in finishing process of hard turning, know-how of machining characteristics of hardened materials by cutting force analysis should be accumulated in company with achievement of precision of elements and high stiffness design technology in hard turning. Considering chip formation mechanism of hardened materials, adequate cutting conditions are selected for machining experiments and cutting forces are measured according to cutting conditions. Increase of cutting forces especially thrust force and increase of dynamic instability could occur in hard turning. Analysis of dynamic characteristics of the cutting forces is executed to investigate relation between dynamic instability and surface roughness in hard turning. Investigation on effects of relative motion of machining system generated by vibration due to dynamic instability shows that ultimate surface roughness could be predicted considering relative motion of machining system with geometrical surface roughness.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.4
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• pp.585-594
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• 2006

This study focused on the causes of fish kills and its prevention methods in Yudeung Stream, Daejeon, Korea. Intense field data, continuous water quality monitoring system and water quality modeling were applied to analyze the causes. Pollutant can be delivered to urban streams by surface runoff and combined sewer overflows in rainfall events. However, water quality analysis and water quality modeling results indicate that the abrupt fish kills in the Yudeung stream seems to be caused by combined effect of DO depletion, increase in turbidity and other toxic material. Excessive fish population in the study area may harm the aesthetic value of the stream and also has greater potential for massive fish kills. It is suggested to implement methods to reduce delivery of pollutants to the stream not only to prevent fish kills but also to keep balance of ecosystem including human uses. Frequent clean up of the urban surface and CSO, installation of detention basin will be helpful. In the long run, it seems combined sewer system has be replaced with separate sewer system for more effective pollutant removal in the urban area.