• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1998.03a
• /
• pp.94-99
• /
• 1998

In bulk metal forming processes prediction of tool life is very important for saving production cost and achieving good material properties. Generally the service life of tools in metal forming process is limited to a large extent by wear, fracture and plastic deformation of tools. In case of hot and warm forging processes, tool life depends on wear over 70%. In this study finite element analyses are applied to warm forging and hot forging by adopting suggested wear model. By comparision of simulation and real profile of die, suggested model is verified

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1995.03a
• /
• pp.178-185
• /
• 1995

Warm deep drawing for optimum forming conditions to give the maximum drawing depth is investigated and compared with the results at room temperature. Experiments which draw square cups of STS 304 stainless steel sheet under the constant lubrication condition of teflon film made both in a crank and hydrqulic press for two kinds of specimens . The maximum drawing depth at warm forming condition reaches 1.4 times the drawing depth at room temperature in a crank press, whereas 1.6 times in a hydrqulic press, and also more uniform distribution of thickness in case of warm deep drawn cup is observed. The effects of other factors on formability , such as forming temperature, speed of press and cooling of punch are examinnied and discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.05a
• /
• pp.556-559
• /
• 2008

In this study, the failure in circular cup deep drawing simulation at warm temperature is predicted using forming limit diagram (FLD). The FLD is used in sheet metal forming analysis to determine the criterion for fracture prediction. The simulation with heat transfer of circular cup deep drawing at warm temperature was conducted. To predict the failure, the simulation with heat transfer used FLD at temperature in the vicinity of maximum thinning. The result of the simulation with heat transfer shows that the drawn depth increases with increasing temperature and is in accord with the experimental results above $150^{\circ}C$. The FLD provides a good guide for the failure prediction of warm forming simulation with heat transfer.

• Journal of the Korean Society for Precision Engineering
• /
• v.34 no.2
• /
• pp.83-87
• /
• 2017

A multi-step warm forging process for subminiature screws is investigated. Due to the low formability of Titanium alloys, bit forming of Titanium screws is difficult by cold forging. In order to overcome this low formability of Titanium alloys, two candidate processes, i.e., multi-step forging and warm forging are introduced. First, a multi-step (two-step) forging process is investigated. The punch shape and stroke of forging during the first step is designed via various analyses. Finally, the bit formability is investigated at different forging temperatures. Analyses are carried out for two-step forging at various temperatures and the formability under these thermal conditions is compared.

• Ocean and Polar Research
• /
• v.35 no.2
• /
• pp.127-134
• /
• 2013

In this study we investigated changes in the Tsushima Warm Current (TWC) under the global warming scenario RCP 4.5 by analysing the results from the World Climate Research Program's (WCRP) Coupled Model Intercomparison Project Phase 5 (CMIP5). Among the four models that had been employed to analyse the Tsushima Warm Current during the 20th Century, in the CSIRO-Mk3.6.0 and HadGEM2-CC models the transports of the Tsushima Warm Current were 2.8 Sv and 2.1 Sv, respectively, and comparable to observed transport, which is between 2.4 and 2.77 Sv. In the other two models the transports were much greater or smaller than the observed estimates. Using the two models that properly reproduced the transport of the Tsushima Warm Current we investigated the response of the current under the global warming scenario. In both models the volume transports and the temperature were greater in the future climate scenario. Warm advection into the East Sea was intensified to raise the temperature and consequently the heat loss to the air.

• Ocean and Polar Research
• /
• v.31 no.4
• /
• pp.283-296
• /
• 2009

Oceanographic survey data were analyzed to understand the characteristics of a warm eddy observed in the Ulleung Basin in July 2005. The temperature distribution at 200 db and vertical sections provided evidence of the warm eddy in the Ulleung Basin (UWE05). Based on the 5$^{\circ}C$ isothermal line on 200 db temperature, the major axis was 160 km from southwest to northeast, and the minor axis was 80 km from southeast to northwest. The homogeneous layer in the thermocline of UWE05 had mean values of 10.40$^{\circ}C$ potential temperature, 34.35 psu salinity, and 26.37 kg/m$^3$ potential density (${\sigma}_{\theta}$) and provided evidence that UWE05 also existed during the winter of 2004-2005. A warm streamer initially flowed along the circumference of UWE05 and mixed with the upper central water. Two northward current cores were found on the western side of the measured current section at the central latitude of UWE05. One was the East Korean Warm Current (EKWC) and the other was the main stream of the western part of UWE05. Geostrophic transport of the upper layer (from the surface to the isopycnal surface of 26.9 ${\sigma}_{\theta}$) was approximately 2.5 Sv in the eastern side of UWE05. However, the measured transport was twice as large as the geostrophic transport. Mass conservation of geostrophic transport was well satisfied in the upper layer. The direct current measurements and geostrophic transport analysis showed that the EKWC meandered around UWE05.

• Transactions of Materials Processing
• /
• v.15 no.2 s.83
• /
• pp.148-152
• /
• 2006

In this study, the experiments of warm deep drawing were done with heated die, and with heated die, and blankholder, and cooled punch in order to investigate the formability of AZ31 magnesium alloy sheet in warm deep drawing. For this, warm deep drawing experiments were executed under various temperatures and punch velocities. The results of warm deep drawing with heated die showed that fracture occurred around the punch part at punch velocity of 75mm/min and punch stroke of 10mm under temperature range of 373-523K, but did not occur under temperature range of 548-673K even punch stroke of 25mm. And fracture at the punch stroke of 25mm and the temperature of 523K did not occur under the punch velocity of 30mm/min, but occurred under punch velocity of 75 and 125mm/min. Also warm deep drawing with heated die and blankholder, and cooled punch showed that the temperature range happening maximum height under punch velocity of 10-100mm/min was around 498-523K. Finally, with heating and cooling technique necking of AZ31 magnesium alloy occurred at punch shoulder part under the temperature range of 293-423K, but at die wall part under the temperature range of 473-573K.

• Journal of Ocean Engineering and Technology
• /
• v.10 no.2
• /
• pp.120-135
• /
• 1996

The characteristics and fluctuations of structures and spatial distributions of thermal fronts and warm eddy in the Southeastern part of the East sea are discussed based on the data collected by the Naval Academy, Korea during Feb. 6-9, May 9-19 and Oct. 12-18, 1995. The thermal fronts existed very often at the sea off the Pohang-Ulsan, The generation of the thermal front is related with the development of the North Korea Cold Current. The warm eddy is located in the central part of the Ulleung basin where the local depth exceeds 1500m. This warm eddy is a major contributor to mass transport in the northern part of the East Sea. It is evident that knowledge of warm eddy is important in understanding the circulation in the western part of the East Sea.

• Ocean and Polar Research
• /
• v.42 no.2
• /
• pp.97-113
• /
• 2020

In-situ observations were carried out in April 2015 to investigate the occurrence of water temperature inversion in a region west of Jeju Island. Analysis of in-situ in the western part of Jeju island showed that cold water moved to the southeast from the surface to the middle layer and warm water moved from the middle to the lower layer of the northwest direction. The water temperature inversion occurred at 84 stations (63.1%) out of 133 stations. At the boundary of the water temperature inversion layer, it was formed in the middle layer and disappeared. In the strongly appearing, it started from the middle layer to the lower layer. The shape of the water temperature inversion layer was different. As a result of horizontal water temperature slope analysis of the water temperature inversion zone, maximum 0.23℃/km was obtained and the mean was 0.06℃/km. The role of water temperature inversion as an indicator to determine the formation of water front. As a result of the water mass analysis, Jeju Warm Current Water and Tsushima Warm Current Water of high temperature and high salt intruded from the middle to the bottom. In the middle layer occurred as the Yellow Sea Cold Water of low water temperature and low salinity expanded.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.17 no.2
• /
• pp.22-29
• /
• 2018

The purpose of this study was to evaluate the performance of a solar collector to introduce natural convection in a water tank as a means of obtaining warm water. Numerical analysis was performed to predict the characteristics of the solar collector and its performance was verified using an experimental method. The single vacuum structure of the collector enabled natural convection when it was fitted on the water tank. Based on numerical analysis, warm water of $31-54^{\circ}C$ was obtained when the inlet temperature of cold water was $20^{\circ}C$. Furthermore, the temperature of the warm water could be predicted under various conditions as well as the experimental conditions created for this study.