• Journal of Power System Engineering
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• v.22 no.1
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• pp.87-93
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• 2018

Specimens were machined out from hot-rolled AZ31 magnesium alloy, and deformed at 623K with rolling reduction of 30%. After hot rolling, specimens were annealed at various range of temperature and time. In this study, static recrystallization was occurred during heat treatment, however, variation of main component and intensity of texture was not revealed. The results of microstructure observation, damping capacity test and dislocation mechanism indicated that increasing of damping capacity was caused by grain growth. It means that grain size is effective factor to damping capacity.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.668-673
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• 2004

The Friction Stir Weld (FSW) has been prevailing in the rolling stock manufacturers now a day especially in Europe and Japan, that will be an inevitable welding method in Korean domestic railway industry in the near future. The Welding Institute (TWI) in United Kingdom (UK), who has the right of international patents, invented FSW. To meet the recommendation of Cullen's Report for Ladbroke Grove Rail Inquiry (LGRI) in UK, the FSW is considering for the only alternative welding method to improve the aluminium welding quality, i.e. for improve unzipping defect and crashworthiness on car body in Europe Railways within Railway Safety Research Program.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.11 s.254
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• pp.1461-1471
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• 2006

This paper presents the mathematical model for rolling behaviors of a small regular polygonal part on an inclined plane. Throughout the numerical analysis performed with the simulation program which has been experimentally validated, it is shown that the number of edges of the rolling polygonal part can be a measure for the energy dissipation rather than the coefficient of friction. The appropriate slope angle has been found to be around 20 degree for roughness-separation as well as shape-separation of polygonal parts which have small number of edges. In additions, the vibratory motion applied to the inclined plane is able to cause mixed parts to be separated more effectively according to the shape or the roughness. Finally, a couple of parts separation methods based on the analysis results are presented, and are validated through the numerical simulation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.400-403
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• 2004

A non-heat기leafed steel does not need quenching and tempering processes that are called a heat treatment differently from conventional steel. Since the tensile strength of this steel is higher than 900MPa, a conventional forming process should be changed to incremental forming process such as a cross wedge rolling that requires lower load capacity than conventional ones. In this paper, the cold cross wedge rolling (CWR) die has been designed using CAD/CAE In order to produce near-net-shaped component of ball stud of non-heat-treated cold steel. Finite element analyses were applied in order to investigate process parameters of CWR. Results provide that the stretching angle and the forming angie at knifing zone in CWR process is important parameter to be the stable process under the low friction coefficient condition.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.78-87
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• 1999

A mathematical model for the stress free surface profile in Over-Round and Round-Oval grove rolling, which can be used effectively in the calculation of pass area, is presented. The new model has generality, simplicity and accuracy for practical usage. The stress free surface profile of an outgoing stock can be modeled when the maximum spread of it known a priori. The equation for the stress free surface profile is formulated from the linear interpolation of the radius of curvature of an incoming stock and that of roll groove to the axis direction. In developing the analytical model, the effect of rolling temperature and friction between roll and work piece(stock) were not considered since the geometry of roll groove and the incoming work piece were assumed a dominant factor which decides the stress free surface profile of the outgoing stock. A simulation with the analytical model developed also has been carried out to demonstrate the stress free surface profile of the outgoing stock.

• Transactions of Materials Processing
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• v.10 no.2
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• pp.130-136
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• 2001

The mathematical set-up model was developed to reduce the mechanical property deviation in annealed and slightly rolled steel strip. The mechanical peculiarities of skin pass rolling process, such as high friction value and non-circular contact arc, low reduction and non-negligible entry and exit elastic zones as well as central restricted deformation zone are all taken into account. The deformation of work rolls is calculated with the influence function method and arbitrary contact arc shape is permitted. The strip deformation is modeled by slab method and the entry and exit elastic deformation zones are included. The strip restricted deformation zone near the neutral point is also considered. It was revealed that the new model has better accuracy than present regression model by statistical analysis with actual mill rolling data.

• Journal of Mechanical Science and Technology
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• v.17 no.5
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• pp.668-678
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• 2003

For the purpose to facilitate development of high-speed spindle units (SUs) running on rolling bearings, we have developed a beam element model, algorithms, and software for computer analysis of thermal characteristics of SUs. The thermal model incorporates a model of heat generation in rolling bearings, a model of heat transfer from bearings, and models for estimation of temperature and temperature deformations of SU elements. We have carried out experimental test and made quantitative evaluation of the effect of operation conditions on friction and thermal characteristics of the SUs of grinding and turning machines of typical structures. It is found out that the operation conditions make stronger effect on SU temperatures when rpm increases. A comparison between the results of analysis and experiment proves their good mutual correspondence and allows us to recommend application of the models and software developed for design and research of high-speed SUs running on rolling bearings.

• Tribology and Lubricants
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• v.17 no.2
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• pp.138-145
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• 2001

The rolling piston type rotary compressor has been widely used for refrigeration and air-conditioning systems due to its compactness and high-speed operation. The present analysis is a part of research program directed toward maximizing these advantages of refrigerant compressors. The study of lubrication characteristics in the critical sliding component is essential for the design of refrigerant compressors. Therefore, theoretical investigation of the lubrication characteristics of a rotary compressor used for refrigeration and air-conditioning systems is studied. Newton-Raphson method is used for the partial elastohydrodynamic lubrication analysis between vane and rolling piston in the rotary compressor. The results show that the rotational speed of a shaft and the discharge pressure influence significantly the friction force and the energy loss between vane and rolling piston.

• Transactions of Materials Processing
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• v.8 no.6
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• pp.583-590
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• 1999

New forward slip model has been developed for the precise prediction of rolling speed in the hot strip finishing mill. Besides those influential factors such as neutral point, work roll diameter, friction coefficient, bite angle and the thickness at each side of entry and delivery of the rolls, roll torque was specifically taken into account in this study. To consider the effect of width change on forward slip, calibration factors obtained from rolling torque has been added to new prediction model and refining method has also been developed to reduce the speed unbalance between adjacent stands. The application of the new model showed a good agreement in rolling speeds between the predictions and the actual measurements, and the standard deviation of prediction error has also been significantly reduced.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.04b
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• pp.133-141
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• 1996

The rolling piston type rotary compressor has become one of the most successful types because of its compactness and high-speed operation. The analysis described here is part of a research program directed toward maximising these advantages in refrigerant compressors. The study of lubrication characteristics in the critical sliding component is essential for the design of refrigerant compressors. Therefore, theoretical investigation of the lubrication characteristics of rotary compressor for refrigeration & air-conditioning system is studied. And the Newton-Raphson method is used for the EHI. analysis between vane and rolling piston in the rotary compressor. The results show that the rotational speed of shaft and the discharge pressure have an important effect upon the friction force and the energy loss between vane and rolling piston. This results give important basic data for the further lubrication analysis and design of the rotary compressor.