• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.102-105
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• 2001

The spring back taking place after the coiling process of steam generator tube leads to the dimensional inaccuracy. In order to reduce the spring back, tension force was applied to the one end of the tube during forming. In this work, parametric study using FEM was performed to find the appropriate magnitude of tension force. The force that induces minimum suing back was found by simultaneously taking account of suing back amount, cross-sectional ovality, and thickness of the tube wall after deformation. In addition, stress relieving by heat treatment was also simulated as an alternative to the former method. The latter was found to be more effective under the given constraints.

• Transactions of Materials Processing
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• v.11 no.3
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• pp.238-245
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• 2002

The spring back taking place after the coiling process of steam generator tube leads to the dimensional inaccuracy. In order to reduce the spring back, tension force was applied to the one end of the tube during forming. In this work, parametric study using FEM was performed to find the appropriate magnitude of tension force. The force that induces minimum spring back was found by simultaneously taking account if spring back amount, cross-sectional ovality, and thickness of the tube wall after deformation. In addition, stress relieving by heat treatment was also simulated as an alternative to the former method. The latter was found to be more effective under the given constraints.

• Journal of Ocean Engineering and Technology
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• v.17 no.2
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• pp.21-26
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• 2003

The reel-lay method of submarine pipelines a continuous string of pipe coiled onto a reel. Assembly of this pipe that is string is accomplished onshore by welding, and nondestructive testing is carried out prior to coiling the pipe. The total length of pipes on the reel depends on the reel and pipe diameters. Pipeline installation is accomplished by uncoiling, straightening the pipe, and laying out the pipe string onto the seabed as the barge moves forward. Installation associated with coiling and uncoiling is related to the bending moment and strain relationship of the pipeline, A highgrade pipe material is required when the reel-lay method is used. This paper is concerned with the highly plastic bending moment of the pipeline, including the effect of ovality. Moment calculation in the pipe is accomplished by the numerical method, including the variable ovalities during the plastic bending of the pipe string. The new calculation method of the high plastic bending moment was applied to the reel-lay method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.10a
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• pp.86-89
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• 2000

In cold forging by multi stage former, crowing process is important process for the high production rate and automation of forging process. But various cropping defects occur in cropping process such as orthogonality, ovality and unevenness, etc. These defects have harmful effects on the dimensional tolerance of products and tool life. So in this study, the cropping experiment is performed to examine influence of cropping process variables(clearance, cutting velocity, H/D) on occurrence of crowing defects and optimum process variables are selected, and then FE analysis is performed to verify influence of these defects on dimensional tolerance and tool life.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.324-325
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• 2005

The primary aim of this paper is to develop an automated welding system capable of adapting to variation in the weld seam center in order to allow higher welding speeds and improved welding quality by using a laser vision sensor. The system is designed to compensate for production problems such as pipe ovality, variation in bevel geometry and track misalignment.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.76-82
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• 1998

In this study, the Ball screw and Servo motor Mechanism is considered as a High Speed Tool Feed System for the machining of a piston of a reciprocating engine. For the machining of a piston, that shapes oval, high speed servo mechanism is needed as a positioning of a cutting tool, and the stroke of tool is 0.1 mm ~ 1 mm. Ball screw and servo motor Mechanism is available very much because this mechanism is used widely in general machine. This Mechanism has been designed with the use of the decrease in mass and partial wear of the ball screw for high speed positioning of tool. Also the periodic learning control method with the inverse transfer function compensation has been applied to the positioning control for the high accuracy positioning of tool. These applications lead the achievement of the machining of a piston with an accuracy of 5${\mu}{\textrm}{m}$ at 2500 rpm in CNC turning.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1131-1137
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• 2012

Subsea pipelines have been operated with buried depths of 1.2-4m underneath the seabed to prevent buoyancy and external impacts. Therefore, they have to show resistance to both the soil load and the hydrostatic pressure. In this study, the structural integrity of a subsea pipeline subjected to soil load and hydrostatic pressure was evaluated by using FE analyses. A parametric study showed that the internal pressure increased the plastic collapse depth by increasing the resistance to plastic collapse. The hoop stress increased with an increase in the buried depth for the same water depth; however, the hoop stress decreased with an increase in the water depth for the same buried depth.

• Transactions of Materials Processing
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• v.18 no.4
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• pp.336-341
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• 2009

Hydroformed parts have higher dimensional accuracy, structural strength, and dimensional repeatability. Particularly in the automotive industry, manufacturing of parts with complex shapes from tubular materials sometimes requires one or more pre-forming operations such as bending before the hydroforming process. The pre-bending process is an important process for the successful hydroforming in the case where the perimeter of the blank is nearly the same as that of final product. The bendability of a tube depends on the parameters such as the bending radius, welding methods, mechanical properties and hardness. Through the stainless steel tubes bent by rotary draw bending machine, this study shows the following : (1) The influence on spring back ratio variation with stress level in the welded bent tube. (2) The Cross-section ovality variation with weld seam position and bending radius. (3) The relation between elongation and thickness reduction of tension zone with weld seam position and bending radius. (4) Workability evaluation of bent stainless steel tubes through the hardness of materials and hardness increment. The results of this study may help to understanding of characteristics on bendability of stainless steel tubes.

• Journal of Mechanical Science and Technology
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• v.17 no.5
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• pp.629-636
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• 2003

This paper introduces the developed geometry PIG (Pipeline Inspection Gauge), one of several ILI (In-Line Inspection) tools, which provide a full picture of the pipeline from only single pass, and has compact size of the electronic device with not only low power consumption but also rapid response of sensors such as calipers, IMU and odometer. This tool is equipped with the several sensor systems. Caliper sensors measure the pipeline internal diameter, ovality and dent size and shape with high accuracy. The IMU (Inertial Measurement Unit) measures the precise trajectory of the PIG during its traverse of the pipeline. The IMU also provide three-dimensional coordination in space from measurement of inertial acceleration and angular rate. Three odometers mounted on the PIG body provide the distance moved along the line and instantaneous velocity during the PIG run. The datum measured by the sensor systems are stored in on-board solid state memory and magnetic tape devices. There is an electromagnetic transmitter at the back end of the tool, the transmitter enables the inspection operators to keep tracking the tool while it travels through the pipeline. An experiment was fulfilled in pull-rig facility and was adopted from Incheon LT (LNG Terminal) to Namdong GS (Governor Station) line, 13 km length.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.281-284
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• 2007

The effect of Ca addition on the microstructure evolution and deformation behavior of AZ31 magnesium alloy produced by hot extrusion was investigated. For this purpose, Ca was added into AZ31 melts to the level of 0.7 and 2.0 wt.% Ca. Then, AZ31 base alloy and Ca modified AZ31 alloys were extruded at $383^{\circ}C$. Ca added alloys showed finer grain size and increased hardness value rather than AZ31 base alloy. After isothermal hot compression, the shape of tested specimen exhibited a noticeable anisotropy due to the crystallographic texture effect. The ratio of major and minor axes of ovality was not directly related to test condition and Ca amount. Flow stress level increases with the increase of Ca addition at temperature below $300^{\circ}C$ because of fine microstructure. However, at high temperature and low strain rate region ($400^{\circ}C$ and $10^{-3}s^{-1}$), reverse tendency was observed since main deformation mechanism changes from dislocation slip to grain boundary sliding or diffusional process at high temperature.