• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.401-404
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• 2007

Inertia welding is a solid-state welding process in which butt welds in materials are made in bar and in ring form at the joint face, and energy required for welding is obtained from a rotating flywheel. The stored energy is converted to frictional heat at the interface under axial load. The quality of the welded joint depends on many parameters, including axial force, initial revolution speed and energy, amount of upset, working time, and residual stresses in the joint. Inertia welding was conducted to make the large rotor shaft for low speed marine diesel engine, alloy steel for shaft of 140mm. Due to different material characteristics, such as, thermal conductivity and flow stress, on the two sides of the weld interface, modeling is crucial in determining the optimal weld geometry and parameters. FE simulation was performed by the commercial code DEFORM-2D. A good agreement between the predicted and actual welded shape is observed. It is expected that modeling will significantly reduce the number of experimental trials needed to determine the weld parameters.

• Journal of Welding and Joining
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• v.30 no.1
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• pp.51-58
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• 2012

To assess hydraulic connections between sub-components of the International Thermonuclear Experimental Reactor (ITER) diagnostic port plug, the laser welding and ablation cutting process were investigated in order to be applied the remote handling maintenance. In this study, laser ablation cutting, which vaporizes a small amount of solid material directly into gas by focusing a laser beam of high density energy, is adopted in order to overcome the limitation of the normal laser cutting technology that the head should be placed as close to the work piece as possible to blow out melt metal at a distance. Complete cutting of a work piece is obtained by repetitive multi-passes of the laser beam. The welding and cutting process were tested on the sample work pieces and finally on a prototype of a hydraulic connection module for remote handling. The results showed that this process can be a promising candidate for hydraulic connections by remote handling.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.4
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• pp.700-707
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• 2013

Owing to high oil prices and environmental issues, the automobile industry has conducted considerable research and made large investments to manufacture a high-efficiency automobiles. In the case of automobile wheels in which a lightweight material is used to increase the fuel efficiency a mold is used to increase the production efficiency; however, the use of the molding method for this purpose is very expensive. Therefore an automobile wheel consists of two parts. In this study a two-piece automobile wheel is manufactured by the friction stir welding(FSW) of Al6061-T6 to reduce the manufacturing cost and process complexity. The FSW welding tool geometry and rotational speed, and the feed rate are key factors that significantly affect the weld strength. Therefore tensile tests were conducted on specimens produced using various welding conditions, and the optimal FSW welding conditions were applied to manufacture aluminum wheels. To ensure reliability, prototype aluminum wheels were manufactured and their mechanical reliability and safety were evaluated using a durability test, fatigue durability test, and impact test. Through this study, aluminum wheel production was made possible using the FSW method.

• Transactions of Materials Processing
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• v.20 no.3
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• pp.236-242
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• 2011

The two objectives of this study were, first, to determine the optimal friction welding process parameters using finite element simulations and, second, to evaluate the mechanical properties of the friction welded zone for large piston rods in marine diesel engines. Since the diameters of the rod and its connecting part are very different, the manufacturing costs using friction welding are reduced compared to those using the forging process of a single piece. Modeling is a generally accepted method to significantly reduce the number of experimental trials needed when determining the optimal parameters. Therefore, because friction welding depends on many process parameters such as axial force, initial rotational speed and energy, amount of upset and working time, finite element simulations were performed. Then, friction welding experiments were carried out with the optimal process parameter conditions resulting from the simulations. The base material used in this investigation was AISI 4140 with a rod outer diameter of 280 mm and an inner diameter of 160 mm. In this study, various investigation methods, including microstructure characterization, hardness measurements and tensile and fatigue testing, were conducted in order to evaluate the mechanical properties of the friction welded zone.

• Journal of Ocean Engineering and Technology
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• v.8 no.1
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• pp.33-40
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• 1994

Welding of structure produces welding residual stresses which influence buckling strength, brittle fracture strength and cold crack on the weld parts. Therefore, it is very important to accurately analyze the residual stress before welding in order to guarantee the safety of weldment. If the weld length is long enough compared to the thickness and the breadth of plate, thermal and mechanical behaviors in the middle portion of the plate are assumed to be uniform along the thickness direction(z-axis). Thus, the following conditions(so-called plane deformation) can be assumed for the plate except near its end;1) distributions of stress and strain are independent on the z-axis;2) plane normal to z-axis before deformation remains plane during and after deformation. In this paper, plane-deformation thermal elasto-plastic problem is formulated by being based on the finite element method. Moreover special regards and paid to the fact that material properties in elastic and plastic region are temperature-dependence. And the method to solve the plane-deformation thermal elasto-plastic problem is shown by using the incremental technique. From the results of analysis, the characterisics of distribution of welding residual stress and plastic strain with the production mechanism are clarified.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.4
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• pp.378-386
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• 2017

Friction stir welding was performed using six welding conditions to evaluate the mechanical properties and microstructure of the welded zone based on its temperature change in the extruded plate of magnesium alloy AZ61. The welded zone temperature was measured using a thermocouple, and the maximum temperature ranges for the advancing and retreating sides were approximately $210-315^{\circ}C$ and $254-339^{\circ}C$, respectively. Depending on the welding conditions, a temperature difference of more than $100^{\circ}C$ was observed. In addition, the maximum yield strength and maximum tensile strength of the welded component was 84.4% and 96.9%, respectively, of those of the base material. For the temperatures exceeding $300^{\circ}C$, oxidation defects occurred in the weld zone, which decreased the mechanical strength of the weld zone. The microstructure and texture confirmed that fracture occurred because of the grain size deviation of the welding tool and the severe anisotropy of the texture of the welded joints.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.600-605
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• 2002

The keyhole formed by high energy density laser-material interaction periodically collapses due to surface tension of the molten metal in partial penetration welds. The collapse sometimes traps a void at the bottom of the keyhole, and it remains as welding defects. This phenomenon is seen as one cause of the instability of the keyhole during laser beam welding. Thus, it seems likely that improving the stability of the keyhole can reduce voids and uniform the penetration depth. The goal of this work is to develop techniques for controlling laser weld keyhole dynamics to reduce weld defects such as voids and inconsistent penetration. Statistical analysis of the penetration depth signals in glycerin determined that keyhole dynamics are chaotic. The chaotic nature of keyhole fluctuations and the ability of laser power modulation to control them have been demonstrated by high-speed video images of laser welds in glycerin. Additionally, an incident leading beam angle is applied to enhance the stability of the keyhole. The quasi-sinusoidal laser beam power of 400Hz frequency and 15$^{\circ}$ incident leading beam angle were determined to be the optimum parameters for the reduction of voids. Finally, chaos analyses of uncontrolled signals and controlled signals were done to show the effectiveness of modulation on the keyhole dynamics. Three-dimensional phase plots for uncontrolled system and controlled system are produced to demonstrate that the chaotic keyhole dynamics is converted to regular periodic behavior by control methods: power modulation and incident leading beam angle.

• Journal of Welding and Joining
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• v.11 no.2
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• pp.53-61
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• 1993

One of the most interesting and promising steel groups considered for the rocket motor case, aircraft and aerospace component is the maraging(martensitic plus aging) nickel steel, developed by International Nickel Company in 1960. This material attains a very high strength with good fracture toughness by simple heat treatments which do not involve a quenching. Full strength can be obtained by "maraging" at 480.deg. for 3 hours for the 18% Ni maraging steel. The effect of heat treatments was considered on the residual stress field of 18% Ni maraging steel weldments. In experiments, various heat treatments such as stress relieve heat treatment, aging and solution heat treatment were carried out of the GTA weldments and the residual stresses were measured by using the hole drilling method. Whereas the conventional pattern of residual stress shows the stresses to be maximum along the weld centerline with tensile stress extending into the heat affected zone, the pattern in maraging steels shows the centerline stress to be compressive. After welding, a series of aging, solution heat treatment and solution heat treatment plus aging treatment were carried out and the residual stresses were measured to reveal that these heat treatments almost completely remove the welding residual stresses.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.63-65
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• 2006

The paper deals with the effect of hydrogen or helium in argon as a shielding gas on GTA welding of austenitic stainless steel. The studies were carried out in GTA(Gas Tungsten Arc) welding with a non-consumable electrode in case with different volume additions of hydrogen or helium to the argon shielding gas, i.e $5%H_2,\;10%H_2$, 30%He and 67%He. The penetration, welding voltage, microstructure and mechanical property were examined. The deepest penetration was obtained from the sample which was welded under shielding gas of $10%H_2$. The studies showed that hydrogen or helium addition to argon changes the static characteristic of the welding arc. The hydrogen or helium addition to argon increases arc power and the quantity of the material melted. The weld metal penetration depth and its width increased with increasing hydrogen or helium content. Additionally, welding voltage increased with increasing hydrogen or helium content.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.253-255
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• 2006

Grey relational analysis has been carried out to develop a new approach for optimization of Nd:YAG laser and MIG hybrid welding parameters. The quality of welded material depends on welding parameters. The parameters chosen for current study include wire type, shielding gas, laser energy, laser focus, traveling speed, and wire feed rate. The welding experiments were performed on 6K21-T4 aluminum alloy sheet. Functional demands on products may vary widely depending on their use. The ultimate tensile stress, width, and penetration were chosen as the optimization criterion. Practice based on an orthogonal array which is following Taguchi's method has been progressed. Base on the results of grey relational analysis, the optimal process parameters were obtained. This integrated work was judged and it is observed that the results obtained by using the optimal parameters are much improved compared to those obtained through initial setting.