Papers by Author: Manabu Tanaka

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Authors: Manabu Tanaka, Shinichi Tashiro, Takayuki Kashima, John J. Lowke, Anthony B. Murphy
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Authors: Shinichi Tashiro, Toru Iwao, Tuginori Inaba, Manabu Tanaka
Abstract: We have developed non-equilibrium simulation model of GTA. In this paper, simulation results of plasma property of argon GTA at atmospheric pressure are presented and, furthermore, the reliability of the simulation model is evaluated. As a result, it was revealed that non-equilibrium characteristic appears in regions close to both electrodes and the fringe of the arc column where the temperatures decrease below approximately 10000K. It was also found that non-equilibrium region near the anode surface has thickness of 0.3mm. This result agrees with the simulation result predicted with one-dimensional electrical sheath model.
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Authors: Hidetoshi Fujii, Takahiro Tatsuno, Takuya Tsumura, Manabu Tanaka, Kazuhiro Nakata
Abstract: A new welding technique called hybrid FSW was developed to decrease the tool load and the defects during the FSW of high melting point materials. This method consists of FSW and a laser for preheating ahead of the tool. The hybrid FSW enables the proper welding conditions to be significantly expanded, and the joint characteristics are similar to those obtained by the normal FSW at the same welding speeds.
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Authors: Souta Matsusaka, Toshiro Uezono, Takuya Tsumura, Manabu Tanaka, Takehiro Watanabe
Abstract: Galvanized steel sheets with a lap joint were welded by a laser-arc hybrid process. The hybrid system consisted of 2kW LD or YAG laser oscillator and frequency-modulated DC pulsed MAG welding machine. In this experiment, the arc traveled on the specimens, following the laser beam with the interval of 2 mm. The results showed that the hybrid process had some advantages, such as deep penetration depth, high welding speed and high gap-tolerance, in comparison with the conventional MAG welding. Observations from a high-speed digital video-camera suggested that the zinc and iron vapors induced by laser beam irradiation stabilized the arc plasma. Effects of the incidence angle between a welding head and a specimen on the weld bead formations were also discussed. As a result, the welding speed of 2.0 m/min was achieved at 1.0 mm of gap length condition when the incidence angle was 50 degree.
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Authors: Kyohei Konishi, Manabu Tanaka, Akihisa Murata, Tadasuke Murata
Abstract: GTA (Gas Tungsten Arc) welding process has been studied as a higher level welding process. The “GTA welding process with constricted nozzle” is one of new welding processes [1]. In this new process, arc stiffness is greatly improved by attaching an additional gas nozzle which is called “constricted nozzle” inside the shielding gas nozzle. The design of a constricted nozzle is shown in Figure 1. With this new process, a butt joint of thin-sheet metals can be achieved although that is difficult with a conventional GTA welding process. In this study, numerical simulation is conducted to understand phenomena of arc plasma in a GTA welding process with a constricted nozzle scientifically.
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Authors: Kentaro Yamamoto, Manabu Tanaka, Shinichi Tashiro, Kazuhiro Nakata, Keiichi Suzuki, Kei Yamazaki
Abstract: It is important to consider the interaction between arc plasma and electrodes because melting of electrodes strongly affects arc plasma. Therefore, a GMA model will be developed, based on the unified model of TIG arc. As a first step, a TIG arc model with a calculation for molten cathode shape has been proposed. This model is calculated in two cases; molten W cathode and Calculation result of W cathode. In the case of W cathode, cathode shape change was found to affect the arc plasma property strongly. Calculated results of radial temperature distributions on electrode surface and arc pressure distributions at the anode surface are very similar to the experimental results.
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Authors: Manabu Tanaka
Abstract: In this study, distributions of temperature and metal vapor during MIG welding of aluminum are obtained. Since a droplet forms and detaches at a tip of wire, and pass through the arc plasma during MIG welding, dynamic plasma diagnostics are demanded. This study aims to develop method for measuring dynamical variation of two-dimensional distribution of temperature and metal vapor concentration in the arc through optical measurement and to analyze behavior of the metal vapor in MIG welding. As the results, in MIG welding of aluminum, the arc plasma has double structure consisting of high temperature region apart from the arc axis and low temperature region near the arc axis due to influence of the aluminum vapor. Furthermore, the low temperature region near the arc axis occurs because the arc plasma is cooled especially through the intensive radiation loss caused by high concentration of the metal vapor.
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Authors: Manabu Tanaka, Kentaro Yamamoto, Shinichi Tashiro, John J. Lowke
Abstract: Study of current attachment at thermionic cathode for TIG arc at atmospheric pressure is attempted from numerical calculations of arc-electrodes unified model. The calculations show that the maximum temperature of arc plasma close to the cathode tip for W-2% ThO2 reaches 19,000 K and it is the highest value in comparison with the other temperatures for W-2% La2O3 and W-2% CeO2, because the current attachment at the cathode tip is constricted by a centralized limitation of liquid area of ThO2 due to its higher melting point. The calculations also show that, in cases of W- 2% La2O3 and W-2% CeO2, the liquid areas of La2O3 and Ce2O3 are widely expanded at the cathode tip due to their lower melting points and then produce uniform current attachments at the cathode. It is concluded that the current attachment at thermionic cathode is strongly dependent on work function, melting point and Richardson constant of emitter materials.
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