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Yoshinori Hirata - One of the best experts on this subject based on the ideXlab platform.

  • Discussion of the Effect of Shielding Gas and Conductivity of Vapor Core on Metal Transfer Phenomena in Gas Metal Arc Welding by Numerical Simulation
    Plasma Chemistry and Plasma Processing, 2020
    Co-Authors: Yosuke Ogino, Yoshinori Hirata, Satoru Asai
    Abstract:

    Gas metal arc welding is indispensable in many fields of industry. In this process, various kinds of shielding gas are used, and they significantly affect the behaviors of the arc plasma and metal Transfer. In this study, these behaviors with various kinds of shielding gas are numerically investigated. In addition, the influence of the electrical conductivity of the metal vapor is discussed. Simulation results show that with Ar gas, Spray Transfer occurs at an arc current of more than 240 A, and with CO_2 gas, the Transfer mode is globular, even at an arc current of 300 A. The calculation results show that the current path near the wire tip critically determines droplet behavior. With Ar gas, the current path is spread out, covering the molten wire, whereas with CO_2 gas, the current path is concentrated at the bottom of the molten wire. Therefore, to achieve Spray Transfer, the current path needs to be spread at the wire tip; however, if the spreading is excessive, the Transfer mode becomes streaming Transfer. To investigate the influence of the metal vapor, a numerical experiment using pseudo metal vapor was carried out. Even with CO_2 gas, the electrical conductivity of the metal vapor was low, and thus the current path was not concentrated at the bottom of the molten wire, allowing Spray Transfer. The numerical results show that metal Transfer phenomena can be regulated by controlling the electrical conductivity of the metal vapor.

  • Numerical simulation of GMAW process using Ar and an Ar–CO_2 gas mixture
    Welding in the World, 2016
    Co-Authors: Yosuke Ogino, Yoshinori Hirata, Anthony B Murphy
    Abstract:

    The gas metal arc welding (GMAW) process involves arc plasma, metal Transfer, and weld pool phenomena. In addition, metal vapor is formed by evaporation from the high-temperature metal and mixes with the arc plasma. These phenomena interact with each other and are very complicated. A numerical approach that includes their interaction is therefore important for clarifying the GMAW phenomena. We have developed a unified model and used the model to investigate the influence of the shielding gas on the metal Transfer. When argon shielding gas was used, for an arc current of less than 230 A, globular Transfer occurred. For higher currents, Spray Transfer occurred. On the other hand, when Ar + 18 %CO_2 gas was used, the transition from globular to Spray Transfer occurred at around 280 A. This difference was caused by changes in the driving force exerted on the molten metal by the arc plasma. The arc pressure that lifts up the molten metal and interferes with its detachment from the wire tip becomes stronger when the gas mixture is used.

  • numerical simulation of gmaw process using ar and an ar co2 gas mixture
    Welding in The World, 2016
    Co-Authors: Yosuke Ogino, Yoshinori Hirata, Anthony B Murphy
    Abstract:

    The gas metal arc welding (GMAW) process involves arc plasma, metal Transfer, and weld pool phenomena. In addition, metal vapor is formed by evaporation from the high-temperature metal and mixes with the arc plasma. These phenomena interact with each other and are very complicated. A numerical approach that includes their interaction is therefore important for clarifying the GMAW phenomena. We have developed a unified model and used the model to investigate the influence of the shielding gas on the metal Transfer. When argon shielding gas was used, for an arc current of less than 230 A, globular Transfer occurred. For higher currents, Spray Transfer occurred. On the other hand, when Ar + 18 %CO2 gas was used, the transition from globular to Spray Transfer occurred at around 280 A. This difference was caused by changes in the driving force exerted on the molten metal by the arc plasma. The arc pressure that lifts up the molten metal and interferes with its detachment from the wire tip becomes stronger when the gas mixture is used.

  • Tomographic spectroscopic observation of argon and metal vapor behavior in MIG arc welding
    Welding in the World, 2016
    Co-Authors: Kazufumi Nomura, Yoshinori Hirata, Kotaro Kataoka, Kohei Mimura, Takashi Kishi
    Abstract:

    Spectroscopic measurements for GMA phenomena have been performed. The studies have reported that the metal vapor behavior greatly affects the arc properties. However, they can be applied only to axially symmetric phenomena because of the assumption used for the measurement. GMA welding is normally performed while moving and most of the phenomena become axially asymmetric. In this study, we constructed a simultaneous and multi-directional measurement system using multiple CCD cameras which can capture such axially asymmetric GMA phenomena. We measured the arc radiation by means of two types of narrowband interference filters for Ar and Fe during one measurement and observed axially asymmetrical intensity distributions in the globular and Spray Transfer mode. We found that the globular Transfer mode that has seemingly chaotic distribution can be regarded as a distribution where the deviation of Ar is larger than Fe from an axially symmetric double-ring distribution.

  • Numerical simulation of metal Transfer in argon gas-shielded GMAW
    Welding in the World, 2015
    Co-Authors: Yosuke Ogino, Yoshinori Hirata
    Abstract:

    The gas metal arc welding (GMAW) process combines aspects of arc plasma, droplet Transfer, and weld pool phenomena. In the GMAW process, an electrode wire is melted by heat from an arc plasma, and molten metal at the wire tip is deformed by various driving forces such as electromagnetic force, surface tension, and arc pressure. Subsequently, the molten droplet detaches from the tip of the wire and is Transferred to the base metal. The arc plasma shape changes together with the metal Transfer behavior, so the interaction between the arc plasma and the metal droplet changes from moment to moment. In this paper, we describe a unified arc model for GMAW, including metal Transfer. In the model, we do not account for heat Transfer in the metal, but the wire melting rate is determined by the arc current. The developed model can show transition from globular Transfer at low currents to Spray Transfer at higher currents. It was found that electromagnetic force is the most important factor at high currents, but surface tension is more important than electromagnetic force at low currents in determining the Transfer mode.

S W Simpson - One of the best experts on this subject based on the ideXlab platform.

  • Metal Transfer instability in gas metal arc welding
    Science and Technology of Welding and Joining, 2009
    Co-Authors: S W Simpson
    Abstract:

    AbstractThis work presents a simplified model of metal Transfer in gas metal arc welding. The model incorporates key features of metal Transfer including the change in droplet diameters as welding moves from the globular into the Spray metal Transfer region, and the increase in welding voltage that is observed to occur as the pendant droplet grows. The model predicts that an instability arises in the globular metal Transfer region, which leads to deterministic chaos and complex limit cycles with many droplet sizes. The instability also causes deterministic chaos with a characteristic gap in droplet diameters at the transition to Spray mode metal Transfer. The model explains observed features of metal Transfer in some detail, including the existence and location of preferred bands of droplet sizes. Whether the instability is present or not defines the boundary between chaotic globular metal Transfer and the stable drop Spray Transfer mode. The identification of deterministic chaos in gas metal arc welding ...

  • Signature image stability and metal Transfer in gas metal arc welding
    Science and Technology of Welding and Joining, 2008
    Co-Authors: S W Simpson
    Abstract:

    This work presents a method for determining a stability index during welding by comparing signature images calculated successively from the welding voltage and current data. It is shown that, with a reasonable choice for the signature image window scaling, the stability index agrees with welding experience in the common gas metal arc welding Transfer modes of short circuiting and Spray Transfer and reflects the decrease in stability inherent in the globular Transfer mode. The effect of changing welding consumables, wire and shielding gas, is illustrated. The connection between the stability index and metal Transfer phenomena is investigated, and it is shown that very detailed aspects of metal Transfer are reflected in the stability index. It is concluded that the signature image stability index not only provides valuable data on the operating regions of welding processes, but also gives information which otherwise would only be available from cumbersome optical diagnostics.

  • Metal Transfer measurements in gas metal arc welding
    Journal of Physics D: Applied Physics, 2001
    Co-Authors: Q Lin, S W Simpson
    Abstract:

    The present work reports results obtained using combined laser shadowing and cross correlation techniques to investigate the metal Transfer process. Experimental results of the droplet size and velocity of 0.9 mm and 1.2 mm wires from the globular region to the Spray Transfer region are presented. The results indicate that the droplet size is not continuous in the narrow region of mode transition, and also preferred bands of droplet size exist. Droplet velocity measurements show good agreement with a simple model based only on the electromagnetic pinch force.

  • A theoretical study of a gas metal arc welding system
    Plasma Sources Science and Technology, 1995
    Co-Authors: P. Zhu, M Rados, S W Simpson
    Abstract:

    A theoretical model of a gas metal arc welding system has been developed to make predictions of the anode temperature profile, welding arc length and arc current. The model incorporates a one-dimensional thermal model of the moving consumable anode and a two-dimensional model for the arc plasma. The model makes possible the calculation of the relationship between the welding arc current, wire feed rate and the supply voltages, for various wire diameters and shielding gases. The predicted welding current for a given wire feed rate shows good agreement with our experimental observation for operation in the Spray Transfer mode, for steel wire of two different diameters, assuming a workpiece sheath voltage of 15 V.

Pratim Biswas - One of the best experts on this subject based on the ideXlab platform.

  • the influence of operating parameters on number weighted aerosol size distribution generated from a gas metal arc welding process
    Journal of Aerosol Science, 2002
    Co-Authors: Anthony T Zimmer, Paul A Baron, Pratim Biswas
    Abstract:

    Abstract In light of recent research on the potential health problems associated with sub-micrometer aerosols, a study was conducted to determine the effect that droplet mass Transfer mode, shield gas composition, and welding spatter had upon the aerosols generated from a Gas Metal Arc Welding (GMAW) Operation. The results revealed that the sub-micrometer aerosols produced during Spray Transfer resulted in markedly higher concentrations of nucleated particles than those produced during globular Transfer. This probably resulted from a larger droplet surface area for vaporization of metallic species. The shield gas experiments results revealed that as the percentage of carbon dioxide increased the number of nucleated particles also increased. It appears that oxygen may have facilitated chemical reactions with the alloy constituents, thereby increasing the mass Transfer rate from the evaporating metal droplets in the plasma. Finally, an attempt to characterize the spatter aerosol revealed a distinct particle size distribution with a mode particle diameter of 6.8 μm . This particle size distribution appeared to be independent of shield gas composition, and the particle number concentration was significantly smaller than the sub-micrometer aerosols formed during the GMAW process (i.e., two-orders of magnitude smaller when weighted by particle mass).

Satoru Asai - One of the best experts on this subject based on the ideXlab platform.

  • Discussion of the Effect of Shielding Gas and Conductivity of Vapor Core on Metal Transfer Phenomena in Gas Metal Arc Welding by Numerical Simulation
    Plasma Chemistry and Plasma Processing, 2020
    Co-Authors: Yosuke Ogino, Yoshinori Hirata, Satoru Asai
    Abstract:

    Gas metal arc welding is indispensable in many fields of industry. In this process, various kinds of shielding gas are used, and they significantly affect the behaviors of the arc plasma and metal Transfer. In this study, these behaviors with various kinds of shielding gas are numerically investigated. In addition, the influence of the electrical conductivity of the metal vapor is discussed. Simulation results show that with Ar gas, Spray Transfer occurs at an arc current of more than 240 A, and with CO_2 gas, the Transfer mode is globular, even at an arc current of 300 A. The calculation results show that the current path near the wire tip critically determines droplet behavior. With Ar gas, the current path is spread out, covering the molten wire, whereas with CO_2 gas, the current path is concentrated at the bottom of the molten wire. Therefore, to achieve Spray Transfer, the current path needs to be spread at the wire tip; however, if the spreading is excessive, the Transfer mode becomes streaming Transfer. To investigate the influence of the metal vapor, a numerical experiment using pseudo metal vapor was carried out. Even with CO_2 gas, the electrical conductivity of the metal vapor was low, and thus the current path was not concentrated at the bottom of the molten wire, allowing Spray Transfer. The numerical results show that metal Transfer phenomena can be regulated by controlling the electrical conductivity of the metal vapor.

Sun Jun - One of the best experts on this subject based on the ideXlab platform.

  • The fluid flow of GMAW weldpool and its effect on weldpool geometry
    Materials Science and Technology, 1999
    Co-Authors: Sun Jun
    Abstract:

    The weldpool fluid flow field is studied by means of numerical simulation when the metal mode is globular or Spray Transfer and its effect on weldpool geometry is analyzed. The experiment result shows that the calculated weld size is in good agreement with the experiment result. The simulation model established can accurately simulate the fluid flow field of the GMAW weldpool. Therefore, it has great significance in controlling weld geometry and increasing weld quality.