Kazufumi Nomura

Numerical analysis of the heat source characteristics of a two-electrode TIG arc

Various kinds of multi-electrode welding processes are used to ensure high productivity in industrial fields such as shipbuilding, automotive manufacturing and pipe fabrication. However, it is difficult to obtain the optimum welding conditions for a specific product, because there are many operating parameters, and because welding phenomena are very complicated. In the present research, the heat source characteristics of a two-electrode TIG arc were numerically investigated using a 3D arc plasma model with a focus on the distance between the two electrodes. The arc plasma shape changed significantly, depending on the electrode spacing. The heat source characteristics, such as the heat input density and the arc pressure distribution, changed significantly when the electrode separation was varied. The maximum arc pressure of the two-electrode TIG arc was much lower than that of a single-electrode TIG. However, the total heat input of the two-electrode TIG arc was nearly constant and was independent of the electrode spacing. These heat source characteristics of the two-electrode TIG arc are useful for controlling the heat input distribution at a low arc pressure. Therefore, these results indicate the possibility of a heat source based on a two-electrode TIG arc that is capable of high heat input at low pressures.

Shape Control of TIG Arc Plasma by Cusp Type Magnetic Field with Permanent Magnets

The shape of arc plasma in gas-shielded arc welding is an important factor for the quality and efficiency of the welding. The arc plasma changes its shape by an external magnetic field because the arc is a flow of electricity and is subjected to the electromagnetic force. In this study, we examined the control of arc plasma by a cusp-type magnetic field. The field produces a high and low magnetic area alternatively, and changes the cross-section of the arc plasma from a circular to an elliptical shape. The previous study using solenoid coils to produce a cusp-type magnetic field reported that magnetized arc plasma provided deeper penetration. However, the solenoid device developed for the cusp magnetic field was too large in comparison with the size of the welding torch used for production welding. Therefore, this study investigated the magnetic control of arc plasma with permanent magnets that have recently become smaller in size and higher in intensity. Theoretical analysis model was constructed to determine the optimum arrangement of the magnets. This analysis requires a three-dimensional numerical model because the temperature-, velocity-, and electromagnetic fields of arc plasma change three-dimensionally by the additional magnetic field. It was analytically and experimentally shown in TIG arc welding that the arc shape could be elliptical cross-section even using the permanent magnets. Furthermore, our analysis showed that the effective magnetization direction of magnets was vertical, and this result was confirmed experimentally. As a result, we obtained the good bead appearance in the high-speed welding with this magnetic control.

Synthesis of 3,4,5‐Tris(alkyloxy)benzyl Glycosides as Glycolipid Analogues

Abstract A series of 3,4,5‐tris(alkyloxy)benzyl glycosides of D‐glucose, D‐galactose, D‐mannose, N‐acetyl‐D‐glucosamine and N‐acetyl‐D‐galactosamine were prepared by the trichloroacetimidate procedure. After immobilization on a hydrophobic surface, the affinity of the carbohydrate to a lectin was evaluated using a surface plasmon resonance biosensor. The selective interaction achieved with the lectin showed that the glycosides had potential for use as glycolipid analogues. The 3,4,5‐tris(dodecyloxy)benzyl glycosides were soluble in ethanol, and potentially would be useful for cell culture experiments.

Magnetic Control of Arc Plasma and its Modelling

This paper describes the control of arc plasma by a cusp-type magnetic field. The cusp-type magnetic field, which is produced by four magnetic poles, changes the cross-section of arc plasma from the conventional circular shape to an elliptical shape. Previous studies using solenoid coils to produce a cusp-type magnetic field reported that magnetized arc plasma provides deeper penetration. However, the solenoid device developed for the cusp-type magnetic field was too large, in comparison with the size of the welding torch used for production welding. In the present study, magnetized arc plasma with the use of high-performance permanent magnets is experimentally and theoretically investigated. It is confirmed experimentally by tungsten inert gas (TIG) arc welding that permanent magnets can produce arc plasma with an elliptical cross-section. In a series of experiments, a good bead appearance was obtained in high-speed welding with magnetic control. A three-dimensional numerical model of arc plasma was also constructed to determine the optimum arrangement of the magnets. It was analytically shown that the elliptical shape of the magnetized arc plasma and its effect on welding depended on the magnet height from the base metal and the magnetization direction.

Numerical analysis of arc plasma and weld pool formation by a tandem TIG arc

Multi-electrode welding processes are used in various industrial fields for higher productivity. These processes can use many combinations of welding methods, current values and polarities, and electrode alignments. However, this complicates welding phenomena. In this research, we focused on the tandem tungsten inert gas (TIG) arc, which is a relatively simple multi-electrode welding process. We performed a numerical investigation into the tandem TIG arc plasma and weld pool formation to clarify the phenomena involved. The weld spot of a tandem TIG weld is ellipsoidal in appearance and is deeper than that of a single-electrode TIG weld. Reduction in the shear stress of the plasma flow in the tandem TIG weld leads to a deeper penetration. Furthermore, the influence of the electrode alignment is calculated, and it is determined that the weld spot appearance significantly changes. The appearance is strongly related to the arc plasma shape. These numerical results show good agreement with the experimental results, which proves that our model has relatively high reliability.

Effect of galactose residue in glycolipid coated onto a dish on ammonia consumption activity of primary rat hepatocytes

Coating a dish for suspension culture with 3,4,5-tris(dodecyloxy)benzyl alcohol (TDOB-OH), TDOB glucoside (TDOB-Glc), or TDOB galactoside (TDOB-Gal) did not change the morphology of hepatocytes and decreased cell adhesion density to 70%–84% of that without the coating. However, the specific ammonia consumption rate of the culture on a TDOB-Gal-coated dish was 1.81 times that without coating, whereas those of TDOB-OH-and TDOB-Glc-coated dishes were 1.18 and 0.31 times that without coating, respectively. TDOB-Gal coating on a dish for adhesion culture decreased cell adhesion density only by 10% and did not disturb cell spreading. The coating of TDOB-Gal at 1/10 to 1/4 density of that for a monolayer resulted in a higher specific rate of ammonia consumption than that at monolayer density, and the rate reached 1.97 times that without coating. The ammonia consumption activity of hepatocytes was considered to be increased specifically not by the glucose residues but by the galactose residue of the glycolipid, independently of cell spreading.

3D temperature measurement of tandem TIG arc plasma

Measurements of arc plasma are important for determining the associated physical properties. Such measurements usually involve spectroscopic techniques that measure the temperature distribution in free-burning arcs. Most existing studies have reported the temperature of axially symmetric arc plasma using Abel inversion. This method cannot be used for axially asymmetric arc plasma such as tandem tungsten inert gas (TIG) arc plasma. It is a complex phenomenon because the arc plasma generated from each electrode is affected by the plasma of the other due to electromagnetic force. We measured the temperature distribution of tandem TIG arc plasma in 3D with one camera rotation. The measurement method is based on computed tomography consisting of multidirectional detections and image reconstruction. As a result, we could measure the temperature distribution of the coupled arc plasma provided by the two-electrode TIG arc. In addition, we evaluated the influence of detection directions and numbers on the reconstructed emission intensity distribution.

Study on temperature measurement of two-electrode TIG arc plasma

Measurements of arc plasma are important for determining the associated physical properties. Such measurements usually involve the use of spectroscopic techniques to measure temperature distribution in free-burning arcs. Most studies have reported the temperature of axially symmetric arc plasma using Abel inversion. This method cannot be used for axially asymmetric arc plasma such as two-electrode TIG arc plasma. It is a complex phenomenon because the arc plasma generated from each electrode is affected by the other due to electromagnetic force. We measured the temperature distribution of tandem TIG arc plasma three dimensionally with a one camera rotation system. The measurement method includes the multi-directional detections and the image reconstruction technique: maximum likelihood–expectation maximization. We evaluated the influence of the number of detection directions on the reconstruction by virtual intensity distribution and found that the sufficient direction number is 6. As a result, we could measure the temperature distribution of the inclined, drawn and coupled arc plasma provided by a two-electrode TIG arc.

Numerical analysis of arc plasma behaviour in groove welding with 3D TIG arc model

Arc welding phenomena have been theoretically investigated by using various numerical models, which have been proposed and developed together with rapid progress of the computer technologies. However, most of the numerical models are two-dimensional axial symmetric models that are available only for stationary arc on the flat plate. Actual welding processes applied to the manufacturing field are carried out with various joint geometries and the welding arc moves on the base metal. Therefore, they should be non-axial symmetric phenomena and it is required to be discussed with a three-dimensional (3D) model. In this research, TIG arc characteristics in V-groove welding are numerically investigated by using our 3D numerical model. It is shown that both heat input and arc pressure on the groove surface are significantly different from the flat plate surface. In the groove heat input and arc pressure are varied sensitively with location and aiming of the TIG torch. Experimental results show the validity of calculation results of TIG arc heat input distribution on the groove surface.

Tomographic spectroscopic observation of argon and metal vapor behavior in MIG arc welding

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.