Reiichi Suzuki

Spatter And Fume Reduction In Co2 Gas- Shielded Arc Welding By Regulated Globular Transfer

The CO2 gas-shielded arc welding process with solid wire is widely used in Japan due to its good weld quality, high efficiency and reasonable wire and shielding gas costs. However, this process has its drawbacks, especially in the globular transfer mode at a high welding current, where significant amounts of spatter and fume are generated. To solve this problem, the author has investigated how to control globular transfer with a special pulsed current and has developed a regulated method and power source for practical use. The present report discusses the mechanism of this new method of regulating the globular transfer of molten droplets, in which each droplet is squeezed at its upper part in peak current duration and is detached silently in base current duration. Also various effects are reported concerning this new method and its application in the welding robot system for fabricating steel frames for buildings.

State of the art of process control of molten droplet and pool in gas metal arc welding

The fundamentals of welding can be understood simply as (i) partially melting the welding metal and base metal and (ii) forming a molten pool and solidified weld metal. What is used as the power source for this series of processes and how the active droplets and molten pool are protected and how the metallurgical reaction within the molten pool is controlled have been the subjects of a range of technological studies, and technological solutions have been developed. In gas-shielded arc welding, in particular, the basic simpler requirements for (1) reduction in spatter and (2) stabilization of bead shape have been and continue to be of the greatest importance. These elements have direct relationships with (i) and (ii) above, and there has been continuing research in the fields of welding consumables, power sources, equipment, gas, etc. but it remains true that no single factor is in itself capable of providing a major improvement. Accordingly, there has been an increasing amount of research activity directed to combinations of these with the aim of achieving a breakthrough. In this paper, we describe trends in methods of controlling droplets and molten pool through such combinations with a focus on technologies developed by Kobe Steel.

An estimation of factors influencing residual stress characteristics of fillet welded lap joints

Abstract The residual stress behaviours in fillet welded lap joints of sheet metal have been researched in a systematic testing procedure with varied steel types, steel thicknesses and welding wires having different transformation points. Consequently, under the simulated fabrication welding conditions (with a constant amount of deposited metal), the transverse residual stress at the weld toe, which is deemed critical in fatigue strength, has been found almost invariable to a change in steel type and thickness, but it has been clarified to become compressive to a greater extent as the wire’s transformation point is lower. Moreover, as for the residual stress inside the weld metal, the compressive residual stress area has been found to expand as the welding wire’s transformation point reduces, from the results of the thermo-elastic-plastic analysis.

Study of wind-toughness of metal arc welding with reference to multi-pass weld metal quality

Abstract The maximum cause to make mechanical toughness of a weld metal reduce in process management is known to be a mixture of nitrogen including in the atmosphere by breaking the shield condition. Mixture of the atmosphere is prevented by blowing the shielding gas such as carbon dioxide, argon, and this mixture to the arc and the molten pool in gas metal arc welding, but it is easily affected by wind. Therefore, it has been recommended conventionally that wind velocity should be controlled to less than 2.0 m/s. But it is thought that this recommendation value is unsuitable to produce multi-pass weld metal with high mechanical and porosity toughness properties because this was provided from examination results by only consideration of porosity toughness of single-pass weld metal but non-consideration mechanical toughness. In this paper, the shielding condition is evaluated not only chemical analysis and mechanical properties of multi-pass weld metal in some velocity wind environment but also visualizing varied shielding gas behaviour by the Schlieren method. As a result, it is necessary to control the wind velocity to less than 0.5 m/s to produce multi-pass weld metal with good properties. And the calculated velocity of shielding gas should be controlled to more than twice the wind velocity.

Improvement of the deformation capacity of the column-to-beam joint by the reinforce welding method around the scallop bottom

Abstract Improvement of deformation capacity for a column-to-beam joint is an important theme for improving the earthquake-resistance performance of building structures. One of the causes of decreasing deformation capacity is the existence of stress concentration against the beam flange by the scallop (access hole). The non-scallop method is generally recommended to improve this problem, but it has a large disadvantage in that it is not able to apply to the on-site joint process. The reinforce welding method around the scallop bottom has been developed to be able to apply to an on-site joint and obtain better performance than the non-scallop method. The improved mechanism is a combination of: (1) decreasing the stress concentration; (2) increasing effective thickness; and (3) increasing total length of the breaking line. The deformation capacity by the reinforce welding method around the scallop bottom is a maximum 3.2 times that for the conventional scallop method in the reverse repeating bend test using an actual structure with a beam flange of 19 mm thickness and 490 N mm−2 class steel. This improving effect is better than the non-scallop method.