Yasuyuki Yokota

Development and Application of the 3-Electrode MAG High-Speed Horizontal Fillet Welding Process

In the shipbuilding industry, welding efficiency without deteriorating weld quality has been desired to, as a consequence of the recent increase in the amount of shipbuilding and the size of ship hulls. Especially, an innovation in the welding efficiency and weld quality in horizontal fillet welding is a more important issue, because the amount of horizontal fillet welding work generally accounts for 70 percent or higher of the total welding work for ship hulls. One of high-speed horizontal fillet welding processes known as “Twin Tandem One Pool process” has been used in actual fabrication. However, the maximum welding speed of the twin tandem one pool process is approximately 1.5 m/min. In order to increase welding speed and welding quality of the twin tandem one pool process, the authors have employed an additional filler wire positioned between the two wires of the twin tandem one pool process. The additional wire carries DC-EN currents, opposite to DC-EP currents for the main welding wires, thereby reducing arc interference and arc blow at high currents. With this new technique, the authors have improved the stability of the weld pool formation at high currents. Consequently, horizontal fillet welding at a speed of 2.0 m/min on primer-coated steel plates has been achieved with excellent bead appearance, shape, and porosity resistance. Recently, this new process has just been installed in actual shipbuilding and it is confirmed that it truly contributes to improve welding efficiency and minimize repair time.

Joule heating of solid wires in MAG welding

Abstract There are numerous studies1–12 concerning the melting rate of welding wire and various investigations have been carried out on welding current, welding current waveform, wire extension, polarity, chemical composition, wire diameter, arc length, shielding gas composition and melting rate. Joule heating of bulk wire has been a large contributory factor to the melting rate of solid wire for carbon steel (hereafter referred to as either wire or solid wire) and Joule heating is a crucial factor in aspects of melting stability. However, there are few case studies concerning the detailed measurement of Joule heating at the contacts between the contact tube and wire and the calculation of melting rate.

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.

Wear Mechanism in Contact Tube during MAG Welding

Stable sliding contact is the most important factor for stable arc discharge of solid wire. If the contact tube wore seriously, arc discharge would become unstable and wire position would be shifted. Ordinary non-Cu-coated solid wire has much wear of contact tube about ten times comparing to Cu-coated solid wire. The mechanism of contact tube wear is not only friction at high temperature but also molten bridge formed between contact tube and wire surface. Some complex of superfine particles decreases the amount of contact tube wear. For example, the mixture of graphite and magnetite reduces the amount of contact tube wear by 80%. These particles form interface layer on inner surface of contact tube, and the layer prevents the transfer of molten Cu to wire surface. The interface layer mainly consists of FeO and complex oxides.