Toshiro Uezono

Development of a plasma MIG welding system for aluminium

A new coaxial plasma MIG welding system is developed for the purposes of improvement of weld bead, reduction of spatter and fume generation. Welding power sources of MIG and plasma, wire feeding equipment and a coaxial plasma MIG welding torch are described in detail. The metal transfer of plasma MIG welding in aluminium is observed and compared with that of pulsed MIG welding. Although one droplet per pulse is obtained by both processes, plasma MIG welding shows more smooth metal transfer than pulsed MIG welding. The result shows that spatter and fume generation are drastically reduced, and clean and good weld bead appearance is obtained by the new system.

Solution to problems of arc interruption and arc length control in tandem pulsed gas metal arc welding

Abstract In the tandem pulsed gas metal arc welding, it is the most important issue to prevent adverse effects caused by electromagnetic interaction between the two adjacent arcs to prevent arc interruption. A pulse timing control can reduce arc interference in tandem pulsed gas metal arc welding. One effective way is to delay the pulse end timing of trailing arc by 0·4–0·5 ms from that of leading arc. In addition, arc length control is assured by pulse frequency modulation for the leading wire and pulse peak modulation for the trailing wire with the pulse timing synchronised with the leading pulse. Consequently, leading and trailing arcs are maintained stable without arc interruption and a stable arc length control is established, which is hardly affected by fluctuations of wire feedrate and extension length.

Solution to problems of arc interruption and stable arc length control in tandem pulsed GMA welding. Study of arc stability in tandem pulsed GMA welding (Report 2)

During tandem pulsed GMA welding, two arcs are generated in close proximity so the action of the magnetic field formed by both arcs causes arc interference and, in the worst case, arc interruption occurs. In the previous report, an investigation was carried out upon the effects of the inter-wire distance and the Ar+CO 2 shielding gas mixture ratio upon abnormal arc voltage rise, and the consequential frequency of arc interruption. The results demonstrated that these occur frequently at the time of staggered phase where one side arc is the pulse peak current and the other arc is the base current, and under conditions where the CO 2 mixture ratio exceeds 10% with an inter-wire distance of around 10 mm. Consequently, in order to avoid these problems, it is considered that the inter-wire distance should be reduced to approximately 5 mm and the Ar+CO 2 shielding gas should be employed with the CO 2 mixture ratio decreased to less than 5%. By contrast, the authors examined the effects of the 2 wire arrangement upon the bead formation during high speed steel sheet welding and demonstrated that highspeed welding performance improves the most when interwire distance is 9–12 mm and 80%Ar+20%CO 2 mixed gas is used as a shielding gas. Satisfactory high-speed welding performance cannot be achieved when the interwire distance is 5 mm. Furthermore, with a reduced CO 2 mixture ratio, the penetration becomes shallow and, in some cases, a problem of poor penetration is apparent during high-speed welding. In addition, there may be an increase in the cost of shielding gas. Therefore, approximately 10 mm inter-wire distance and the employment of a shielding gas no greater than 20 % CO 2 mixture ratio is required to achieve holding without arc interruption. Furthermore, it has been reported that pulse timing control, which can pass current to the leading and trailing wires, is essential for the arc stabilisation during tandem pulsed GMA welding. However, to date there is no report of a detailed investigation into arc length control for external disturbances such as wire feeding fluctuations and variations in wire extension during pulse timing control. Accordingly, for this report, with the aim of arc stabilisation during tandem pulsed GMA welding, an investigation was carried out into methods that prevent abnormal rise in arc voltage and arc interruption, and which maintain a stabilised arc length even under circumstances where external disturbances occur, such as fluctuations in the wire feeding and variations in the wire extension. Arc displacement control, due to the pull force, can be expected by setting the base current output high and, therefore, as part of the investigation, the effect of the base current upon the frequency of arc interruption was examined. The effects of current pulse timing control of the leading and trailing wires upon arc interruption frequency were also studied. From the information obtained, an arc stabilisation control method was devised for tandem pulsed GMA welding, which prevents arc interruption and also achieves the arc length stabilisation function.

Laser-Arc Hybrid Welding Process of Galvanized Steel Sheets

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.

Application of digital inverter-controlled AC pulsed MIG welding system to light metal joining

A digital inverter-controlled AC pulsed GMAW system has been developed for welding sheet metal structures. The arc is quite stable by extracting arc-length-related voltage through the intelligent filter. The synergic AC pulse control automatically adjusts wire feed speed to keep the setting current when the EN ratio (ratio of electronegative current integration to electrode negative plus electrode positive current integration over one pulse cycle) changes. These features make finding optimum welding conditions for gap existing joint.

Controlled bridge transfer (CBT) gas metal arc process for steel sheets joining

In non-pulsed gas metal arc welding (GMAW), spatter can be reduced by lowering the short-circuit current to a low level just before the re-arcing. The reduction in spatter requires an improvement in the accuracy of predicting the re-arcing by stabilizing the metal transfer and improving the robustness of the accuracy against disturbances. The controlled bridge transfer (CBT) process optimizes the accuracy of predicting the re-arcing in real time in response to the metal transfer, realizes spatter reduction and stable arc in non-pulsed GMAW. Traditionally, GMAW is carried out using electrode positive polarity. However, this polarity is not sufficient for welding extra-thin steel sheets, specifically those thinner than 1.0 mm. With electrode negative (EN) CBT process, although slight arc voltage fluctuation occurs caused by the behaviour of cathode spots on the tip of the wire during EN polarity GMAW, instantaneous voltage uses command computation to improve the transient response against the disturbance. Consequently, a stable arc can be obtained without increasing the number of short circuits in a unit time to obtain spatter-free welds.

Spatter reduction in GMAW of stainless steel sheets using CBT process

In non-pulsed gas metal arc welding (GMAW), spatter can be reduced by lowering the short-circuit current to a low level just before the re-arcing. The controlled bridge transfer (CBT) process, which optimizes accuracy of predicting the re-arcing in real time in response to the molten metal transfer, realizes stable, low spatter level. In this paper, the methods for controlling short-circuit transfers to minimize spatter and to realize stable arcs in GMAW of stainless sheet using argon-rich shielded gases are investigated. The new CBT process has been developed by applying the specific arc length control that is not affected by abnormal rise in arc voltage in argon-rich shielded gas welding. This process can suppress the spatter generation caused by fluctuation in the vibratory motion of the weld pool or inaccurate prediction of the re-arcing in the succeeding short-circuit/re-arcing cycle, and thereby spatter-free GMAW in the short-circuit transfer mode can be carried out even on stainless steels.

Spatter Reduction of Steel Sheets Welding Using Controlled Bridge Transfer (CBT) GMA Process

In non-pulsed GMA welding, spatter can be reduced by controlling the short-circuit current to a low level just before the re-arcing. The reduction of spatter requires improving the accuracy of predicting the re-arcing by stabilizing the molten metal transfer, and improving the consistency of accuracy against disturbances. The Controlled Bridge Transfer (CBT) process, which optimizes the accuracy of predicting the re-arcing in real time in response to the molten metal transfer, realizes stable, low spatter level GMA welding.