Toshiharu Myoga

Development of hot wire TIG welding methods using pulsed current to heat filler wire – research on pulse heated hot wire TIG welding processes

The hot wire process is a method of forming a deposited metal by passing current through, and thus heating, the filler wire. As indicated in “Consumable Electrode Arcless Electric Working” the title of the patent for which Manz and others in the U.S. applied in 1962, essentially, the filler wire can be melted independently of the arc heat source which melts the base metal; thus, the distinctive features are that the deposition rate is controllable and a high deposition rate is also feasible. As well as the the TIG arc, this hot wire process was formerly employed in combination with the submerged arc and the plasma arc; most recently, combination with lasers was also anticipated. During common TIG welding which employs a “cold” wire through which there is no current passed, the deposition rate is slow; consequently, there have been many cases where the hot wire process has been employed to advantage. However, there have been some problems outstanding from aspects of workability; consequently, there are some areas for which this process cannot be described as being technically established and in general use. Figure 1 shows the principle of the arrangement of a hot wire TIG welding machine which consists of a wire torch to supply the current to the wire and a wire heating power source in addition to the TIG welding power source, TIG torch and wire feeder. The principle problem of hot wire welding is that the arc can be deflected to the hot wire side or the opposite side of the hot wire due to the interaction of electromagnetic forces between the wire current and the arc current. This “magnetic arc blow” phenomenon destroys the arc directivity and complicates welding operations. When the hot wire TIG welding process was first developed it was recommended that the wire should be heated by means of commercial frequency AC supply. It is thought that the reason for this is probably that when the wire is heated by AC current the arc becomes in an oscillating state and the welding operation is facilitated. In Japan, equipment which heats the wire with DC, where the wire side is selected as ‘+’ pole, have been developed, such as welding equipment with the characteristic of deflecting the TIG arc to the direction of the welding progress by taking advantage of this magnetic arc blow in the reverse direction and welding equipment which embodies compact and low cost power sources where the arc current from the arc power source is partly distributed to the wire for heating. Furthermore, equipment which employs a wire heating current where the wire side is selected to be the ‘–’ pole have come on the market from overseas manufacturers. In addition to these, equipment in which the filler wire is heated by passing the current between two electrical connections have also come onto the market. Furthermore, in recent years, a technique has been developed such that two wires are inserted at the front and the back of the arc, in the direction of the welding progress and a direct current is passed between those wires. The purpose of this technique is to support the molten metal which tends to droop during horizontal position (three o’clock) welding by means of the interaction of the arc current and the hot wire current flowing transversely through the molten pool. For the hot wire TIG welding process, including the equipments just described, to date both AC and DC continuous waveform current has been employed for wire heating, but heating of the wire with pulsed current has not been investigated, either at home or abroad. The authors and others previously developed a hot wire switching TIG welding process in which a low pulsed Welding International 2004 18 (6) 456–468 Selected from Quarterly Journal of the Japan Welding Society 2003 21 (3) 362–373; Reference JJ/03/3/362; Translation 3281