All position TIG welding process

#The present invention relates to an all-position TIG (tungsten-inert gas) welding process.

#Since excellent qualities of welds are obtained by TIG welding processes, the latter are widely used in welding various pipes in any welding position. In general, TIG welding processes may be divided into low-frequency pulse TIG welding processes which are most commonly practiced and high-frequency pulse TIG welding processes which are reserved for special purposes.

#In the case of the low-frequency pulse TIG welding process, the welding current is controlled by the electric current pulses of low frequencies of a few hertz while the welding torch is moved. The weld zone is subjected to repeated melting and solidification and a bead is obtained. Therefore, the low-frequency pulse TIG welding process is best adapted in welding in any position. In addition, the low-frequency pulse TIG welding machines are simple in construction and are highly efficient in operation when used at field sites. However, the low-frequency pulse TIG welding has an inherent disadvantage in welding efficiency; that is, the metal deposition rate is low. For instance, in the case of a vertical downward welding position, which is most commonly practiced, the metal deposition rate is less than 8 g/min (with heat input of 7,500 Joule/cm). As a result, the number of passes must be increased so that the set-up time required for rewinding the welding cables and the hoses for inert gas is increased and subsequently the welding must be interrupted intermittently for a relatively long period. Thus, the productivity is low.

#FIG. 1 is a view used for the explanation of the molten metal pool in the case of a vertical position welding;

#FIG. 2 is a schematic view showing the equipment used in the present invention;

#FIGS. 3(a) and (b) are views used for the explanation of swinging of an arc;

#In FIG. 2, reference numeral 3 denotes a welding torch; 8, a tungsten electrode; 2, a base metal; 5, a filler wire; and 6, a wire holder attached to the torch 3 backwardly of the direction A of the welding in such a way that the filler wire 5 may be held as much in parallel with the tungsten electrode 8 as possible.

#A DC pulse source 7 is connected to the tungsten electrode 8 and the base metal 2, and a pulse source 9 for filler wire is connected to the filler wire 5 and the base metal 2. The pulse sources 7 and 9 are interconnected through a phase control unit 10 which locks the pulses generated by the power sources 7 and 9 in predetermined phase relationship.

#The DC current pulses (main current) at the frequency of from tens to hundreds Hz flows from the DC pulse source 7 through the tungsten electrode and base metal 2 8 so that the arc 4 is obtained between them. At the start of the welding, the phase control unit 10 so controls the pulse source 9 that the latter transmits the sub-current pulses in synchronous phase relationship with the main current pulses to the filler wire 5. The tip of the filler wire 5 is fed into the high-temperature plasma jet in the welding arc so that the filler wire 5 is quickly melted into the molten metal pool 1.