The invention relates to an improved arc welding method for higher deposition rate implementing a non-consumable electrode and an electrically connected filler wire protected by shielding gas. More particularly, the invention relates an improved arc welding method that uses a non-consumable electrode connected to one polarity and a consumable filler wire connected to the other polarity.

Tungsten Inert gas welding is traditionally identified for producing good quality welds. However, the speed of welding and metal deposition rate associated with the conventional TIG welding process, have been amongst the lowest in the welding technology. Further TIG welding process is associated with relatively large heat input that results in a wide heat-affected zone accompanied by an increased softened zone and thermal strain. However it has the advantages of producing welds characterized by superior bead shape, less porosity and higher corrosion resistance. Due to the problem of melt through arc current, TIG welding cannot be employed for welding of thin plates. Hence it is desirable to

improve the welding rate without increasing the arc current to reduce the dilution and distortion. In view of these short coming, TIG welding finds application, only in welding of critical components like the root pass welding of small diameter pipes and tubes, excluding welding of thin section joints. Also, TIG welding is preferred in high quality requirement applications like the nuclear and space related components where the economics of welding is seen as secondary to the quality of weld. However, in many other general and engineering related product production, involving welding productivity, job completion time and economics of welding are treated equally if not higher with the product quality.
Patent no. : KR900000712B discloses a Hot wire TIG welding method in which: I) the output from a wire heating power source is controlled according to a detected wire heating electrical power signal for an electrical power to commensurate with the obtained wire feed speed; or ii) wire heating current is not supplied when the arc current is at peak level but is supplied when the arc current is at the base level, and wire heating electrical power is controlled by controlling the duration of wire heating current supply in each period in which the arc current is at the base level. The invention further discloses a hot wire TIG welding apparatus in which the heat input for the main welding arc is augmented by the heat input for heating the wire. Also an additional heating source and a method are required.

Patent no.: US 6,982,397 B2 describes a TIG welding apparatus comprising a twin electrode welding torch. The apparatus comprises a first and a second welding electrode arranged approximately parallel and disposed either side of an insulation plate of predetermined thickness. The main unit supplies to the first welding electrode a first welding current which is varied at a first period, and to the second welding electrode a second welding current which is varied at the first period but at an opposite phase to the variation of the first welding current, wherein said main unit superimposes a variation of a second period being shorter than a first period, on to the first and second welding currents. In this method also additional heat input is given to the arc that would increase the dilution. In conventional Tungsten Inert Gas welding, due to the electrically active base metal, considerable penetration and hence dilution of the deposited filler metal takes place. Further, the electrically neutral and cold wire feeding leads to low metal deposition rates in Tungsten Inert gas welding. The new invention addresses these factors. Since the electrode is connected to one of the polarities of the welding power supply and the non-consumable electrode to the other, the arc is generated between these two enabling further deposition than cold wire which is not electrically connected as in conventional welding. Further, since the base metal is not electrically connected, the dilution is also considerably reduced due to lower base metal melting (penetration).
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved arc welding method using a non-consumable electrode, which provides electrical power to the filler wire by assigning one of the polarities to the consumable filler wire.

Another object of the invention is to propose an improved arc welding method using a non-consumable electrode, which is capable of achieving a higher deposition rate and faster job completion rate.
Yet another object of the invention is to propose an improved arc welding method using a non-consumable electrode which creates a welding arc between the filler wire and the non-consumable electrode.
A further object of the invention is to propose an improved arc welding method using a non-consumable electrode which is capable of remelting and smothering the deposited material by the heat from the welding arc between the filter wire and the electrode.
A still further object of the invention is to propose an improved arc welding method using a non-consumable electrode which selects an appropriate direction of travel of the electrode to vary the penetration and/or dilution.
SUMMARY OF THE INVENTION
The invention relates to an improved method of arc welding by melting and depositing the weld metal and involving generation of arc (9) between non-consumable electrode (6) and the consumable filler wire (2). The non-consumable electrode is connected to one polarity and a consumable filler wire is connected to the other polarity. The method uses a shielding gas for protecting the consumable electrode coming out of the nozzle, the non-consumable electrode, molten drops, molten weld pool and the arc zone. The electric arc is initiated directly between the electrode and filler wire, by the high


frequency unit, and the molten drops from the melting consumable electrode deposits on the base metal.

Figure 1 illustrates a method according to the invention for arc welding of different components.
Figure 2 shows the conventional arrangement and process for welding.
Figure 3 shows the arrangement and the process according to the present invention.

As shown in Figure 1, the arrangement for coding comprises a spool (1) containing a continuous filler wire (2) of desired diameter. A wire feeder (3) draws the wire (2) from the spool (1) and feeds it through a nozzle (4). A welding power supply unit (5) is connected between the nozzle (4) and a non-consumable electrode (6) mounted on a torch (7). A shielding gas (8) is provided

during welding operation to protect a welding arc (9), including a deposited weld
(10) molten drops (11) and the filler wire (2). The weld metal is deposited on a
base metal (12). A high frequency unit (13) is connected between the wire
feeding nozzle (4) and the non-consumable electrode (6).
The improved method of melting and depositing the weld metal involves generation of an electric arc (9) between the non-consumable electrode (6) and the consumable filler wire (2). The filler wire (2) from the spool (1) is drawn by a wire-feeding device (3) and fed into the nozzle (4). The wire tip is initially positioned near the non-consumable electrode (6). A high frequency unit (13) initiates the arc (9) between the consumable filler connected to one polarity and the non-consumable electrode (6) to other polarity. In case the electrode (6) is made of tungsten the same is generally connected to the negative polarity even though it can also be connected to the positive polarity for lower welding currents. The consumable filler wire (2) is connected to the positive polarity (or negative depending on the requirement). The arc (9) generated melts the wire (2) and the droplets (11) are propelled down on the base plate (12). When the direction of welding is such that the arc (9) follows the droplets (11) then the arc
(11) heat also further melts and smoothens the weld bead (10). The entire
welding operation is carried out under a shield of protective gas (8).
The method uses a shielding gas for protecting the consumable electrode coming out of the nozzle, the non-consumable electrode, molten drops, molten weld pool and the arc zone.

The electric arc is initiated directly between the electrode and filler wire, by the high frequency unit, and the molten drops from the melting consumable electrode deposits on the base metal.
The metal deposited is smoothened by the heat of the arc to produce a smooth bead. By controlling the process parameters (proper selection of process parameters values) the penetration, dilution and deposition rate can be varied.
The low dilution levels that can be achieved would lead to considerable savings in the filler metal and hence the cost of surfacing. The low dilution levels are made possible due to the electrical neutrality of the plate in which the filler metal is deposited.
The electrically active filler wire and the arcing between the consumable filler and the non-consumable electrode, higher filler metal deposition rates are possible as compared to the electrically neutral and cold wire feeding, as in the case of conventional TIG welding.

1. An improved arc welding method for higher deposition rate implementing a non-consumable electrode and an electrically connected filler wire protected by shielding gas for joining and surface application in a device, the device comprising a consumable filler wire (2) being drawable from a spool (1), the filler wire (2) being fed through a nozzle (4) by a drive device (3); a welding power supply unit (5) connected between the nozzle (4) and a torch (7) mounted with a non-consumable electrode (6); and a high frequency unit (13) initiating an electric arc (9) between the electrode (6) and the filler (2), the method comprising the steps of:
- generating an electric arc (9) between the non-consumable
electrode (6) and the consumable filler wire (2);
- drawing and feeding the filler wire (2) into the nozzle (4) via the
feeding device (3), the tip of the wire (2) being positioned near to
the non-consumable electrode (6);
- allowing the wire to melt and causing the droplets to propel down
on the base plate (12), the arc heat further melting and smoothing
the weld bead (10);
- supplying a protective gas (8) through out the welding duration
wherein, the consumable filler wire (2) and the non-consumable
electrode (6) is connected to the opposing polarity of the welding
power supply unit (5).

2. The method as claimed in claim 1, wherein the non-consumable electrode (6) comprises of water-cooled material, preferably tungsten.
3. The method as claimed in claim 1, wherein the consumable filler wire (2) is connected to the positive polarity.
4. The method as claimed in claim 1, wherein the non consumable electrode (6) is connected to the negative polarity.
5. The method as claimed in claim 1, wherein the electric arc (9) is
generated directly between the electrode (6) and the filler (2) by the high
frequency unit (13).

ABSTRACT

AN IMPROVED ARC WELDING METHOD FOR HIGHER DEPOSITION RATE IMPLEMENTING A NON-CONSUMABLE ELECTRODE AND AN ELECTRICALLY CONNECTED FILLER WIRE PROTECTED BY SHIELDING GAS

The invention relates to an improved arc welding method for joining and surfacing applications in a device. The device comprises of a consumable filler wire (2) being drawable from a spool (1), the filler wire (2) being fed through a nozzle (4) by a drive device (3); a welding power supply unit (5) is connected between the nozzle (4) and a torch (7) mounted with a non-consumable electrode (6). A high frequency unit (13) initiates an electric arc (9) between the electrode (6) and the filler (2). An electric arc is generated between the non-consumable electrode (6) and the consumable filler wire (2). The filler wire (2) is drawn and fed into the nozzle (4) via the feeding device (3). The wire (2) is allowed to melt and the droplets is made to propel down on the base plate (12) when the arc heat further melts and smoothens the weld bead (10). A protective gas (8) is supplied through out the welding duration. The consumable filler wire (2) and the non-consumable electrode (6) is connected to the opposing polarity of the welding power supply unit (5).