Claims:We claim:
1) A method of feeding filler material in a welding machine (13), said method comprising the steps of:
a) feeding a pair of filler wires (1a and 1b) mating at a contact location (2) of a wire holder (26) continuously up to a predefined position in the vicinity of a tungsten electrode (3); and
b) melting of said pair of filler wires (1a and 1b) simultaneously by an arc (4) generated from said tungsten electrode (3) forming a permanent joint between a pair of workpieces (7a and 7b) positioned therein and continuously rotating in mating condition.

2) The method as claimed in claim 1, wherein said pair of filler wires (1a and 1b) extends from a pair of filler wire spools (19 and 20) positioned in freely rotating condition on a pair of spool holders (24 and 25) mounted on said welding machine (13).

3) The method as claimed in claim 2, wherein at least one double groove feeding roller (17) positioned in a wire feeding unit (18) in continuous rotation pulls the said pair of filler wires (1a and 1b) into a flexible hose (16).

4) The method as claimed in claim 3, wherein a spring sleeve (27) provided in said flexible hose (16) ensures smooth flow of said pair of filler wires (1a and 1b) up to said predefined position.

5) The method as claimed in claim 1, wherein said pair of workpieces (7a and 7b) in mating condition forms a V-shaped groove (28).
, Description:A METHOD OF FEEDING FILLER MATERIAL IN A WELDING MACHINE

FIELD OF THE INVENTION:
The present invention relates to the field of welding. Particularly, the present invention relates to a method of reducing cycle time involved in welding.

BACKGROUND OF THE INVENTION:
Generally, a single wire is used as a filler material during welding process. The generation of high pressure and high temperature steam is done in boilers, super heaters, reheaters etc., having a long extending coils. The coils of standard length are supplied by the vendor to the boiler OEM (Original Equipment Manufacturer) and the boiler OEM needs to go for a butt welding of the coils of standard length to achieve the coils of desired length. The coils are typically made of stainless steel super 304 grade and necessarily needs to be weld only through TIG (Tungsten Inert Gas) welding to avoid weld defects like porosity.

An experiment is conducted by welding coils having an outside diameter of 51mm and a wall thickness of 9.1mm through TIG welding and feeding a single wire as a filler material.

The weld parameters are tabulated in the below Table 1.
Layers 1 2 3 4 5
Peak current (A) 130 132 135 135 135
Base current (A) 120 120 125 125 125
Wire Feeding
Speed (mm/min) 1500 1600 1650 1650 1650
Peak time (S) 1.2 1.2 1.2 1.2 1.2
Base time (S) 0.5 0.5 0.5 0.5 0.5
Weld Speed (mm/min) 74 60 50 45 40
OSC Speed (mm/min) 0.0 800 800 800 800
OSC With
(mm)
Left - 0.0 -1.2 -3.0 -3.9 -5.0
Right+ 0.0 1.2 3.0 3.9 5.0
Dwell Time (S) Left - 0.0 0.02 0.03 0.04 0.04
Right+ 0.0 0.02 0.03 0.04 0.04

Table 1
It can be inferred from the above table 1 that to perform complete butt welding on the coils of 51mm diameter and 9.1mm thickness, five layers are needed. As the number of joints for the coils of the boiler are huge, the power consumption is more considering the number of layers per joint. The productivity of the TIG welding operation is also low because of the lower metal filling rate from the single wire.

Therefore, there is felt a need for development of a method of feeding a filler material in a welding machine to overcome the drawbacks of the prior art and thereby improve the productivity of the weld operation.

OBJECTS OF THE INVENTION:
An object of the present invention is to provide a method to reduce filler material melting time.

Another object of the present invention is to provide a method to reduce melted filler metal penetration time.

One more object of the present invention is to provide a method to reduce cycle time involved in welding operation.

Still another object of the present invention is to provide a method to increase surface contact area of the filler material with the arc.

Further another object of the present invention is to provide a method for lower power consumption in welding operation.

Yet another object of the present invention is to provide a method for improving melted filler metal penetration in welding operation.

Still one more object of the present invention is to provide a method for improving the productivity of the welding operation.

SUMMARY OF THE INVENTION:
In accordance with the present invention a fixture for a machining operation is provided, the fixture comprising a workpiece mounting plate placed at a predefined position on a base plate bolted to a machining table of a boring machine, a plurality of locators bolted at either ends of the axes of the base plate and held against the periphery of the workpiece mounting plate and a plurality of bolts extending from the workpiece mounting plate and the plurality of locators towards a workpiece mounted on the workpiece mounting plate to facilitate in achieving a uniform surface at top face of the workpiece and to facilitate in achieving concentricity between the workpiece and the workpiece mounting plate respectively.

BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will now be described with reference to the accompanying drawings in which:

Figure 1(a) illustrates a schematic arrangement of a TIG welding machine in accordance with the present invention; and

Figure 1(b) illustrates an enlarged view of portion ‘A’ of the TIG welding machine of figure 1(a).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
A preferred embodiment will now be described in detail with reference to accompanying drawings. The preferred embodiment does not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.

Referring to fig 1(a) and 1(b), In accordance with the present invention, there is provided a TIG welding machine 13 comprising a pair of filler wires (1a and 1b), a tungsten electrode 3, a pair of workpieces (7a and 7b), a gas nozzle 8, a current conductor 9, a cooling hose 10, a shielding gas pipe 11, a TIG torch 12, a TIG torch holder 14, a horizontal stud 15, a flexible hose 16, a plurality of double groove feeding rollers 17, a wire feeding unit 18, a pair of filler wire spools (19 and 20), a cooling system 21, a power source 22, an inert gas supply cylinder 23, a pair of spool holders (24 and 25), a wire holder 26 and a spring sleeve 27.

The configuration and the method of working of the TIG welding machine 13 is explained in detail with reference to the figures 1(a) and 1(b) as follows:

The TIG torch holder 14 is attached to the horizontal stud 15 and the vertical stud 29 so as to move the TIG torch 12 to and fro as well as up and down. The power source 22 supplies the current through current conductor 9 to the tungsten electrode 3 through the TIG torch 12. The inert gas supply cylinder 23 supplies the inert gas (argon gas) through the inlet of the shielding gas pipe 11. The gas nozzle 8 ensures the gas distribution in such a way to form a gas shield 5 during the arc 4 formation. The pair of spool holders (24 and 25) mounted on the TIG welding machine 13 and provided with the pair of filler wire spools (19 and 20) therein to supply the filler wires (1a and 1b) to the wire feeding unit 18. The double groove feeding rollers 17 provided in the wire feeding unit 18 ensures the feeding of the pair of filler wires (1a and 1b) to the flexible hose 16. The spring sleeve 27 provided in the flexible hose 16 ensures the smooth flow of the filler wires (1a and 1b) up to a predefined position in the vicinity of the tungsten electrode 3. The pair of filler wires (1a and 1b) comes out through the wire holder 26 mating at a contact location 2 and melts simultaneously by an arc 4 generated through the tungsten electrode 3. The pair of workpieces (7a and 7b) are adapted to mate with each other to form a V-shaped groove 28 and positioned below the tungsten electrode 3 in proximity to the filler wires (1a and 1b) extending therethrough. Due to the high heat in the arc 4 of the TIG welding, both the filler wires (1a and 1b) melts at the same time and forms a permanent joint with the pair of workpieces (7a and 7b). The cooling system 21 supplies the cooling water through the cooling hose 10.

During the root deposition, the pair of work pieces (7a and 7b) are rotated simultaneously to complete the root welding. After the completion of the root welding, the remaining welding is carried out by moving the TIG torch 12 horizontally left to right for one complete revolution and then upward movement is carried out to start the next layer. The process is repeated till the entire process of welding is completed up to the outside diameter of the work pieces (7a and 7b).

TEST RESULTS:
An experiment is conducted by welding coils having an outside diameter of 51mm and a wall thickness of 9.1mm through TIG welding and feeding a pair of filler wires (1a and 1b) as a filler material from the same wire holder 26.

The results of the experiment are tabulated in the below table 2.
Layers 1 2 3
Peak current (A) 145 145 145
Base current (A) 120 120 120
Wire Feeding
Speed (mm/min) 1700 1700 1700
Peak time (S) 1.2 1.2 1.2
Base time (S) 0.5 0.5 0.5
Weld Speed (mm/min) 85 65 60
OSC Speed (mm/min) 00 800 800
OSC With
(mm)
Left - 00 -3.5 -5.2
Right + 00 -3.5 5.2
Dwell Time (S) Left - 00 0.03 0.05
Right + 00 0.03 0.05

Table 2
As the experiments of the prior art and the present invention are carried out on the workpieces of the same design specification, a comparison can be drawn from the results of the experiments tabulated in Table 1 and Table 2. It can be deduced from the table 1 and table 2 that the number of layers required for the complete welding of the workpieces (7a and 7b) has been reduced to three in welding with the pair of filler wires (1a and 1b) instead of five in welding with single filler wire.

Further, it can be observed from the table 1 and table 2 that the weld speed in the present invention is also increased.

In this context, a question might arise to feed a single filler wire of diameter equal to the combined diameter of the pair of filler wires (1a and 1b), but in that case, the surface area of contact of the filler material with the arc 4 is reduced resulting in the high melting time and high penetration time.

In the present invention, cycle time involved in welding is reduced by 50%, power consumption is reduced and as the number of butt joints required for manufacturing the coils of the boiler are more, productivity is also improved.

TECHNICAL ADVANCEMENTS:
A method of feeding filler material in a welding machine has several technical advantages including but not limited to the realization of:
• a method to reduce filler material melting time;
• a method to reduce melted filler metal penetration time;
• a method to reduce cycle time involved in welding operation;
• a method to increase surface contact area of the filler material with the arc;
• a method for lower power consumption in welding operation;
• a method for improving melted filler metal penetration in welding operation; and
• a fixture on which the workpiece can be setup by semiskilled operators also.

Although the invention has been described herein above with reference to the embodiments of the invention, the invention is not limited to the embodiments described herein above. It is to be understood that modifications and variations of the embodiments can be made without departing from the spirit and scope of the invention.