-2-FIELD OF INVENTION
The invention relates to an improved process and apparatus for carrying out GMA welding with alternating shielding gas supply to the arc.
BACKGROUND OF THE INVENTION
GMAW is one of the important arc welding processes widely used in the fabrication industries all over the world. This is an electric arc welding process, which produces coalescence of metals by heating them with an arc established between a continuous filler metal (consumable) electrode and the job. Shielding of the arc and molten weld pool is obtained by an externally supplied gas, which may be inert, reactive or a mixture of inert and reactive gases. The GMAW process is known as Metal Inert Gas (MIG) welding, when the shielding gas used is inert, known as Metal Active Gas (MAG) welding, when the shielding gas contains reactive gases, such as 02 or CO. sub. 2 or mixtures of inert and reactive gases. Each shielding gas has its own properties, including ionization potential, and produces unique arc characteristics. For instance 100%CO2 shielding in mild steel application produces somewhat harsh arc with associated spatter but gives better weld penetration. On the other hand, 100% argon shielding for mild steel applicatign produces very stable arc but results in very poor bead wetting. In order to achieve stable arc and also good bead wetting characteristics in ferrous applications, a shielding gas mixture containing argon+C02 or argon+02 of different proportions is used in the industries for over two decades. Though GMAW with argon+C02 and argon+02 mixed gas is successful in welding of ferrous metals, there are some limitations.

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The mixed gases used in industries are generally rich in argon (argon > 80%) resulting higher shielding gas cost.
In this regard, the alternate shielding gas supply technology overcomes the limitations of mixed gas method. The technology of alternate supply of shielding gas has influence on every aspect of the arc welding. The alternate supply of shielding gas causes a dynamic action on the molten weld pool, which results in Improved weld quality both in terms of fusion characteristics and bead appearance.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an apparatus and process for carrying out welding with two different shielding gases alternatingly supplied from a source.
Another object of the invention is to propose an apparatus and process for carrying out welding with two different shielding gases alternatingly supplied from a source, which is capable of delivering the shielding gas directly to the GMAW torch to minimize mixing of the gas before entering the torch.
A still another object of the invention is to propose an apparatus and process for carrying out welding with two different shielding gases alternatingly supplied from a source, which is capable of delivering the shielding gas directly to the GMAW torch without backflow of one gas into another.

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These and other objects and advantages of the invention will be apparent from
the ensuring description. ,
At the outset of the description, which follows, it is to be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only an exemplary embodiment and the teachings of the invention are not intended to be taken restrictively.
SUMMARY OF THE INVENTION
In conventional GMAW for welding of ferrous metals, it is the standard practice to use 100%CO2 or argon+C02 gas mixture depending on the quality requirement and application. The use of 100% C02 or argon+C02 gas mi:!(ture produces a constant arc dynamics. The arc pressure and weld pool fluidity remain constant. Alternate supply of shielding gas produces a pulsing effect somewhat similar to pulsed GMAW but better than that in dynamics. The pulsed GMAW technique produces one-dimensional impact on the weld pool whereas the alternate shielding gas supply technology causes multiple Impacts to weld pool resulting in much improved weld quality.
The present invention arranges an alternate supply of two different shielding gases to the GMAW torch directly without any pre-mixing and backflow. The pulsing frequency is adjustable from 10 to 60 cycles/min. The welding parameters and the alternate shielding gas supply frequency for improved weld quality is also established.

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This welding system uses a timer controlled gas supply unit for alternating the shielding gas supply at different frequencies.
The process is developed to achieve improved weld quality and also reduction in shielding gas consumption.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 (Schematic)- shows an embodiment of the apparatus according to the invention.
Figure 2 (Schematic)- Shows a block diagram of the GMAW torch for welding with alternating shielding gas supply according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Referring now to the drawings. Wherein like reference numerals designate identical or corresponding parts throughout the several views. Fig 1 shows the schematic of the alternate gas supply system. At least two hoses (3,4) carrying argon and C02 gases from Individual gas cylinders (1,2) are connected to the respective Input terminals (19,20) provided in respective gas supply alternators (5,6). The duration of flow for each individual gas is controlled through timer knobs (7,8) provided In the front panel of a shielding gas alternator (9). At least two gas outlets (10,11) provided on the front panel of the shielding gas alternator (9) is connected to the nipples (14„15) provided in GMAW torch

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nozzle directly through individual hoses (12,13) for each gas. Also the hose length from the shielding gas alternator (9) to the torch is kept to the minimum to make it dynamically more responsive. Adjusting the timer knobs (7,8) varies the shielding gas alternating/pulsing frequency. A consumable wire (16) is fed through a wire feader (28). A GMAW torch (25) with nozzles (26) including the job (27) to be welded is shown.
Fig 2 shows the schematic of the GMAW torch developed for welding with alternating shielding gas supply. The consumable wire (16) is fed through a spiral guide (17) which passes through a contact tip (18). The two hoses (12,13) carrying argon and C02 gases supplied by the shielding gas alternator (9) are connected to input terminals (19,20) respectively of the GMAW torch (25). At least two non-return valves (21,22) allow gas flow towards the nozzle (26) and prevents backflow. The length of the cable between the non-return valves (21,22) and a ceramic gas diffuser (23) is kept short to minimize gas mixing. Also the hose length from the shielding gas alternator (9) to the torch (25) is kept to the minimum to make it dynamically more responsive. The gas cup (18) directs gas flow to the arc and a trigger (24) is provided for on/off function of the torch.

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WE CLAIM:
1. An improved process for carrying out GMA welding with two different
shielding gases comprising the steps of:
- alternatingly supplying to a GMAW torch at a preset gas pulsing
frequency, characterized in that the two different shielding gases
are directly supplied to the GMAW torch without any pre-mixing
and backflow. " ,
2. The process as claimed in claim 1,
wherein carbon steel, alloy steel is welded with alternatingly supplied shielding gases of argon and C02, wherein aluminum is welded with argon and Helium , and wherein stainless steel is welded with argon and 02.
3. The process as claimed in claim 1, wherein the shielding gas supply is alternated at a frequency range of 1 to 30 cycles/minute.
4. An apparatus for carrying out GMA welding with two different shielding gases, comprising:
- a GMAW torch (25) having at least one nozzle (26);

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- at least two input terminals (19,20) for connecting the two hoses (12,13) supplying two different gases from a shielding gas alternator (9);
- a spiral guide (17) for allowing a consumable wire (1) to ipass through a contact tip (18);
- at least two non-return valves (21,22) which allows the gas flow towards the nozzle (26) but prevents the backflow, a ceramic gas diffuser (23) connecting the atleast two non-return valves (21,22), and a trigger (24) for on/off function of the torch (25); and
- a shielding gas alternator (9) having two gas outlets (10,11) connecting the torch (25) via two nipples (14,15) provided on the latter; •
- the alternator (9) receiving two different gases from two gas supply alternators (5,6) via two individual gas supply hoses (3,4).
5. The apparatus as claimed in claim 4, wherein two different gases are supplied from two individual gas cylinders (1,2).

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6. The apparatus as claimed in claim 4, wherein the shielding gas alterhator comprises at least two timer knobs (7,8) for regulating the flow-duration of each individual gas.
7. An improved process for carrying out GMA welding with two different shielding gases comprising as substantially described and illustrated herein with reference to the accompanying drawings.
8. An apparatus for carrying out GMA welding with two different shielding gases, comprising as substantially described and illustrated herein with reference to the accompanying drawings. ' ,

The invention relates to an improved process for carrying out GMA welding with two different shielding gases comprising the steps of alternatingly supplying to a GMAW torch at a preset gas pulsing frequency. The two different shielding gases are directly supplied to the GMAW torch without any pre-mixing and backflow. The invention further relates to an apparatus for carrying out GMA welding.