FIELD OF INVENTION
The invention generally relates to Rotary Arc Gas Metal Arc Welding (RA-
GMAW) technique for Narrow Gap GMA welding. More particularly, the invention
relates to an improved rotary arc gas metal arc welding system which provides
improved fusion and bead characteristics in both groove and fillet joints even at
higher welding speeds. The invention further relates to a process in a rotary arc
gas metal welding system providing improved fusion and bead characteristics.
BACKGROUND OF THE INVENTION
Narrow Gap Welding technique is an economic way of producing welded joints.
This technique reduces the volume of weld-metal to be deposited in butt joints.
The economic advantage becomes more significant with increased plate
thickness. Though the economic advantage is enormous for plate thickness more
than 30 mm, it also involves some technological challenges posed by the narrow
groove. One of the technological challenges is achieving good sidewall fusion in
such narrow groove.
GMAW is one of the welding processes that have been adopted for Narrow Gap
welding applications. Number of techniques like Twisted Wire, Bent Wire etc.,
has been developed in GMAW for achieving the sidewall fusion in Narrow Gap
welding. Each of these techniques has their own advantages and limitations.
The twisted wire method is somewhat complex and requires special consumable.
The twisted wire is not a standard product and cannot be wound on normal wire
drums because of the non-uniform shape of the wire. Feeding the twisted wire is
also a problem due to the shape. The arc rotation diameter being fixed, the joint

gap needs to be very accurate. Any variation in joint gap can lead to defects for
example, lack of sidewall fusion.
The bent wire method involves feeding the wire through a bent contact tube and
swiveling the contact tip by more than 120 degrees to achieve the sidewall
fusion. The technique also gives wire-feeding problem particularly with soft wires
like aluminum.
Iregard, Rotary Arc GMA welding technique overcomes the limitations of
the other techniques. But the rotary arc GMAW, in particular for narrow groove,
for providing the desired results require suitable apparatus and an associated
process for implementing the apparatus.
In Rotary Arc GMA welding, the arc is rotated at high speed causing a stirring
effect on the weld pool, which results in improved fusion and bead
characteristics. The weld pool stirring caused by the Rotary Arc helps in
achieving porosity free welds. In narrow gap situation, the high-speed rotary arc
ensures good sidewall fusion. This Rotary Arc GMA welding technique also
provides improved fusion and bead characteristics for fillet welding applications.
Rotary Arc Gas Metal Arc Welding has been developed for narrow groove butt
joints and normal fillet joints. In case of Narrow Gap joints, Rotary Arc GMA
welding provides the advantage of higher joint completion rate. This is primarily
due to the reduced weld volume. In normal fillet welding applications, Rotary Arc
GMA welding provides better side wall fusion and improved fillet weld shape and
thereby avoids hot cracking problem.

However, the Narrow Gap application requires a much smaller torch, which can
move and weld inside a narrow gap of 12 to 14 mm. The normal butt and fillet
welding applications do not require such a small torch.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved Rotary Arc GMA
welding system, which eliminates the disadvantages of prior art.
Another object of the invention is to propose an improved Rotary Arc GMA
welding system, which is capable of physically rotating the arc at high speed to
obtain desired side-wall fusion both in narrow groove and filet joints.
A still another object of the invention is to propose a process in a rotary arc GMA
welding system that provides improved fusion and bead characteristics, and
capable of implementing rotating speed, diameter of rotation and other
associated technical parameters to achieve desired weld joints.
Yet another object of the invention is to propose a process in a rotary arc GMA
welding system that provides improved fusion and bead characteristics, which is
capable of transmitting the welding current to the rotating torch without sparking
problem.
These and other objects and advantages of the invention will be apparent from
the ensuing 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
Accordingly, there is provided an improved Rotary Arc GMA welding system
capable of welding Narrow Gap joints as well as normal butt and fillet joints. In
the Rotary Arc GMA welding system developed, the arc can be rotated at
different speeds ranging from 0 to 2000 rpm. The diameter of rotation is
optimized at 2.0 mm. The arc rotation speed has significant influence on the
various bead parameters. The optimum rotation speed, which gives best results
in terms of bead characteristics and mechanical properties, has been
established.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 - Shows an embodiment of the improved system 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. Fig1 shows the
schematic of the Rotary Arc Gas Metal Arc Welding system. In the system, a

MIG welding wire available in standard spool (1) is fed by a wire feeder (2)
through a torch (14). A Motor (3) mounted on a Top Cover Plate (4) transmits the
power through a spur gear chain (5) and effects rotation of the torch (14). The
current required for the welding arc is supplied from a constant voltage power
source (8). The positive terminal of the power source (8) is connected to the
torch (14) directly. The current is transferred to the rotating torch (14) by a spring
loaded Carbon brush type power supply means (6). The hollow torch body has
an eccentric hole through which the wire (1) is fed into a contact tube. A
shielding gas consisting of a mixture of argon and CO2 is supplied to the nozzle
of the torch (14) through a nipple (7) provided in the gun. A job (9) is mounted
directly below the torch (14). The Rotary arc GMA welding head [comprising of
the wire spool, wire feeder, rotating motor and torch] is mounted on a Torch
Positioning means (10), which has up and down movement. The torch
positioning maens (10) is mounted on a linear carriage (11), which has
adjustable linear motion. The linear carriage (11) is mounted on a carriage base
(12), which is a static structure.
The advantages of the invention can be seen, inter alia, in the fact that Rotary
Arc GMA welding produces excellent butt and fillet welds. The weld metal
mechanical properties is also improved.

WE CLAIM
1. An improved Rotary Arc Gas Metal Arc Welding system for providing
desired side-wall fusion and bead characteristic in groove and fillet joints,
the system comprising:
- a spool (1) including a wire feeder (2) for feeding a wire through a
rotatable a rotatable torch (14),
- a motor (3) connected to a gear train (5) for rotating the torch (14)
with different eccentricity and rpm causing arc rotation;
- a Power source (8) for carrying out the GMA welding, the power
source (8) being connected directly to the torch (14);
- a contact tube to allow feeding of the strip electrode through the
torch (14);
- the welding head (1,2,3,13) mounted on a torch positioning means
(10), the torch positioning means (10) enabled to move vertically
and mounted on a linear carriage (11) having adjustable linear
motion;
- a spring - loaded power supply means (6) transferring welding
current to the rotating torch (14), and

- a shielding gas being supplied to the nozzle (3) of the torch (14) via
a nipple (7).
2. An improved Rotary Arc Gas Metal Arc Welding system for providing
desired side-wall fusion and bead characteristic in groove and fillet joints,
as substantially described and illustrated herein with reference to the
accompanying drawings.

This invention relates to an improved Rotary Arc Gas Metal Arc Welding system for providing desired side-wall fusion and bead characteristic in groove and fillet joints, the system comprising: a spool (1) including a wire feeder (2) for feeding a wire through a rotatable a rotatable torch (14), a motor (3) connected to a gear train (5) for rotating the torch (14) with different eccentricity and rpm causing arc
rotation; a Power source (8) for carrying out the GMA welding, the power source (8) being connected directly to the torch (14); a contact tube to allow feeding of the strip electrode through the torch (14); the welding head (1,2,3,13) mounted
on a torch positioning means (10), the torch positioning means (10) enabled to move vertically and mounted on a linear carriage (11) having adjustable linear motion; a spring - loaded power supply means (6) transferring welding current to
the rotating torch (14), and a shielding gas being supplied to the nozzle (3) of the
torch (14) via a nipple (7).