FIELD OF THE INVENTION
The present invention relates to Gas metal arc welding, and in particular to
process and apparatus for gas metal arc welding with cold wire addition.
BACKGROUND OF THE INVENTION
Gas metal Arc Welding (GMAW) involves formation of an arc between a
continuously fed bare wire electrode and a work piece. The (GMAW) process
uses a gas to protect the molten pool and form the slag, and alloying elements
are added to the weld pool. The arc zone on the work piece surface is covered
with a shielding gas prior to welding. The arc moves along the joint line to form
the weld joint, and the remaining fused slag layers are removed after welding.
As the arc is completely covered by the gas, the weld area remains visible during
the welding.
Gas metal arc welding (GMAW) commonly referred to as metal inert gas (MIG) or
metal active gas welding (MAG) is a welding process in which a consumable weld
wire and a shielding gas are fed through a welding torch. In GMAW, the weld
wire is fed through the welding torch via its contact tip made of copper or a
copper alloy. The contact tip guides the weld wire and also provides a continuous
electrical supply from a power source to the weld wire as the weld is fed.

The weld wire is held near or in contact with a weld metal surface such that an
electrical arc is generated between the weld wire and the surface. The arc
causes the weld wire to liquefy and is subsequently applied to the welding
surface.
US Patent No. 4,572,936 discloses a multiple wire welding process in which wires
are fed separately using different power sources for different wire feeders.
Hence requirement of individual power source with high current feed is needed -
which add to cost.
Cold metal transfer (CMT) is a technique described in US Patent No.
201002246094 in which a CMT welding apparatus having a weld wire and a wire
feeder for feeding and oscillating the weld wire forward and backward through
the wire is used, and wherein the weld shares a concentric axis with the wire
passage. Hence an additional system programmed for feeding the wire according
to the current condition as well as wire feed rate, is required.
In conventional GMAW process the heat energy is distributed in such a way that
only 20-25% of the heat energy is used for melting the filler wire and the rest is
utilized in melting the flux, super heating the molten weld pool and melting the
parent plate. In this high dilution process twice as much plate are being melted
as wire, which is undesirable.

OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose an improved wire
feeding system for butt joints in a single wire gas metal arc welding procedure.
Another object of the present invention is to propose an improved method of
hard facing of stainless steels filler of similar / dissimilar chemistry in a twin-wire
based gas metal arc welding procedure.
A still another object of the present invention is to propose an improved method
of hard facing of stainless steels filler of similar / dissimilar chemistry in a twin-
wire based gas metal arc welding procedure, which is enabled to create a
common weld pool to attain required chemistry according to the code of highest
quality welds.
Yet another object of the present invention is to propose an apparatus interfaced
to wire feeding device attached to a gas metal arc welding (GMAW) machine for
addition of cold wire during GMAW welding.
A further object of the invention is to propose an improved method of hard
facing of stainless steels filler of similar / dissimilar chemistry in a twin-wire
based gas metal arc welding procedure, which eliminates excess arc energy
leading to deformation of micro-structure, shrinkage and distortion of the main
plate.

A still further object of the present invention is to propose an improved method
of hard facing of stainless steels filler of similar / dissimilar chemistry in a twin-
wire based gas metal arc welding procedure which is capable to enhance the
deposition rate by 40% and thereby achieving better mechanical properties.
Yet a further object of the present invention is to propose an improved method
of hard facing of stainless steels filler of similar/ dissimilar chemistry in a twin-
wire based gas metal arc welding procedure which enables at least 50%
reduction in cycle time including consumables.
SUMMARY OF THE INVENTION
The cold wire addition process of the invention is essentially characterized by the
use of an additional apparatus for cold wire feeding without any power source,
which is interfaced with the existing wire feeder with a system for controlling the
wire feed rate. In a single wire feeder, with the main wires, the cold wires are
fed simultaneously. The wires in the contact nozzles are tangential to the
welding direction which facilitates super heating of the molten weld pool and
subsequent melting the parent plate. Gas metal arc welding (GMAW) is therefore
a high dilution process enabling melting of twice as much plates as wire. The
cold wire addition is one of the advanced techniques to make use of the excess

energy available in the arc cavity for addition of the filler material in the form of
wire. With addition of the cold wire, the excess heat energy is used efficiently
for melting the wire. The addition of "cold wire" in the arc stream can increase
the deposition rate. Thus, the addition of cold wire ensures increased transfer
efficiency compared to other known methods. This results in a highest usable
melting rate for a given arc energy and unwanted heat on the weld surface is
reduced which otherwise causes heavy penetration, unfavorable microstructures,
high shrinkages and distortion. Thus this cold wire addition technique results in
40% increase in deposition rate and better mechanical properties over
conventional single gas metal arc welding process. In current practice, for
addition of cold wire is required to interface one additional wire feeder along with
the main wire feeder with a control system to attain the required chemistry and
mechanical properties.
The process utilizes a two or three bead per layer deposition technique, and is
particularly suitable for welding of thin and thick-section material.
In a multiple wire welding system, out of the plurality wires used for welding,
one or two of the welding wires used are micro alloyed wires. The wires are
commercially available unalloyed or low-alloyed solid wires. The inventive
process uses a weld metal, which has unexpectedly high toughness value, used
in single or multi-pass welding operation.

The Gas metal arc welding (GMAW) process of the invention uses one additional
wire feeder with a torch without any power source, and is interfaced with the
existing wire feeder with a system for controlling the wire feed rate. Along with
the main wire, the cold wire is fed either simultaneously at different wire feed
rate or at the same feed rate.
In the invented process of the excess energy available in the arc cavity is used
for addition of filler material in the form of wire. With addition of the cold wire,
the excess heat energy is used efficiently for melting the wire.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1: View of cold wire addition technique and the torch for single Gas metal
arc welding technique for butt welding plate.
The invention will now be described in detail in an exemplary embodiment as
depicted in the accompanying drawing. There can however be other
embodiments of the same invention, all of which are deemed covered by the
description.

DETAIL DESCRIPTION OF THE INVENTION
As best seen in Figure 1
The improved cold wire feeder can be fitted to a conventional Gas metal arc
welding machine. By this technique same/different composition (1) of filler
materials weld metal combination can be done effectively. The construction of
the cold wire feeder (2) and a gas supply (3) assembly is shown in figure 1. The
dissimilar/similar wire combination is fed using a single wire feeder with two
nozzles (4) drawing power from a single power source (6) with parameters of
current, voltage, and wire feed rate for example, 250 A, 28V and 10.5 m/min
respectively to create a single weld pool (5) in which the required weld chemistry
is obtained by the use of two wires of different chemistry. The process further
provides the required hardness properties as well as the required micro structure
of the weld metal. In the arc cavity, the cold wire fillers with different / same
chemical composition of different alloy wires are fed simultaneously in a twin-
nozzle is shown in figure 1 i.e. one after another. This creates the common weld
pool to give the desired weld properties.
Not limiting the scope of the invention, the process and apparatus of the
invention can be applied for welding to be carried out in wide grooves having
different width. The cold wire addition process, by using a cold wire feeder with
a torch, can be used for welding of butt joints, valve wedges and seat rings of
different sizes. This process can be manual as well as automatic. This will result
in savings in consumables cost, cycle time reduction and higher productivity with
savings of weld materials.

WE CLAIM:
1. An improved method of hard facing of stainless steels filler of
similar/dissimilar chemistry in a twin-wire based gas metal arc welding
procedure the process comprising the steps of-
- providing a wire-feeding system on a gas metal arc welding machine, the
wire-feeding system augmented with an apparatus interface without
additional power source;
- preparing wide sides edges of the weldable work piece for welding;
- positioning the work piece such that the included angle for the joint is in
the range of 25-45° and that width of the joint at the root is in the range
of 22~25 mm;
- feeding an additional wire through the apparatus;
- interfacing the apparatus with the existing wire feeder having control
means for controlling the wire feed rate,

wherein the cold wire is fed along with the main wire simultaneously
either with a different wire feed-rate or with the same wire feed-rate;
wherein the special nozzles are arranged tangentially to the welding
direction,
characterized in that the process enables savings of upto 40% in energy
consumption, reduction of cycle time about 50%, and reduction in welding
consumables and in that the excess energy available in the arc cavity
allows melting of the cold wire to eliminate excessive penetration,
unfavorable micro-structure formation, high shrinkage and distortion of
the main plate.
2. The process as claimed in claim 1, wherein a single pass welding is
performed to avoid buffering layer of welding and machinery.
3. An apparatus for the gas metal arc welding process as claimed in claims 1
to 4 comprising:

- a main wire-feeder assembly (2) attached to a gas metal arc welding
machine, the main wire feeder (2) having a nozzle (4), and attached to a
power source (6);
- a main filler wire from a spool fed through the wire feeder (2),

characterized in that a cold wire feeder assembly (3) with a nozzle (5)
tangentially disposed to the welding direction, and receiving power from
said power source (6) is disposed to allow a cold wire to be
simultaneously fed with the main wire.
4. An apparatus for the gas metal arc welding as claimed in claim 3, wherein
the main wire and the cold wire fed into the weld can be of similar or
dissimilar combination.
5. An apparatus for the gas metal arc welding as claimed in claim 3, wherein
the similar / dissimilar wire combination fed through the wire feeders
having feed nozzles creates a common weld pool for achieving required
chemistry and hardness.

ABSTRACT

The invention relates to an improved method of hard facing of stainless steels filler of similar/dissimilar chemistry in a twin-wire based gas metal arc welding procedure the process comprising the steps of providing a wire-feeding system on a gas metal arc welding machine, the wire-feeding system augmented with an apparatus interface without additional power source; preparing wide sides edges of the weldable work piece for welding; positioning the work piece such that the included angle for the joint is in the range of 25-45° and that width of the joint at the root is in the range of 22~25 mm; feeding an additional wire through the
apparatus; interfacing the apparatus with the existing wire feeder having control means for controlling the wire feed rate wherein the cold wire is fed along with the main wire simultaneously either with a different wire feed-rate or with the same wire feed-rate; wherein the special nozzles are arranged tangentiaily to the welding direction. The process enables savings of upto 40% in energy consumption, reduction of cycle time about 50%, and reduction in welding consumables and in that the excess energy available in the arc cavity allows
melting of the cold wire to eliminate excessive penetration, unfavorable micro-structure formation, high shrinkage and distortion of the main plate.