FIELD OF INVENTION
This invention generally relates to a process for manufacturing a T joint between
a plate to plate for transmission of current in power generating plants. More
particularly, the invention relates to an improved friction stir welding process to
form a plate-to-plate T joint for transmission of current in power generation
plant.
BACKGROUND OF INVENTION
In bus duct construction for transmission of current in a power generation plant,
it is necessary to join a conductive material particularly aluminum alloy to
another conductive material in the plate form perpendicular to each other. For
this purpose, hitherto plates are kept one over another in a perpendicular
manner, and a fillet joint is made by conventional arc welding. The conventional
arc welding of aluminum alloy is rather challenging in terms of using more
rigorous welding procedure, use of additional filler metal and a more demanding
skill on the personnel producing the joint in T form.
JP-A-11/081656 discloses a process to manufacture a hollow scaffolding material
and provides a means capable of forming non slip projections on the surface and
back face plate sections capable of applying non slip machining even if a
scaffolding board is long.

JP-A-2001/176655 describes a friction stir welding method and a device in which
shaped projected pieces are used as rails for guiding the friction stir welding
device along the curved surface.
US-A 6051325 discloses a method of joining machined sandwich assemblies by
friction stir welding. The disclosure describes in the description part of prior art,
an interlocking structural assembly that includes first and second machine
components, which are machined to include generally planar surface portions
having a plurality of integral ribs, which extend outwardly form a respective
surface portion and coincide with the ribs of the other component. The ribs of
the first component are further machined to include grooves for matingly
receiving the distal ends of the corresponding ribs of the second component.
JP-A 2001/246482 discloses a method of welding where run out of a material
during friction stir welding is prevented without using a pressing jig or a
supporting member or without increasing the thickness of the material.
According to the invention, a cover is provided at the opening part of a main
body and a probing pin made of a material harder than the materials of the main
body. The cover is inserted while being rotated into a joining part of the main
body and the cover which are fixed together by moving the probe pin along the
joining zone while the pin is rotated. A groove is formed on a face of the cover
and the edge of the cylindrical main body is inserted into the groove and moved
along the groove while the probe is inserted on the face opposite to the groove.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved friction stir
welding process to form a plate-to-plate T joint for transmission of current in
power generation plant, which eliminates the disadvantages of prior art.
Another object of the invention is to propose an improved friction stir welding
process to form a plate-to-plate T joint for transmission of current in power
generation plant, which enables manufacturing of a simple conductive bus duct
with multifold productivity.
A further object of the invention is to propose an improved friction stir welding
process to form a plate-to-plate T joint for transmission of current in power
generation plant, which allows welding of a blanking plate of the T assembly
without distortion throughout the thickness.
SUMMARY OF THE INVENTION
Accordingly, there is provided a process for joining a palm plate to a blanking
plate of a bus duct which enables joining of the palm to the blanking plate in a
perpendicular way to produce a T joint configuration.
The invention allows a joint formation in a single-shot operation as opposed to
conventional fillet welding operation by fusion welding technique, in which the
joint is made through a multi-pass operation.

Consequently, an enormous time saving occurs, and the manufacturing process
is shortened by about less than 50%.
Further, the cost of new joining method is substantially less compared to the
existing method where rejection rates are high. The process runs largely
automatically and is therefore economical and repeatable quality is possible.
It is advantageous that the prior art weld design between a first plate and a
second plate is modified according to the invention to suit the palm plate to
blanking plate welding by the improved friction stir welding.
According to the invention a palm and blanking plate assembly is formed by
adapting a solid state friction stir welding process, which replaces the prior art
process of welding with conventional MIG / TIG welding. The inventive method
produces under optimum conditions welds of high quality without defects
associated with the arc welding method there by increasing the acceptability rate
of the welds made. The method eliminates the steps of edge preparation of the
palm plate as required in the MIG/TIG welding, and further eliminates the need
for the welding consumables such as the filler wire and the shielding gas. The
inventive process increases the productivity due to its faster single pass welding,
and produces good surface appearance of the weld. The method does not
require the time consuming and cumbersome steps of cleaning of the contacting
surfaces of the joint prior art to welding as well as during welding. The new
method does not require highly skilled man power for welding, and produces no
distortion.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure -1 Schematically shows a prior art welding sequence for joining a
banking plate and a palm plate by adapting conventional arc
welding procedure.
Figure - 2 Schematically shows a T-joint weld structure formed according to
the invention by adapting an improved friction stir welding
procedure
Figure - 3 shows a known Friction stir welding system
Figure - 4 shows a friction stir welding process used for joining a blanking
plate and a palm plate according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
The power transmission from the generator to transformer requires bus ducts
made of aluminum alloys shells of varying configurations in a power station. The
circular shells are made out of thick Aluminum sheets, in which the palm and
blanking plate assembly (figure 1) is inserted. According to prior art, both the
palm and the blanking plate are welded by conventional arc welding. As shown in
figure-1, a first end of the circular shell is closed by a fillet welding (3) to a palm
and blanking plate assembly which consists of a circular blanking plate (1) and a

plurality of palms or vertical plates (2) to facilitate flow of current. The typical
blanking plate and palm assembly is shown in the figure 1. In the prior art, as
shown in Figure-1, the welding was done by Metal Inert Gas welding technique
or Tungsten Insert Gas welding technique which makes use of the arc heat to
fuse both the plate metal (1,2) including any extra metal through a filler metal in
the form of a wire in the weld area. Further, an inert gas shielding of argon is
provided to protect the weld metal from being contaminated from atmosphere.
This prior art welding requires a proper sequence to ensure a distortion-free
weldment of this assembly. Further, this method is being done at present
manually. Therefore, this prior art method of manufacturing is having the
disadvantages such as slow production, use of consumables such as argon and
filler wire, requirement of skilled manpower for performing welding, fatigue of
the operator and fumes from the weld environment. This calls for a simpler and
faster method of manufacturing of palm to blanking plate assembly.
Figure-3 shows a Friction Stir Welding (FSW) system, which includes a tool (7)
having a shoulder (6) and a pin (5). The Pin (5) extends from the shoulder (6)
upto a substantial length depending on the plate thickness. The tool rotates (9)
and is forced (10) into the material below the joinable surface generating a
frictional heat. As the tool (7) traverses (8) along an weld seam (12), an weld
(11) is produced. Figure-2 shows a welding process according to the invention
which enables to form a T joint for palm to blanking plate assembly. A friction
stir welding process as illustrated in figure-3 is used to the join the palm plate to
blanking plate as shown in the figure-4.

The FSW system as illustrated in figure-3, according to the invention is provided
with a control device that directs the tool (7) and pin (5) to rotate (9) for
performing an FSW operation. During the welding operation, the palm plate (1)
and blanking plate (2) are positioned and retained firmly by a fixture 13, as
shown in figure-4, where an inner surface of the blanking plate (2) rests on the
palm plate (1). The tool (7) and pin (5) of the FSW system are positioned above
the palm plate (1) and aligned as per the assembly. The FSW system directs the
tool (7), and the pin (5) correspondingly rotates (9) and move downwards (10)
towards the top of the blanking plate (2). On further advancement of the tool
(7), the pin (5) contacts the blanking plate (2) and generates a frictional heat.
This heat plasticizes the material around the pin (15). This operation continues
until the tool shoulder (6) touches the blanking plate (2). The plunging of the
tool (7) is stopped and the tool (7) traverses along the length of the palm (2).
The plasticized material around the pin (5) swirls and fuses the contacting
surfaces at an intersection (4) of the joint together.

WE CLAIM
1. An improved friction stir welding process to form a plate-to-plate Tee joint
for transmission of current in power generation plant, the process
comprising the steps of:
- providing a friction stir welding system (FSWS) having at least one
rotatable tool comprising a shoulder including a pin, and a control means
to monitor and direct the rotational and transitional movement of the tool;
- locating a palm plate and a blanking plate such that an inner surface of
the blanking plate rests on the palm plate;
- fixing the palm plate and the blanking plate in said located position by
adapting a fixture;
- placing the fixture on the FSWS such that the tool is positioned above the
top surface of the palm plate;
- rotating the tool including pin and causing the tool to move towards the
top of the blanking plate after penetrating the palm plate;
- advancing the tool further downward so as to contact the blanking plate
to generate a frictional heat which plasticizes the base material around the
pin;

- continuing the advancement of the tool till the shoulder of the tool firmly
touches the blanking plate; and
- allowing a swirling and a fusion of the material around the pin which joins
the contacting surface of the palm and the blanking plate at an
intersection.
2. An improved friction stir welding process to form a plate-to-plate Tee joint
for transmission of current in power generation plant as substantially
described and illustrated herein with reference to the accompanying
drawings.

The invention relates to an improved friction stir welding process to form a plate-
to-plate Tee joint for transmission of current in power generation plant, the
process comprising the steps of providing a friction stir welding system (FSWS)
having at least one rotatable tool comprising a shoulder including a pin, and a
control means to monitor and direct the rotational and transitional movement of
the tool; locating a palm plate and a blanking plate such that an inner surface of
the blanking plate rests on the palm plate; fixing the palm plate and the blanking
plate in said located position by adapting a fixture; placing the fixture on the
FSWS such that the tool is positioned above the top surface of the palm plate;
rotating the tool including pin and causing the tool to move towards the top of
the blanking plate after penetrating the palm plate; advancing the tool further
downward so as to contact the blanking plate to generate a frictional heat which
plasticizes the base material around the pin; continuing the advancement of the
tool till the shoulder of the tool firmly touches the blanking plate; and allowing a
swirling and a fusion of the material around the pin which joins the contacting
surface of the palm and the blanking plate at an intersection.