FIELD OF INVENTION
The invention generally relates to a method of welding a Tee joint formed by two
or more members assembled together. More particularly, the invention relates to
an improved friction stir welding process enabled to form a Tee joint covering
the entire abutting surface of two or more components.
BACKGROUND OF INVENTION
Prior art provides several welding processes for Welding Tee joints for example,
different types of arc welding, resistance welding, flash butt welding, electro slag
and electro gas welding. The selection of a welding process depends on the
material composition of the joinable components including their thickness.
Depending upon the selected welding process, the edge preparation or use of a
filler material is decided. The known friction stir welding process joins the
components in a solid state. Tee joints of different joint configurations can be
efficiently made by the friction welding process. Welding techniques including
process parameters vary corresponding to the joint configuration. Different
techniques require different levels of forces and power for carrying out the
friction stir welding process. Further, the productivity requirement, type of joint,
machine and/or process parameters, post weld dressing and other specific
requirements of the joint, are the influencing factors towards selection of a
welding technique to be adapted.
European Patent No EP 20022919 A2 : describes a process for welding of hollow
sections involving welding of TEE sections or Tee joints. This patent addresses
the development of a tool that penetrates both the components to be joined.
The tool is profiled in such a way that a complete fusion of the joint interface in
a single pass can be achieved.

European Patent No. EP 1 498 21 Bl: discloses a Friction stir welded T joint
assembly and the method of forming such a T joint assembly. The invention
addresses some of the disadvantages associated with known Friction stir welding
techniques. In particular, this invention provides a solution to the problems
associated with forming the friction stir welded Tee joints between relatively thin
walled ribs and skin sheets. The invention further teaches the tooling required
for friction stir welding of such an assembly.
The prior art friction stir welding process warrants that the friction forming tool
be penetrated through both the joinable components to create a weld by stirring
the plasticized material. In this prior art technique, the tool penetrates to a
substantial depth below the joint interface, which increases the weld time, forces
required to be applied, higher machine capacity, enhances the possibility of tool
or fixture damage.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved friction Stir welding process enabled
to form a Tee joint covering the entire abutting surface of two or more
components. In the improved process, the friction stir welding process allows the
tool pin to penetrate only the top member such that the tip of the tool pin
reaches very close to the top surface of the underlying second member. Heat
generated by the tool, plasticizes the material around the tool pin including a
substantial amount of the material below the tool pin. This causes the material
around the joint interface to be fused together to form a weld.

The inventive process ensures a complete welding of the abutting surfaces of the
joint (cross section of the web as shown in figure 1) The joint below the tool is
welded mainly by the heat generated due to rotation of the tool pin including
swirling of the plasticized material under the tool pin. According to the invention,
only a fully abutting joint is required to make a complete weld. The process does
not require the bottom plate (web) to be penetrated. Only the top plate is to be
penetrated to a required depth depending upon its thickness, thus enables the
welding tool to be traversed only within the top plate (flange). The process
involves a simplified programming of the tool travel from start to finish. The
process further enables multiple joints to be welded in a single sequence when
required with one start and one stop for multiple welds. The quantum of post
weld dressing is reduced due to lesser number of starts. Due to optimization of
the tool configuration, the length of the tool (heat generating portion) gets
reduced. The innovative process enables welding of a given flange thickness with
the web with reduced forces. According to the invention, the welding productivity
gets enhanced. The tool cost and tool wear is reduced due to application of
lower force including lesser penetration. The process is enabled to employ both
monolithic as well as retractable pin tools, and can be adapted for other Tee joint
configurations, and other weld configurations like corner joint, and lap joint. The
inventive process is implementable with lower consumption of power.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved friction stir
welding process enabled to form a Tee joint covering the entire abutting surface
of two or more components, which eliminates the disadvantages of prior art.
Another object of the invention is to propose an improved friction stir welding
process enabled to form a Tee joint covering the entire abutting surface of two
or more components, which reduces the applied force on the job by the tool to
form a good weld quality.
A still another object of the invention is to propose an improved friction stir
welding process enabled to form a Tee joint covering the entire abutting surface
of two or more components, which allows a continuous welding with reduction in
number of start and stops where multiple adjacent joints are welded.
Yet another object of the invention is to propose an improved friction stir welding
process enabled to form a Tee joint covering the entire abutting surface of two
or more components, which reduces the quantum of post weld processing and
dressing.
A further object of the invention is to propose an improved friction stir welding
process enabled to form a Tee joint covering the entire abutting surface of two
or more components, which enables reduction in cost by way of lesser power
requirement and adaptation of a dimensionally optimized tool.

A still further object of the invention is to propose an improved friction stir
welding process enabled to form a Tee joint covering the entire abutting surface
of two or more components, which is easy to implement being designed with a
simplified programming of the welding operation.
Yet further object of the invention is to propose an improved friction stir welding
process enabled to form a Tee joint covering the entire abutting surface of two
or more components, which reduces the risk of tool damage including damage to
the fixture.
Another object of this invention is to propose an improved friction stir welding
process enabled to form a Tee joint covering the entire abutting surface of two
or more components, which provides a consistently good quality of the joint.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Schematically illustrates the principle of operation of a friction stir
welding process according to prior art.
Figure 2 - Schematically illustrates the principle of operation of an improved
friction welding process to form Tee joints according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT OF THE INVENTION :
Figure 1 indicates the principle of a conventional friction stir welding of Tee
joints. A Tee joint assembly is formed by a flange (1) and a web (2) is along the
entire interface (5). The Tee joint assembly may include one or more webs (2).
The Assembly is held together on a base (B) by a fixture (F) schematically
indicated, and tightly fixed by clamps (C). The forming tool comprises a shank
(3), and a tool pin (4) which is placed above the joint and rotated in
anticlockwise direction (TR). A vertical force (VL) is applied on the tool. As the
pin (4) touches the top surface of the flange (1), a frictional heat is generated
which plasticizes the material of the top component around the pin (4). The pin
(4) penetrates the flange (1) including a substantial depth of the web (2). The
plasticized material is stirred and as it cools down, a weld (6) is formed.
Figure 2 indicates the principle of operation of the inventive friction stir welding
process for Tee joints. According to the invention, a tool comprising a shank (3)
and a pin (4) is positioned above the joint interface to be welded. The length of
the pin (4) is optimized to be shorter than that of the tool for conventional
friction stir welding technique. The pin (4) is allowed to penetrate the flange (1)
until the tip of the pin (4) reaches very close to but above the top surfaces of an
interface (5), of the top and bottom component to be welded. The heat
generated by the pin (4), plasticizes the material around the pin including a
substantial quality of material below the interface (5). The pin (4) does not
penetrate the web (2). A sound weld (6) is thus created between the flange (1)
and the web (2) around the interface (5). The depth of the weld (6) is lesser
than that obtained through the previous technique as indicated in Figure 2.

WE CLAIM :
1. An improved friction stir welding process enabled to form a Tee joint
covering the entire abutting surface of two or more components,
comprising the steps of:
- providing a base (B);
- disposing horizontally an upper component (1) to be joined;
- arranging a joinable lower component (2) vertically to be entirely
interfacing with the upper component (1);
- providing a fixture (F) to hold together both the upper and lower
components (1,2) to form an assembly;
- firmly holding the assembly by providing suitable clamps (C) at each end;
- arranging a friction stir welding machine such that the welding tool (4) is
positioned just above the welded joint to be formed;
- allowing the tool to commence rotation and gradually touch the upper
component (1) at an intended location for welding;

- continuing the tool rotation till the tool penetrates the upper component
(1) and reaches close to but without touching the interface (5) of the two
components (1,2);
- applying a vertical force (VL) on the tool (4) which on touchingly
generates heat, the generated heat plasticizing the material around the
tool (4) including a substantial amount of material below the interface (5);
and
- forming the weld joint (6) by stirring the plasticized material (4) and
allowing the stirred material to cool down.
- The process as claimed in claim 1, wherein the tool (4) is rotated.

2. The process as claimed in claim 1, wherein the size of the tool, rotational
speed of the tool, and penetration depth is optimized based on
composition of the joinable materials, thickness of the materials, and the
associated process parameters including application requirements.
3. An improved friction stir welding process enabled to form a Tee joint
covering the entire abutting surface of two or more components,
comprising the steps of : providing a base (B); disposing horizontally an
upper component (1) to be joined; arranging a joinable lower component
(2) vertically to be entirely interfacing with the upper component (1);
providing a fixture (F) to hold together both the upper and lower
components (1,2) to form an assembly; fixing the assembly by

providing at each end with suitable clamps (C); arranging a friction stir
welding machine such that the welding tool (4) is positioned just above
the welded joint to be formed; allowing the tool to commence rotation
and gradually touch the upper component (1) at an intended location for
welding; continuing the tool rotation till the tool penetrates the upper
component (1) and reaches close to but without touching an interface (5)
of the two components (1,2); applying a vertical force (VL) on the tool (4)
which on touchingly heat, the generated heat plasticizing the material
around the tool (4) including a substantial amount of material below the
interface (5); and forming the weld joint (6) by stirring the plasticized
material (4) and allowing the stirred material to cool down as substantially
described and illustrated herein with reference to the accompanying
drawings.

The invention relates to an improved friction stir welding process enabled to
form a Tee joint covering the entire abutting surface of two or more
components, comprising the steps of : providing a base (B) disposing
horizontally an upper component (1) to be joined; arranging a joinable lower
component (2) vertically to be entirely interfacing with the upper component
(1); providing a fixture (F) to hold together both the upper and lower
components (1,2) to form an assembly; with suitable clamps(C); arranging a
friction stir welding machine such that the welding tool (4) is positioned just
above the welded joint to be formed; allowing the tool to commence rotation
and gradually touch the upper component at the intended location for
welding; continue the tool rotation till the tool penetrates the upper
component (1) and reaches close without touching to an interface (5) of the
two components (1,2); applying a vertical force (VL) on the tool (4) which on
touchingly generates heat, the generated heat plasticizing the material
around the tool (4) including a substantial amount of material below the
interface (5); and forming the weld joint by stirring the plasticized material
with the tool (4) and allowing the stirred material to cool down.