Field of the invention
The present invention relates to a process of butt welding of materials. The
invention; particularly relates to a process of welding using the friction heat
generated between two relatively moving surfaces under pressure. More
particularly the invention relates to an improved tool for carrying -out friction stir
welding of non-ferrous plates of higher thickness.
Background of the invention
r
Friction stir welding utilizes the frictional heat generated between a non
consumaDie rotating tool and the materials to be joined to create a sound butt
weld. This technique: is used for making butt joints. The effectiveness of
obtaining a defect free weld joint using a rotating tool is largely influenced by the
configuration of the tool including the welding parameters like the RPM of the
tool and the rate of advancement of the tool.
Conventional welding techniques make use of energy sources to create a molten
pool to form the required weld. The process of creating a molten pool raises the
temperature of the weld including the surrounding area to a high temperature
which indeed affects the property of the weld. Further, in most of the arc
welding procedure, a separate filler material'is generally required for welding of
medium thickness plates.
The publication titled 'Welding On A Machining Center', by Peter Zelinski ; MMS
Online, October 2002, Gardner Publications, Inc, discloses a friction stir welding
procedure in which a plurality of parallely disposed machined fins are separately
provided which dissipate the heat conducted to a tool from the friction interface
generating the heat necessary for plasticizing the material to be joined to
produce a weld.
Patent Up. US6676004 discloses a tool pin configured in the form of a close
pitched threads for controlling the flow of the material plasticised by the heat
generated by friction between the conducting surfaces in relative motion under
pressure
However, none of the prior art describes a friction stir welding process applicable
to non-ferrons members of higher thickness which can economically produce
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defect-free weld joints by adapting a simple tool which is cheap and has larger
operating life.
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Objects of the Invention
It is an object of the present invention to propose an improved tool for carrying
-out friction stir welding of non-ferrous plates of higher thickness which is
capable of dissipating the heat transmitted to it from the interacting surfaces of
the tool and the materials to be joined.
Another object of this invention is to propose an improved tool for carrying -out
friction stir welding of non-ferrous plates of higher thickness which has means
for homogenious transportation and distribution of plasticised material generated.
by the heat to fill a cavity formed by the tool.
A further object of the invention is to propose an improved tool for carrying -out
friction stir welding of non-ferrous plates of higher thickness which creates a
joint without voids consistently.
A still further object of the invention is to propose an improved tool for carrying
-out friction stir welding of non-ferrous plates of higher thickness which is
simple, economic and haying larger operating life.
SUMMARY OF THE INVENTION
Accordingly, in one aspect of the invention there is provided an improved tool for
carrying-out friction stir welding of metal plates of higher thickness comprising: a
tool body in the form of a cylindrical shank, a lower end of the shank acting as
an operating end provided with a pin, and a shoulder configured in a shape of a
spiral to allow flow_of plasticised_rnateriaLwhen formed towards.the center of the
pin. The pin is provided with a helical flute which acts in combination with the
spiral. Atleast one spiral fin being provided at the operating end for
homogeneous dissipation and conduction of generatable heat during the process
of welding, towards an upper end of the tool.
The invention in a second aspect provides a process which makes the use of
heat generated by the friction between two relatively moving surfaces under
pressure to create the required weld. In this method, the improved tool is
touchably rotated to create the necessary frictional heat. The temperature of the
material under the rotating tool is raised to an extent where the material can
flow plastically under pressure. The flow of plasticised material creates a
metallurgical bond like any typical fusion welding procedure and exhibits weld
characteristics, superior to that of the fusion welded joints achieved through
typical process.
Brief description of the accompanying drawings
Fig-1 A schematic diagram of the improved tool according to the invention.
Fig-2 showing a view of the tool from the pin side, indicating the helical flute on
the tool shoulder.
Detailed description of a preferred embodiment of the invention
. As shown in figure 1, the improved tool for friction stir welding of materials has a
cylindrical shape with a pin shaped tip (5) at an operating end. The operating
end of the] tool is so configured to allow a smooth flow of the plasticised material
upto the rear end of the tool for creating a weld without any discontinuities. The
tool has a shank (1) and a shoulder (2). The pin (5) has a single square helical
flute (6) running through out its length from top to bottom of the pin (5). The
shoulder (2) is shaped in; the form of a spiral (3) to enable the material flow
towards the center of the pin (5). The spiral configuration including the single
square flute (6) in the pip (5) enables the required movement of the plasticised
material to create a defectless joint to be made. The tool may also use plurality
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of flutes depending on topi dimensions. The operating end of the tool has also
been provided with a plurality of spiral fins (4) for dissipating the heat generated
during the welding and conducting the heat upwards in the tool. The tool is
insertable in a tool-holder of a friction-welding machine.
The improved tool is particularly suitable for friction butt welding of materials.
The tool is provided with different profiles at one end of the shank (1), and, at
the operating surface of the tool shoulder (2), and the pin projecting below the
operating surface of the tool shoulder (2). The heat generated due to friction
between the contacting surfaces of the tool and the members to be joined
enables the plasticised material to be produced. The profiles (3) on the shoulder
(2) and the pin (5) enables proper churning of the plasticised material to create a
weld joint: as the tool progresses along the line of the welding. The frictional heat
generated at the contacting surfaces of the tool and the material to be welded is
dissipated to the material! to be welded, and to the rotating tool used for creating
the weld, The heat dissipated into the rotating tool progressively raises the
temperature of the operating end (4) of the tool. The wear and tear of the tool is
also dependent on the temperature generated and sustained by the tool. This
requires the tool to be maintained at lower temperature as feasible. The
operating efficiency is enhanced by the profiles provided on the operating
surfaces of the tool and the special profiles on the tool shank. The tool has an
integrated pin but can also use a replaceable pin with suitable retaining studs.
The helical square flute at one end of the tool shank that forces the ambient air
to flow through the helical flute increases the effectiveness of the cooling of the
tool. The tool has a concave shoulder, which has a profiled shoulder surface
configured as a groove (square or round) spiraling inwards towards the central
axis of the tool. The .'invention enables the plasticised part of the material from
the surfaces in contact with the shoulder of the tool to be radially transported
towards the pin located at the center of the tool, particularly when the direction
of rotation of the tooi is rightly selected. The pin has spiral flute extending from
the top of the pin to its bottom. The invention further enables the plasticised
material from the parts being joined, to be transported to the bottom and rear of
the tool. Such a movement of the materials including the compressive action of
the rear end of the suitably inclined tool, results in the formation of a void free
weld.i
WE CLAIM
1. An improved tool for carrying-out friction stir welding of metal plates of
higher thickness comprising:
- a tool body in the form of a cylindrical shank (1), a lower end of the shank
(1) acting as an operating end provided with a pin (5); and
- a shoulder (2) configured in the shape of a spiral (3) to allow flow of
plasticized material when formed towards the center of the pin (5),
characterised in that the said shoulder (2) configured in the shape of a
spiral (3) and the said pin (5) is provided with a helical flute (6) which
acts in combination with the spiral (3) enables homogeneous dissipation
of plasticized material when formed towards the centre of the pin (5) and
in that at least one spiral fin (4) being provided at the operating end of
the tool for homogeneous dissipation and conduction of heat generated
during the process of welding towards an upper end of the tool.
2. The tool as claimed in claim 1, wherein the operating end of the tool is
touchably placed on joinable members and rotated.
3. The tool as claimed in claim 1 or 2, wherein the top end of the tool is
inserted on a tool-holder of a friction-welding machine.
4. The tool as claimed in claim any of the proceeding claims, wherein the
tool is caused to rotate on the surface of the joining members, the
generated friction heat at the contacting surfaces raising the temperature
of the materials to transform a portion to a plasticised condition, and
wherein the shoulder (2) and the pin (5) enables churning of the
plasticised material to create a weld-joint in correspondence to an
advancement of the tool along the line of welding.
5. An improved tool for carrying-out friction stir welding of metal plates of
higher thickness as substantially described herein with reference to the
accompanying drawings.

An improved tool for carrying-out friction stir welding of metal plates of higher
thickness comprising a tool body in the form of a cylindrical shank (1), a lower
end of the shank (1) acting as an operating end provided with a pin (5); and a
shoulder (2) configured in the shape of a spiral (3) to allow flow of plasticized
material when formed towards the center of the pin (5), characterised in that the
said shoulder (2) configured in the shape of a spiral (3) and the said pin (5) is
provided with a helical flute (6) which acts in combination with the spiral (3)
enables homogeneous dissipation of plasticized material when formed towards
the centre of the pin (5) and in that at least one spiral fin (4) being provided at
the operating end of the tool for homogeneous dissipation and conduction of
heat generated during the process of welding towards an upper end of the tool.