FIELD OF INVENTION
The invention relates to the field of welding of tube to tube sheets in general,
and to the method of joining tube to tube sheets without filler metal addition
using heat generated through a friction process, in particular.
BACKGROUND AND PRIOR ART
Heat exchangers are components that are used for transfer of heat from one
medium to the other. This is done through the use of tubes and tube sheets.
Heat exchangers are fabricated using thin walled tubes that are connected to a
tube sheet that is having a higher thickness as compared to the tubes. This is
achieved through a welding process without the addition of filler metal. Normally
one or two passes of mechanized welding is employed for completing a single
weld joint. This dissimilar thickness joint welding is normally achieved through
the use of fusion welding processes especially tungsten inert gas welding. This
fusion welding processes involve a high heat input that melts the faying edges of
the joint to form a weld pool which on solidification forms the weld. This method

of welding is prone to defects related to the melting and solidification of metal as
well as the influence of the surrounding atmosphere. The defects involved
normally are porosity, cracks and oxidation. When such defects occur in the weld
in the tube to tube sheet joints it becomes difficult for repairing them since the
thickness of the tube involved may be extremely thin of the order of 0.6 mm.
The defect sizes are bigger than the thickness of the tubes joined. This causes
relatively considerable amount of metal to be removed and normally require a
manual welding to be employed for the repair. In order to overcome these
difficulties a new method of friction forge welding has been developed through
this invention. This process of friction forge welding is a solid state welding
technique that does not involve melting of the faying edges to be joined.
STATE OF ART
United States Patent No. 4403135, discloses a method of arc welding.
Specifically, a method of pulsed DC arc welding is disclosed wherein the pulse
width of the current pulses are modulated to maintain a constant time averaged
power flow to the work pieces being welded. This method of arc welding is
especially useful with a type of pulsed DC arc welding wherein the ratio of peak
current to maintenance current is maintained at a selected high value and the
current is cycled in a time duration whereby oxides on the surface of the work
pieces are dissipated as the weld is made. When used with this type of pulsed

DC arc welding the present method is especially suited for fluxless welding of
aluminum work pieces, such as thin wall aluminum tubing used in making heat
exchangers for air conditioning systems.
The patent search on Aluminum tube to tube sheet welding did not yield any
results.
OBJECTS OF THE INVENTION
The following are the objects of invention to overcome the drawbacks of the
prior art:
An object of the invention to propose an improved welding method using a non
consumable rotating tool that generates the necessary heat energy for joining of
the materials.
Another object of the invention is to propose an improved method of welding
that utilizes frictional heat energy for raising the material to plastic state.
Yet another object of the invention is to propose an improved method of welding
in which the plasticized material is forged by the applied force to form the weld.

Still another object of the invention is to propose an improved method of
welding, which is capable of achieving faster job completion rate.
DESCRIPTION OF INVENTION
Tube to tube sheet welding invokes the use of conventional fusion welding
techniques. These techniques require consumables either in the form of filler
metal or gas. The conventional fusion welding techniques are prone to defects
originating from fusion and solidification of molten metal. The new invention
addresses these factors. Only a solid rotating tool and a mechanism for
application of required pressure is all that is necessary for creating the required
heat and simultaneous forging process to complete the welding. Thus the joint is
welded throughout its entire length simultaneously. No consumables are
required. In addition, the process is fast leading to high productivity.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - illustrates the typical arrangement of the components to be welded
according to the invention of friction forge welding of tube to tube sheets
Fig.2 - illustrates a method according to the invention of friction forge welding of
tube to tube sheets

DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described with the help of accompanying drawings
which depict an exemplary embodiment of the invention. However, there can be
several other embodiments, all of which are deemed covered by the description.
As shown in Fig-1, the arrangement of the components for the welding
comprises of a thick section component (1) in which a thin walled tube (2) is
placed inside a hole drilled in component (1) such that the tube is firmly located
in the position. Fig-1 shows the arrangement of the component before welding.
As shown in Fig-2, arrangements for welding comprises the component to be
welded (1,2). A solid welding tool (3) made of suitable material is rotated by a
prime mover (4). The speed of the prime mover can be varied according to the
requirements of welding. The tip of the tool is shaped to match the inside
diameter of the tube (2). Depending on the joint configuration, the middle
portion of the tool (3) has a shape which can be flat or inclined as indicated in
Fig-2. The prime mover and the tool can be moved along their axis by a linear
actuating device (6). In order to carry out the welding, the arrangement of the
tool (3) prime mover (4) and the linear actuator (5) are located axially and
concentrically above the tube (2).

The prime mover (4) rotates the tool (3) at the pre-determined speed and the
actuator (5) moves the prime mover (4) and the tool (3) towards the tube (2)
and the thick section component (1). The tip of the tool (3) enters to tube (2)
and as the tool contacts the tube (2) under axial pressure from the linear
actuator (5), necessary heat for welding is generated by the frictional force
between the rotating tool (3) and the tube (2) thick section component (1). As
the temperature rises due to frictional heating, the tube and the thick section
component are brought to their plasticizing temperature. The tool advances
further axially into the tube, the plasticized material flows out until the flat
portion of the tool (3) touches the torch surface of the thick section of the
component (1). At this point, the advancement of the tool is stopped and it is
withdrawn from the tube. The plasticized material of the tube (2) and the thick
section component (1) in contact of the tool (3) before it is withdrawn solidifies
to form the weld (6) joining the thick section component (1) and the tube (2).
As described above, this method of invention is used for welding of circular joints
of different configurations where outer component can be thicker and the inner
component is thinner in section.

WE CLAIM
1. A method of friction forge welding of aluminum tube to tube sheet joints
comprising the steps of:
- rotating the tool (3), made of material in accordance with the material to
be welded, at pre-determined speed of revolution by the prime mover (4);
- forwarding of the tool (3) by the linear actuator (5) to come in contact
with the material to be welded;
- heat generation by the rotating tool (3) under pressure exerted by the
linear actuator (5) plasticizing the material to be weided that is in contact
with the tool;
- forwarding of the tool (3) to desired depth;
- withdrawal of the tool (3) from the material being welded;
- cooling of the plasticized material to form the weld
wherein frictional heat energy generated under pressure by a non-
consumable rotating tool (3), is utilized for raising the material to plastic state
and the plasticized material in contact of the tool is forged to solid state weld
(6) joining the thick section of the component (1) and the tube (2) in short
time without melting the faying edges to be joined and eliminating the need
of any consumables.

2. The method as claimed in claim 1, wherein a non consumable tool which
has a higher melting point than the material being welded is used.
3. The method as claimed in claim 1, wherein the joint is welded throughout
its entire length simultaneously.
4. The method as claimed in claim 1, wherein the welding is used in any
position.
5. The method as claimed in claim 1, wherein the welding is carried out
without the need for consumables like filler wire or shielding medium.
6. The method as claimed in claim 1, wherein the welding is carried out for
different configurations of circular joints.
7. The method as claimed in claim 1, wherein the welding can be utilized for
different materials like steel, stainless steel, copper, etc. with tool (3)
made of material having higher softening temperature than the material
welded.
8. A device to carry out the method of friction forge welding of aluminum
tube to tube sheet joints, as claimed in claim 1, consisting:

- a solid welding tool (3);
- a prime mover (4); and
- a linear actuator (6)
9. The device as claimed in claim 8, wherein the solid welding tool (3) is
rotated by a prime mover (4) at a variable speed according to the
requirement of welding.
10.The device as claimed in claim 8, wherein the welding tool (3) has a tip,
shaped to match the inside diameter of the tube (2).
11.The device as claimed in claim 8, wherein said linear actuator (5) actuates
linearly the welding tool (3) driven by a prime mover (4) towards the tube
(2) and thick section of the component (1).

A method of friction forge welding of aluminum tube to tube sheet joints
comprising the steps of rotating the tool (3), made of material in accordance
with the material to be welded, at pre-determined speed of revolution by the
prime mover (4); forwarding of the tool (3) by the linear actuator (5) to come in
contact with the material to be welded; heat generation by the rotating tool (3)
under pressure exerted by the linear actuator (5) plasticizing the material to be
welded that is in contact with the tool; forwarding of the tool (3) to desired
depth; withdrawal of the tool (3) from the material being welded and cooling of
the plasticized material to form the weld.
The invention also relates to a device for the above method.