FIELD OF INVENTION
The invention generally relates to an apparatus and process for welding of
bifurcates. More particularly, the invention relates to a lathe type welding fixture
with double end drive for aligning the irregularly shaped bifurcates and rotating
at preset speed to enable mechanized welding. The invention further relates to a
change of welding process whereby the number of start stops is reduced and
provides improved productivity and quality.
BACKGROUND OF THE INVENTION
Bifurcates involved in power boilers are produced by joining a U-tube to an
irregularly shaped tube by arc welding. At the center of the U-tube, a hole of
diameter matching to the ID of the irregularly shaped tube is drilled and then
pullout operation is done to create sufficient material for edge preparation. After
pullout, edge with lip is prepared by machining. The joint configuration thus
created is similar to a tube-to tube butt joint. However the joint configuration at
the U-tube side is not uniform and the joint is dissimilar in shape. The irregularly
shaped tube with pre bend is 2.5 m in length and the U-tube is 0.5 m in length.
The dissimilar shape of the weld joint and longer length of the parts makes the
welding operation difficult. Bifurcate joints are welded manually employing

Tungsten Inert Gas [TIG] for root pass and Shielded Metal Arc Welding [SMAW]
for filler passes. The parts being joined have irregular shape and joint itself is
asymmetrical in geometry. Due to these reasons the manual welding becomes
difficult and time consuming. At least two helpers are needed to hold the job
while the welder is engaged in welding. Thus the productivity is low and the
defect rate is also significant. TIG and SMAW are low productive processes.
Manual positioning and manipulation of the job further reduces the welding
speed. TIG root pass with wave form controlled Gas Metal Arc Welding [GMAW]
Filler pass improves the quality and productivity.
Hence there exists a need to invent a fixture and the process for the same which
eliminates disadvantages of prior art.
OBJECTS OF THE INVENTION
Therefore it is an object of the invention to propose a lathe type rotating fixture
for welding bifurcates which eliminates the disadvantages of prior art.
Another object of the invention is to propose a lathe type rotating fixture for
welding bifurcates which makes the welding process simpler and fast.
A still another object of the invention is to propose a lathe type rotating fixture
for welding bifurcates which is capable of performing the process with reduced
manpower.

A further object of the invention is to propose a lathe type rotating fixture for
welding bifurcates which enables to lower down the defect rate significantly.
A still further object of the invention is to propose a lathe type rotating fixture for
welding bifurcates which is capable of improving the productivity and quality.
SUMMARY OF THE INVENTION
Accordingly, in the present invention a lathe type rotating welding fixture holds
and rotates the geometrically irregular bifurcate components at preset speed and
is also equipped with foot pedal switch facilitating easy access to the joint and
mechanized manipulation of the job. The head and tail stocks of the fixture
makes a synchronous rotation through a motor and drive shaft. The head stock
fixture holds the U-tube while the tail stock fixture holds the long tube. A
supporting platform supports the job during alignment and tack welding. The
welder actuates a foot pedal switch to control the process during welding.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig.1- shows an embodiment of the improved system according to the
Invention

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
In the present invention, the welding lathe with double end drive with special
holding fixtures at head and tail stocks to align the geometrically irregular
components and the hydraulically actuated joint supporting fixture makes the
welding easier. Further introducing pulsed GMAW process in place of SMAW
further increases the quality and productivity.
Referring now to the drawings wherein like reference numerals designate
identical or corresponding parts throughout the description. Fig.1 shows the
schematic of the lathe type rotating fixture for welding of bifurcates. In the
system, the fabricated lathe (1) structure supports the head stock (2) and tail
stock (3). The lathe type rotating fixture is equipped with a double end drive,
with the power from the motor (5) transmitted to the head and tail stocks
through a common drive shaft (4) to have a synchronous rotation at head and
tail stocks. The head stock fixture (6) holds the U tube of the components and it
is provided with adjustable screws for mechanical adjustments for centering and
aligning the bore of the U tube with respect to the long tube. The tails stock
fixture (7) holds the long tube with eccentric bend and aligns it with the U tube.
It is provided with radially adjustable slots for accommodating different
eccentricity of the long tubes. The power from the drive shaft is transmitted to

the head and tail stocks through the sprocket and pulleys (10) available at both
ends of the lathe. The rotation speed and forward and reverse direction change
is regulated through the controller (8). A hydraulically actuated supporting
platform (11) with adjustable stroke length located just below the joint supports
the job during alignment and tack welding. The platform will withdraw once the
welding operation is started to make way for full welding of the job. A foot pedal
switch (9) located ergonomically enables the welder to have full control over the
process during welding.
Two process combinations are established for the bifurcate welding. TIG root
pass with GMAW filler pass welding. Alternately root and filler passes by wave
form controlled GMAW process.
The advantages of the invention can be seen, inter alia, in the fact that the lathe
type rotating fixture for welding of bifurcates produces improved weld quality
and productivity.

WE CLAIM
1. A lathe type rotating fixture for welding bifurcates characterised in that;
a fabricated lathe (1) structure having a head stock (2) and a tail stock (3)
at two ends;
a motor (5) and a drive shaft (4) for transmitting synchronous rotation to
head stock (2) and tail stock (3);
at least one sprocket and pulley (10) for transmitting the power of drive
shaft to head stock (2) and tail stock (3);
a head stock fixture (6) for holding the U tube;
a tail stock fixture (7) for holding the long tube with eccentric bend and
for aligning with the U tube;
a supporting platform (11) for supporting the job during alignment and
tack welding;
a controller (8) for regulating the speed and direction of rotation of head
stock (2) and tail stock (3); and
a foot pedal switch (9) is operated to control fully the process of welding.
2. A lathe type rotating fixture for welding bifurcates, wherein the head stock
fixture is provided with mechanical adjustments for centering and aligning
the bore of the U tube with respect to the long tube.

3. A lathe type rotating fixture for welding bifurcates, wherein the platform
(11) is hydraulically operated.
4. A lathe type rotating fixture for welding bifurcates, wherein the tail stock
fixture (7) is provided with a plurality of radially adjustable slots.
5. A lathe type rotating fixture for welding bifurcates, wherein the head stock
fixture (6) is provided with a plurality of adjustable screws for mechanical
adjustments.
6. A lathe type rotating fixture for welding bifurcates as substantially
described and illustrated herein with reference to the accompanying
drawings.

A lathe type rotating fixture for welding bifurcates consists of a fabricated lathe
(1) structure having a head stock (2) and tail stock (3) at two ends. A motor (5)
and a drive shaft (4) transmit a synchronous rotation to the head stock (2) and
tail stock (3) through sprocket and pulley (10). A head stock fixture (6) holds the
U tube while a tail stock fixture (7) holds the long tube with eccentric bend and
actuates the alignment with the U tube. A supporting platform (11) supports the
Job during alignment and tack welding. A controller (8) regulates the speed and
direction of head stock (2) and tail stock (3) when a foot pedal switch (9)
operates and controls fully the process of welding.