FIELD OF INVENTION
The present invention relates to the field of welding fabrication and welding
processes and in particular to solid state welding of thick walled tubes. More
particularly, the invention relates to a method for reducing the internal flash
generated during a solid state joining process of thick-walled tubes.
BACKGROUND OF INVENTION
This solid state welding, namely, Magnetically Impelled Arc Sutt (MIAS) welding,
is not in practice in India, except at Welding Research Institute (WRI). MIAS
welding is predominantly employed for joining of only thin walled tubes in
automobile components in European countries.
MIAS welding is a solid state joining process, similar to another solid state
welding process, namely, Flash Sutt Welding process. The only difference is that
the arc is magnetically impelled or rotated in MIAS welding whereas the arc is
not rotated in Flash butt welding. The rotation of arc in MIAS welding results in
uniform distribution of the arc including the heat energy and thereby facilitates
to achieve a consistent weld joint.
Due to limitations of technology and the SUbsystems like power sources,
magnetic elements, hydraulics and controls, the MIAS welding has so far been
used for joining of thin walled tubes and small diameter solid rods only.
However, at present, suitable subsystems are available to expand the application
window for MIAS welding. Accordingly, research is underway for making MIAS
welding amenable for joining of thick walled tubes and higher diameter solid
rods.
MIAS welding generally uses a straight butt joint design (Fig.!) at the faying
edges like in the case of Flash butt and Induction pressure welding. This joint
design is capable of producing acceptable welds with thin walled tubes.
However, during joining of thick walled tubes, straight butt joint design results in
higher flash volume at the internal sides of the tubes. Higher volume of internal
flash reduces the volume of medium flow in the tube assembly and thus
negatively affect the efficiency of the welded component or assembly.
The inventors of this disclosure observed that the internal flash can be controlled
by suitably modifying the joint design at the faying edges and the welded
assemblythen shall have the better utilization efficiency.
OBJECTIVES OF THE INVENTION
It is therefore an object of this invention to propose a method for reducing the
internal flash generated during a solid state joining process of thick walled tubes
for example, MIAS welding of thick walled tubes.
Another object of the invention is to propose a method for reducing internal flash
generated during a solid state joining process, for example, Flash butt or
Induction pressure welding.
A still another object of the invention is to propose a method for reducing the
internal flash generated during a solid state joining process, in which an
improvedjoint design at the faying edges of the tubes to be joined is adapted.
A further object of the invention is to propose a method for reducing the internal
flash generated during a solid state joining process, in which the volume of
medium flow can be improved at the joining portion in the inner diameter of the
tube assemblies.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure - 1 - shows a conventional joint design for MIAB welding which is known
as straight butt joint design.
Figure - 2 - shows a first embodiment of the "Internal Bore design" in which
the bore length and depth is varied to optimize the flash volume at
the internal diameter of the thick walled tubes that are to be
joined.
Figure - 3 - shows a second embodiment of the "Internal Chamfer design" in
which variations of chamfer length and width and in addition the
chamfer angle, allowable.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE
INVENTION
The proposed joint designs may be more appropriate for joining tubes with thick
wall sections, Le higher thickness than 3 or 4mm. The proposed joint designs in
this invention are suitable for mass production as well as batch production with
significant improvement in productivity.
As shown in Figure 1, MIAS welding of thick walled tubes with straight butt
welding joint design of prior art, results in higher volume of internal flash, i.e. a
higher volume of material, is ejected from the faying edges. This reduces the
effective internal diameter size at the weld zone adversely affecting the flow
volume of the working medium, namely steam in boiler tubes and liquid or gas in
processand automobile industries.
As shown in Fig. -2, a first embodiment of the invention describes an Internal
Bore design which is made by boring the internal diameter of the tube with a pre
determined bore length and depth. The bore size is directly related to the volume
of the flash to be controlled or reduced to obtain the desired optimum internal
diameter at the weld zone. MIAS welding with this joint design have been carried
out on sufficient number of tubes with the outer diameters (00) of the tubes
ranging from 40 to 60mm. The wall thickness of the tube varied from 4 to 8mm.
It is observed that minimum volume of flash is obtained with bore depth of 0.5
to 1.5mm, depending on the wall thickness. An optimum bore length is observed
to be in the range of 1 to 2.5mm for Internal Bore design.
As shown in figure - 3, a second embodiment of the invention, namely, Internal
Chamfer design in which chamfering at the internal diameter corner or edge with
a pre determined chamfer length and depth in combination with chamfer angle,
is carried-out. Dimensions of the proposed chamfer is directly related to the
volume of the flash to be controlled or reduced to obtain the desired optimum
internal diameter at the weld zone. The chamfer dimensions were optimized
based on the results obtained from a sufficient number of MIAS welding trials.
The optimum chamfer length is found to be 1.0 to 2.0mm, depending on the wall
thickness of the tubes to be joined by MIAS welding. A chamfer depth in the
range of 0.5 to 2.0mm results in an optimum internal flash. A chamfer angle
between 30 to 60degrees is found to provide, optimum results of internal flash in
the process of MIAS welding of thick walled tubes using the Internal Chamfer
design.
WE CLAIM:
1) A method of reducing the internal flash generated during a solid state
joining process of thick-walled tubes with a reconfiguration of internal
bore of the tubes, the method comprising the steps of:
- carrying out an internal bore configuration of the tubes with a bore
depth of 0.5 to 1.5 mm wherein the outer diameter of the tube and
the wall thickness of the tube varying respectively between 40 to
60mm, and 4 to 8 mm; and
- restricting the optimum bore length in the range of 1 to 2.5 mm.
2) A method for reducing the internal flash generated during a solid state
joining process of thick-walled tubes with an improved internal chamfer
design, the method comprising the steps of:
- chamfering at the internal diameter corner or edge of the tubes with a
predetermined chamfer length and depth including a chamfer angle;
wherein
- the predetermined chamfer length, the chamfer depth, and the
chamfer angle can be optimized respectively to 1.0 to 2.0 mm, 0.5 to
2.0 mm, and 30° to 60° depending on wall thickness for example 4 to
8 mm of the tubes.
3) A method of reducing the internal flash generated during a solid state
joining process of thick=walled tubes with a reconfiguration of internal
bore of the tubes as substantially described and illustrated herein with
reference to the accompanying drawings.
4) A method of reducing the internal flash generated during a solid state
joining process of thick-walled tubes with an improved internal chamfer
design, as substantially described and illustrated herein with reference to
the accompanying drawings.