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 and an apparatus for magnetically
impelled arc butt (MIAB) welding of different diameter tubes and rods.
BACKGROUND OF INVENTION
Magnetically Impelled Arc Butt (MIAB) welding is not in practice in India, except
at the Welding Research Institutes (WRI). MIAB welding is predominantly
employed for joining of only thin walled tube components in automobile
industries in European countries.
MIAB welding is a solid state joining process, similar to other known solid state
welding processes, namely, Flash Butt Welding process employed in power plant
manufacturing industries and joining of rails. The distinct difference between
these tow types of welding processes, is that the arc is magnetically impelled or
rotated in MIAB welding whereas the arc is not rotated in Flash butt welding. The
rotation of arc in MIAB welding results in uniform distribution of the heat energy
and thereby a consistent weld joint is formed
Due to limitations of technology and the subsystems like power sources,
magnetic elements, hydraulics and controls, the MIAB 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 extend the application
window for MIAB welding.
MIAB welding generally uses a straight butt joint design at the faying edges like
in the case of Flash butt and Induction pressure welding. The tubes to be joined
are clamped using a hydraulically operated clamping fixture. The clamping fixture
is split into one of upper and lower to facilitate loading / unloading of the tubes
before and after welding. One side of the fixture is static and the other one has a
provision to move in linear direction to transfer the upset force to realise the final
joining of the tubes. The clamping fixture, having an internal radius
corresponding to that of the outer diameter (OD) of the tubes to be joined.
Hence, it becomes necessary to have individual clamping fixtures for different
tube diameters. Frequent and case-to-case replacement of the clamping fixture is
however cumbersome and affects the alignment of the clamping fixture, and
finally the weld quality.
The inventors of this disclosure observed that an independent clamping fixture
can be configured to operate as an universal clamping fixture for welding of
different diameter tubes by MIAB welding. Such a development shall entail a
minimum modification of an existing main clamping arrangement.
OBJECTS OF THE INVENTION
It is therefore an object of this invention to propose an universal clamping fixture

to weld different diameter of tubes by MIAB welding, which eliminates the
disadvantages of the prior art.
Another object of the invention is to propose a method for configuring an
universal clamping fixture to weld different diameter by tubes of MIAB welding.
SUMMARY OF THE INVENTION
Accordingly, there is provided an universal clamping fixture for MIAB welding of
different diameter of tubes comprising a main clamp with inner radius varying in
correspondence with the outside diameter of the tube to be welded, the width,
length, and height of the main clamp being selected to maintain a ratio of 3:4:1;
the main clamp provided with a through-hole to flexibly fix the welding head to
allow axial including angular offset of the welded tubes; a collar with a radius
provided on either side of the main clamp to releasably fix on the welding head,
the outer radius of the main clamp is selected about equal to the height of the
clamp, the main clamp being configured with a plurality of holes to allow fixing of
at least one auxiliary clamp over the main clamp; and the at least one auxiliary
clamp having an outer radius and a length substantially equal to that of the inner
radius and length of the main clamp, the inner radius, the height and width of
the auxiliary clamp being selected in a ratio of 1:0.55:2, at least two
corresponding holes provided on the auxiliary clamp to fix the main clamp
beneath the auxiliary clamp, the auxiliary clamp being enabled for easy
replacement without deviating the alignment of the main clamp with the welding
head which remains permanently fixed with the welding head.

The invention provides a readily usable universal clamping apparatus for MIAB
welding of different tube diameters without alignment or adjustment of the
welding head after replacing or changing the auxiliary clamp.
The invention provides an universal clamping fixture which can replace auxiliary
clamp with two screws only for improving the machine availability in production
environment.
This invention is also applicable for other solid state welding processes like flash
butt and induction pressure welding of tubes.
The universal clamping fixture of the invention can be employed to weld pipes
also using MIAB, flash butt and other similar processes.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a main clamping fixture in a MIAB welding of tubes/rods, which
can be modified to configure an universal clamping fixture according to the
invention.
Figure 2 - shows a first embodiment of the "Universal clamping fixture",
specifically depicting an auxiliary clamping fixture.
Figure 3 - shows the "Universal clamping fixture" depicting a cross sectional
assembly of the main and auxiliary clamp.

Figure 4 - shows the assembly of the universal clamping fixture consisting of a
main and an auxiliary clamp in three dimensional form.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE
INVENTION
According to the invention, a Universal clamping fixture and a corresponding
method is provided for joining of tubes with thick wall section, i.e. higher
thickness than 3 or 4mm. The proposed universal clamping fixture is suitable for
MIAB welding of tubes with 30mm to 60mm OD.
Figure 1, shows the main clamping arrangement. The dimension of the inner
radius (R1) of the main clamp (01) corresponds to OD of the tubes to be welded,
with maximum 2 to 5% variation in OD. The inner radius (R1) varies according to
the OD of the tube to be welded. To avoid changing/replacing the clamping
fixtures depending on OD of the tubes, one main clamp (01) with 30mm inner
radius (R1) is selected as shown in figure 1. The width (W1) of the main clamp
(01) varies between 60 to 80mm and the length (L1) between 80 to 120mm. The
height (H1) of the main clamp (01) is 30 to 40mm and a through hole (D2) of 8
to 12mm diameter is provided to fix the main clamp (01) to the welding head. A
proper alignment is done after fixing the main clamp (01) to the welding head to
ensure acceptable axial and angular offset of the welded tubes. The alignment is
disturbed whenever the clamp is replaced. A collar with a radius (R3), and
thickness (T) is provided on either side of the clamping fixture for locating the

collar on the welding head. The outer radius (R2) of the main clamp (01) is
selected between 35 to 40mm. A plurality of fastening holes (D3) are provided in
the main clamp (01) to facilitate fixing of an auxiliary clamp (02). A counter-sunk
with diameter (D1) is configured on the main clamp (01).
Figure 2, shows an auxiliary clamping fixture (02). The outer radius (R4) of this
auxiliary clamp (02) is same as that of the inner radius (R1) of the main clamp
(01) as given in figure 1. Based on the OD of the tubes to be welded a plurality
of auxiliary clamps (02) are provided with inner (R5) radius varying between 15
to 27 mm with 3 to 4mm thickness. The width (W2) of the auxiliary clamp (02) is
between 30 to 40mm and the length (L2) is equal to that of the main clamp
length (L1).
The Height (H2) of the auxiliary clamp (02) is selected between 8 to 15mm. At
least two holes (D4) are provided for fastening the auxiliary clamp (02) with the
main clamp (01). Fastening of the auxiliary clamp (02) upon the main clamp (01)
does not disturb the alignment of the clamping fixture (01) with the welding
head. Hence the machine is ready for welding without any further alignment
during replacement / changing the auxiliary clamp (02) to weld any tube
between 30 to 60mm OD.
Figure 3, illustrates a universal clamping fixture for MIAB welding of different
tube diameter. The cross sectional assembly of the main clamp (01) and the
auxiliary clamp (02) and the overall assembly is shown with fastening
arrangement. The fixing of the auxiliary clamp (02) on the main clamp (01) is
facilitated by at least two M4 screws for easy replacement of the auxiliary clamp
(02) depending on the diameter of the tube to be welded.

WE CLAIM
1. An universal clamping fixture for MIAB welding of different diameter of
tubes, comprising:
- a main clamp (01) with inner radius (R1) varying in correspondence with
the outside diameter of the tube to be welded, the width, length, and
height of the main clamp (1) being selected to maintain a ratio of 3:4:1;
- the main clamp (01) provided with a through-hole (D2) to flexibly fix the
welding head to allow axial including angular offset of the welded tubes;
- a collar with a radius (R3) provided on either side of the main clamp (1) to
releasably fix on the welding head, the outer radius (R2) of the main
clamp (01) is selected about equal to the height of the clamp, the main
clamp (01) being configured with a plurality of holes (D3) to allow fixing
of at least one auxiliary clamp (02) over the main clamp (01); and
- the at least one auxiliary clamp (02) having an outer radius (R4) and a
length (L2) substantially equal to that of the inner radius (R1) and length
(L1) of the main clamp (01), the inner radius (R5), the height (H2), and
width (W2) of the auxiliary clamp (02) being selected in a ratio of
1:0.55:2, at least two corresponding holes (D4) provided on the auxiliary
clamp (02) to fix the main clamp (01) beneath the auxiliary clamp (02),
the auxiliary clamp (02) being enabled for easy replacement without

deviating the alignment of the main clamp (01) with the welding head
which remains permanently fixed with the welding head.
2. The clamping fixture as claimed in claim 1, wherein the auxiliary damp
(02) is enabled to cater for different tube diameters from 30 to 60mm OD
and wall thickness 3 to 6mm.
3. An universal clamping fixture for MIAB welding of different diameter of
tubes as substantially described and illustrated herein with reference to
the accompanying drawings.

The invention relates to an universal clamping fixture for MIAB welding of
different diameter of tubes comprising a main clamp (01) with inner radius (R1)
varying in correspondence with the outside diameter of the tube to be welded,
the width, length, and height of the main clamp (1) being selected to maintain a
ratio of 3:4:1; the main clamp (01) provided with a through-hole (D2) to flexibly
fix the welding head to allow axial including angular offset of the welded tubes; a
collar with a radius (R3) provided on either side of the main clamp (1) to
releasably fix on the welding head, the outer radius (R2) of the main clamp (01)
is selected about equal to the height of the clamp, the main clamp (01) being
configured with a plurality of holes (D3) to allow fixing of at least one auxiliary
clamp (02) over the main clamp (01); and the at least one auxiliary clamp (02)
having an outer radius (R4) and a length (L2) substantially equal to that of the
inner radius (R1) and length (L1) of the main clamp (01), the inner radius (R5),
the height (H2), and width (W2) of the auxiliary clamp (02) being selected in a
ratio of 1:0.55:2, at least two corresponding holes (D4) provided on the auxiliary
clamp (02) to fix the main clamp (01) beneath the auxiliary clamp (02), the
auxiliary clamp (02) being enabled for easy replacement without deviating the
alignment of the main clamp (01) with the welding head which remains
permanently fixed with the welding head.