FIELD OF THE INVENTION
The invention relates generally to magnetically impelled arc butt (MIAB) welding.
More particularly the invention relates to a controller development and an
apparatus for the same.
BACKGROUND OF THE INVENTION
Magnetically impelled Arc Butt Welding is a solid state joining method
predominantly used in automobile applications for joining of tubes and rods. It
employs electric arc to obtain melting of faying edges and uses final forging
known as upset force to produce the solid state weld. It is classified under
electric arc welding process, since electric arc is used as the energy source for
producing the heat, through pressure from the forging is essential to complete
the joining. The magnetic flux density, the arc current and the length of the arc
in the gap between the two tubes are the major parameters governing the
welding process. These parameters contribute to an electromagnetic force that
plays a significant role in the rotation of the arc and the quality of the weld
produced.
In MIAB welding, welding current, magnetic flux density, length of the arc,
forging pressure and welding time are the main input parameters which have a
direct effect on the weld quality. The welding time is governed by the
electromagnetic force which is developed in the system due to interaction of the

welding current and magnetic field. Generally the arc rotation speed is around 50
to 200 m/sec depending on the thickness of the tube to be welded. The typical
welding time is around 15 to 20 sec for a 44mm dia tube with 5mm wall
thickness.
As assessed through different and sufficient number of experiments, it is
observed that at the range of welding current of 300 to 350 amps, there is a
variation of ± 10% during the welding process. The welding current decides the
time required for melting of the tubes for subsequent weld to be achieved. The
welding current is proportional to the electromagnetic force that impulse the arc
causing a heating of the peripheral edges of the tubes. The higher the welding
current, the stronger would be the electromagnetic force leading to a better
weldment. The electromagnetic force, which is mainly responsible for the
rotation of the arc, depends upon the magnetic flux density, the welding current
and the length of the arc. The electromagnetic force proportionally varies with
varying magnetic flux density. Higher the magnetic flux density, the stronger is
the electromagnetic force generated, leading to rotation of the mobile arc at a
greater speed. It indicates that the magnetic field indirectly contributes in
achieving a higher speed thereby reducing the weld duration. Welding voltage
employed for MIAB is about 22 to 30 volts. It is necessary to maintain the
voltage at the above mentioned value in order to initiate and sustain the arc.

Weld quality deteriorates with reduction of the upset force below 30KN. All the
variables are interdependent on each other and hence, monitoring and control of
these variables at designated values assumes a high significance. The weld
quality is dependent on a successful control of the process variables through a
controller. Existing mechanisms deal with setting up of different parameters and
running the process. In course of running the process, deviations in the
parameters if any, are not however accounted for and such deviations have a
direct impact on the weld quality.
US5508492 discloses an apparatus for extending broad metal surface areas with
a magnetically impelled arc. According to this invention, there is provided an
apparatus for electric arc graining, the surface of a travelling electrically
conductive work piece, the surface having a substantial area.
US6211489 teaches a method of magnetically impelled arc butt welding. This
invention relates to the press welding process called MIAB and details of the
construction and working of the MIAB welding process.
US6414265 patent describes a method and apparatus for drawn arc welding
including the step of applying a magnetic field transversely to the arc to impel
the arc along the welding gap.

US7161115 discloses a magnetically impelled arc butt welding method for
pipelines and a vehicle mount apparatus for laying pipelines in which adjacent
pipe are joined by the technique of MIAB.
US4273986 talks about a method and apparatus for arc butt welding where the
arc is moved between the faces of the parts to be joined by a magnetic field. In
order to insure that the arc travels over the whole of the faces to be welded the
parts are moved generally parallel to the faces so that the overlapping area of
the faces changes during the arc heating.
To summarize the prior art, the inventions on Magnetically Impelled Arc Butt are
related to the construction and working of the MIAB welding principle.
To the extent of the knowledge offered by the prior art search, there exists no
patent or IPR in the area of MIAB welding machine or controller designed for
MIAB welding machines in India.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose an apparatus to monitor,
regulate and control welding parameters through a feedback control loop to
maintain an improved weld quality.

Another object of the invention is to propose an apparatus to monitor, regulate
and control welding parameters through a feedback control loop to maintain an
improved weld quality in which the rated values of current and voltage is
provided to the MIAB welding process.
A further object of the invention is to propose an apparatus to monitor, regulate
and control welding parameters through a feedback control loop to maintain an
improved weld quality which reduces wastage of material and time in welding to
improve productivity.
SUMMARY OF THE INVENTION
Accordingly, there is provided a closed loop controller apparatus for MIAB
welding machine for monitoring and control of welding voltage and current in
MIAB welding process. Compared to the open loop parameter settings adopted in
the prior art, the present invention provides a precise control over the process to
ensure weld quality and improve productivity and consistency in results. The
apparatus could become a standard accessory to any MIAB welding machine.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a schematic block diagram of a closed loop controller apparatus
according to the invention.

DETAILED DESCRIPTION OF THE INVENTION
As shown in figure 1, the apparatus consists of a series of electronically
interconnected components and circuits capable of measuring up to 0 - 1200A
using current and voltage sensors (1). A first signal conditioning circuit (2)
consists of a low pass filter, an amplifier for the signal to be conditioned for a
value commensurating with an operating range. This value is compared with a
set point (SP) to generate an error voltage to be fed to a first Programmable
Logic Controller. The first Programmable Logic controller offers flexibility to
accommodate different types of settings, signals and also timer intervals to
differentiate various stages of the process. The switching actions for
starting/stopping different stages of the MIAB welding process is also enabled
through a second Programmable Logic Controller. The control signals are further
amplified and modified in a second circuit (4) to suit the requirements of
controlling the voltage and current source in the Power supply (P). The
modulated power thus reach the MIAB welding machine (M) for welding process.
This process happens in real time and is in continuous nature throughout the
welding process.

WE CLAIM :
1. A controller apparatus for Magnetically impelled Arc Butt Welding machine
comprising:
- a plurality of sensors for measuring voltage and current from a power
source;
- a first signal conditioning circuit for transforming the sensor signals for
amplification and processing;
- a first PLC program for evaluation and delivering the processed signal, and
- a second signal conditioning current to effect the final control signal to the
power source connected to effect the final control signal to the power
source connected to a MIAB welding machine, wherein the process
parameters of welding voltage, welding current and time, are controlled
and fed back to the welding machine to produce improved weld quality.
2. The welding apparatus as claimed in claim 1, wherein the first signal
conditioning circuit comprises a tow pass filter, and an amplifier to
condition the input signal corresponding to an operable range, and
wherein the conditioned signal is compared with a pre-stored value to
generate an error voltage which is fed the first PLC.

2. The apparatus as claimed in claim 1 or 2, wherein the control signals are
further modified through a second PLC to control the voltage and current
of the power source, and wherein the modulated power is supplied to the
welding machine.

ABSTRACT

The invention relates to a controller apparatus for Magnetically impelled Arc Butt
Welding machine comprising: a plurality of sensors for measuring voltage and
current from a power source; a first signal conditioning circuit for transforming
the sensor signals for amplification and processing; a first PLC program for
evaluation and delivering the processed signal, and a second signal conditioning
current to effect the final control signal to the power source connected to effect
the final control signal to the power source connected to a MIAB welding
machine, wherein the process parameters of welding voltage, welding current
and time, are controlled and fed back to the welding machine to produce
improved weld quality.