Moinuddin, S Q and Sharma, Abhay
(2018)
ASSESSMENT OF ARC STABILITY AND ITS IMPACT
IN ANTI-PHASE SYNCHRONIZED TWIN-WIRE GAS
METAL ARC WELDING.
PhD thesis, Indian institute of technology Hyderabad.
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Abstract
Gas Metal Arc Welding (GMAW) process is a well-established process, widely
used in industries due to its economic efficiency. The present scenario in
industries is to increase the productivity with low cost. Due to this necessity,
improvement of existing process and development of new process came in to
existence with help of advanced technology. One such process is arc-welding
process wherein single wire has extended to multiple-wire welding process.
Twin-wire welding process is one of a kind in multiple-wire welding process
that has been fully developed and used at shop floor. This technique was first
implemented in submerged arc welding process later on gas metal welding
process. From literature, it is known that submerged arc twin-wire welding
process has been full-fledged developed, whereas gas metal arc welding is in
developing stage. The major concern in twin-wire gas metal arc welding is that
arc interactions caused by electromagnetic fields affect arc stability of the
process. The present work addresses the solution to this issue with help of
experimental study. Process parameters such as current values and wire
diameters at lead and trail position were considered as variables. Bead-onplate
experiments conducted on low carbon alloy steel. Welding signals were
captured with the help of data acquisition system. A qualitative (cyclograms
and probability density distribution) and quantitative analysis (wavelet energy
entropy) were carried out on stability of the process. Further, mathematical
formulation has developed to calculate the melting efficiencies that has been
related to arc stability, heat input and weld bead features. The interconnection
between process – structure – properties has been analyzed. The two-stage
arcing in twin-wire welding facilitates slow heating and cooling that leads to
weld metal and heat affected zone softening. A combination of polygonal
ferrite, pearlite, and bainite with varying compositions are observed across the
weldment. Hardness in the heat affected zone and weldment reduced with
increase in heat input. The maximum transverse residual stresses found at the
weld toe region that is close to the yield strength of the base material. From
the combined analysis, the present investigation suggest that for a stable arc
the current value at lead should be more than trail and current difference
between them should be large. In addition the wire diameter at lead should be
large than trail. Combination of both process variables allow the process with
stable metal transfer with reduced arc interactions. The difference in process
variables between lead and trail wire has made the arc to concentrate towards
one wire and withdraw sufficient energy to interact with fresh material and
thereby enhanced structure along with properties. The scope of the present
work in future may be directed towards the additive manufacturing,
fabrication of functionally graded material using two different electrodes.
Applications in which the present work can be utilized includes joining huge
pipes for oil industries, boilers, automotive industries, subway transportation
industries and shipbuilding industries etc
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