International Journal of Engineering Trends and Technology (IJETT) – Volume 18 Number 6 – Dec 2014
Investigation on Temperature Distribution in SAW Weld Using 2D Mesh
Model
Vijaya Bhaskar Sirivella #1
#
Principal & Prof. in Mechanical Engineering Chilkur Balaji Institute of Technology
Aziz Nagar, Hyderabad, India
Abstract— Submerged arc welding is most widely used welding
process in a variety of industries such as aerospace, shipbuilding,
automotive, energy generating systems, satellites and etc., due to
its advantages such as high quality, smooth, uniform finished
weld with no spatter. During the welding process, it will impact
on may mechanical attributes such as heat affected zone, stresses,
distortions, change in microstructure and deformations. This
paper focuses on study the temperature distribution during the
SAW welding with 2D heat flow mesh model. In the analysis, it
was observed that the heat source acts from 0.001s to 1.000s and
the shape of the weld is not formed by the time the heat source is
terminated. It also point out that the node situated close to the
boundary of the weld on the top surface of the plate reaches its
maximum temperature value at ~10s. The temperature in the
similar node on the bottom of the plate passes its maximum at
~15 and can distinguish gradual temperature equalization.
shape, because the machinist cannot precisely watch the weld
pool, great reliance must be placed on parameter setting and
positioning of the filler wire. Although submerged arc
welding is typically operated with a single wire electrode,
there are many of variants including the use of two or more
wire electrodes, adding chopped wire to the joint prior to
welding, and the use of metal powder additions. These options
are used in specific circumstances to increase and or improve
the productivity through increasing travel speed and/or
deposition rates.
Keywords— Submerged Arc Welding, Heat Source Density,
Temperature Distribution, 2D FEM, Weld Thermal Cycles.
I. INTRODUCTION
Submerged arc welding (SAW) is a conventional and
extremely efficient method of welding which produces high
quality weld with accuracy. It involves the formation of an
arc between a continuously fed electrode and the work piece.
Powdered flux, which generates a protective gas shield and a
slag, protects the weld zone. The arc is submerged beneath the
flux blanket and is not normally visible during welding;
moreover shielding gas is not required. So the heat energy loss
is reduced and this makes SAW is one of the most efficient
and competent welding processes that delivers high quality,
smooth and homogenous finished weld with no spatter. The
diameter of the consumable electrode ranges from 1 to 5mm.
An invariable potential DC power source, which allows the
arc length control by self-adjusting effect, is most commonly
used with thin wires up to 2.4 mm and constant current DC
source is used for wires having bigger diameter. However, at
very high welding currents, AC is preferred in order to
minimize arc blow. [1] In this welding process higher heat
generation is required and can be attained by high welding
speeds up to 5 m/min. Higher heat generation and rapid
welding considerably reduces the distortion during welding,
which occurs due to the expansion and contraction of the weld
adjacent base metal. [2]
SAW is usually operated as a mechanized process
and the welding current may be usually between
300 and 1000 Amps. The depth of penetration and
chemical composition of the deposited weld metal,
travel speed and welding arc voltage depends on the bead
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Fig. 1 SAW: (a) Overall Process; (b) Welding Area
Enlarged[3]
In general, submerged arc welding (SAW) is used for butt
welding longitudinal and circumferential components such as
line pipe and pressure vessels. Welding is typically performed
in the flat position because of the high fluidity of the weld
pool and molten slag and need to maintain a flux layer. Also
fillet joints may be produced, welding in either the flat or
horizontal-vertical positions.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 18 Number 6 – Dec 2014
II. LITERATURE SURVEY
Temperature distribution has a very extensive impact on
residual stresses, distortions and microstructure of the weld
and thus study of heat transfer analysis is very important. This
essentially involves consideration for the type of heat source,
temperature dependent material properties, effect of latent
heat, heat of phase transformation, plate geometry, and
convection and surface depression in weld pool, and
convective and radiant heat loss at boundaries.[4] Practically in
submerged arc welding process, the shape of heat source
changes with the change of input parameters such as current,
voltage, travel speed, stick out, electrode wire diameter,
polarity and etc. Rosenthal instigated an analytical solution in
a semi-infinite body to study the transient temperature fields
subjected to an instant point heat source, surface heat source,
or line heat source. [5] Lin et al. emphasized on the necessity to
consider the non-constant thermal properties, heat input
magnitude, heat of phase transformation, and distribution,
convection and surface depression in weld pool in transient
heat flow model to improve its accuracy. [6] Malmuth et al.
reveled in their paper: “Transient thermal phenomenon and
weld geometry in GTAW”, the latent heat effect will also
generates 5–10 percent error in prediction of weld geometry. [5]
Research into the actual heat intensity distribution in welding
arcs on a water-cooled copper anodemade, it is possible to
determine the effect of distributed heat source on the weld
geometry. [7] The assumptions in Rosenthal’s analysis retained,
including absence of weld pool convection, material
properties variations, and latent heat of phase transformation
other than the assumption to consider welding arc as a point
heat source. Nevertheless, solutions considering welding arc
as a distributed heat source were able to get rid of much of the
experimental variations or deviations in the close environment
of weld pool. Tsai et al. made to order to include a twodimensional surface Gaussian circulated high temperature
vitality source with a consistent appropriation parameter and
discovered a scientific answer for the temperature of a semiendless body subjected to this moving heat source. [8]
Although the 2-D Gaussian heat distribution was able to
reduce the experimental scatter, it yet could not include weld
penetration into the picture. A finite element analysis was
performed utilizing the two-fold ellipsoidal high temperature
source, and it was discovered to be precise in anticipating
temperature circulation in welds having deeper infiltration.[9]
Eagar and Tsai modified Rosenthal’s solution to include 2-D
surface Gaussian distributed heat source with a constant
distribution parameter (which can be considered as an
effective.[10] In this paper, numerical solution using finite
element approach has been applied to model transient
temperature field in SAW process and assumptions regarding
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constant material properties, semi-infinite plate geometry, and
no heat losses at boundary have been eliminated for realistic
simulation of transient temperature field.
III. HEAT SOURCE OF THE WELDING ARC
Heat input is a fundamental measure of the energy
transferred/unit length of weld. It is a significant characteristic
because, like pre-heat and inter-pass temperature, it influences
the cooling rate, which may change the structure and
mechanical properties of the weld. All electrical energy of the
arc converts into heat energy. But not all the energy is used
for the heating of the electrode and base metal. Energy goes to
heat dissipation such as losses to the surroundings, gas or flux
heating, etc. So, the effective energy of the welding arc can be
expressed in this way:
W= VA
efficiency coefficient; V is the voltage of the arc, [in Volts]; A
is the current, [in Amps].
The heat source power density is also a significant
attribute of the welding process. Figure.2 shows
how significantly different can be the action of the
welding heat source. As shown in Figure 2, the
curve for flame is wide and low, on the contrary to
it, the welding arc curve is narrow and high, and
the curve for curve for plasma, electron and laser beam
welding is even higher and narrower. These facts form the
basis for the heat source approximation principles. It helps us
to choose what kind of model for the source we should take:
the line, the point, or the arbitrary distributed heat source.
Radial Distance from Centre
Fig 2 Heat Source Density of Flame and Arc
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International Journal of Engineering Trends and Technology (IJETT) – Volume 18 Number 6 – Dec 2014
In this paper, the following assumptions are considered for
the analysis of temperature distribution:
the plate is isotropic, moderately thick and substantially
wide and long
the distribution of the heat source through the plate
thickness can be arbitrarily
needed only in the region with high temperature gradient. In
such a way the height of the elements increases with the
distance from the weld centerline.
chosen but must be specified
the material physical properties such as thermal
conductivity
and
thermal
diffusivity
are
temperature independent
the initial temperature T0 is constant
The basic steady state solution for the moving point source in
a thin medium thick plate is
Fig. 3 FE Mesh used for 2D X-Y plane model
Where
is the distance from the real and imaginary heat
source to point P and q0 is the heat source net power,  is the
welding speed, and x, y are Cartesian co-ordinates.
IV. 2-D HEAT FLOW MESH MODEL
Variety of finite element models can be applied to resolve
the different convective heat transfer problems. The
appropriate model should be selected considering the sort of
results expected from the model. Within the limits of this
paper implementation of 2D models in the XY and YZ planes
will be reviewed. Abaqus Unified FEA is used for solving the
heat transfer problems. The Abaqus Unified FEA product
provides comprehensive solution for engineering problems
including vibrations, thermal coupling, and acoustic structural
coupling using a common model data structure and integrated
solver technology.
Heat transfer problems can be non-linear because the
properties of the material are temperature dependent or for the
reason that the boundary conditions were non-linear. The
nonlinearity associated with the temperature dependence of
the properties of the material is mild because the properties
would not change rapidly with the temperature. The simplest
model for the heat transfer analysis is 2D YZ-plane model that
gives results for input data to the plane strain thermal stress
analysis. This transient problem is handled as totally
uncoupled with the mechanical part of the task ie., without
considering the stress/deformation the temperature field will
be calculated.
The model considered for this paper is based on the mesh
shown in Figure 3. The mesh has a constant step in the xdirection. This model consists of elements that are rather long
in the welding direction. Along the y-direction the dimensions
of the elements vary. The smallest elements of the presented
mesh have dimensions 550mm. The small size elements are
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Fig 4 Scheme of 2D FE heat flow model
In Figure.4: the scheme of the 2D heat flow model is
presented. The size of the acting heat source spot is assumed
to be a square 10x10 mm. The heat source retention time is
assumed to be 1s, in order to have comparable models. As for
all the models under consideration, the way to cool the plate
down is to keep the outer edge of the plate at constant zero
temperature. Quite simple DC2D4 (after ABAQUS coding
system) heat conduction elements were used in the model.
For the 2D model a 1 mm wide slice transverse to the arc
welding path was chosen. To facilitate the experimental
welding conditions such as welding speed =10mm·s-1,
assumed size of the heat source spot, the heat source stays
active in a 1s interval from 0.001 until 1.001 th secs from the
beginning. The source in the mesh itself is distributed in
conjunction with 36 elements arranged in the shape of the gap
between the welding plates. The first and the third elements
are distributed among 13 elements each; the second – among
10 elements.
Time incremention in the analysis is controlled automatically
by FEM software that means it chooses the time step such as
to keep the largest temperature change at every integration
point less than an allowed value. In this paper Tmax=500C
was used. At the time when the heat source starts to be active,
the time step ΔT is approximately 6.5x10-3s. By the end of the
heating process, the time increment is slightly increased up to
8.3x10-3s. The 2-D shell-elements have supplementary
integration points and has some elements in the throughthickness direction, then the diminution of the dimensionality
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International Journal of Engineering Trends and Technology (IJETT) – Volume 18 Number 6 – Dec 2014
of the problem does not lead to reduction of computation time.
A. Element Birth Technique
If material is added to or removed from a system, certain
elements in the model may become existent or non-existent. In
Abacus coding in the model change option, the parameters
add and remove can be used to deactivate or reactivate
selected elements. This procedure can be used for modeling
the effects of structural changes. In finite element models
created for welding applications, it can model the process of
filler metal addition.
V. CONCLUSIONS
gradual temp passes its maximum at ~15s. Also gradual
temperature equalization can be observed.
REFERENCES
[1]
[2]
[3]
[4]
[5]
The heat flow in the cross-section of the plate is
demonstrated in Figure.5 and the temperature is represented as
a function of time and spatial co-ordinates.
[6]
[7]
[8]
[9]
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Sindo Kou, “Welding Metallurgy”, John Wiley & Sons, Inc., Hoboken,
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N. D. Malmuth, W. F. Hall, B. I. Davis, and C. D. Rosen, “Transient
Thermal Phenonenon and Weld Geometry in GTAW,” Welding
Journal, vol. 53, no. 9, pp. 388S–400S, 1974.
D. Rosenthal, “Mathematical Theory of Heat Distribution During
Welding And Cutting” Welding Journal, vol. 20, no.5, p220S–
234,1941. [6] M. L. Lin, T. W. Eagar, “ Influence of Surface
Depression and Convection on weld Pool Geometry”, M.S. thesis, MIT,
Cambridge, Mass, USA, 1982.
M. L. Lin, T. W. Eagar, “ Influence of Surface Depression and
Convection on weld Pool Geometry”, M.S. thesis, MIT, Cambridge,
Mass, USA, 1982.
O. H. Nestor, “Heat Intensity and Current Density Distributions at the
Anode of High Current, Inert Gas Arcs” Journal of Applied Physics,
vol. 33, no. 5, pp. 1638–1648, 1962.
N.S. Tsai and T. W. Eagar, “Temperature Fields Produced by
Traveling Distributed Heat Sources,” Welding Journal, vol. 62, no. 12,
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Fig
5
Temperature distribution after 2D YZ-plane model
As we see, the weld shape was not produced by the time the
heat source is terminated and the heat source is active from
0.001s to 1.000s. Moreover, by this time the liquid metal not
yet been formed on the bottom side of the plate. Fig.8 also
points out that the node situated close to the boundary of the
weld on the top surface of the plate reaches its maximum
temperature value at ~10s. The temperature in the similar
node on the bottom of the plate passes its max at ~15s. Also
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