st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Distribution of Driving Force in Weld Pool Affected by Temperature near Anode
in Pulsed Arc Welding with Iron Vapor
Y. Goto1, T. Iwao1, M. Yumoto1
1
Tokyo City University
Abstract:.TIG arc welding is high-quality joining technology. However, current becomes
small because cathode does not melt. Thus, weld pool should be shallow and poor depth, so
weld defect sometimes occur. Pulsed arc has widely used for improvement of weld defect.
Weld shape depend on driving force, and driving force is decided by arc temperature and current density. In this paper, distribution of driving force in weld pool affected by temperature
near anode in pulsed arc welding with iron vapor is elucidated. As a result, the marangoni effect is 10 times as high as the electromagnetic force. However, the peak position of each distribution is different. The radial positions which across the driving force to the radial direction
are almost same with any frequency, and the electromagnetic force distribution is almost same.
And the radial expansion could trend to restrict with increasing the frequency.
Keywords: Arc welding, Pulsed arc, Driving force, Iron vapor, Arc temperature
1. Introduction
The TIG (Tungsten Inert gas) arc welding is the welding technology which uses the cathode (Tungsten) and the
inert gas. It has the characteristics of prevention of melting the electrode, because the shielding gas can separate
the inert gas and air at the weld pool. TIG arc welding can
prevent the contamination of the impurities to the weld
pool, the reliability and quality of welding become very
high, and the kinds of joining materials for welding are a
lot. Therefore, TIG arc welding has been used for various
construction with reliability well. However, TIG arc
welding has some defects. Because the cathode does not
melt, the high current should not be used. Therefore, the
heat transfer of TIG arc welding is smaller than that of
MIG welding. The TIG arc welding cannot melt the weld
pool, deeply. In this case, the weld pool spreads to the
radial direction, and the weld defect sometimes occurs.
The pulsed arc welding has been used for the improvement of this defect. The pulsed arc welding can control
the heat flux to the anode, the convection and driving
force in the weld pool, because the current and temperature of arc can change periodically. However, the pulsed
TIG arc welding has not been researched theoretically
because of the transient phenomena, which has a lot of
control parameter. Some researchers have researched the
shape of weld pool after the welding, and most case is the
constant arc[1-3]. In addition, the pulsed arc phenomena
for making the weld pool have not been researched. The
convection of pulsed arc welding differs from that of constant arc in the weld pool, because the current changes
with time. This reason is that the balance of driving
force[1][2] for convection in the weld pool is changed
when the heat flux to the anode changes with changing
the input power.
Fig.1 Current waveform.
Generally, the pulsed arc changes the current periodically, the electromagnetic force changes instantly. However, the marangoni effect derived from temperature gradient and drag force derived from flow velocity near the
anode which is one of the driving forces in the weld pool
cannot depend on the current, because they are decided by
the arc temperature, flow velocity, heat flux to the anode.
Especially, the balance of these driving forces is main
factor of weld width and depth.
In this paper, the distribution of driving force affected
by temperature near anode in pulsed arc welding with iron
vapor was elucidated.
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
2. Calculation method
This calculation is analyzed with one model of electrode and arc simultaneously and the boundary condition.
It adapts the all calculation area. This calculation is used
by SIMPLER method[4] under consideration of the LTE,
laminar flow, flat weld pool and not consideration of
metal contamination from weld pool. The calculation
condition is 2D cylindrical coordinates, interelectrode
distance is 5 mm, cathode is tungsten and the diameter is
1.6 mm, anode is SUS 304, and ambient gas is argon and
shielding gas flow rate is 10 slm. Fig.1 shows the current
waveform.
The parameter of current is frequency because the main
factor of welding penetration is frequency. The frequency
is used at f=100, 500 Hz. The peak current is 200 A, and
base one is 100 A.
The calculation point is A, B, C and D, these points are
at same time each parameters. The result is at these
points.
3. Results and discussion
Figs. 2 and 3 show the temperature distribution of arc
near anode. Each plots show the each time. The points at
A and B are the base current. The points at C and D are
the peak current. The temperature at radial center at point
A and B are almost same to be 6000 K at 100 Hz. However, the temperature at axial center is to be 7000 K at A
and 6000 K at B. The arc temperature is the maximum
near the cathode when the current is concentrated. The
temperature distribution changes because the joule’s
heating occurs near the anode, and the high temperature
medium neat the cathode transports neat the anode. The
maximum flow velocity to the axial direction is to be 90.3
m/s, 93.6 m/s at 100 Hz and 500 Hz, respectively at point
A. And when the current transfers to the bases to peak, the
plasma flow velocity of 500 Hz is higher than that of 100
Hz. Therefore, the point A is different from the other point.
Figs. 4 and 5 show the current density distribution to the
radial direction in the case of each frequency of current.
This shows the position for electromagnetic force on the
anode surface. The plots are defined by same temperature
distribution. The relation between the point A, B and C, D
is quite different because the instant value before each
points are 100 and 200 A, respectively. The current density is same distribution which does not depend on the
frequency and before or after current transition. This
phenomenon occurred because the iron vapor contaminates in the arc. The temperature is transient reply and
does not catch up with the current waveform after the
peak current in the case of not contamination of iron vapor. The high electrical conductivity as a function of
temperature concentrated at central part because the high
temperature medium concentrated at central part. In this
case, the current density increases because of the mainte-
nance of current continuity derived from j=σE[5]. On the
other hand, in the case of contamination of iron vapor, the
current continuity is easy to maintain because the iron has
electrical conductivity even if the temperature is low[6].
Therefore, the high temperature medium does not concentrate at central part. Thus, the current density distribution does not change so much, because the temperature
distribution does not change, even if the frequency
changes.
The temperature near anode is changed in the case of
the pulsed arc. The current density depends on the temperature near anode. Thus, the driving force in the weld
pool is contributed to the marangoni effect derived from
the temperature gradient and electromagnetic force derived from the current density.
Fig.2 Temperature near anode (f＝100 Hz).
Fig.3 Temperature near anode (f=500 Hz).
Figs.6-9 show the marangoni effect and electromagnetic force in the case of 100 Hz and 500 Hz. The marangoni effect for current frequency is different from each
position because the anode surface temperature changes
the time. In the case of point A and D, the marangoni effect becomes high because the high temperature medium
concentrated at central part. And the marangoni effect at
point A, 500 Hz becomes high because the temperature
near anode at 500 Hz is higher than that at 100 Hz as
shown in Fig.3.
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Fig.7 Marangoni effect at anode surface (f=500 Hz).
Fig.4 Current density at anode surface (f=100 Hz).
Fig.8 Axial Lorenz force at anode surface (f=100 Hz).
Fig.5 Current density at anode surface (f=500 Hz).
Fig.9 Axial Lorenz force at anode surface (f=500 Hz).
Fig.6 Marangoni effect at anode surface (f=100 Hz).
The electromagnetic distribution is almost same one
even if the frequency is changed. This reason is that the
current density distribution does not change. The radial
distance of maximum value is r=1.9 at all case. This reason is that the cross point which is calculated by the
magnetic flux density derived from the high current density at the center part and current at periphery part occurred.
When the radial position which the marangoni effect is
low and electromagnetic force is high, it is predicted that
the depth in the radial position increases. The radial positions which across the driving force to the radial direction
means to change the direction of driving force. The radial
driving force is to be plus at the periphery position of the
cross point. At this time, the direction of driving force is
outward direction. The radial driving force is to be minus
at the position inner the cross point. Thus it is easy to increase depth of weld pool. Therefore the radial positions
which across the axial axis is used for increment of depth.
Figs. 10 and 11 show the driving force and temperature
distribution to the radial and axial direction in the weld
pool. The driving force to the radial direction is total of
marangoni effect and electromagnetic force.
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
4. Summary
The distribution of driving force affected by the temperature near anode in pulsed arc welding with iron vapor
was elucidated. The main results are shown below.
Fig.10 Driving force and temperature at anode surface (f=100
Hz).
(1) The temperature distribution of arc changes with
changing the current waveform. Especially, it occurs
in the case of the different frequency and transition to
base current, because of plasma flow velocity difference.
(2) The current density distribution does not change so
much with contamination of iron vapor, because the
electrical conductivity increases with contamination of
iron vapor, and it is easy to maintain the current continuity.
(3) The marangoni effect is 10 times as high as the electromagnetic force. However, the peak position of each
distribution is different. The position of electromagnetic force > marangoni effect exits near the center
part, the weld pool is expected to be better.
(4) The radial positions which across the driving force to
the radial direction are almost same with any frequency, and the electromagnetic force distribution is
almost same.
Therefore, the weld depth in the weld pool could not
change so much in this frequency band in the case of
pulsed arc with iron vapor. However, the radial expansion
could trend to restrict with increasing the frequency because the maximum value of driving force to the radial
direction decreases in the case of high frequency.
Fig.11 Driving force and temperature at anode surface (f=500
Hz).
The axial direction is the electromagnetic force which
is only down direction. The driving force direction has
plus or minus sign. The driving force to the radial direction is periphery direction from the center for plus and
opposite direction for minus. It to the radial direction is
up direction for plus and down direction for minus. The
marangoni effect is 10 times as high as the electromagnetic force. The radial positions which across the driving
force to the radial direction are r=1.9 mm at point A and
r=1.4 mm at point B-D in the case of 100 Hz. In addition,
they are less than those at r= 1.5 mm in the case of 500
Hz. Thus, they are almost same with any frequency, and
the electromagnetic force distribution is almost same.
Therefore, the weld depth in the weld pool could not
change so much in this frequency band in the case of
pulsed arc with iron vapor. However, the radial expansion
could trend to restrict with increasing the frequency because the maximum value of driving force to the radial
direction decreases in the case of high frequency.
References
[1] Fenggui Lu, Shun Yao, Songnian Lou, Yongbing Li,
“Modeling and finite element analysis on GTAW arc
and weld pool”, Computational Materials Science,
Vol.29, pp.371-378, 2004.
[2] A.Traidia, F.Roger, A computational investigation of
different helium supplying methods for the improvement of GTA welding”, Journal of Materials
Processing Technology, Vol.211, pp.1553-1562, 2011.
[3] W.-H. Kim, S.-J. Na, Heat and fluid flow in pulsed
current GTA weld pool, Journal of Heat Transfer
Vol.41, pp.3213-3227, 1998.
[4] S.V.Patanker, Numerical Heat Transfer and Fluid
Flow, Hemisphere Publishing Corp, pp.116-139,
1980.
[5] T. Momii, T. Iwao, and M. Yumoto, “Contribution
for Heat Transfer and Heat Flux to Anode Affected
by Rise Current Transition Time in Pulse Arc”, IEEJ
Trans. PE, Vol.133, pp.409–416, 2013.
[6] T. Shimokura, Y. Mori, T. Iwao, and M. Yumoto,
Contribution for Iron Vapor and Radiation Distribution Affected by Current Frequency of Pulsed Arc,
IEEJ Trans.PE, Vol.132, No.8, pp.718-727, 2012.