CFD ANALYSIS OF GAS METAL ARC WELDING1

CFD ANALYSIS OF GAS METAL ARC
WELDING
PRESENTED BY UNDER GUIDANCE OF
PRATIK S. JOSHI Dr. N. YAGNESH SHARMA
REG.NO.110926007 PROFESSOR,
M.TECH (MET) DEPT. OF MECH. AND MFG.ENGG.
MIT,MANIPAL
1
DEPT.OFMECH.ANDMFG.ENGG.8/3/2015

CONTENT
• Introduction
• Literature review
• Problem definition
• Objectives
• Methodology
• Theory
• Modeling
• Result and Analysis
• Conclusion
• Future scope of work
• References 2

INTRODUCTION
3

GAS METAL ARC WELDING(GMAW)
• Gas metal arc welding
(GMAW) is defined as(10)
“an arc welding process
that produces coalescence
of metals by heating them
with an arc between a
continuous filler metal
electrode and the work
piece. Shielding is obtained
entirely from an externally
supplied gas.”
• The GMAW process is
multi-energy process
involving plasma physics,
heat flow, fluid flow, and
metal transfer. 4
Fig.1 Energy involved in GMAW(6)

GMAW PROCESS
• GMAW process uses solid
electrode that continuously
feed into the weld pool.
The wire electrode is
consumed which becomes
the filler metal.
• GMAW is done using DCEP(
direct current electrode
positive). AC is never used
for GMAW process.
• GMAW is constant voltage
process.
5
FIG.2 GMAW machine(12)

WELDING ARC
• A welding arc can be defined as “A controlled electrical
discharge between the electrode and the workpiece that is
formed and sustained by the establishment of a gaseous
conductive medium, called an arc plasma.”
• The amount of heat that an arc produces mainly depends on
arc current and arc length.
6
Fig.4 Arc-conversion device

METAL TRANSFER MODES
• There are basically two metal transfer modes in GMAW
process
1. Short circuit transfer
2. Globular transfer
• Metal transfer modes is mainly depends on the current
and voltage value set on the machine.
7

SHORT CIRCUIT TRANSFER
• In the short-circuiting mode,
metal transfer occurs when the
electrode is in contact with the
weld pool.
• In this mode of metal transfer,
the relationship between the
electrode melt rate and its feed
rate into the weld zone
determines the intermittent
establishment of an arc and the
short circuiting of the electrode
to the workpiece.
8
Fig.5 short circuit transfer(12)

GLOBULAR TRANSFER
• The filler material transfers in
the form of globules
propelled by arc forces.
• The metal transfers across
the gap in the form of large
,irregularly shaped droplets.
The drops are usually higher
than that of electrode wire
diameter.
9
Fig.6 Globular transfer(12)

LITERATURE REVIEW
10

• Anthony B. Murphy (1) ,studied the transport properties of arc
plasma. Calculated values of viscosity, thermal conductivity,
and electrical conductivity of argon and helium at high
temperatures were presented.
• T.W. Eagar and Y.S. Kim(2), studied droplet size produced in the
GMAW electrode both theoretically and experimentally. The
transition of metal transfer mode was investigated
experimentally using high speed videography. The causes for
the deviation of predicted droplet size from measured size
are discussed with suggestion for modification in theory in
order to model more accurately metal transfer in GMAW
process.
11

• P. G. Jonsson and J. Szekely[3] studied the arc parameters and the
metal transfer in GMAW process using mild steel and helium and
argon gases as shielding gases. The governing equations for the
computational domain are developed. The solution of the governing
equations, boundary conditions, and source terms was obtained .
The arcs behaved very differently for the argon and helium
atmospheres and have pronounced effect on the system
performance.
• J. Hu, H.L. Tsai(4) prepared a unified comprehensive model to
simulate transient phenomenon occurring during the GMAW
process. Based on the unified model, a thorough investigation of the
plasma arc characteristics during the gas metal arc welding process
was conducted. It was found that the droplet transfer and the
deformed weld pool surface have significant effects on the transient
distributions of current density, arc temperature and arc pressure,
which were normally assumed to be constant. 12

• M. Schnink, M.Dreher(5)studied experimental methods for
visualization and quantification of gas flows in GMAW process.
Advanced Particle Image Velocimetry(PIV) and Schilerin technique
were used for characterization of flow field in the direct vicinity of
the arc.
• Takehiko TOH, Jun TANAKA et.al [9] studied the behavior of DC arc
plasma under a magnetic field imposed perpendicular to the plasma
current. The behavior is studied both theoretically and
experimentally by changing various parameters such as plasma
electric current, nozzle diameter, argon flow rate and magnetic flux
density. DC plasma was mathematically modeled by use of three
dimensional magneto hydrodynamics (MHD) theory and numerical
simulation performed using finite volume approach. By experimental
and theoretical analysis controlling parameters of DC plasma are
stated.
13

PROBLEM DEFINITION
• The problem being taken up for the computational analysis
pertains to GMAW process. This domain is two phase domain
consisting of mixture of molten metal and shielding gas. The
need for determining effect of nozzle geometry on shielding
gas flow and consequently on welding arc characteristics is felt
much actual in GMAW process and problem will be solved
covering both.
14

OBJECTIVES
1. Developing a numerical computational model to represent
complex two phase GMAW process.
2. To study welding arc characteristics such as electric
potential, current density, Joule heat.
3. To study effect of nozzle geometry on fluid dynamics of
shielding gas flow.
15

METHODOLOGY
• Using computational fluid dynamics (CFD)as a tool to
understand complex physics involved in the GMAW process.
• Preparing numerical domain which is two dimensional
axisymmetric model to reduce computational analysis time.
• Suitable boundary conditions to be imposed corresponding to
shielding gas enveloped molten metal so as to satisfy physics of
the problem.
• The computation will be carried out as a transient fluid flow
coupled with heat transfer by stating relevant initial conditions.
• A grid independent solution will be obtained after several trials
with different grid geometry and size and the output results are
obtained in the form of contours for distribution of
temperature and velocity and welding arc characteristics. 16

THEORY
• Theoretical study is based on static force imbalance theory(2).
• Static force imbalance theory
• The static force imbalance theory postulates that the drop
detaches from the electrode when the static detaching force
exceeds the static retaining force.
• Four different forces are considered-gravitational force,
electromagnetic force, plasma drag force are detaching forces
while the surface tension force is retaining force.
• Gravitational force is due to mass of the droplet
𝐹 𝑔 =
4
3
𝜋𝑅3 𝜌 𝑑 𝑔 ……(1)
where R= droplet radius in m
𝜌 𝑑=density of drop in kg/m3
17

• The electromagnetic force is given by Lorentz law
𝐹 𝑚 = 𝐽 × 𝐵 ……(2)
where J=current density in a/m2
B= magnetic flux in Tesla
By assuming current density on the drop uniform, the total
force can be obtained by integrating equation (2) over the
droplet surface as
𝐹 𝑚 =
𝜇0
𝐼2
4𝜋
f ..….(3)
where 𝜇0=permeability of the free surface
I =welding current in a
f= [ln
𝑅 sin 𝜃
𝑟
−
1
4
−
1
1−cos 𝜃
]
18

• The plasma drag force is given by
𝐹 𝑑 = 𝐶 𝐷 𝐴 𝑓
𝜌 𝑓
𝑣 𝑓
2
2
……(4)
where CD=drag coefficient
Af =𝜋(𝑅2 − 𝑟2) projected area in m2
𝜌 𝑓= density of fluid in kg/m3
𝑣 𝑓= velocity of fluid in m/s
• Surface tension force is given by
𝐹 𝑠 = 2𝜋𝑟𝜎 …….(5)
where r=radius of the electrode in m
𝜎= surface tension of liquid metal in N/m
• According to theory droplet size is calculated as
𝐹 𝑠 = 𝐹𝑚 + 𝐹𝑔 + 𝐹𝑑 ………(6)
19

GOVERNING EQUATION
• Governing equation is derived based on following
assumptions(3):
1. The arc is axially symmetric.
2. The arc is in Local Thermodynamic Equilibrium (LTE) that is
the electron and heavy particle temperatures are nearly
same.
3. The plasma is optically thin so that radiation may be
accounted.
4. The consumable electrode is cylindrical and tip of the
electrode and workpiece are flat.
5. The consumable electrode is in quasi state.
20

21
• Conservation of mass
𝜕𝜌
𝜕𝑡
+
1
𝑟
𝜕𝜌𝑟𝑢
𝜕𝑟
+
𝜕𝜌𝑤
𝜕𝑧
= 0 ….(7)
• Conservation of radial momentum
𝜕(𝜌𝑢)
𝜕𝑡
+
1
𝑟
𝜕𝜌𝑟𝑢2
𝜕𝑟
+
𝜕𝜌𝑢𝑤
𝜕𝑧
= −
𝜕𝑃
𝜕𝑟
+
2
𝑟
𝜕
𝜕𝑟
𝜇𝑟
𝜕𝑢
𝜕𝑟
− 𝜇
2𝑢
𝑟2
+
𝜕
𝜕𝑧
𝜇
𝜕𝑢
𝜕𝑧
+
𝜕𝑤
𝜕𝑟
− 𝐽𝑧𝐵 𝜃
.…(8)
• Conservation of axial momentum
𝜕(𝜌𝑤)
𝜕𝑡
+
1
𝑟
𝜕𝜌𝑟𝑢𝑤
𝜕𝑟
+
𝜕𝜌𝑤2
𝜕𝑧
= −
𝜕𝑃
𝜕𝑧
+
1
𝑟
𝜕
𝜕𝑟
𝜇𝑟
𝜕𝑢
𝜕𝑧
+
𝜕𝑤
𝜕𝑟
+ 2
𝜕
𝜕𝑧
𝜇
𝜕𝑤
𝜕𝑧
− 𝐽𝑟𝐵 𝜃
.…(9)
Where 𝜌= Mass density in kg/m3 r=Radial distance in m
z= Axial distance in m u= radial velocity in m/s
w= axial velocity in m/s Jr=Radial current density in a/m2
Jz= axial current density in P= pressure in N/m2
a/m2
𝜇= Viscosity in N-s/m2 𝐵 𝜃=Azimuthal magnetic field in Tesla

• Conservation of energy
𝜕𝜌ℎ
𝜕𝑡
+
1
𝑟
𝜕𝜌𝑟𝑢ℎ
𝜕𝑟
+
𝜕𝜌𝑤ℎ
𝜕𝑧
=
1
𝑟
𝜕
𝜕𝑟
𝑘𝑟
𝐶 𝑝
𝜕ℎ
𝜕𝑟
+
𝜕
𝜕𝑧
𝑘
𝐶 𝑝
𝜕ℎ
𝜕𝑧
+
𝐽 𝑧
2 + 𝐽𝑟2
𝜎 𝑒
− 𝑆𝑅 +
5𝐾𝑏
2𝑒
𝐽 𝑟
𝐶 𝑝
𝜕ℎ
𝜕𝑟
+
𝐽 𝑧
𝐶 𝑝
𝜕ℎ
𝜕𝑧
…(10)
Where h= Enthalpy in joule k=Thermal conductivity in w/m-k
Cp=Specific heat at 𝜎 𝑒=Electrical conductivity in1/Ω-m
constant pressure
SR=Radiation heat loss Kb=Boltzmann constant
term 8.617 332× 10−5 eV/k
e=elementary charge 1.602176× 10−19 C
• Conservation of electric charge
1
𝑟
𝜕
𝜕𝑟
𝜎 𝑒 𝑟
𝜕∅
𝜕𝑟
+
𝜕
𝜕𝑧
𝜎 𝑒
𝜕∅
𝜕𝑧
= 0
…(11)
where ∅=Electric potential in V
22

MODELLING
23

CFD MODELLING OVERVIEW
24
GAMBIT
ANSYS
FLUENT
Fig.5 CFD modeling overview (16)

25
Fig.7 Elements of nozzle(12) Fig.8 Modeling parameters (10)
MODELLING PARAMETERS FOR
GEOMETRY

STANDARDS USED FOR MODEL
26
Table of AWS standards(11)

27

28

THERMOPHYSICAL PROPERTIES
OF ARGON
29
Fig.9 Graph of temperature versus
properties of argon(1)

MATERIAL PROPERTIES
Densit
y(Kg/
m3)
Specific
heat(Cp)
(j/kg-k)
Thermal
conductiv
ity(w/m-
k)
Electrical
conductiv
ity(1/oh
m-m)
Magnetic
permeabi
lity (h/m)
Viscosity
(kg/m-s )
Steel 8030 502.48 16.27 8.33e6 1.257e-06 NA
Argon 1.6228 520 1.58 1000000 1.257e-06 2.125e-05
Oxygen 1.299 919.31 2.46 1000000 1.257e-06 1.919e-05
30
Material
Property

GEOMETRIC MODEL
31
Fig.10 Geometric model with boundary condition

32
Fig.11 meshing of domain
Element type: Quad-map(solid),Quad –pave(fluid)
No. of elements:89553
No. of nodes:90104

INLET VELOCITY
• Calculations for inlet velocity
𝑄 = 𝐴 𝑛 × 𝑉
where Q= flow rate(m3/min)=14 e-3m3/min
An= exit area of nozzle(m2)
V= velocity of gas flow(m/s)
𝐴 𝑛 = 𝜋/4(𝑑2
)=6.09e-4 m2
• Inlet velocity(V)=74.8 m/s
33

SOLVER INITIAL SETTING
34
Initial
boundary
conditions
• Initial velocity=74.8m/s
• Electric potential(electrode)=25 V
• Electric potential(workpiece)=0V
• Electric current=275 A
• Temperature= 300K
Models
used
• Multiphase-Volume of fluid
• Energy-On
• Viscous-Standard k-ε
• MHD model-Electric potential
Solution
methods
• Scheme-SIMPLE
• Discretization-Second order upwind
• Transient Formulation-First order implicit
Residuals &
time step
• Residuals-10e-5
• Time step-10e-4

SCALED RESIDUALS
35

RESULT AND
ANALYSIS
36

CONTOUR OF VELOCITY IN (m/s)
37
Fig. 12(a) Contour of velocity at t=100 ms

CONTOUR OF VELOCITY IN (m/s)
38
Fig. 12(b) Contour of velocity at t=400 ms

CONTOURS OF VELOCITY(m/s)
39
Fig. 12(c) Contour of velocity at t=800 ms

CONTOURS OF TURBULENT
ENERGY(m2/s2)
40
Fig.13(a) Contour of turbulent energy at t=100ms

ENERGY(m2/s2)
41
Fig.13(b) Contour of turbulent energy at t=400ms

ENERGY(m2/s2)
42
Fig.13(c) Contour of turbulent energy at t=800ms

CONTOUR OF ELECTRIC POTENTIAL(V)
43
Fig.14(a) Contour of electric potential at t=100ms

44
Fig.14(b) Contour of electric potential at t=400ms

45
Fig.14(c) Contour of electric potential at t=800ms

CONTOUR OF CURRENT
DENSITY(a/m2)
46
Fig. 15(a) Contour of current density at t=100ms

CONTOUR OF CURRENT
DENSITY(a/m2)
47
t=300ms
Fig. 15(b) Contour of current density at t=400ms

CONTOUR OF CURRENT
DENSITY(a/m2)
48
Fig. 15(c) Contour of current density at t=800ms

GRAPH OF JOULE HEAT VS
DISTANCE
• The formula for joule heat is given as,
𝑗 = 𝑉𝐼𝑡 .…(12)
• The current value is 275 A and voltage value is 25 V for 1 second of
time.
𝑗 = 6875 W
• Heat generated per unit volume is given as,
𝐽 =
𝑗
𝑣
....(13)
𝑣 =
𝜋
4
𝑑2 𝑙 ....(14)
• Diameter of electrode is 1.6mm and length is 5mm, thus
𝐽 =
6875
1.005 × 10−9
𝐽 = 6.838 × 1013
W/m3 49

DISTANCE
50
Fig 16(a) graph of joule heat vs distance at t=100 ms

DISTANCE
51
Fig 16(b) graph of joule heat vs distance
at t=400 ms
Fig 16(c) graph of joule heat vs
distance at t=800 ms

CONTOUR OF TEMPERATURE (K)
52
Fig. 17 (a) Contour of temperature at t=100 ms

53
Fig. 17 (b) Contour of temperature at t=400 ms

54
Fig. 157(c) Contour of temperature at t=800 ms

CONCLUSION
• A unified model has been developed to simulate the transport
phenomenon occurring during GMAW process.
• The heat transfer and fluid flow in the arc column were studied
based on the transient distributions of velocity, current,
temperature in the arc plasma region.
• From the study it is found that as the arc struck the shielding gas is
accelerated towards axis. When the plasma reaches towards
workpiece axial momentum of gases is changed to radial
momentum and flows away from workpiece. The shielding gas also
carries current from electrode to workpiece which helps in reducing
spatter of arc and concentrated arc is obtained.
• There are two distinct regions of electric potential contour
observed. One is around electrode with upside contour showing
current diverges from centre and another is at cathode with
downside contour showing current converges to centre. The electric
current density is concentrated at the tip of electrode causing large
amount of heat generation.
55

SCOPE OF FUTURE WORK
• Transient simulation of molten metal droplet and influence of
shielding gas flow on weld bead characteristics.
• Experimental validation of the theoretical results.
56

REFERENCE
1. Anthony B. Murphy, “Transport coefficients of helium and argon
plasmas”, IEEE transaction on plasma science,Vol.25,No.5 Oct. 1997
2. T.W. Eagar and Y.S. Kim, “Analysis of metal transfer in gas metal arc
welding”, Welding research supplement, June 1993.
3. P. G. Jonsson and J. Szekely, “Heat and mass transfer in gas metal arc
welding using argon and helium”, Metallurgical and Materials transaction
B, Volume 26B, April1995, 383-395.
4. J. Hu, H.L. Tsai, “Heat and mass transfer in gas metal arc welding”,
International journal of heat and mass transfer, Vol.50,Oct. 2006,833-846.
5. M. Schnink, M.Dreher, “Visualization and optimization of shielding gas
flows in arc welding”, Welding in the world, Vol.56, No.01, 2012.
6. H.G. Fan and R. Kovacevic, “A unified model of transport phenomenon in
gas metal arc welding including electrode, arc plasma”, Journal of physics
D: Applied Physics, Vol. 37, 2004, 2531-2544.
7. G.Wang, P.G. Huang, Y.M. Zang, “Numerical analysis of metal transfer in
GMAW under modified pulsed current condition”, Metallurgical and
material transaction B, July2003.
57

REFERENCE
8. U. Fussel, M.Dregher, M. schinck, “Numerical optimization of GMAW
torches using ANSYS CFX”, 63rd Annual assembly and International
conference of international institute of welding, Istanbul, Turkey, 11-17
July 2010.
9. Takehiko Toh, Jun Tanata, Yasho Maruki, “Magneto hydrodynamic
simulation of D.C. arc plasma” ISIJ International, Vol.45,No.7,2005, 947-
953.
10. Larry Jeffus, “Welding principles and applications”, Delmar publications,
4th edition, ISBN 0-8273-8240-5.
11. W. Hoffman, "Modern welding", The goodheart-willcox co. ltd., 3rd
edition.
12. Desineni naidu, Selahattin Ozcelik, “Modelling sensing and controlling of
GMAW”, Elsevier publications, 1st edition, ISBN 0-0804-4066-5.
13. Praxair shielding gas selection manual.
14. Suhas V. Patankar, “Numerical heat transfer and fluid flow”, McGraw-Hill
book Company, New york, ISBN 0-07-048740-5.
15. Ansys, Inc.: Ansys-GAMBIT 2.4 user Guide. Canonsburg / U.S.A.
16. Ansys, Inc.: Ansys-FLUENT 14 Solver Theory Guide. Canonsburg / U.S.A.
58

THANK YOU
59

CFD ANALYSIS OF GAS METAL ARC WELDING1

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