8/6/2019 CFDandFEMAnalysisofLaserWeldShapeanditsCharacteristic
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CFD and FEM Analysis of Laser Weld Shape and its Characteristic
M Sundar, R Eghlio and L LiLaser Processing Research Centre, School of Mechanical, Aerospace and Civil Engineering
1. IntroductionLaser butt welding simulation has been performed by many researchers in the past and in all previous simulations, the
urface of the weld bead is assumed to be perfectly flat which is a crude assumption. In this work a coupled thermo-structural
nalysis was carried out with an objective to predict the effect of laser parameters on change in surface topology of the weld
ead and also its subsequent effect on thermal and structural results. The numerical simulation results agree well with the
xperimental results conducted on a mild steel sheet using a 1 kW fibre laser.
2. FormulationThe 3D CFD analysis was performed incorporating Navier-
Stokes mass, energy and momentum equations. Heat input
is modelled as a Gaussian volumetric heat source and heat
loss is due to convection and radiation in the surfaces. The
weld surface topological changes are primarily due to the
fluid flow in the weld pool, which is driven by combined
surface tension and buoyancy force. The FEM
4. FEM Results
Speed = 75 mm/s
Speed = 100 mm/s
Speed = 125 mm/s
0.0E+00
5.0E+07
1.0E+08
1.5E+08
2.0E+08
2.5E+08
3.0E+08
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
Stress(Pa)
Distance (mm)
Sp ee d = 75 mm/s Sp ee d = 10 0 m m/ s S pe ed = 1 25 mm /s
geometry and the temperature history predicted by the CFDanalysis. To understand the effect of bead geometry on the
tensile strength characteristics of the welds, a non-linear
finite element analysis incorporating multilinear isotropic
hardening was performed.
3. CFD Results
6. DiscussionAt low weld speeds, the molten pool on the surface flows
outwards causing a depression in the weld pool centre and
at high speeds, the molten pool flows inward causing a
humped weld and at some particular welding speed there
Figure 1: Different weld bead top surface profiles for 600 W laser powerand speed: a) 75 mm/s, b) 100 mm/s, c) 125 mm/s
(a) (b) (c)
Fi ure 2: Com arison of ex erimental (left side) and simulated (ri ht side) weld(a) (b) (c)
Figure 4: Comparison of residual stress for difference welding conditions
a) along the cross section b) across the weld bead surfaces
(a) (b)
Figure 5: Comparison of experimental and simulated tensile test resultsfor a speed of : a) 75 mm/s, b) 100 mm/s, c) 125 mm/s
(a) (b) (c)
5. Tensile Test Results
Weld line
Failure zone
-
.22E-4
-.1
71E-4
-.1
22E-4
-.7
34E-5
-.1
85E-7
7. ConclusionsThe CFD simulation effectively predicts and paves way to control the weld bead surface geometry. CFD modelling has
shown the main reason for the different weld bead surface geometry formation as the Marangoni effect with flipping
surface tension gradient signs as the melt pool temperature changes. In FEM analysis the net-shape weld shows smooth andminimal stress distribution also, it shows better tensile test performance largely due to the lack of stress concentrators at the
weld zones which is also the case in experimentation.
gradients. The FEM results show relatively smaller and
smoother residual stresses for net shape welding shape,
possibly due to reduced heat input to the material. In the
tensile test simulation the net shaped weld, shows high
distortion away from the welding zone because of its flat
surface geometry shifting and spreading the stress
concentration to places away from the weld zones.
bead cross section profiles for a speed of: a)75 mm/s, b)100 mm/s, c)125 mm/s
Figure 3: Comparison of top surface velocity vector for 600 W laser powerand speed: a) 75 mm/s, b) 100 mm/s, c) 125 mm/s
(a) (b) (c)