FEM of Laser Spot Welding
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Transcript of FEM of Laser Spot Welding
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Finite Element Analysis of Pulsed
Laser Spot Welding
Rohit RaiRituraj Nandan
Chandan Kumar
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Introduction: Laser spot welding
Highlights
Highly localized heating
High temperatures High precision and control
Applications
Electronic packaging in various industries, viz.automobile, medical equipments, semiconductors.
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Problem Description
r
z
y
x
z
Laser
spot
b
l
h
Uniform input energy flux of 75 x 106 W/m2
Convective loss at surfaces, h=15 W/m2
Clamping on ends
Temperature distribution, andStress field
Boundary Conditions
Initial Condition
Temperature = 298 K
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Assumptions
1. Uniform laser beam energy distribution overcircular spot.
2. Constant absorptivity.
3. Negligible heat loss by radiation.
4. z-direction d.o.f is zero for the clamped faces.
5. Free surface deformation due to melting, the
accompanying expansion, and vaporization isneglected.
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Solution Procedure
Transient thermal analysis: 0.1 s of heating
0.05 s of cooling
Temperatures are written in a file. Structural Analysis
Static analysis done for the particular time step.
Elements above melting point are killed.
Temperatures assigned to live nodes. Constraints applied.
Structural calculations for live elements.
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Finite Element Issues
Element Type
Solid 90 for thermal analysis
Shape/Characteristic: Brick, 20 nodes
d.o.f.: Temperature at each node
Solid 95 for structural analysis
Allows element death and birth d.o.f.: Diplacement at each node
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Material Properties
Elastic Modulus in Pascal
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Material Properties Contd.
Specific Heat in J/kg-K
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Material Properties Contd.
Thermal conductivity in W/m-K
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Results and Discussion
1. Temperature
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R n D contd.
Thermal Strain
t=0.075 s
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Simplified Analytical Solution
0.002 0.004 0.006 0.008
400
600
800
1000
1200
Temperature,K
Depth, m
FEM
Approximate analytical
solution
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R n D contd.
Deformation
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R n D contd.
von Mises stress
0.025 s 0.05 s
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R n D contd.
von Mises stress
0.075 s 0.1 s
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R n D contd.
Plastic strain
t=0.075 s
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Non FE verification of stress
Calculated from
+=
)()(12
)(1
2/
2/
3
2/
2/
zTzdzzTt
dzzTt
E
t
t
t
t
-6.07e8 Pa: near the surface of the workpiece
Cheng et al.
Calculated by FE model:~1.51e8 Pa
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Summary and Conclusions
Thermal modeling of heating and cooling
Structural modeling of heating phase
No stress calculation in liquid metal pool Maximum stresses in HAZ
More prone to cracking
Model can be used to find safe weldingparameters
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Future work
Stress analysis for cooling part
Consider phase transformation
Affects stresses and mechanical properties If one has time, and resources
Use of a finer mesh, esp. for stress analysis
Consider radiation loss CFD analysis for the molten metal pool
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References
1. Li Yajiang, Wang Juan, Chen Maoai and Shen Xiaoqin, Finite elementanalysis of residual stress in the welded zone of a high strength steel, Bull.Mater. Sci., Vol. 27, No. 2, April 2004, pp. 127132.
2. Justin D. Francis, Welding Simulations of Aluminum Alloy Joints by FiniteElement Analysis, MS Thesis, Virginia Polytechnic Institute and StateUniversity, Blacksburg, Virginia, April 2002.
3. Product Manual, ANSYS, v.10.
4. http://www.mece.ualberta.ca/tutorials/ansys/
5. P. J. Cheng and S. C. Lin, An analytical model to estimate angle formed bylaser, Journal of Materials Processing Technology, Volume 108, Issue 3, 17January 2001, pp. 314-319.
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