fem of laser spot welding

8/8/2019 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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fem of laser spot welding

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