Laser Beam Characterization with FEM Modeling in Laser Cladding

1
Laser Beam Characterization with FEM Modeling in
Laser Cladding
Guofang Zhou zhou2001_at_iit.edu T. Calvin
Tszeng tszeng_at_iit.edu Philip Nash nash_at_iit.edu
Feb. 7th, 2003
2
Characteristics of High Power Diode Laser (HPDDL)
in the NUVONYX ISL-4000L

• Wavelength 805 nm
• Working Distance 82 mm
• Beam Dimensions at the focal point 12.5 mm 1
  mm
• Min Pulse Width 500 ?s
• Maximum Output Power 4000 Watts
• Heat Profile

Nearly tophat intensity profile along the long
axis Gaussian profile perpendicular to the line
along the short axis.
Reference http//www.nuvonyx.com, ISL-4000L
Operators Manual
3
Determination of Surface Heat Flux
Material 430 Melting Temperature 1510 C k
23.392 W/K/m rc 4.968 J/cm3/K
6000 kW/m2/s
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FEM Solution

• Newton's Law

Heat Transfer Rate Heat Transfer
Coefficient Instantaneous Temperature
Envoinment Temperature
Inverse calculation is performed with FEM
program HOTPOINT.
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Analytical Solution

• Conduction Heat Transfer by Vedat S. Arpaci

6
Temperature Distribution at 1 Second
TC
7
Comparison of FEM and ANA Results

• The accuracy of both solutions are pretty good.
• Analytical solution is more convenient and
  straightforward.

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Determination the Distributed Heat Flux
Material 430 Melting Temperature 1510 C k
23.392 W/K/m rc 4.968 J/cm3/K
10000
5000
5000
Unit kW/m2/sec
9
Temperature Distribution at 0.5 Second
6
2
4
5
1
3
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Comparison of FEM and ANA Results

• Both results are sound.
• FEM result is more accurate

FEM
Reasons The formula is based on one dimensional
heat flux but distributed heat flux has the heat
transfer at the normal direction.
ANA
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Discussion

• For one dimensional steady state heat flux,
  analytical solution is more desirable.
• For two dimensional distributed heat transfer
  problem, inverse calculation with FEM can
  characterize the heat flux rate on the surface
  with temperature histories obtained from the back
  installed thermocouples.
• One issue is the possible distortion may be
  induced in laser cladding.
• Another issue is the number and locations of
  thermocouples.
• Control of various parameters in inverse
  calculation.

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Thermophysical Property Data
MPDB Program
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Mechanical Properties
Allegheny Ludlum Company
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FEM Modeling for Distortion Consideration
Material 430 Melting Temperature 1510 C
10000
5000
5000
y
y
x
Unit kW/m2/sec
15
Distortion Grid and Temperature Distribution at
0.5 Second
Strain Contour
Temperature Contour
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Distortion Issue

• The distortion may change the actual heat flux
  into the specimen slightly.
• In the FEM calculation, the distortion can be
  ignored in the model.

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FEM Model with Temperature Dependence Properties
Material 430 Melting Temperature 1510 C
6000
4500
3000
Unit kW/m2/sec
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Temperature Distribution at 1 Second
2
3
1
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Calculated Heat Flux
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6 Unknown Thermal Boundary Conditions
5
3
4
6
2
1
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Calculated Heat Flux
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Conclusions

• FEM inverse calculation with measured temperature
  from back installed thermocouple is reliable to
  characterize the heat flux in laser cladding.
• Along the long axis, six thermocouples are
  reasonable and capable to trace the heat flux on
  the top surface.
• The characterization of short axis is need to
  experimentally further investigated.
• Mathematical model is needed to be developed to
  reconstruct the 3-dimensional profile.