Modeling in Laser Cladding

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Modeling in Laser Cladding
TPTC Seminar 02/06/2004

• Guofang Zhou
• Prof. Calvin Tszeng
• Prof. Philip G. Nash

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Outline

• Literature Survey on Modeling of Laser Cladding
• Calculation of the Laser Absorption Rate of the
  Workpiece

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Part I Literature Survey on Modeling of Laser
Cladding

• Thermocapillary Phenomena
• Brewster Effect

E. Toyserkani etc. Three-dimensional finite
element modeling of laser cladding by powder
injection effects of powder feed rate and travel
speed on the process Journal of Laser
Applications V. 15, Aug. 2003 pp. 153160
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Thermocapillary Phenomena (Marangoni Effect)

• Causes
• Surface tension gradient
• Density difference
• When modeling, to account for this phenomena a
  modification to thermal conductivity is
  introduced as a
• a the correction factor, at least 2

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Surface-Active Elements on Thermocapillary
Phenomena

• (a) low-sulfur (10 ppm) material (b) high-sulfur
  (150 ppm) material

S. W. Pierce etc. Welding Research Supplement
1999, pp. 45-52s
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Brewster Effect

• The absorption rate is related to the incident
  angle of the laser which varies during melting

constant coefficient obtained experimentally
for each material
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Part 2 Calculation of The Surface Absorption in
Laser Processing
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Parameters Determining the Nature of the
Interaction

• Energy density of the laser beam
• Wavelength of the laser
• Optical properties of the material
• Surface condition
• Surface roughness
• Oxidation
• Coating

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Surface Roughness

• Multiple bounces enhance absorption rate
• The absorption rate for single reflection can be
  obtained from the model in Ang. 1997

L.K. Ang etc. Appl. Phys. Letter 70 (6) 10
February 1997 pp. 696-698
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Estimate of the Absorption Coefficient in Single
Reflection
S Polarization
Incident angle Electron plasma frequency Frequency
of the light wave Electrical conductivity of the
target metal Free space permittivity

• L.K. Ang etc. Appl. Phys. Letter 70 (6) 10
  February 1997 pp. 696-698

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Estimate of the Absorption Coefficient in Single
Reflection
Determination of electron plasma frequency

• If surface plasmon energy is known
• If electron concentration is known

h Planck constant
e electron charge m mass of an electron

• For pure Iron (bcc) with a diode laser (wave
  length 808 nm), the absorption coefficient of
  single reflection is about 2 .

C. Kittel, Introduction to Solid State Physics
(Wiley, New York, 1996)
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Modeling the Interaction of Laser with Surface

• Input Values
• the coordinates of peaks and valleys
• laser power, wave length, incident angle and
  position
• material optical properties
• Results
• surface roughness
• cumulative absorption rate

At this time our program is not ready
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Work for the Next Weeks

• Finish the program for calculating the absorption
  rate
• Model the laser cladding process with powder
  feeding
• Continual work will extend the model to wire
  feeding
• Simulate the laser cladding process

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Thank you!