Characterization of Heat Absorption in Laser Processing

1
Characterization of Heat Absorption in Laser
Processing

• Guofang Zhou
• Jaimin Rao
• Dr. T. Calvin Tszeng
• Dr. Philip Nash
• Dec. 4th, 2003

This Project is financially supported by Alion
Science and Technology Inc.
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Objectives

• To quantify the heat absorption from the diode
  laser into the workpiece
• To gain the knowledge of heat absorption that
  will be utilized to determine the heat transfer
  and metallurgy in laser cladding

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Approach
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Experimental Setup
410 Stainless Steel
K-type thermocouples

• Thermocouples installed at the back
• one left in the air to get the environment
  temperature

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Line Collimated Arrays of NUVONYX ISL-4000L

• Focused Configuration of Line Source HPDDL

Wave Length 808 nm
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Experiments at Alion Sci. Tech. Inc.
1500 W Laser Source (NUVONYX Inc.)
95 mm
(Focal Distance)
22 mm
0.91 mm
20 mm
Computation Domain
SS 410 strip
Data Acquisition System
Thermocouple wires labeled 1,2,,7 from left to
right
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Measured Temperature from Laser Experiment
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Sampling Rate 500 Hz
2
4
1
5
6
2 mm
4 mm
6 mm
Failed
2
3
4
5
6
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Thermocouple Locations
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Comparison of the Calculated and Measured
Temperature
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Power Intensity during Heating Period
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Calculated Distribution of Power Intensity at
Different Area
at 0.18 Second
Thermocouples Locations
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Observations

• The absorption rate is around 20.
• The absorbed heat flux into the sample is
  relatively steady.
• The fluctuation of the very first 0.04 s is to be
  investigated.
• Heat loss in the width direction may not be
  negligible.

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Study of Heat Loss Using SYSWELD
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Temperature Contour at 0.31 second
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Heat Flux Vector of Top Surface at 0.31 s
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Observations

• Heat transfer along the short axis is very
  important.
• A new model is needed to account for the heat
  transfer along the short axis.

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Model along Short Axis
22 mm
0.91 mm
20 mm
Computation Domain
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Case 1 Power 400W Working distance
95mm Pulse width 1.5 ms Laser beam dimensions
12 0.5 mm
Heating time 1 sec Sample material 410
SS Sample size - 2220 mm Sample thickness
0.91mm Average power intensity (long axis)
33.33 W/mm
3
4
5
2
1
6
18
1 sec
0.75 sec
0.5 sec
0.25 sec
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Computational domain
0.91 mm
20 mm
22 mm

• Six independent computational models along AB,
  CD, EF,GH,IJ and KL

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Calculation Results

• Here shows the comparison of three temperature
  histories
• Calculated temperature at the T/C location
• Measured temperature at the T/C location
• Calculated temperature at the top surface which
  is right above the T/C location

Graph of temperature contour of one of your
calculations at the end of laser heating
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Comparison between calculated and experimentally
recorded temperature
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Results from thermocouple 3
Temperature contour after 0.32 seconds
Temperature contour after 0.96 seconds
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• Power intensity increases from 0.2 sec to 0.4
  sec but after that it drops , as we loose energy
  from the model
• Absorption is in the range of 50 75

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Case 2 Power 600W Working distance
95mm Pulse width 1.5 ms Laser beam dimensions
12 0.5 mm
Heating time 1 sec Sample material 410
SS Sample size - 2220 mm Sample thickness
0.91mm Average power intensity (long axis) 50
W/mm
3
4
2
5
1
6
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1 sec
0.75 sec
0.5 sec
0.25 sec
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• Power intensity drops with time as we loose
  energy from the model
• Absorption is in the range of 40 60

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Observations

• Power intensity distribution is not top hat as
  claimed by manufacturer
• Absorption for case 2 and3 ranges from 40- 75.
• Heat absorption decreases in later stages of
  heating

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Presentations and publications

• Presented at 2nd surface engineering conference
  held by ASM International at Indianapolis in
  September 2003 Net heat input by diode laser
  beam
• Submitted abstract at paper prize competition
  2004 held by Bodycote Determination of heat
  absorption in substrate during diode laser
  surface modification process

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Work Plan

• Use specially designed calorimeter at Alion
  Science and Technology to confirm the results
  from inverse heat calculation and study change
  in absorption behavior in molten phase.
• Study the effect of surface roughness, working
  distance and power intensity on heat absorption .
• Submit abstract for 3rd surface engineering
  conference to be held by ASM International at
  Orlando in August 2004

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Thank you!