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Diode Laser Evaluation

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					    Diode Laser Evaluation
          Georgette Kotsagrelos
Concurrent Technologies Corporation (CTC)
               (412) 577-2655
            kotsagre@ctcgsc.org
                  Overview

•   Background
•   Diode Laser Evaluations
•   Diode Laser Status
•   US Air Force Diode Laser Evaluation
•   Summary
                Background

• Current methods for the removal of DoD
  coating systems from on- and off-
  equipment components are:
  – Costly
  – Time consuming
  – Labor-intensive
  – Environmentally unfriendly
                Background

• Diode lasers are viable coating removal
  alternatives
  – Require more optimization efforts than CO2
    and Nd:YAG lasers
• Current uses include
  – Coating Removal
  – Surface treatment
  – Surface metallurgy
  – Cleaning
  – Welding
  – And more…
                        Background

• Benefits
  – High Efficiency
     • 25+ Percent higher than other lasers (i.e., CO2)
     • Lower Cost
     • Longer Life
  – Rugged Construction
     •   Stack of Laser Diodes
     •   Mechanically Solid
     •   No delicate internal mirrors to adjust
     •   Lower voltages
  – Power levels to 4000 Watts practical
        Diode Laser Evaluations

• Navy radomes
• Portable Handheld Laser Small Area
  Supplemental Coating Removal System
  (PLCRS)
• Specialty Coatings Laser Removal
  Systems (SCLRS)
             Navy Radome Evaluation

• National Defense Center for Environmental Excellence
  (NDCEE)
   – Navy Environmental Leadership Program (NELP) Demonstration
     Project, Paint/De-paint Task 3a
• Laser
   –   Pulsed diode laser
   –   Robot controlled
   –   Laser head working distance of 3.5 inches
   –   Wavelength: 808 nm
   –   Air flow: nitrogen blow-off jet at 10 psi
   –   Frequency: up to 20 kHz
   –   Power: up to 4000 Watts
        Navy Radome Evaluation

• Substrate
  – Honeycomb composite
• Coating System
  – Primer: epoxy, MIL-PRF-23377 (4 mils)
  – Topcoat: polyurethane, MIL-PRF-85285 (4 mils)
               Navy Radome Evaluation

        Peak   Pulse    Robot    Frequency
                                    (Hz)        # of
Zone   Power   Width    Speed
                                               Passes
                                                                    Results
         (W)    (µs)   (M/min)     (pass)
 1     2000    150       30      6000 (1-3),     5      Removed down to green primer
                                  3000 (4),
                                  2000 (5)
 2     2000    150       30      6000 (1-3),     7      Reached primer
                                 3000 (4-7)
 3     2000    150       30      6000 (1-5),     10     Reached substrate
                                 3000 (6-10)
            Navy Radome Evaluation

• NDCEE Task No. 308
  – Coatings Removal from Delicate Substrates and Application
    Process Improvements for Department of Defense (DoD)
    Industrial Facilities
• Laser
  –   Pulsed diode laser
  –   Robot controlled
  –   Pulse Width: 150 – 400 µs
  –   Wavelength: 808 nm
  –   Air flow: nitrogen blow-off jet up to 44 psi
  –   Frequency: up to 6000 Hz
  –   Power: up to 6000 Watts
          Navy Radome Evaluation

• Coating System
   – Primer: White high build epoxy (4-6 mils)
   – Topcoat: Gray aliphatic polyurethane (4-6 mils)
• Substrate
   – Honeycomb composite
   – Test pieces: 14” x 5” and 17” x 5”
• Strip rate
   – Range: 160 - 182 ft2/hr
Navy Radome Evaluation




Radome: 14” x 5”
Power: 2 kW
Temperatures: 118°F – 200°F
Average Strip Rate: 171 ft2/hr

Results: Removed coating down to primer
         with substrate showing in small
         area after 6 passes.
                   PLCRS
           Diode Laser Evaluations
• Laser
  –   Robot controlled diode laser
  –   Constant airflow and exhaust system
  –   Laser head working distance: 79 mm
  –   Power: 250 Watt
  –   Wavelength: 808 nm
• Substrates
  – 2024-T3 aluminum (clad)
  – 1010 Steel (cold rolled)
  – Graphite epoxy (GE) composite (14-ply)
                   PLCRS
           Diode Laser Evaluations
Coating Systems
1)   Primer: MIL-PRF-23377G
     Topcoat: Advanced Performance Coating (APC)
     (3-6 mils)
2)   Primer: MIL-PRF-23377G
     Topcoat: MIL-PRF-85285 (3-6 mils)
3)   Primer: MIL-P-53030
     Topcoat: MIL-C-46168 (CARC) (3-6 mils)
                           PLCRS
                   Diode Laser Evaluations
                                    Scan      Line                Strip
Top Coating                Power                      Elapsed
               Substrate           Speed    spacing                rate           Results
(Thickness)                 (W)                       Time (s)
                                   (mm/s)    (mm)                (mm2/s)
APC (6 mils)      Al        185     500      0.27      12.6        84      Coating totally removed
APC (3 mils)      Al        185     700      0.27       8.7       121      Clean substrate surface
MIL-C-46168       Al        185     350      0.27      17.4        61      Coating totally removed
(6 mils)
MIL-C-46168       Al        185     600      0.27      12.8        82      Coating totally removed
(3 mils)
MIL-C-46168      Steel      185     400      0.27      14.8        71      Down to the substrate
(3 mils)
MIL-P-85285       Al        185     600      0.27      10.8        98      Coating totally removed
(6 mils)
MIL-P-85285       Al        185     650      0.24       9.7        97      Coating removed
(3 mils)
MIL-P-85285       GE        185     400      0.42      17.3       104      Almost all primer
(6 mils)                                                                   removed
                     PLCRS
              Diode Laser Evaluation
             Scan      Line                Strip
    Power                      Elapsed
#
     (W)
            Speed    spacing
                               Time (s)
                                            rate                   Results
            (mm/s)    (mm)                (mm2/s)
1    185     700      0.27       8.8       120      Thin film of primer left. Surface of
                                                    substrate dirty.
2    185     600      0.27      10.8        98      Very thin film of primer left.

3    185     550      0.27      12.1        87      Nearly clean surface.

4    185     500      0.27      12.6        84      Coating totally removed.



                                                               Coating System:
                                                               MIL-P-23377G primer
                                                               APC topcoat

                                                               Thickness: 6 mils

                                                               Substrate: 2024
                                                               Aluminum
                     PLCRS
              Diode Laser Evaluation
             Scan      Line                Strip
    Power                      Elapsed
#
     (W)
            Speed    spacing
                               Time (s)
                                            rate                   Results
            (mm/s)    (mm)                (mm2/s)
1    185     680      0.42        --        --      Not through topcoat
2    185     600      0.27       9.7       109      Topcoat left
3    185     550      0.27      12.1        87      Not even through topcoat
4    185     400      0.27      15.8        67      Thin film of primer left
5    185     350      0.27      17.4        61      Coating totally removed



                                                          Coating System:
                                                          MIL-P-23377G primer
                                                          MIL-C-46168 topcoat

                                                          Thickness: 6 mils

                                                          Substrate: Aluminum
                     PLCRS
              Diode Laser Evaluation
             Scan      Line                Strip
    Power                      Elapsed
#
     (W)
            Speed    spacing
                               Time (s)
                                            rate                  Results
            (mm/s)    (mm)                (mm2/s)
1    185     650      0.27       9.7       109      W/o air flow not through
2    185     650      0.27       9.7       109      Strong air flow coming deeper
3    185     550      0.27      12.1        87      Ok
4    185     600      0.27      10.8        98      Maximum speed, ok




                                                         Coating System:
                                                         MIL-P-23377G primer
                                                         MIL-P-85285 topcoat

                                                         Thickness: 6 mils

                                                         Substrate: Aluminum
                     PLCRS
              Diode Laser Evaluation
             Scan      Line                Strip
    Power                      Elapsed
#
     (W)
            Speed    spacing
                               Time (s)
                                            rate                   Results
            (mm/s)    (mm)                (mm2/s)
1    185     600      0.27      10.3       102      Primer left
2    185     500      0.27      12.1        87      Thin film of primer left if substrate is
                                                    black
3    185     700      0.27       8.4       125      Only topcoat removed
4    185     400      0.27      14.8        71      Down to the substrate




                                                            Coating System:
                                                            MIL-P-53030 primer
                                                            MIL-C-46168 topcoat

                                                            Thickness: 3 mils

                                                            Substrate: Steel
                     PLCRS
              Diode Laser Evaluation
             Scan      Line                Strip
    Power                      Elapsed
#
     (W)
            Speed    spacing
                               Time (s)
                                            rate                 Results
            (mm/s)    (mm)                (mm2/s)
1    185     550      0.42      12.9       140      Topcoat not removed
2    185     450      0.42      15.2       119      Uneven removal of topcoat and primer
3    185     400      0.42      17.3       104      Almost all primer removed
4    185     350      0.42      19.8        91      Too much power




                                                           Coating System:
                                                           MIL-P-23377G primer
                                                           MIL-P-85285 topcoat

                                                           Thickness: 6 mils

                                                           Substrate: Graphite Epoxy
                     SCLRS
              Diode Laser Evaluation
• Laser
   –   Robot controlled continuous wave (CW) diode laser
   –   Constant airflow and exhaust system
   –   Laser head working distance: 79 – 195 mm
   –   Power: 200 W
   –   Wavelength: 960 nm
• Substrate
   – 2024-T3 aluminum (bare)
• Coatings
   –   Primer MIL-PRF-23377 (0.9 mils)
   –   Topcoat MIL-PRF-85285 (3-6 mils)
   –   Sheet Radar Absorbing Material (RAM) (40 mils)
   –   Sealant PR1440-B2 (125 mils)
                                   SCLRS
                            Diode Laser Evaluation
                              Scan      Line                Strip     Removal
                     Power                      Elapsed
 Top Coating
                      (W)
                             Speed    spacing
                                                Time (s)
                                                             rate       Size         Results
                             (mm/s)    (mm)                (mm2/s)   (mmxmm)
MIL-P-85285           200     300      0.45      16.4       123       45 x 45   Removed coating
                                                                                down to substrate
Sealant               200     NA       0.45       90         NA        Line     Removed coating to
                                                                                substrate, but very
                                                                                slow. Recommend
                                                                                higher power.
Sheet RAM             200     NA       0.45       90         NA        Line     Removed coating
                                                                                and adhesive, but
                                                                                very slow.
                                                                                Recommend higher
                                                                                power.
NA = Not Available
              Diode Laser Status

• Currently no handheld capabilities of diode lasers
• Preliminary stripping showed positive results
  – Confident in diode laser coating removal capabilities
• Potential for faster strip rates than Nd:YAG and
  CO2 lasers
• U.S. Air Force working with laser institutes for
  diode laser optimization and materials interaction
     USAF Diode Laser Evaluation

• Project Objectives
  – Develop a test plan for evaluation and
    optimization of the diode laser system
  – Determine diode laser system operating
    parameters that will provide the fastest strip
    rates without damaging the substrate
     • Determine materials interaction results
     • Develop handheld capabilities
       Stakeholders & Resources

• Team
  – Team effort between personnel from
    Concurrent Technologies Corporation (CTC),
    Air Force (AF), and AF contractors

• Resources
  – Laser vendors and system integrators
  – Fraunhofer Institute
  – Other research and development (R&D) and
    educational institutions
                              Goals

• Evaluate and optimize 250 W diode
  laser system
   – Develop parameters using:
      • Wavelengths of 808 & 940 nm
      • Pulsed and continuous wave modes of
        operation
   – Monitor performance indicators
      • Surface temperature
      • Strip rate
      • Visual damage, etc.
   – Determine optimal stripping parameters
     for all substrates and coatings tested
   – Evaluate the impact caused by the
     diode laser to the substrate
                      Phase I
                     Evaluation
• Coatings to test
  –   Epoxy primer
  –   Polyurethane topcoat
  –   Polysulfide sealant
  –   Epoxy powder coating
  –   Spray Urethane
  –   Conductive Coating
                     Phase I
                    Evaluation
• Substrates to test
  –   2024 Al
  –   4130 ST
  –   Graphite Epoxy (GE) composite
  –   Bismaleimide (BMI) composite
  –   Polyetheretherketone (PEEK) composite
             Extended Evaluation

• After initial evaluation, if positive results:
   – Use optimal parameters on additional
     coating/substrate panels
   – Determine potential of diode laser to selectively
     remove individual layers of conductive coating
   – Determine recommended parameters and range of
     laser optimal performance
              Project Status

• In process of awarding Phase I evaluation
  to Fraunhofer Institute, Michigan
• Expected completion date March 2004
                   Summary

• Diode lasers have the potential to:
  – Enhance/replace current hazardous coatings removal
    processes
  – Enhance/replace time consuming coatings removal
    processes

				
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