Industrial Lasers for Welding

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Industrial Lasers for Welding
Ing. M. Muhshin Aziz Khan
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Facts About Laser
Laser
Basics
Light Amplification by Stimulated Emission of
Radiation

• Laser Components
• Lasing Medium
  Provides appropriate transition and
  Determines the wavelength (it must be in a
  metastable state)
• Pump
  Provides energy necessary for
  population inversion
• Optical Cavity
  Provides opportunity for
  amplification and Produces a directional
  beam (with defined length and transparency)

• Properties of Laser
• Coherent (synchronized phase of light)
• Collimated (parallel nature of the beam)
• Monochromatic (single wavelength)
• High intensity (1014W/m2)

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Facts About Laser
Laser
History
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Facts About Laser
Laser
Material Energy Levels of Atomic or Molecular
System
Laser operation takes place via transitions
between different energy levels of an atomic or
molecular system
Population inversion is impossible
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Facts About Laser
Laser
Material Energy Levels of Atomic or Molecular
System
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Facts About Laser

Optical Pumping Population Inversion
More atoms or molecules are in a higher energy
state Nonequilibrium distribution of atoms among
the various energy level of atomic system
Is population inversion by thermal excitation
possible!!??!!
Process producing population inversion is called
Pumping Energy needed for population inversion is
supplied by optical excitation with light
source Flash lamps (Pulsed laser), Arc lamp (CW
Laser), Semiconductor Diode Excitation by
electron collisions and resonant transfer of
energy (Gaseous)
Is population inversion a necesary condition for
laser operation!!??!
Light with intensity I(z) passing through a laser
medium with densities of atoms N1 and N2 in
higher and lower energy levels
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Facts About Laser

Optical Cavity Mirror Configuration

• Resonator cavity is formed by placing
• mirrors at the ends of the active medium
• The mirrors are perpendicular to the axis along
  which the laser light travels
• Acts as Positive feedback system
• Provides amplification and
• directionality to a laser beam via
• oscillation
• The resonant cavity generally is much
• longer than its width

• Mirror configurations are judged on two criteria
• Stability
• Light rays bouncing back and forth
• between mirrors will be re-entrant.
• Filling of the active medium by light
• Spatial profile defined by the light rays
  fills
• all the volume of the active medium

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Facts About Laser

Optical Resonator Mirror Configurations

• Plane paraller and Confocal Mirror Configurations
• Both mirror configurations have marginal or
• delicate stability
• Plane parallel mirrors have good filling
  whereas
• confocal mirrors offers poor filling of
  active
• medium
• For plane parallel mirrors, allignment is
  really
• crucial. However, for confocal mirrors even
  if the
• configuration is not exactly perfect, the
  light rays
• will still be reentrant.

• Long-radius mirror configuration is most often
  used in modern comercial lasers
• It falls within a region of good stability
• Beam spatial profile fills active medium
• reasonably well

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Facts About Laser

Optical Resonator Gain

• Optical loss in resonant cavity
• r1 and r2 mirror loss/coupling loss
• Due to non-unity reflectivity on the
• mirrors
• Loss is Independent of cavity
• length
• exp(-2aL) 1-2aL distributed
• loss/internal loss
• Due to absorption/scattering in
• the cavity material
• Loss is proportional to cavity
• length

Oscilation Condition Gain Losses
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Facts About Laser
Laser
Efficiency
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Facts About Laser
Laser Quality and Its
Effect
Effects of Beam Quality
Beam Quality

• A measure of Lasers capability to be
• propagated with low divergence and
• focused to a small spot by a lens or mirror
• Beam Quality is measured by M2 or BPP (Beam
• Product Parameter, mm.mrad)
• Ratio of divergence of actual beam to a
  theoretical diffraction limited beam with same
  waist diameter
• M2 1 Ideal Gaussian Beam, perfectly
  diffraction limited
• Value of M2 tends to increase with
  increasing
• laser power

• Smaller focus at constant aperture and focal
  length
• Longer working distance at constant aperture
  and spot diameter
• Smaller aperture (slim optics) at constant
  focal diameter and working distance

A higher power density by a smaller spot size
with the same optics, or The same power density
at lower laser power
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Facts About Laser
Primary Adjustable Parameters
and Their Effects
Change in Pulse Duration
Primary Controllable Parameters

• Laser Beam Energy Output Characteristics
• (i) Voltage (ii) Pulse Duration
• Laser Focus Characteristic
• (iii) Laser Beam Diameter

Increased pulse duration results in deeper and
wider melting
Change in Voltage
Change in Voltage and Pulse Duration
Increased voltage results in deeper physical
penetration with less melting due to physical
pressure
Simultanous increase in voltage and pulse
duration results in deeper melting
Change in Beam Diameter
Increased beam diameter results in shallow soft
penetration and wide, but soft melting
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Facts about lasers for welding Laser
Characteristics, Quality and Application

• Typical commercial lasers for welding
• CO2 Laser
• Nd3YAG Lasers
• Lamp-pumped
• LD-pumped
• Disk Laser
• Diode Laser
• Fiber Laser

CO2 Laser M2 values CW
Output power (W) M2
lt500 1.1-1.2
800-1000 1.2-2
1000-2500 1.2-3
5000 2-5
10,000 10
CO2 Laser Characteristics CO2 Laser Characteristics
Wavelength 10.6 µm far-infrared ray
Laser Media CO2N2He mixed gas (gas)
Average Power (CW) 45 kW (maximum) (Normal) 500 W 10 kW
Merits Easier high power (efficiency 10 20)
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Facts about lasers for Welding YAG Laser Laser
Characteristics, Quality and Application
Lamp-pumped YAG Laser Characteristics Lamp-pumped YAG Laser Characteristics
Wavelength 1.06 µm near-infrared ray
Laser Media Nd3 Y3Al5O12 garnet (solid)
Average Power CW 10 kW (cascade type fiber-coupling) (Normal) 50 W4 kW
Merits Fiber-delivery, and easier handling (efficiency 14)
YAG Laser Application Automobile Industries YAG Laser Application Automobile Industries
Lamp-pumped 3 to 4.5 kW class SI fiber delivered (Mori, 2003)
LD-pumped 2.5 to 6 kW
New Development Rod-type 8 and 10 kW Laboratory Prototype
New Development Slab-type 6 kW Developed by Precision Laser Machining Consortium, PLM
YAG Laser M2 values CW PW
Output power (W) M2
0-20 1.1-5
20-50 20-50
50-150 50-75
150-500 75-150
500-4000 75-150
LD-pumped YAG Laser Characteristics LD-pumped YAG Laser Characteristics
Wavelength about 1 µm near-infrared ray
Laser Media Nd3 Y3Al5O12 garnet (solid)
Average Power CW 13.5 kW (fiber-coupling max.) PW 6 kW (slab type max.)
Merits Fiber-delivery, high brightness, and high efficiency (1020)
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Facts about lasers for welding Disk Laser Laser
Characteristics, Quality and Application
Disk Laser Characteristics Disk Laser Characteristics
Wavelength 1.03 µm near-infrared ray
Laser Media Yb3 YAG or YVO4 (solid)
Average Power CW 6 kW (cascade type max.)
Merits Fiber-delivery, high brightness, high efficiency(1015)

• Recent Development (Mann 2004 and Morris 2004)
• Commercially available disk laser system 1 and
  4 kW class
• Beam delivery with 150 and 200 µm diameter
  fiber
• Even a 1 kW class laser is able to produce
• a deep keyhole-type weld bead
• extremely narrow width
• in stainless steel and aluminum alloy

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Facts about lasers for welding Diode Laser Laser
Characteristics, Quality and Application
Diode Laser Characteristics Diode Laser Characteristics
Wavelength 0.80.95 mm near-infrared ray
Laser Media InGaAsP, etc. (solid)
Average Power CW 10 kW (stack type max.) 5 kW (fiber-delivery max.)
Merits Compact, and high efficiency (2050)

• Recent Development (Hayashi 2004 and Zediker
  2001)
• Commercially available Diode laser system
  Direct and/or fiber-coupled modes
• Found suitable for welding of
• plastics and
• thin sheets of aluminum or steel
• at high speed
• Fiber-delivered laser is used for brazing Zn-
  coated steel using robot.

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Facts about lasers for welding Fiber Laser Laser
Characteristics, Quality and Application
Fiber Laser Characteristics Fiber Laser Characteristics
Wavelength 1.07 µm near-infrared ray
Laser Media Yb3 SiO2 (solid), etc.
Average Power CW 20 kW (fiber-coupling max.)
Merits Fiber-delivery, high brightness, high efficiency(1025)

• Recent Development (Thomy et.al. 2004 and Ueda
  2001)
• Fiber lasers of 10kW or more are commercially
  available
• Fiber lasers of 100kW and more are scheduled
• Fiber laser at 6.9kW is able to provide deeply
  penetrated weld at high speed
• Fiber laser is able to replace high quality
  (slab) CO2 laser for remote or scanning welding

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Facts about lasers for welding Comparison of
different laser systems

• Correlation of Beam Quality to Laser Power
  (Katayama 2001 ONeil et. al. 2004 Shiner 2004
  Lossen 2003)
• Overlaid with condition regimes
• Beam quality of a laser worsens with an
  increase in power
• LD-pumped YAG, thin disk, CO2 and fiber lasers
  can provide high-quality beams
• The development of higher power CO2 or YAG
  lasers is fairly static and, hence Main
  focus on development i. high-power
  diode, ii. LD-pumped YAG, iii. disk and/or
  iv. fiber lasers

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Facts about lasers for welding Wavelengths of
some important laser sources for materials
processing
Expanded portion of the electromagnetic spectrum
showing the wavelengths at which several
important lasers operate
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