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Industrial Lasers for Welding Ing. M. Muhshin Aziz Khan.

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Presentation on theme: "Industrial Lasers for Welding Ing. M. Muhshin Aziz Khan."— Presentation transcript:

1 Industrial Lasers for Welding Ing. M. Muhshin Aziz Khan

2 Facts About Laser: Laser Basics Light Amplification by Stimulated Emission of Radiation Laseroptical amplifier Laser is essentially an optical amplifier that Generates and Amplifies Stimulated Emission Laser Components Lasing Medium: Lasing Medium: Provides appropriate transition and Determines the wavelength (it must be in a metastable state) Pump: Pump: Provides energy necessary for population inversion Optical Cavity: Optical Cavity: Provides opportunity for amplification and Produces a directional beam (with defined length and transparency) Properties of Laser Properties of Laser Coherent Coherent (synchronized phase of light) Collimated Collimated (parallel nature of the beam) Monochromatic Monochromatic (single wavelength) High intensity High intensity (~10 14 W/m 2 )

3 Facts About Laser: Laser History

4 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 + - E3E3 E2E2 E1E1 Energy Ground State 1 ° Excited State 2 ° Excited State Highly excited State Ground State Excitation Laser Transition Population Inversion Two- Level For material with Two-Level system Absorption and stimulated processes neutralize one another.  The material becomes transparent. Population inversion is impossible

5 Facts About Laser: Laser Material: Energy Levels of Atomic or Molecular System Three- Level Excitation Laser Transition Population Inversion Highly excited State Ground State Metastable State Fast Decay Four- Level Excitation Laser Transition Population Inversion Highly excited State Ground State Higher Metastable State Lower Metastable State Fast Decay Natural Depopulation

6 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 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 by thermal excitation possible !!??!! According to Boltzmann Ratio Where E 2 > E 1 Is population inversion a necesary condition for laser operation!!??! Light with intensity I(z) passing through a laser medium with densities of atoms N 1 and N 2 in higher and lower energy levels Absorption by atoms in Level 1 decreases the Intensity according to I(z) = I(0) exp -(σz) Amplification by stimulated emission increases the Intensity according to I(z) = I(0) exp -(gz) Net effect of passage of light through the material

7 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 it’s 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 Stability Diagram for laser resonators consisting of two mirrors Condition for stability of a resonator

8 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 Possible Mirror Configurations

9 Facts About Laser: Optical Resonator: Gain Laser turn-on and gain saturation Gain decreases as output power increases Saturation Laser gain and losses Optical loss in resonant cavity  r 1 and r 2 : mirror loss/coupling loss Due to non-unity reflectivity on the mirrors Loss is Independent of cavity length  exp(-2αL) ~ 1-2αL : distributed loss/internal loss Due to absorption/scattering in the cavity material Loss is proportional to cavity length Oscilation Condition : Gain ≥ Losses

10 Facts About Laser: Laser Efficiency Output versus input power for an optically pump power Slope efficiency (or differential efficiency ) The slope of the curve obtained by plotting the laser output versus the pump power.

11 Facts About Laser: Laser Quality and Its Effect measurecapability  A measure of Lasers’ capability to be propagateddivergence ☺ propagated with low divergence and focusedlens mirror ☺ focused to a small spot by a lens or mirror  BeamM 2 BPPB  Beam Quality is measured by M 2 or BPP ( B eam PPmm.mrad P roduct P arameter, mm.mrad ) divergenceactual theoretical diffraction samewaist Ratio of divergence of actual beam to a theoretical diffraction limited beam with same waist diameter M 2 = 1 ; Gaussian Beam M 2 = 1 ; Ideal Gaussian Beam, perfectly diffraction limited Valueincreaseincreasing Value of M 2 tends to increase with increasing power laser power Effects of Beam Quality Beam Quality Smallerconstant Smaller focus at constant aperture and focal length Longerconstant Longer working distance at constant aperture and spot diameter Smallerconstant Smaller aperture (‘slim optics’) at constant focal diameter and working distance higher power densitysmaller same optics A higher power density by a smaller spot size with the same optics, or same lowerlaser The same power density at lower laser power

12 Facts About Laser: Primary Adjustable Parameters and Their Effects  Laser Beam Energy Output Characteristics (i) Voltage (ii) Pulse Duration  Laser Focus Characteristic (iii) Laser Beam Diameter Primary Controllable Parameters Change in Voltage Increaseddeeper penetrationless physical Increased voltage results in deeper physical penetration with less melting due to physical pressure Change in Pulse Duration Increased deeperwider Increased pulse duration results in deeper and wider melting Change in Voltage and Pulse Duration Simultanous increase deeper Simultanous increase in voltage and pulse duration results in deeper melting Change in Beam Diameter Increased shallow softwide soft Increased beam diameter results in shallow soft penetration and wide, but soft melting

13 Facts about lasers for welding Laser Characteristics, Quality and Application Typical commercial lasers for welding  Typical commercial lasers for welding CO 2 1. CO 2 Laser Nd 3+ :YAG 2. Nd 3+ :YAG Lasers Lamp- Lamp- pumped LD- LD- pumped 3. Disk 3. Disk Laser 4. Diode 4. Diode Laser 5. Fiber 5. Fiber Laser CO 2 Laser: Characteristics Wavelength 10.6 µm; far-infrared ray Laser Media CO 2 –N 2 –He mixed gas (gas) Average Power (CW) 45 kW (maximum) (Normal) 500 W – 10 kW Merits Easier high power (efficiency: 10– 20%) Output power (W) M2M2M2M2< ,00010 CO 2 Laser: M 2 values [CW]

14 Lamp-pumped YAG Laser: Characteristics Wavelength 1.06 µm; near-infrared ray Laser Media Nd 3+ : Y 3 Al 5 O 12 garnet (solid) Average Power [CW] 10 kW (cascade type & fiber- coupling) (Normal) 50 W–4 kW Merits Fiber-delivery, and easier handling (efficiency: 1–4%) LD-pumped YAG Laser: Characteristics Wavelength about 1 µm; near-infrared ray Laser Media Nd 3+ : Y 3 Al 5 O 12 garnet (solid) AveragePower [CW] : 13.5 kW (fiber-coupling max.) [PW] : 6 kW (slab type max.) [PW] : 6 kW (slab type max.) Merits Fiber-delivery, high brightness, and high efficiency (10–20%) Output power (W) M2M2M2M YAG Laser: M 2 values [CW & PW] 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 Slab-type: 6 kW; Developed by Precision Laser Machining Consortium, PLM Facts about lasers for Welding: YAG Laser Laser Characteristics, Quality and Application

15 Disk Laser: Characteristics Wavelength 1.03 µm; near-infrared ray Laser Media Yb 3+ : YAG or YVO 4 (solid) Average Power [CW] 6 kW (cascade type max.) Merits Fiber-delivery, high brightness, high efficiency(10–15%) Recent Development Recent Development (Mann 2004; and Morris 2004):  Commerciallydisk 1 4  Commercially available disk laser system: 1 and 4 kW class delivery150 fiber  Beam delivery with 150 and 200 µm diameter fiber 1 kWable  Even a 1 kW class laser is able to produce deepkeyhole-type a deep keyhole-type weld bead extremely extremely narrow width stainlessaluminum in stainless steel and aluminum alloy Facts about lasers for welding: Disk Laser Laser Characteristics, Quality and Application

16 Diode Laser: Characteristics Wavelength0.8–0.95 mm; near-infrared ray Laser Media InGaAsP, etc. (solid) Average Power [CW] 10 kW (stack type max.) 5 kW (fiber-delivery max.) MeritsCompact, and high efficiency (20–50%) Recent Development Recent Development (Hayashi 2004; and Zediker 2001):  CommerciallyDiode Directfiber-coupled  Commercially available Diode laser system: Direct and/or fiber-coupled modes suitable  Found suitable for welding of plastics plastics and thinaluminumsteel thin sheets of aluminum or steel high at high speed Fiber-deliveredZn- coatedrobot  Fiber-delivered laser is used for brazing Zn- coated steel using robot. Facts about lasers for welding: Diode Laser Laser Characteristics, Quality and Application

17 Fiber Laser: Characteristics Wavelength1.07 µm; near-infrared ray Laser Media Yb 3+ : SiO 2 (solid), etc. Average Power [ Power [CW] 20 kW (fiber-coupling max.) MeritsFiber-delivery, high brightness, high efficiency(10–25%) Recent Development Recent Development (Thomy et.al. 2004; and Ueda 2001):  Fiber10kWmore commercially  Fiber lasers of 10kW or more are commercially available 100kWmore scheduled  Fiber lasers of 100kW and more are scheduled Fiber6.9kW deeply penetratedhigh  Fiber laser at 6.9kW is able to provide deeply penetrated weld at high speed Fiberreplace CO 2 laserremotescanning  Fiber laser is able to replace high quality (slab) CO 2 laser for remote or scanning welding Facts about lasers for welding: Fiber Laser Laser Characteristics, Quality and Application

18 Correlation of Quality Power Correlation of Beam Quality to Laser Power (Katayama 2001; O’Neil et. al. 2004; Shiner 2004; Lossen 2003):  Overlaidcondition  Overlaid with condition regimes qualityworsens increasepower  Beam quality of a laser worsens with an increase in power LD-pumpeddiskCO 2 fiber high-quality  LD-pumped YAG, thin disk, CO 2 and fiber lasers can provide high-quality beams higherCO 2 fairly focus development: high-powerLD-pumped diskfiber  The development of higher power CO 2 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 Facts about lasers for welding Comparison of different laser systems

19 Expanded portion of the electromagnetic spectrum showing the wavelengths at which several important lasers operate Facts about lasers for welding Wavelengths of some important laser sources for materials processing CO 2 Laser

20 Thank You for Patience Hearing


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