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Laser beam welding

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welding

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Laser beam welding

  1. 1. Laser beam welding:Laser beam welding:  High energy density input process Precisely controllable (close tolerence: ± 0.002 in.)  Low heat input produces low distortion  Does not require a vacuum (welds at atmospheric pressure)  No filler metal required Why do we need laser for welding?Why do we need laser for welding? Traditional welding:Traditional welding:  Natural limitations to speed and productivity  Thicker sections need multi- pass welds  A large heat input  Results in large and unpredictable distortions  Very difficult to robotize
  2. 2. The term laser is an acronym for Light Amplification by Stimulated Emission of Radiation. A laser beam is a powerful, narrow, monochromatic and directional beam of electromagnetic radiation. Often, these beams are within the visible spectrum of light. A laser device excites the atoms in a lasing medium. The electrons of these atoms move to a higher orbit, then release photons, creating a laser beam.
  3. 3. Laser BasicsLaser Basics Laser ComponentsLaser 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 LaserProperties of Laser CoherentCoherent (synchronized phase of light) CollimatedCollimated (parallel nature of the beam) MonochromaticMonochromatic (single wavelength) High intensityHigh intensity (~1014 W/m2 ) LLightight AAmplification bymplification by SStimulatedtimulated EEmission ofmission of RRadiationadiation
  4. 4. Laser beams are used in industry to cut and weld metal and to survey land and construct buildings.  In scientific research, they're used in laser spectroscopy and chemical analysis. They are used in medical procedures such as eye, cancer and heart surgery, as well as in cosmetic procedures. Dental applications include cavity treatment, nerve regeneration and reshaping gum tissue.
  5. 5. Laser beams can measure distances with a high degree of accuracy. Laser scanners in grocery stores save time in pricing products and in processing the customer's purchase.  In industry, laser cutting and welding are faster and more precise than other methods. In medical and dental procedures, lasers do less damage than scalpels and drills. Scientific research using lasers has led to real- world advances, such as the use of fiber optics in telephone communications and computer networking.
  6. 6. When overlaying with a laser an optical arrangement is used to focus the laser beam on the work piece and heat it. Simultaneously hardfacing material in the form of powder is introduced into the laser beam and melted. Due to the narrow heat affected zone and the fast cooling rate the heat input is low, thereby producing an almost stress free overlay. The beam is focused towards the joint which causes the materials to change from solid to liquid state. Upon cooling it returns to a solid state.
  7. 7. Low heat input Fast cooling Almost stress free overlays High hardness Fine microstructure
  8. 8. lasers used for weldinglasers used for welding  COCO22 Laser  NdNd3+3+ :YAG:YAG Lasers Lamp-Lamp-pumped LD-LD-pumped  DiskDisk Laser  DiodeDiode Laser  FiberFiber Laser
  9. 9. CO2 laser  The carbon dioxide laser (CO2 laser) was one of the  earliest gas lasers to be developed  in 1964[ , and is still one  of the most useful.   Carbon dioxide lasers are the highest-power  continuous wave lasers that are currently available. They  are also quite efficient: the ratio of output power to pump  power can be as large as 20%.   The CO2 laser produces a beam of infrared light with the  principal wavelength bands centering around 9.4 and 10.6  micrometers CO2 Laser: Characteristics Wavelength 10.6 µm; far-infrared ray Laser Media CO2 –N2 –He mixed gas (gas) Average Power (CW) 45 kW (maximum) (Normal) 500 W – 10 kW Merits Easier high power (efficiency: 10– 20%)
  10. 10. 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 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 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 (10–20%) YAG Laser Application: AutomobileAutomobile IndustriesIndustries Lamp- pumped 3 to 4.5 kW class; SI fiber delivered (Mori, 2003)(Mori, 2003) LD-pumped 2.5 to 6 kW New Development (Bachmann(Bachmann 2004)2004) Rod-type:Rod-type: 8 and 10 kW; Laboratory Prototype Slab-type:Slab-type: 6 kW; Developed by Precision Laser Machining Consortium, PLM YAG Laser
  11. 11. 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(10–15%) Disk LaserDisk Laser A thin disc is used as lasing medium… it is often called active mirror as  it is used as mirror with laser gain. Within resonator, it acts as end  mirror… 
  12. 12. 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(10–25%) Recent DevelopmentRecent Development (Thomy et.al. 2004; and Ueda 2001):  FiberFiber lasers of 10kW10kW or moremore are commerciallycommercially available  Fiber lasers of 100kW100kW and moremore are scheduledscheduled  FiberFiber laser at 6.9kW6.9kW is able to provide deeply penetrateddeeply penetrated weld at highhigh speed  FiberFiber laser is able to replacereplace high quality (slab) COCO22 laserlaser for remoteremote or scanningscanning welding Fiber LaserFiber Laser Fiber laser is meant to be lasers with optical fiber as gain medium….Fiber doped with rare earth ions e.g. erbium, neodymium or ytterbium is used as gain medium and fiber brag gratings made either directly in doped fiber or in an undopped fiber which is spliced to an active fiber are commonly used as optical resonator
  13. 13. Types of LBWTypes of LBW Conduction WeldingConduction Welding DescriptionDescription  Heating the workpiece above the melting temperature without vaporizing  Heat is transferred into the material by thermal conduction. CharacteristicsCharacteristics  Low welding depth  Small aspect ratio (depth to width ratio is around unity)  Low coupling efficiency  Very smooth, highly aesthetic weld bead ApplicationsApplications Laser welding of thin work pieces like foils, wires, thin tubes, enclosures, etc.
  14. 14. Types of LBWTypes of LBW Keyhole WeldingKeyhole Welding DescriptionDescription  Heating of the workpiece above the vaporization temperature and forming of a keyhole  Laser beam energy is transferred deep into the material via a cavity filled with metal vapor  Hole becomes stable due to the pressure from vapor generated CharacteristicsCharacteristics  High welding depth  High aspect ratio (depth to width ratio can be 10:1)  High coupling efficiency
  15. 15. LaserLaser Beam Delivery UnitBeam Delivery Unit Workpiece Positioning UnitWorkpiece Positioning Unit ProcessingProcessing OpticsOptics SchematicSchematic DiagramDiagram BeamBeam DeliveryDelivery unitunit Lasers Beam WeldingLasers Beam Welding
  16. 16.  Low possibility of HAZ in the joint  No need for filler metal  Reduce Latency  No tool wear  LBW is not influenced by magnetic fields
  17. 17. Joints must be accurately positioned Maximum weld penetration is limited (19-21mm) High reflectivity and high thermal conductivity of materials like Aluminum effect the weldability of the joint

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