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Lasers

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Mapa Mental sobre Lasers, criado por smith_legend em 21-01-2014.
smith_legend
Mapa Mental por smith_legend, atualizado more than 1 year ago
smith_legend
Criado por smith_legend aproximadamente 12 anos atrás
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Resumo de Recurso

Lasers
  1. Summary
    1. Basics
      1. Absorption
        1. Spontaneous Emission
          1. Stimulated Emission
            1. Population Inversion
      2. components
        1. Gain/Laser medium
          1. Pump Source
            1. Optical Resonator
            2. Absorption mechanisms
              1. Fresnal
                1. Ablation
                  1. Inverse Bremstrahlung
                  2. Laser Types
                    1. Excimer
                      1. 248nm
                      2. Diode
                        1. 808-1100nm
                        2. Nd:YAG
                          1. 1064nm
                          2. Fibre
                            1. 1070-1080nm
                            2. CO2
                              1. 10600nm
                          3. Laser Welding
                            1. Conduction Welding
                              1. Process
                                1. Laser absorped at surface
                                  1. Heat transfer: conduction and melt pool convection
                                2. Advantages
                                  1. Stable
                                    1. High Quality
                                      1. No material loss
                                        1. Large spot size
                                        2. Disadvantages
                                          1. Surface Reflectivity
                                            1. Slow process
                                              1. Depth limited by heat transfer
                                              2. Lasers
                                                1. CO2 (10600nm)
                                                  1. Diode (808-1100nm)
                                                2. Conduction Limited Transmission Welding
                                                  1. Near IR to weld transparent polymers
                                                    1. Interface or bottom of workpiece IR absorbing
                                                      1. heat energy absorbed enough to form weld
                                                      2. Deep Penetration (Keyhole Welding)
                                                        1. Process
                                                          1. High laser power density
                                                            1. fast vapourisation
                                                            2. vapour causes pressure depression in melt
                                                              1. keyhole forms (directly below)
                                                              2. Energy absorption
                                                                1. different to conduction
                                                                  1. In Plasma: Inverse Bremstrahlung (point like)
                                                                    1. At walls: Fresnal (line like)
                                                                  2. Advantages
                                                                    1. High aspect ratio
                                                                      1. Deep penetration
                                                                        1. High weld speed
                                                                          1. Low heat input
                                                                            1. less distortion
                                                                          2. Disadvantages
                                                                            1. Joint fit-up
                                                                              1. Defects
                                                                                1. Spatter
                                                                                  1. Cracking
                                                                                    1. Porosity
                                                                                2. Assist Gas
                                                                                  1. Cools and removes plasma
                                                                                    1. Protects from atmosphere and oxidation
                                                                                      1. Protects optics from vapour
                                                                                    2. Laser Cladding
                                                                                      1. Process
                                                                                        1. heating
                                                                                          1. Metling
                                                                                            1. dynamic melt pool
                                                                                              1. Rapid solidification
                                                                                          2. material fed into laser path
                                                                                            1. fused to substrate
                                                                                          3. Methods
                                                                                            1. Preplaced Powder
                                                                                              1. highly complex geometries
                                                                                                1. very slow
                                                                                              2. Wire fed
                                                                                                1. more heat energy
                                                                                                  1. larger melt pool
                                                                                                    1. straight line only
                                                                                                      1. high deposition rate
                                                                                                2. Blown powder
                                                                                                  1. Most versatile
                                                                                                    1. Pore free tracks
                                                                                                      1. Feeding
                                                                                                        1. Off-axis
                                                                                                          1. Coaxial
                                                                                                            1. dis/continuous
                                                                                                      2. Output variables/defects
                                                                                                        1. Microstructure
                                                                                                          1. Geometric tolerence
                                                                                                            1. Oxidisation
                                                                                                              1. Porosity
                                                                                                                1. Surface roughness
                                                                                                                  1. Dilution
                                                                                                                    1. Spallation
                                                                                                                    2. Lasers
                                                                                                                      1. C02 (10600nm)
                                                                                                                        1. Poor absorption
                                                                                                                        2. Nd:YAG (1060nm)
                                                                                                                          1. Good absorption
                                                                                                                          2. Diode (808-1100nm)
                                                                                                                            1. good absorbtion
                                                                                                                              1. High surface coupling
                                                                                                                              2. Fibre (1070-1080nm)
                                                                                                                                1. Good absorption
                                                                                                                                  1. Best for pre-placed
                                                                                                                              3. Laser Drilling
                                                                                                                                1. Lasers
                                                                                                                                  1. Nd:YAG (1064nm)
                                                                                                                                    1. Excimer (248nm)
                                                                                                                                      1. Fibre (1070-1080nm)
                                                                                                                                      2. Stages
                                                                                                                                        1. 1. Surface heating without phase change
                                                                                                                                          1. 2. surface melting
                                                                                                                                            1. 3. Vapourisation
                                                                                                                                              1. 4. Melt ejection
                                                                                                                                              2. Defects
                                                                                                                                                1. Hole tapering
                                                                                                                                                  1. Spatter
                                                                                                                                                    1. Dross
                                                                                                                                                      1. Recast layer
                                                                                                                                                        1. Micro-cracking
                                                                                                                                                        2. Types
                                                                                                                                                          1. Single Pulse
                                                                                                                                                            1. large no. holes
                                                                                                                                                              1. Nd:YAG (1064nm)
                                                                                                                                                                1. shallow, less than 1mm
                                                                                                                                                                2. Percussion
                                                                                                                                                                  1. higher aspect ratio
                                                                                                                                                                    1. inconsistent quality
                                                                                                                                                                      1. 20mm depth, 1mm dia.
                                                                                                                                                                      2. Trepanning
                                                                                                                                                                        1. combined drilling and cutting with pulses
                                                                                                                                                                          1. Freeform and contours
                                                                                                                                                                          2. Helical
                                                                                                                                                                            1. vapourization dominated
                                                                                                                                                                              1. very precise
                                                                                                                                                                                1. good microstructure
                                                                                                                                                                              2. Pulse Duration
                                                                                                                                                                                1. Long
                                                                                                                                                                                  1. Large plasma plume
                                                                                                                                                                                    1. Large HAZ
                                                                                                                                                                                      1. Shockwaves
                                                                                                                                                                                        1. Microcracking
                                                                                                                                                                                          1. Recast layer
                                                                                                                                                                                          2. Short
                                                                                                                                                                                            1. Smaller plasma plume
                                                                                                                                                                                              1. smaller HAZ
                                                                                                                                                                                          3. Laser Cutting
                                                                                                                                                                                            1. Process
                                                                                                                                                                                              1. heating
                                                                                                                                                                                                1. melting/exothermic
                                                                                                                                                                                                  1. vapourization/ejection
                                                                                                                                                                                              2. Types (relative energy)
                                                                                                                                                                                                1. Vapourization (40)
                                                                                                                                                                                                  1. Focussed beam: keyhole
                                                                                                                                                                                                    1. deepens fast
                                                                                                                                                                                                      1. vapour blows out melt
                                                                                                                                                                                                    2. Thin and nonconductive metals
                                                                                                                                                                                                    3. Fusion Cutting (20)
                                                                                                                                                                                                      1. 'melt and blow'
                                                                                                                                                                                                        1. melts material and blown out by gas jet
                                                                                                                                                                                                        2. No boiling-low HAZ
                                                                                                                                                                                                        3. Reactive Fusion Cutting(10)
                                                                                                                                                                                                          1. 'melt burn and blow'
                                                                                                                                                                                                            1. reactive gas used also
                                                                                                                                                                                                              1. less heat input
                                                                                                                                                                                                          2. Controlled Fracture Cutting (1)
                                                                                                                                                                                                            1. Brittle materials sensitive to thermal fracture
                                                                                                                                                                                                              1. localzed heating
                                                                                                                                                                                                                1. local expansion:stress build up
                                                                                                                                                                                                                  1. rapid cooling
                                                                                                                                                                                                                    1. Crack: stress raiser
                                                                                                                                                                                                              2. Scribing (1)
                                                                                                                                                                                                                1. Grooves/lines of holes in brittle material
                                                                                                                                                                                                                  1. weaken sturcture allowing mechanical break
                                                                                                                                                                                                                2. Cold Cutting (100)
                                                                                                                                                                                                                  1. Ultra short UV pulses cut without melting
                                                                                                                                                                                                                    1. breaks molecular bonds
                                                                                                                                                                                                                    2. no melt or charr or boiling
                                                                                                                                                                                                                  2. Spot size and mode
                                                                                                                                                                                                                    1. smaller spot size
                                                                                                                                                                                                                      1. less power density
                                                                                                                                                                                                                        1. higher absoprtion
                                                                                                                                                                                                                          1. lower kerf width
                                                                                                                                                                                                                      2. High brightness beam
                                                                                                                                                                                                                        1. deeper cut
                                                                                                                                                                                                                          1. narrower kerf
                                                                                                                                                                                                                            1. material removal issue
                                                                                                                                                                                                                      3. Gas jets
                                                                                                                                                                                                                        1. Too high velocity
                                                                                                                                                                                                                          1. side burning
                                                                                                                                                                                                                            1. cooling and less efficient
                                                                                                                                                                                                                            2. O2
                                                                                                                                                                                                                              1. reactive fusion cutting
                                                                                                                                                                                                                              2. Argon
                                                                                                                                                                                                                                1. Aerospace
                                                                                                                                                                                                                                2. Nitrogen
                                                                                                                                                                                                                                  1. thin sheets
                                                                                                                                                                                                                                    1. avoid oxygen scales on steel
                                                                                                                                                                                                                                    2. compressed air
                                                                                                                                                                                                                                      1. Low cost
                                                                                                                                                                                                                                        1. increased oxidation/dross

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