Mind Map by , created over 5 years ago

Mind Map on Lasers, created by smith_legend on 01/21/2014.

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Created by smith_legend over 5 years ago
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1 Summary
1.1 Basics
1.1.1 Absorption Spontaneous Emission Stimulated Emission Population Inversion
1.2 components
1.2.1 Gain/Laser medium
1.2.2 Pump Source
1.2.3 Optical Resonator
1.3 Absorption mechanisms
1.3.1 Fresnal
1.3.2 Ablation
1.3.3 Inverse Bremstrahlung
1.4 Laser Types
1.4.1 Excimer 248nm
1.4.2 Diode 808-1100nm
1.4.3 Nd:YAG 1064nm
1.4.4 Fibre 1070-1080nm
1.4.5 CO2 10600nm
2 Laser Welding
2.1 Conduction Welding
2.1.1 Process Laser absorped at surface Heat transfer: conduction and melt pool convection
2.1.2 Advantages Stable High Quality No material loss Large spot size
2.1.3 Disadvantages Surface Reflectivity Slow process Depth limited by heat transfer
2.1.4 Lasers CO2 (10600nm) Diode (808-1100nm)
2.2 Conduction Limited Transmission Welding
2.2.1 Near IR to weld transparent polymers
2.2.2 Interface or bottom of workpiece IR absorbing
2.2.3 heat energy absorbed enough to form weld
2.3 Deep Penetration (Keyhole Welding)
2.3.1 Process High laser power density fast vapourisation vapour causes pressure depression in melt keyhole forms (directly below) Energy absorption different to conduction In Plasma: Inverse Bremstrahlung (point like) At walls: Fresnal (line like)
2.3.2 Advantages High aspect ratio Deep penetration High weld speed Low heat input less distortion
2.3.3 Disadvantages Joint fit-up Defects Spatter Cracking Porosity
2.4 Assist Gas
2.4.1 Cools and removes plasma
2.4.2 Protects from atmosphere and oxidation
2.4.3 Protects optics from vapour
3 Laser Cladding
3.1 Process
3.1.1 heating Metling dynamic melt pool Rapid solidification
3.1.2 material fed into laser path fused to substrate
3.2 Methods
3.2.1 Preplaced Powder highly complex geometries very slow
3.2.2 Wire fed more heat energy larger melt pool straight line only high deposition rate
3.2.3 Blown powder Most versatile Pore free tracks Feeding Off-axis Coaxial dis/continuous
3.3 Output variables/defects
3.3.1 Microstructure
3.3.2 Geometric tolerence
3.3.3 Oxidisation
3.3.4 Porosity
3.3.5 Surface roughness
3.3.6 Dilution
3.3.7 Spallation
3.4 Lasers
3.4.1 C02 (10600nm) Poor absorption
3.4.2 Nd:YAG (1060nm) Good absorption
3.4.3 Diode (808-1100nm) good absorbtion High surface coupling
3.4.4 Fibre (1070-1080nm) Good absorption Best for pre-placed
4 Laser Drilling
4.1 Lasers
4.1.1 Nd:YAG (1064nm)
4.1.2 Excimer (248nm)
4.1.3 Fibre (1070-1080nm)
4.2 Stages
4.2.1 1. Surface heating without phase change
4.2.2 2. surface melting
4.2.3 3. Vapourisation
4.2.4 4. Melt ejection
4.3 Defects
4.3.1 Hole tapering
4.3.2 Spatter
4.3.3 Dross
4.3.4 Recast layer
4.3.5 Micro-cracking
4.4 Types
4.4.1 Single Pulse large no. holes Nd:YAG (1064nm) shallow, less than 1mm
4.4.2 Percussion higher aspect ratio inconsistent quality 20mm depth, 1mm dia.
4.4.3 Trepanning combined drilling and cutting with pulses Freeform and contours
4.4.4 Helical vapourization dominated very precise good microstructure
4.5 Pulse Duration
4.5.1 Long Large plasma plume Large HAZ Shockwaves Microcracking Recast layer
4.5.2 Short Smaller plasma plume smaller HAZ
5 Laser Cutting
5.1 Process
5.1.1 heating melting/exothermic vapourization/ejection
5.2 Types (relative energy)
5.2.1 Vapourization (40) Focussed beam: keyhole deepens fast vapour blows out melt Thin and nonconductive metals
5.2.2 Fusion Cutting (20) 'melt and blow' melts material and blown out by gas jet No boiling-low HAZ
5.2.3 Reactive Fusion Cutting(10) 'melt burn and blow' reactive gas used also less heat input
5.2.4 Controlled Fracture Cutting (1) Brittle materials sensitive to thermal fracture localzed heating local expansion:stress build up rapid cooling Crack: stress raiser
5.2.5 Scribing (1) Grooves/lines of holes in brittle material weaken sturcture allowing mechanical break
5.2.6 Cold Cutting (100) Ultra short UV pulses cut without melting breaks molecular bonds no melt or charr or boiling
5.3 Spot size and mode
5.3.1 smaller spot size less power density higher absoprtion lower kerf width
5.3.2 High brightness beam deeper cut narrower kerf material removal issue
5.4 Gas jets
5.4.1 Too high velocity side burning cooling and less efficient
5.4.2 O2 reactive fusion cutting
5.4.3 Argon Aerospace
5.4.4 Nitrogen thin sheets avoid oxygen scales on steel
5.4.5 compressed air Low cost increased oxidation/dross

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