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Slovak University of Technology Faculty of Material Science and Technology in Trnava. Machine T ools A nd D evices F or S pecial T echnologies. Laser beam machining. Processing by laser beam. L ight A mpliplification by S timulated E mission of R adiation = LASER
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Slovak University of Technology Faculty of Material Science and Technology in Trnava Machine Tools And Devices For Special Technologies Laser beam machining
Processing by laser beam Light Ampliplification by Stimulated Emission of Radiation = LASER • Light increasing with using of stimulated energy of emission • Laser is monochromatic and coherent light emission
Principle of the becoming of laser beam 1 – no permiable mirror 2 – semipermiable mirror a – using of active background b – atoms of active background emitted photons in various directions c – photons in active background excited next atoms, photons no moving straight to mirrors are lost d – part of photons coming out as beam, next (inversion population) are returned into active background
Laser dividing • By active background, • By using kind, • By wave length of emitted light, • By processing mode • continual, • pulse.
Laser dividing by active background • Solid material (fe. ruby, neodymium, ...) • Liquid, • gas: • molecularly (fe. excimer laser, CO2), • neutral gas lasers (He – Ne), • ion lasers (ions of Ar, Xe, Kr), • Semiconductive.
Laser dividing by kind of using • optical – by discharge, by another laser, by sunlight, ... • elektrical – by electrical discharge, by beam of charged elements, … • chemical – chemical or photochemical reaction, chemical relation, … • termodynamical – heating and cooling of gas substances, … • nuclear reaction – nuclear reactor, nuclear explosion, ...
Laser dividing by wave length of emmited light • Infrared area, • Area of visible light, • ultravioletarea, • röntgen area.
Conditions of laser emission beginning • Possibility of constrained emission – size of constrained energy must be higher than border of constrain, • Suitable material of active background: • Suitable system of energy bosoms (minimum 3 layers), • Large absorption straps, • Suitable lifetime of electrons (short for absorption and long on metastable energy layers), • Suitable intensity of active ions (higher energy emission), • Thin metastable energy layer (high monochromaticion), • Good thermal conductivity (laser cooling).
Mirrors of optical rezonator They are two mirrors reversed against them with refleect side. Their tasks is reflecting particular photons of inversion population back into active background. Reflecting of impermeable mirror is coming near to 100%. Reflecting of second semi permeable mirror is between from 8 to 50% in impulse lasers till 90% in continual lasers. They are made by steaming of some layers with other indexes of refraction in the vacuum.Layer thickness is 50% of wave length of used laser.
Solid material lasers Active background is created by matrix (optical permeable solid material) that is doped by ions from the group of transition elements (Cr 3+, Nd3+) • crystals: • oxides (Al2O3), • garnets (Y3Al5O12 – YAG, Y3Ga5O5 – YGAG), • aluminates (YAlO3 – YALO), • other (fluorides, wolframs, ...), • glasses: • Neodym glass • ceramics
Rubin laser • Active background – Al2O3 + 0,05% Cr3O2 (Cr get him red colour) • Wave length – 693,4 nm • Medium output – 1W • Pulse output – around 100W • Length of impulse – 1ms • effectiveness – 0,1% • using – measuring, holography
Neodym laser Nd – YAG • Active background – yttrium – aluminium granite Y3Al5O12 (YAG) doped by neodymium Nd3+ • Wave length – 1,06 m • Medium output – 600 W • Pulsation output – 2.104 kW • Length of impulse – 10 ms • effectiveness – more than 10% • using – cutting, welding, drilling, ...
Gas lasers Active background is gas or mix of gases. For using of these lasers usually suffices sufficiently intensively electrical discharge. In technical praxis is most often used molecular lasers (CO2 and excimer).
CO2 lasers • Active background – mixture of gases CO2, N2, He filled in silicon tube in low pressure • Wave length – 10,6 m • Kind of using – high frequency discharge • power – tenths ofkW • Length of impulse – 10 ms • efectiveness – more than 15% • using – cutting, welding, drilling, ...
Excimer laser • Active background – excimer – non stabile molecule of gas (halogen, dimer, oxides of special gases) • wave length – 120 – 350 nm • Kind of using – electrical discharge, electron beam, • power – tenth of W • Length of impulse – 10 ns • effectiveness – 2% emitted by discharge, 10% emitted by electron beam • using – medicine, fine accurate machining • Only impulse process schedule
Kinds of material machining by laser • cutting, • welding, • drilling, • turning, • thermal machining, • engraving and marking.
Materials suitable for machining by laser • Low thermal conductivity, • Low thermal capacity, • Low reflection in the area of wave length of using laser, Metals have in generous high reflection and whereby is needed to use suitable surface adjusting (sanding, paintcoat). After melting the reflecting is better. Fine machined are plastic, wood, ceramics...
Material cutting by laser 1 – cutting material, 2 – laser beam, 3 – moving direction, 4 – flow of cutting gas, 5 – melted area, 6 – elements of blow out material, 7 – evaporated material.
Material cutting by laser Advantages: • High uprights of cut, • High cutting speed (0,5 until 10 m/sec), • Simply creating of difficult curve cuts, • High dimension accuracy, • Thin cut, • Cut without influence of mechanical forces, • Small thermal influenced area,
Material cutting by laser Cutting methods: • melted – melted material is blow out by inert gas flow that is not in cutting. Quality of the cutting surface is worse . There i becoming the burs. • oxidation – material is heated to burning temperature and in flow of active gas is burned. Oxidation increased absorption of laser beam and exotermic reaction is usefull for cutting. • sublimation – material is heated to evaporation temperature, flow of inert gas removing the reeks. High quality of cut. Thin materials, only impulse systems.
Drilling by laser • Nd – YAG – holes with diameter above 5mm, practically into all materials, • CO2 – usually only drilling of no metal materials, • Excimer laser – metal drilling, fine structure, to focused in the area of 1mm, • ruby laser – thin foils, hole of diameter 3mm.
Drilling by laser Kinds of laser drilling: • One impulse drilling – the hole is created for one laser impulse. There is usedNd – YAG laser, L/D < 10, diameter of hole above 5mm • percusiondrilling – some of the consecutive impulses (0,1 ms), • trepanation – hole is into the workpiece cutted and can have difficult shape.
Marking, engraving and describing by laser By influence of laser on the surface of the workpiece can set up: • Colour transmission of surface without his melting, • Melting of surface layer, • Evaporation of the surface layer, • Evaporation of surface layer and present colour transmission.
Marking, engrawing and describing by laser Surface marking – depth of influenced area thousandths till hundredths mm. Using of marking of bearings, decorative describing and identification labels.
Marking, describing and engrawing by laser Marking in depth (engraving) – becoming slot with depth till 1mm and with thickness of particular tenths mm. It is used for scales, signs...
Thermal processing by laser beam • Without melting of surface layer – surface layer is heated above temperature of phase transmission, thermal conductivity and thermal capacity of workpiece become fast cooling, after cooling in this layer becoming strong metastable phase (cementite)
Thermal processing by laser beam • With melting of surface layer: • glazzing – surface layer is melted and after cooling become fine-grain structure on the surface • cladding – surface coating by layer of other metal.Surface layer is melted in to the limit to can become diffusion process and connection of both materials. • alloying – surface doping of the base material. Surface of material is melted, additional material is completely melted and become mixturing of these materials in the surface layer.
Welding by laser beam • No become evaporation of the base material only his melting. • Heat is soar fast and accurately – small influenced area by heat. • Most often used CO2 laser, safety gas Ar, He, N2 • Nd – YAG laser is used for welding in the soft mechanics.
