A PPT on Laser Beam Machining containing Introduction, Working, Schematics, Types of laser, Advantages, Disadvantages and Limitations

1. LASER
BEAM
MACHINING

2. CONTENTS
 Laser
 Laser Beam
Machining
 Type of Laser
 Laser Application
 Parameters Affecting
LBM
 Advantage
 Disadvantage
 References

3.  Laser Beam Machining (LBM) is thermal
processes considering the mechanisms
of material removal.
 As laser interacts with the material, the
energy of the photon is absorbed by the
work material leading to rapid
substantial rise in local temperature.
This in turn results in melting and
vaporization of the work material and
finally material removal.
 Laser beam machining is best suited for
brittle materials with low conductivity,
but can be used on most materials.

4. What is laser?
 LASER is the acronym for Light Amplified
Stimulated Emission of Radiation .
 Laser is a device which generates or amplifies
light .
 Stimulated emission of electromagnetic
radiation.
 Coherent, monochromatic, directional and
high power laser beam is used.

5. PROCESS
• At the zero level condition the atom is considered at the
ground level, this is because all the electrons occupy the
lower potential energy.
• From the external sources, the ground level electrons
absorb some energy to stimulate high stage. The electrons
are moving from the lower to higher energy level.
• When the electron reaches the higher energy level, at that
instance we observe the unstable band of energy.
• By releasing the photons with in a short time, it reaches the
ground level. So the process is known as the spontaneous
emission.
Coherent Laser Beam is created in this way.

7. Fig: ENERGY BANDS IN MATERIAL

8. LASER BEAM MACHINING
 Laser beam machining process uses highly
coherent light source.
 This beam can be focused by means of a lens
on a very small spot in the work piece.
 The equipment consists of ruby crystal placed
inside a flash lamp. The flash lamp is used to
produce high intensity light rays.

9. LASER BEAM MACHINING
 The ruby crystal is thus
simulated and this
produces highly spatial
laser beam. When the
rays hit the work
surface it causes partial
or complete
vaporization of surface
material.

10. SCHEMATICS

11. Effect of beam on material

12. Characteristics:
• Material removal technique: Heating, Melting and
Vaporisation.
• Work material: All materials except those having high
thermal conductivity and high reflectivity.
• Tool: Laser beam in wavelength range of 0.3 to 0.6μm.
• Power density: Max 107 W/mm2.
• Output energy of laser : 20J
• Pulse duration : One millisecond
• Material removal rate : 6 mm3/min
• Dimensional accuracy : ± 0.025mm
• Medium : Atmosphere
• Specific power consumption: 1000W/mm3/min
• Efficiency : 10 to 15%

13. PROCESS PARAMETERS
It greatly depend on
 Workpiece properties
 Laser intensity.
 Assist Gases
 Focusing lens
 Interaction time.
• For every material there is a threshold intensity that needs to be achieve for
evaporation to occur.
• LBM processes are located slightly above melting line that enables melting
and then evaporation.

14. Material Removal Rate
Basic Assumptions:
1. The intensity of LASER beam does not vary with time.
2. LASER beam is uniform over the entire area of
hotspot.
3. The material being removed is both melting and
evaporating.
4. The steady state ablation is characterized by constant
rate of material removal and by the establishment of a
steady state distribution.

15. Material Removal Rate
According to the above assumptions, the steady
temperature distribution is given by,
Where,
T = temperature at distance x below the ablating surface,
To = initial uniform temperature of the work piece,
Tm = melting point of the work piece
V = steady ablation velocity,
a = thermal diffusivity of work piece, i.e., (K/ρ) * Cp
K, , Cp= thermal conductivity, density, and specific heat,
respectively, of the work piece.

16. Material Removal Rate
After steady ablation is realized, the relationship
between the intensity, exposure time, thickness of
material which has been removed, and thermal
properties of the material is:
Where, t is the exposure time.

17. TYPES OF LASER
GAS LASERS: An electric current is liberated from a gas to generate a consistent light.
Some of the most commonly used gases consist of He-Ne, Ar, and CO2.
Fundamentally ,these gases act as a pumping medium to ensure that the necessary
population inversion is attained.
SOLID STATE LASERS: They are designed by doping a rare element in to various host
materials. Unlike in gas lasers ,solid state lasers are pumped optically by flash lamp or
arch lamps. Ruby is one of the frequently used host materials in this type of laser. A
Ruby Laser is a type of the solid state laser whose laser medium is a synthetic ruby
crystal. These ruby lasers generate deep red light pulses of a millisecond pulse length
and a wavelength of about 694.3nm. The synthetic ruby rod is optically pumped
using a xenon flash tube before it is used as an active laser medium.
EXCIMER LASERS: The state is different than in solid state or gas lasers. The device
utilizes a combination of reactive and inert gases to produce a beam. This machine is
sometimes known as an ultraviolet chemical laser.

18. He- Ne : Gas Laser

19. RUBY LASER: SOLID STATE LASER

20. • Uses a combination of
an inert gas and
reactive gas
• Excimer is form of
Ultraviolet Chemical
Laser
Excimer Laser

22. • The cutting depth of a laser is directly proportional to the
quotient obtained by dividing the power of the laser beam
by the product of the cutting velocity and the diameter of
the laser beam spot.
• t ∝P/vd
• t ≡Depth of cut
• P ≡laser beam power
• v ≡cutting velocity
• d ≡laser beam spot diameter.
• The depth of the cut is also influenced by the work piece
material. The material’s reflectivity, density, specific heat,
and melting point temperature all contribute to the lasers
ability to cut the workpiece.
Cutting Depth

23. • Lasers can be used for welding ,cladding ,marking ,surface
treatment, drilling, and cutting among other manufacturing
processes.
• It is used in the automobile, shipbuilding, aerospace, steel,
electronics, and medical industries for precision machining of
complex parts. Laser welding is advantageous in that it can
weld at speeds of upto 100mm/s as well as the ability to weld
dissimilar metals.
• Laser cladding is used to coat cheep or weakparts with a
harder material in order to improve the surface quality.
• Drilling and cutting with lasers is advantageous in that there is
little to no wear on the cutting tool as there is no contact to
cause damage.
Applications

24. Advantages
Sincetheraysofalaserbeamaremonochromaticandparallelitcanbefocusedtoaverysmalldiamete
randcanproduceenergyashighas100MWofenergyforasquaremillimeterofarea.
Itisespeciallysuitedtomakingaccuratelyplacedholes.
Laserbeammachininghastheabilitytoengraveorcutnearlyallmaterials,wheretraditionalcutting
methodsmayfallshort.
Thecostofmaintaininglasersismoderatelylowduetothelowrateofwearandtear,asthereisnophy
sicalcontactbetweenthetoolandtheworkpiece.
Themachiningprovidedbylaserbeamsishighprecision,andmostoftheseprocessesdonotrequire
additionalfinishing.
Laserbeamscanbepairedwithgasestohelpthecuttingprocessbemoreefficient,helpminimizeoxi
dizationofsurfaces,and/orkeeptheworkpiecesurfacefreefrommeltedorvaporizedmaterial.

25. Limitations
Theinitialcostofacquiringalaserbeamismoderatelyhigh.
Therearemanyaccessoriesthataidinthemachiningprocess,andasmostoftheseaccessoriesareas
importantasthelaserbeamitselfthestartupcostofmachiningisraisedfurther.
Handlingandmaintainingthemachiningrequireshighlytrainedindividuals.
Operatingthelaserbeamiscomparativelytechnical,andservicesfromanexpertmayberequired.
Laserbeamsarenotdesignedtoproducemassmetalprocesses.Forthisreasonproductionisalway
sslow,especiallywhenthemetalprocessesinvolvealotofcutting.
Laserbeammachiningconsumesalotofenergy.
Deepcutsaredifficultwithworkpieceswithhighmeltingpointsandusuallycauseataper.