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Laser beam machining (lbm)

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Working of Laser beam machining process. Its one kind of non traditional or advanced manufacturing process.Production of laser beam and with the use of lasers how can material can be removed is to be explained over here...

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Laser beam machining (lbm)

  1. 1. Laser Beam Machining (LBM) Prepared by, Vaishali Desai Yaminiba Chudasama M. Tech (CAD/CAM)
  2. 2.  Content  Introduction.  Basic Principle.  Laser Concept.  Actual LBM process.  Mechanism of material removal.  Advantages of LBM.  Disadvantages of LBM.
  3. 3.  Introduction:-  The term “laser” is an stands for Light Amplification by Stimulated Emission of Radiation. LBM is nontraditional thermal process.  In thermal removing processes, thermal energy, provided by a heat source, melts or vaporizes the volume of the material to be removed.  Among thermal removal methods,  Electrical discharge machining or EDM is the oldest and most widely used.  Electron-beam (EBM) and laser beam machining (LBM) are newer thermal techniques also widely accepted in industry today.
  4. 4. Principle;- Laser beam machining is based on the conversion of electrical energy into light energy and then to thermal energy.
  5. 5. • Laser Concept  The electrons are charged particles, they carry some energy. The energy related with the orbit in which the electrons revolve.  Generally the electrons are present in the outer most orbit of the atom take part in the process of energy absorption or emission.  Ground state, the state with lowest energy is the most stable state for the electrons. After absorbing the energy electron jump to the higher energy state and staying there for some seconds jump to the ground state and release the absorbed energy.
  6. 6.  This jump may be in two stages:-  Electron from higher state may not come directly to the ground state but may halt for some micro seconds on some intermediate state before finally coming to the ground state.  The period for which electron stays in a higher energy state is known as the lifetime of that energy state.  Lasing action:-  The emission of photon is not done by only one atom at upper energy level but on the influence of external light, a sort of chain reactions occurs and one after other atoms start emitting photons. Thus whole avalanche dumps down together. This is called lasing action.
  7. 7.  Not all the materials are suitable for producing laser beam.  One of the most common laser materials and also one capable of delivering high power is the chromium on a ruby crystal.  Crystal ruby is aluminum oxide.  Generally the ruby rod 1 cm diameter and 10 cm long with ends polished fully is used.
  8. 8. Actual LBM Process  1) In the beginning in atom all the crystals are in ground state  2) When the light is flash over the crystal, most of the atoms are raised to the excited state. Some light waves incline to the axis of the crystal will leave the box either after only a few reflections or without strike on mirror.  3) Some of the waves that travel parallel to the axis of the crystal, will spontaneously emit photon from chromium ions. These photon stimulate another atom to contribute a second photon. This process continues as the photons are reflected to and fro between the mirror.  4) At the each reflection a certain loss occurs
  9. 9. Fig. Laser Mechanism
  10. 10.  It is very interesting that laser has to be used on materials where it absorbs laser energy.  Upon absorption of the laser energy, there is rapid rise in the temperature leading once again to melting and vaporization and material removal.  Although several types of laser exist, all lasers produce (emit) intense, coherent, highly collimated beam of single wavelength light. In material processing applications, this narrow beam is focused by an optical lens to produce a small, intense spot of light on the work piece surface, as shown in figure.  Optical energy is converted into heat energy upon impact and temperatures generated can be high to melt and/or vaporize any material.
  11. 11. Absorb the laser energy Rapid rise in temperature Melting & evaporation Material Removal Gas Assist Mechanism of Material Removal In LBM
  12. 12.  Advantages:  Excellent control of the laser beam with a stable motion system achieves an extreme edge quality. Laser-cut parts have a condition of nearly zero edge deformation, or roll-off  It is also faster than conventional tool-making techniques.  Laser cutting has higher accuracy rates over other methods using heat generation, as well as water jet cutting.  There is quicker turnaround for parts regardless of the complexity, because changes of the design of parts can be easily accommodated. Laser cutting also reduces wastage.
  13. 13.  Disadvantages:  The material being cut gets very hot, so in narrow areas, thermal expansion may be a problem.  Distortion can be caused by oxygen, which is sometimes used as an assist gas, because it puts stress into the cut edge of some materials; this is typically a problem in dense patterns of holes.  Lasers also require high energy, making them costly to run.  Lasers are not very effective on metals such as aluminum and copper alloys due to their ability to reflect light as well as absorb and conduct heat. Neither are lasers appropriate to use on crystal, glass and other transparent materials.
  14. 14. Thank You…..!!

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