09-05-2012, 05:18 PM
Laser Beam Machining (LBM)
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In laser beam machining, the source of energy is a laser (Light Amplification by Simulated Emission of Radiation), which focuses optical energy on the surface of the workpiece. A laser beam can melt and vaporize diamond when focused by lens system, the energy density being of the order of 105 kW/cm2. Such tremendous energy release is due to certain atoms which have higher energy level and oscillate with particular frequency.
There are several types of lasers used in manufacturing operations, e.g., solid state, gas, liquid and semi conductor. For machining and welding, high power lasers are required and, in general, only the solid state lasers can provide the required power levels.
The most commonly used solid-state laser is the ruby laser (crystalline aluminium oxide or sapphire). These lasers are fabricated into rods about 150 mm long and their ends are furnished to close optical tolerances.
Advantages
There is no direct contact between tool and workpiece. As such no tool wear problems are faced. Metal, non-metal irrespective of their brittleness and hardness, and even soft metals like plastics and rubber can be machined.
Laser beam can be sent to longer distances, without diffraction. It can also be focused at one place thereby generating lot of heat. It is thus possible to weld, drill and cut areas not readily accessible.
The advantages of laser welding are that heat treated and magnetic material can be welded without losing their properties all over the material except a small region of heat-affection. Laser welding is possible in any environment through transparent materials and magnetic fields as well. Distortion is negligible and any two materials can be joined together. However, it is important that the vaporization of the metal must be avoided.
Micro-sized holes can be laser drilled in difficult-to-machine or refractory materials. Precision location is ensured by focusing of the beam. Deep holes of very short diameter can be drilled by using unidirectional multiple pulses.
Beam configuration and size of exposed area can be easily controlled.
Disadvantages
High initial cost and short life of flash lamp
Safety procedures to be followed strictly
Over-all low efficiency (0.3% to 0.5%)
Very low material removal rate
Notable to drill too deep holes
Machined holes not round and straight and
No possibility of machining some plastics which bum or char.
Applications
Used for making very small holes (holes in rubber baby bottle nipples), difficult welding of non-conductive and refractory materials, cutting complex profiles in thin and hard materials. Also used for partial cutting or engraving.
Can be used for mass micro-machining production.
Can also be used for selective heat treating of materials
It is also sometimes used for dynamic balancing of rotating parts.
It is very useful for producing very fine and minute holes etc.