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Laser Beam Cutting -
Principle
Unlike common light where (light) waves are incoherent and of varied lengths and frequencies that shoot off in numerous directions, the laser (i.e., light amplification by stimulated emission of radiation) is a highly monochromatic and coherent beam of light having a very high energy density to cut metals. In laser, tremendous amounts of energy are concentrated on a small area to melt the metal.
Procedure
In gas jet laser cutting of metal, the surface of the workpiece heated by the laser is reacted upon by an oxygen jet which increases the cutting performance of the laser by ten times. The heat is provided by a CO2 laser beam which is directed via the center of the oxygen stream.
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The apparatus comprises a small vessel placed between the focusing lens and the workpiece surface. Oxygen for metal cutting enters through the side of the vessel and exits through a small nozzle of 1 to 2 mm in diameter in the base of the vessel.
The focused laser beam, therefore, impinges on the surface of the workpiece with a velocity of typically 100 m/s.
The cutting oxygen fulfils the following functions:
(i) It oxidizes the surface of the metal so that laser energy is readily absorbed.
(ii) It produces additional heat from the exothermic oxidation reaction.
(iii) The high speed gas stream sweeps the molten metal oxide from the cut.
Non-metals (since their thermal conductivity is lower compared with metals and therefore less heat is lost into the surrounding) can be cut rapidly by vaporization with the laser alone. However, gas jet if employed can be of an inert gas such as nitrogen or argon.
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