Laser is a highly coherent beam of electromagnetic radiation with wavelength varying from 0.1 to 70 mm. It may be used for machining or welding purposes depending on the wavelength of radiation used.
Figure 20.47 shows schematic diagram of laser beam welding. A coiled xenon flash tube is placed around the ruby rod and the internal surface of the container is made highly reflective. A very high voltage is applied from charged capacitor to triggering electrode for flashing. The reflected rays from the surface of container on the ruby rod help in pumping operation. The emitted laser beam is focused on the work surface with the help of a lens system which results in melting of the metal. The average duration of the laser beam is 0.002 s. During this short duration, two welding methods may be adopted—the workpiece is rotated or moved fast enough so that the entire joint is welded with a single burst of light or method where many pulses are used to form the weld joint. With the pulsed technique, the weld is comprised of round solidified weld puddles. An advantage of laser pulse method is the multiple laser pulses approximately 10 times per second because of that the workpiece does not even get hot except at one point, which is one of the metallurgical advantages of laser welding.
Figure 20.47 Laser Beam Welding
Advantages
- It provides deep penetration without affecting the base metal.
- The process is fast due to instantaneous increase in temperature of workpiece.
- Vacuum is not required as in electron beam welding.
- Welding can be done in inaccessible locations.
- It has very small thermal distortion.
- It can be easily automated.
Disadvantages
- Better edge preparation and close dimensional tolerance are required.
- Equipment cost is very high.
- It can be used only for thin sheet.
- Laser rays are dangerous for skin as well as for eyes.
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