New developments in advanced welding
Applications of laser welding
Car manufacturing companies use large numbers of 2.5 to 6kW class lasers to weld various parts, tailored blanks and bodies-in-white.612101 Two laser machines can be separately or simultaneously used, and this system is effectively operated where one laser robot can cover the whole area while the other is out of order. Steels, zinc-coated steels or aluminum alloys are welded with several kW class CO2 lasers, or 2.5 to 4kW lamp-pumped or LD-pumped YAG lasers.6,12,101 Laser blazing as well as laser lap-welding is considered a promising method in welding Zn-coated steels.101 Most car companies are also interested in remote laser welding systems.1618
The steel industry introduced high power lasers to weld thin and thick plates in the 1980s and 1990s. Steel and stainless steel sheets or plates are welded
to produce coils, long plates or pipes. Two sets of 45 kW CO2 lasers are operated to weld 30 to 40 mm thick hot slabs at about 1300K, where laser beams delivered by mirrors are used to weld moving plates.10 This advanced system has been developed in conjunction with the development of many other peripheral technologies.
Laser welding of high quality and high productivity is used in nuclear and thermal power plants of heavy industry. High power lasers are utilized to weld thin stainless steel sheets of 1 mm thickness as well as thick plates of about 16 mm.29,30 Laser welding of Co-base or Ni-base alloys for turbines is also performed. Laser underwater welding and/or repairing as well as laser cladding and laser peening are also investigated in heavy industry. Underwater welding can be carried out with a fiber-delivered YAG laser system, as shown in Fig. 6.36.102 High power diode lasers, YAG lasers, disk lasers and fiber
|
Laser beam |
|
Underwater YAG 6.36 Schematic representation of underwater welding and a fiber - delivered YAG laser system. |
lasers are possible heat sources for welding, repairing and cladding. Recently laser-arc hybrid welding has also received attention for welding of thick plates in ships.
6.5.4 Electronic and electrical industries
The electronic and electrical industries make considerable use of pulsed YAG lasers as micro-welding sources. Battery cell cases of A3003 aluminum alloy are welded with a pulsed YAG laser and this alloy is essentially resistant to hot cracking. However, crater solidification cracks are present in the last spot weld, and this is a very important problem in the behaviour of aluminum alloys.103 There is an increasing demand for the welding of small parts as well as a variety of materials, such as stainless steels, Al, Cu, Ti, precious metals or alloys of Au, Ag and Pt, high temperature alloys of W, Mo, Ta and Nb, and dissimilar materials. Therefore the use is anticipated of pulsed normal or second harmonic generation (SHG) YAG lasers, disk lasers and fiber lasers of high beam quality and single mode fiber lasers and SHG YAG lasers are especially expected to be developed further. A recent example is an IC chip welded with an SHG YAG laser.9 Interesting and promising applications are the micro-spot welding of copper sheets.
