AWS WHC-3.14:2008

Laser Beam Welding, Cutting and Associated Processes
Scope : Laser beam welding (LBW) produces coalescence with the heat from a laser beam impinging on the joint. Filler metal occasionally may be used, but the process is primarily used autogenously. Laser beam cutting (LBC) is a thermal cutting process that utilizes highly localized melting or vaporizing to sever metal with the heat from a laser beam. The process is used with or without a gas to aid in the removal of molten and vaporized material.1, 2 Laser is an acronym for light amplification by stimulated emission of radiation. A laser is a device that uses an optical resonating system incorporating a crystal or gas medium and reflective mirrors or focusing lenses to amplify and synchronize light waves into a coherent beam. Coherence of the beam is produced by stimulated electronic or molecular transitions to lower levels of energy. The laser emits this concentrated beam as energy that can be focused on the weld joint or cutting site and applied as heat to make the weld or cut. The engineering disciplines involved in laser beam material processing include laser mechanics, optics, fluid dynamics, and materials science. The first laser was introduced in 1960. It used a ruby crystal electrically excited (pumped) by a flashlamp to produce a laser beam. By the late 1960s, the beam was successfully performing the first laser material processing application: the drilling of diamond dies used in wire drawing. Solid-state lasers of this type produce only short pulses of light energy at repetition frequencies limited by the heat capacity of the crystal. Consequently, even though individual pulses exhibit instantaneous peak power levels in the megawatt range, pulsed ruby lasers are limited to low average power output levels. They have largely been replaced by continuous wave (CW) solid-state lasers, many of which use neodymium-doped, yttrium aluminum garnet (Nd:YAG) crystal rods to produce a continuous, monochromatic beam output in the average power range of 0.5 kilowatt (kW) to 4 kW. Other lasers use carbon dioxide (CO2) and other gases as the lasing medium, with output power ranges of 0.5 kW to 45 kW. Among laser material-processing applications, cutting is the most common, with many types of machines used in industrial production systems worldwide. It is estimated that laser cutting and related equipment for drilling, trimming, machining, scribing, and laser transformation hardening represent well over 50% of industrial laser installations. Laser beam welding is widely used for the high-quality welds required by the automotive, aerospace, shipbuilding, pipeline, and air conditioning industries. Examples of other applications are the fabrication and hermetic sealing of relay containers, cases for electronic, medical, and other devices, and the production of aluminum tubing. Many of the laser techniques associated with welding, cutting, marking, and surfacing processes also are associated with other industries. Different types and power levels of lasers are used for industrial, medical, construction, and office applications. In medicine, lasers are used for welding and cutting applications such as eye repair welding and self-cauterizing surgical cutting and repairing. In offices around the world laser printers use laser surfacing techniques to apply dry ink to paper; in plastics-painting applications lasers are used to prepare the surface for better adhesion. It is not unusual to hear typical welding terms applied to many uses of lasers in non-traditional applications. This chapter is devoted to the fundamentals of the laser beam welding and cutting processes, modes of operation, and equipment. Other topics include laser beam welding operating systems, applications, joint design and preparation, weld quality, and the economics of using these processes. Similar information is presented for laser beam cutting, drilling, and related processes. The chapter concludes with a discussion on safety issues specific to laser beam operations and the safety codes that must be followed to provide the best working environment where lasers are in use.