**1. Introduction**

Since 1962, there have been numerous reports on the metallurgical applications of lasers, including welding. The first laser welding operation was reported in 1963 for the butt welding of steel sheets using a pulsed ruby laser. In 1965, laser systems were developed to be used for welding electronic circuits, vacuum tubes interior, and other special applications that conventional technologies at the time could not provide. Due to the limited power source, until 1970, laser welding was limited to welding lowthickness materials at low speed. Later, high-power continuous laser sources were employed for welding procedures. In 1971, the presence of high-penetration welding or keyhole welding via laser beam welding (LBW) and electron beam welding (EBW) was reported. In other words, by this technique at high laser intensities (MW/cm<sup>3</sup> ), it is possible to make keyholes in metals, which is not practical for pulsed laser welding because the formation of keyholes needs prolonged times to form and does not occur simply [1, 2]. Since 1972, the use of continuous CO2 lasers changed this direction and

high-thickness stainless steel joints with full penetration were welded similar to those welded by the EBW process using the keyhole mode. These investigations were conducted in Japan, Germany, and the United Kingdom. Subsequent advances in CO2 laser welding were focused on further optimization of laser resources, laser beam quality, and understanding the interaction of joint design, welding speed, radiation concentration, and the plasma effects on weldability. Studies in this field have continued using sources with the power of up to 12-15 kW. Using the neodymium-doped yttrium aluminum garnet (Nd:YAG) sources can be more applicable than CO2 lasers due to their short wavelength and reduced radiance from the metallic materials (**Figure 1**). Currently, laser sources have many applications in the field of material processing. LBW as a new technology in recent years has found wide applications in various industries such as automotive, military, aerospace, shipbuilding, electronics, etc. Based on the assessments, it has been estimated that in the near future, the practice of diode lasers will have made great strides in LBW [3, 4].

The laser welding technique differs from conventional fusion welding methods in terms of equipment and operation. In laser welding, a thin and deep weld pool is achieved and the applied heat input to the joint is very low compared to conventional methods. This property allows the LBW to be used in certain applications where the welding depth requires a high width. The penetration depth and welding width can be

**Figure 1.** *Schematic of the laser beam production.*

#### *Laser Welding DOI: http://dx.doi.org/10.5772/intechopen.102456*

adjusted by controlling the laser power, changing the focal position of the beam, welding speed, distribution mode of energy transfer (pulsed or continuous mode), and shielding gas parameters. This enables the LBW to join and fabricate critical components with minimum risk. Features such as low welding width, high penetration depth, excellent joint strength, and low workpiece distortion in addition to fulfilling the need for low-weight joints with high corrosion resistance, proper weld appearance, low electrode consumption, eradicating machining process, and ability to weld unreachable areas have made industries interested in this technique.

There are two main methods for laser welding. The first is to move the workpiece rapidly underneath the beam to obtain continuous welding. The second route, which is more common, is to weld by irradiating a series of beams. Since during LBW both the melting and solidification processes occur in a few microseconds, almost no reactions take place between the melt and the surrounding atmosphere; therefore, generally using shielding gas is not necessary.

The most optimum joint design for LBW is the butt joint, however, due to the thickness limit, T-joints or corner joints are also desirable.

Hybrid processes that use a combination of laser and gas metal arc welding (GMAW) are also developed to be used in a fixed position. In addition, the equipment used to prepare the joint design is no longer needed. The alloys of the filler metals are specifically designed to make the joint physically uniform. In addition, the hybrid processes can significantly increase the production speed. Moreover, they also affect the penetration depth and sealing of the joint. Recent exclusive advances in the fabrication of laser diodes have provided a new opportunity to solve persistent industrial problems. These processes must be modified to be assimilated with the desired purposes [3, 4].
