**5. Laser welding**

Laser welding has shown remarkable progress as a high-efficiency welding technique through the years. The process of Laser welding for metal is based on melting metal under a highly concentrated beam of radiation that is focused on the surface metal to join two parts. Radiation is partially absorbed by the upper layer of the metal, causing it to heat to the melting point. The important processing parameters involved in laser welding include laser properties (average and peak power, beam quality, beam diameter, wavelength, and focal length), weld setting (focus position toward the material surface, weld type, and shielding gas), and physical properties of the parent metal. There are two types of welding area, namely conduction or keyhole mode. The obvious width and depth difference in this welding area is due to the energy *E* and peak power density *PPD* applied.

Laser welding has many advantages over the conventional joining method, such as deep penetration, low heat input, small heat-affected zone (HAZ), and high speed. In terms of production, some of the advantages of laser welding are high speed, high process productivity, flexibility in control, and automation. Three common types of laser machines, namely CO2, Nd:YAG, and fiber lasers, are widely used in the industry for welding purposes. CO2 is known as a gas laser with a wider wavelength compared with solid-state lasers Nd:YAG and fiber lasers. Unlike solid-state lasers, the wide wavelength of the CO2 laser results in poor absorption by a wide range of materials. Meanwhile, the fiber laser presents several advantages over the Nd:YAG laser because of the former's compact design, good beam quality, and low cost of ownership and maintenance.
