**2. Laser welding process**

LBW is one of the innovative methods of fusion welding. By irradiating a highenergy laser beam to the intended gap, the heat required to melt the edges and fill them is provided and the joining process is achieved. It should be noted that the equipment and operation of the LBW are dissimilar to the conventional fusion welding methods. In LBW, a thin and deep joint is achieved, and the heat input applied to the workpieces is so much lower than the conventional welding methods. This property allows LBW to be widely used in certain applications in which a high ratio of penetration depth to joint width is required [5–7].

LBW is a balance between heating and cooling in a certain volume of one or two solids, leading to the melting and solidification of a material. LBW is characterized by the creation of a molten region by the absorption of intensified radiation, which allows the molten pool to expand into the solid interface region, resulting in a continuous joint between the components. Failed joints occur when the molten area is too large, too small, or the material is excessively evaporated. Weld quality is analyzed according to the evaporation of alloying elements and the thermal gradient of the phenomena leading to the crack formation [8–11]. An imbalance in the volume and scale of the weld area leads to porosity. Achieving a balance between the heat input and output depends on the constant absorption of laser radiation and the uniform distribution of heat in the workpieces. The path of the laser beam to the weld pool is often disrupted by the accumulation of hot fumes at the beam focus point. In certain conditions, these hot fumes can turn into a plasma cloud that strongly affects the

**Figure 2.** *The keyhole formation and laser welding using keyhole mode.*

beam and absorbs and disperses it (**Figure 2**). The first stage in studying LBW is to determine the parameters affecting the heating/cooling balance, molten pool, welding area, reproducibility of the process, and the development of methods to control these parameters [5–7].
