For many years low-power Nd:YAG lasers (100-500 W) have been used for welding small elements such as medical devices and electronic units. High-power Nd:YAG lasers (with a kilowatt range) are frequently used together with fiber optics and robots. The important field of application is welding of the vehicle components, for example, parts of the vehicle body.
The laser beam is focused to a small spot where the generated intensity is enough for material melting and evaporating. The water cooled mirrors are usually instead of the lens for high-power CO2 lasers focusing. The welding is usually done by two methods. The thermal conductivity method provides for heat transfer from the material surface to its depth due to thermal conductivity. It is typical for welding with low-power Nd:YAG lasers and relatively small thickness of the welded parts.
High-power laser welding is marked by caving. The laser energy melts and evaporates the metal. The vapors pressure pushes out the melted metal, which leads to a cavity formation. The cavity adds to the laser energy transmission into the metal and directs the beam deep into the metal. Thus welding with caving allows achieving very narrow and deep welds, that’s why it is also called deep-penetration welding.
Welding gases shall correspond to some requirements – they shall shield the welding pool and heat affected area, protect the optics against the fumes and spitting, protect and prevent plasma creation when welding with CO2 laser. Plasma is a cloud of ionized metal vapor and gases, which can be generated over the cavity. This cloud absorbs the lasing and interrupts the welding process. This event depends upon the laser type and applied power, that’s why different gases are used for laser welding.