**12. Seam welding**

Sequential irradiation of laser pulses on the workpiece, while the workpiece is moving at a slight velocity perpendicular to the axis of the radiation, creates a continuous chain of welding cones. Sometimes their overlapping extends to the lower sections and the depth of the workpiece (**Figure 19**). The percentage of overlap is a function of the speed, frequency, and diameter of the laser spot. This parameter is used to determine the most suitable laser conditions for work and to determine the total time of the welding cycle [3, 4, 6].

If a balance is struck between the parameters of pulse penetration, welding speed, and pulse frequency, seam welding has reached the desired state. Usually, at first, the laser parameters such as pulse width and power are selected and the welding speed is determined by considering the spot diameter and the overlap required (**Figure 20**). The overlap factor (Qf) is given in Eq. (10) [3, 4, 6].

$$Q\_F = \left[1 - (V/f)/(\text{S} + VT)\right] \times \mathbf{100} \tag{10}$$

where V (mm/s) is the travel speed of the workpiece (Travel speed) below the welding head, f is the working frequency of the laser (Hz), φ is the beam spot size (mm) and T is the pulse width of the laser (ms)) [3, 4, 6].

**Figure 19.** *Schematic of linear welding with a pulsed laser.*

**Figure 20.**

*The effect of overlap on penetration depth in seam laser welding.*

The best conditions are obtained when complete and defectless welding is created with the least energy and number of pulses and with a reasonable speed [3, 4, 6].
