**3. Advantages of laser beam welding**

Proper joining rate, excellent welding quality, very high accuracy, high automation capability, and exceptional appearance of the welded joint are included as beneficial factors, leading to the application of LBW in various industries. Economically, the reduced production costs and low consumption of consumables have made this method one of the finest joining methods. To recognize why LBW is one of the best welding solutions, the top five advantages of this technique are listed below [5–7]:

### **3.1 Ability to join complex joints and high accuracy**

LBW can weld complex joints successfully, especially it can join dissimilar materials or areas very difficult to reach using traditional welding techniques.

One of the main advantages of LBW is that it can offer a high level of accuracy and control, i.e. it can be used to join the smallest workpieces together without damaging them.

Strong potentials can be proposed for weight reduction and joint design opportunities. Typically edge welding is carried out by direct fusion of two base metals. Using

**Figure 3.** *Joining of edge seams by LBW: (a) flanged butt joint and (b) flare-V groove.*

this tactic, it is vital to maintain an almost zero gap between the workpieces to ensure suitable joining. Using the LBW, high fusion depth can be gained while reducing flange length by more than 50% of current standards. This can be obtained by employing hybrid features of integrated clamping, optical seam tracking, and beam oscillation capabilities (known as laser welding optic).

Like other welding processes, during LBW it is challenging to guarantee the accurate positioning of the energy at the joint. But a combination of process robustness, workpiece tolerances, and robot accuracy results in obtaining proper welds. Finding the joint by optical seam tracking and laser triangulation provides accurate positioning for the laser spot during the process. This seam tracking data is then sent back to the optic controller, translating the required data for repositioning of the head galvo motors to point the laser beam to the desired coordinates. The system is capable of providing several inclination angles to accommodate the adjustments of joint position for two and three-layer joints as flange heights variation relative to one another. By adding an integrated clamping unit to the head not only the workpiece can be fixed at the desired position, but also provides the tooling costs to clamp the seam can be reduced (**Figure 3**).

The clamping unit design allows the reaching into flanges openings or structures and rapid open/close clamping mechanism (200 ms), providing a good foundation for high-volume applications. The innovative technologies offer extra advantages to meet the welding requirements for base metals such as ultra-high-strength steels, aluminum, and boron. By utilizing oscillation motors along with those directly tied to beam location two-axis oscillation can be obtained at frequencies up to 1 kHz, which eliminates the oxide layers, extra time for the gas to exist the weld pool, or post-weld annealing of brittle microstructures. An instance of the cleaning of the welding area can be seen during the zero-gap welding of galvanized materials. To this end, a gap (0.1 mm) is characteristically required to provide a place for evaporation of the zinc at temperatures higher than 0.5 Tm of the base material. If not correctly set up, the gas expulsion can be trapped within the solidifying melt and form porosity in the final weld. The oscillation feature grants a remelting phenomenon for the weld pool and allows the zinc to escape to the surface and leave the weld. For structural applications, it is frequently necessary to join dissimilar materials for example boron steels to electrolytically or hot-dipped galvanized steels. According to the beam location control feature using oscillation, a melt pool is formed, which floats on the workpiece.

However, a distortion in the workpiece is not essentially attributed to the adaptive nature of the process.

#### **3.2 Low heat input**

LBW method uses a low heat input rate that minimizes the joint distortion. Hence, it is the preferred method for those who wish to make luxury products such as custom jewelry. Laser sources employ tremendously localized energy and allow non-contact use, which applies lower heat input on the workpieces. This method is ideal for noncontact applications, which protects other areas of the parent material from the adverse effects of heat.

The feature 'line energy' is commonly used as a denominator to compare welding processes carried out in 1F and 2F positions. Moreover, heat input determines the joint geometry, which can be controlled via the modification of the welding parameters. In other words, the heat input is directly correlated to the laser power (or arc power) and the welding speed. The heat input for the LBW process is calculated according to Eq. (1).

$$Q\_{laser} = \text{PL}/\text{vt} \tag{1}$$

where Qlaser is the laser heat input (kJ/mm), PL is the output power of the laser source (kW), and vt (mm/s) is the travel speed. The heat input of the hybrid laser-arc welding (HLAW) considers the additional energy delivered by the arc and is determined by Eq. (2).

$$Q\_T = Q\_{arc} + Q\_{laser} = \frac{\text{UI\'\'60}}{vt} + (PL\,\text{60})/v\,\text{Qt} \tag{2}$$

where Qlaser is the LBW heat input (kJ/mm), PL is the source output power (kW), vt (m/min) is the travel speed, QT is the HLAW heat input (kJ/mm), Qarc is the arc welding heat input (kJ/mm), U is the arc voltage (V), and I is the arc current (A).

### **3.3 Compatibility and replicability**

LBW can provide continuous and repeatable component fabrication. This helps industries to reduce their manufacturing costs significantly. LBW is far more quickly and much more versatile than the conventional methods. Laser welding can also be used for cutting and drilling.

When a lap fillet is the functional joint, which should be processed, similar issues are apparent as well as the joint location and overlap. To resolve the issues optical seam tracking and beam oscillation are employed. However, gap bridging technology can also be used instead of clamping equipment. In most LBW applications, zero-gap is a similar challenge as well as the joint location and ideal fusion between sheets. In lap edge configurations gaps should be seen; hence, options are currently developed to produce sound joints in this configuration.

If a filler wire is required for modification of the chemical composition or other gaprelated conditions, options are developed to use the tactile seam tracking system and utilize the filler metal to bridge the gaps (**Figure 4**). But, using remote laser welding, it is not practicable to insert the wire into the melting pool when optical seam tracking is employed for beam placement. Additionally, it is possible to weld the gap automatically without filler metal. Remote laser welding – adaptive (RLWA) is a unit, utilizing a

**Figure 4.** *Laser welding using brazing filler metal.*

real-time seam finding and tracking by internal controlling of the head, which is called gap bridging. The final result is the dynamic control of the laser spot position relative to the seam, not only irradiating a predetermined point in coordinates. When the beam is accurately placed into the seam, joining a lap point with high reliability is possible. This issue is attributed to gaps in the material, which typical laser processes struggle to accommodate. With gap bridging algorithms, which are predefined in the system controls, the LBW optic can identify gaps in the joint via the seam tracking package and adjust various conditions automatically to process the joint.

By modulation of laser power, y offset of the beam relative to the joint edge, spot size, and using beam oscillation in the x and y directions, the melt can bridge the joint. Gaps with 50% or less of the upper sheet thickness can easily be addressed with both aluminum and steel materials, while recent studies show capabilities beyond that in certain situations (**Figure 5**).

### **3.4 High-strength joints**

Since the heat input rate is significantly lower than the conventional methods, the heat affected zone (HAZ) of laser-welded joints is very small that allowing manufacturers to perform high-strength welds.

The laser beam machining (LBM) parameters such as laser intensity, beam distribution, scanning speed, spot size, and relative motion between the laser beam and workpiece can be adjusted according to different base materials. Currently, lasers are

**Figure 5.** *Different LBW gaps and RLAW equipment.*

**Figure 6.**

*Difference between the properties of (a) long-pulsed and (b) short-pulsed durations.*

substituting conventional machining equipment because of their superior advantages. Major advances have been made in this area to shorten the pulse time for various machining processes. Prolonged pulse durations increase the HAZ and induce high thermal stresses, which result in the formation of cracks, voids, and surface debris. Short pulse times decline the thermal conduction, provide accurate machining operation, and proper surface finish. **Figure 6** reveals the difference between the properties of long and short pulse times [6].
