**6. FSW**

**3. GMAW**

2 Joining Technologies

**4. GTAW**

and alloys, aluminum alloys, and stainless steel [2].

be cooled to avoid overheating during welding.

**5. Laser welding**

GMAW is also known as metal inert gas (MIG) welding in which an external gas, such as argon, helium, carbon dioxide, argon + oxygen, and other gas mixtures, is used as a shielding gas [1]. Consumable electrode wire, having the same or approximate chemical composition to that of parent metal, is continuously fed from a spool to the arc zone. The arc from the welding parameters (voltage and current) heats and melts the samples' edges and the filler wire. The fused filler metal is supplied to the surface of the workpiece, fills the weld pools, and forms the joint between the workpieces similarly or dissimilarly. The overall process in GMAW is described as a semi-automatic method because of the automatic feeding of the filler rod while the welder controls only the position and speed of the torch. GMAW can weld almost all metals

GTAW is also known as tungsten inert gas (TIG) welding, in which heat from an electric arc is used. The arc sparks between a tungsten non-consumable electrode and the workpiece [1]. The molten pool is shielded by an inert gas such as argon, helium, and nitrogen. The shield‐ ing gas prevents the molten pool from atmospheric contamination. The heat produced by the arc melts the samples' edges. The filler rod can be used if required, especially in welding aluminum. GTAW produces a high quality weld of most metals because it does not use flux. An externally supplied shielding gas is necessary because of high temperatures involved to prevent metal from oxidation. Direct current is typically used, and its polarity is important as this welding method still uses current and voltage as critical parameters. Given that the tungsten electrode is not consumed during welding, a stable and constant arc is preserved at a constant current level. The filler metals used are usually similar to the parent metals to be welded, without using flux. The shielding gas used is normally argon or helium (or a mixture of gases). GTAW is used for a wide variety of metals and applications. Metals that usually can be welded by GTAW are aluminum, magnesium, titanium, and copper and its alloy. The tungsten electrode is usually in contact with a water-cooled copper tube (contact tube), which is connected to the welding cable from the terminals. Both the weld current and electrode must

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

FSW is a welding process that involves solid-state joining; this process has expanded rapidly since its development in 1991 by The Welding Institute, UK [3–6]. FSW is a solid-state welding technique that does not involve melting and occurs below the melting point. It uses a rotating tool to generate necessary heat for welding. This tool consists of three parts: the shank, shoulder, and pin. The shank is the part where the tool is attached to the FSW machine, whereas the shoulder and pin are attached to the workpiece. The shoulder and pin provide additional frictional treatment and prevent the plasticized material from escaping from the weld region. During FSW, the rotating tool moves along the joint of two plates that generate heat. This tool then recirculates flow of the plasticized material near the tool surface. The size of the tool shoulder is larger than that of the pin tool. The FSW tool serves two main functions, namely workpiece heating and material movement to produce a joint [4]. Heating is produced by friction of the pin and workpiece and plastic deformation of the workpiece. The heat that is produced will soften the material around the pin, and tool rotation will move the material from the front of the pin to the back of the pin. The result of this process is a joint produced in solid state.

FSW can be utilized in a wide variety of industries, such as automotive, aerospace, maritime, and railway [3, 4, 7–11]. FSW has been considered the most substantial joining process in the past decade because it offers many advantages such as energy efficiency, environmental friendliness, and versatility [4]. Compared with arc welding, FSW uses less energy and does not require a shielding gas and flux, thereby making this process an eco-friendly one. This joining process does not need any filler, so it is suitable to join many types of dissimilar metals. FSW is a technique that can avoid drawbacks from common fusion welding because FSW can be conducted under solid state. Several problems (e.g., spatter, hot cracking, and distortion) in other types of welding are eliminated by using FSW [12]. Defects such as voids, lack of penetration, and broken surface can be minimized by using this welding technique.
