MIG (Metal Inert Gas) welding — more precisely called GMAW (Gas Metal Arc Welding) — uses a continuously fed consumable wire electrode that simultaneously acts as both the arc conductor and the filler metal, shielded by a flow of inert gas (argon for MIG) or an active gas mixture (CO₂ or Ar+CO₂ for MAG — Metal Active Gas). The arc melts both the wire and the base metal, creating a weld pool that is protected from atmospheric contamination by the shielding gas. MIG/MAG accounts for approximately 70% of all robotic welding applications globally — a testament to its outstanding balance of speed, versatility, and automation compatibility.

The process offers three distinct metal transfer modes that operate at different current ranges and produce different weld characteristics. Short-circuit transfer (low current, thin materials) produces a small, fast-freezing weld pool — ideal for sheet metal and out-of-position welding. Globular transfer (medium current) produces larger, irregular droplets — high spatter, generally avoided in production. Spray transfer (high current, above spray transition threshold with argon-rich gas) produces a fine, continuous stream of tiny droplets — smooth welds, deep penetration, high deposition rate, but requires flat or horizontal position. Pulsed MIG (electronically switches between high and low current) achieves spray-quality welds at lower average heat input — the preferred mode for thin aluminium and for reduced distortion applications.

For automotive chassis welding, agricultural equipment, and structural steel fabrication — anywhere that high production volumes, medium-to-heavy material thickness (1.5–25mm), and repeatable quality are required — robotic MIG/MAG welding is the definitive choice. A robotic MIG cell welding automotive body components achieves travel speeds of 500–1,200 mm/min with arc-on times exceeding 85%, replacing a welder who might achieve 30–40% arc-on time with significantly more variation. The main limitation is weld appearance — MIG welds typically have spatter deposits requiring post-weld grinding for cosmetic applications, and the process is less suited than TIG to the highest aesthetic standards.

TIG (Tungsten Inert Gas) welding — formally GTAW (Gas Tungsten Arc Welding) — uses a non-consumable tungsten electrode to create the arc, with the filler metal (when required) added separately by the welder's free hand or by an automated wire feeder. The weld zone is shielded by pure argon or helium. Because the tungsten electrode does not melt, the welder has independent control of heat input (via foot pedal current control) and filler metal addition — a level of control that no other arc welding process can match. The result is the highest-quality, cleanest, most precise weld achievable with arc welding.

TIG welding's non-consumable electrode and separate filler addition allow the welder to control the weld pool with surgeon-like precision — managing heat input to avoid burn-through on thin material, controlling penetration depth, preventing oxidation with comprehensive inert gas coverage, and achieving a smooth, spatter-free, oxide-free weld that needs no post-weld grinding for aesthetic applications. This precision comes at a cost: TIG welding travels at 200–500 mm/min — roughly one-third the speed of MIG — and requires the highest skill level of any fusion welding process. It is categorically the right choice for aerospace components, pharmaceutical and food-grade stainless steel vessels, titanium, inconel, and any application where weld quality, corrosion resistance, and appearance are non-negotiable.

Orbital TIG welding — where the torch rotates automatically around a fixed tube — is the standard process for pharmaceutical, semiconductor, biotechnology, and food industry tube systems, where full-penetration welds on small-diameter tubes must achieve surface roughness Ra <0.8μm on the bore face, with no internal crevices or undercut that could harbour bacteria or contamination. Every semiconductor fab clean room and every pharmaceutical process line uses orbital TIG-welded 316L stainless or high-purity PFA connections as the standard of tube joining quality. Hot Wire TIG passes current through the filler wire to preheat it, increasing deposition rate by up to 100% without increasing heat input to the joint — bridging the speed gap between TIG and MIG for cladding and thick-section applications.

Resistance Spot Welding (RSW) joins overlapping sheet metal panels by passing a high electrical current through copper electrodes pressed against the sheets. The electrical resistance at the interface between the sheets generates concentrated heat — heating the metal to its melting point at the contact interface only, forming a lens-shaped molten nugget (the spot weld). When the current ceases, the electrode pressure is maintained while the nugget solidifies under compression. The entire cycle — squeeze, weld, hold, release — takes less than one second for most automotive sheet gauges. No filler metal, no shielding gas, no consumables beyond the electrodes themselves — RSW is the most cost-effective, production-efficient welding process for automotive body assembly.

Every passenger vehicle body-in-white (BIW) contains between 3,000 and 6,000 spot welds applied by robotic welding cells operating at cycle rates of one spot every 1–3 seconds. The robots not only weld — they also apply precise electrode force (typically 2,000–6,000 N), control welding current and time to within ±1% accuracy, and monitor the weld signature (dynamic resistance, electrode displacement, welding current) to detect defective welds in real time. Modern RSW controllers using adaptive weld monitoring can detect the electrode coating build-up that shifts the weld current distribution, adjust parameters automatically, and flag electrodes requiring dressing — maintaining consistent nugget size without operator intervention.

The increasing use of Advanced High Strength Steels (AHSS) — dual phase, complex phase, martensitic, and press-hardened steels with tensile strengths from 600 to 1,800 MPa — has made RSW significantly more challenging. AHSS requires higher electrode force, modified weld schedules (multi-pulse or stepped current programmes), and more frequent electrode dressing compared to conventional mild steel. The HAZ of AHSS spot welds can undergo significant microstructural changes — martensite formation and tempering — that must be validated against the OEM's minimum nugget diameter specification and peel/chisel test requirements per AWS D8.1 or the relevant OEM welding standard.

Laser Beam Welding (LBW) focuses a high-power laser beam (typically from a fibre laser, diode laser, or Nd:YAG laser) to a spot diameter of 0.1–1.0mm, achieving power densities of 10⁵–10⁷ W/cm² — sufficient to vapourise metal and create a keyhole: a narrow vapour capillary surrounded by molten metal that penetrates deep into the material at the laser focal point. As the beam traverses the joint, the keyhole moves forward and the molten metal flows around it and solidifies, creating a narrow, deep weld with an aspect ratio (depth-to-width) of up to 10:1 — achieved at travel speeds of 1,000–8,000 mm/min. No other fusion welding process produces this combination of depth, speed, and minimal heat input simultaneously.

The fundamental advantage of laser welding is its minimal heat-affected zone and negligible distortion. The concentrated heat input melts and solidifies the weld zone so rapidly that the surrounding material sees very little thermal energy — heat-affected zones measured in tenths of a millimetre rather than the centimetres typical of arc welding. For precision assemblies where post-weld straightening or machining would destroy dimensional accuracy — gear assemblies, medical instruments, electronics housings, precision optical devices — laser welding is often the only viable fusion joining process. Fibre lasers (1,070nm wavelength) with output powers of 1–20kW are now the standard production laser for industrial metal welding, offering wall-plug efficiencies of 25–35% (versus 2–5% for CO₂ lasers) and fibre delivery that makes robotic integration straightforward.

Laser-Hybrid Welding — combining a laser beam with a MIG arc in a single weld head — achieves the best of both processes: laser speed and penetration with MIG's bridging ability (tolerance for fit-up gaps and joint misalignment). Laser-hybrid is the dominant process for automotive door and body panel laser welding (Class A visible surfaces where distortion and surface finish are paramount) and for structural steel welding where deep penetration at high speed is required on joints with real-world fit-up variation. The global automotive industry's transition to electric vehicles is dramatically expanding laser welding use: EV battery cell tab welding, hairpin motor stator welding, and battery pack lid sealing are all laser welding applications growing exponentially.

Friction Stir Welding (FSW), invented by Wayne Thomas at The Welding Institute (TWI) in Cambridge, UK, in 1991, is the most significant welding innovation of the 20th century. Unlike all fusion welding processes, FSW joins metals without melting them. A rotating cylindrical tool with a probe (pin) and shoulder is plunged into the joint line between two rigidly clamped workpieces. Friction between the rotating shoulder and the workpiece surface generates heat (typically 80–90% of the melting temperature of the metal), softening the material into a plasticised, dough-like state. As the tool traverses along the joint, the probe stirs the plasticised material from the leading edge to the trailing edge, where it consolidates under the forge pressure of the tool shoulder, creating a solid-state bond with no solidification defects.

Because FSW never melts the base material, it avoids the full spectrum of fusion welding defects: no porosity (no gas entrapment from solidification), no hot cracking (no solidification shrinkage), no liquation cracking, no hydrogen embrittlement, and no loss of alloying elements through vapourisation. The mechanical properties of FSW joints in aluminium alloys approach or exceed those achievable by any other joining method — typically 80–95% of the base metal tensile strength, compared to 50–70% for MIG-welded joints in the same alloy. This is why FSW has become the dominant joining process for aerospace aluminium structures, EV battery enclosures, ship hulls, and rail vehicle bodies.

The EV manufacturing revolution has made FSW commercially critical. Electric vehicle battery enclosures — large, thin-walled aluminium structures that must be hermetically sealed, dimensionally precise, and resistant to crash energy — are exactly the application where FSW excels over MIG: lower distortion, no porosity (critical for hermetic sealing), higher joint efficiency in the high-strength aluminium alloys used in battery boxes, and no shielding gas requirement. Robotic FSW systems with multi-axis motion and real-time force feedback now enable automated welding of complex battery pack geometries at automotive production rates. Robotic FSW cells from EWI, Grenzebach, and HITACHI now achieve cycle times compatible with body shop takt rates.

Flux-Cored Arc Welding (FCAW) is a variant of MIG where the electrode wire contains flux materials in its hollow core rather than relying on external shielding gas (self-shielded FCAW) or supplementing it (dual-shielded FCAW). The flux produces slag that covers and protects the weld pool, enabling higher deposition rates than solid wire MIG and excellent performance in out-of-position and outdoor welding where wind disrupts shielding gas coverage. FCAW is the process of choice for heavy structural steel fabrication — shipbuilding, bridge construction, offshore platforms, and thick-section pressure vessels — where deposition rates of 4–8 kg/hour (compared to 1–3 kg/hour for MIG) justify the post-weld slag removal step.

Submerged Arc Welding (SAW) buries the arc beneath a blanket of granular flux, producing the highest deposition rates of any arc process (8–20 kg/hour) with excellent weld quality and minimal fume — making it the preferred process for flat and horizontal heavy-section welding on pipe, plate, and structural members where single-pass welds through 25–75mm thickness are required. Pipe mills use SAW to weld spiral and longitudinal seams in large-diameter steel pipe. Shipyards use SAW for main deck plating. SAW cannot be used out of position.

Plasma Arc Welding (PAW) is a refinement of TIG that constricts the arc through a copper nozzle to create a plasma jet — achieving higher energy density, deeper penetration, and faster travel speed than TIG for the same current. In keyhole mode, PAW can penetrate and weld 8–12mm stainless steel in a single pass without a backing bar — a significant productivity advantage. PAW is used for titanium aerospace components, stainless steel food and pharma vessels, and precision instrumentation.

Electron Beam Welding (EBW) focuses a beam of accelerated electrons in a vacuum chamber, achieving the highest energy densities and greatest penetration depths of any welding process — single-pass welds through 150–300mm of steel are possible. EBW produces the narrowest HAZ of any fusion process and welds refractory metals, titanium alloys, and dissimilar combinations impossible for conventional processes. The vacuum requirement makes it expensive and limited to batch production — but for aerospace turbine discs, nuclear fuel elements, and surgical implants, nothing else delivers the same combination of depth, precision, and metallurgical cleanliness.