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MIG (GMAW) uses a continuously fed consumable wire electrode with shielding gas — fast and easy, good for production. TIG (GTAW) uses a non-consumable tungsten electrode with a separate filler rod — slower but gives precise, high-quality, clean welds, ideal for thin materials and aesthetics.

Arc welding uses an electric arc between an electrode and the workpiece to generate intense heat that melts and fuses metals. The arc may use a consumable electrode (SMAW/stick, MIG) or non-consumable (TIG). Shielding (gas or flux) protects the molten pool from contamination.

Shielding gas (argon, CO2, or mixtures) protects the molten weld pool from atmospheric oxygen, nitrogen, and moisture, which would cause porosity, oxidation, and weak welds. The choice of gas affects penetration, spatter, and bead appearance.

Penetration is how deeply the weld fuses into the base metal. Adequate penetration ensures a strong joint; too little gives a weak weld prone to failure, while excessive penetration can burn through or weaken thin material. It's controlled by current, speed, and technique.

Porosity (gas trapped — contamination or poor shielding), cracks (stress, fast cooling, hydrogen), undercut (excess heat/wrong angle), incomplete fusion/penetration (low heat or speed), spatter, and distortion (uneven heating). Each is prevented by correct parameters, cleanliness, and technique.

Spot welding joins metal sheets at discrete points using electrodes that pass current and pressure — widely used in car body assembly. Seam welding produces a continuous leak-tight weld using rotating wheel electrodes — used for fuel tanks and similar.

Resistance welding joins metals by passing current through them; electrical resistance at the contact point generates heat that fuses the metal under pressure — no filler needed. Spot, seam, and projection welding are types. It's fast and ideal for sheet-metal mass production.

A welding helmet with the correct shade filter (protects eyes from arc radiation), flame-resistant clothing and leather gloves, safety boots, respiratory protection against fumes, and ear protection. Proper ventilation/fume extraction is also essential.

Distortion results from uneven heating and cooling causing expansion/contraction. Minimise it with proper fixturing/clamping, balanced/symmetrical welding sequence, lower heat input, intermittent (skip) welding, pre-setting parts, and post-weld stress relief.

A fixture holds parts in precise position and alignment during welding, ensures repeatability, reduces distortion by restraining movement, improves productivity and safety, and maintains dimensional accuracy across many assemblies — essential in mass production.

A WPS is a documented, qualified procedure defining welding parameters — process, materials, joint design, electrode, current, voltage, travel speed, preheat, etc. — to produce a sound weld consistently. It ensures repeatable quality and compliance with codes.

Welding melts the base metals to fuse them (strongest). Brazing joins metals using a filler with melting point above 450°C without melting the base metal. Soldering is similar but below 450°C (weakest, used for electronics/sheet metal). Brazing and soldering rely on capillary action.

Visual inspection, dye penetrant testing (surface cracks), magnetic particle testing (surface/near-surface in ferrous metals), ultrasonic testing (internal flaws), and radiographic testing (X-ray for internal defects). NDT checks weld integrity without damaging the part.

The HAZ is the area of base metal next to the weld that didn't melt but whose microstructure and properties were altered by the welding heat. It can become brittle or hardened and is often where cracks initiate, so controlling heat input and cooling matters.

The flux coating shields the arc and weld pool from atmosphere by producing gas and slag, stabilises the arc, adds alloying elements, controls penetration, and slows cooling. The slag also protects the cooling weld and must be chipped off afterward.

Sheet metal fabrication shapes flat metal sheets into parts through cutting (shearing, laser, plasma), forming (bending, rolling, stamping), and joining (welding, riveting, fastening). Car body panels are a prime example.

All are sheet-metal cutting operations using a punch and die. Shearing cuts along a straight line. Blanking punches out a piece that becomes the product (the removed piece is the part). Piercing punches a hole where the removed piece is scrap (the sheet is the part).

Springback is the elastic recovery of metal after bending — the part partially returns toward its original shape once the forming force is removed, so the final angle is less than the bent angle. It's compensated by over-bending or by adjusting tooling.

Hazards: arc flash/burns, fumes/gases, fire/explosion, sharp edges, moving machinery, electric shock, and noise. Controls: PPE, ventilation/fume extraction, machine guarding, fire precautions, proper electrical grounding, training, and following safe work procedures.

Use qualified fixtures/jigs, follow a controlled welding sequence to manage distortion, tack-weld and check before full welding, verify with measuring tools/gauges against the drawing, apply post-weld correction if needed, and use first-article inspection plus periodic checks.