Electric Arc Welding

Presented by: Prof. dr. ir. Wim De Waele, Laboratory Soete - Ghent University
Academic Year: 2025 - 2026

How it Works
The Electric Arc - Arc Physics - Drop Transfer - Power Sources for Arc Welding
Non-Consumable Electrode Arc Welding Processes - Tungsten Inert Gas (TIG) Welding - Plasma Arc (PA) Welding
Consumable Electrode Arc Welding Processes - Manual Metal Arc (MMA) Welding - Gas Metal Arc (GMA) Welding - Metal-Cored and Flux-Cored Arc Welding (MCA, FCA) - Electrogas (EG) Welding - Submerged Arc (SA) Welding

Heat required for welding is generated by an electric arc.
Involves high electrical current (50 - 2000 A) and low voltage (7-50 V).
Results in conductive plasma with high energy density (temperature can reach up to 20,000 °C).
Metals become chemically reactive to O2, N2, H2 in the environment at these temperatures, potentially degrading mechanical properties of the joint.
Arc shielding is essential and can be provided by shielding gases or solid flux, or a combination of both.

Heat Generation Mechanism: Electrical discharge occurs between two electrodes through an ionized hot gas (plasma).
Ohmic Heating Formula: $P = U imes I = R imes I^2 = rac{U^2}{R}$
The electric arc consists of three parts: - Voltage drop at cathode and anode is approximately constant, hence: - Heating power and melting rate are proportional to current. - Voltage drop in the neutral column varies, influenced by arc length and shielding gas properties (e.g., He: 42 V/cm).

Various drop transfer types dependent on current, voltage, and shielding gas chemistry.
Low welding current: Electromagnetic forces are negligible; gravity and surface tension dominate.
High welding current: Electromagnetic forces dominate; influences droplet transfer and stability.
Droplet transfer modes: - Globular transfer: Large droplets form but are to be avoided. - Short arc transfer: Current causes short circuiting, resulting in stable arc and reduced heat input. - Spray arc and pulsed arc transfer: High currents lead to stable processes for thicker materials.

Uses a non-consumable tungsten electrode.
Often referred to as Gas Tungsten Arc Welding (GTAW).
Filler metal is added separately, and shielding gas (like Ar or He) protects the weld and tungsten.
Advantages: - Stability of arc. - High quality welds with precision. - Minimal thermal distortions due to focused heating. - No spatter, eliminating the need for slag removal.
Disadvantages: - Low welding rate, requiring skilled operators. - Higher equipment costs.

Employs the principle of constricting the arc through a fine-bore nozzle.
Advantages over TIG welding: - More stable arc, - Higher welding speeds, - Reduced distortion and deep penetration capabilities.
Applications include micro plasma welding (for thin sections) and fill-in plasma welding (for thicker plates).

Also known as Shielded Metal Arc Welding (SMAW).
The process utilizes coated electrode rods (diameter 1.6-6.3 mm) that serve as filler metal.
Equipment Requirements: - Power source with a drooping characteristic. - Ignition method: High current density and short-circuiting initiate the arc.
Coating Functions: - Protects against air reactions, - Stabilizes arc and shapes weld bead, - Influences deposition rate and mechanical properties.
Electrode Types: - Rutile: Easily (re)strike, smooth welds; suited for carbon steel. - Basic: Offers high strength and toughness, suitable for structural steels. - Acid: Offers efficiency and smooth weld beads, generally for low carbon content.

Process details: - The arc heats and melts both the workpieces and the electrode wire. - Solid metal wire is automatically fed from a spool, providing filler seamlessly.
Inert (MIG) vs. Active (MAG): - MIG: Uses inert gases like Ar or combinations with He. - MAG: Uses active gases like CO2 to enhance arc stability.
Modes of Transfer: - Spray Transfer: Fine droplets, suitable for thicker materials. - Short Circuiting Transfer: Good for thinner sections, utilizes rapid short-circuiting. - Pulsed Arc: Low heat input and based on controlled current pulses.

Characteristics include stable arcs, improved mechanical properties due to flux, and high deposition rates.
FCAW can be self-shielded or require external shielding gas.

The process involves vertical edge-to-edge welding with possible dimensions of weld thickness from 12 to 75 mm.
Utilizes shielding gas (typically CO2).

The technique utilizes granular flux to shield the weld and promote significant heat penetration.
Common in industries requiring deep welds and high deposition rates.
Variants of SAW: - Tandem: Multiple wires increase productivity. - Twin Wire: Increases deposition rates while using one power source for two wires. - Cold Wire: Adds a wire into the arc without a current to enhance deposition. - Hot Wire: Pre-heated to improve melting and deposition rates.

Electric arc welding is a versatile and vital process in engineering and manufacturing. Each process has unique characteristics, advantages, and applications. Understanding these can lead to optimized techniques in different welding scenarios.