Gas Metal Arc Welding

DEFINITION Intense heat of an electric arc is used to melt filler material and base metal while a wire electrode is continuously fed into the arc. A shielding gas protects the weld from contamination.

Equipment Direct Current Constant Voltage Power Source Wire Feeder w/control system Electrode wire Welding gun Electrical Cable Shielding Gas

Types of Metal Transfer Short Circuit- molten metal is deposited in repeated short circuits Globular- molten metal is transferred across arc in large droplets Spray- molten metal is propelled axially across the arc in small droplets

Advantages High Deposition Rates High Utilization of Filler Material Elimination of Flux/Slag Removal Reduction of Smoke & Fumes Can be Automated Less Skill Required

Disadvantages 1. Cost 2. Metal preparation time 3. Unsuitable for outdoor welding 4. Fast cooling rates 5. Unsuitable for thick metals 6. Shielding gas required

Internal Diagram of Wire Feed System

Tip Distance Diagram

Welding Terminology

Arc Welding Type of welding when weld is produced by heating metal with an arc with or without the use of filler material or pressure

Electrode A component of the welding circuit through which current is conducted to the arc, molten, slag or base metal

Flux Material used to prevent, dissolve or remove oxides and other undesirable materials from a weld

The metal to be welded, soldered or cut Base Metal The metal to be welded, soldered or cut

Cavity formed by gas entrapment during solidification Porosity Cavity formed by gas entrapment during solidification

Splatter Metal particles expelled during welding that does not form as part of the weld

Tack Weld Weld made to hold part of the weldment in proper alignment until the final welds are made

Inert Gas A gas that goes not normally combine chemically with the base metal or filler metal. Creates a protective atmosphere.

Undercut A groove melted into the base metal adjacent to the toe or root of a weld and left unfilled by weld metal

A localized joining of metal produced by heat Weld A localized joining of metal produced by heat

Filler Metal The metal to be added in making a welded joint.

ER-70S-6 E=Electrode R=Filler Metal Rod 70= Tensile Strength Reading Electrodes ER-70S-6 E=Electrode R=Filler Metal Rod 70= Tensile Strength

ER-70S-6 S= Solid Wire 6=Chemical Composition of the Wire

Practice Reading Electrodes

Weld Anatomy