Welding Methods

Introduction to Welding

• Fusion welding is a process that involves melting the edges of two metal pieces to join them together.
• There are three general types of fusion welding: gas, electric arc, and electric resistance.

Gas Welding

• Gas welding involves heating metal parts to a molten state using a high-temperature flame.
• The oxyacetylene flame is produced by burning acetylene and mixing it with pure oxygen.
• Hydrogen can be used in place of acetylene for aluminum welding.
• The equipment used in gas welding includes two cylinders (acetylene and oxygen), pressure regulators, hoses, a torch, and safety gear.

Electric Arc Welding

• Electric arc welding is used extensively in the aircraft industry for both manufacturing and repair.
• There are four types of electric arc welding: manual metal arc (MMAW), gas metal arc (GMAW), gas tungsten arc (GTAW), and flux cored arc (FCAW).

Manual Metal Arc Welding (MMAW)

• MMAW is also known as "stick" welding.
• The equipment consists of a metal wire rod coated with a welding flux, clamped in an electrode holder connected to a low-voltage, high-current source.

Gas Metal Arc Welding (GMAW)

• GMAW was formerly known as metal inert gas (MIG) welding.
• An uncoated wire electrode is fed into and through the torch, and an inert gas (argon, helium, or carbon dioxide) flows out around the wire to protect the puddle from oxygen.
• GMAW is suitable for large-volume manufacturing and production work, but not for repair work.

Gas Tungsten Arc Welding (GTAW)

• GTAW is preferred for welding stainless steel, magnesium, and thick aluminum.
• A tungsten rod is used as the electrode, and a stream of inert gas (argon or helium) flows out around the electrode.
• A filler rod is manually fed into the molten puddle in a manner similar to oxyacetylene welding.

Welded Joints

• There are three basic types of joints: butt, tee, and edge joints.

Butt Joints

• A butt joint is made by placing two pieces of material edge to edge, without overlap, and then welding.
• A plain butt joint is used for metals 1.6-3.2 mm (1/16-1/8 in.) in thickness.
• A flanged butt joint is used for thin sheets 1.6 mm (1/16 in.) thick or less.

Tee Joints

• A tee joint is formed when the edge or end of one piece is welded to the surface of another.
• Tee joints are commonly used in aircraft construction, particularly in tubular structures.
• The plain tee joint is suitable for most thicknesses of metal used in aircraft, but heavier thicknesses require beveling to permit heat penetration.

Edge Joints

• An edge joint is used when two pieces of sheet metal must be fastened together and load stresses are not important.
• Edge joints are usually made by bending the edges of one or both parts upwards and welding along the outside of the seam formed by the two joined edges.