WELDING

• Welding

  A technique used for joining metallic parts usually through the application of heat
• Welding was discovered during efforts to manipulate iron into useful shapes
• Prominent methods of welding aircraft structures and components

  • Fusion welding
  • Non-fusion welding
• Fusion welding

  The blending of compatible molten metals into one common part or joint
• Fusion welding

  1. Producing sufficient heat for the metals to melt, flow together and mix

  2. Removing the heat to allow the fused joint to solidify
• Non-fusion welding

  The joining of metals by adhesion of one metal to another
• Good weld

  • Uniform in width, with even ripples that taper off smoothly into the base metal
  • Shows good penetration, or depth of fusion
  • Penetration is the most important characteristic
• Welder

  Must use the correct type and size of filler rod and appropriate welding technique for the thickness and type of material to be joined
• Types of fusion welding


  • Gas welding
  • Electric arc welding
  • Oxyacetylene welding
  • Shielded metal arc welding
  • Gas metal arc welding
  • Gas tungsten arc welding
  • Electric resistance welding
• Oxyacetylene welding

  Uses oxygen and acetylene (C₂H₂) gases to produce a flame with a temperature range of 5,600°F to 6,300°F
• Acetylene

  A colorless, one of the most common and simplest hydrocarbons that is highly explosive when liquefied, compressed, heated, or mixed with air
• Oxyacetylene flame

  • Carburizing flame - relatively rich in acetylene, burns much cooler, used for brazing and soldering
  • Neutral flame - optimal mixture, used primarily when welding aircraft steel
  • Oxidizing flame - rich in oxygen, used for cutting
• Oxyacetylene welding was once used almost exclusively in the fabrication of welded-tube aircraft fuselage structures
• Shielded metal arc welding (SMAW)

  Also known as Stick welding, is the most common type of Arc Welding.

  A metal wire rod, which is composed of approximately the same chemical composition as the metal to be welded, is clamped in an electrode holder.
• Shielded metal arc welding normally is used for welding heavy gauge steel, and seldom is used for aircraft construction or repair
• Gas metal arc welding (GMAW)

  Formerly called Metal Inert Gas (MIG) welding, is used primarily in large volume production work. An advantage is that no slag is deposited on the weld bead. An uncoated filler wire acts as the electrode and is connected to one terminal on the power supply and fed into the torch.
• Gas tungsten arc welding (GTAW)

  Also known as Tungsten inert gas welding (TIG), is the form of electric arc welding that is used most in aircraft maintenance. Unlike SMAW and GMAW, which use consumable electrodes, TIG welding uses a tungsten electrode that does not act as filler rod.
• Spot welding

  1. Two copper electrodes are held in the jaws of a vise-like machine and the pieces of metal to be welded are clamped between them

  2. Pressure is applied to hold the metal together while electrical current passes between the electrodes, generating enough heat to melt the metal
• Seam welding

  1. The metal is drawn between two copper wheels

  2. Pressure is applied to the wheels and timed pulses of current flow through the metal between them, creating spots of molten metal that overlap to form the continuous seam
• Types of welded joints


  • Butt joints
  • Lap joints
  • Corner joints
  • Tee joints
  • Edge joints
• Welded Joints

  The result of a weld
• Butt Joints

  • Generally not used for joining tubing in aircraft applications because they are too weak for aircraft structures
• Lap Joints

  • Seldom used in aircraft structures when welding with gas but commonly used when spot welding
  • The single lap joint has very little resistance to bending and will not withstand shearing stresses
  • The double lap joint is stronger, but requires twice the welding of the simpler, more efficient, butt weld
• Corner Joints

  • Can only be used where load stresses are not significant
• Tee Joints

  • Quite common in aircraft work, particularly in tubular structures
  • The plain tee joint is suitable for most aircraft metal thickness
• Edge Joints

  • May be used to join two pieces of sheet metal
  • To form an edge joint, bend the edges of one or both parts upward and place the two ends parallel to each other
  • Weld along the outside of the seam formed by the two edges
• Parts of the Weld


  • Bead
  • Face
  • Root
  • Throat
  • Toe
  • Reinforcement
• Brazing

  • A form of metal joining in which an iron-free metal, usually brass or bronze, is used as a cohesive material
  • The non-ferrous material is melted with an oxyacetylene torch at a temperature below that of the base metal, but above 800°F
  • Flux is used to clean the surfaces of the metal being joined
• Braze Welding

  Like brazing, but the filler rod is deposited on the surface rather than depending only upon capillary action to produce the joint
• Soldering

  • Like brazing, using many of the same techniques and devices as when making brazed joints
  • Brazing materials normally melt at temperatures above 800°F, while solders melt at temperatures considerably lower than this
• Types of Soldering

  • Soft solder (tin and lead mixture)
  • Hard and silver soldering (forms of brazing where the filler material melts at a temperature more than 800°F)
• The oxyacetylene flame for silver soldering should be neutral but may have a slight excess of acetylene
• Stainless steel oxygen lines often have their end fittings attached by silver soldering
• •Bead is the metal that is deposited as the weld

  is made.

  •Face is the exposed surface of the weld.

  •Root is the depth that fusion penetrates the base metal.

  •Throat is the distance through the center from

  the root to the face.

  •Toe is the edge formed where the face of the

  weld meets the base metal.

  •Reinforcement is the quantity of weld metal

  added above the surface of the base metal.