welding

• Metallic aircraft structures are composed of many individual pieces that must be securely fastened together to form a complete structural unit
• Fusion welding, non-fusion welding, hardware fasteners, and adhesives are the principal methods used in the construction and repair of metal aircraft joints.
• welding is defined as a process that joins metal by melting or hammering the work pieces until they are united together.
• There are three general types of welding: gas, electric arc, and electric resistance
• When your joining the metals, you have two parts:

  •Base Metal (primary metals)

  •Filler Metal  ( which you will use to reinforce the joints)
• HEAT -  is necessary to melt the pieces of metal being welded  so that  it can be fuse together .
• The shielded is necessary because molten metals easily oxidized and absorb atmospheric contaminants.
• Gas welding is accomplished by heating the ends or edges of metal parts to a molten state with a high temperature flame.
• The oxy-acetylene flame, with a temperature of approximately 6,300 °Fahrenheit (F), is produced with a torch burning acetylene and mixing it with pure oxygen. Hydrogen may be used in place of acetylene for aluminum welding, but the heat output is reduced to about 4,800 °F.
• Gas welding was the method most commonly used in production on aircraft materials under 3⁄16 inch in thickness until the mid 1950s
• Nearly all gas welding in aircraft fabrication is performed with oxy-acetylene welding equipment consisting of:

  • two cylinders
  • pressure regulators and cylinder pressure gauges
  • two lengths of colored hoses (red for acetylene, green for oxygen)
  • welding torch
  • welding goggles
  • flint or spark lighter
  • special wrench
  • fire extinguisher
• Gas welding advantages:

  • easy to handle  or hold the oxy- acetylene torch
  • It doesn’t requires any electricity
  • And the torch also can be used other purposes such as cutting.

  Disadvantages :

  • Needed 2 HP tanks of flammable gasses nearby
• Gas welding – is also known as OXY-FUEL welding / TORCH  welding
• Electric arc welding is used extensively by the aircraft industry in both the manufacture and repair of aircraft.
• Shielded metal arc welding (SMAW)-  is the most common type of welding and is usually referred to as “stick” welding.
• in SMAW, an arc is struck between the rod and the work and produces heat in excess of 10,000 °F, which melts both the material and the rod.
• The welding circuit consists of:

  • a welding machine,
  • two leads,
  • an electrode holder,
  • an electrode,
  • and the work to be welded
• If the correct gap is maintained, the current bridges the gap to form a sustained electric spark called the arc.
• SMAW Advantages :

  • Popular  because of its simplicity and versatility
  • Constant current power supplies are fairly inexpensive compound to other welding machines
  • Sticks welding can be performed in most any environment  including under water

  Disadvantages

  • Only works in certain metals ( mostly Iron and Steel)

  Messy process with lots of molten spatter and fumes
• Gas metal arc welding (GMAW) was formerly called metal inert gas (MIG) welding.
• It is an improvement over stick welding because an uncoated wire electrode is fed into and through the torch and an inert gas, such as argon, helium, or carbon dioxide, flows out around the wire to protect the puddle from oxygen.
• Low-voltage, high-current DC is typically used with GMAW welding.
• This method of welding can be used for large volume manufacturing and production work; it is not well suited to repair work because weld quality cannot be easily determined without destructive testing.
• In GMAW, usually , the gas shielded is a Mixture of Argon and carbon dioxide.
• It can be use both an Inert gas and flux core wire , and this process known as a dual shield welding
• Gas metal arc and flux core arc , are two of the fastest welding methods in terms of disposition rate, since it doesn’t have to stop to get a new rod.
• GMAW is also considered the easiest  method to learn , because there are fewer variables to control during the process
• Gas tungsten arc welding (GTAW) is a method of electric arc welding that fills most of the needs in aircraft maintenance and repair when proper procedures and materials are used.
• GTAW is the preferred method to use on stainless steel, magnesium, and most forms of thick aluminum.
• GTAW is more commonly known as Tungsten Inert Gas (TIG) welding and by the trade names of Heliarc or Heliweld.

  
  

  These names were derived from the inert helium gas that was originally used.
•  In TIG welding, the electrode is a tungsten rod that forms the path for the high amperage arc between it and the work to melt the metal at over 5,400 °F.
• DC straight polarity (the work being the positive and the torch being negative) when welding mild steel, stainless steel, and titanium; or

  Select AC for welding aluminum and magnesium.
• Electric resistance welding, either spot welding or seam welding, is typically used to join thin sheet metal components during the manufacturing process.
• In spot welding, Two copper electrodes are held in the jaws of the spot welding machine, and the material to be welded is clamped between them.
• In seam welding, the metal to be welded is moved between series of spot welds