| Aircraft repair and fabrication of structural | | | | commonly known as Tungsten Inert Gas (TIG) |
| components and high temperature components like | | | | welding and by the trade names of Heliarc or |
| exhaust systems and ducting components often calls | | | | Heliweld. These trade names were derived from the |
| for NADCAP approved welding. | | | | fact that the inert gas originally used was helium. |
| Gas welding | | | | Rather than using a consumable electrode such as is |
| A fuel gas such as acetylene or hydrogen is mixed | | | | used in both of the other two methods we have |
| inside a welding torch with oxygen to produce a | | | | discussed, the electrode in TIG welding is a tungsten |
| flame with a temperature of around 6,300 degrees F. | | | | rod. (In earlier procedures using this form of welding, |
| (3,482 degrees C). This flame is used to melt the | | | | a carbon electrode was used, but it has been |
| materials to be welded. A filler rod is melted into the | | | | replaced almost exclusively with tungsten.) |
| puddle of molten metal to reinforce the weld. When | | | | The 250+ amp arc between the electrode and the |
| highly-reactive metals such as aluminum are gas | | | | work melts the metal at 5,432 degrees F, and a filler |
| welded, they must be covered with flux to exclude | | | | rod is manually fed into the molten puddle. A stream |
| oxygen from the molten metal and keep oxides from | | | | of inert gas such as argon or helium flows out of the |
| forming which would decrease the strength of the | | | | torch and envelopes the arc, thereby preventing the |
| weld. | | | | formation of oxides in the puddle. |
| Shielded Metal Arc Welding (SMAW). | | | | The versatility of TIG welding is increased by the |
| This method is the most familiar and common type | | | | power supply that is used. Direct current of either |
| and is known in the trade as stick welding. A metal | | | | polarity or alternating current may be used. |
| wire rod coated with a welding flux is clamped in an | | | | Electric-resistance welding |
| electrode holder connected to the power supply with | | | | For aerospace welding, many thin sheet metal parts |
| a heavy electrical cable. The metal to be welded is | | | | for aircraft, especially stainless steel parts, are joined |
| also attached to the power supply. The electrical | | | | by one of the forms of electric resistance welding, |
| power is supplied to the work at a low voltage and | | | | either spot welding or seam welding.a. Spot Welding. |
| high current and may be either AC or DC, depending | | | | Two copper electrodes are held in the jaws of the |
| upon the type of welding being done. An arc is | | | | spot welding machine. and the material to be welded |
| struck between the rod and the work and produces | | | | is clamped between them. Pressure is applied to hold |
| heat in excess of 10,000 °F, which melts both | | | | the electrodes tightly together, and electrical current |
| the material and the rod. As the flux melts, it | | | | flows through the electrodes and the material. The |
| releases an inert gas which shields the molten puddle | | | | resistance of the material being welded is so much |
| from oxygen in the air and prevents oxidation. The | | | | higher than that of the copper electrodes that |
| molten flux covers the weld and hardens to an | | | | enough heat is generated to melt the metal. The |
| airtight slag cover that protects the weld bead as it | | | | pressure on the electrodes forces the molten spots |
| cools. This slag must be chipped off to examine the | | | | in the two pieces of metal to unite, and this pressure |
| weld. | | | | is held after the current stops flowing long enough |
| Gas Metal Arc Welding (GMAW). | | | | for the metal to solidify. Refer to MIL HDBK-5 for |
| This method of welding was formerly called Metal | | | | joint construction and strength data. The amount of |
| Inert Gas (MIG) welding and is an improvement over | | | | current, pressure, and dwell time are all carefully |
| stick welding because an uncoated wire electrode is | | | | controlled and matched to the type of material and |
| fed into the torch and an inert gas such as argon, | | | | the thickness to produce the correct spot welds.b. |
| helium, or carbon dioxide flows out around the wire | | | | Seam Welding. Rather than having to release the |
| to protect the puddle from oxygen. The power | | | | electrodes and move the material to form a series of |
| supply connects between the torch and the work, | | | | overlapping spot welds, a seam-welding machine is |
| and the arc produces the intense heat needed to | | | | used to manufacture fuel tanks and other |
| melt the work and the electrode. Low-voltage | | | | components where a continuous weld is needed. |
| highcurrent DC is used almost exclusively with GMAW | | | | Two copper wheels replace the bar-shaped |
| welding. GMAW is used more for large-volume | | | | electrodes. The metal to be welded is moved |
| production work than for aircraft repair. | | | | between them, and electric pulses create spots of |
| Gas Tungsten Arc Welding (GTAW). | | | | molten metal that overlap to form the continuous |
| This is the form of electric arc welding that fills most | | | | seam. |
| of the needs in aircraft maintenance. It is more | | | | |