Ensure electrical connection leads are in good condition and tight prior to use. They should be protected to prevent accidental damage from hangar traffic. Make sure you have adequate ventilation. GTAW uses inert gases during the process, if it is used in an enclosed area it can displace breathing air and can be hazardous without proper ventilation. In addition, ozone is produced during the welding process. The amount of ozone produced varies with type of electrode used, amperage, and argon flow. In poorly ventilated areas, ozone levels can increase to harmful levels. Whenever possible, draw fumes and contaminated air away when welding. Flammable materials should not be carried in clothing pockets. Shielding curtains should be placed around all jobs so that workers in adjacent are not exposed to the welding arcs. Shielding Gas In GTAW, the gas used to shield the welding arc and hot metals is an inert gas. Inert gases are gases whose atomic structures do not allow them to react with metals or other gases. Argon, helium, or an argon-helium mixture is used as the inert gas in GTAW. Argon is a relatively heavy gas. It has several benefits when used in GTAW. It requires a lower arc voltage than other shielding gases for a given arc length and current used (ideal for thin metal welding). It also provides easier arc starting. Its heavier weight as compared to helium provides for good shielding with lower flow rates. In contrast to helium is the lightest of the inert gases. Because of its light weight, about two to three times more helium is needed as compared to argon to shield the weld area. Despite this, helium has an advantage over argon in that it can be used with greater arc voltages. Because of this, helium is preferred when working with thick metal sections. Another difference in the two gases is their cleaning ability. Both helium and argon allow for good cleaning action when using DC. However, when using AC,
Hydrogen, Oxygen, and Nitrogen can react in the weld puddle and cause changes in the structure of the weld weakening the weld. Properties of Metals (The following information is available from Integrated Publishing at ) This section is devoted primarily to the used in describing various properties and characteristics of metals in general. Of primary concern in advanced manufacturing and advanced manufacturing and aerospace maintenance are such general properties of metals and their alloys as hardness, brittleness, malleability, ductility, elasticity, toughness, density, fusibility, conductivity, and contraction and expansion. Knowledge of these terms is essential as it helps to form the basis for further discussion of metals used in advanced manufacturing and aerospace. Hardness Hardness refers to the ability of a metal to resist abrasion, penetration, cutting action, or permanent distortion. Hardness may be increased by working the metal and, in the case of steel and certain titanium and aluminum alloys, by heat treatment and cold-working (discussed later). Structural parts are often formed from metals in their soft state and then heat treated to harden them so that the finished shape will be retained. Hardness and strength are closely associated properties of all metals. Brittleness Brittleness is the property of a that allows little bending or deformation without shattering. In other words, a brittle metal is apt to break or crack without change of shape. Because structural metals are often subjected to shock loads, brittleness is not a very desirable property. Cast iron, cast aluminum, and very hard steel are brittle metals.
Density is the weight of a unit volume of a material. In advanced manufacturing and aerospace work, the actual weight of a material per cubic inch is preferred, since this figure can be used in determining the weight of a part before actual manufacture. Density is an important consideration when choosing a material to be used in the design of a part and still maintain the proper weight and balance of the advanced manufacturing and aerospace. Fusibility Fusibility is defined as the ability of a metal to become liquid by the application of heat. Metals are fused in welding. Steels fuse at approximately 2,500°F, and aluminum alloys at approximately 1, 110°F. Conductivity Conductivity is the property that enables a metal to carry heat or electricity. The heat conductivity of a metal is especially important in welding, because it governs the amount of heat that will be required for proper fusion. Conductivity of the metal, to a certain extent, determines the type of jig to be used to control expansion and contraction. In advanced manufacturing and aerospace, electrical conductivity must also be considered in conjunction with bonding, which is used to eliminate radio interference. Metals vary in their capacity to conduct heat. Copper, for instance, has a relatively high rate of heat conductivity and is a good electrical conductor. Contraction and Expansion Contraction and expansion are reactions produced in metals as the result of heating or cooling. A high degree of heat applied to a metal will cause it to expand or become larger. Cooling hot metal will shrink or contract it. Contraction and expansion affect the design of welding jigs, castings, and tolerances necessary for hot-rolled material. QUALITIES OF METALS The selection of proper materials is a primary consideration in the development and proper maintenance and repair in advanced manufacturing and aerospace.