SMAW , Sheild Metal Arc Welding
Is the most widely used electric arc welding process and the first type to use consumable electrodes. The process also is referred to as manual metal arc welding (MMAW). Shielded metal arc welding uses heat that is produced by an electric arc to melt the metals. The electric arc is maintained between the welding joint at the surface of the base metal and the tip of the covered welding electrode.
During operation, the core rod conducts electric current to produce the arc and provides filler metal for the joint.
The core of the covered electrode consists of either a solid metal rod of draw or cast material or a solid metal rod fabricated by encasing metal powders in a metallic sheath. The electrode covering provides stability to the arc and protects the molten metal by the creation of shielding gases from the vaporization of the electrode cover. The arc characteristics of the electrode and the mechanical properties, chemical composition, and metallurgical structure of the weld are influenced by the type of shielding used, along with other ingredients within the covering and core wire. Each type of electrode used in SMAW has a different type of electrode covering, depending on the application. The advantages of the SMAW process include its simplicity, low cost, portability, and the fact that a shielding gas is not needed. One restriction of SMAW is that the deposition cycle is normally less than for processes using continuous electrodes.
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GTAW , Gas Tungsten Arc Welding
Uses a no consumable tungsten electrode that creates an arc between the electrode and the weld pool. An inert shielding gas is used in the process at no applied pressure. Argon is most commonly used as the shielding gas, and the process may be employed with or without the addition of filler metal. An illustration of the gas tungsten arc welding process, also referred to as no consumable electrode welding, and tungsten inert gas(TIG) welding.
Advantages of GTAW include its versatility, low equipment costs, control, and weld quality. It is widely used for the welding of light gauge stainless steel and aluminum and root passes in pipe butt joints. The GTAW process can easily be set up as an automated process. Another positive attribute of GTAW is the very low fume formation rate. This procedure is different from other processes that require the fill material to pass through the arc. Since filler is fed directly to the weld pool. Disadvantages of GTAW are its low speed and deposition rate which utilizes hot or cold wire feed and high heat input efficiency. By using shielding gas, these problems can be overcome. The GTAW weld zone is also difficult to shield properly in drafty environments
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SAW , Submerged Arc Welding
Produces an arc between a bare metal electrode and the work contained in a blanket of granular fusible flux. The flux submerges the arc and welding pool. Generally, the electrode serves as the filler material, although a welding rod or metal granules may be added. The flux covering the arc in submerged arc welding is an important factor in the process. The flux`s role influences the stability of the arc and the mechanical chemical properties of the final weld deposit.
The quality of the weld is dependent on the handling and care of the flux. Medium and heavy fabrication industries use the SAW process for fillet and main butt joints in pipe, cylinders, pressure vessels, columns, and beams. Generally, the welding head is fully automatic and mounted on a manipulator or carriage; however, for fillet welding hand held torches are available. Although SAW is limited to the down hand and horizontal positions, these positions can be utilized by informed design and job positioning. The process is also restricted by the high proportion of time needed to align the torch with the joint. Since the arc operates in a cavity under the flux.
There is no visible arc light, welding is spatter-free and there is no need for fume extraction. SAW is usually operated as a fully mechanized or automatic process, but it can be semi-automatic. Welding parameters, which include current, arc voltage and travel speed, all affect bead shape, depth of penetration and chemical composition of the deposited weld metal. Because the operator cannot see the weld pool, reliance must be placed on parameter settings. There is virtually no restriction on the material thickness, provided the work piece is suitably prepared. Most commonly welded materials are carbon-manganese steels, low alloy steels and stainless steels, although the process is capable of welding some non-ferrous materials with judicious choice of electrode filler wire and flux combinations
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GMAW , Gas Metal Arc Welding
Is a consumable electrode welding process that produces an arc between the weld pool and a continuously supplied filler metal. An externally supplied gas is used to shield the arc. GMAW originally was referred to as metal inert gas (MIG) welding because it used an inert gas for shielding.
Although it still is sometimes called MIG welding, developments have led to the use of both inert and reactive gases. A variation of the GMAW process, referred to as metal cored electrodes, uses a tubular electrode filled mostly with metallic powders forms. These types of electrodes must use a gas shield to prevent contamination of the molten weld by the atmosphere.
The American Welding Society (AWS) considers metal cored electrodes a part of GMAW, although metal cored electrodes are grouped with flux cored electrodes by foreign welding associations. Advantages of GMAW include it�s ability to be operated in semiautomatic, machine, or automatic modes. It is the only consumable process that can weld all commercially important metals, such as carbon steel, high-strength low alloy steel, stainless steel, nickel alloys, titanium, aluminum, and copper. A weld can be performed in all positions with the proper choice of electrode, shielding gas, and welding variables. Compared with shielded metal arc welding (SMAW), the deposition rates and welding rates are higher for GMAW. Also, the continuous electrode feed makes long welds possible without stops and starts
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FCAW , Flux Core Arc Welding
Is a consumable electrode welding process that uses shielding from flux contained within the tubular electrode. The heat-generating arc for FCAW operates between a continuous filler metal electrode and the weld pool.
Additional shielding may or may not be supplied by an external gas, and the process is used without the application of gas pressure. The flux cored electrode consists of a metal sheath surrounding a core of various powdered materials. The FCAW process is unique in its method of enclosing the fluxing ingredients within the continuously fed electrode. The electrode core material produces a slag cover on the face of the weld bead during the welding process. The two major process variations of FCAW protect the weld pool from contamination by the atmosphere with different methods. The first method, called self shielded FCAW, protects the welding pool by the break down and vaporization of the flux core through the heat of the arc. The second FCAW variation uses a shielding gas to protect the welding pool, in addition to protecting the vaporized flux core. Compared to SMAW, the FCAW process provides a high-quality weld metal at lower cost and with less effort by the welder. The process allows for more versatility than submerged arc welding and proves to be more forgiving than gas metal arc welding
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