Welding Practice - The Hong Kong Polytechnic University

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Welding Practice Shielded metal-arc welding is probably the most widely used welding process. For the most part, welding with this process is done manually. It may be used in all positions: flat, vertical, horizontal, and overhead. Suitable electrodes are available for shielded metal-arc welding of plain carbon steel, low-alloy steel, stainless steel, copper 'and its alloys, aluminium and its alloys, and cast iron. A diagram of shielded metal-arc welding is as shown in Fig 3. Submerged-arc welding can be used in a fully automatic system set-up with the electrode and granular flux (see Fig 4) feed-controlled and either the welding head traversing the work or the work moving under a fixed head. Because it is necessary that the flux remains on the joint, this welding method is restricted to the flat position except for horizontal fillet welds. Inert gas arc welding employs either consumable electrodes (see Fig 5) or nonconsumable electrodes, (see Fig 6) with the arc drawn between the electrode and the work piece. Inert gas such as carbon dioxide, helium, or argon is used to provide shielding of the arc and the molten metal. Consumable electrode inert gas arc welding is commonly referred to as Metal-arc Inert Gas welding (MIG) whilst non-consumable electrode inert gas arc welding is referred to as Iungstenarc Inert Gas welding (TIG) because tungsten electrodes are used in the process. In the case of TIG filler metal, where needed, is provided by a welding rod inserted into the arc without forming a part of the welding circuit. Page 4 IC Professional Training
Welding Practice Inert gas arc welding was originally developed for welding light metals, aluminium and magnesium. Its use has been extended to the welding of stainless steels, mild steels, copper and nickel and their alloys, and the more recent high temperature metals such as titanium and zirconium. 2.1 Brazing The brazing process differs from welding processes in that the non ferrous filler metal used has a melting point below that of the metal to be brazed, but higher than 450°C, and further, the flow of filler metal through the joint is by capillary attraction. To accomplish this action, the joint should have a clearance of 0.05 to about 0.25 mm depending upon the shape of the joint. Page 5 IC Professional Training
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Welding Practice - The Hong Kong Polytechnic University

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