Welding
There are many methods for fusing or welding metal together. Depending upon the type of metal involved, the nature of the task, and the desired strength of the bond, there are welds to fit every need. The forge, or fire, method is generally used in blacksmithing. This method is the oldest welding process and establishes fusion by hammering the heated pieces of metal together. Blacksmithing fell into disuse at the end of the nineteenth century when more accurate welding techniques became available.
In the late 1860s, electric welding was introduced in America and oxyacetylene welding followed in 1903. Oxyacetylene welding has become the most common type of welding in non-industrial settings. In high-pressure oxyacetylene systems, which are most often used for small jobs, oxygen and acetylene are fed by hoses from separate cylinders to a torch mechanism where the two gases are mixed and burned at a high temperature. Low-pressure oxyacetylene systems generate acetylene from calcium carbide. This method is more attractive to users of large quantities of acetylene, since it eliminates the need to store a large number of acetylene tanks. Oxyacetylene welding is inexpensive, easy to use, and applicable to many types of metal.
Metal-inert gas (MIG) welding uses an inert-gas shielded arc of electricity. The arc is struck between the object being welded and a filler metal electrode. During the welding, the electrode continuously melts and is fed by a motor drive. In tungsten-inert gas (TIG) welding, the arc is struck between the work and a tungsten electrode, which is not consumed by the process. A filler metal is fed separately. The advantage of MIG welding is that it requires no flux (a substance applied to the metal to aid its bonding). The most common inert gas used for welding in the United States is argon, while helium is preferred in the United Kingdom and many other countries. Thermit welding uses a chemical reaction between aluminum and iron oxide. The resulting flame burns at 5000° F--twice the temperature of liquid steel.
An energy-efficient microwave welding was developed in the early 1990s. It ionises a gas, argon for example, using microwave energy which is maximized by a tuned cavity that centers the microwave welderÕs electric field. It can reach temperatures of 4000° F. Ultrasonic welding was first developed in the 1960s, but refined in the 1990s to be clean and fast and regulated by a microprocessor. An ultrasonic welder transforms electrical energy to ultrasonic frequency mechanical vibratory energy. This energy is transferred to a horn via a booster; the horn transfers the energy to the objects being welded. The actual weld is made by friction. Another welding technique developed in the 1990s is fiery foils. The foils are ultrathin (no thicker than a strand of human hair), highly reactive metallic films made of two layers of elements that have a strong desire to bond with each other, like aluminum and nickel. The foil is placed over the two surfaces, and a one small spark, from a match for example, causes the foil to ignite itself, giving off enough heat in mere milliseconds to weld the surfaces without damaging the rest of the objects. Extremely portable, fiery foils can be used anywhere, including places traditional welding equipment could never be carried. Because no oxygen is required, fiery foils can also be used in outer space or under water.
Welding is used extensively in construction and manufacture, serving as a substitute for or in addition to bolts and rivets. Welding is often utilized by metal sculptors as well.
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