LYCOS RETRIEVER 
Welding: Process
built 622 days ago
To supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common classification is constant current power supplies and constant voltage power supplies. In arc welding, the length of the arc is directly related to the voltage, and the amount of heat input is related to the current. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and ... voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding.
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Spot, seam, and projection welding are resistance welding processes in which the required heat for joining is generated at the interface by the electrical resistance of the joint. Welds are made in a relatively short time (typically 0.2 seconds) using a low-voltage, high-current power source with force applied to the joint through two electrodes, one on each side.
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This is one of the most common questions that come up during discussions on reactive metal welding. Another way of stating the question is "How do you know (nondestructively) if a discolored weld is contaminated?" A discolored weld condition or even lack of weld color may or may not be significant to determine whether the weld is acceptable. Weld discoloration is "one way" to determine whether contamination is present in a weld. If weld discoloration is free from each pass during the welding process and it passes all other weld quality testing criteria, then the weld should be fully ductile and acceptable. The significance of the weld coloration is "when was the color formed?" If the weld coloration was formed during the time the weld was molten or at an elevated temperature, an extremely contaminated weld would result. If the discoloration occurs at temperatures less than 425°C during weld cooling, then this is probably only a thin oxide coating and not detrimental to the weld itself.
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The history of joining metals goes back several millennia, with the earliest examples of welding from the Bronze Age and the Iron Age in Europe and the Middle East. Welding was used in the construction of the Iron pillar in Delhi, India, erected about 310 and weighing 5.4 metric tons.[1] The Middle Ages brought advances in forge welding, in which blacksmiths pounded heated metal repeatedly until bonding occurred. In 1540, Vannoccio Biringuccio published De la pirotechnia, which includes descriptions of the forging operation. Renaissance craftsmen were skilled in the process, and the industry continued to grow during the following centuries.[2] Welding... was transformed during the 19th century—in 1800, Sir Humphry Davy discovered the electric arc, and advances in arc welding continued with the inventions of metal electrodes by a Russian, Nikolai Slavyanov, and an American, C. L. Coffin in the late 1800s, even as carbon arc welding, which used a carbon electrode, gained popularity. Around 1900, A. P. Strohmenger released a coated metal electrode in Britain, which gave a more stable arc, and in 1919, alternating current welding was invented by C. J. Holslag, but did not become popular for another decade.[3]
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Streamlining to one wire, one gas and one welding system is saving OEM Fabricators up to $2,000 per day. Benefits are derived from .045 ER70S-6 wire, 90/10 argon/CO2 shielding gas and the Accu-Pulse™ (GMAW-P) welding process provided by Miller Electric’s Axcess™ multi-MIG welding systems.
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The course will help you develop skill in the SMAW process for welding in the flat, vertical and horizontal positions. You will practice full strength groove welds in the flat, vertical and horizontal positions. The groove weld is subjected to bend testing and is evaluated against a standard similar to that used in journey or ASME code qualification tests.
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