LYCOS RETRIEVER 
Welding: Materials
built 638 days ago
The effects of welding on the material surrounding the weld can be detrimental—depending on the materials used and the heat input of the welding process used, the HAZ can be of varying size and strength. The thermal diffusivity of the base material plays a large role—if the diffusivity is high, the material cooling rate is high and the HAZ is relatively small. Conversely, a low diffusivity leads to slower cooling and a larger HAZ. The amount of heat injected by the welding process plays an important role as well, as processes like oxyacetylene welding have an unconcentrated heat input and increase the size of the HAZ. Processes like laser beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with the individual processes varying somewhat in heat input.[29][30] To calculate the heat input for arc welding procedures, the following formula can be used:
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Training in welding is offered to those who wish to learn basic welding skills or to upgrade their knowledge in welding. All welding classes are offered on an open-entry, open-exit self-paced basis. Classes use course outlines, books, videos, and instructor-assisted instruction with practical hands-on training. Various types and thicknesses of material are welded in all positions with different welding processes. Courses in ornamental ironwork are ... available. Three certificate options are available in pipe welding, structural welding, and combination pipe, structural, and advanced processes.
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Gordon Rutherford, 34, of Waxahachie, Texas, was killed in January 2003 while employed by Circle 4M Welding, a TXI contractor. According to the lawsuit filed by his wife, Amy, TXI directed Mr. Rutherford and a crew of three other welders to work in a location near an environmental scrubber that contained "extremely hazardous and flammable materials." During the course of the work, 5.5 tons of combustible plastics caught on fire and engulfed Mr. Rutherford. Following the explosion, a construction crane malfunctioned and left Mr. Rutherford suspended 90 feet above the ground and unable to reach safety.
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Aluminum alloys are susceptible to hot cracking, and to combat the problem, welders increase the welding speed to lower the heat input. Preheating reduces the temperature gradient across the weld zone and ... helps reduce hot cracking, but it can reduce the mechanical properties of the base material and should not be used when the base material is restrained. The design of the joint can be changed as well, and a more compatible filler alloy can be selected to decrease the likelihood of hot cracking. Aluminum alloys should also be cleaned prior to welding, with the goal of removing all oxides, oils, and loose particles from the surface to be welded. This is especially important because of an aluminum weld's susceptibility to porosity due to hydrogen and dross due to oxygen.[37]
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For manual welding methods, labor costs generally make up the vast majority of the total cost. As a result, many cost-savings measures are focused on minimizing the operation time. To do this, welding procedures with high deposition rates can be selected, and weld parameters can be fine-tuned to increase welding speed. Mechanization and automatization are often implemented to reduce labor costs, but this frequently increases the cost of equipment and creates additional setup time. Material costs tend to increase when special properties are necessary, and energy costs normally do not amount to more than several percent of the total welding cost.[41]
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Laser welding offers the advantages of deep penetration and high speed. It is used where other welding processes can’t deliver either the required distortion control or productivity. Depending on material and application, the process can use a variety of shield gases based on helium, argon or mixtures.
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