Welding

Welding is a group of processes used to join non-metallic and metallic materials, by applying heat, pressure, or a combination of both. Most welding procedures require heat, although some procedures require only extreme pressure (cold welding). The welding process chosen to join materials together depends upon the mechanical, physical, and chemical properties of the materials to be joined, and the use for which the product is intended. The welding processes most commonly used today are resistance welding, gas welding, and arc welding. Special welding processes used include electrogas, electroslag, plasma arc, submerged arc welding, underwater, electron beam, laser beam, ultrasonic, friction welding, thermit, brazing, and soldering.

In industry, welding usually refers to joining metals, although materials such as plastics or ceramics are welded. Thermoplastics, such as polyvinylchloride, polyethylene, polypropylene, and acrylics can be welded. Like metal, plastics are welded with localized heat. New welding processes have been developed as new metals, alloys, plastics, and ceramics have been created. Welding is a means of construction, and a method for maintenance and repair. Various welding processes are used in numerous industries, such as aircraft, automotive, mining, nuclear, railroad, shipping, building construction, tool-making, and farm equipment. Welding by robots is one of the more common—and spectacular—applications of robots in industry.

When welding, wearing protective clothing is necessary to avoid injury from sparks, metal fragments, flames, and ultraviolet and infrared rays. Different welding processes require specific clothing. Clothing should be flame resistant, hair and skin should be covered, and special goggles must be worn. Sometimes leather clothing and helmets are recommended, as are steel toed boots. The work area should be properly ventilated; some welding procedures are required to be done in specially vented areas or booths to avoid toxic fumes.

Tests have been devised to inspect welds for flaws and defects. There are two types of testing, nondestructive and destructive. Often, a visual inspection is all that is needed but to test for internal or extremely small defects, other methods are necessary. Some nondestructive methods include air pressure leak tests, and ultrasonic, x ray, magnetic particle, and liquid penetrant inspections. Nondestructive tests do not damage the weld. Destructive tests are used to test the physical properties of the weld. Usually a test piece is removed from the weld, or a sample weld is made and then tested, completely destroying the weld. Some examples of destructive tests are tensile, hardness, bend, impact, pressure, and fillet testing.