<P> Filing is combination of grinding and saw tooth cutting using a file . Prior to the development of modern machining equipment it provided a relatively accurate means for the production of small parts, especially those with flat surfaces . The skilled use of a file allowed a machinist to work to fine tolerances and was the hallmark of the craft . Files can vary in shape, coarseness, and whether the teeth or single cut or double cut depending on what application the file is to be used for . Today filing is rarely used as a production technique in industry, though it remains as a common method of deburring . </P> <P> Broaching is a machining operation used to cut keyways into shafts . Electron beam machining (EBM) is a machining process where high - velocity electrons are directed toward a work piece, creating heat and vaporizing the material . Ultrasonic machining uses ultrasonic vibrations to machine very hard or brittle materials . </P> <P> Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence . This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, but sometimes pressure is used in conjunction with heat, or by itself, to produce the weld . </P> <P> Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound . While often an industrial process, welding can be done in many different environments, including open air, underwater and in space . Regardless of location, however, welding remains dangerous, and precautions must be taken to avoid burns, electric shock, poisonous fumes, and overexposure to ultraviolet light . </P>

The operation of joining two or more parts together by molten metal is called