Welding is a fabrication process that joins materials, usually metals or thermoplastics by causing coalescence. This is often done by melting the work pieces and adding a filler material to form a pool of molten material (the weld puddle) that cools to become a strong joint, but sometimes pressure is used in conjunction with heat or by itself to produce the weld. This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the work pieces to form a bond between them, without melting the work pieces.
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.
Energy Beam Welding
Energy beam welding methods, namely laser beam welding and electron beam welding, are relatively new processes that have become quite popular in high production applications. The two processes are quite similar, differing most notably in their source of power. Laser beam welding employs a highly focused laser beam, while electron beam welding is done in a vacuum and uses an electron beam. Both have a very high energy density, making deep weld penetration possible and minimizing the size of the weld area. Both processes are extremely fast, and are easily automated, making them highly productive. The primary disadvantages are their very high equipment costs (though these are decreasing) and a susceptibility to thermal cracking. Developments in this area include laser-hybrid welding, which uses principles from both laser beam welding and arc welding for even better weld properties.
Electron Beam Welding
Electron Beam Welding (EEW) is a unique way of delivering large amounts of concentrated thermal energy to materials being welded. It became viable as a production process in the late 1950's. At that time, it was used mainly in the aerospace and nuclear industries. Since then, it has become the welding technique with the widest range of applications. This has resulted from the ability to use the very high energy density of the beam to weld parts ranging in sizes from very delicate small components using just a few watts of power to welding steel at a thickness of 10 to 12 inches with 100 Kilowatts or more. However, even today most of the applications are less than 1/2" in thickness, and cover a wide variety of metals and even dissimilar metal joints
How it works:
The most common Electron Beam systems used in manufacturing today are of the high vacuum design. The other machine types are: 1- Partial vacuum equipment.
2- Non-vacuum equipment.
These two types are used in mass production where high output is important. The diagram shown shows the classic triode gun and column assembly. The triode gun design consists of the cathode (Filament), Bias cup (Grid) and Anode. Other sub-assembly components that contribute to the triode are: High voltage insulator Feed-through, high voltage cable and deflection coils. All these components are housed in a vacuum vessel called the upper column. The column assembly is held under a high vacuum by an isolation valve positioned below the anode assembly.
The vacuum environment provides several benefits:
•Removes the bulk gas molecules necessary for a stable triode. •Provides protection for the incandescent filament against oxidization. •Provides a controlled environment to protect the gun against welding by product.
The beam formatting begins with the emission of electrons from the incandescently heated tungsten...