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Electron Beam Engineering

Energy Beam Welding

Electron Beam Welding

High energy beam welding identifies a category of processes, each of which is capable of transferring a beam of such high energy intensity it can be used to melt and vaporize metals. This ability is useful for precision welding, drilling and cutting. Electron beam and laser are the two precision welding processes in this unique high energy category. It is important to note electron beam and laser are energy, not thermal transfer, processes.

The electron beam consists of a dense stream of electrons magnetically squeezed and focused into a concentrated, directional, energy column. The electrons are propelled at velocities reaching 130,000 miles per second depending on anode voltage. When impinged on the workpiece the electrons convert their high velocity kinetic energy into heat. The heat thus generated within the focused spot diameter can reach an equivalent of millions of watts per square inch.

This high energy density process is seconded only by that of the laser whose energy is transferred as photons moving at the speed of light. The level of energy and importantly, the light wave frequency, are dependent on the laser type and the characteristics of its atomic source. The energy transfer is optically (rather than magnetically) focused into a column whose diameter at the focal point can be smaller than .005 inches, resulting in heat generation at the workpiece surface equivalent to millions of watts per square inch. It is important to note the laser beam is not dependent on electrical conductivity as are the electron beam and arc welding processes. Therefore non-metallics, ceramics for example, respond equally well to the light wave energy transfer. Additionally, magnetic fields emanating from fixtures, the workpiece, etc. do not distort or disturb the laser beam.

A particular advantage of the high energy beam welding processes is their ability to produce very narrow welds accompanied by minimal heat affected zones. This is an ideal combination both metallurgically and structurally.

Electron beam has the additional and remarkable capability for exceptionally deep weld penetration while still maintaining the narrow welds and minimal heat affected zones. This achievement (accomplished utilizing the "keyhole" mode) cannot be duplicated by laser or any other process. Laser using the "keyhole" mode is limited to perhaps one or two inches. Penetration achievements beyond this have been reported in the use of very powerful, multikilowatt lasers. In fact the primary limitation of the laser welding process is its limited penetration ability.

There are costs with either electron beam or laser welding which must be considered. Both require very significant capital investment. They require close tolerance preparation of the weld joint, and though this may not be difficult to achieve with machined workpiece components it is not easily accomplished with sheet metal details. Electron beam is further disadvantaged by the necessity for it to function in a vacuum thus imposing the restrictive, physical limits of vacuum chambers.

Both processes have safety considerations. Electron beam generates X-rays due to the high voltage requirement of the electron gun column. Lasers have the potential for eye and tissue damage, inherent with the monochromatic and collimated light waves.

As stated, electron beam must function in a vacuum to prevent the dispersal of the focused electrons by collision with air or other gaseous or physical molecules. The required vacuum chamber, though a limiting restraint on workpiece accommodation, does simplify shielding of personnel from the harmful X-rays, by lead lining the chamber.

For laser, safety shielding can be accomplished with light absorbing or low reflectance baffles constructed using the appropriate materials. These devices are located to envelop the optical path of the beam including the workpiece or its potential reflectance from surfaces in the area. However, full safety assurance and protection is achieved with enclosures. Since the enclosures need not be gas tight they can be relatively inexpensive to construct and sized for anticipated workpiece needs.

Ideally, the laser system and workpiece station are located within partitions, room, or work cell, and thus isolated from the general production area and from uncontrolled and unauthorized personnel access. In any case there are strict regulations involving laser safety. These safety assurances when thoughtfully implemented, in no way jeopardize the laser's exceptional compatibility with sophisticated cost-reducing automation processes, whether it be robotics, conveyors, multi-axes motion systems, etc.

In conclusion, high energy beam welding is used to produce high quality welds both metallurgically and structurally. Their focused beams are free of peripheral thermal radiation and convection and ideal for precision welding tasks. They reduce costs by minimizing distortion and reducing the need for elaborate clamping fixtures and the use of automation. Lastly, they are not labor intensive nor do they require skilled machine operators.

This technical information has been contributed by
Electron Beam Engineering

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