Electron Beam Welding

Electron beam welding is the fusing together of two or more materials using a beam of high-velocity electrons. All rely on the properties of electrons that permit them to be accelerated by an electrostatic field.

In an electron beam welding machine, electrons are accelerated to more than half the speed of light. The beam of high-velocity electrons impinges upon the material to be welded where it is focused to a minute spot by electromagnetic lenses. At this point, the kinetic energy of the electrons is transformed into the thermal energy; melting the material to form a fusion weld.

Electron beam welding overcomes the limitations of conventional welding techniques. When designing and producing precision products, conventional welding techniques present several draw-backs:

distortion due to shrinkage
low joint strength caused by excessive weld-heat input
contamination of the weld zone due to impurities in the surrounding atmosphere
inability to weld many materials
too much dependence on operator skill to keep the process under control.

Electron beam welding minimizes the distortion and shrinkage because of the low total energy input to the workpiece. This low energy input is possible because complete fusion occurs almost instantaneously due to the high power density of the beam. When 7500 watts of power are concentrated into a spot .010 inch in diameter, power density is 100,000 kilowatts/square inch and welding occurs at tremendous speeds. At these speeds, heat does not travel from the weld zone to the surrounding material, therefore, penetration in electron beam welding does not depend on the thermal conductivity of the material being welded, as with most other welding techniques.

Electron beam welding typically produces a very narrow fusion zone which has a depth to width ratio of approximately 15 to 1. Fusion zones of an electron beam weld and a conventional weld are compared in the figure. The energy input to a weld is approximately proportional to its cross-sectional area, so the energy requirement for electron beam welding is 4 percent of that required by other fusion welding processes.

Because electron beam welding takes place in a vacuum of 10^-4 Torr or greater (gas molecules scatter an electron beam), contaminaton or oxidation of the workpiece is virtually eliminated.

The high purity of the electron beam welding process permits welding reactive materials such as tungsten which are very sensitive to oxidation at high temperatures. Parts are joined without generating oxides or introducing fluxes and other residues. The purity of the material during welding fusion is higher than that of the parent material due to the "vacuum melting" that takes place during the process.

Repeatability and reliability are key-notes of the electron beam welding process. Once the machine power settings have been established for a weld, the same weld can be repeated without variation in quality. Weld location is precisely controlled within .005 of an inch through the use of 40X visual optical system so that weld integrity is guaranteed.

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