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