2. INTRODUCTION
Electron-beam welding is fusion welding process in which a
beam of high velocity electrons is applied to two materials to
be joined.
Free electrons in vacuum can be accelerated, with their paths
controlled by electric and magnetic fields.
Narrow beams of electrons carrying high kinetic energy can be
formed, which upon collision with atoms in solids transform
their kinetic energy into heat.
3. How does the Process Work?
In an electron beam welder electrons are “boiled off” as current
passes through filament which is in a vacuum enclosure.
Electrons are emitted from the heated filament called electrode.
An electrostatic field, generated by a negatively charged filament
and bias cup and a positively charged anode, accelerates the
electrons to about 50% to 80% of the speed of light and shapes
them into a Beam, having high kinetic energies.
4. Electron beams are composed of electrons that are
charged particles having a rest mass of 9.1x10-31 kg.
The electrons are accelerated from the source with high
voltage potential difference (30 kV to 175 kV) between a
cathode and anode.
The stream of electrons then pass through a hole in the
anode. The beam is directed by magnetic forces of
focusing and deflecting coils.
5. This beam is directed out of the gun column and strikes
the work piece. The kinetic energy of the electrons is
transferred to heat upon impact of the work piece and
cuts a perfect hole at the weld joint. Molten metal fills in
behind the beam, creating a deep finished weld.
7. Electron gun
The electron beam is most often formed by a triode style
electron gun under high vacuum conditions.
A grid cup, a specially shaped electrode that can be negatively
biased with respect to the hot cathode emitter (filament).
And an anode, a ground potential electrode through which
the electron flow passes in the form of a collimated beam.
8. There are two type of electron guns
• Self accelerated – Electrons are accelerated by applying
potential difference between the cathode and anode.
• Work accelerated - potential difference is applied between
work piece and anode (Diode type).
9. Focusing of electron beam
It has two parts: Electron focusing lens and deflection coil.
Electron focusing lens focuses the beam into work area.
deflection coil (positioned below the magnetic lens) can be
employed to “bend” the beam, thus providing the flexibility
to move the focused beam spot.
10. Vacuum chamber
Generally EBW performed in vacuum.
Vacuum in the gun region is needed to maintain gun
component cleanliness, prevent filament oxidation, and
impede high-pressure short circuiting between the cathode
and the anode or the filament and the grid cup.
11. Steps Used in EBW process
Joint preparation.
Cleaning of work piece.
Fixturing of work piece.
De-magnetization of work piece.
Setting up work piece in chamber.
Pump down air form chamber.
Carry welding process.
12. Process parameters
Major Process Parameters are
1. Accelerating voltage:
• The potential difference between two electrode which is
usually expressed in kilovolts, being utilized to accelerate
and increase the energy of the electrons.
• Increase in the voltage results into increase in the speed of
electrons.
• This equation can use to calculate the acceleration of an
electron using this equation −
𝑑𝑉
𝑑𝑥
= 𝑚𝑒𝑎
13. 2. Beam current:
• Beam current is the measure of
the quantity of charge (ie:
number of electrons),usually
expressed in units of
milliamperes (mA), that flow per
unit time in an electron beam.
• There is a close relation
between electron beam current
and depth of penetration as in
the graph (Fig 9).
14. 3. Welding speed :
• Higher welding speeds results into lower
depth of penetration
4. Beam Focusing
16. a) Impact of high energy electron beam on w/p surface. The
penetration depth into the workpiece is very low, just a few μm.
Most of the kinetic energy is released in the form of heat.
b) The high energy density at the impact point causes the metal
to evaporate thus allowing the following electrons a deeper
penetration.
c) This finally leads to a metal vapour cavity which is surrounded
by a shell of fluid metal, covering the entire weld depth.
d) Capillary action results into formation of weld
18. In Vacuum
a) Thin and thick plate welding (0,1 mm bis 300 mm).
b) Extremely narrow seams (t:b = 50:1).
c) Low overall heat input => low distortion =>Welding of
completely processed components.
d) High welding speed possible.
e) No shielding gas required.
f) High process and plant efficiency.
g) Material dependence, often the only welding method.
Advantage of EBW
19. At atmosphere
a) Very high welding velocity.
b) Good gap bridging. No problems with reflection during
energy entry into work piece.
20. In Vacuum
Electrical conductivity of materials is required.
High cooling rates => hardening => cracks.
High precision of seam preparation.
Beam may be deflected by magnetism.
X-ray formation.
Size of work piece limited by chamber size.
High investment.
Disadvantage of EBW
21. At Atmosphere
X-ray formation.
Limited sheet thickness (max. 10 mm).
High investment.
Small working distance.
22. • Almost all steels.
• Aluminium and its alloys.
• Magnesium alloys.
• Copper and its alloys.
• Titanium.
• Tungsten.
• Gold.
• Material combinations (e.g. Cu-steel, bronze-steel).
• Ceramics (electrically conductive).
Material favorable for electron beam welding
23. Applications of EBW
Mostly used in joining of refectory materials like
columbium, tungsten, ceramics.
High Precision Welding of electronics components.
High precision welding of nuclear fuel elements.
Special alloy components of jet engines.
Pressure vessels for rocket.
Joining of Dis similar metals.
Welding of Titanium medical implants.
