I discuss more about electron gun column, thermionic emission of electrons, using Taguchi method with ANOVA analysis one welded joint was studied.

1. CONTENTS
1. Introduction
2. Description of an EBW Setup
3. Design Considerations of the Electron Gun Column
4. Electron Beams for Micro Operations
5. Statistical Analysis and Constrained Optimization on the
Results of Macro Electron Beam Welding Process on
ASS 304 Steel
6. Summary
• References

2. 1. Introduction
• Electron beam welding (EBW) is a metal-joining
technology that is about 60 years old.
• A high-energy focused electron beam is used as an
intense heat source.
• The applicability of electron beams to both macro- and
microwelding has also been discussed.
• EBµW can be thought of as a scaled-down, high-precision
version of the conventional EBW.
• EBµW machine development is expected to play a major
role in realizing modern, cutting-edge technologies.

3. 2. Description of an EBW Setup
• An EBW machine
is an engineered
ensemble of
various
components.
• Multidisciplinary
expertise is
required to realize
the hi-tech metal-
joining process on
the shop floor.
FIGURE 1
Schematic of an EBW machine.

4. 3. Design Considerations of the
Electron Gun Column
• The following issues are receiving the attention of EBW
machine developers from all over the world:
 Miniaturization
 Operator friendliness
 Machine intelligence
 Low production and maintenance time
 Standards for beam quality

5. 3.1 Electron Source
• An electron source is capable of supplying an abundance of
free electrons continuously with time.
• Thermionic emission is the most preferred method of electron
generation for welding applications.
• The emitter should have the following characteristics:
 Shape stability at high (more than 2000°C) temperatures
 High ratio of extraction to radiation area (emitter efficiency)
 Low lead losses
 High emitter life
 Dimensional tolerances achievable during manufacture

6. 3.2 Electrostatic Lens
• The electron cloud generated by thermionic emission explained
earlier is required to be shaped and accelerated suitably.
• The electric field is produced between suitably shaped
(contoured) electrodes (Figure 2)
FIGURE 2
Line diagram of an electron gun and its power supplies. (Vf, filament heating voltage; If, filament
heating current; Vb, bias voltage; kV, acceleration voltage; Ib, beam current; It, target current; Ia
anode current.) The currents indicated in the circuit are the conventional currents whose
direction is opposite to that of the electron flow.

7. Continued…
• The technique for contouring the electrodes is fairly complex.
Conventionally, this problem is solved using electron optics.
• The desired electrode shapes are arrived at using the principle
of ray tracing (a classical method in light optics) by either
analytical or numerical methods.
• The exquisite properties of electrons such as relativistic effects,
mutual coulomb repulsion, self-generated magnetic fields, and
random velocities at the emission point are included for more
accurate calculations.
FIGURE 3
Photograph of the fabricated 80-kV, 12-kW
EBW gun in open condition (filament is not
seen). (Source : BARC)

8. 3.3 Electromagnetic Lens and Its Basic
Design
• The electron beam formed by the electron gun is transported to
the target with the help of lenses.
• A diverging beam from an electron gun is caused by:
Diverging lens effect of the anode aperture
Space charge effect
 Thermal velocity distribution of electrons at the cathode (in
thermionic emission guns)
• When an electron enters the magnetic field, it experiences a
force that always acts toward the axis.
• The number of turns should hence be judiciously chosen.

9. Continued…
• The beam cannot be focused by an EM lens to a point on the
target, and is limited by some defects (called aberrations) listed
below.
Spherical aberration
Space charge aberration
Thermal velocity aberration
Chromatic aberration
Lens machining tolerances
Lens alignment (tilt and axial shift)
• An important component for the operation of an electron gun is
its power source.
• The deflection and oscillation lens is used to obtain a precise
beam alignment or to steer the beam

10. • The engineering design of an electron gun column incorporates
the following points:
Material selection and qualification
Tolerance on the components
Choice of vacuum pumping, vacuum plumbing, and
instrumentation
Assembly procedure and quality assurance
Water cooling requirements

11. FIGURE 11.4
(a) Electron gun column of an 80 kV, 12 kW EBW machine developed at BARC, Mumbai.
FIGURE 11.4 (b) electron trajectories of the 80 kV,
12 kW EBW gun design

12. 4. Electron Beams for Micro
Operations
4.1 Electron beam as Microwelding Tool
•Micro electron beams are between the two classes of beams.
•The first challenge is to handle both the space charge and
aberrations.
• Spot size 40 µm
Beam power 5 W
Beam power density 1 × 106 W/cm2 .
•Electrons do not contaminate the target material during the
interaction.
•The generation and transport of an electron beam needs a
vacuum of 10-6 mbar.

13. 4.2 Choice of Parameters for EBµW
• The major parameters of electron beam machines are:
Acceleration voltage (10-100 kV)
Beam current (10-100 mA)
Spot size on the target (10-100 µm)
Welding speed (25-100 µm/s)
Pressure in the vacuum chamber (1 × 10-6 mbar)

14. 4.3 Special Features for Micro Electron Beam Machines
• Pulsed beam
• Multibeam
• Imaging facility
• Preloading

15. 4.5 Challenges and Unsolved Issues in Electron Beam
Microwelding
• Electron beam characterization
• Precise job-maneuvering device
• Weld parametric studies for microjobs
• Quality assurance of welds

16. 5.
Statistical Analysis and Constrained
Optimization on the Results of Macro
Electron Beam Welding Process on ASS
304 Steel

17. 5.1 Soft-Computing-Based Approaches
• Dey et al. performed bead-on-plate welding on stainless steel
(ASS 304) and aluminum plates (Al 1100) with EBW.
• Weld runs were performed in accordance with a central
composite design (CCD).
• They used a genetic algorithm (GA) with penalty approach to
look for welding parameters that would minimize weldment
area, while maintaining the maximum BP.

18. 5.3 Description of Experimental Setup and
Data Collection
FIGURE 5
Photograph of the electron beam welding machine at M/s Siddhi Engineering Company,
Mumbai, India. (From Saha, T.K. and Ray, A.K. International Symposium on Vacuum Science and
Technology, Journal of Physics

19. • General Specifications of the 6-kW EBW Machine
TABLE 1
General Specifications of the 6-kW EBW Machine
• In the studies conducted, three working parameters, namely,
accelerating voltage, beam current, and welding speed, were
varied to see their effects on bead geometry.

20. 5.3.1 ASS-304 Welded Samples
FIGURE 6
A stainless steel plate showing six weld
runs.
FIGURE 7
Photograph of the etched section of
the weldment of an ASS-304
specimen
Working Parameters Range of values
Accelerating voltage (V) 60-90 kV
Beam current (I) 7-9 mA
Welding speed (S) 60-90 cm/min

21. FIGURE 11.8
Schematic view of the fusion zone of ASS-304 welded specimens.
5.4 Statistical Regression Analysis of
Stainless Steel (ASS-304) Data

22. Continued…
TABLE 2
Significance Test for BP

23. FIGURE 9
Surface plots of bead penetration (BP) for ASS-304 with varying input parameters:
(a) accelerating voltage and beam current, (b) accelerating voltage and weld speed, and (c) weld
speed and beam current.

24. FIGURE 10
Percentage deviation in the prediction of BP
for ASS-304 from the experimental values.
Bead Geometry Correlation Coefficient Mean Square Deviation
BP 0.9469 0.0789
BW 0.7676 0.0124
BH 0.9067 0.0004

25. 6. Summary
• The importance of electron beams in both micro- and
macrowelding has been felt.
• A considerable amount of literature is available on experimental
studies related to macrowelding.
• The experimental results obtained have been analyzed.
Electron beam macrowelding is used nowadays in modern
industry.
• However, electron beam microwelding is still in the
research phase.
• Research issues, as mentioned above, are to be solved first
before electron beam microwelding finds its place in industries.

26. References
• Electron Beams for Macro and Microwelding Applications ,
D.K. Pratihar and V. Dey , A.V. Bapat and K. Easwaramoorthy.

27. Thank you !!