ELECTRON BEAM MACHINING PPT BY POLAYYA CHINTADA...USED FOR ENGINEERING AND POLYTECHINCC STUDENTS

1. ELECTRON BEAM MACHINING
Polayya chintada

2. ELECTRON BEAM MACHINING (EBM)
• Invented in Germany in 1952 by Dr. K. H. Steiger wald.
• EBM is a High-Energy-Beam Machining process
• Electrical energy is used to generate high-energy electrons
• The mechanism of material removal is primarily by melting and
rapid vaporization due to intense heating by the electrons.
An electron beam

3. EBM (LINE DIAGRAM)

4. EBM – PROCESS
• Electron beam (negatively charged
particles) is generated in an
electron beam gun.
• Electron beam gun provides high
velocity electrons over a very
small spot size.
• Due to pattern of electrostatic field
produced by grid cup, electrons
are focused and made to flow in
the form of a converging beam
through anode.

8. EBM – PROCESS (CONT.)
• The electrons are accelerated while passing through the anode by
applying high voltage at anode.
• A magnetic deflection coil is used to make electron beam circular
and to focus electron beam at a point (localized heating).
• The workpiece to be machined is located under the electron beam
and is kept under vacuum.
• The high-energy focused electron beam is made to impinge on the
workpiece with a spot size of 10 – 100 μm
• The kinetic energy of the electrons, upon striking the workpiece,
changes to heat, which melts and vaporizes minute amounts of the
material.

9. EBM – PROCESS (CONT.)
• The “melt – vaporization” front gradually progresses
• Finally the molten material, if any at the top of the front, is expelled
from the cutting zone by the high vapour pressure at the lower part.
Localized heating by focused
electron beam
Gradual formation of hole

10. EBM – PROCESS (CONT.)
• The whole process is carried out in a vacuum chamber
• The gun in EBM is used in pulsed mode. Holes can be drilled in thin
sheets using a single pulse. For thicker plates, multiple pulses would
be required.
Penetration till the auxiliary support Removal due to high vapour pressure

11. WHY VACUUM CHAMBER ?
• The entire process occurs in a vacuum chamber because a collision
between an electron and an air molecule causes the electrons to
scatter and thus loose their energy and cutting ability .

12. EBM – EQUIPMENTS
• Electron Beam Gun

13. • Electron beam gun is the heart of EBM.
• The basic functions of any electron beam gun are to generate free
electrons at the cathode, accelerate them to a sufficiently high
velocity and to focus them over a small spot size.
• Cathode is generally made of tungsten or tantalum. Such cathode
filaments are heated, often inductively, to a temperature of around
25000C. Heating leads to thermo-ionic emission of electrons.
• A combination of repelling forces from the negative cathode and the
attracting forces from the positive anode causes the free electrons to
be accelerated and directed toward the work piece.
• One of the major requirements of EBM operation of electron beam
gun is maintenance of desired vacuum.

14. • vacuum is achieved and maintained using a combination of rotary
pump and diffusion pump. Diffusion pump is attached to the
diffusion pump port of the electron beam gun
• Diffusion pump is essentially an
oil heater. As the oil is heated
the oil vapour rushes upward.
• Nozzles change the direction of
motion of the oil vapour and
the oil vapour starts moving
downward at a high velocity.
• Such high velocity jets of oil
vapour entrain any air molecule
present within the gun. This oil
is evacuated by a rotary pump
via the backing line.

15. • Power Supply
– The high-voltage power supply used for EBM systems generates
voltages of up to 150 kv to accelerate the electrons.
– The most powerful electron beam machining systems are
capable of delivering enough power to operate guns at average
power levels of up to 12 kw.
– Individual pulse energy can reach 120 joules/pulse.
– To avoid the possibility of arcing and short circuits, the high-
voltage sections of the power supply are submerged in an
insulating dielectric oil.

16. EBM PROCESS – PARAMETERS
Process parameters which directly affect the machining characteristics
in EBM are:
• The accelerating voltage
– electrons get accelerated at high voltage.
• The beam current
– related to the number of electrons emitted by the cathode or
available in the beam. Beam current can be as low as 200 μamp
to 1 amp.
• Pulse duration
– pulse duration can be as low as 50 μs to as long as 15 ms.
• Energy per pulse

17. • Power per pulse
• Lens current
• Spot size
– Spot size is controlled by degree of focusing achieved by the
electromagnetic lenses. For a lower spot size, the material
removal would be faster though the size of the hole would be
smaller.
• Power density
– The energy density and power density is governed by energy per
pulse duration and spot size .

18. • Total penetration range = 2.6 * 10-17 (V2 / ρ) mm
where,
and
V = accelerating voltage in volts
ρ = density of material in kg/mm3
• Speed of electron under control of electric field
V = E √(2e/m) m/s
where,
Thus,
m = mass of electron in kg = 9.1 * 10-31 kg
e = charge of electron in coulomb = 1.6 * 10-19
E = voltage of electric field in volts
V = 600 E
• Total power for beam current of I amperes
P = E I watts

19. • Force of beam on molten metal
F = 0.34 I √E dynes
• Power Requirement (P) for EBM process is approx. proportional to
MRR
i.e. P α MRR
P = C * MRR
where C is specific power consumption = 12 W / mm3 / min for
tungsten and 7, 6, and 4 W / mm3 / min for iron, titanium and
aluminium respectively.

20. ELECTRON BEAM PROCESS CAPABILITY
• EBM can provide holes of diameter in the range of 100 μm to 2 mm
with a depth upto 15 mm, i.e., with a l/d ratio of around 10. There
would be an edge rounding at the
entry point.
• Materials such as steel, stainless
steel, Ti and Ni super-alloys, Al as
well as plastics, ceramics, leathers
can be machined successfully using
EBM.
• The heat-affected zone is rather
narrow due to shorter pulse duration
in EBM. Typically the heat-affected
zone is around 20 to 30 μm.
Typical kerf shape of electron beam drilled hole

21. • materials like Al and Ti alloys are more readily machined compared
to steel.
Variation in drilling speed with volume of material removal
• EBM does not apply any cutting force on the workpieces. Thus very
simple work holding is required.
• Holes can also be drilled at a very shallow angle of as less as 20 to
300.

22. DESIGN CONSIDERATIONS
• Non-reflective workpiece surfaces are preferable
• Sharp corners are difficult to produce; deep cuts produce tapers
• Consider the effects of high temperature on the workpiece material
• Parts should match the size of the vacuum chamber
• Consider manufacturing the part as a number of smaller components

23. COMPARATIVE PERFORMANCE

24. EBM - ADVANTAGES
• Extremely close tolerances can be maintained
• Heat affected zone are minimum
• It can machine almost any material irrespective of their mechanical
properties
• The beam can be concentrated on a very small area
• It produces better surface finish and narrow kerf
• Thermal distortion is least
• The process is fast because it is entirely non-mechanical.

25. EBM - LIMITATIONS
• The equipment cost is very high.
• The interaction of the electron beam with work piece surface
produces hazardous X-ray. Hence shielding is necessary
• Vacuum is essentially required.
• Because of very low material removal rate, the process is
economical only for small volume cuts.
• Skilled labour is required to accelerate the electrons.
• Very high voltage is required to accelerate the electrons.
• The process can machine only thinner parts.

26. EBM - APPLICATIONS
• EBM is particularly suitable for producing very small diameter
holes – down to 0.002 in.
• It is especially adapted for micromatching.
• Major applications of EBM include matching in thin materials,
cutting of slots and drilling of holes with very high depth to
diameter ratios, usually more than 100:1.
• Machining of wire drawing dies having small cross sectional area.
• EBM is also used as an alternative to light optics manufacturing
methods in the semiconductor industry.

27. • Because electrons have a shorter wavelength than light and can be
easily focused, electron-beam methods are particularly useful for
high-resolution lithography and for the manufacture of complex
integrated circuits
• Welding can also be done with an electron beam, notably in the
manufacture of aircraft engine parts

28. EBM CHARACTERISTICS
• Mechanics of material removal – melting, vaporization
• Medium – vacuum
• Tool – beam of electrons moving at very high velocity
• Maximum MRR = 10 mm3/min
• Specific power consumption = 450 W/mm3/min
• Critical parameters – accelerating voltage, beam diameter, work
speed, melting temperature
• Materials application – all materials
• Shape application – drilling fine holes, cutting contours in sheets,
cutting narrow slots
• Limitations – very high specific energy consumption, necessity of
vacuum, expensive machine

29. EBM VIDEOS
• https://www.youtube.com/watch?v=dP2m7-WAdos
• https://www.youtube.com/watch?v=25LMYY9KZds
• https://www.youtube.com/watch?v=jbY-tOcI2tM