Introduction and details about electron Beam Machining

1. Electron Beam
Machining
Er. Mohit Ostwal
Assistant Professor
Department of Mechanical Engineering
Jodhpur Institute of Engineering and Technology, Jodhpur
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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2. Content
• Introduction
• Equipment/Setup
• Process
• Mechanism of material removal
• How vacuum is created?
• Process capabilities
• Advantages
• Disadvantages
• Application
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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3. Introduction - EBM
• Electron beam machining (EBM) is a thermal material removal
process that utilizes a focused beam of high-velocity electrons
to perform high-speed drilling and cutting.
• Used with high power density to machine materials.
• The mechanism of material removal is primarily by melting
and rapid vaporization due to intense heating by the electrons
• Also known as “Electro-optical-thermal process”.
• Very high drilling rates are achievable.
• Can machine almost any material.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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4. Equipment/Setup
High voltage supply to
cathode
Cathode Cartridge
Bias grid
Anode
Port for vacuum
gauge
Diffusion pump
Magnetic Lens
Illuminating
system
Aperture
Telescope
Electromagnetic coils
Deflector coils
Slotted Disc
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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5. Equipment/Setup
• Cathode Cartridge
• Tungsten/Tantalum
• High voltage is
applied
• 2500’C
• Thermo-ionic
emission of
electrons (Vacuum)-
thermally induced
flow of electrons
from surface.
• Negatively biased –
repel the electrons
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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6. Equipment/Setup
• Bias Grid
• Highly negatively
biased
• Controls the flow of
electrons.
• To avoid the
divergence of the
electrons and send
them as a beam to
the next step
(anode)
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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7. Equipment/Setup
• Anode
• Positively biased
terminal
• Due to the potential
difference b/w
cathode and anode
the electrons
accelerates.
• Velocity is approx.
half the velocity of
light – passing
through anode.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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8. Equipment/Setup
• Magnetic Lens
• Same function as
that of any lens.
• Concentrates the
beam of electrons.
• Shape the beam.
• Reduce the
divergence of the
beam.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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9. Equipment/Setup
• Aperture
• Capture the stray
electrons present
near the frame.
• (Diverged low
energy electrons.)
• Captured electrons
are then set for
obtaining a
concentrated beam
of electrons.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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10. Equipment/Setup
• Electromagnetic
Lens
• Focuses the electron
beam onto the
workpiece.
• On a particular spot.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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11. Equipment/Setup
• Deflector coils
• Deflect the electron
beam by small
amount.
• Correct the beam in
case of not getting
proper hold-ship.
• Improve the shape
of the machined
holes.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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12. Equipment/Setup
• Illuminating system
& Telescope
• Both are used
simultaneously to
align the electron
beam with the
workpiece.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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13. Equipment/Setup
• Slotted Disc
• To avoid obstruction
of vapor of metal
into the optical
window of EBM.
• Allow Electron beam
to pass but not the
vapors/metal fumes
to pass through it.
• Synchronized with
the pulsed beam.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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14. How vacuum is created ?
DIFFUSION PUMP
Heater
Backing
Pump
Boiler
Nozzle
Cooling
Coils
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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15. How vacuum is created ?
 Main element for creating the vacuum is DIFFUSION PUMP.
 The oil diffusion pump is operated with an oil of low vapor pressure. Its
purpose is to achieve higher vacuum.
 Diffusion pump is essentially an oil heater. As the oil is heated the oil
vapour rushes upward where gradually converging structure.
 The nozzles change the direction of motion of the oil vapour and the oil
vapour starts moving downward at a high velocity as jet.
 Such high velocity jets of oil vapour entrain any air molecules present
within the gun. (Due to the high momentum of oil jet air is removed)
 This oil is evacuated by a rotary pump via the backing line.
 Level of vacuum – 10-4 to 10-6 Torr
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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16. Mechanism of material
removal
• As high voltage is applied across the Cathode filament ,
thermo-ionic emission of electrons takes place.
• These Thermo-ionic electrons are replied by the cathode and
attracted by anode through the bias grid, electrons are
accelerated to the half of the velocity of the light.
• These electron/beam of electron is shaped and focused with
the help of series of magnetic and electromagnetic lenses.
• Finally the electron beam impinges the workpiece.
• Upon impingement the kinetic energy of the electron is
absorbed by the workpiece which will result into heating,
melting and vaporization – drilling.
• Spot size – 10 to 100 microns – high energy density
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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17. Mechanism of material removal
Localized heating by
focused electron beam
Gradual formation of hole
Auxiliary
workpiece
Auxiliary
workpiece
W/P W/P
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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18. Mechanism of material removal
Penetration till the
auxiliary support
Removal due to high
vapour pressure
Auxiliary
workpiece
W/P
Auxiliary
workpiece
W/P
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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19. Process Parameters
• Accelerating Voltage (Va )– 100 KV
• Beam current (Ib)– 250 μA to 1 A
• Pulse duration (ton) – 50 μs to 50 ms
• Energy per pulse – 100 J/Pulse
• Spot size - 10 μm to 500 μm
• Power Density
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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20. Process capabilities
• 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.
• The hole can be tapered along the depth or barrel shaped. By
focusing the beam below the surface a reverse taper can also be
obtained.
• Generally burr formation does not occur in EBM.
• A wide range of materials such as steel, stainless steel, Ti and Ni
super-alloys, aluminium as well as plastics, ceramics, leathers can be
machined successfully using electron beam. Typically the heat-
affected zone is around 20 to 30 μm.
• Some of the materials like Al and Ti alloys are more readily
machined compared to steel.
• EBM does not apply any cutting force on the workpieces. Thus very
simple work holding is required. This enables machining of fragile
and brittle materials by EBM. Holes can also be drilled at a very
shallow angle of as less as 20 to 300.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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21. Advantages
 EBM provides very high drilling rates when small holes with
large aspect ratio are to be drilled.
 Moreover it can machine almost any material irrespective
of their mechanical properties. As it applies no mechanical
cutting force, work holding and fixturing cost is very less.
 Further for the same reason fragile and brittle materials
can also be processed. The heat affected zone in EBM is
rather less due to shorter pulses.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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22. Disadvantages
 The primary limitations are the high capital cost of the
equipment and necessary regular maintenance applicable for
any equipment using vacuum system.
 Moreover in EBM there is significant amount of non-
productive pump down period for attaining desired
vacuum.
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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23. Application
1. Drilling
2. Perforating of sheet
3. Pattern generation (associated with integrated circuit fabrication)
3/28/2016
Er.MohitOstwalAsst.Prof.JIET-
Jodhpur
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