Non Traditional Machining ProcessesMIME - 6980

Presented by, Abhijit Thanedar Naga Jyothi Sanku Pritam Deshpande Vijayalayan Krishnan Vishwajeet Randhir

Electron Beam Machining

Introduction - A Brief History

• Development of EB technology is closely related with advances in vacuum engineering and electron optics

• In 1905, Marcello von Pirani successfully melted Tantalum

• In 1938, magnetic lens were introduced to focus EB• It was only in 1965, all techniques were put

together and secured a place in production processes list.

Classification of NTM processes

Classification based on the energy source

• Mechanical

• Electro-chemical

• Chemical

• Thermo-electric

EBM uses Thermo-electric Energy.

NON TRADITIONAL MACHINING PROCESSES - THERMOELECTRIC

THERMOELECTRIC

VAPORIZATION

HOT GASES

IONIZED MATERIAL

PLASMA ARC

HIGHVOLTAGE

ION STREAM

RADIATION

AMPLIFIED LIGHT

ELECTRONS

LASER

ION BEAM

EDM

ELECTRON BEAM

GENERATION OF ELECTRON BEAM:

The electron beam is formed inside an electron gun,

which is basically a triode and consists of:• A cathode which is a hot tungsten filament

emitting high negative potential electron • A grid cup, negatively biased with respect to

filament , and• An anode at ground potential though which

the accelerated electrons pass

Energy Conversion at the point of action

electrons are accelerated in the electrostatic field of the beam source to attain a kinetic energy,

E = e UB

• the kinetic energy absorbed by the electrons during their trajectory through the accelerating field is

E = (me0/2) ve2 (1 + 3 ve

2/4c2 + 5 ve4/8 c4 +…)= e UB

Where me0 is the electron rest mass, ve is the electron velocity, c is the

velocity of light and e is the electron charge.

Relation between velocity and acceleration voltage

VELOCITY OF LIGHT

610

Ub

3

10

10

8

6

1

Ve (m/s)

X-RAYSE=hv eU

ELECTRON BEAM e=EU

THERMIONIC ELECTRONS E<1eV

SURFACE TEMPERATURE (T)

RANGE OF ENERGYCONVERSION

SECONDARY ELECTRONS E50eV

BACKSCATTERED ELECTRONSHEAT RADIATION E=hv

BEAM ACTION ON IMPINGEMENT ON MATTER

Machine Tools

The three major subsystems that make up an electron beam machining system are

– power supply, – electron beam gun, and– the vacuum system.

Modern EBM Drilling Machine

POWER SUPPLY

• Pulsed DC

• Voltage range up to 150 kv to accelerate electrons

• Systems capability can go as high as 12 kw

• high-voltage sections of the power supply are submerged in insulating dielectric oil

ELECTRON GUN

• gun is designed to be used exclusively for material removal applications and can be operated only in the pulse mode

• It has a cathode, bias electrode, anode, magnetic coil/lens (to converge the beam), variable aperture, 3 final magnetic coils (used as magnetic lens, deflection coil, and stigmator) and rotating disc.

Gun Types

• 2 electrode gun

3 Electrode Guns

Modified 3 Electrode Guns

• Rogowski gun • Telefocus gun

Four Electrode Array gun

High-perveance guns

Pierce gun

Guns with Curved Electron Trajectories

Guns with Concave Emmiting Surface and center bore in cathode

Beam Guidance

ELECTRON GUN

FOCUSING

SOURCE

BEAM GUIDANCE SYSTEM

DEFLECTION

WORK CHAMBER

MATHEMATICAL MODEL:

Energy of Electrons:

The kinetic energy of the electrons can be written as:

K.E.=Ee=1/2 mV2.

Where,

m= mass of electron.

e= charge on electron.(joules)

E= voltage.

V= velocity of electron.(cm/sec)

Number of electrons per second (N):

N= I n.

Where ,

I= beam current.

n= electron per second per amp current.

Total Power :P= E I

Energy Required to vaporize Workpiece:

Material removal rate :

G = nP/W.(cm3/sec)

Where:

P = Power.(watts)

n= cutting efficiency.

W= Specific energy required to vaporize metal. (joules/cm3)

W=[C(Tm-20)+C(Tb-Tm)+Hf+Vv]

Where:

C= Specific Heat, Tm = Melting temperature

Tb = Boiling temperature, Hf = Heat of fusion,

Hv = Heat of vaporization

IRON

TITANIUM

ALUMINUM

POWER

TUNGSTEN

METAL REMOVAL RATE

MRR Vs POWER

Parameter Zones

Thermal processing of solids.

Thermal processing of thin films

Non – thermal processing

Parameters and their influence

Power density

FLOW OF ELECTRONS

FILAMENT

ANODE

MOLTEN METAL

METAL VAPORHOLE

DEFLECTION COIL

FOCUS COIL

BIAS CUP

Drilling of all materials

Parameters for drilling various materialsThickness

(in)

Hole

diameter (in)

Drilling speed

(Sec)

Acclerating

voltage(kv)

Avg beam

current

(microamp)

Pulse

width

(micro

sec)

Pulse

Frequency

(cps)

0.010 0.0005 <1 130 60 4 3000

0.030 0.012 30 125 60 80 50

0.010 0.001 <1 140 50 20 50

0.040 0.005 <1 140 100 80 50

0.40 0.005 <1 140 100 80 50

0.100 0.005 10 140 100 80 50

0.016 0.003 <1 130 100 80 50

0.125 0.001 <1 140 10 12 50

Examples of EBM Drilling

Examples of EBM Drilling

Examples of EBM Drilling

Examples of EBM Drilling

Hole Diameter Vs Pulse Charge

Depth & Diameter Vs Beam Current

Depth of Cut, Milling Width Vs Input Energy

Relation between material thickness s, hole diameter dB, and perforation rate ns

db

0.01

S

.1

1

2