NTMP -EBM.ppt

5/19/2018 NTMP -EBM.ppt

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Electron Beam Machining

Electron Beam Machining (Drilling) was first introduced in 1952

and EBW was introduced in industry in 1959.

Basic Process:EBM !hermal "rocess# similar to $BM

Materialheating% &tri'ing of highelocity electrons with

wor'"iece.

inetic energy of electrons heat *a"id melting anda"ori+ing

Drilling, cutting, slotting, welding, annealing, milling, and rapid

manufacturing by controlling arious o"erating "arametersElectron ,eam "rocessing% -sually done in acuum unli'e $BM.

n atmos"here% /re0uent collisions with air molecules$ateral dis"ersion due to &cattering# Energy loss#

*eduction in ower density at the wor' "iece.

High Power with high Accelerating Voltage E-Beam !sed in normal Atmos here


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"epth of penetration: 2.34116(728) mm

7ccelerating 7oltage (7olts)

Material density ('g8mm:)

#inetic Energy of Electron me.c2; in e.7

('m8s) ? 37182

me rest mass of electron 9.141:1'g#

e1.34119

@oulom,.

!y"ical range% 75'7# Ag8cm:

Am

Electron 7elocity15 of

$ight elocity

C Energy of Electrons in e

,eam Electrons and latticeofmaterial through collisions.

C Energy transfer

/unction of electron energy.eenergy# !ransfer rate C Ma4imum rise in tem"erature

t a certain de"th# not at the

surface# unli'e laser heating.

C Due to scattering ofelectrons# its energy not locali+ed

within the area determined ,y the

diameter of ,eam oor material

remoal efficiency

!otal range

iEnergy

Electron

7acuum

Material

*egion of ery little

energy transfer


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$aser Beam @ou"ling s Electron Beam @ou"ling

$aser

EBeam

$aser ower Density

(4#t) (t)(1*) e4

e4

! Due to heat conduction

2FF1

ierfc (48 2)

G

Electron Beam ower Density

$aser ower a,sor,edwithin

ddif

2

during the "ulse HI

(4#t) (t)(1*e) e4"


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Electron Beam Drilling rocess% /our &tages.

1. Wor'"iece% Ln an organic or synthetic ,ac'ing

C E,eam focal s"ot diameter Desired diameterC ower density % ?1AW8cm2# sufficient to melt J

a"ori+e materials of any thermal conductiity

2. 7a"ori+ation of a small fraction of melted

materialC *ecoil "ressure of esca"ing a"our "ushes the

molten material aside creating a hole.

:. E,eam "enetrates in till it reaches the ,ottom

surface of wor' "iece.

. s e,eam stri'es the au4iliary su""ort olume

in contact is totally a"ori+ed resulting in the

e4"losie release of ,ac'ing material a"our

C igh elocity a"our carries along with it the molten walls of the ca"illary# creatinga hole in the wor' "iece and a small caern in the ,ac'ing material.


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Mode of E,eam L"eration%

/or drilling and cuttingulsed electron ,eam

&ingle "ulse % single hole in thin sheetN

Multi"le "ulses% !o drill in a thic'er material.

/or welding % D@ electron ,eam

arameters so chosen that loss of material due

to a"ori+ation is minimum.

Electron Beam Machine

$our sub-systems

*otating shutter

Electron beam gun% Electrons are

generated ,y thermionic emissionfrom hot tungsten cathode.

n E,eam gun for

cutting J drilling a""lications#

there is a grid ,etween anode J

cathode on which negatie oltage

is a""lied to "ulse 8 modulate the

e,eam.

Power supply: -" to 15'7#

@urrent % 11.5.

Vacuum-chamber% 113 !orr

achieed ,y rotary "um" ,ac'ed

diffusion "um".

7acuum com"ati,le %&%

wor'station


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%urrent %ontrol:

ot cathode emits electrons and the thermionic emission is gien ,y the

*ichardson Dushman e0uation%

O !2 e4"(eW8'!)

Where

O @urrent density (am"8cm2) from the cathode surface

W Wor' function of the cathode material (7olts)! ,solute !em"erature of cathode ()

e Electron charge (@oulom,)

' Bolt+mann constant (1.:412:P8)

@onstant (?12m"8cm2.2)

!em"erature ! O

Electrons emitted from cathode are in thermal e0uili,rium at tem"erature !

and their elocity is goern ,y Ma4wellian distri,ution. !his is reflected in

focusing the electrons on the wor'"iece.

@athode Material% !ungsten or thoriated tungsten


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Effect of Electron Beam Process Parameters:

!he "rocess "arameters# which directly affect the machining

characteristics in EBM are%ccelerating 7oltageEBeam @urrentulse duration

Energy "er "ulseea' "ower$ens current which determines the focusing J focal length&"ot si+eower density

Beam deflection signal

Beam Energy is increased "refera,ly ,y increasing current than

accelerating oltage to aoid more scattering at higher electron

energy and slower cou"ling of energy.


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Process Parameters:

Electron cceleration 7oltage % 115'7

Electron ,eam current % 1 1.5

Electron ,eam ower deliered(ccelerating 7oltage 4 Beam @urrent) % :W1'W

rocess Medium 8Enironment % 7acuum# 113!orr

(mm of g)

/ocal length of magnetic lens % 7e

8m

2

Wavelength of an electron of a velocity V:

where h lanc'Is constant# me electron mass## eelectron charge J 7eis

accelerating oltage&imilar to the laser ,eam# the theoretical limit of the focal s"ot diameter ?


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oweer# the actual focal s"ot si+e is influenced ,y

(a) e,eam diergence

(,) Mutual re"ulsion ,etween electrons

(c) &"herical a,erration of lens and(d) &"read in electron elocity.

!hese factors in turn de"end on the electron energy i.e. accelerating

oltage and electron ,eam current.

!y"ical s"ot diameter for e,eam cutting# drilling J welding%

m mm.

n electron ,eam lithogra"hy% E ,eam is focused down to a few tens

of ngstroms.


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Pulse mode operationulse duration% 5s 15ms,y controlling modulation oltage on the ,iased cathode grid

Beam pulse duration ulse energy De"th and Diameter

Beam current: 1 to 1.5ulse energy

Energy in e4cess of 12P8"ulse can ,e deliered and ra"id

drilling of ery dee" and large hole are o,tained.

(ens current: "etermines the focal "oint of electrongun (the wor'ing distance) and the si+e of the focused

s"ot on the wor' "iece.

$ens current /ocal distance J &"ot si+e

)apered, straight, in*ersely tapered,and bell-shapedholes ,y adOusting the location of thefocal "oint with res"ect to the to"surface of the wor'"iece

Hole of non-circular shape,y deflecting

the ,eam ,y energi+ing the deflection coil.Beam deflection is limited within +mm.

E- Beam elding

.peeds/"epth of

Penetration

eld- depth


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Process %apabilities :

EBM:

C wide range of materials# such as stainless steel# @u# l# Qi and co,alt alloys#

su"er alloy# titanium# tungsten# ceramic# leather and "lastic.C @utting u" to a thic'ness of 1mm % material removal by vaporization

C olediameter ranging from .1 1.mm in thic'ness u" to 1mm.

C igh as"ect (de"th to diameter) 15%1

C oles at ery shallow angle from 29

C Qo much force to the wor'"iece# there,y allowing ,rittle and fragile materialsto ,e "rocessed without danger of fracturing.

C ole diameter accuracy R .2mm in thin sheets

EB 0welding1:

C Dee" "enetration welding u" :mm in high (13

!orr)acuum# 5mm ( 1

!orr)C igh de"th to width as"ect ratio 125%1

C 7arious weld geometry% Butt# $a"# ! Ooints

C Lwing to ery high "ower density a wide range of metals can ,e welded%

steel# co""er# nic'el ,ased alloys# aluminum alloys and refractory such as

+irconium# tantalum# titanium and nio,ium.


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E-Beam elding in Air

igh ower and igh ccelerating 7oltage

ir !em"erature # ir density# Beam Dis"ersion minimum

E4"erimental results %

E,eam energy 53'W# 7oltage 15165'7

&tand off distance 15cm

: &teel Welding % Butt Point !hic'ness 5mm

Welding &"eed 16cm8s $ow heat conduction loss

Weld width with Welding &"eed

igher Efficiency u" to 55


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Application E2amples:

EB "rilling% &uita,le where large no. of holes is to ,e drilled

where drilling holes with conentional "rocess is difficult due to

material hardness or holegeometry.

-sed in aeros"ace# instrumentation# food # chemical J te4tile industries.

!housands of tiny holes (.1 .9R.5mm) in

!ur,ine (steel) engine com,ustor.

@o,alt alloy fi,er s"inning heads.

/ilters J &creens used in food "rocessing.

erforation in artificial leather to ma'e shoes for air,reathing%

.12mm hole made at 58s.

EB: Welding with minimum distortion /inished com"onents

arts of target "istols#Bimetal stri"s#

Dissimilar metals#

ircraft gas tur,ine com"onents#

utomo,ile catalytic conerter# etc.


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34# 5utput )ypical Autogeneous

0no filler added1 elds


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Ad*antages of EBM:

"rilling 6 %utting

ny material can ,e machinedQo cutting forces are inoled so no stresses im"osed on "artE4ce"tional drilling s"eeds "ossi,le with high "osition accuracy and formE4tremely small 'erf width# little wastage of material$ittle mechanical or thermal distortion

@om"utercontrolled "arametersigh as"ect ratioigh accuracy

EB 0welding1Minimum thermal in"utMinimum S J &hrin'ageigh as"ect ratio J Dee" "enetrationigh "urity# no contaminationWelds highconductiity materials


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"isad*antages of EBM :

igh ca"ital cost

Qon"roductie "um" down time*ecast at the edgesigh leel of o"erator s'ill re0uiredMa4imum thic'ness that can ,e cut a,out 1mm (:8AT) suita,le ,ac'ing material must ,e used/errous material to ,e demagneti+ed as otherwise could affect the e,eamWor' area must ,e under a acuum

igh Ooint "re"aration J tooling costs for weldingGray shielding re0uired&eam trac'ing sometimes difficult.


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&umerical Problems:

1. Estimate the "enetration de"th of electron ,eam accelerated at 1'7

im"inging in steel haing density of 6.3g8cc.

2.34116(72 8) mm# 7 in 7olts J in 'g8mm:

.:m2. Electron Beam "ower re0uired is "ro"ortional to material remoal rate% @.U

Where @ is constant of "ro"ortionality# called s"ecific "ower J U is M** in

mm:

8min.!y"ical energy re0uirements for cutting are#

@ 8U 12 W8mm:8min 1W 8 ( 2541:4.547 in mm8min)7 in mm8min 18(12 4 .254.5) 336mm8min 11mm8s

Determine the cutting s"eed to cut a

25 micron wide slot in a .5mm

thic' tungsten sheet using a 1'Welectron ,eam


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eat conduction e0uation for Electron Beam "rocessing%

'2!8 42R (4#t) .@"!8 t (4#t) (t) (1*e)


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E4am"le% n a 1mm tungsten sheet a 2micron wide slot is to ,e cut using a :3 'W

electron ,eam. Estimate the ma4imum cutting s"eed and e,eam s"ot diameter.

19:'g8m:# @" 1P8'g@# $f 1A5'P8'g

$ 2'P8'g# ' 13W8m.@# ! 59:@

W 2 micron

w 0

7d/*1 ---------------081

( .1) w.t.. .


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.ummary of EBM %haracteristics:

Mechanics of material remoal % Melting# 7a"ori+ation

Medium % 7acuum ( 1

13

!orr)#ir with high "ower# high 7oltage

,eam (not yet commercially "o"ular)

!ool % igh elocity electron ,eam

Ma4imum material remoal rate % ?5mm:8min

&"ecific cutting energy % ?15P8mm:

@ritical arameters % ccelerating oltage# ,eam current#

,eam diameter# wor' s"eed# melting

tem"erature

Material a""lications % ll materials

&ha"e a""lications % Drilling fine holes# contour cutting#

cutting narrow slots

$imitations % igh s"ecific energy#

Qecessity of acuum#

7ery high machine cost.

NTMP -EBM.ppt

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