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ELECTRON BEAM WELDING
Submitted by:
Ankit SaxenaPGMSE-136013
Submitted to:
Mr Harish Arya
Introduction
i. Electron Beam Welding is afusion welding process inwhich a beam of high-velocityelectrons is applied to thematerial to be joined.
ii. The work-piece melt as thekinetic energy of the electronsis transformed into heat uponimpact.
iii. The EBW process is well-positioned to provideindustries with highest qualitywelds and machine designsthat have proven to beadaptable to specific weldingtasks and productionenvironments.
Fig.1: Key hole penetration in EBW
Electron Beam?
i. In an electron beamwelder electrons are“boiled off” as currentpasses through filamentwhich is in a vacuumenclosure.
ii. An electrostatic field,generated by a negativelycharged filament and biascup and a positivelycharged anode, acceleratesthe electrons to about50% to 80% of the speedof light and shapes theminto a Beam.
Fig 2:Electron beam source for EB disposal
How does the Process Work?i. The electron beam gun has a tungsten
filament which is heated, freeingelectrons.
ii. The electrons are accelerated from thesource with high voltage potentialbetween a cathode and anode.
iii. The stream of electrons then passthrough a hole in the anode. The beamis directed by magnetic forces offocusing and deflecting coils.
iv. This beam is directed out of the guncolumn and strikes the work piece. Thepotential energy of the electrons istransferred to heat upon impact of thework piece and cuts a perfect hole atthe weld joint. Molten metal fills inbehind the beam, creating a deepfinished weld.
Steps Used in EBW process
Joint preparation.
Cleaning of work piece.
Fixturing of work piece.
De-magnetization of work piece.
Setting up work piece in chamber.
Pump down air form chamber.
Carry welding process.
Classification of EBW Machines
• High voltage machine (U =150 kV)
• Low voltage machine (U=60kV)
By Accelerating Voltage
• High vacuum machine
• Fine vacuum machine
• Atmospheric machine (NV-EB welding)
By pressure
• Conveyor machine• Clock system• All-purpose EBW
machine• Local vacuum
machine• Mobile vacuum
machine• Micro and fine
welding machine
By Machine concept
High vacuum machine Fine vacuum machine
Atmospheric machine (NV-EB welding)
Machine Concept - Conventional Plant
EBW Clock System Machine
EBW Conveyor Machine
Comparison with different welding techniques on the basis of Parameter
PARAMETER TIG PLASMA LASER EB
Power input to W-P
2kW 4kW 4kW 5kW
Total power used
3kW 6kW 50kW 6kW
Traverse speed 2mm/s 5.7mm/s 16mm/s 40mm/s
Positional welding
Good penetration
Good penetration
Yes Require optics to move the beam
Requires mechanism to move the beam
Distortion shrinkage
Nominal significant in V-shaped weld
Nominal significant in V-shaped weld
SmallMinimum
MinimumMinimum
PARAMETER TIG PLASMA LASER EB
Special process requirement
Normal light screening
Normal light screening
Safety interlock against misplaced beam reflection
Vacuum chamber-ray screen
Surface geometry
Underside protrusion
Underside protrusion
Very fine ripples
Ruffled swarf on back face
Comparison of conventional weld and EB weld
i. EBW is suitable for a variety of difficult applications, such as weldingstructures on which the reverse side of the butt is inaccessible ; gravitywelding of thin metal ; and welding in various spatial positions.
ii. This Provides a low level of over all heating of the structures ; and has theability to vacuumed the inner volume simultaneously, which is suitable forsealing instruments. Because EBW is an automated process , the welded jointquality is consistent .
iii. The process does not require shielding gases , tungsten electrodes , or edgepreparation for welding thick metal .
iv. Finally , it can be used to weld some joints that cannot be made by otherwelding processes.
v. Compared with arc weldingprocesses, EBW improves jointstrength 15 per cent to 25 percent.
vi. It has a narrow heat-affectedzone(HAZ), which results inlighter-weight products.
vii. Geometric shapes and dimensionsare highly stable, particularlywhen it is used as a finishoperation.
viii. It eliminates oxide and tungsteninclusion sand removes impurities.
ix. The weld metal has a finecrystalline structure.
Graph showing areas of different welding processes on the plot of feature size v/s power density.
Advantage of EBWIn Vacuum
a) Thin and thick plate welding (0,1 mm bis 300 mm).
b) Extremely narrow seams (t:b = 50:1).
c) Low overall heat input => low distortion =>Welding of completely processedcomponents.
d) High welding speed possible.
e) No shielding gas required.
f) High process and plant efficiency.
g) Material dependence, often the only welding method.
At atmosphere
a) Very high welding velocity.
b) Good gap bridging. No problems with reflection during energy entry into work
piece.
Disadvantage of EBW
In Vacuum
• Electrical conductivity of materials is required.
• High cooling rates => hardening => cracks.
• High precision of seam preparation.
• Beam may be deflected by magnetism.
• X-ray formation.
• Size of work piece limited by chamber size.
• High investment.
At Atmosphere
• X-ray formation.
• Limited sheet thickness (max. 10 mm).
• High investment.
• Small working distance.
Field of Application
Industrial areas
• Automotive industries
• Aircraft and space industries
• Mechanical engineering
• Tool construction
• Nuclear power industries
• Power plants
• Fine mechanics and electrical
• Industries
• Job shop
Material
• Almost all steels.
• Aluminium and its alloys.
• Magnesium alloys.
• Copper and its alloys.
• Titanium.
• Tungsten.
• Gold.
• Material combinations (e.g. Cu-steel, bronze-steel).
• Ceramics (electrically conductive).