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).