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TRANSCRIPT
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Electron Beam Welding
o A fusion joining process producing coalescence ofmaterials with heat obtained by high energy
electron beam impingement on to joint.o Operating principle CRT
o Gun cathodep Thermionic emission of ed
o Biasing control electrodep anode
o Supplementary devicesp Focus & deflectioncoils.
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Electron beam gun column
o ed acceleration & beam shaping in gun column.
o Beam divergence upon exit from gun Radialvelocity due to thermal energy & mutual repulsion.
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Counter divergence through use of EM lens systemsto produce a converging beam instead.
o eld energy input (1)Beam current (2) edspeed (3)Focal beam spot size & (4) Welding speed.
o Power density 10 MW/in2 (higher than arcwelding)
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Process Features (II)
Advantages
o Electrical Beam output energy highly efficient!
o High aspect ratio single pass welding!
o Localized action lesser distortion/deleterious effects
o Vacuum environment minimizes contamination.
o Distance projection welding in complicated locations.
o Rapid travel speeds productivity & energy efficiency.
o Dissimilar metals & high thermal conductivity metals can be
welded.
Limitations
o High capital cost.
o Precise joint machining to cater for small beam size.
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Long chamber evacuation time - med/high vacuum welding.o Restricted work distance in non vacuum mode limit
product design.
o Radiation shielding additional safety measure
o Proper ventilation toxic gas/vapor removal.
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Equipment & Respective Functions
Electron Beam Gun
o Beam current (I) = kV1.5
o Performance (1) Gun configuration (2) Emitter characteristics (3) Power capability & (4) Focusing
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Generate, accelerate & collimate electrons into a BEAMp Rastered to control heat input!
Power Supply
o Gun power source (max 300 KW) One main supply or auxiliary back up p (1) Gives high voltage power to
emitter & (2) power for the beam control.o Emitter power supply Preferably d.c.! WHY?
o Bias voltage supply Controls beam current (1.5-3 kV for cutting off the beam)
o EM lens & deflection coil Permit x-y deflection of beam (potential changes in coil induced by heating) beaminstability thus is balanced through a feedback mechanism that lowers potential drop across coil).
Vacuum Pumping Systems
o Vacuum pumping systems Air evacuation from (1) Electron beam gun chamber (2) Work chamber for highmedium vacuum modes (3) Orifice assembly used on the beam exit portion of column assembly.
o 2 step process (1) Mechanical pistonp 0.1 torr & (2) Oil diffusion type pumpp 10-4 torr or lower..
o Evacuation rate (1) Pump capability (2) Work /fixturing load (3) Chamber size (4) Total leakage rate of system
o Leakage rate (1) Real leaks (2) Virtual leaks.
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