Electron Beam Welding (EBW) Basics

This Presentation covers the basic concepts of EBW in a easy version. For more information, please refer the books mentioned in the references slide.... Thank you

1. Electron Beam Welding Melwin D’mello M.E (Welding Engineering) Department of Manufacturing Engineering, Annamalai University Presented by

2. What is the need ?

3. Discovery William Rontengen in 1800s found that beam of electron is suddenly stopped by impact with target, then it start heating and melting the target . Dr. Karl Heinz (German) – Development of first practical welding machine in 1958.

4. Introduction It is fusion welding process in which a beam of high velocity electrons is applied to two materials to be joined. Free electrons in vacuum can be accelerated, with their paths controlled by electric and magnetic fields . In this way narrow beams of electrons carrying high kinetic energy can be formed. which upon collision with atoms in solids transform their kinetic energy into heat .

5. Principle Electron beams are composed of electrons that are charged particles and can be accelerated in electron guns to high velocities , giving them high kinetic energies . At 10 kV, electrons travel at approximately 20 % of the speed of light, while at 200 kV they travel at approximately 70% the speed of light . Electron beam welding process is carried out in vacuum. In this process, electrons are emitted from the heated filament called electrode.

6. Principle These electrons are accelerated by applying high potential difference (30 kV to 175 kV) between cathode and anode . The higher the potential difference, the higher would be the acceleration of the electrons. The electrons get the speed in the range of 50,000 to 200,000 km/s . When high kinetic energy electron beam strikes the work piece, high heat is generated resulting in melting of the work material. Molten metal fills into the gap between parts to be joined.

7. EBW Setup An EBW set up consists of the following major parts 1 . Electron Gun 2 . Power Supply Unit 3 . Vacuum Chamber 4 . Work piece Handling Device

8. EBW Setup

9. 1. Electron Gun The electron beam is most often formed by a triode style electron gun under high vacuum conditions .

10. 1. Electron Gun The triode assembly consists of a cathode, a heated source (emitter) of electrons that is maintained at some high negative potential . A grid cup, a specially shaped electrode that can be negatively biased with respect to the hot cathode emitter (filament ); And an anode, a ground potential electrode through which the electron flow passes in the form of a collimated beam . The hot cathode emitter (filament) is made from a high- emission material, usually tungsten or tantalum, which is usually available in wire, ribbon, or sheet form .

11. Triode Diode

12. Types of Electron Guns Self accelerated Electrons are accelerated by applying potential difference between the cathode and anode. Work accelerated potential difference is applied between work piece and anode (Diode type).

13. Emitter/Filament : It generates electrons on heating. Anode : Positively charged element near cathode across which high voltage is applied to accelerate electrons. For high voltage equipment's potential difference 70-150 kV & for low voltage equipment’s potential difference is 15-30 kV . Grid Cup: Negative voltage with respect to cathode is applied . Grid cup controls the beam.

14. Electron Beam Focusing It has two parts , An Electron focusing lens and deflection coil . Electron focusing lens focuses the beam into work area . The focusing of the electrons can be carried out by deflection of beams .

15. Electron Beam Focusing This focusing lens reduces the diameter of the electron beam and focuses the beam down to a much smaller beam cross section in the plane of the Work piece. Thus reduction of beam diameter results into producing very small high intensity beam spot . Deflection coil can be employed to “bend” the beam, thus providing the flexibility to move the focused beam spot.

16. Beam Focusing

17. Power Supply It mainly consisting high power DC power supply source for gun, focusing and deflection coil . It provides power supply for acceleration of the electrons. The potential difference for high voltage equipment ranges from 70-150 kV and for low voltage equipment 15-30 kV . The current level ranges from 50-1000 mA . The amount of current depends upon the diameter and type of the filament.

18. Vacuum Chamber Generally EBW performed in vacuum . The gun portion of an electron gun/column assembly generally is isolated from the welding chamber through the use of valves when desired. Vacuum in the gun region is needed to maintain gun component cleanliness, prevent filament oxidation, and impede high-pressure short circuiting between the cathode and the anode.

19. EBW Equipment

20. Vacuum Chamber Maintenance of this degree of vacuum is important because of the effect that ambient pressure has on both the beam and the weld produced . Based on vacuum intensity the EBW have following 3 types 1 .Non vacuum EBW – atmospheric pressure 2 .Medium Vacuum EBW – ( 10-3 to 25 torr ) 3 .High Vacuum EBW – ( 10-6 to 10-3 torr )

21. Effect of Vacuum on Beam Beam scatter due to collision of electrons with atmospheric molecules

22. Effect of Vacuum on Penetration Increase in the beam diameter reduces the power & produces welds with greater width and less penetration.

23. Beam Diameter

24. Penetration V s Vacuum D e pth of p e n e t r a tion v s V ac uum in p r esc r ib e d time

25. Penetration V s Vacuum

26. Work piece Handling Quality and precision of the weld profile depends upon the accuracy of the movement of work piece . There is also provision for the movement of the work piece to control the welding speed . The movements of the work piece are easily adaptable to computer numerical control (CNC )

27. Process Parameters Major Process Parameters are, 1. Accelerating voltage 2. Beam current 3. Welding speed 4. Beam Focusing

28. Accelerating Voltage A value of electrical potential, usually expressed in kilovolts, being utilized to accelerate and increase the energy of the electrons being emitted by an electron beam gun. Increase in the voltage results into increase in the speed of electrons. At 10 kV electrons travel at approximately 20% of the speed of light, while at 200 kV they travel at approximately 70% the speed of light.

29. Electron Beam Current Close relation between electron beam current and depth of penetration . Beam current : measure of the quantity of usually expressed in units of mill amperes (mA ),that flow per unit time in an electron beam

30. Cont.

31. Welding speed Welding speed directly affects on depth of penetration of electron beam into work piece . Higher speeds results into lower depth of penetration .

32. Advantages High penetration to width can be obtained . High welding speed is obtained . Material of high melting temperature can be welded . Superior weld quality due to welding in vacuum i.e. welds are corrosion free . Distortion is less due to less heat affected zone . Very wide range of sheet thickness can be joined (0.025 mm to 100 mm).

33. Disadvantages Transportation of equipment is not easy . Vacuum is required . Skilled person is needed . X-rays generated during welding 60 kV 4 kW (610 mm3) electron beam welding machine including CNC controlled work manipulation systems costs £220,000.00 i.e. 17609882.40 INR (1 £ = 80.02 INR)

34. Applications of EBW Mostly used in joining of refectory materials like columbium , tungsten, ceramics . High Precision Welding of electronics components. welding of nuclear fuel elements. Special alloy components of jet engines . Pressure vessels for rocket . Joining of Dis similar metals . Welding of Titanium medical implants.

35. References Text Book : “Welding Process and Technology” by Dr. R.S Parmar , 2015 edition. Text Book : “Welding Engineering and Technology” by Dr. R.S Parmar , 2015 edition

36. Thank You