Electron Beam Welding

Metallurgy and Materials Engineering Department, University of Punjab Lahore

1. Electron Beam Welding Shan Kazmi E12-324 Waqas Ahmed E12-326 Wadood Jamal E12-325

2. Electron Beam Welding Electron beam welding is a fusion welding process in which a beam of high-velocity electrons is applied to the material to be joined. The work-piece melt as the kinetic energy of the electrons is transformed into heat upon impact. The EBW process is well-positioned to provide industries with highest quality welds and machine designs that have proven to be adaptable to specific welding tasks and production environments. Fig 1. Keyhole penetration in EBW

3. Electron Beam? In an electron beam welder electrons are boiled off as current passes through filament which is in vacuum enclosure. An electrostatic field, generated by a negatively charged filament and bias cup and a positively charged anode, accelerates the electrons to about 50% to 80% of the speed of light and shapes them into a beam. Fig 2. Electron beam source for EB disposal

4. How does the process work?

5. How does the process work?

6. How does the process work?

7. Steps 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 from chamber Carry welding process

8. Classification of EBW machines

9. Use of Vacuum Chamber

10. Some Features of EB Weld EBW is suitable for a variety of difficult applications, such as welding structures on which the reverse side of the butt is inaccessible; gravity welding of thin metal; and welding in various spatial positions. This provides a low level of overall heating of the structures; and has the ability to vacuumed the inner volume simultaneously, which is suitable for sealing instrument. Because EBW is an automated process, the welded joint quality is consistent. The process does not require shielding gases, tungsten electrodes, or edge preparation for welding thick metals. It can be used to weld some joints that cannot be made by other welding processes. Compared with arc welding processes, EBW improves joint strength 15% to 25%.

11. Some Features of EB Weld It has a narrow heat affected zone (HAZ) which results in lighter-weight products. Geometric shapes and dimensions are highly stable, particularly when it is used as a finish operation. It eliminates oxide and tungsten inclusion and removes impurities. The weld metal has a fine crystalline structure . EBW process forms extremely narrow and deep joints having the ratio of weld thickness to weld width between 5:1 to 25:1 .

12. EBW process of Aluminum Alloy 7050 (AlZnMgCu) Operating principle of an electron beam welding equipment Process steps of the deep welding process Electron beam welding of butt joints Terms used for describing a weld Electron beam weld-ability of aluminum alloys Electron beam welds in aluminum alloys Rate of vaporization during electron beam welding of 7050 (AlZnMgCu) Tensile strength of electron beam welded 7050 (AlZnMgCu)

13. Operating principle of an EBW Equipment Requires energy density of more than 10^8 W/square cm. Vaporization of metal occurs at above 10^6 W/square cm. Electrons emitted from an incandescent electrode accelerated by electron gun and are then focused on the work-piece placed in vacuum chamber. The beam is moved by using an array of deflecting systems such as focusing lens etc. Work can also be moved along different axis to make the welding position accessible

14. Process steps of the deep welding process Formation of a vapor cavity or deep-weld effect is typical for EBW processes. A cavity consisting of a vapor core surrounded by molten metal is created. Which allows the beam penetration through whole thickness of metal. Vapor pressure and surface tension keep the cavity open towards the top allowing unhindered beam penetration and at the same time allow the weld pool to flow together or allow crystallization in the beam vicinity thus playing a two-fold role. The vapor cavity should exists long enough for weld porosity elimination.

15. Electron beam welding of butt joints The surfaces to be joined are mechanically worked and have especially formed lips which help to position the part and serve as weld pool supports. Weld pool supports in the form of grooves are not used, since the high energy beam reaches right through the bottom of the joint which leads to undesired welding. Remaining weld pool supports tend to reduce dynamical strength and thus require designing of machine allowances and joint forms .

16. Electron beam weld-ability of aluminum alloys Al and its alloys can be welded easily by using EBW. Among the non-heat-treatable alloys, the hot-cracking tendency increases with increasing magnesium content. At the same time, the high vapor pressure of magnesium increases the danger of porosity in welds. Cracking tendency depends on the contents of magnesium. AlMg3 should be avoided. The heat-treatable alloys have only a limited suitability. The high vapor pressure of zinc leads unavoidably to weld porosity. Due to the reduced heat input, the alloys containing copper can be easily welded (the weld-ability of copper-containing alloys with other welding processes is poor ).

17. Electron beam welds in aluminum alloys Materials up to 40 mm in thickness can be welded. AlMg3 alloys can be welded only by adhering to special measures. It is just this magnesium content which causes a maximum amount of cracking. An explanation for the hot cracking tendency lies in the fact that the beam with its high energy density causes a relatively high amount of magnesium to vaporize so that the remaining content now lies in the range of 1.5 %.

18. Rate of vaporization during EBW of 7050 (AlZnMgCu) The alloying elements magnesium and zinc, with their low vapor pressures, reduce the suitability of these alloys for welding. This tendency, however, decreases with increasing material thickness, so that problems occur especially during the welding of thin sheets. The reason for this is that thicker sheets conduct heat more rapidly away than thin sheets.

19. Tensile strength of EBW 7050 (AlZnMgCu ) Electron beam welded joints of the alloy 7050 (AlZnMgCu) exhibit weld performance factors which vary with rolling direction and thickness of the material. The unshaded third columns in ( Figure ) show that the weld performance factors for samples transverse to the rolling direction is almost equal to 1 for the 6 mm and 27 mm thick samples (i.e., the weld joint has a tensile strength almost equal to that of the base material ). The weld performance factors of the longitudinal samples is almost independent of the thickness and is about 80 %.

20. Advantages Thin and thick plate welding (0.1 mm bis 300 mm) Extremely narrow seams ( t:w = 50:1) Low overall heat input  low distortion Welding of completely processed components. High welding speed possible. No shielding gas required. High process and plant efficiency. Material dependence, often the only welding method. Good gap bridging. No problems with reflection during energy entry into work piece .

21. Limitations Electrical conductivity of materials required. High cooling rates  Hardening Cracks High precision of seam preparation. Beam may be deflected by magnetism. Size of work piece limited by chamber size. X-Ray formation. High investment. Limited sheet thickness (max 10 mm) Small working distance .

22. Field of application (Industrial Areas) Automotive Industries. Aircraft and space industries. Mechanical Engineering. Tools construction. Nuclear power industries. Power plants. Fine mechanics and electrical industries. Job shop.

23. Materials Almost all steels. Aluminum and its alloys. Magnesium alloys. Copper and its alloys. Titanium. Tungsten. Gold. Material combinations (e.g. Cu-steel, Bronze-steel). Ceramics (electrically Conductive )

24. Thank You