What is Electron Beam Welding?

Tavné svařování

The following paper displays a summary of illustrative presentation of electron beam welding. This presentation is a part of Days of Science, taking place regularly in ISI Brno, usually at the beginning of November. The visitors may see in operation an electron beam welding equipment in the laboratory of electron beam welding. The principle and use of the electron beam welder are explained in popular form. The process of welding is practically demonstrated.

Definition of fuse welding

  • To join two metal parts together by welding means to melt them temporarily and locally in the vicinity of their contact. In case of electron beam welding, the kinetic energy of fast moving electrons is applied to fuse the material. For intensive local heating the electrons for welding are concentrated into a narrow beam by means of electron optics.

Applications of electron beam welding

  • Compared with other methods of welding, the equipment for electron beam welding is considerably expensive. The economic considerations therefore limit its applications, particularly in industry. It founds its use mainly in nuclear, cosmic and aviation industry and research. The acquisition costs may be, in case of mass production, compensated by low operational costs.

Examples of electron beam welding in ISI Brno

In our institute the electron beam is used for:

  • welding of various components needed in vacuum and cryogenic engineering. We can make welds up to 10 mm deep in stainless steel, as well as very fine welds of thin parts, e.g. 0.05 mm thick membrane bellows.
  • Electron beam heating can also be used for joining parts made of two quite different materials, e.g. aluminium to steel, titanium to aluminium, and many other combinations.

Samples of electron beam welded components in ISI Brno can be seen in picture gallery.

Essential features of electron beam welding

  • Thanks to extreme concentration of power, the electron beam can penetrate very fast (with the velocity of tens of centimetres per second) into any metal, producing a deep but narrow weld. With the power of tens of kilowatts welds as deep as 30 cm in aluminium or 10 cm in stainless steel can be realized. (With the power of 2 kW in our welder we can make welds in stainless about 1 cm deep, as mentioned above.)
  • Thermally influenced zone in the vicinity of the the weld is minimal. as well as deformations of the work-piece.
  • In mass production the electron beam welding can be very economical and productive.
  • Electron beam heating in vacuum may be the only one method to join some materials.

Where can you meet electron beam in everyday life

  • I guess you do not realize that you meet electron beam working for you in every day life
  • in older TV sets with CRT (cathode ray tube) monitor. Here you can find the same construction elements as in an EB welder: electron gun with electric and magnetic lenses accelerating and focusing the electrons into a narrow beam, which is scanned by electromagnetic deflection coils over the viewing screen. Here the kinetic energy of electrons is changed, – not only into heat, but also – into visible light.
  • In principle, the electron beam welder is also similar to scanning electron microscope. That is practically utilized in our welders, which can be operated in „scanning mode“, enabling fast and very precise computer control of the beam.

Construction of EB welders

There is no universal construction of electron beam welder. The design depends on purpose which it is determined for. The dimensions of the vacuum working chamber are given by the biggest work-piece which is to be welded. The designer must also keep in mind that acquisition costs grow rapidly with the dimensions of the working chamber and electron gun power. The welders also differ in the design of welding manipulators and other construction parts.

Types of electron beam welders

  • As explained above, the EB welders must be „tailored“ individually to the given demands. For this reason hundreds of different welders have been designed during their 50 years old history. The volume of vacuum working chamber may be as big as hundreds of cubic meters, or as small as e.g. 20 litres. Even in such a small equipment we have welded zirconium tubes 5 meters long.

(One, not negligible advantage of small vacuum chambers compared with the big ones, apart of lower costs, is that nobody can be forgotten in it, closed and evacuated.)

Demonstration

  • To make it more attractive for visitors of our Opened Door Days, we do not show only simple welding, but also „engraving“ of pictures on metal surface. The welder is operated in Scanning mode. In this case the electron beam is scanned over the surface with speed dependent on light intensity of the spot in image. The lower is the speed (inversely proportional to the light intensity in the image), the more is the metal surface melted, so producing the contrast. In this way, we are able to take your snapshot (by digital camera) and in a few minutes give you your photo „burned“ on a metal sheet.