Our group is part of the research department of Electron and Plasma Technologies at the Institute of Scientific Instruments of the CAS in Brno. We mainly deal with electron beam welding, vacuum soldering/brazing and the development of vacuum feedthroughs associated with the possibility of their subsequent production. We also engage in contract research in the field of electronics development and device design based on electron-optical devices that work in vacuum, or ultra-vacuum environment.
Electron beam welding
Welding of a combination of metals with similar or different physical properties using an electron beam without filler material.
The cathode (an electron source) for electron beam welding is usually made of tungsten, or tantalum. The reason is the high temperature needed to melt the metal. Operating temperature cathode exceeds 2500 °C, which is necessary to overcome the work function of metal and allow transfer of electrons into space.
The pressure in the working chamber of the electron welder is in the order of 10 ^ -3 to 10 ^ -5 mbar, i.e. 10 ^ -1 to 10 ^ -3 Pa. The pressure around the cathode in the electron nozzle should be as good as possible (better than about 10 -4 mbar) to prevent high voltage surges and to protect the hot cathode.
Electron beam welding takes place in principle in a vacuum, here in an environment completely (or almost) free of any particles that could interact with the weld metal. Therefore, no shielding gas is used. An exception is systems (very sparsely distributed) that allow the electron beam to be released into the atmosphere. In these cases, the use of a protective atmosphere is appropriate. However, our workplace does not deal with this way.
Vacuum feedthroughs are electric single or multi-conductors. They are used for electrical connection of places with different pressure of the surrounding atmosphere. Vacuum feedthroughs are designed for situations where there is a vacuum on one side and mostly air at normal atmospheric pressure on the other side. The design of the bushing ensures gas impermeability (vacuum tightness), which is important for maintaining a good vacuum. Vacuum feedthroughs are usually applicable for larger pressure differences than one atmosphere.
Electron beam welding is one of the fusion welding methods, which uses a focused high-energy electron beam to heat the joined materials. Upon impact, the kinetic energy of the electrons is converted into heat, which is used to heat the welded parts. Welding usually takes place without additional material. Thanks to the so-called depth effect, depending on the parameters of the welder, considerable thicknesses of material can be welded per pass – over 10 cm in stainless steel.