electron beam welding
EBW at ISI brno
The Institute of Scientific Instruments (ISI) was established as a part of the Czechoslovak Academy of Science (CSAS) in 1957 as a successor to the Scientific Workshops located on Leninova (now Kounicova) Street in Brno. In 1960, the founders of ISI, together with the three CSAV Laboratories, moved to a new building at 147 Královopolská Street. The new director, prof. Julius Strnad, with his deputy Ing. Armin Delong (who replaced the previous deputy director Ing. Zdeněk Buřival) established three basic directions of scientific research: infrared spectroscopy, nuclear magnetic spectroscopy and applied electron optics (electron microscopy). The idea of using the thermal effects of the electron beam for technological purposes was born in the Electron Microscopy Department and the first experiment, melting of a metal plate with an electron beam, was carried out by Ing. Karel Hladil directly in the electron microscope.
First experience with electron beam welding
An electron gun practically usable for technological applications (similar to the electron microscope gun) was incorporated by Ing. Ladislav Zobač (in 1963-4) into the design of a multifunctional vacuum furnace ES-1 (figure below). The beam power of this gun was limited by the maximum power of the accelerating voltage source to 250 W (50 kV/5 mA). This device was already used in 1964-66 for practical welding of vacuum device components, but mainly for various experiments. The most interesting results were published in 1967 in the journal Low Current Horizon.
Welding Machine ES 2
The information about the new technology published in the Low Current Horizon was very interesting for the head of the workshops at the Institute of Nuclear Research in Řež, Ing. J. Busta. He organized a joint self-help action of interested persons from five departments who wanted to obtain their own electron welding machine for their department in a way other than buying it abroad for the limited foreign exchange. Specifically, included persons were:
- Ing. Zobač from Institute of Scientific Instruments in Brno
- Ing. Bušta from the Institute of Nuclear Research in Řež
- Ing. Sika from the Nuclear Power Plant in Bolevec
- p. Mrázek from Tesla-Opočno
- Ing. Ustohal from VTA AZ in Brno
These workers agreed at the end of 1968 to contribute, each according to his own possibilities, to a joint self-help action, by which each of them would get one electron welder for his workplace.
- Ing. Zobač designed the concept and prepared the basis for the manufacture of the vacuum working chamber, the motion mechanisms, the vacuum system (diffusion pump, vacuum valves) and the electron gun
- Ing. Bušta ensured the design and production of control electronics in the UJV
- Ing. Sika ensured the production of vacuum working chambers at the Škoda-Plzeň plant
- p. Mrázek ensured the production of the pumping system in Tesla-Opočno
- Ing. Ustohal secured funds for the production of electron guns in ISI
This action was successfully implemented in 1969. In the following years, starting in 1970, each of the partners, at their own workplace, with the help of workers from ISI, assembled and put into operation their own electron welding machine, which was named ES-2.
ES-2 at ISI 1970-1990
Since its installation at the Institute in 1970, the ES2 welder has been used extensively, especially for the needs of the Institute. Very often, however, it also helped to solve various technological and design problems of other departments. It was also used for interesting technological experiments. This gradually expanded the knowledge and experience of the staff involved in the Institute.
In order to meet the ever increasing demands, the ES-2 equipment had to be continuously improved and supplemented. First of all, Ing. J. Husták replaced the inadequate control electronics from the UJV. A great contribution of his new solution was the control of the electron beam including the possibility to deflect the beam as in a scanning mode microscope. This made it possible, for example, to observe the weld just made at a magnification of up to 30 nm before the working chamber was vented. Any shortcomings could thus be corrected immediately. The imaging system also facilitated the gun adjustment required after cathode replacement.
Furthermore, the original electron gun, derived from the electron microscope gun, was replaced by a new design, simpler and much better suited to the needs of electron welding. The beam from this gun was able to penetrate 10 mm deep into the stainless steel at 1.5 kW.
The ES-2 welder at ISI was also continuously adapted to new needs and increasing demands. For example, it was equipped with vacuum chamber extensions that made it possible to weld objects with a diameter of 60 cm and a length of 50 cm in a chamber of relatively small dimensions. The number of different aids for fixing and clamping welded parts, etc., was constantly growing.
Welding machines at ISI after 1991
ES-2U
After the departure of Ing. L. Zobac at the end of 1990, all activities in the field of electron beam welding were taken over by Ing. Jan Dupák. He and his co-workers gradually made the following changes. He also improved the vacuum system, control electronics, the HV source and the motion mechanism. In truth, only the vacuum working chamber remained from the original welder, and thus the proven basic concept of the welder. Rotary motion mechanism vertically at the bottom, electron nozzle horizontally from the side or vertically at the top. This is the form in which the ES-2U (modified) welding machine still operates at ISI today.
SES-1
In addition to the renovation of the ES-2 welding machine, Ing. Dupák has designed a new welding machine SES-1, designed as a “table-top”. His idea was apparently to build a “handy” versatile welder for welding small parts. He chose a concept that proved very successful with the ES-2 welder: a horizontal cylindrical chamber, but with much smaller dimensions (diameter 235 mm, length about 125 mm. The shape and dimensions of the main mounting holes are identical, allowing the electron gun to be mounted in three positions. The newly designed electron gun of this welder delivers a beam power of up to 1.5 or 2 kW, depending on the HV source used.
The vacuum pumping system of the SES-1 consists of one pre-pump (diaphragm) and two turbo pumps. One of them pumps the working chamber, the other the electron gun. All pumps are switched on (for pumping) and off (for aeration) simultaneously. Pumping to working vacuum takes 2 to 3 minutes, aeration about 30 seconds. Except for aeration, there are no vacuum valves in the system.
MEBW 60/2-E
In 2007, when the director of the German company FOCUS GmbH confirmed his interest in including the SES-1 welder in his company’s production program and concluded a contract for the delivery of one prototype with complete detailed documentation, it became clear that some parts of the welder would have to be modified and others completely changed. Minor modifications were sufficient for the electron gun and the working chamber, while the entire electronics had to be actually re-developed. The production documentation had to be converted or re-created in digital form.
The new electronics are definitely worth mentioning in more detail, with an advanced accelerating voltage source of 2 kW at 60 kV, and control and monitoring electronics that enabled, among other things, the entire device to be controlled by computer (see figure with software). The possibility of operating the welder in a similar way to a scanning microscope with a magnification of up to about 30× is also very useful. The control program allows image scanning in raster mode, welding along any curve (“Draw-a-weld” mode), micro-engraving and other functions.
