Electro beam Welding

Applications of a New Electron Beam Welding
Technology in Vacuum Equipment Design

Nova tehnologija varjenja
z elektronskim curkom
vakuumskih sistemov
Duphk J., P. Kapounek, M. Hor%ek, Institute of Scientific Instruments, Brno
When constructing vacuum and high vacuum systems and parts, we often encounter
the task of joining materials with considerably different metallurgical properties, e.g.,
stainless steel-Al, stainless steel-& Ti-AI. If the classical melting technique is used for
welding, in most cases fragile intermetallic compounds arise and the quality of joints is
often inadequate. Mechanically resistant and vacuum tight joints can be produced by
electron beam heating so that only the material with the lower melting temperature is
melted and in this melt the higher-melting-point material is partially dissolved. The
contribution describes a novel form of a joint in construction of vacuum devices.
Key words: electron beam welding, novel form of joints, new technology of welding
Pri konstruiranju visokovakuumskih sistemov in sestavnih delov Cesto naletimo na
problem spajanja materialov z razliCnimi fizikalnimi lastnostmi, kot n.pr. nerjavno jeklo -
aluminij nerjavno jeklo - baker, titan - aluminij. Pri uporabi klasiCne varilne metode s
taljenjem v mnogih primerih dobimo krhke intermetalne zlitine in neprimerno kvaliteto
zvarov. Mehansko odpornost in vakuumsko tesnost zvarov lahko dobimo z ogrevanjem
z elektronskim curkom tako, da se stali samo material, ki ima nizjo temperaturo talEa,
v talini pa je delno topljen material z visjo temperaturo talis’Ca. Opisana je nova oblika
spojev, nova tehnologija izdelave spojev in prikazana praktiCna uporaba spojev v
konstrukcijah vakuumskih naprav.
KljuCne besede: varjenje z elektronskim curkom, nove oblike zvarov, nova tehnologija
spajanja
The weld joints of materials which have considerably
different metallurgical properties, such as stainless
steel-aluminium, titanium-aluminium, etc. made
using the classical way of melting, during which both
materials in liquid state mix, are of limited use, because
in most cases fragile intermetallic compounds
arise which decrease the strength’. Efforts to influence
the composition of the weld metal by deflecting
the electron beam toward one of the welded materials*,
when two independent beams3 or the welding
technique which makes use of an additional material
in the form 3 flake4 are used, mostly do not prevent
establishment of concentration conditions giving
the rise of fragile phases. The prerequisite for the
creation of vacuum-tight and mechanically strong
joints of quite different metallic materials is the
preparation of a weld metal in the form of a solid
1 Dr. Sc. Jan DUPAK
Institute of Scientific Instruments of the
Academy of Sciences of the Czech Republic,
Krllovopolske 147,
(X-61 264 Brno, Czech Republic
solution composed of components of both materials
to be welded. This can be achieved by heating the
parts to be joined so that the electron beam melts
only the lower-melting-point material in which the
higher-melting-point metal is partially dissolved and
so a peripheral solid solution is produced. The precondition
for the creation of the solid solution is the
existence of a partial solid-state solubility region in
the phase diagram, and of a sufficiently high difference
in melting temperatures of both metals.
Using the mentioned method, we made welds of
aluminium with copper, nickel, titanium, silver, stainless
steel, and of stainless steel with copper, molybdenum
and niobium. All joints of the mentioned combinations
are vacuum-tight and mechanically
resistant, even after repeated heating to a temperature
of 4OO”C, followed by cooling that was carried
out by immersing the joint into liquid nitrogen. So far,
main attention has been paid to the welding of aluminium
with titanium. These welds were investigated
metallographically. Mechanical tests were made and
the distribution of elements in the joint was determined5v6.
431
Dup&k J., P. Kapounek, M. HorBCek: Applications of a New Electron Beam Welding Technology in Vacuum Equipment Design
Figure 1: Constructional arrangement of the joint ILower-
melting-point material, II- Higher-melting-point
material
The described welding technology makes certain
demands on the constructional arrangement of the
joint. A suitable arrangement is shown in Fig. 1.
The steps of the welding technigue are as follows:
(1) Both parts to be welded are rotated and, by using
a defocused electron beam, they are heated in the
region of the joint to a temperature close to the melting
temperature of the lower-melting-point material.
(2) Using the focused beam, the lower-melting-point
material is melted so that it wets the other material
which is in the solid state.
The following are examples of use of the joints in
vacuum engineering. When constructing a zeolite
sorption vacuum pump, we weld its body made of a
ribbed aluminium sheet and neck of stainless steel.
The use of an aluminium body leads to a decrease in
time necessary for cooling the vacuum pump. The
stainless steel - silver joint was used for the construction
of an oxygen valve where a 0,5 mm thick
silver tube of 12 mm in diameter was welded to a
flange of stainless steel. The aluminium - stainless
steel weld joints enable the use of copper-ring sealed
flange connections (CF) of apparatus made of aluminium.
In this case it is more appropriate to weld
rings of aluminium and of stainless steel first and, after
verifying the vacuum tightness of the joint (after
multiple heating and cooling), to produce the less demanding
joints aluminium - aluminium, and stainless
steel - stainless steel.
The use of the weld joints of materials with considerably
different properties can bring an improvement
of properties of vacuum and ultrahigh vacuum equipment
or some simplification in their construction.
References
’ A. H. Maleka: Electron-Beam Welding, McGraw-Hill,
London, 1971,169
’ B. A. Schutov, A. A. lerochin, Control of the Composition
of a Weld Joint when an Electron Beam is Used for
Welding Heterogeneous Metals, Svarochnoie proizvodstvo,
1971, 10, 10 (in Russian)
3 B. A. Schutov, A. A. lerochin, Experience of Welding
Heterogeneous Metals by Using Two Electron Beams,
Avtomaticheskaia svarka, 1972, 1, 71 (in Russian)
4 L. N. Sayer, Bit. Weld. Journal, 4, 1967, 163
5 J. Dupak, P. Michalicka, J. Viestal, P. Kapounek,
Zvaranie, 43, 1994, 13 (in Czech)
6 J. Dupak, P. Michalicka, J. Viestal, Proceedings of the
Fourth International Conference on electron beam technologies,
Varna, 1994, 115
432