Advanced Welding Processes: Technologies and Process Control

8.4.5 Practical considerations
High-energy density processes 161
Use of a vacuum
The EBW process is normally performed in a vacuum to avoid dissipation of
the beam by collision with gaseous atoms and to protect both the electron
gun and the weld area. The advantage of this technique is that it provides a
clean, inert environment, which is conducive to the attainment of consistently
high joint quality. The major disadvantage is the time wasted in loading and
pumping down the enclosure. The harder the vacuum the more difficult it is
to achieve and, to alleviate the need for very high vacuum in the complete
chamber, many systems allow a differential pressure between the gun and
the welding area. In these systems, the gun vacuum may be maintained at
5 ¥ 10 –4 mbar whilst the chamber is held at 5 ¥ 10 –2 mbar.
The need to operate in a vacuum also implies the need for cleanliness and
the avoidance of low-vapour pressure compounds in the weld fixturing and
positioning equipment.
Safety
The collision between the electron beam and a metal surface will generate xrays;
suitable screening is incorporated in the equipment to ensure that the
operator is not exposed to this secondary radiation.
Joint configuration
The joint configurations are usually variants of square butt, lap and stake
welds as previously shown in Fig. 8.14. Again accurate positioning and joint
preparation is usually necessary due to the small spot size.
8.4.6 Developments
Although the basic process has remained unchanged for many years, some
significant advances have been made in the maximum power available, the
operating techniques and the equipment.
EBW beam power
Whilst for many applications beam powers of up to 25 kW are quite adequate,
there has been an attempt to extend the weldable thickness range, particularly
for out of vacuum applications and systems with output powers up to
200 kW have been built.