Advanced Welding Processes: Technologies and Process Control

High-energy density processes 159
pressure at 3.5 ¥ 1010 W m –2 has been calculated as 10 7 N m –2 . Although it
is not possible to equate these forces directly, the surface tension force for a
0.5 mm diameter keyhole would be only just over 7 ¥ 10 3 N m –2 .
Under these circumstances, very deep penetration keyhole welds can be
made with EBW, although the general form of the speed/penetration curve
(Fig. 8.16) is similar to that found with both laser and keyhole plasma welds.
8.4.3 Control of EBW
Primary and secondary control variables may be identified for electron beam
welding as shown in Table 8.3. However, although the inter-relationship
between beam power–travel speed and thickness is clearly established, the
welding performance may be changed significantly by means of the secondary
controls. In particular, beam focus and deflection may be used to control the
depth-to-width ratio of the welds and intentional defocusing may be used to
enable cosmetic finishing runs to be made after completion of the penetration
weld.
8.4.4 Applications
The EBW process has been used for joining a wide range of materials including
alloy steels, nickel alloys, titanium, copper and dissimilar metals in thicknesses
Travel speed (m min –1 )
2.5
2
1.5
1
0.5
60 kW Carbon steel
100 kW Aluminium
0
0 100 200 300 400 500 600 700
Thickness (mm)
8.16 Thickness versus travel speed for electron beam welding of
various materials.
Table 8.3 Control parameters for EBW
Primary variables Secondary variables
Filament current Beam focus
Voltage Beam deflection
Travel speed Power supply
Vacuum