Page 172 - Welding of Aluminium and its Alloys

Other welding processes 155

Table 8.2 Summary of laser welding defects and corrective actions

Unacceptable defect Corrective action

Cracks Check material specification
Check filler metal composition if used
Check welding speed
Check weld shape
Lack of penetration Increase laser power
Reduce welding speed
Improve beam focus
Improve gas shielding
Lack of fusion Improve beam alignment with respect to the joint
Porosity Check for and remove surface contamination
Check gas for moisture and contamination
Improve gas shielding
Undercut Improve fit-up, eliminate gaps
Check welding parameters
Consider wire feed
Sheet misalignment Improve fit-up and accuracy of weld prepared
components
Discoloration/oxidation Improve gas shielding
Improve gas quality

The MIG, TIG and plasma-arc processes have been used, enabling higher
welding speeds to be achieved, particularly in thin sheet for the automotive
industry. Of these options MIG welding is the preferred fusion welding
process, although the plasma/laser process is also being actively developed
and is producing good results. Figure 8.6 illustrates a commercially avail-
able laser/MIG welding head and Fig. 8.7 the principles of operation.
In addition to higher speeds the enhancement of the laser beam enables
greater variations in fit-up to be tolerated. Penetration, it is claimed, is
increased and the change in shape of the weld pool assists in allowing
hydrogen to diffuse out of the joint, reducing the porosity often encoun-
tered in laser welds. At present (2002) these augmented laser processes
are in the early stages of development but show great promise in widening
the field of applications of the process.

8.4 Electron beam welding

Electron beam welding is, like laser welding, a power beam process ideally
suited to the welding of close square joints in a single pass. Unlike the laser
beam, however, the electron beam process utilises a vacuum chamber in