Page 164 - Welding of Aluminium and its Alloys

8

Other welding processes

8.1 Introduction

While MIG and TIG welding may be regarded as the most frequently used
processes for the joining of aluminium and its alloys there are a large
number of other processes that are equally useful and are regularly
employed although perhaps in rather more specialised applications than
the conventional fusion welding processes. Some of these processes are
discussed here.

8.2 Plasma-arc welding

As described in Section 4.3 a modification to the TIG welding torch enables
a strong plasma jet to be produced that has some very desirable features
for both welding and cutting. Despite these advantages the process found
little application for the welding of aluminium when DC electrode nega-
tive or electrode positive were used because of extensive lack of fusion
defects. Alternating current gave no better results as high currents were
required, resulting in rapid electrode deterioration. The pulsing of the
current also caused weld pool instability, poor bead shape and lack of fusion
defects. These limitations were overcome with the development of square
wave power sources, already mentioned in Chapter 6, since which time
plasma-TIG has become accepted as a viable production process.

8.2.1 Plasma-TIG welding

8.2.1.1 Main characteristics
As mentioned above, the basic principles of the plasma-TIG process (EN
process number 15) have been covered in Section 4.3 which describes the
use of the heat from the plasma-arc for cutting purposes. For welding the
transferred arc plasma-jet is used as the heat source, the major difference

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