Page 92 - Module DMV20173

5. 0 JOINING PROCESSES

5.2 FUSION WELDING

1. Fusion welding is defined as melting together and coalescing materials by means of

heat.
2. Filler metals (which are metals added to the weld area during welding) may be used.
3. Fusion welds made without the use of filler metals are known as autogenous welds.
4. Table 5.1 shows the characteristics of several fusion welding processes.

Table 5.1 General characteristics of fusion welding processes.

5.2.2 SHIELDED METAL ARC WELDING (SMAW)

1. SMAW is based on providing an electric circuit comprising the electric current source

the feed and return path, the electrode and the workpiece.
2. The arc welding process involves the creation of a suitable small gap between the
electrode and the workpiece.
3. When the circuit is made a large current flows and an arc is formed between the
electrode and the workpiece. The resulting high temperatures (6,000°C) causing the

workpiece and the electrode to melt.
4. The electrode is consumable. It includes metal for the weld, a coating that burns off
to form gases, which shield the weld from the air and flux, which combines with the
nitrides and oxide generated at the weld. When the weld solidifies a crust is formed

from the impurities created in the weld process (slag). This is easily chipped away.
5. Localized melting is obtained using the heat from an electric arc established between
a consumable metal electrode and the work material.
6. Electrode, which is coated, act as filler material. The coating decomposes in the arc,
providing a gas shield around it, as well as forming a protective slag that prevents

oxidation and other contaminant of the weld.

BPLK 124 DMV 20173