Manual Metal Arc Welding (MMAW)

Introduction：

Manual Metal Arc Welding (MMAW) is one the earliest of the arc welding processes, but has remained popular despite the introduction of newer and more sophisticated processes. Indeed, this lack of sophistication is one of the major attractions of the process.

The Process：

The MMAW process operates as follows.

A low voltage, high amperage current flows to create an arc between the tip of the electrode and the work piece. This generates the heat for welding and causes the work piece and the tip of the electrode to melt.

The flux coating on the electrode decomposes (burns) due to the intense heat of the arc and generates a gaseous shield, which protects the weld pool and surrounding hot metal from the atmosphere.

The electrode melts off and is transferred across the arc in the form of droplets. The molten metal provided by the electrode adds to the molten parent metal and they become the weld metal when solidified.

Molten electrode flux which is transferred across the arc acts as a scavenger, picking up impurities from the surface of the parent metal. The slag which forms covers the

weld pool, solidifies, and protects the hot weld metal as it cools.

The flux ingredients provide arc ionisation (the air gap between the tip of the electrode becomes electrically conductive), enabling the use of alternating current.

Equipment：

1. Equipment for manual metal arc welding consists of the following.

2. Power source – usually a constant-current type output transformer or transformer rectifier is used, although various other types of power sources, such as generators or inverters can also be used. The function of the power source is to supply welding current with sufficient amperage to provide the necessary heat, at a voltage which is safe to use.

3. Electrode handpiece and lead – to carry current to the arc via the electrode.

4. Work return lead – connects the work piece to the power source thereby completing the welding circuit. (A closed circuit is necessary for current flow)

MMAW variables：

The major variables of the MMAW process are:

1. amperage

2. arc length

3. travel speed

4. angle of approach

5. angle of travel