MANUAL METAL ARC (MMA) WELDING IS AN ELECTRIC ARC WELDING PROCESS IN WHICH THE ARC IS STRUCK BETWEEN A COVERED METAL ELECTRODE AND THE WORKPIECE. THE CENTRAL METAL ELECTRODE OR CORE WIRE IS CONSUMABLE TO PROVIDE THE FILLER METAL FOR THE WELD. SHIELDING OF THE WELD POOL IS PROVIDED BY THE DECOMPOSITION OF SOME COMPONENTS OF THE ELECTRODE COVERING.
- MMA welding is the most flexible and one of the most widely used arc welding processes.
- The process uses an electric arc to fuse joint areas.
- The consumable electrode consists of a metal core wire covered in a concentric clay-like mixture.
- The process may be operated with an AC or DC power source.
- This process requires highly skilled welders to produce good quality welds.
- The process does not require a separate shielding gas.
Engine driven generators can be used in the field as well as in the workshop, and in remote areas where mains power is not available, thereby extending MMA welding’s versatility.
With MMA welding, only a limited amount of weld metal can be deposited from one electrode. This means electrodes have to be replaced frequently, making it a less productive process than other welding methods.
OPERATION
MMA is a fusion welding process that uses the heat generated by an electric arc to fuse metal in the joint area, the arc being struck between a covered consumable electrode and the workpiece.
The process consists of a welding power source that may provide either an AC, DC or DC and AC electric current. Connected to this power source is an electrode holder into which the electrode is placed. The circuit is completed with an earth return cable fixed between the power source and the workpiece.
When the arc is struck between the tip of the electrode and the workpiece, the core wire begins to melt, and the coating provides a protective gas and slag covering to the weld.
As the core wire melts, the operator must maintain a constant arc length – distance between the end of the electrode and the workpiece – to prevent the arc extinguishing. Parent metal in the immediate area of the arc is also melted and this combines with molten metal from the electrode to form a weld pool.
