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ELECTRODE WELDING AND GOUGING Power source characteristics A welding power source shall not only supply current of a set amperage and voltage, it shall also automatically adjust these values as conditions in the welding arc changes. A quick response to changes in the arc characterizes a well designed welding power source and is a prerequisite for good welding properties. When welding with electrodes with large droplet transfer, small short circuits will constantly occur in the arc. As the short circuit starts, a current peak will occur before the machine adjusts to the short circuit condition. When the short circuit is broken a voltage peak will occur. Excessive height or duration of these peaks will give an unstable arc and spatter from the weld pool, and may increase the possibility of welding faults. These dynamic properties of the welding power source are expressed in the dynamic characteristic of the machine.

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The relation between amperage and voltage supplied from a welding power source is called the static characteristic of the machine. The two basic types of static characteristics are constant current (CC) and constant voltage (CV).

with very little current variation is best. For Air Carbon Arc gouging a flatter characteristic, with more current variation and high short circuit current, is preferred. Welding with coated electrodes needs characteristics between these two. Some welding power sources will have adjustable characteristics to enable the welder to choose exactly the characteristic suited for the job at hand, as shown in the figure below. Constant voltage characteristic (CV) This characteristic is used only for the Wire Welding process when a wire feeder with constant feed speed is used.

The power source will attempt to keep a constant arc voltage by increasing / decreasing the amperage as the arc length shortens / increases, and the characteristic curve will therefore be practically flat.

This characteristic is required for gas metal arc welding in the short arc range, and will also offer advantages in the spray arc range.

Constant current characteristic (CC) Machines with constant current characteristic are designed to keep the welding current approximately constant, with variations within a narrow range when the arc length, and thereby the arc voltage, increases or decreases. The optimal current variation range is different for different processes.

For TIG welding a steep characteristic

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Dynamic characteristics of a short circuit