The arc needed in welding is a burst of electricity between the welding electrode and the weld piece. The arc is generated when a sufficiently great voltage pulse is generated between the pieces. In TIG welding this can be accomplished by trigger ignition or when the welded material is struck with the welding electrode (strike ignition).

Thus the voltage is discharged like a bolt of lightning allowing the electricity to flow through the air gap, which creates an arc with a temperature of several thousand degrees centigrade, at maximum as much as 10,000 degrees (18,000 degrees Fahrenheit). A continuous current from the welding power supply to the work piece is established through the welding electrode, and therefore the work piece must be grounded with a grounding cable in the welding machine before welding is started.

In MIG/MAG welding the arc is established when the filler material touches the surface of the workpiece and a short-circuit is generated. Then efficient short-circuit current melts the end of the filler wire and welding arc is established. For a smooth and durable weld, the welding arc should be stable. Therefore it is important in MIG/MAG welding that a welding voltage and wire feed rate suitable to the weld materials and their thicknesses are used.

Additionally, the working technique of the welder affects the smoothness of the arc and, subsequently, the quality of the weld. The distance of the welding electrode from the groove and a steady speed of the welding torch are important for successful welding. Assessing the correct voltage and wire feed speed are an important part of the welder’s competence.

Modern welding machines, however, have several features that make the welder’s work easier, such as saving previously used welding settings or using preset synergy curves, which make it easier to set the welding parameters for the task at hand.