1 The Power Source Direct current, constant potential (voltage) power sources are used for most mig welding. This contrasts with tig and stick electrode welding which use constant current power sources. A mig power source provides a relatively constant voltage to the arc during welding. This voltage determines the arc length. When there is a sudden change in wire-feed speed, or a momentary change in arc length, the power source abruptly increases or decreases the current (and thereby the wire burnoff rate) depending on the arc length change. The burnoff rate of wire changes automatically to restore the original arc length. As a result, permanent changes in arc length are made by adjusting the output voltage of the power source. The wire-feed speed, which the operator selects prior to welding, determines the arc current (see Fig. 3-1). It can be changed over a considerable range before the arc length changes enough to cause stubbing to the workpiece or burning back to the guide tube. Power Source Variables The self-correcting arc length feature of the constant voltage welding system is very important in producing stable welding conditions. Specific electrical characteristics are needed to control the arc heat, spatter, etc. These include voltage, slope, and inductance.
Slope
Inductance

 

 

 

Variations-
Metal
Transfer
Description
Equipment
Voltage
Power
Supply
Shielding
Gases
Wire
Electrodes
Safety
Welding
Techniques
Welding
Conditions
Economics
Weld
Defects
Mig Spot
Welding
Tables

 

Figure 3-1 - Affect of Wire Feed Speed