1 Continued on next page... Welding Parameters and Techniques Their Effects On The Weld After having selected the wire and gas for a weld, operating conditions must be chosen. The four important parameters are the welding current, wire electrode extension, welding voltage and arc travel speed. These parameters will affect the weld characteristics to a great extent. Because these factors can be varied over a large range, they are considered the primary adjustments in any welding operation. Their values should be recorded for every different type of weld to permit reproducibility. WELDING CURRENT The welding current is the electrical amperage in the power system as the weld is being made. It is usually read from the power source meter, but a separate ammeter is often used. In the mig process, welding current is directly related to wire- feed speed (if the wire extension beyond the guide tip is constant). As the wire-feed speed is varied, the welding current will vary in the same direction. In other words, an increase (or decrease) in the wire-feed speed will cause an increase (or decrease) of the current. Figure 7-1 shows the typical wire-feed speed vs. welding current relationship for various diameter E70S-3 wires. This relationship is commonly called the ”burn-off’ characteristic. The graph also shows that when the diameter of the wire electrode is increased (or decreased) at any wire-feed speed, the welding current is higher (or lower). Each type of wire (steel, aluminum, etc.) has a different burn-off characteristic. One important fact that should be noticed in Figure 7-1 is the shape of each burn-off curve. In the lower current range for each wire size, the curve is nearly linear. In other words, for every addition to the current, there is a proportional (and constant) increase in the melt off. However, at higher welding currents, particularly with small diameter wires, the burn-off curve becomes non-linear. In this region, higher welding currents cause larger increases in the burn-off. This is due to resistance heating of the wire extension beyond the guide tube. This resistance heating is known at PR heat where I = welding current and R = resistance. The greater the welding current, the greater the PR heating.
Effects
Weld Bead
Torch Position
Characteristics

 

 

 

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