Selecting the Mode of Transfer
There are four basic modes of transfer in the welding process: short circuit, globular, spray and pulsed spray.
Selecting the proper mode of transfer depends on the welding process, welding power supply and consumable that is being used. Each mode of transfer has its own distinct characteristics and applications for which it is best suited.
Short Circuit Transfer
The short circuit transfer gets its name from the wire actually "short circuiting" or touching the base metal many times per second as it makes electrical contact. While some spatter is produced, this mode of transfer can be used in all welding positions and on all thicknesses of steel. The short circuit transfer mode is typically found in solid MIG or metal cored wires when the ratio of Argon in the shielding gas is 75 to 85% Argon and the welding voltage is low.
In the globular transfer mode, the weld metal transfers across the arc in a gravity feed. The droplets across the arc are usually larger than the diameter of the electrode. Globular transfer does not produce a very smooth weld bead appearance and some spatter can occur. The use of a globular transfer is usually limited to heavier plate thicknesses and limited to the flat and horizontal positions. Globular transfers are typically found in solid MIG wires, gas shielded metal cored wires and gas shielded flux cored wires when 100% CO2 shielding gas is applied.
The spray transfer is named for the spray of tiny molten droplets across the arc, not unlike the spray coming out of a garden hose when the opening is restricted. A spray transfer is usually smaller than the diameter of the wire and uses relatively high voltage and wire feed speeds or amperage. Unlike the short circuit transfer, once the arc is established, the arc is "on" at all times. There is very little spatter with the spray transfer mode and it is usually used on thicker metals in the flat and horizontal positions. The spray transfer is normally found in solid MIG wires and metal cored wires with a high ratio of Argon in the shielding gas, usually above 90%. A partial or semi spray transfer is found in gas shielded flux cored wires when an Argon CO2 shielding gas is used.
Pulse Spray Transfer
For this variation of spray transfer, the welding machine "pulses" or cycles the output between high peak currents and low background currents. This allows the weld pool to cool slightly in the background cycle, making it slightly different than a true spray transfer. This advantage allows for welding in all positions on either thin or heavy plate material. Solid MIG wires and Gas Shielded Metal Cored wires show the greatest advantage when the pulse mode of transfer is used.