When using the GMA welding
process, metal is transferred by one of three methods: spray transfer, globular transfer,
or short-circuiting transfer. The type of metal transfer depends on the arc voltage,
current setting, electrode wire size, and shielding gas.
Spray-Arc Welding
Spray-arc transfer is a high-current range method that produces a rapid disposition of
weld metal. This type of transfer is effective for welding heavy-gauge metals because it
produces deep weld penetration. The use of argon or a mixture of argon and oxygen are
necessary for spray transfer. Argon produces a pinching effect on the molten tip of the
electrode, permitting only small droplets to form and transfer during the welding process.
Spray transfer is useful when welding aluminum; however, it is not practical for welding
light-gauge metal.
Globular Transfer
Globular transfer occurs when the welding current is low. Because of the low current, only
a few drops are transferred per second, whereas many small drops are transferred with a
higher current setting. In this type of transfer, the ball at the tip of the electrode
grows in size before it is transferred to the workpiece. This globule tends to reconnect
with the electrode and the workpiece, causing the arc to go out periodically. This results
in poor arc stability, poor penetration, and excessive spatter.
Globular transfer is not
effective for GMA welding. When it is used, it is generally restricted to thin materials
where low heat input is desired.
Short-Circuiting Arc
Transfer
Short-circuiting arc transfer is also known as short arc. Short arc was developed
to eliminate distortion, burn-through, and spatter when welding thin-gauge metals. It can
be used for welding in all positions, especially vertical and overhead where puddle
control is more difficult. In most cases, it is used with current levels below 200 amperes
and wire of 0.045 of an inch or less in diameter. Small wire produces weld puddles that
are small and easily manageable.
The shielding gas mixture for
short-arc welding is 75% carbon dioxide and 25% argon. The carbon dioxide provides for
increased heat and higher speeds, while the argon controls the spatter. Straight CO2is now being used for short-arc welding; however, it
does not produce the excellent bead contour that the argon mixture does.
Published
by SweetHaven Publishing Services
Based upon a text provided by the U.S. Navy
