Metal Transfer
WITH DCEP POWER, the filler metal will be transferred across the arc as a stream of fine, superheated droplets when the welding current and arc voltage are above certain threshold values. These values will depend upon the electrode alloy, size, and feed rate. This mode of transfer is known as spray transfer. It is the one normally used for GMAW of aluminum. The spray transfer mode may be continuous or intermittent. Intermittent transfer is called pulsed spray welding.Pulsed spray welding may be used for welding in all positions. Metal transfer takes place during the periods of high welding current, but ceases during the intervening periods of low current. However, the cleaning action is continuous at both current levels. This pulsing action reduces the overall heat input to the base metal for good control of the molten weld pool and penetration. The lower heat input makes it easier to gas metal arc weld thin aluminum sections. Pulsing also allows
the use of larger electrodes than what is practical with steady current, especially on thin metal. The amount of spatter during welding may be more severe with electrodes that contain low-vapor-pressure elements. The aluminum-magnesium alloy electrodes (ERSXXX series) commonly cause the most spatter. The vapor pressure of the magnesium tends to cause
disintegration of the droplets as they separate from the electrode tip. This produces small spatter balls that are often thrown clear of the arc. When the arc voltage (arc length) is decreased to below a certain value for a specific electrode and amperage, the size of the droplets will increase and the form of the arc will change. Electrode melting rate and
penetration will increase. This has a distinct advantage when welding thick sections. When the arc voltage is in the spray transfer range and the welding current is decreased to below some threshold value, metal transfer will change from spray
to globular type. This latter type is not suitable for aluminum welding because fusion with the base metal will be incomplete. Conversely, when the arc voltage (length) is decreased significantly with adequate current, short circuiting will occur. This type of transferalso is not recommended for aluminum for the same reason.