Gas Metal Arc Welding (GMAW) is one of the most common welding processes in industrial facilities around the world.
When using MIG/MAG welding, according to the different welding process parameters, there are four different basic modes to transfer weld metal (filler material) across the arc to the base material: Short-circuiting Transfer, Pulsed Transfer, Globular Transfer, and Spray Transfer. As shown in the figure.
They are identified and characterized by the size and frequency of the droplet. The different transfer methods are how the weld metal from the consumable electrode is transferred to the base material over the arc.
The GMAW drop transfer mode is associated with many factors, including current level, wire diameter, arc length, voltage level, specific power supply characteristics, and shielding gas.
The short-circuiting transfer is the coldest form of MIG welding and uses low voltage. This type of transfer produces a small, fast-freezing weld pool generally, sometimes referred to as “fast freezing.” The Short Circuit method is great for the joining of thinner material sections, out-of-position welding, and filling of large root openings, but you risk “cold lapping” on thicker materials.
As metal transfer only occurs during short-circuiting, shielding gas has very little effect on this type of transfer. Spatter can occur, and it is usually caused either by gas evolution or electromagnetic forces on the molten tip of the electrode.
The pulsed transfer method is a modified form of the Spray Arc method, taking the best parts of all the transfer methods and minimizing their disadvantages. The advantage of this transfer mode is the regularity of the transfer, it is possible to obtain a sequence of small droplets detaching in a very regular free-flight form (spray-like). A droplet is created for every pulse and then the droplet across the arc into the weld puddle.
Every voltage drop on the pulse creates a longer cooling-off period and may reduce the heating effect from the weld, minimizes spatter or the risk of cold lapping, and weld positioning is not as limited as the Globular and Spray methods.
The globular transfer method is very similar to the short-circuiting transfer method, in which the consumable electrode wire arcs and touches the base material and shorts. The difference comes in how long the consumable electrode melts. The globular transfer method is characterized by a drop size of greater diameter than that of the electrode. In the globular method, the wire is heated longer and creates a large volume of weld metal that drips into the weld joint. As the weld is made, a larger diameter ball of molten metal from the electrode tends to build up at the end of the electrode, often in irregular shapes. As a result of the large molten droplet, the process is generally limited to flat and horizontal welding positions.
When the drop finally detaches, mainly due to the gravity force, it falls to the workpiece, leaving an uneven surface and often causing spattering. As a result of the large molten droplet, the process is generally limited to flat and horizontal welding positions.
Spray transfer was the first metal transfer method used in GMAW.
In a gas shield of at least 80% Ar or He, for a given size electrode, as a result of a high average current (high electromagnetic forces). Filler metal transfer changes from globular to spray type. Very small droplets are detached at a high frequency and sprays into the weld joint. This method uses a high heat input, and you risk burn-through on thinner materials and only allows for limited to flat and horizontal weld positions.