Talk to any experienced welder and they’ll tell you what the “best” transfer mode is for any application. In manual welding specifically, best is a relative term because specific travel speed,
angle and welding style are personal to each welder. How does someone who is inexperienced know which transfer mode will fit their application?
Just about any gas metal arc welding (GMAW) machine can be used for the three standard transfer modes: short circuit, spray and globular. Some modern machines even offer a fourth mode called pulse. To understand the differences, a quick review of transfer modes is necessary.
At its most basic, MIG welding is a process whereby a metal wire electrode is fed through the torch along with a shielding gas. The gas protects the arc that’s created when electrical current connects with the wire. The transfer mode is the method used to move the molten wire from the arc to the base material. Each of the standard transfer modes uses constant voltage (CV).
Most new welders begin with short circuit arc welding. In this transfer mode, the electrode creates a short circuit when it touches the base material. The heat of that short circuit ignition transfers a molten droplet of electrode into the weld puddle. Short circuit welding uses low energy and is the coldest of the CV transfer modes.
Spray arc welding is just as it sounds – a constant stream of tiny molten droplets that are much smaller in diameter than the electrode. The spray arc is hotter than with short circuit and creates a larger weld pool, which limits this process to horizontal and flat welding positions.
Globular welding is the transition phase between short circuit and spray. Here, the droplets are inconsistent in size, some
small like spray and others larger like short circuit. The inconsistency produces a greater amount of spatter. Like spray, globular is generally only used in horizontal or flat welding.
Pulse welding is a modified spray arc that requires a specialized power source. It has the best qualities of all the modes and
minimizes their disadvantages. “Pulse” refers to how the current is pulsed at a set frequency. Each pulse creates a single molten droplet and transfers it into the weld pool. Between pulses the current drops, cooling the weld pool slightly before the next droplet detaches. This cooling allows pulse to be used in any welding position, unlike a standard spray arc.
Every transfer mode has a purpose with benefits and downfalls alike. Short circuit is often cheaper than the other modes and, while all welding is better with clean base materials, it handles dirtier material better than most. As a low amperage and voltage process, it has the least amount of heat input, which makes it an excellent option for thin materials (1/8 in. and less) and open root groove welds. It digs into the toes of the weld without blowing them out because it uses just enough heat to create a solid seam.
Short circuit is ideal for open root passes with no backing such as pipe welding because it’s easy to control the weld pool and it creates good reinforcement backing during the process. Short circuit generally produces low spatter, especially with waveform controlled processes.
Pulse has an overall higher heat input than short circuit, which makes it a poor choice for very thin metals or applications with gap conditions, particularly in manual welding. Pulse can allow for much faster travel speeds over short circuit in automated applications such as in the automotive industry.
The constant transfer of material in spray arc welding is almost short-circuit-free due to the high power necessary. This produces higher heat input and penetration, which is great for thicker materials. It also works well with high deposition rates to fill weldments with fewer passes. Though it has little spatter, the resultant weld puddle can be very fluid, which is sometimes a problem, even with the limitations of flat or horizontal welds.
In the same application, pulse welding is an excellent alternative with its intelligent arc and lower heat-affected zone (HAZ). While it has a lower heat input, the regulated arc of pulse allows for higher travels speeds, both manual and robotic. When part fit-up is a problem, the machine can stabilize the pulse arc to make up for gap inconsistencies.
Globular welding is most often done on carbon steel and excels with material thicknesses of 1/8 in. to 3/16 in. It is low cost, using basic MIG equipment and inexpensive CO2 shielding gas. The inconsistent droplet size creates a lot of spatter, which is difficult to remove because of the high heat and size of the spatter. While not a commonly favored transfer mode, globular is often used with flux-cored wire using 100 percent CO2 shielding gas in shipyards, railyards, construction and other similar industries.
Though globular can handle dirtier materials, pulse is universal for a multitude of applications and industries. It allows for welding in any position and maintains a low spatter emission throughout the available amperage range.
Because pulse welding relies on a specialized digital power source, it’s considered an advanced process. Thanks to the on-board computer, a pulse power source can regulate the arc in a way that others can’t. The advantages of this process affect everything from user ability to part fit-up. Advantages, such as automatic adjustment for differences in stickouts, make it easier to weld.
In aluminum welding, the lower heat input of pulse contributes to a smaller HAZ, reducing the warping and burnthroughs common with this highly conductive material.
Overall, pulse is a transfer mode that can do most welding better than the standard modes. To get the best performance with pulse welding, the metal should be clean and not too thin.