Power Shopping: Choosing the Ideal Welding Power Source by Selecting the Proper Welding Process

The process of choosing a welding power source is much like that of buying a car. It involves searching for a product that is efficient, powerful, easy to handle and, most importantly, suited to the customer's particular needs. But with such a wide selection of power sources on the market, how do welders select the right one for them?

The first step is to understand their shop's internal needs. To determine this, examine some commonly used welding processes and for which materials they are best suited.

Gas Metal Arc Welding (GMAW)/Flux-Cored Arc Welding (FCAW)
GMAW/FCAW (most commonly referred to as MIG or Flux-Cored Welding) uses a spool of wire that is either housed inside the power source or fed from an external wire feeder. This wire or filler material is fed through a welding gun. The power source is used to start and maintain the arc between the wire and the base metal.

GMAW or MIG welding utilizes solid metal wire, which requires the use of a shielding gas to protect the weld puddle from the atmosphere. FCAW uses a hollow wire filled with a flux powder that may or may not need an external shielding gas, because the gas may be produced from the flux within the wire as it burns in the arc. The flux in the wire serves many of the same purposes as the electrode coating in SMAW.

GMAW requires the least operator skill, because the machine feeds the wire. The welding operator holds the gun in one hand, squeezes the trigger, and welds. It's that easy! The shielding gas makes for a very smooth arc that remains stable. Since other processes typically require very specific electrode positioning and manipulation, GMAW is the fastest growing process. With compact units now retailing for less than $500 and the ability to easily weld on much thinner material than stick electrode, this type of unit has become very popular.

Welding speeds are also higher because of the continuously fed electrode, absence of slag (with GMAW) and higher filler metal deposition rates. Its operating factor is typically 30-50 percent so 3-5 minutes out of every 10 can be spent creating an arc. In addition, GMAW/FCAW does not require the degree of operator skill that TIG or stick welding does.

GMAW can be used on all of the major commercial metals. FCAW is currently used primarily on steels and stainless steels. These two processes also can be used over a wide range of material thickness and operate in all positions. For these reasons, they are usually the welding processes of choice for most fabrication and production shops.

On the downside, equipment for GMAW and FCAW is more complex, more costly and traditionally less portable than stick welding processes (although some new portable models do exist). Welding is typically done within a 10 to 12 foot radius of the wire feeder and the work is usually brought to the weld station.

Shielded Metal Arc Welding (SMAW)
SMAW, or stick welding, is the most common form of arc welding. In the process, a stick or electrode is placed at the end of a holder. Using electricity from the power source, an arc is struck between the tip of the electrode and the metal welding surface. The heat of the arc melts the tip of the electrode creating the filler material that is deposited as the electrode is consumed. A coated material on the electrode burns and protects the arc from the atmosphere. The burning of the coating produces CO2, which becomes the shielding gas. A slag is also formed which helps refine the weld metal and protect it as it freezes.

SMAW is one of the easiest and most versatile ways to weld, since filler material can be easily changed to match different metals just by switching stick electrodes. Whether it is steel, stainless steel, cast iron or high alloy metals, users can clamp in a new rod to be ready for the next project. In addition, stick is versatile because it takes the least equipment, which makes it easy to setup or move to a new location.

When compared to other types of power sources, SMAW welders are generally the least expensive. As a result, they are utilized most often by novice welders, farmers, smaller fabricating shops, maintenance shops and large field construction contractors that weld on a variety of jobs over a large physical area.

The main disadvantage to SMAW is the amount of downtime associated with the process. An electrode is only so many inches in length and must be changed once it is consumed. This requires the operator to stop welding to change the electrode. Frequently, the amount of skill required by the operator is greater than that required for wire fed processes.

In addition, it takes time to chip or grind the slag or impurities from the weld. The operating factor or time that the welder is actually "creating sparks" is typically two to three minutes per 10-minute interval. In general, stick welders sacrifice productivity for versatility.

Gas Tungsten Arc Welding (GTAW)
In GTAW, an electric arc is established between a non-consumable tungsten electrode and the base metal. The arc zone is filled with an inert gas, typically argon, which protects the tungsten and molten metal from oxidation and provides an easily ionized path for the arc current. GTAW produces high quality welds on almost all metals and alloys. Because it can be controlled at very low amperages, it is ideally suited for welding on thin metal sheets and foils.

The biggest advantage of GTAW is that high quality welds can be made on almost any weldable metal or alloy. Another major advantage is that filler metal can be added to the weld pool independently of the arc current. With other arc welding processes, the rate of filler metal addition controls the arc current. Other advantages include low spatter, no slag and relatively easy clean up.

The main disadvantage of GTAW is that it produces the slowest metal deposition rate of all the processes. The emphasis is on making welds that are perfect in appearance, which means lower welding current and more welding time. The operator needs to learn to coordinate precise movements of the torch in one hand with adding filler metal from the other hand and controlling current with a foot pedal.

The operator also needs to learn how to properly setup the GTAW machine. Tungsten preparation, spark intensity, upslope, downslope, pulsing rate, peak intensity, background current, high frequency and proper grounding can all be very important issues for a GTAW welder. Combined with lower deposit rates, it's easy to see how the GTAW process has a great following in industries such as aerospace, where quality is much more important than cost.

Submerged Arc Welding (SAW)
SAW uses a continuously fed wire with a granular material called flux to cover the weld area. This type of welding is used primarily on heavier plate applications such as structural steel and on specialized high speed welding of light sections.

The flux plays a central role in achieving high speed and a quality weld. Very little welding fume is produced, leaving the shop air much cleaner. Since the flux covers the whole arc, a welding helmet is not required, leading to a higher operating factor. On long, large welds, multipass and overlay applications, the process can approach a 100 percent operating factor. Productivity can be very high with welding currents over 1000 amps common on automatic applications.

Disadvantages include limited welding positions, because flux comes in granular form. Operators must weld on flat surfaces to assure the flux covers the weld puddle. Another disadvantage is that hot flux can burn shoes and cause handling problems that must be addressed.

With some knowledge of the types of welding processes that are available, you should now be able to make a decision as to which process best suits your needs. The next step is to start looking for a power source. Your ideal power source should accommodate your welding process, meet your size requirements, fit within your budget and offer the technology features that are needed in your shop. In the end, a reliable power source-like a reliable car-will continue to serve you for many years to come.

Lincoln Electric Products