Welding Processes: A Closer Look at GMAW PulseMarch 18, 2015
The strength and quality of welds is one of the single most important aspects of safe, reliable industrial fabrication and construction. This makes choosing the best welding process for a given application of paramount importance. By far one of the most commonly used and valuable welding processes is gas metal arc welding (GMAW), especially the pulsed transfer mode (GMAW-P).
What Is GMAW-P?Pulsed gas metal arc welding (GMAW-P) is a variation on the spray transfer mode of the process. Basic spray gas metal arc welding involves the use of a stable electric arc between the electrode and the metal being welded. It uses a high voltage and current which results in the molten metal from the electrode being vaporized into a steam. This eliminates spatter and creates a high-quality weld finish. However, the high amount of voltage and current also results in high heat output and a large weld pool that thus is not suitable for all weld positions and which may also result in burn through, especially on thinner work metals. GMAW pulsed solves this problems by rapidly alternating electrical pulses between high and low current, often as many as 30 to 400 times every second. Each time the current pulses a small molten metal droplets falls from the electrode to the work surface, preventing spatter without the need for the high heat required in basic spray GMAW that results in vaporizing. Since the heat is drastically reduced, the weld pool is also much smaller and thus welding can be done in any position The lower heat also makes it possible to weld even thin, non-ferrous pieces of metal or alloy.
The Industrial Uses of GMAW-PGMAW-P was originally developed for welding aluminum. Aluminum is very important in a wide range of industrial applications because it is lightweight, yet strong, has high corrosion resistance, and is very thermally conductive. However, because it is so thermally conductive it posed a challenge to weld with other welding processes because it would rapidly transfer heat away from the weld, making it difficult to establish a weld pool without very high temperatures. This in turn made it prone to burn-through and other defects. GMAW-P solves this problem by offering greater weld pool control, improving fusion, and preventing problems like warping and burn-through. GMAW-P is also well suited to welding on stainless steel. Stainless steel is another commonly used metal in industrial applications because like aluminum it also offers high corrosion resistance. Additionally stainless steel has a high tensile strength and is very ductile, able to withstand demanding conditions and temperatures. However, unlike aluminum, stainless steel is a very poor conductor of heat which creates its own set of challenges for welding since the weld pool is typically sluggish and doesn't flow well. Likewise, stainless steel may be subject to thermal expansion during welding, which can lead to warping and distortion. Once again GMAW-P solves these problems thanks to the excellent control it offers over the weld pool as well as its ability to offer good penetration.
Challenges Associated with GMAW-PNo welding process is perfect, however, and as with other processes there are some challenges associated with GMAW-P. For example:
- GMAW-P utilizes more expensive, complicated equipment than many other welding processes.
- GMAW-P requires a shielding gas to function and is thus not well suited to welding outdoors or in other areas with a draft.
- GMAW-P requires either pure argon or high argon blends, which is more expensive than shielding gases such as carbon dioxide.
- GMAW-P is slightly more sensitive to surface contamination than non-pulsed GMAW, which in turn is also more sensitive to contamination than other welding processes.
- GMAW-P is much less portable than SMAW.
- GMAW-P requires careful setup of welding parameters (speed, voltage, distance from welding surface, etc.) for best results.