Pulsed Gas Metal Arc Weld...

     During welding, electrode current adjusts instantaneously to the heat requirements of the arc, decreasing before the electrode first contacts the weld pool, then increasing to a pinch current that speeds up the transfer of the drop before reducing to a lower level to allow drop separation with minimal spatter. The current then returns to a high level to establish arc length and form the next droplet before reducing to a medium or background value. This control over the arc current eliminates the sometimes violent and explosive nature of short circuiting transfer.
     Pulsed Gas Metal Arc Welding (GMAW-P) applies waveform control logic to produce a very precise control of the arc through a broad wire feed speed range. With precise control of arc dynamics, GMAW-P can be used as a fast-follow process at high travel speeds, or it can be run as a high deposition rate, fast-fill process.
    The pulse metal transfer allows a spray arc in procedure ranges that would normally be either globular or short circuiting transfer. Because the arc is very stable and has lower heat input than spray transfer, it allows out-of-position welding. Major benefits of the process include: better arc characteristics, greatly reduced spatter and fume generation, less incomplete fusion than short circuiting transfer and lower heat input than spray transfer at a given wire feed speed.
     The pulsing transfers small droplets directly through the arc, one droplet during each pulse. As the wire is advanced, the current pulses and transfers the next droplet. This kind of metal transfer requires either pure argon or high argon blends for shielding, and is somewhat more sensitive to surface contaminants than nonpulsed GMAW.

What to Look for in GMAW Consumables

     After examining the GMAW process in detail and the types of transfer modes available, it is time to evaluate GMAW consumables. It is very important that wire electrodes provide consistent feedability, control and a stable arc. To find a wire that can provide those attributes, look for premium quality wire manufactured under processes that ensure consistent chemistry, constant diameter and tight tolerances. Look for manufacturers that use quality raw materials, analyze each raw steel coil before using it, replace dies frequently to ensure constant diameter and test chemistries often.
     How do you know if your wire is premium? Try these tests:
     1) To test the feedability of wire, take a 12- to 15-ft. gun cable and loop it round a 5-gal pail. Pull the trigger and test the feedability. A premium wire will be stiff but supple enough to feed at a consistent wire feed speed, even with the gun cable in such a tight radius. Cut off a small piece of wire. It should be able to bend around a pencil without snapping off.
     2) Test the copper coating on the wire by bending it around itself as tight as it will go. On a premiurn wire, the copper will elongate rather than flake off.
     3) Weld with the wire at low voltages. The consistent chemistry of a premium wire will permit consistent feeding and a stable arc even at low voltages. Less heat input means less warping and distortion.
     4) Welding wires that conform to AWS A5.18-93 Specification for Carbon Steel Electrodes and Rods for Gas Shielded Arc Welding and certificates are available from the manufacturer.
     Not all gas metal arc welding wires are alike. Consistency is the key, especially in robotic applications where repeatability without problems is a must.


Recommendated Applications

     Typical applications (Fig. 2) for GMAW include construction and agricultural equipment, automotive, pipe and tubular work, ornamental iron, sheet metal, light to medium structural fabrication or wherever a "finished" weld appearance is desired. Common material thicknesses welded are 24 gauge to 3/4 in.

Conclusion

     Gas metal arc welding has a number of advantages including ease of use, fast travel speeds and versatility in welding positions and in joining a wide variety metals and alloys. Consider its use for your next welding application. 

Fig. 2 - One of the advantages of GMAW is it performs well on a variety of metals and thicknesses.