Welding's Wave of the Future

Here's what happens during each of these processes:
Short-Circuiting (short-arc) Transfer occurs when molten drops of electrode short- circuit the arc in a range from 20 to more than 200 times a second. Metal is transferred with each short circuit, rather than across the arc as in spray transfer welding. However, the process produces some spatter when shorting is not perfect. It also gives low deposition rates, and lack of fusion (cold lapping) can be a problem.

Globular Transfer occurs as droplet size grows on the end of the electrode to a diameter greater than that of the electrode. These larger droplets are acted upon by gravity, because the process does not develop a current density high enough to pinch them off. This generally limits successful application to flat position welds.

Spray Arc (axial spray) Transfer offers a very stable arc, and a high concentration of inert gas creates a very stable, spatter-free "axial spray" transfer mode. Raising the current level above a critical value, known as the spray transition current, causes the mode of transfer to change and creates a spray of very fine droplets that are formed and detached at the rate of hundreds per second. Transfer occurs as they are accelerated across the arc gap.

Surface Tension Transfer (STT) is a proprietary Lincoln Electric process that makes use of waveform technology to control current precisely, rapidly, and independently of wire feed speed during the entire welding cycle (Fig. 2). The Invertec® STT II power source (Fig 3) adjusts current automatically to the instantaneous heat requirements of the arc, decreasing it as the electrode first contacts the puddle, 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. Next, the current returns to a high level to establish arc length and form the next droplet before reducing to a medium or background value. This instantaneous control over the arc current eliminates the highly violent and explosive energy of short-arc MIG welding.

Pulsed MIG (GMAW-P) applies wave form control logic in another way, to produce a very precise control of the arc through a broad range of wire feed speeds. The pulsing process 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 precise control of arc dynamics allows the process to be used for fast-follow with high travel speeds or for fast-fill with high deposition rates. The Lincoln Power Wave 455 and other Power Wave power supplies are pre-programmed with optimal procedures for pulsed GMAW as well as all other applicable processes. This allows the operator to change many output variables by simply setting the proper material type. However, operators can adjust procedures when necessary by using controls provided in the system. Using appropriate software, customized waveforms can also be developed.

What's a Waveform?
A waveform is a representation of the dynamic, ever-changing output response of an arc welding machine to the actions of the electric arc itself. Every arc welding machine has a waveform characteristic. Simple machines rely on the design of a transformer and choke to produce a useable waveform. More sophisticated machines combine hardware design with electronics to produce optimized control of the waveform. Many modern industrial machines have mode switches that offer the user multiple waveform options from one machine. Through the use of computer software problems and advanced electronic control, Waveform Control Technology manages all aspects of the waveform to produce output dynamic characteristics tailored to the needs of a specific application. Typical waveforms are shown in (Fig. 4).

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