Let’s have a brief discussion of Pulsed MIG Welding before we go on with its application…

What is Pulsed MIG?

Pulsed MIG/MAG welding is a variant of the conventional MIG/MAG welding process in which the current is pulsed. Pulsing was introduced originally for control of metal transfer at low, mean, current levels by imposing short duration high current pulses. The cycle consists of applying the repeated pulse current over a constant background current.

Modern welding sets allow the use of a wide range of pulse amplitudes, durations and waveforms at frequencies from a few Hertz to a few hundred Hertz. Pulse amplitude and duration are best combined to melt and detach a single droplet of the same/slightly smaller diameter as the electrode wire. Selection of pulse parameters for a given wire feed speed is a complex operation. Pulse height and duration are a function of wire composition, diameter and to a lesser extent, shielding gas composition. This has led to the advent of Synergic welding sets.

The Major advantages of pulsed MIG welding are:

• It allows the use of smooth, spatter free welding at mean currents (50-150A), which would otherwise be too low for all except dip transfer with it’s irregular transfer and associated spatter.
• Pulsing can extend spray operation below and through the natural transition (180-220A for 1.0-1.2mm mild steel wire) from dip to spray where globular transfer would normally occur.
• Pulsed transfer is midway between the spray transfer and the dip transfer mechanism, which can be too ‘cold’ (due to non-continuous arcing; the arc effectively ‘goes out’ between each melting cycle). This makes it ideal for welding thicker sections where more heat is needed but for which spray transfer is still too ‘hot’.
• Pulsed MIG allows welding at higher deposition rates in all positions where dip or spray transfers are not applicable.

When MIG welding on stainless, you usually have three choices of transfer depending on your equipment: spray-arc, short-circuiting, or pulsed-arc transfer.

Here, we will be concentrating on Pulsed-Arc Transfer.

Let’s have a quick overview of what Pulsed-Arc Transfer is…

Pulsed-Arc Transfer

The pulsed arc process is normally a process wherein one small drop of molten metal is transferred across the arc for each high current pulse of weld current. The high current pulse must be of sufficient magnitude and duration to cause at least one small drop of molten metal to form and be propelled by the pinch effect, from the end of the wire to the weld puddle. During the low current portion of the weld cycle, the arc is maintained and the wire is heated, but the heat developed is not adequate to transfer metal. For this reason, the time duration at the low current value must be limited otherwise metal would be transferred in the globular mode.

The Challenges with conventional MIG welding are minimized through Pulsed MIG

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MIG Welding sheet metal efficiently involves obtaining good fusion while simultaneously controlling:

• Heat input
• Weld bead profile
• Arc starts/stops
• Arc maintenance

Pulsed MIG has good control, and with the proper settings, together with a well-trained welder, the job could have a near flawless result.

Pulse MIG Welding Stainless Steel

Stainless steel does not adequately dissipate heat when welded. Instead, it holds heat in the area where the welding arc is concentrated, which can lead to warping and rust. Manufacturers scrap warped parts, which wastes time and materials. Plus, it can be the biggest hurdle when trying to meet production goals.

Stainless parts can rust because excess heat concentrates carbon in the heat-affected zone, where it becomes trapped as the metal cools. Given time, the area overloaded with carbon will rust. This phenomenon is commonly called carbide precipitation or “burning out the chrome.” Burning out the chrome counteracts stainless steel’s defining property, which may, in turn, increase warranty costs.

Wire diameters of 0.8mm/0.030″, 0.9mm/0.035″, and 1.2mm/0.045″ are most commonly used with this process. Gases for pulsed arc welding are argon plus 1% oxygen, the same as is used for spray arc welding. These and other wire sizes can be welded in spray transfer mode at a lower average current – with pulsed current – than with continuous weld current. The advantage of this is that thin material can be welded in spray transfer mode, which produces a smooth weld with less spatter than short circuiting mode. Another advantage is that for a given average current, spray transfer can be obtained with a larger wire. Larger diameter wires are less costly than smaller sizes, and the lower ratio of surface to volume reduces the possibility of weld contamination from surface oxides.

Pulsed MIG welding characteristics are excellent with lower currents. There are many advantages with the process including low spatter, penetration without melt-through and excellent operator appeal.

Aside from all that would be the importance of picking the right equipment for the job. So if you would need assistance with choosing the equipment for your fabrication and manufacturing needs – whether you’re in the Brisbane area or any part of Australia, don’t hesitate to contact us and we’ll provide you with the right gear to get the Job done…here at Weldmax, we are always aiming high!