What is a Pulse MIG? A how & why a guide to Pulse MIG welding

What is Pulse MIG Welding? 

Pulse MIG offers fast, high quality, low spatter and consistently great-looking welds, with better thermal control vs. conventional MIG welders. 

Pulse MIG is best known as a great process for welding aluminium, however, it is also an excellent process for welding with stainless-steel and bronze wires. In many cases, Pulse MIG can achieve results that are comparable to TIG welding, but with speed and productivity that is superior to TIG. 

In technical terms, Pulse MIG is a highly-controlled spray-transfer MIG process. Unlike the traditional ‘short-circuit’ MIG process, the filler metal is transferred from the wire to the weld pool, without the wire contacting the weld pool. The current alternates, or pulses, between a high peak current and a low background current at a frequency of up to several hundred times per second. With each pulse, the peak current pinches off a droplet of wire and propels it to the weld joint, while the background current maintains the arc at a low enough power level so that short-circuit can’t occur.

Why use Pulse MIG? 

Among other benefits, Pulse MIG is best known (or desired) because it offers;

• Lower heat = minimal distortion, reduced burn-through
• Reduced spatter: Spatter is significantly reduced, or even eliminated = Minimal cleanup
• Visually appealing welds = Added value to the finished product
• Higher deposition rates = Increased efficiency & faster travel speeds
• Tighter weld pool control = Ideal for out-of-position welding 
• Reduced welding fumes = Safer & cleaner work environment

What metals can you weld with Pulse MIG?

Pulse MIG is ideal for metals and applications where controlling heat is difficult when using a standard MIG process, and/or where high weld quality and appearance are desired. 

Pulse MIG welding Aluminium

Aluminium is a high thermal conductor (which means that heat is quickly transferred away from the weld pool), with a relatively low melting temperature. The pulse MIG process allows the operator much greater thermal control to apply enough heat for a successful weld, whilst avoiding distortion or burn-through.  

Pulse MIG welding with Bronze wires (MIG brazing)

Bronze wires are typically applied at a temperate that is lower than the melting point of the parent material – where the materials are essentially “stuck” rather than welded together – and are commonly used on thin materials (eg car body panels) where low-temperature welding is essential to avoid distortion. Also commonly used on galvanised or zinc-coated steels (up to 2mm thickness) because the weld metal does not rust and the lower application temperature prevents disturbance (evaporation) of the zinc coating.  The ability to control and reduce heat makes pulse an ideal process for brazing wires.  

Pulse MIG welding with Stainless-Steel

Because stainless steel is a poor thermal conductor, heat is typically ‘trapped’ close to the weld zone. This can result in expansion/distortion and rust contamination due to concentrated carbon in the weld zone. The weld pool is comparatively sluggish with poor wetting/flow into the parent metal. The pulse process allows stainless wires to be applied at lower temperatures to minimise distortion and imperfections. Pulsed MIG is especially beneficial for welding thin stainless material where it is often extremely difficult, if not impossible, to avoid warpage/distortion with the conventional MIG process. 

In all these applications, Pulse allows successful welding at lower temperatures with much better control of the weld pool. 

Pulse MIG welding mild steel

Mild steel does not present the same “thermal challenges” as other metals like aluminium or stainless, and therefore pulse does not necessarily offer the same advantages. For this reason, conventional MIG (rather than pulse MIG) is still the best process for welding mild steel in many applications – especially in the material thickness range that is achievable with single-phase machines.

Pulse MIG can offer some productivity advantages for welding heavy steel, however, this requires a high “peak” current which is available only from three-phase pulse machines.

For this reason single-phase pulse machines like the MIG-230 PLUS MIG MAG IGBT Inverter Welding Machine don’t offer a pulse mode for mild steel – although the 220MP does offer excellent results when welding mild steel in non-pulse modes, including welding thin materials down to 0.5mm, thanks to the ATC (Advanced Thermal Control) technology. 

What is Double-Pulse MIG? 

Also known as dual-pulse or pulse-on-pulse (PoP), this adds an additional pulse ‘wave’, where the current alternates (or cycles) between the main current level and a secondary current level. This effectively multiplies the benefits of single-pulse, with even better thermal control, weld quality and appearance.

Pulse MIG vs TIG Welding

TIG is traditionally the go-to process when there is a need to weld materials to a higher standard (quality and/or appearance) than conventional MIG. Aluminium and stainless steel are commonly welded with TIG, as these materials are often used in projects where the finish of the final product is critical – for example; boats & marine, architectural fixtures, food handling equipment, etc.

The disadvantage of TIG is that it is a comparatively slow & inefficient process, which increases cost and processing time. 

Enter Pulse MIG! Essentially, Pulse MIG offers;

• Weld quality and finish comparable or very close to TIG in many applications
• Superior speed and efficiency vs TIG
• Compared to TIG, typically requires less skill and is easier to learn, which reduces training time 

While the TIG process will always have its place, Pulse MIG is certainly replacing TIG as the logical choice for many applications, especially production work. 

Pulse MIG Weld Cycle, Settings & Adjustments

If you’re new to Pulse MIG, one of your questions is likely going to be;  What are the different parameters and adjustments involved with MIG pulse welding? 

This is best answered by looking at the typical pulse MIG ‘wave’ or weld cycle, as shown in this diagram:

As follows are the main ‘components’ of this cycle and the associated adjustments.

Note that most reputable pulse MIG machines have synergic control, where the Volts and Amps/Wire Speed are adjusted together automatically.  For the sake of simplicity, we are going to refer to these collectively as “Current”.

Start Current: Current level at the start of the weld. Usually set as a % of the main current. When welding aluminium, typically this will be higher than the main current, to help break through the oxide layer for a clean start to the weld. 

Start Current Time: Duration of start current.

Main Current: Main welding current/amps.

Secondary Current: Also known as Background Current, this applies to double-pulse only. Usually set as a % of the main current. Typically this will be lower than the main current for a cooler weld pool. 

End Current: Current level at the end of the weld. Usually set as a % of the main current. Typically this will be lower than the main current. End Current & End Slope work together to prevent/minimise ‘craters’ etc for a clean & aesthetic finish to the weld (also known as crater fill).

End Current Time: Duration of end current.

Start Slope Time: Duration of the gradual change in output from start current to main welding current

End Slope Time: Duration of the gradual change in output from main welding current to end current

Pulse Frequency: Used in double-pulse only. Adjusts the pulse ‘cycle’ (main current pulse, followed by secondary current pulse) frequency in Hz (cycles per second)

Pulse Balance: Used in double-pulse only. Adjusts the length (%) of the main current pulse within each cycle. Increasing this % means the main pulse will be longer and the second pulse will be shorter. Typically main current setting will be higher than the secondary current, in which case increasing balance % will increase ‘heat’.

Arc Length (also known as arc control or trim): Adjusts the distance from the end of the wire to the weld pool. If the arc length is too short (longer wire stick out) the arc will be very ‘crackly’ and produce a lot of spatter. If too long this can make the weld black and cause porosity. 

Single-Phase vs Three-Phase Pulse MIGs

If you have ready access to a 3-phase power supply, then it usually makes sense to opt for a 3-phase machine for higher output and capacity. However, if you don’t have this luxury, or just prefer the portability of single-phase, then there are a few factors to be aware of.

There’s a good reason why there are fewer options on the market for single-phase (230/240V) pulse MIG machines. These present a particularly difficult challenge for welder manufacturers. Pulse is more complex, with multiple current levels (start, base, peak, secondary & end current), which all have to be factored into the limited input & output power range that is available from a single phase.  This makes it challenging to develop a machine that works well, and it also impacts the capacity or the maximum thickness that a single-phase pulse MIG can weld. 

What is the maximum thickness you can weld with a Pulse MIG?

This firstly depends on whether the machine is 240V/single-phase or 3-phase. With 415V of power to draw from, three-phase machines, are typically capable of welding up to 10-20mm thick material or even more (depending on their rated size). 

Single phase Pulse machines are typically able to weld up to 5-6mm maximum if they are in pulse mode. Here’s a few points to be aware of;

• Pulse mode requires higher output (amps) than non-pulse, which means that the ‘maximum weldable thickness’ will be less in pulse modes than it will in non-pulse modes. 
• The same applies to single-pulse and double-pulse: Single-pulse will typically allow welding of slightly heavier materials compared to double-pulse.
• In NON-pulse modes (essentially turning the machine into a conventional MIG), single-phase MIGs can weld 8-12mm material, depending on their rated size.
• The maximum thickness capacity can vary from one application to another. One important factor is the ‘heat sink’. Larger workpieces absorb more heat than smaller components (especially aluminium which is a very good thermal conductor), which means more/higher current is required, which then reduces the maximum weldable thickness.

What to look for in a Pulse MIG welder

Pulse MIG can open up a lot of new opportunities for your workshop or fabrication business, and improve your productivity.  However, the pulse is much more complex and costly than conventional MIG, which makes it important to choose a machine that will give you the best results and return on your investment in the long term. Here are a few points to keep in mind;

Single-Pulse or Double-Pulse?  Double-pulse takes the benefits of a single pulse (weld quality, finish, etc) to a new level. Not all pulse MIGs will have double-pulse mode. Single-pulse can be considered as an “entry-level” option if you are learning or trialling pulse MIG, and will typically have fewer features and adjustments. However many operators nowadays prefer double pulse. Check the machine specs so you know what you’re getting. 

Track Record: It’s a fact that when it comes to developing a truly functional and reliable Pulse MIG, many welder manufacturers have tried and failed. As they say ‘nothing beats experience, and this is certainly true when it comes to pulse. So our best advice is to choose a proven machine from a well-established manufacturer. 

Simple vs Complex: Pulse welding is much less forgiving than conventional MIG and often it’s the little things – for example, a slightly loose connection, or an incorrect setting – that can make the difference between a happy result or a frustrating waste of time. It’s easy to be wowed by a lot of features and options, but keep in mind that this also adds to the “list of things that can go wrong”. The most reliable and user-friendly pulse machines are typically those with a comparatively simple design that is primarily focused on pulse MIG function. 

Controls: Sadly, it’s not uncommon to find operators who have been lured by the benefits of pulse, but have found their machine difficult, confusing and time-consuming to learn and operate. On the other hand, controls that are intuitive and easy to follow will maximise your welding time, minimise downtime…. and make it much easier to train new operators.

Single Phase?  As we have already covered earlier in this article, producing a single-phase Pulse MIG that works well is a very challenging task. Once again, look for a reputable and experienced manufacturer, and be wary of single-phase pulse machines that are ‘loaded’ with other functions not related to pulse MIG.

Wire feed system: With pulse, it is critical that wire feeding is 100% consistent and reliable. Reputable drive systems are often made by specialist manufacturers who then provide this componentry to welding machine manufacturers, so it pays to dig into the detail of where the drive system comes from and its track record. The robust build is important, but other less obvious aspects are also critical, such as whether the system is purely mechanical or does it electronically synchronise with other machine controls. 

Push-Pull Ready?  Once you get the hang of pulse welding, you’ll likely want to do more of it. A push-pull torch (typically 8m long) is a great way to extend the reach and portability of your machine, especially when welding aluminium were using conventional torches longer than 3m can be troublesome.  In the case of push-pull torches, both the torch ‘pull’ motor and the machine ‘push’ motor must be synchronised – which means that the torch and the machine need to be compatible with each other. With this in mind, you’ll not only want a machine that is “push-pull ready”, but you also want to make sure that;  a) there’s a push-pull torch available specifically to suit the machine you’re looking at, and b) the torch is a tried & tested quality design from an experienced manufacturer to ensure you get reliability and value from your investment. 

How much does a Pulse MIG cost?

Welders with MIG Pulse function (that are readily available from reputable suppliers and brands in Australia) range from around $3,000 up to $15,000… or more. 

Here are some of the main factors that influence the cost;

Pulse MIG – vs – a MIG with Pulse
There’s a big difference between a machine that has been designed ‘from the ground up to be a pulse MIG and a machine that is primarily designed as a conventional MIG with a pulse as an added feature.  
‘Professional’ pulse MIGs traditionally start at around $4,000-$6,000. These will have all or most of the settings outlined above, including double pulse, slope up/down, frequency, arc length, etc. Also, a reputable manufacturer will have invested a lot of time/experience/money fine-tuning these features and the parameters that are built into each program for different materials, material thickness, etc. This doesn’t mean that the machine won’t have other functions (such as conventional MIG, TIG or stick), however, it is first and foremost a pulse MIG. 
By comparison, some machines may have a pulse MIG function but are essentially a conventional MIG (or multi-function MIG/Stick/TIG) with a pulse as an added feature. These are often available at a lower cost (some less than $3,000) and can be a good option for a ‘beginners’ pulse MIG. However, usually, they will lack some of the functions, adjustments and ‘programming smarts’ found on professional pulse MIGs. 

Size and Output
Welders with higher output obviously cost more. Single-phase pulse MIGs start from around $3,000-$5,000, and three-phase pulse MIG typically range from $5,000-$15,000. 

Country of Manufacture
It’s no secret that the majority of conventional MIG welders sold in Australia are made in China, due to their lower price point. Chinese manufactured machines with Pulse MIG function are also becoming available, however, it should be noted that compared to conventional MIG, Pulse MIG technology is much more complex and difficult to get right. This is especially the case with single-phase pulse machines, where a lot has to be ‘packed’ into the limited input/output power available from a single phase.
For this reason, most professional pulse MIGs come from manufacturers in Europe or the USA who have many decades of experience in developing pulse technology and can deliver a product that is tried, tested and proven… with the necessary features and software intelligence to give the operator control and confidence. 

Warranty and Support
The following aspects can increase the cost of a machine, because of the higher cost and investment involved for the manufacturer/supplier;
> Well thought out machine controls that are easy to learn and use
> Longer warranty period 
> After-sales support, including the availability of technical/service staff/agents
> User manual that is comprehensive and easy to follow