Pulse welding is a form of welding in which the amperage alternates between a high point and a low point. It keeps the overall heat input of a weld low while still getting proper penetration.
How often it pulses, what the peak amps are, what the base amps are, and how long it spends on either amp setting can all be adjusted to suit the weld you’re doing.
Pulse Frequency/Pulse Hertz
The pulse frequency or pulse hertz are the same thing: the number of pulses per second. For example, the UNIMIG AC/DC machines have a pulse frequency range of 0.5-200Hz per second. That means that 1Hz equals one pulse per second, and 50Hz is 50 pulses per second.
One pulse per second is relatively slow and easy to follow with your eyes. 30 pulses or more is pretty fast, and it’s hard to see the individual pulses. Anything between the 5-30 pulse range is painful on the eyes. It’s kind of like staring at a strobe light, which is super unpleasant to look at and really hard to concentrate on timing a weld with.
When it comes to picking how many pulses a second you want, it really depends on the application. If you’re welding thin material, then a fast pulse is usually better, and it will leave a high profile bead. If you’re welding thick material, then a slow pulse is usually better, and it will leave a low profile bead.
Pulse Percentage (%)
The pulse percentage is the amount of time spent in the peak and base amps for each pulse. If you set the percentage to 50%, that means 50% of the pulse cycle will be the peak amps, and 50% of the pulse will be the base amps.
You can adjust this either way, where 90% is almost entirely peak amps and 20% is almost no peak amps. The more time spent on the peak amps part of the pulse, the more penetration you’re going to get and vice versa.
Pulse welding with TIG is done almost the same way as standard TIG welding. There are just a few extra settings to adjust on the machine first. But, when you pulse weld with TIG, you can feed your filler rod in two ways (rather than one).
- The first way is your standard dabbing. Depending on how many pulses a second you’ve got it set to, you can dab on the peak and pause on the base amps. If you’re only on one pulse per second, this isn’t too hard to get used to. However, if you’re welding at around 50 pulses a second, your dab time can just be consistent, as there’s not really a way to time it with the pulses because your eyes almost can’t see them anymore.
- The second way is to just lay the wire in the joint. Now, you don’t just lay it flat and weld over it, but instead, you have the tip of your rod in the leading edge of the puddle, and you drag it down the weld, keeping it in the leading edge so that it melts in.
Both techniques work, and you can do either regardless of your pulses per second, but if you use the lay method on high pulses, you won’t get the stacked dimes look. It’s still a good, penetrative weld, but it just won’t be as aesthetically pleasing.
You can still use your foot pedal when you pulse as well. You can hold it at full throttle and have your peak amps sit at what you set them to, or you can pulse within the pulse.
What that means is if you’re pulsing along and you still believe that the weld is getting too hot, you can ease off the pedal, lowering the peak amps in the pulse. Your background (base) amps will remain the same, but the high part of your cycle will be slightly cooler.
For example, say you’ve set your machine to a peak amps of 200 and your base amps to 50. Holding the foot pedal down will leave your peak amps at 200 for the whole weld.
However, if you were to ease up on the foot pedal, your peak amps would reduce, say to 150, while your base amps would remain at 50. So, overall, the entire weld would cool as your peak amps aren’t as hot.
Then if you decided you needed more heat again, you could go back to full depression of the pedal and increase back to your original 200 amps.
There are two kinds of pulse MIG welding:
Single Pulse – Single pulse MIG is a type of spray transfer that, like TIG, alternates between the peak current and the background current.
MIG pulsing is generally spatter free because the wire never actually touches the weld. Droplets of metal are ‘sprayed’ into the weld on the peak part of the cycle.
The background current of the pulse cycle isn’t hot enough to transfer metal. It simply maintains the arc. It produces all the benefits of spray transfer (speed, no spatter, deep penetration) without all the excess heat.
Single pulse MIG welding sounds similar to an AC TIG weld, with a constant high pitched buzzing.
Double Pulse – Double pulse is two pulses that happen simultaneously.
The first pulse is your standard (see: single) pulse with a peak amp and a base amp.
The second pulse, which doesn’t transfer any wire, turns the first pulse on and off in its cycle. During this second pulse, the arc remains on, but the temperature is so low there is no welding happening.
When the second pulse is ‘on’, the first pulse takes over (turning on) and alternates between the peak amps and base amps, creating the weld the same way a single pulse does. When the second pulse is ‘off’, nothing is happening.
The ‘off’ part of the second pulse can be adjusted to be hotter or colder, but its purpose is to give the base material a moment to cool. In order to make the most out of a double pulse, leaving the base of this cycle low is recommended.
Double pulse MIG welding is a cooler procedure as there’s even more downtime between the high amperage moments, so you need more amps in the peak to get full penetration.
It’s great for a good-looking weld because it creates the stacked dime effect of TIG with a MIG machine and no effort from the operator. It has an on-and-off high pitched buzzing that accompanies it.
These processes can either be synergic, in which the welder makes your life really easy and picks all the best settings for you. Or, it can be non-synergic, and you’ll have to input every value yourself (which, let’s be honest, takes some serious trial and error, especially when it comes to the double pulse).
While the arc itself doesn’t look like it’s pulsing, it definitely sounds different to a normal MIG weld, whether you single or double pulse.
Despite it sounding convoluted and confusing, making the actual weld while pulse welding with MIG is just like standard MIG welding. Once the machine is set, just press the trigger on your torch and weld along the joint. It does the rest for you.
Why should you pulse weld?
Pulse welding focuses the arc and keeps the bead smaller, so it stays in place. Not only is it easier to control, but you still get full penetration.
When you enter the base amps part of the pulse cycle, the puddle freezes, and that moment of cool helps the weld to sit down flat. The longer you spend in the background amps, the better the ‘puddle freeze’, which is what creates the stacked dimes look.
Pulse welding also totally eliminates spatter, so you won’t have any post-weld clean up.
When should you pulse weld?
Out of position welding
The cooling of the puddle that keeps it small means it’s not as likely to drip. If you’re welding out of position, then using the pulse will keep the weld where it’s meant to be, rather than on you.
Pulse welding is a cooler process than standard welding because of the moments of low amperage. With less heat in the metal, you get less distortion, which is perfect for thin materials.
Different metal thicknesses
Like with welding out of position, the pulses help hold the weld puddle exactly where you want it, which makes it much easier to weld thin pieces to thick pieces. It’s especially true when welding a lap joint that’s made up of two different sizes. You don’t need to worry about the pool spilling over the top edge.
Stainless steel, aluminium and other high thermal conductivity metals
Not only is pulsing good for keeping the distortion out of sheet metal, but it’s also often used with metals that are known heat sinks. The cooler welding provides all the needed penetration without having to blast the metal with too much heat.
Having the ability to weld without putting excess heat into the metal makes filling holes a lot easier. There’s way less chance of blowing further through a hole (or through metal in general) with the lower heat levels.
It’s not really an issue when you’re TIG welding anyway, but reduced spatter when you’re MIG welding means less clean-up once the weld is done.
Pulse welding isn’t the only way that works with any of these applications, but it certainly makes some of the more difficult kinds of welding a lot easier.