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Practical TIG Welding: Frequency and AC Balance

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Frequency and AC Balance


00:00 - When we want to weld aluminium, we need to make sure that our machine has been switched to AC which as we've discussed stands for alternating current.
00:07 When we weld on DC or direct current, which we use for ferrous materials, the current is travelling from the electrode, the tungsten into the workpiece.
00:16 This is also known as electrode negative.
00:19 With alternating current, as the name suggests the current instead oscillates between travelling from the electrode into the workpiece and then travelling from the workpiece back to the electrode, known as electrode positive.
00:31 This happens pretty quickly at anything from 60 times a second through to several hundred times per second, depending on your machine's available settings.
00:40 This adjustment is called AC frequency and is measured in hertz.
00:46 We need to use AC when welding aluminium due the oxide layer that forms on the surface of the aluminium which melts at a far greater temperature than the base material beneath.
00:56 This means that we need the alternating current to break down the oxide layer before we can weld the underlying metal.
01:04 The fraction of a second that the machine is operating on electrode positive, it's breaking down the oxide layer and this is usually referred to as a cleaning action.
01:13 Then it switches back to electrode negative so that we can actually weld the aluminium.
01:19 The higher the AC frequency, the less time the arc is spending on each of the previously mentioned scenarios.
01:26 This means that the arc has less time to fan out and gives a focused, tighter and cooler arc and resultant weld pool.
01:34 This is useful in places where you need that focus like corner welds and when welding thinner materials.
01:41 A lower AC frequency on the other hand gives the arc more time to fan out and gives a wider and hotter weld pool.
01:48 This is then useful on thicker materials and fillet welds.
01:52 When talking about AC frequency, we also need to understand the AC balance because these two go hand in hand and need to both be adjusted accordingly.
02:01 AC balance is the percentage of time that the welder spends on each side of the alternating current wave.
02:08 Old traditional machines were fixed at 50/50 balance, meaning that the machine spent half its time on electrode positive and half on electrode negative.
02:17 This would in turn create a ball on the end of the tungsten due to the amount of time focused on the cleaning action.
02:24 It's harder for the arc to be stable when the tungsten is bald like this as it's not firing from a sharp point anymore.
02:31 Some welders still prefer to ball up their tungsten as it's how they learn to weld and this has become habit.
02:38 There's nothing specifically wrong with that and as we continue through this course, you're going to learn that a lot to do with TIG welding is not black or white and more comes down to your own personal preference.
02:50 With more modern inverter machines, we can adjust the balance down, allowing the machine to spend less time on the electrode positive side.
02:58 This means the cleaning side is reduced and thus less balling of the tungsten occurs.
03:02 It's still will ball a small amount but less than a traditional machine using 50/50 balance.
03:09 This reduced balling helps to keep a tighter more focused arc.
03:13 Hopefully after this explanation of frequency and balance, it's easier to understand how they both affect each other and how they're both important settings to adjust on your machine to get the desired finished weld.
03:25 It's worth noting that some machines display balance on electrode negative and some on electrode positive.
03:32 A quick way to find out which way your machine displays this setting is to turn the balance setting to 70% and strike an arc on some scrap alloy.
03:40 If the tungsten starts to ball up very quickly then the machine is showing this reading on the cleaning side of the wave, also known as electrode positive.
03:49 If on the other hand your tungsten tip remains sharp, then your machine is displaying electrode negative.
03:55 The AC balance is a setting that will need to be adjusted to suit your preference as well as the specific welding job.
04:01 However a good place to start is with a 70% penetration and 30% cleaning setting.
04:07 We'll see these settings in action and the effects of adjusting both frequency and balance later as we progress through the course.

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