Welder Inverter Waveforms
Credit to Mark Fedkin
What is sine and square wave?
A Sine is an electrical current which reverses direction, also known as Alternating Current. Its waveform can be represented by smooth periodic oscillation, in plain English this is a smooth curve through each peak and trough of oscillation. This means the polarity is in a constant state of change.
AC is most frequently used in residential and commercial settings, as this power is originally created by rotating machines called an alternator.
A Square Wave is a steady frequency between two fixed points, the maximum and minimum frequency. Unlike a sine, the square will switch instantaneously between its minimum and maximum frequency with the same duration at both ends of the spectrum.
Lincoln are the primary manufacturer of square wave machines on the market, - you may find welder reviews helpful in semester 2 when we see how different waveforms affect different applications in welding. We will touch on this more in our next lecture.
The ratio between the high and low period is called a duty cycle, with a typical duty cycle being 50% (half of the time at maximum, half of the time at minimum frequency). Miller have a good discussion about duty cycles which you may find useful when we start welding in practical exercises.
Advantages of a sine inverter
Gives the soft-arc feel provided by conventional power sources, whilst also being able to use square transitions to eliminate the need for continuous High Frequency to maintain the arc.
Disadvantages
As a larger duration of the wave near or at zero volts, it can extinguish itself. To help remedy this issue, High Frequency arc stabilization is needed, especially when welding Aluminum.
Without this technology your arc can extinguish, or will lead to poor weld quality. These systems aren’t always perfect which reduces your productivity compared to a square inverter machine.
Advantages of square inverter
Squarewave is more efficient compared to sinewave, as sinewave spends most of its time either rising or falling from its maximum frequency. As there is a smaller amount of time where the voltage is at zero or near it, meaning it’s more difficult for the arc to extinguish.
Therefore as Squarewave spends more time at its peak, it needs less time at electrode positive for cathodic cleaning. This enables you to bias your balance towards electrode negative which will heat the work piece, but still have the option for more cleaning action if needed.
As you have greater control over the Electrode Positive and Negative, you can achieve better arc stability therefore getting a neater looking weld. Most square wave machines also offer balance control, allowing you to vary the percentage of time that the electrode is negative which heats up the workpiece, versus electrode positive which cleans surface oxidation.
AC Balance also helps reduce arc rectification whilst welding Aluminum in AC.
Disadvantages
SquareWave technology can only be used on your welders AC mode, and isn’t compatible with DC. Due to Direct Current having one stable voltage with no wave, it’s not possible for an inverter to convert to AC without additional equipment.