The Basics of Plasma Cutting
Action Stainless IT
Tuesday, June 16, 2020
Plasma cutting is a common process in most metal
fabrication shops. Developed in the 1960s, engineers took what they had learned
from welding machines to create a tool that could cut through thick metal by
simply speeding up the gas flor and reducing the size of the release hole. This
innovation led to increased speed and accuracy, as well as allowing
manufacturers to make different types of cuts in a wide variety of metals. We
will go over some of the basic components and operating principles below.
What Is a Plasma Arc?
In arc cutting, plasma is an electrically heated gas stream. By heating the gas to high temperatures, it becomes ionized, allowing it to freely exchange electrons between atoms which gives the gas its cutting amperage. By constricting the ionized gas stream with a nozzle, it concentrates all the energy to a small cross section.
Understanding Gas Swirling
Before we dive into the components of the plasma arc, we need to discuss the concept of gas swirling and the benefits it provides.
The biggest advantage is that swirling the gas increases cooling. By swirling the gas, the cooler, heavier, un-ionized gas atoms are thrown to the outside of the gas stream, providing a cooler protective barrier for the copper nozzle.
Swirling the gas also improves cut quality by evenly
distributing the arc along one side of the cut – this is due to the electrical
arc attaching itself to the leading edge of the cut. Without swirling, there
would be a bevel on both sides of the cut.
Starting the Arc
In a plasma torch, there are three main components working together: the
electrode, the gas/swirl baffle, and the nozzle. The electrode is connected to
the negative side of a DC plasma power supply while the nozzle is connected to
the positive side (note: the nozzle remains electrically isolated through a
normal open relay).
At the beginning of the phase, the power supply places a high negative voltage
on the electrode and gas begins to flow to the torch (while being swirled by
the baffle). This leads to the contacts in the nozzle circuit to close which
provides a path to the positive side of the power supply.
Once this point is reached, a high-frequency generator provides the
high-frequency, high-voltage potential between the electrode and the nozzle,
creating a small spark that ionizes a path through the gas. Through this path,
a larger DC arc begins to flow between the electrode and nozzle to create the
pilot arc, which is then blown out of the nozzle by the gas flow to contact the
The main arc is
created when the pilot arc transfers to the work material when the torch is
close enough. This is where the nozzle relay is opened and removes the nozzle
from the circuit, establishing a transferred arc condition and increasing the
main arc to the required cutting amperage needed for the job.
There are many variables to consider when plasma
cutting, but these are the absolute basics needed to understand how plasma
cutting works. For more information, feel free to contact Action Stainless with
your questions and follow us on LinkedIn!
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