The Anatomy of a Great Plasma Cutter
The manufacturing industry counts on various types of machinery to cut and shape all sorts of metals and alloys. The transportation and construction sectors, for instance, are just two from a nearly endless list that require metal components produced accurately. So, how do companies manufacture the steel trusses that make up the span of a suspension bridge or the metal that becomes the massive wing of an airplane? Often, they use a plasma cutter.
Although plasma cutters may not be as well-known as some other metal-cutting machinery, they have been around since World War II. During that time, they were used for welding the armor and aircraft components that would eventually lead to the defeat of the Axis powers.
Several years after the war, engineers found that they could increase temperatures with the combination of speeding up the flow of gas and shrinking the release hole. These systems could reach temperatures that allowed them to work as a saw, cutting through the toughest metals with relative ease.
With this revolutionary plasma arc, manufacturers could now cut any metal with both speed and accuracy. And while it might sound like science fiction, it's nothing more than innovative science. Here's how it works:
What is Plasma?
As we all learned in school, there are three states of matter: solids, liquids, and gasses. Applying heat (energy) to a solid block of ice breaks its molecular bond and turns it into water. With enough heat in the water, it becomes a gas. But what happens if you subject gas to extremely high temperatures? You create plasma.
All this heat and energy breaks apart the gas molecules, causing its atoms to split. Under normal conditions, atoms are made up of protons and neutrons in a nucleus that is surrounded by a cloud of electrons. In plasma, the electrons separate from the nucleus and begin to move rapidly. The negatively-charged electrons leave behind their positively-charged nuclei, a.k.a. ions.
When these speeding electrons collide with other electrons and ions, they release tremendous amounts of energy, which is what provides plasma with its exceptional cutting power.
How Does a Plasma Cutter Work?
Plasma cutters operate by sending an electric arc through a gas that is passing through a restricted opening. There are options for the type of gas: nitrogen, oxygen, argon, or just plain shop air. This process boosts the temperature of the gas to the point that it enters the fourth state of matter mentioned earlier—plasma.
The electrical conductivity of the plasma causes the arc to transfer to the metal, completing the circuit. The constricted opening, which is called a nozzle, causes the gas to squeeze through at an extremely high speed, cutting through the molten metal. The cutter nozzle has a second set of channels that release a constant flow of shielding gas around the cutting area. The pressure from this flow of gas controls the radius of the plasma beam.
What Are the Main Parts of a Plasma Cutter?
Modern plasma cutting machines consist of these plasma cutter parts:
- A light-weight unit
- Torch cable
- Ground cable
- Power cable
- Torch head
On the front of a typical unit is a control panel on which an operator can adjust air pressure, amperage, and post flow to cool the torch. There will also be an air pressure gauge.
The consumables are part of the torch and include the nozzle, which is responsible for constricting the ionized gas stream and focusing the energy to a smaller cross-section.
The electrode is another consumable whose primary function is to provide power to the plasma arc, connecting to the negative output from the power supply. Its secondary purpose is to conduct high-voltage energy when a start input is given to the system, adding energy to ionize the cutting gas, and allowing the plasma arc to start.
The gas baffle is also a consumable. Sometimes referred to as the swirl baffle, it "swirls" the gas and distributes it evenly along one side of the cut, providing it with a sharp, clean look.
The torch head and its components control the cutting process, but a trained and experienced operator will have an impact on the quality of the cut and its kerf.
The diagram below provides a detailed look at the anatomy of the PrimeWeld CUT60 Dual Voltage Plasma Cutter:
Diagram of PrimeWeld CUT60 Dual Voltage Plasma Cutter
Parts list for PrimeWeld CUT60 Dual Voltage Plasma Cutter
What is Kerf?
Kerf is simply the width of material removed during the cutting process, and three variables have a direct effect on it, all of which are controlled by the plasma cutter operator:
Cutting Speed: Moving the cut faster will produce a narrower kerf. The operator could increase the cutting speed to a point at which there will be a loss of penetration. On the other hand, slower travel speeds will give a wider kerf and a too slow can result in the loss of the arc.
Cutting Amperage: By increasing the cutting amperage and keeping the other two variables constant, there will be a wider kerf. Continuing to boost the current will widen the kerf and could eventually destroy the nozzle. Decreasing the amperage will result in a narrower kerf and could lead to loss of penetration.
Standoff: The distance between the torch and the work-piece during cutting is known as standoff. Increasing the arc voltage requires an increase in the standoff distance and widens the kerf. Increasing the standoff will eventually lead to a loss of the cut, while lowering it will result in a narrower kerf and, once again, loss of cut.
Even the best plasma cutter is only as effective as the person using it. And even though many of today's models are considered to be "user friendly," a certain amount of training and experience will translate into the desired results.
Plasma Cutter Sizes and Capabilities
There are large plasma cutters with one-hundred-foot tables that have robotic arms to make their cuts. And, on the other end of the spectrum, there are excellent compact, handheld units to be found on construction sites, in machine shops, and the garages of many hobbyists. No matter what size they are, all plasma cutters work on the same principle and are generally manufactured around the same design.
That's not to say that all plasma cutters are made of the same quality or provide exceptional value for their price. But here is one that meets all the criteria for an excellent plasma cutter at a price that fits into just about anyone's budget: the PrimeWeld CUT60 Dual Voltage Plasma Cutter.
Front panel view of PrimeWeld CUT60 Dual Voltage Plasma Cutter
Rear panel view of PrimeWeld CUT60 Dual Voltage Plasma Cutter
What Makes a Plasma Cutter Stand Above the Crowd?
Once prohibitively expensive, plasma cutters were used exclusively for the most significant metal-cutting jobs. Today, however, plasma cutters, such as the CUT60, have become an essential part of so many industries. They are very popular in custom auto shops for creating chassis and frames, while construction companies employ them to cut and fabricate steel beams and sheet metal. Even locksmiths are using plasma cutters to bore into vaults and safes after their customers have been locked out.
Most of today's best plasma cutters, including the CUT60, use a pilot arc between the electrode and nozzle to ionize the gas and generate the plasma before the arc is transferred. Other methods include touching the torch tip to the work to create a spark and using a high-frequency starting circuit that works much like a spark plug.
Price is almost always a consideration (the very popular CUT60 is moderately priced at $649)
Other things to look for when purchasing a plasma cutter include:
- User-friendly operation: find one you can learn to use quickly and safely
- Portability: light-weight units that go anywhere and can easily be attached to generators or welders
- Low power consumption
- Fine-quality cuts