Metal cutting can be categorized into two – mechanical and thermal cutting. Plasma cutting is a thermal cutting method where ionized gas is used for cutting the metal.
It is one of the most widely used techniques to cut thick metal plates but is also available for sheet metal. Before diving into the advantages and capabilities of plasma cutting, we should tackle another question.
What Is Plasma Cutting?
Plasma cutters work by sending an electric arc through a gas that is passing through a constricted opening. The gas can be shop air, nitrogen, argon, oxygen, etc. This elevates the temperature of the gas to the point that it enters a fourth state of matter, known as plasma.
Plasma cutting (plasma arc cutting) is a melting process in which a jet of ionized gas at temperatures above 20,000°C is used to melt and expel material from the cut. During the process, an electric arc is struck between an electrode (cathode) and the workpiece (anode).
The electrode is recessed in a water- or air-cooled gas nozzle which constricts the arc causing the narrow, high-temperature, high-velocity plasma jet to form.
Because the metal being cut is part of the circuit, the electrical conductivity of the plasma causes the arc to transfer to the work. The restricted opening (nozzle), which the gas passes through, causes it to squeeze by at a high speed like air passing through a venturi in a carburetor.
This high-speed gas cuts through the molten metal. The gas is also directed around the perimeter of the cutting area to shield the cut.
Unlike the oxyacetylene process, which is only used to cut oxidizable parts, the plasma-cutting process can be used to cut any conductive metal—aluminum, brass, cast iron, copper, steel, stainless steel, and titanium.
Though the plasma arc temperature is 40,000 degrees Fahrenheit, it is so constricted, and the cutting speed is so fast that the thermal distortion to the metal being cut is very minimal.
Plasma cuts are clean and often weldable with little or no additional cleanup, if the base metal was initially clean. Performed properly, the kerf it produces is a straight-sided cut with very little to no slag present.
Plasma Cutting Safety.
Plasma cutting produces sparks, smoke, fumes, and ultraviolet light. It is important to wear the proper eye and face protection; a shade-8 lens is recommended.
Proper ventilation is also required, as cutting materials that contain chromium, nickel, or that are galvanized produce fumes that can be toxic.
Never cut through paint or oil/dirty material, because as they burn off during the cutting process, they can produce hazardous smoke.
Because of the high level of open-circuit voltage, plasma cutting has an added electrical shock hazard. Make sure all surfaces around the cutting area, as well as you’re clothing and gloves, are dry. Turn off the power to the machine before changing any torch parts.
Never cut containers, tanks, or cylinders that may have held flammable materials. Even a small amount of flammable residue can cause fumes to accumulate inside an enclosed vessel, causing an explosion when cut.
Equipment.
Plasma-cutting machines can be expensive, costing several thousand dollars, but as technology advances are made and demand increases, companies are introducing smaller, less expensive small shop equipment.
If you regularly need to cut steel, stainless steel, and aluminum, this machine can be worth the cost. Small, 115-volt plasma cutters are available that will cut up to 3 ⁄8″ material. Larger 220-volt machines can cut thicker materials and have a higher duty cycle.
Aluminum and stainless steel require higher amperages for cutting, so check to make sure the machine can cut the materials with which you typically work.
Most plasma cutters require a compressed air source. Any shop air compressor that can deliver a constant 65 to 80 psi will be sufficient. It is critical that a filter and or water separator unit be installed to keep the air dry and oil-free. Follow the manufacturer’s directions for installation and placement of the unit.
Some plasma cutters have an internal air compressor—these units are more expensive and typically require more maintenance.
Most plasma torches have a manual switch on the torch body (handle). The cutting tip, electrode, and nozzle are consumable parts, so check these parts frequently for wear and replace them when necessary.
Precutting Checklist:
- Compressed air fittings are tightly attached.
- The cables are in good condition.
- Ventilation is sufficient to remove fumes from the cutting area.
- The work area is dry.
- Flammable materials are removed from the area.
- Sparks and slag from cutting will be contained.
How To Plasma Cut?
Check the manufacturer’s recommended settings for the material to be cut. Arrange the material on a cutting table and determine the most comfortable cutting position. Attach the work clamp to the workpiece or welding table. Dry run through the cutting motion to practice speed and cutting position.
Check the manufacturer’s directions for the arc-starting procedure. Most current machines are designed to drag the nozzle directly on the material’s surface. Activate the arc and hold the torch perpendicular to the surface of the material. Move steadily and smoothly along the entire length of the cut. Do not stop the arc until you have passed through the end of the cut.
A good plasma cut has squared edges, small vertical ripples, and little or no slag.
Plasma Cutting Troubleshooting & Techniques
A high-quality circle-cutting attachment for a plasma cutter is expensive, but worth the investment if you are making repeated circle cuts. Inset: This unit comes with a magnetic pivot holder for steel and a suction cup pivot holder for all other metals.
Arc Does Not Start.
Solutions:
- Connect the work clamp to a workpiece.
- Turn on the power source.
- Tighten cable connections.
- Make sure the electrode is in working condition.
Cut Does Not Penetrate Through Material.
Solutions:
- Cut more slowly.
- Make sure the torch is held perpendicular to the material.
- Make sure the machine is capable of cutting that thickness.
- Increase amperage setting.
- Verify correct airflow and pressure.
Excessive slag or dross is generated.
Solutions:
- Increase cutting speed.
- Decrease torch standoff distance.
- Replace worn torch parts.
- Adjust the amperage setting.
Torch Parts Are Consumed Quickly.
Solutions:
- Install or replace the air filter to prevent oil or water from reaching the torch.
- Cut metal within the capability of the machine.
- Make sure the gas pressure is correct.
Making a good-quality plasma cut is dependent on a consistent travel speed. Consult the owner’s manual for cutting speeds for different material thicknesses and amperage settings. With the machine off,
practice moving across the planned cut at the correct speed.