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Getting Started in The World of CNC Plasma Cutting - Part 2

News Tips and Advises Tutorials

   There are many ways to cut a variety of materials. However, plasma cutting is becoming the preferred choice when cutting conductive metals. Whether your metal is being cut by hand or through a CNC (Computer Numeric Control) operation, plasma cutting stands above other cutting and punching processes. In this article, we will discuss what plasma cutting is, how it works, and cutting abilities.

What is plasma cutting?

   Plasma cutting is the process of cutting conductive metal with a high-intensity plasma arc. This jet melts through the workpiece and pushes away the molten material creating the cut. The primary components of a plasma cutter are the power supply, arc starter, and the torch. The power supply is responsible for supplying constant DC voltage through the entirety of the cut. The arc starter then creates the arc inside the torch to begin the cutting process. The primary purpose of the torch whether operated handheld or though CNC, is to provide intended cut and cool the consumables that are inside the torch. These parts are called consumables because they will need to be replaced after a given lifespan and changed depending on cut conditions. The primary consumables inside the torch are the swirl ring, electrode and nozzle. Additionally, the need of an electrically conductive gas will be needed to assist in the cutting process and be used to help penetrate the workpiece and act as a shield for the torch consumables.  All these components work together to create a plasma arc that is then used to cut through the conductive metal. There are many companies that sell plasma cutters and supply the consumables you need to operate your cutter. These cutters can be used handheld or in conjunction with a CNC machine. Depending on your intended use and material thickness, will determine what plasma cutter is right for you. When looking at plasma cutters, be sure to read the manufacturer's specifications. This will tell you the requirements needed to operate the cutter and recommend the use of the plasma cutter. The manufacturer's specifications will also tell you the electrical requirements, such as the supplied electricity and amps needed, along with the needed gas pressure and capacity for varying cut lengths. Additionally, most manufacturers have recommended lists that designate which nozzles and amps to use for a given material and thickness.

How plasma cutting works?

   To understand how plasma cutting works, you must first know what plasma is. Plasma is the fourth state of matter. This occurs when a matter is subjected to increasing levels of energy. The three common states of matter are solid, liquid and gas. Once enough energy is introduced, the fourth state will occur producing plasma. This plasma is technically superheated electrical ionized gas. The fundamental act of plasma cutting occurs when an electrical channel is made from the cutter to the material and back to the cutter by means of grounding. Thus, the material that’s being cut must be conducive to complete this electrical circuit. In addition to having an electrical circuit created, the plasma cutter needs electrically conductive gas to help transfer the plasma’s energy to the workpiece. This is commonly in the form of either compressed air, nitrogen, oxygen or argon-hydrogen mixtures. This forced gas will work in conjunction with the torch and its components to deliver the high-intensity arc. The torch has a swirl ring, electrode, and nozzle on the inside. On the outside sits the shield. When the gas is introduced the swirl ring produces a vortex of gas down around the electrode in between the nozzle producing proper arc attachment. Without the swirl ring, there can be improper gas mixing which sends the hottest gas touching the nozzle thus burning it up. Additionally, the swirl ring helps to pull heat off the electrode. Thus, without the swirl ring, two primary components can get burned up very quickly. When the spark is generated from the arc starter the gas inside at this point will become ionized and create a current from the electrode down to the nozzle creating the plasma arc. From here the arc will then jump to the workpiece creating the cut. The nozzle’s job is to focus the arc and determine the arcs thickness. For thicker material, a wider nozzle will be needed and for thinner material and more precise cuts a thinner nozzle would be preferred. Now that the piece is being cut, a hot molten material is being blasted through the back of the piece causing extremely hot conditions for your consumables. This is where the shield comes into play. The primary job of the shield is to protect your torch’s consumables. It does this by allowing gas to travel along the nozzle thus creating a heat barrier and focusing the plasma’s arc, even more, creating a safer and more precise jet.  

Plasma cutting abilities.

   When looking at other cutting options, the plasma cutter stands above other operations in simplicity and cost-effectiveness. This is what makes plasma cutting so popular. However, there are a few drawbacks that come with plasma cutting. The first restriction as stated above is that it can only cut conductive metals properly. Unlike a waterjet that can cut through a variety of materials because only high-pressure water and abrasives are being used. The second most noticeable restriction is cut quality. Two major things consumers look for in a cut is the dross and bevel. Dross is the buildup of the molten material where the cut is being made. This makes the cut edge jagged and thicker than the other parts of the material. The quick fix to this is to simply grind off the dross making a smooth edge. The bevel is the angle at which the finished edge lays. A quality cut will leave a perfect flat edge. However, plasma leaves a beveled edge, this can vary depending on the material thickness just as the dross. The thicker the material the more severe these attributes can occur. A lot of these negative cut attributes can be solved through proper amperage and nozzle combinations. Along with testing what works best for your machine and material being used. Test cuts are usually performed when setting up your plasma cutter which determines the best torch height, amps and nozzle combination. Another important attribute that can help is the type of gas being used. Depending on the cut being made, the type of gas being used will differ. The most common form of gas is air. However, material thickness range will be capped out and will need other gases for thicker material. When fully optimized, hand-held torches can cut up to 1.5 inches and industrial torches can handle up to 6 inches. When running your plasma cutter for the first time be sure to perform testing and figure out the best combinations of gas, amps, and nozzles to allow for the best cuts.

Conclusion.

   Plasma cutting has developed exponentially over the years and even with the cut restrictions as explained above, plasma cutting stands toe-to-toe with other cutting operations. When looking at cut quality and price, it is clear that plasma cutting is the best operation for most cutting applications. It now should be clear what plasma cutting is and how it works. With this knowledge, you should feel confident to purchase the right plasma cutter for your needs and be able to operate with confidence.

Nicholas Kinney,
Nicholas is employed at Diamond Manufacturing Company as a mechanical engineer. His responsibilities/experience include the CNC programming of their turrets and fiber laser. Outside of work, he enjoys machining, plasma cutting and working on his invention of an electromechanical anti-jackknifing system for tractor trailers.

           



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