How to Select Your Plasma Cutter Air Compressor

Air Supply Requirements for Plasma Cutting Systems (Plasma Cutter Air Compressors)

Plasma is a superheated ionized gas. In a plasma cutting system, you can think of this as a lightning bolt inside a tornado.

The electrical current (lightning bolt) contains a massive amount of heat energy. The gas (tornado) ionizes, controls the arc, and blows away the molten material. In order for a plasma cutting system to perform optimally, the gas supply must be clean, dry, and properly regulated. When using bottled gas, these factors are relatively simple to control. Since most modern plasma cutting systems rely on shop air for the majority of cutting processes, more variables are introduced into the equation, often causing performance and consumable life to suffer when the air supply is less than ideal.

Here we’ll discuss the three factors that contribute the most to the performance of your plasma cutting system, and how to make sure that your tornado can keep up with your lightning bolt. 

Before we can discuss what a plasma cutter needs to breathe, we need to understand the design and operation of air compressors. A typical air compressor is comprised of a motor-driven compressor and a storage tank. The storage tank size will be represented in gallons or liters, with portable systems having tanks as small as 1 gallon and stationary systems having tanks 100 gallons or larger.

Flow rate capacity is a product of output pressure and storage tank size. The higher the output pressure is set, the lower the flow rate capacity will be. It is important that you are confident your compressor can keep up with the flow rate requirement of your cutting system when set at the required output pressure.

It is highly recommended that your plasma cutter air compressor be dedicated to running your plasma cutting system. If you plan to run other pneumatic devices simultaneously, you will have to add the flow rate requirements of all devices together to ensure that your compressor can keep up without exceeding its duty cycle. 

1. Pressure 

Pressure is the force of the compressed air being fed to your plasma cutter. The value for gas pressure may be represented in pounds per square inch (psi), megapascal (MPa) or bar.

Air compressor system pressure is preset and is usually between 100 psi and 135 psi and output pressure is adjustable via the pressure regulator. Inlet pressures vary by system. For a small handheld plasma cutter running at 20-30 amps, you’ll need as little as 80 psi (5.5 bar). Larger, automated plasma cutting systems in the 130 to 800 amp range may require 115 psi (8 bar) or more.

Most commercial industrial air compressors for plasma cutters will be capable of generating pressures in this range. It is important to note that the inlet pressure at your plasma cutting system will be lower than the output pressure of your air compressor due to pressure drops between the two points which can be caused by leaks or restrictions such as undersized fittings or filtration units.

You may need to set your compressor’s output pressure slightly higher than the inlet pressure requirement of your plasma cutter to compensate for pressure drops. Consult your operator’s manual to determine the best pressure for your system. 

2. Flow 

Flow is the rate at which air is being fed to your plasma cutter from the air compressor.

The value for flow rate may be represented in cubic feet per minute (CFM or ft3/min), standardized cubic feet per minute (SCFM), cubic feet per hour (CFH or ft3/h), standardized cubic feet per hour (SCFH), liters per minute (l/min), or liters per hour (l/hr). The flow capacity of a compressed air system is largely determined by the size of the tank.

As a good rule of thumb, select a compressor that has a flow rate capacity of at least 1.5 times the consumption rate of the plasma cutter. You’ll also want to make sure that the hose or tubing in use is rated for the pressure the system will handle, large enough in diameter to handle the flow rate requirements, and will not corrode or cause excess moisture to develop inside the line.

Copper is preferable to steel and aluminum pipe. Lines shorter than 75’ should use 3/8” diameter hose or tubing. Lines longer than 75’ should use ½” diameter hose or tubing. If using a flexible hose, you should take care to make sure the hose is not pinched or kinked.

The orifice size of all fittings used should match the ID of the hose or tubing. Flow rate requirements also vary by system and you’ll need between 3.5 scfm (99 l/min) and 6.7 scfm (189 l/min) depending on your system’s requirements. 

3. Filtration 

While inlet pressure and flow rate vary by system, filtration requirements do not. At surface level, it may seem that this makes filtration the simplest variable to account for.

In truth, filtration is the biggest gremlin in many air supply systems. It is often misunderstood and operators assume that because they have invested in the proper filtration equipment, they cannot possibly be experiencing a filtration issue.

The design and layout of a compressed air system can have a large impact on the amount of moisture that becomes trapped in the system, and where it ends up. Gravity can be your friend or enemy in this regard. Air filtration devices should be used to remove water, oil, and debris from your air supply and should be placed as close to the plasma cutting system as possible.

Under most conditions, a common coalescing filter with an automatic drain is sufficient. If cutting in a high humidity environment, a refrigerated air dryer should be considered. 

Taking the time to ensure a proper supply of clean dry air to your plasma cutting system will provide you with better cut quality, less downtime, and longer-lasting consumables. If you need help selecting the proper air compressor or air system components, visit your local supplier for assistance! 

If you’d like to learn more about plasma cutting, you should read our blog detailing how to properly replace your CNC plasma consumables.

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How to Evaluate Plasma Cut Quality

Evaluating Plasma Cut Quality

Plasma cutting is a tremendously capable technology, but the quality of your cut can vary.

With minimal training, an operator can employ a plasma cutting system for the accurate and efficient fabrication of any electrically conductive material. In most cases, the cut quality produced by modern plasma cutting systems is very good.

There are, however, a great number of variables which when properly understood and addressed will yield the optimum quality cut. 

Don’t worry, we’ll cover the variables you can use to evaluate the quality of your cut based on your plasma cutting equipment.

Evaluating Kerf Width of Industrial Plasma Cutting Equipment

Kerf is the material that is removed from the workpiece by the cutting process. In plasma cutting, kerf width is primarily determined by the amperage of the cut process. Lower amperages will produce a narrower kerf. Higher amperages will produce a wider kerf. To achieve the best cut quality in terms of kerf width, the lowest amperage should be selected that allows for a complete cut of any given thickness of a material.

Kerf width in plasma cutting can be as narrow as .4mm or as wide as 10mm depending on the amperage of the process. When nesting parts on a CNC machine, kerf width can add up quickly and make a difference in the utilization percentage of the material. 

Bevel is an Important Factor in Cut Quality as well

Bevel is a top to bottom variation from perpendicular on the cut edge. Positive bevel indicates that the bottom edge of the cut is protruding. Negative bevel indicates that the top edge of the cut is protruding. In plasma cutting, the most common cause of unintended bevel is improper cut height. When the cut height is too high, a positive bevel will appear. When the cut height is too low, a negative bevel will appear. When a plasma cutting system is operating optimally, bevel on the “good side” of a cut may be less than 1°.

If cut parameters are off, or if there is a problem with the system, bevel may exceed 6°. If you are experiencing an extreme bevel, you should ensure that your torch is moving in the correct direction relative to the part being cut. The “good side” of the cut will be the right side of the direction the torch is moving.

When CNC cutting, the torch must also be square to the plate to avoid unintended bevel. Similar to bevel, a condition called undercut may also develop when cut height is too low. Undercut is indicated by a concave edge on the cut part, usually closest to the top edge. 

Don’t Forget to Evaluate the Quality of Your Edge Rounding 

Edge rounding is the slight melting that occurs at the edge of a cut part. It is similar to bevel, but takes a rounded shape instead of a sharp one.

Top edge rounding occurs most commonly when cut height is too high. While some top edge rounding is normal when plasma cutting, it can become excessive due to a number of factors including worn consumables, improper cut height, and incorrect gas pressures. Arc density also has a large effect on top edge rounding. The more dense the plasma arc is, the less likely top edge rounding is to occur.

Sometimes, rounding can occur on both the top and bottom edges of the material. This usually occurs when too much current (amperage) has been applied and can be remedied by selecting a lower current process. 

Dross / Spatter is an Important Quality-determining Factor for Industrial Cutting Equipment

Dross is re-solidified metal that accumulates at the edge of a cut. There are two major varieties: High speed dross and low speed dross. High speed dross is hard and light and accumulates on the top edge of the material. Low speed dross is thick and bubbly and accumulates at the bottom edge of the material.

As their names imply, both of these types of dross are largely developed as a result of cut speed. When cut speed is too low, the plasma arc begins to widen and molten material is no longer completely discharged from the cut path. This type of dross is undesirable but fairly easy to remove. When cut speed is too high, the arc begins to lag behind and leaves a trail of material which has rolled over the top edge of the cut in the form of high speed dross. High-speed dross is much more difficult to remove and will usually require a secondary operation such as grinding.

Besides dross, the plasma cutting process also causes spatter. Spatter is when the molten material is ejected from the cut due to the swirling of gas that lands on top of the workpiece or torch. Spatter is easily removed once it cools. The use of an anti-spatter solution on the workpiece or torch can prevent spatter from adhering and make it even easier to remove if it sticks. 

Look at Lag Lines in Your Cuts 

Lag lines are small vertical ridges on the cut edge. They indicate the path of the plasma arc as it moves through the material from top to bottom. When cutting with air plasma, the lines should be nearly vertical (perpendicular to the surface). When cutting with oxygen, the lag line should lead slightly. When cutting with nitrogen or argon/hydrogen, the lag lines should trail slightly. If cut-speed is too fast, lag lines will take on an “S” shape. Lag lines are a great indicator of whether or not your cut speed is set appropriately. 

Finally, Evaluate The Surface Finish 

Surface finish of plasma cut parts can be highly variable. Some cuts will be smooth and glossy. Others may be rough, jagged, or inconsistent. Surface finish can be affected by the type of material being cut, the gases being used in the cutting process, or the cutting process itself. In CNC cutting, there are two categories of induced roughness: Those induced by the process (worn or damaged consumables, improper gas flow, etc.) and those induced by the machine (dirty rails, worn bearings, improper alignment, etc.). If cut edge irregularities are consistent through the process, you may have a process deficiency. If cut edge irregularities only appear on one axis, you may have a machine deficiency. 

It is important to note that cut quality is subjective. What one person may consider to be a defective cut, another may deem perfectly acceptable for its intended application. Cut quality should be weighed in the balance against cut speed, intended use, and the potential of the equipment being used. After all, a perfect cut edge would mean little if the parts are not produced in time to be used. 

If this guide was helpful, we wrote plenty of blog posts with in-depth information about plasma cutting, just for you! For example, we recently wrote a blog to help you avoid unintended plasma cutting issues.

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“Dross” refers to the unwanted accumulation of waste and foreign matter resulting from molten metal created during the plasma cut. The term “dross” is often used interchangeably with the words “slag,” and “spatter.” Whichever you choose to call it, excessive buildup of hardened metal on your cut can lead to costly downtime needed for post-cut cleanup. While dross and slag are inevitable in the CNC plasma cutting process, there are several ways to reduce them.

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As anyone working with automated plasma cutting systems can tell you, plasma shops spend a lot of time and money correcting and cleaning up from the results of bad plasma cuts. Whether they’re grinding off excessive dross from the finished work or even having to recut pieces altogether because the cut results didn’t meet the job’s intended specifications. The result is a financial hit to the operation, because there’s nothing but resource drains in cleanup or re-cutting. There’s only a negative cost, both in hours and materials. One of the key issues plasma torch operators encounter is unintended bevel introduced into a plasma cut. To better understand the causes and cures for unintended bevel, here are a couple of things to consider. 

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As anyone working with automated plasma cutting systems can tell you, plasma shops spend a lot of time and money correcting and cleaning up from the results of bad plasma cuts. Whether they’re grinding off excessive dross from the finished work or even having to recut pieces altogether because the cut results didn’t meet the job’s intended specifications. The result is a financial hit to the operation, because there’s nothing but resource drains in cleanup or re-cutting. There’s only a negative cost, both in hours and materials. One of the key issues plasma torch operators encounter is unintended bevel introduced into a plasma cut. To better understand the causes and cures for unintended bevel, here are a couple of things to consider. 

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As anyone working with automated plasma cutting systems can tell you, plasma shops spend a lot of time and money correcting and cleaning up from the results of bad plasma cuts. Whether they’re grinding off excessive dross from the finished work or even having to recut pieces altogether because the cut results didn’t meet the job’s intended specifications. The result is a financial hit to the operation, because there’s nothing but resource drains in cleanup or re-cutting. There’s only a negative cost, both in hours and materials. One of the key issues plasma torch operators encounter is unintended bevel introduced into a plasma cut. To better understand the causes and cures for unintended bevel, here are a couple of things to consider. 

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As anyone working with automated plasma cutting systems can tell you, plasma shops spend a lot of time and money correcting and cleaning up from the results of bad plasma cuts. Whether they’re grinding off excessive dross from the finished work or even having to recut pieces altogether because the cut results didn’t meet the job’s intended specifications. The result is a financial hit to the operation, because there’s nothing but resource drains in cleanup or re-cutting. There’s only a negative cost, both in hours and materials. One of the key issues plasma torch operators encounter is unintended bevel introduced into a plasma cut. To better understand the causes and cures for unintended bevel, here are a couple of things to consider. 

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