Plasma Cutting Stainless Steel:
10 FAQ Answered by Experts
When it comes to cutting stainless steel, there are several methods available, but it’s not always easy to understand which of these is the simplest, which is the most cost-effective, and crucially, which will give you the best results.
In this article, we’re going to answer the 10 most frequently asked questions with regards to plasma cutting stainless steel and whether plasma is the right solution for cutting stainless steel?
The short answer is, yes!
Plasma cutting is a quick, affordable and easy way to cut stainless steel. Modern plasma systems allow you to select from an expanded range of gases and amperages, to produce optimal cut speeds and deliver the desired cut quality for a variety of needs.
But remembering which gasses you need to buy and what the processes are to get the best cut results can be a bit overwhelming.
Therefore we created this article about plasma cutting stainless steel. We have tried to make it the most useful stop on your journey to a solution by answering the 10 most frequently asked questions on this topic!
- Question 1: Can you cut stainless steel with a plasma cutter?
- Question 2: Can you cut polyethylene-coated stainless steel with plasma?
- Question 3: Can plasma cut painted stainless steel?
- Question 4: How clean is the cut on stainless steel?
- Question 5: Does True Hole exist with stainless steel?
- Question 6: What is the right gas for plasma cutting stainless steel?
- Question 7: What cutting speed & amperage can I expect?
- Question 8: What are plasma cutting stainless steel hazards?
- Question 9: Is using plasma the best way to cut stainless steel?
- Question 10: How to choose the best plasma cutter for stainless steel?
Can you cut stainless steel with a plasma cutter?
Absolutely. Plasma is one of the most effective methods to cut stainless steel over a wide range of thicknesses. However, the type of stainless steel cutting table and plasma source you use makes a big difference.
Does the cutting machine make a difference?
The build quality of your cutting machine will make a significant difference in the cut quality in the long run.
Specifically, the edge quality (ripples vs no ripples) and angularity of the cut may be impacted by mechanical imperfections of the cutting table.
You need to assess the stiffness of the gantry (Y-axis that moves over the material to be cut) and whether the construction of the rails can be affected by the heat dissipated by the cut.
Whilst cut quality may look the same when machines are brand new, heat can bow the metal construction of your table over time, which may impact the straightness of the cutting machine.
Next to this, various machine components, like the drives, rails, and gears impact motion. Poorly assembled or poor quality components could lead to motion irregularities.
This, in turn, causes vibrations, which transfer through the machine axis into the cut edge and can cause a rough-cut surface, nonlinear cut edges, and overall poor cut quality.
Therefore, we recommend checking the quality of the drives, rails, and gears before you purchase any plasma cutting machine.
Does the plasma system make a difference?
The main difference between a low-cost air plasma system vs an industrial type of plasma cutting systems relate to the types of gasses that are used to cut and the pressure at which the plasma gas will come out of the torch. Both of these significantly impact the end-result of the cut.
The image below illustrates the quality difference one can expect between using a more expensive F5 blend gas as plasma cutting gas vs. a cheaper solution like compressed air.
F5 plasma cutting gas used vs compressed air to cut stainless steel
Low-cost CNC air plasma systems will only use air to cut stainless. It can cut stainless steel through to around 25mm.
Due to the Nitrogen that is present in air (~78%), you will always get a black finish. In addition, as there is about 20% Oxygen in air, which has the tendency to burn, your edge finish may not be as good, especially on thicker material.
Overall you’re getting a decent cut quality at low running costs.
Industrial CNC plasma cutting systems use a variety of gas combinations to cut stainless steel. Especially the most modern mechanised systems are equipped to cut sharp edges with smooth surfaces and a shiny finish. Systems such as the HyPerformance® HPR800XD® or the Kjellberg HiFocus 600i Neo can cut stainless steel to up to 160mm.
In the range of industrial CNC plasma cutters, there are certainly other variables to take into consideration as well when cutting stainless steel; a range of processes (including output currents and gas combinations) will impact the cut edge results and cut speeds you can achieve.
For example, using nitrogen will give you a faster cut, but can also result in top edge rounding, and using an oxidizing plasma gas (such as air or O2) will produce surface oxides on the face of a cut that will need to be removed with a grinder before welding. These secondary operations take additional time, which you may want to avoid.
Using non-oxidizing plasma such as argon-hydrogen (H35) makes the cutting process slower but produces bright chrome-like edges that need little or no preparation before welding. Using gasses that contain some hydrogen (such as F5) will also result in sharper cut edges.
The most modern industrial plasma sources, such as Hypertherm’s X-Definition™ XPR300™ plasma cutting system enable you to mix gasses. Like this, you will be able to produce a blend that has, for example, the cut-quality of argon-hydrogen, and the cut-speeds of air and nitrogen.
Can you cut polyethylene-coated stainless steel with plasma?
Polyethylene-coated stainless steel sheet is used extensively in industries such as food services. A thin plastic film is applied to the metal after the polishing process and is used to protect the polished stainless steel finish.
In most circumstances you can still use plasma to cut polyethylene-coated stainless steel, but cutting this material without burning and melting the polyethylene film requires the use of low plasma cutting currents and a nitrogen shield gas.
Nitrogen is useful as a shield gas because as well as flushing the slag from the kerf, it also prevents oxygen from entering the cutting zone and causing the polyethylene to melt or burn.
The only condition under which plasma will not work on polyethylene-coated stainless steel is when the material is coated on both sides. This is because a plastic coating on the underside of the steel plate will prevent the positive part of the circuit from being completed.
Can plasma cut painted stainless steel?
Unlike polyethylene, there are no restrictions when it comes to cutting painted or dirty stainless steel with plasma, as neither presents a barrier to the circuit being completed.
However, when cutting painted or very dirty stainless, you’ll need to make sure you have a solid ground connection on a clean part of the work-piece as close to the cutting area as possible.
How clean is the cut on stainless steel?
Difference between Air Plasma & Mechanised Plasma systems
As per the above picture, there is a difference between CNC plasma cutters that use air vs a CNC plasma cutting machine using a mechanised plasma system. The cut is clean for both systems, although a stainless edge that is cut with air will be much rougher.
Both air plasma and industrial plasma systems will provide you with a chart indicating which cutting processes can cut a certain thickness with the cleanest possible cut. In the “best quality” range, sometimes a small amount of dross may be found around sharp corners, but removing this is fairly straightforward.
If you leave the “best quality” range, you will be able to cut faster (production cut), and this will be at the expense of more dross. Note that dross from stainless steel will be harder to remove than dross from mild steel. Unlike molten mild steel, molten stainless has a high level of viscosity, meaning that if lots of dross is deposited, it will be more difficult to remove than dross from mild steel.
Stainless Steel cutting chart 170 A with N2 on a Hypertherm XPR300™ plasma cutting system
Stainless Steel cutting chart 105 A with Air Hypertherm Powermax105® plasma cutting system
Stainless Steel dross is difficult to remove
That viscosity of the molten metal can also make piercing of stainless steel difficult. Dross can accumulate around the pierce hole, which can adversely affect the movement of the torch. In practical terms, if you want to cut a drain cover with very narrow slots, you may need to look at optimizing the slots for the plasma process, and making them thick enough to allow for the torch to avoid the pierce puddle.
Using the right equipment and the optimal settings of speed and voltage (for air plasma) and the right process related to thickness for mechanised plasma normally results in a very clean cut, making stainless steel easy to work with.
The right equipment though is key because lower-end machines and those with less precision in their settings can produce cuts with lots of dross.
This can be a very frustrating experience for fabricators, but it is solvable.
If you want clean and hassle-free cuts on stainless steel, you might want to consider purchasing an industry-leading machine, rather than an entry-level CNC plasma cutting machine.
We would recommend to always contact your machine manufacturer to ask for more advice on machine specs and set up, as this will help you assess the feasibility of cutting the parts represented in your drawings.
Does true hole exist with stainless steel?
True Hole® technology is Hypertherm’s unique solution to producing true, un-tapered holes in mild steel. Unfortunately, it is a process that currently only exists with mild steel due to the physics of the plasma arc and the dross accumulation during the cutting process.
With stainless steel, the arc lags the torch by up to 15 degrees and is therefore not currently consistent enough for True Hole technology.
Plasma cut hole quality in stainless steel is still acceptable for many applications; it is just not currently at the same level of precision as with mild steel.
What is the Right Gas for Cutting Stainless Steel?
When it comes to an air plasma system, the choice is easy – you will always cut with clean, dry air (which is, of course, still 78% nitrogen) as the plasma gas and produce very acceptable cutting results on a wide range of thicknesses. Air is the most cost-effective cutting gas. Cuts will usually have a bronze to dark grey finish and a rougher edge than systems that enable multi-gas processes.
Intermediate (e.g. MAXPRO200®) or industrial, high definition or X-Definition plasma systems (e.g. XPR300™) are a popular choice for many fabricators as they deliver better results on stainless. The best edge finish is often realised with the more exotic gas combinations.
These dual gas systems also more readily produce cuts that are weld-ready without further preparations to the metal needing to be made, because of cutting without oxygen.
Industrial systems (e.g. XPR300™) specifically are capable of producing a high-quality dross free cut of stainless over a broader range of thicknesses.
Here’s a brief rundown of the characteristics of different plasma gasses when cutting stainless steel with a plasma cutter:
|Plasma Cutting Gas||Characteristics|
|1. Argon Hydrogen||Excellent quality cut, and particularly recommended for cutting thicker stainless steel. Argon-hydrogen gas is the hottest burning plasma gas and it is essential that your system is appropriately equipped for working with it.|
|2. Nitrogen||Good cut quality, used across all thicknesses and also has less of an impact on consumables leading to longer parts’ life|
|3. Air||Good cut quality and speed. This is an economical solution that will produce good, though not excellent results, primarily because of the presence of more than 20% of oxygen|
|4. Oxygen||Pure oxygen is not recommended as it leaves an oxidised surface on the face of the cut|
|5. Nitrogen with hydrogen (F5)||A non-oxidising combination that leaves slightly blue hue to the finish, primarily used for processes to cut under 10mm|
Let’s take a look at the characteristics of shield gasses you may use when plasma cutting stainless steel:
|1. Nitrogen||Leaves a well-flushed kerf and a shiny chrome-like edge. A high flow rate also cools the process, leading to less part distortion|
|2. Water*||Through vented water injection, an attractive edge finish can be produced.|
|3. Carbon dioxide||Leaves a slag-free and brown coloured edge|
|4. Air||Flushes the kerf well, and leaves a bronze coloured edge|
*Compatibility with your filter needs to be checked.
You only need to think about the plasma gasses when you have a dual gas or multiple-gas system.
A dual gas system will allow cutting stainless with Nitrogen, giving you a dark edge. Both systems will use Nitrogen as shield gas where it is extremely effective at flushing slag from the kerf, leaving cuts with a smooth edge surface, a neutral, shiny finish, and virtually no dross.
A multi-gas or mechanised system (e.g. XPR170™, XPR300™, HiFocus 360i neo) will cut on the thin end with F5 plasma gas and on the thicker end with a mixture of hydrogen and argon. This will produce a dross-free, excellent finish, with bright, smooth edges and good perpendicularity.
For thinner stainless steel (up to around 10 mm), processes using either nitrogen for the plasma and shield gas or a combination of an F5 plasma gas (5% hydrogen, 95% nitrogen) and nitrogen shield gas deliver excellent edge quality. As a shield gas, nitrogen is extremely effective at flushing slag from the kerf, leaving cuts with a smooth edge surface, a neutral, shiny finish, and virtually no dross.
For the best cut quality on thicker stainless steel pieces (10mm+), we recommend argon hydrogen for the plasma (or argon hydrogen nitrogen), with a nitrogen shield gas.
Discuss your requirements with your machine manufacturer in order to choose the right machine for your needs.
|Plasma Gas /Shield Gas||✓ PRO||✗ CON|
|Air/Air||Fast||Surface is black|
|Low Cost||Rough and heavily
|Minimal dross||Secondary operations|
|N2/N2||Cheaper||Edge is black|
|Fastest cut speed||Top edge is rounded|
|Closer to perpendicular||Has dross|
|N2/Air||Cheaper||Edge is black|
|Fastest cut speed||Top edge is rounded|
|F5/N2||Silver color||Thickness limitations (<10mm)|
|Good cut angles||Slower cut speeds|
|Smooth, shiny cut edge||F5 gas is more expensive than
|Minimal weld prep||Slightly degraded cut quality on
|Ability to use the same consumables|
|H35/N2||Gold to blue color||Gas availibility issues|
|Grey Color (+75mm)||Dross results on thin plates|
|Square cut edge|
|Minimal weld prep|
|Wide cutting range|
|H35-N2/N2||Blue to gray color||Gas availibility issues|
|Faster cut than H35/N2||Auto-gas systems only|
|Minimal weld prep|
|Wide cutting range|
What Cutting Range, Speed & Amperage can I expect?
Thanks to advancements in plasma cutting technology, top range systems such as the Hypertherm XPR300™ can deliver very fast cutting speeds even on stainless steel.
When thinking about thickness, you have to consider a few elements: dross-free limit, pierce capacity and severance cut. Dross-free cutting is the limit until which you can cut without considerable secondary operations. Pierce capacity is the maximum thickness the plasma source can cut without needing an edge-start. Finally, severance cut is the absolute maximum a machine is capable of doing when it starts its cut on the side of the plate.
A fabricator with a mechanized plasma has the luxury to choose between speed and quality. When cutting stainless steel as fast as possible, more dross will be created at the expense of speed. The best cut quality is obtained by a process which is often slightly slower, but results in a cut that is nearly dross-free:
Cutting speeds are generally proportional to cutting current (amps), example:10mm stainless on an XPR300.
We highly recommend cutting this on 130amp, resulting in a cut quality of 1 (the best) unless 400mm/min additional speed would be critical for your operations. Yet that increase in speed will result in a lot more secondary operations
|Amperage||Cut quality level||Speed(mm/min)||Result|
(N2/N2, N2/H2O, MIX/N2 )
|2||~1,000||Dross and slow|
(N2/N2, N2/H2O, MIX/N2 )
|1||~1,600||Black edge (N2/N2)
Shiny edge (Mix/N2)
(N2/N2, N2/H2O, MIX/N2 )
|3||~2,000||Lots of dross|
In general, cutting speeds for stainless steel are lower than they are for mild steel at a given thickness and cutting current. As an example, the Hypertherm XPR300 will cut 12mm mild steel at nearly 3 meters per minute (quality = 1), whereas it would cut stainless steel at 1.7m/min (quality 1).
In the table below you find the cutting range (in mm) for each gas combination at a given amperage:
|Plasma Gas / Shield Gas||45A||80A||130A||200A||260A||400A||600A||800A|
|N2/N2||0.8 - 4||*||6 - 20||10 - 20||*||*||40 - 80||*|
|N2/Air||*||*||*||*||6 - 50||12 - 45||*||*|
|F5/N2||0.8 - 6||4 - 10||*||*||*||*||*||*|
|H35/N2||*||*||10 - 25||10 - 20||8 - 50||20 - 60||40 - 100||50 - 160|
|H35-N2/N2||*||*||6 - 20||10 - 20||6 - 50||12 - 80||*||*|
What are Plasma Cutting Stainless Steel Hazards?
Safe and effective plasma cutting requires the implementation of safety procedures and practices to regulate aspects such as the management of dangerous electrical currents, fire hazards and personal operator protection. But is there anything else we need to be aware of when plasma cutting stainless steel specifically?
The primary concern is how to control the potentially hazardous fumes. Stainless steel fumes will contain more chromium and nickel than mild steel, and both of these metals are toxic. The type of chromium released is called Hexavalent Chromium (or Hex Chrome), which is a highly carcinogenic gas with links to health conditions such as cancer and respiratory problems.
Many thousands of different substances are used in the workplace, but the UK’s Health and Safety Executive has outlined exposure limits for 500 of them. Chromium and Nickel are both listed. Research into the damaging effects of breathing these fumes is on going, but the risk can be easily managed with an appropriate fume extraction system, cutting table and filtration system.
Fume extraction and filtration systems remove the damaging particles from the air and make it safe to breathe. When considering the filtration system that’s right for you, it’s helpful to consider your safety to end up with a filter that is strong enough. Whatever filter, always ensure that the cutting area is covered with at least 80% of the material.
This will ensure better air suction. The higher the amperage of the plasma (i.e. the thicker the material) and the wider the cutting bed, the more powerful your fume extraction system needs to be. It’s possible to bring in specialists to measure your air quality and advise you on the type of ventilation that will be best for your work environment.
Last but not least, cutting with H35 or an H2-Ar-N2 mix underwater is not without risks. If a plate is left submerged on the table for an extended period of time, hydrogen bubbles can accumulate under the plate. Piercing such a plate with a plasma torch could ignite that bubble of hydrogen and a serious explosion can occur.
Is using Plasma The Best Way to cut Stainless Steel?
The answer to which cutting system is best ultimately depends on the requirements of the job. But when it comes to stainless steel, the versatility of plasma makes it the all-rounder that fabricators tend to opt for.
This is especially true for thicker stainless steel plates, where plasma cutting is almost universally considered the best solution. Precision plasma can pierce and cut stainless steel up to around 40mm and high amperage plasma systems can pierce and cut stainless steel up to around 100mm. With an edge start, plasma can cut up to about 160mm.
Lasers can be used for thinner stainless materials where intricate detail is required, and they can also offer higher cutting speeds in the thinner ranges. If the product does require extreme hole accuracy, (PCD insert or 4-bolt pitch for a pump or motor to go on) you have to work with laser-cutting technology, whereas if you can live with some taper from top to bottom when you put a bolt through the hole, HD plasma cutting machines could also be used.
This being said, laser-cutting technology that cut stainless steel of 15mm and above requires triple the investment of comparable plasma cutting technology, Vented nozzles, originally developed for use on mild steel, are now available for stainless as well. The increased the pressure on the plasma arc produced by the vented nozzle constricts it for a finer and cleaner cut.
This coupled with the fact that the reflective surface of the material can cause back-reflection problems for lasers means than plasma cutting is the preferred option in many cases, especially on thicker stainless where you’ll get a very smooth edge
Using waterjet to cut stainless steel produces high-quality results with smooth cut edges but is limited in application as a result of the very slow cutting speeds compared to other solutions. And although the waterjet cut is extremely smooth, the quality of cut delivered by plasma is considered sufficient for most applications and industries.
How to Choose the best plasma cutter for stainless steel?
When selecting a machine for plasma cutting stainless steel, a useful first task is to prioritize your needs. For some applications, productivity may be the number one concern, while for edge quality may be the most important issue.
Budget is, of course, an important constraint that underpins the whole decision. Cost-effective air plasma solutions are available but will require you to compromise on the speed and cut that a higher quality machine with precision plasma will provide.
Cutting stainless steel with a plasma cutter is not only possible; it’s probably the solution that will give you the quickest, most consistent and overall best results.
If you have any questions about plasma cutting stainless steel, please don’t hesitate to contact us.
Our team of expert engineers can help you to identify the right CNC cutting machine for you and they’d be delighted to talk through your specific requirements and how Esprit Automation could help you to meet them.
CONTACT US For all your stainless steel plasma cutting needs.