Last Updated on November 9, 2020 by Gary Hargrave
Plasma cutting has seen decades of innovations with newer technologies to make the process easier and more accessible than what it was in the mid-1950s. But its reliability is often in question, especially when aluminum is concerned. Perhaps, the unique details involved in the job are the reasons. So, is it possible to cut aluminum with a plasma cutter?
You can plasma cut aluminum using an argon-hydrogen-nitrogen mix. Use a wet table with an aerator for most alloys and a dry table with a dust collector for Al-Li alloys. Choose a plasma system with high cutting speed and use air for cost-effectiveness.
I understand the above answer raises questions as to why I mentioned these particular preferences. I’ll try to clarify my answer throughout the rest of this article.
I’ll talk about the most important considerations that make aluminum different from other materials as plasma cutting is in mind. Should you ensure excellent cut quality with weld-ready edges on most aluminum alloys, these matters come first:
- Gas: Is it air, or a mix of argon and hydrogen, or something else?
- Table: Is it a dry or wet table?
Apart from your experience and skills, your success in it depends mostly on the gas and the cutting table. So, you should learn everything about them, and after that, I’ll provide you some useful insights.
Topics Covered in This Article
- Gas Selection To Cut Aluminum With A Plasma Cutter
- Words About the Surface Dross
- Plasma Cutting Table
- How to Stay Safe?
- What If You Want to Cut Aluminum-Lithium Alloys?
- A few Insights into the Actual Work
- Final Thoughts
Gas Selection To Cut Aluminum With A Plasma Cutter
Many people might say you are better off without a plasma system while cutting aluminum because of the following (potential) problems:
- The material doesn’t do very well against the flame.
- The cut edge features serious porosity.
- There will be a lot of mess (surface dross) on the material.
It happens when you only use air, the most common mistake unaware users make. Even worse, you’ll have rough edges with an aluminum oxide layer which is specifically bad for your purpose of plasma cutting. Why is that?
Aluminum oxide with its high melting point and moisture works as an insulator and causes arc start issues forcing the user to apply high heat for penetration through that layer. That heat can burn through your base material and cause porosity.
Fortunately, there are better alternatives to air. You can explore other selections like an argon-helium or nitrogen-hydrogen mixture, just saying. Much of your concern about the cut edge and/or porosity can be addressed with a proper gas combination. I’m giving you a quick note on this now:
- You can rely on nitrogen (N2) and air with the former as the primary gas if the thickness of your aluminum plate is under 1/2 inch. You can replace air with CO2 when you want to cut faster with smoother edges and better parts.
- To do this on thicker aluminum, you should choose an argon-hydrogen (Ar-H2) mix with nitrogen which is the secondary gas. But you’ll need some prepping to ensure safety while working with the mixture.
But my friend, clean and dry shop air is still more economic than either of the above choices. So, you might want to know if straight air is usable under any circumstances. It is an interesting question, indeed.
For this, you need to be able to optimize your cutting speed against the cutting power. Does your plasma system cut at least 5 inches/minute? Machines with this cutting speed or higher can minimize heat input levels into cut edges and help reduce the likelihood of excessive burning.
It sounds like a new side to the discussion. Yes, it does, and you can expect great results with a modern-day plasma system that features above average cutting speeds.
Check this article to know more in depth about how does a plasma cutter work.
Words About the Surface Dross
The gas you’re going to use has something to do with the issue as the right combination can help you get a nearly clean and smooth material surface.
But it is hard to guarantee that gas is the only factor at play here. The proper setup of your workplace including the plasma system itself is the key to work without much mess to clean after the cutting process.
Let me explain the phrase “proper setup” with relevant details. This brings up the choice of your work table which I’m going to talk about now.
Plasma Cutting Table
Some people emphasize the cut edges and quality while others go by the cost-effective route. A dry cutting table can be more helpful than a wet one if quality is your only focus. But moneywise, a wet table is better.
Cutting aluminum on a dry table results in a lot of dust that may pose extra hassles after the process. You’ll need an additional dust removal system which comes at a considerable cost, at least a few hundred dollars, and up to a thousand for a decent unit. Moreover, you’ll experience a very noisy operation, not to mention the harmful ultra-violet light.
Using a wet plasma cutting table may save you that extra cost and noise but not necessarily the other hazards. Regardless of the aluminum alloy you choose, there are risks of explosion because aluminum being very close to water often begets potential dangers. I hope you won’t mind me describing the situation.
Hazards Involved in the Use of a Wet Table
Aluminum kept under water gets into a chemical reaction with water and generates tiny bubbles of hydrogen gas which resemble the ones you see when you pour some soft drink into the glass. Those hydrogen bubbles will leave the surface of the piece of aluminum in use and eventually start floating upwards.
Two things are important to determine how much of the gas will be produced:
- The specific surface area of the metal being submerged water
- The duration (length of time) the metal is kept that way before retrieval
Again, during a plasma arc process, you’ll see plenty of molten aluminum droplets, most of which will find their way into the wet table. Among those droplets, you’ll see some fine particles with a gradually increasing surface area that may become excessively large in a short time. Those droplets can be on the table’s bottom for some time and keep generating hydrogen bubbles.
As you ignite the torch and start piercing an aluminum plate that has a pocket of hydrogen below it, a deadly explosion, the actual problem, can occur. For your information, hydrogen is associated with “Level 4” that indicates “Severe Flammability Hazard”.
How to Stay Safe?
Although proper outfit, I mean, the right clothing and protective items are always recommended, I would like you to go beyond mere safety equipment in this case.
I’ve already you of the location and the way the gas may accumulate. But you should experience some practical instances and never leave your aluminum workpiece on the table for hours.
Some water tables feature special control systems to allow the operator to raise and drop the water levels as required. These models cost a little extra, but the pay-off is worth it. You can raise or lower the level of water before starting the process so that the hydrogen bubbles, if any, can be dissipated.
Do you think a new water table with water level controls or the learning curve is not an option for you? Well, I can make a more favorable suggestion than either of these ways.
Buy an Aerator/Bubble Muffler/Filtration System
An aerator is the most affordable option. It is a number of pipes arranged in a series with small holes on the table’s bottom. Compressed air through those holes bubbles all the way up to the table’s surface while dissipating and diluting the hydrogen bubbles.
Thus, an aerator prevents the concentrated hydrogen gas from collecting under the aluminum material. However, you must get yourself trained on the use of this device.
A bubble muffler is an easier solution. You have to clamp the device onto your torch. It protects your plasma arc using compressed air straight through its inner nozzle. It covers the arc by pumping a large volume of water on the table through its outer nozzle.
The device is particularly useful when your water table doesn’t come with water level controls. It stirs the table water just enough to break up the hydrogen bubbles. Other benefits that it offers include reduced plasma smoke, noise, and arc glare.
An industry-standard water filtration device includes a series of nozzles and a high-volume pumping kit to force the tiniest particles to get released in the water. The filtration system uses a centrifugal separator to remove those particles from the water.
Besides impeding the generation of the gas significantly, the system also keeps the table water highly agitated to prevent further accumulation. But I am afraid, it is a more complex and expensive choice than the above ones.
What If You Want to Cut Aluminum-Lithium Alloys?
You know the safe ways to handle aluminum alloys on a water table, don’t you? That said, you want to put aluminum-lithium (Al-Li) out of this because certain particles from the molten Al-Li alloys are too dangerous to be allowed anywhere near water.
Dry cutting is the only way, and you must get rid of anything wet in your workplace. Using a water-injected torch is not a good idea either.
You Expect High Precision, Speed, and Perfectly Squared Edges. Now What?
Most people including some experts would say that nothing but tried-and-true skills can help with these demands. They are right but not entirely. With some experience, you might give it a try only if you have access to technologies high tolerance or high-definition arc cutting.
You won’t find hundreds of models in this category because they are a recent and more sophisticated addition to the lineup. The key principle of the design is to ensure a constricted arc that has a diameter smaller than that of the arc of a conventional plasma system.
The nozzle has been designed and magnetic field has been confined in a special way to improve the control of the gas flow. All these efforts account for an increase in energy density which is expected to ensure the following outcomes:
- Increased plasma cutting speed
- Smooth, squared edges
- Improved cut quality with a narrow kerf width
- Reduced heat-affected zone with a very low level of distortion
So, you have a viable option to try when specific limits of tolerance are to be met. At this end, I have a few more things to say. Like I promised above, I’m offering you some tips to help you end up getting poor edges that can’t be welded or damaging the torch or consumables.
A few Insights into the Actual Work
- Choose alloys that are not sensitive to hot cracking because some of them may not be weldable at all. Alloys that contain magnesium or silicone can are ideal.
- Move the plasma torch at a speed that prevents the arc to penetrate the aluminum plate. Read the manufacturer’s instructions to figure out the right amperage settings and travel speed.
- Hold your plasma cutter maintaining a little distance between the tip and the part of the metal you want to cut. Check your plasma system manual for info on the distance.
- Position your plasma cutter keeping the aluminum plate/sheet in between the metal arcs.
- Connect an air source to your plasma cutter appropriately because hot aluminum gets pretty sticky, and a plasma system blows away the liquid using clean, compressed air.
Finally, I am about to recommend you one more thing which is common to any material (including aluminum) that can be cut with a plasma machine.
Since the aluminum metal you choose must stay between the plasma arcs, you should measure the material’s thickness before choosing the plasma cutter. For thicker the metal, you’ll need bigger plasma arcs with more space in between them.
Also, don’t jump into laser cutting aluminum just yet, thinking that it to be more cost-effective than plasma cutting. Plasma operation is usually more affordable than laser considering the cost of cutting per foot of aluminum sheet unless you are too sensitive to accept some surprises.
I hope I’ve been able to satisfy your curiosity about this topic. Please feel free to ask if I’ve missed anything.