What exactly is plasma cutting and can welders adapt it for newer composite materials?

Plasma cutting is a welding process for cutting materials that conduct electricity. It is quick, cheap, and precise, which makes it popular for all sizes of jobs. Technology continues to advance every year. However, when using composite (combo) materials instead of standard ones, like steel, watch for excessive melting.

Let’s learn about the history behind this popular welding process, including how the tech continues to progress. After that, we’ll talk about how exactly the machines work. We’ll then move into how standard and composite materials differ, and how to be successful when using them. Finally, we’ll end by talking about how to purchase and maintain a machine.

First of All, What Is Plasma?

Before we can learn about plasma cutting, we need to learn about plasma. Many people haven’t heard of it before. We all know the three obvious states of matter – solids, liquids, and gases. But did you know there is another one? That’s where plasma comes in! It’s the state of matter just above a gas.

But how do we get plasma?

The way to change any matter from one state to another is by either adding or removing energy (like heat). A good example is to think about an ice cube. How do we make an ice cube? How do we change it back to water? Simple – either freeze it (remove heat) or heat it up (add heat). That’s also how we get plasma. To get matter to progress past the gas state, it needs even more heat. The extra heat ionizes (or charges) the gas which makes it able to conduct electricity. 

People often think of plasma as the stuff in TVs. However, plasma also makes up most of the universe! It is also so hot that is can easily be used for cutting. This is where the plasma cutter comes in.

The History of the Plasma Cutter

Plasma cutting came from plasma welding in the 1950s. It wasn’t super popular until around 20 years later though. In the 1970s, plasma cutting was used more than traditional metal cutting.

While early plasma cutters were large, slow, and clunky, they still had a lot of advantages over other methods. They made cleaner, more accurate cuts without metal chips. They were also more user-friendly, which made them easier to use. It’s not surprising people loved them!

Plasma cutters kept getting more popular through the 1980s and 1990s. With that came smarter machines. That lead to the development of the computer numerical control, or CNC technology. It let the machines be flexible enough to cut unique shapes with ease. Users just program instructions into the numerical control panel and voila! CNC was first available only for steel in flat sheets and using X Y cutting. However, it is even more diverse today.

CNC Technology

CNC is now available right inside the cutting table itself. The benefit is that users can let the table handle control of the torch. This makes for an even sharper, more precise cut. Some of the new CNC also allows for more than just X Y cutting, and on thicker materials. It is also available in both a horizontal and vertical format, which means they are able to take up less physical room.

There are 3 different types of CNC plasma cutter machines.

• 2-axis or 2D plasma cutting – This is the most popular CNC. With 2D cutting, users create a flat profile (where the cut edges sit at a 90-degree angle to the surface). They can also cut metal plates that are up to 150mm thick.
• 3+ axis or 3D plasma cutting – Similar to 2D cutting with an added axis, 3D cutting lets the cutting head tilt. This allows welders to cut at different angles than just 90-degrees.
• Tube or section plasma cutting – This CNC is unique to cutting long sections of pipes or tubes. The torch remains in place, while the workpiece moves and rotates around it. 

Newer Advances With Plasma Cutters

Plasma cutting tech keeps advancing. Since the first machine in the 1950s, they have gotten smaller, smarter, stronger, and more efficient and precise. They also have smaller nozzles and much thinner plasma arcs. Some of the machines are even handheld!

But the largest advance continues to be in automation. Automation is a machine that works with very little human help. Benefits include a rise in productivity and the ability of people who are not familiar with the machine to still be successful. It also makes plasma cutting much safer for the layman. 

How does Plasma Cutting Work?

Plasma cutting starts with compressed gas. The most popular types are oxygen, nitrogen, hydrogen, room air, or argon. The machine takes that air and blows it a super high speed through a focused nozzle. The gas then forms an electrical arc between an electrode on the nozzle and the workpiece. This process also changes it from a gas to plasma.

As the plasma makes contact with the material being cut, it heats it up and melts through it. It then blows the melted material away from the cut, which cuts it away from the rest of the workpiece.

An important difference between plasma cutters and other types of welding machines is that plasma cutters don’t rely on oxidation. This makes it ideal to cut any material that can conduct electricity.

Safety Precautions

No matter how long a person has been using a plasma cutter, everyone should follow the same safety precautions. Common safety protection devices are leather gloves, aprons, goggles/face shields, and jackets. These are mostly to prevent burns.

Eye protection is especially important due to a condition called “arc eye.” Arc eye, or photokeratitis, happens due to UV wave exposure. Basically, arc eye is like getting a sunburn on your eye. It causes symptoms like scratchy eye pain, excessive tears, and eyelid twitching. You can avoid it by using eye protection (green, from a #5 to a #8).

Standard Materials

While plasma cutters work on any material that can conduct electricity, there are a few that are most common. Standard materials are aluminum, mild steel, copper, brass, and stainless steel.

Composite Materials

Now that we know what standard materials are, let’s discuss composite materials. The hard part of defining them is that the “composite materials” category is huge! To fit into this category, a material has to be inhomogeneous. Basically, the material is made from more than one material and is not uniform. Usually, one material is the main one, and the others are binders. A composite material can either be layered or braided together.

Composite materials are more and more in use in the aerospace industry, especially advanced polymers. However, the most common one is the carbon-fiber-reinforced plastic/polymer (or CFRP).

Carbon Fiber-Reinforced Plastics/Polymers, or CFRP

"Broken CFRP hockey stick, close up" (CC BY 2.0) by CORE-Materials

As we said, CFRPs are the most common composite material out there. Its main structural component is carbon fiber, which is where the name comes from. In most cases, they can be cut using a plasma cutter as long as they can conduct electricity. They also have certain qualities that make them unique amongst composite materials. 

• Lightweight – Most materials have a density of 0.065 pounds per cubic inch. CFRP composite materials usually weigh in at 0.055 pounds per cubic inch. This gives them a huge advantage.
• Strong – CFRPs are much stronger as well as stiffer overall. Combined with the fact that they are also lighter, they simply pack more punch per cubic inch.

How Does The Process of Plasma Cutting Composite Materials Differ?

First of all, for a composite material to be cut with a plasma cutter, it has to conduct electricity. This filters out a large number of composite materials. The material will also need to be at least mid-range in thickness. Much more care needs to be taken with these materials as well. Their physical properties can often change a lot, even in the space of millimeters. This means that research should be done before attempting to use one on a plasma cutter.

What Are Some Issues To Expect With Plasma Cutting Composite Materials?

The main issue people find with using a plasma cutter to cut composite materials is their melting point. Since they come in a variety of different combos, they all have their own unique melting points. This can make plasma cutting tricky. High temps can melt them too much, and low temps will fail to cut them at all. One way to fix the melting issue is by using a higher speed to cut them. This reduces the amount of time the cutter is spending on the material, which lowers the possibility of melting it.

Overall, though, plasma cutting composite materials is complicated. This is mainly due to the fact that each composite material is incredibly different in structure. This also makes it hard to give overall advice about what to expect, as that varies widely between materials.

Factors to Consider For When Purchasing a Plasma Cutter

• Material Thickness – Always consider how thick the material is that you plan to cut the most. Plasma cutters get ratings on their amperage, which affects how thick of material it can cut. For example, a low amperage machine is best for materials around ¼” thick (usually with a rating of 25 amps). For materials around an inch thick, you should select a high amperage machine (about 80 amps).
• Necessary Cutting Speed – If you don’t need a lot of speed for what and how you plan to cut, don’t waste money on a fast machine. You should also check out its duty cycle (a higher rating means you can cut longer before needing to take a break).
• High-Frequency Interference – Most of the plasma cutting machines use high-frequency electricity conduction. While this works well, it also can interfere with other machines (especially the type that use wifi). Some of the newer machines also use lift arc technology, so if that is a concern you do have another option. 
• Consider Consumables – While plasma cutting machines tend to last a while, a few parts of it are “consumable”. Most of them will list those parts out, usually in the manufacturer’s specifications. Usually, these parts include the electrode, gas/swirl baffle, and nozzle.
• Check Safety Features – As we talked about above, make sure to check out its safety features before you buy. 
• Try It Out – One of the best ways to find out if a plasma cutter is going to work for you is to just try it out. This will help look at the ease of use, strength, working visibility, cut quality, and more. Some of them sound great on paper but are harder to work with live.

Making the Most Out Of Your Plasma Cutter

Now that you own a brand new plasma cutter, you’ll want to make it last as long as you can. Whether you plan on using standard materials or newer composite materials with it, here are a few tips for making it last.

• Follow Set-Up Procedures Every Time – Prior to using a plasma cutter, create and stick with the same set-up procedure every time you use it. Make sure to check your compressed air supply to make sure it is clean and there isn’t any oil or water. Also, check that your machine is holding the right air pressure. Finally, check that the electrode and nozzle are in the right place and that there is a good connection between them.
• Pierce the Work The Right Way – Always pierce your workpiece at the correct angle. Aim for 30 degrees if working vertically, and 60 degrees if working horizontally to avoid messy and unsafe blowback.
• Avoid Letting the Nozzle and Workpiece Touch – This is most important if it runs more than 45 amps. It is one of the big factors in a shorter nozzle life. There should always be between a 3/16th and a 1/8th-inch space between them.
• Take Care Of Your Parts – While they don’t cost a lot to replace, having your consumables wear out too fast can cost you money. The best way to have them last longer is by following the manufacturer’s instructions closely. Operate the plasma cutter at the settings on the directions. Keep the torch clean and use it only at the correct distance from the workpiece. Also, do not mix and match different brands, and try to use those made by the manufacturer of your machine.  

In Conclusion…

Plasma cutting is very fast, relatively cheap, and precise. This method is useful for a wide variety of materials. As long as it can conduct electricity, it can be cut. However, success can vary. When using composite materials on a plasma cutting machine, make sure to review their “ingredients” ahead of time. The time and amps it will take can change a lot depending on what they are made of.