If you are into metal fabrication techniques like forming, joining, and machining, copper and some of its alloys are materials you’ll find extremely useful at some point. Also, you’ll know how effective plasma cutting can be as long as cutting is a regular part of your job. Thus, the use of a plasma machine to cut copper comes into mind. But is it a possibility? Here goes my answer.
You can cut copper using a plasma cutter because of its electrical conductivity. You’ll need a 50 amp plasma cutter and the same specs as those for plasma cutting steel. Start cutting slowly and then add a piece of steel on top of the copper to make the process easier.
Before I talk about the steps, I’ll share some details regarding the properties and suitability of copper as a metal to be cut with a plasma cutter and a few things to let you know why electrical conductivity is so crucial to this cutting method.
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Is Copper Electrically Conductive?
Most of us who are interested in mechanical or thermal cutting are aware of electrically conductive metals, but many people have little idea about how much conductivity those metals possess. I wouldn’t emphasize this factor much if we were to talk about steel or aluminum. But copper is not as widely used as those metals. So, I guess a little understanding will help you.
Of all non-precious metals, copper comes with the highest electrical and heat conductivity. Some of its important qualities include high ductility, corrosion resistance, ease of joining, and medium strength which make it one of the top choices for electrical projects such as motor and transformer windings, bus bars, and cables. It has 65% higher conductivity than aluminum.
Its heat conductivity is even better. Copper is about 1.5 and 30 times better as a conductor of heat than aluminum and stainless steel respectively. On a project that requires quick heat transfer, copper becomes the first metal of choice. I could mention a few examples like heat sinks used in personal computers and heat exchangers in HVAC units or vehicle radiators.
Why Is Electrical Conductivity Important?
In plasma cutting, hot plasma is created in the form of an accelerated jet by means of which electrically conductive metals are cut. A plasma cutter creates an electrical channel using electrically ionized, super-heated gas through the metals being cut, which forms a complete circuit that goes back to the plasma machine using an earth terminal.
One of the recommended compressed gases such as air, oxygen, or inert gas is required for this process. Depending on the metal being cut, you should choose this gas which gets blown to the metal at a high speed right through a nozzle.
An arc is created within the gas between an electrode and the metal being cut. That is an electric arc which ionizes the gas partially and thus creating the aforementioned plasma channel. The cutting torch, a part of your plasma cutter, passes current through the plasma which gives off a lot of heat or just enough of it to melt through your metal.
The plasma being at a high speed along with the compressed gas blows whatever hot molten is created in the process away and protects the metal in use. This is the process of plasma cutting in brief. I guess that explains why electrical conductivity is a must.
How Can You Cut Copper with a Plasma Cutter?
Frankly speaking, the whole process is about preparing the workplace and getting the settings or specs right because the rest is almost the same as you would get while plasma cutting any other metal.
Ventilate Your Work Area
Much of the challenge with plasma cutting copper stems from one of the properties of copper that is identified with a high ‘smoking’ temperature. As a plasma cutter does its job on your copper piece, it absorbs the heat pretty quickly and efficiently. This very tendency results in its giving off plenty of smoke.
I wouldn’t say there is extreme toxicity to this smoke generated from cutting copper. Despite that, you should ventilate the area properly to keep the surrounding air clean and congestion to a minimum level. Since most plasma cutting projects are completed in confined spaces, I think you could use a breathable air mask.
Get the Specs Right
Here comes the most important part of the job which, if you don’t handle correctly, may result in an utter failure. While I can’t know the particular model or brand of your plasma cutter, I can only recommend that you consult the user manual that came along with your plasma unit.
Check your plasma cutter. If it says 50 amps, you can cut copper pieces with 1/2-inch thickness. Anything lower than 50 amps may not do very well on metals thicker than 1/4 inch. In practice, I got no specific numbers on these matters concerning copper as the workpiece.
From what I got in dozens of plasma cutter manuals, I can tell that most manufacturers provide the settings for aluminum, mild and stainless steel. Instructions for metals like copper or brass are usually left out. You needn’t worry just yet. The specs of steel cutting can always be taken into account since those particulars are proven to be effective for most other metals.
However, you shouldn’t be indifferent to the thickness of copper. Choose the same thickness for your copper pieces, should you be ready to follow the instructions for steel cutting. The next thing is to get the right distance between the torch and the workpiece. You must keep the height constant to avoid poor cuts.
‘Torch to Work’ Distance or Standoff
The only recommended way to adjust the standoff is to monitor the arc voltage and control it. The arc voltage and the output voltage of the power supply are technically the same things. The power supply used in a plasma system is a typical current source, but it generates an operating current which remains very steady as you cut with the torch.
The voltage of the arc may vary depending on how far the electrode or cathode encased in the plasma torch is from the anode or the metal being cut. Both voltage and resistance are in a direct proportion to each other, meaning that the resistance indicates the distance.
According to Ohm’s Law, voltage equals to I*R. So, the voltage goes high as the standoff increases. Similarly, decreased standoff results in decreased voltage. Today’s plasma cutters come with dedicated torch height controls (THC) which use arc voltage to keep the distance from the workpiece consistent during the cutting.
Having a plasma cutter with THC, you can maintain proper height, no matter which metal you’re cutting or how flat your cutting bed is. All you have to do is set the voltage on your remote control. According to what most operation manuals state in their cut charts, you should keep the voltage between 100 VDC and 200 VDC. This also works for copper too.
As you start cutting with the torch, the height control component starts sampling the arc voltage coming from the plasma power supply. Then, it compares that voltage to the voltage you previously set. Upon sensing any difference, the THC adjusts your torch up/down to help maintain the voltage you’ve set.
Each arc voltage setting leads to a specific distance or height that is critical to the quality of the cut. This height affects the bevel angle of your cut piece. If you set the voltage to be too high, the kerf’s top will lose more material than its bottom. So, you’ll get a positive bevel but with excessive top rounding.
Too low voltage does the opposite. You’ll get undercut or negative bevel as the bottom of the kerf loses much material. Maintaining the right height is important as you won’t like poor cut quality or any expensive rework after cutting.
Prepare for Table Cutting
For most professionals, a plasma cutting table can be an excellent tool that helps them have enough surface to rest the workpiece and exercise enhanced control over the process. These tables become more desirable where you’ll use materials thicker than 1 inch. Choose a table that comes equipped to withstand the excessive heat generated by a plasma cutter.
Don’t Cut Too Fast
The reason for me to tell you this is that copper, despite being a great conductor of heat, gets slow when it comes to the rate at which electrical conduction occurs. It is wise to take a test cut on a piece. Do a few strip cuts maintaining a fixed height. These can be straight-line cuts.
Look at the cuts and increase the speed a little bit. Say, 3-5 inches per minute (IPM) for each cut. You’ll see changes on the positive side every time you change the speed. That is how you can improve the cut quality. Keep practicing this way. Once you’ll see minimal dross with even cuts; you can call it ‘a job well done’.
Going slow to let the plasma cutter do its work through the workpiece (copper) evenly and in a straight direction. Make sure the cutter goes all the way to your workpiece. If your plasma cutter is one of the high-end automated systems and you are set to make a long cut, you must monitor the duty cycle consistently to ensure optimal runtime and cutting performance.
Before you move away from this page to another, I would like to offer a couple of suggestions to conclude this discussion. One is about adding an additional piece of metal and the other is about the THC.
I’ve already mentioned that copper conducts more heat than electricity. To avoid any inconsistency or lack of harmony, you can add a piece of scrap steel on top of the workpiece. It can be another metal with higher electrical conductivity. Don’t cover the copper workpiece entirely. Bring a small piece of steel or other metal where the grounding clamp can be placed.
Here is another piece of advice in which I’m going to tell you something about the THC system. Don’t attempt to finish your project with a broken THC because it’ll only add to your challenges. If the THC is too old to be compatible with your plasma cutter, you can pick a retrofitted item.
What if you don’t have any THC at all? You can buy one if your budget allows a few hundred bucks. Otherwise, you’ll have to rely on your own skills. I’ve seen a lot of people become good enough to develop their own plasma cutting specs after a few projects.
Well, you’ve got all the details and insights into plasma cutting copper as far as my understanding goes. But I’ll be happy to help you more. Just send me a message. Stay safe!