Plasma cutting of metal: what is it, types, pros and cons

What it is?

Flame cutting of metal (go to service) is the cutting and cutting of a metal workpiece, sheet or pipe, using a plasma jet.

Plasma is the fourth state of matter. In ordinary life, we are faced with only three states, solid, liquid and gaseous, and from one to another a substance changes when it loses or gains heat: if you add heat to ice (solid), it will turn into water (liquid), and if to water , it will become a gas (gaseous). But if you add heat to the steam, it will begin to ionize and conduct electricity, turning into that same plasma.

A plasma cutter uses electrically conductive steam heated to temperatures of about 22,000°C to cut materials.

Easy to use

This advantage of plasma cutting is achieved due to the absence of the need to regulate the gas supply and control the chemical combustion reaction. The metal plasma cutting machine is designed for contact cutting of sheets, so when using it, there is no need to make efforts to maintain the distance between the cutter and the workpiece.

Optimized cutting parameters of automated plasma systems can be entered and controlled in one step, further simplifying equipment operation. With the ability to perform contact cutting and no need to adjust the gas supply, hand-held plasma cutting systems require less learning curve, meaning plant personnel can get to work faster.

How does plasma metal cutting work?

To be able to cut with plasma, you need an electric arc, which is formed between the electrode and the cutter nozzle as a result of a short circuit. Pressurized gas is supplied to the nozzle, which an electric arc converts into plasma at high speed and temperature. Due to the intensity of the plasma beam, it is capable of cutting even workpieces up to 100 mm thick.

Cooling is carried out by a flow of gas or cool liquid. Liquid cooling is used in high-power applications due to its greater efficiency, but air injectors are slightly more reliable.

Also, different gases are used for cutting different types of metal (go to service). Black ones are more often cut by active gases, which include oxygen and air, while non-ferrous and all kinds of alloys are cut by inactive gases: water vapor, argon, nitrogen, hydrogen.

Good Chinese plasma cutters

The design of an air plasma cutting machine is not so complex that it can be reproduced with errors.
At least this is what those who bought cutters in China say. Products from this country are an excellent choice if you have a limited budget. And when it comes to Chinese models, people most often remember the inexpensive CUT50p. The price of such a compressor is around $350. It is capable of delivering a current of 10 amperes, weighs 13 kilograms and has an operating mode of 60%. (After 6 minutes of work, take a break for 4 minutes.)

The advantages to note are the following:

• Light burner;
• Availability of consumables included;
• Everything is collected in one building. (this plasma cutter has a built-in air compressor);
• Power supply 220/110 volts;
• Good “features-price” ratio;

The disadvantages are obvious: if the transformer winding burns out, or the device is damaged, it will hardly be possible to return it.

But if you decide to purchase an inexpensive plasma cutter with a ready-made compressor from China, it is better to pay attention to the DWT company. It is an international company with headquarters in China and Switzerland. The company has representative offices in Russia, which means there is somewhere to turn for service.

Inverter plasma cutter DWT CUT-40

A basic inverter plasma cutter from DWT can be purchased for $200 and up.

Types of plasma cutting of metal

The division occurs into traditional and high-precision:

• the traditional one is a system that uses ordinary air, the average electric arc current is about 12,000–20,000 amperes per square meter. inch. The size of the arc depends on the diameter of the nozzle. The traditional system can be found in manual and some mechanical instruments,
• high-precision cutters have a high current density and are used for precise plasma cutting of metal. The arc current can reach 40,000–50,000 amperes per square meter. inch, the gas used is not air from the room, but argon, oxygen, nitrogen, and also air that has undergone special preparation.

Automatic machines are machines for high-precision cutting, quite complex and expensive, but they produce clean, quick results and can cope with almost all workpieces of any thickness.

They separate plasma cutting of sheet metal (go to service) and plasma cutting of pipes (go to service):

• Plasma cutting of sheet metal involves cutting and separating sheet blanks of any thickness; various alloys, non-ferrous and ferrous metals, including stainless steel, can be processed. Plasma cutting provides smooth, clean edges without sagging or burrs, as well as the absence of deformation, including on thin sheets. That is why materials can be cut on a plasma machine without preliminary mechanical treatment,
• Plasma cutting of pipes is carried out on a pipe cutting machine with a special rotary table, which fixes the pipe and rotates it under a stream of plasma for a uniform, even and clean cut. Since the plasma jet has a high temperature, it is possible to cut pipes of any thickness, including refractory metals.

More details per unit of time

Due to the significant speed superiority of plasma cutting machines, such systems clearly outperform oxygen systems in terms of productivity, even without taking into account the time required for oxygen preheating and the secondary processing operations that would be required with this technology.

High productivity of plasma cutting is ensured not only due to the high speed of processing metals of different thicknesses and short burning time, but also due to the quick shutdown of the cutter.

Advantages and disadvantages of plasma metal cutting

Advantages of the technology:

1. Relatively cheap for large quantities up to 60 mm thick. You can save money compared to oxygen cutting (go to service) by setting the settings correctly and ensuring a good efficiency-to-price ratio. However, for thicker metal it is better to use oxygen.
2. Versatility - plasma works well on cast iron, steel, copper, aluminum and other types of metals; moreover, the products do not require preliminary cleaning; they can be cut over paint and rust. And there is no need to change equipment for processing other types of metals either.
3. Precision, quality, neat edges. Often the cut does not need to be processed additionally, since it is obtained with a minimum width, with a minimum of burrs and sagging. This occurs due to the relatively small heating area of ​​the metal during cutting.
4. Eco-friendly and safe.

And its disadvantages:

1. The limit on sheet thickness is up to 80–100 mm, while for oxygen cutting of metal the top reaches 500 mm.
2. It is not possible to use two cutters connected to one machine.
3. Mastering the technology of plasma cutting of metal requires preliminary training - this is a rather complex process both when processing materials manually and when using a machine.

DIY production and operating instructions

Due to the wide production capabilities of automatic plasma cutters, not only large workshops, but also garage workshops are interested in them. Professional equipment is quite expensive, so private craftsmen may have the idea of ​​assembling the device themselves. Schemes can be easily found on the Internet, but the main difficulty in their implementation is connecting the automatic system. To do this, you need not only to be able to correctly connect the elements of a plasma cutter, but also to understand the basics of programming.

Gas flame welding - price in Moscow

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Plasma cutting techniques

In practice, two methods of cutting metal with plasma are used:

• plasma jet;
• plasma-arc method.

Plasma jet cutting has found application in the processing of non-metallic products that are not capable of conducting electric current. With this processing method, the product is not part of the electrical circuit. The arc burns between the electrode and the tip of the plasma torch. The product is cut by a plasma jet.

The plasma-arc method is widely used. It is used for: cutting profiles, pipes;

• manufacturing products with straight contours;
• casting processing;
• forming holes in metal;
• production of welding blanks.

The arc burns between the electrode and the workpiece. The arc column is combined with the plasma jet. The jet occurs due to the gas blown through the operating compressor, which becomes very hot and ionized in the process. The gas promotes the formation of plasma, and due to its high temperature, the cutting speed of the metal being processed increases. This method involves the use of a direct current arc with straight polarity.

Plasma welding technology

Plasma welding machines produced by various manufacturers are usually made to be universal. With their help, you can perform various works in all spatial positions: lower, ceiling, vertical, horizontal, inclined. The technological process of manufacturing structures consists of preparing the product for welding, selecting a filler material, if welding is performed with it, and preparing equipment.

Before welding, the part must be degreased, cleaned and carefully secured. During the welding process, the welder must protect his eyes from radiation, use all methods and means of protection to prevent thermal burns, and also use an exhaust ventilation system when welding indoors.

Today, in the trading network you can purchase various models of plasma welding devices, both domestic and foreign. Among domestic devices, mobile plasma devices “PLAZAR”, “GORYNYCH”, “MULTIPLAZ” and others are very popular.

For example, “GORYNYCH” represents a multifunctional portable device consisting of a plasma generator and a power supply and control unit. It is used for a wide range of welding, cutting and soldering of metals. It is powered by a 220 V network. Compact and easy to use, it is especially popular among welders. Depending on the type of work performed, it uses either distilled water or a solution of ethyl alcohol in the same water as the working fluid. Such a device is successfully used not only in production, construction, but also in everyday life.

Among foreign manufacturers, devices made in Germany and Italy attract special attention. Models of plasma welding and cutting machines from MERKLE Schweißanlagen-Technik GmbH are well known in different parts of the world. The company has been specializing in the production of equipment and components for welding operations for more than 50 years. Professional models of plasma devices P 421 DC-PT11, P 601 DC-PT11 and P 601 AC/DC-PT11 are used by well-known companies VOLKSWAGEN, MERCEDES-BENZ and others in the production of their products, which are known in many countries.

Manufacturer from Italy, Telwin company has been specializing in the production of modern devices for plasma welding for more than 50 years. Models Technica Plasma, Technology Plasma, Superplasma and others are equipped with overvoltage, low and high current protection, thermal protection, automatically cool the plasmatron and have a voltage alarm system in the torch. They are distinguished by their small dimensions, weight and are very convenient to use.

Increased flexibility

Plasma technology can be used to cut any metal that conducts current, including mild steel, aluminum, stainless steel, copper and most other types of metal. Unlike plasma, oxyfuel cutting technology involves a chemical reaction between oxygen and iron, so it is only used for cutting low-carbon (mild) steel.

The flexibility and versatility of plasma cutting has other aspects as well. Thus, this technology allows for manual cutting, cutting along a guide and using a pipe cutter, as well as cutting on a convenient coordinate table. In addition, plasma systems can be used for gouging, marking and cutting painted, rusty and even multi-layered metal, the sheets of which are superimposed on each other. Plasma makes it possible to perform both conventional cutting and bevel cutting of metal gratings, which is difficult to achieve using oxyfuel cutting.

Improved Security

Plasma cutting systems use only compressed air, unlike oxy-fuel cutting, which uses a mixture of oxygen and fuel gas (acetylene, propane, propylene and natural gas). Among these compounds, acetylene is the most popular, providing a hotter flame and reducing burn time. However, acetylene is an unstable and flammable gas, sensitive even to static electricity, not to mention elevated pressure and temperature. In such conditions, working on oxygen cutting equipment can no longer be considered completely safe.

In conclusion, we suggest watching a video in which all the advantages of plasma cutting over oxygen are clearly illustrated and therefore become more understandable: