The principle of operation of a plasma cutter. Tips for making a plasma cutter from an inverter with your own hands Do-it-yourself plasma cutting

Typically plasma sheet metal is cut in large industries, and this is done in the manufacture of parts of complex configurations. Industrial machines cut any metals: steel, copper, brass, aluminum, super-hard alloys. It is noteworthy that it is quite possible to make a plasma cutter yourself, although the capabilities of the device in this case will be somewhat limited. In large-scale production, a homemade manual plasma cutter is unsuitable, but it will be possible to cut out parts in your workshop, workshop or garage. There are practically no restrictions regarding the configuration and hardness of the workpieces being processed. However, they relate to cutting speed, sheet size and metal thickness.

Description of a homemade plasma cutter from an inverter

DIY plasma cutter It’s easier to make using an inverter welding machine as a basis. Such a unit will be simple in design, functional, with accessible main components and parts. If some parts are not for sale, you can also make them yourself in a workshop with moderately complex equipment.

The homemade device is not equipped with a CNC, which is its disadvantage and advantage at the same time. The disadvantage of manual control is the impossibility of producing two completely identical parts: small series of parts will differ in some way. The advantage is that you don’t have to buy an expensive CNC machine. For a mobile plasma cutter, CNC is not needed, since the tasks performed on it do not require it.

The main components of a homemade unit:

• plasmatron;
• oscillator;
• DC source;
• compressor or compressed gas cylinder;
• power cables;
• connection hoses.

So, there are no complex elements in the design. However, all elements must have certain characteristics.

Plasma cutting requires that the amperage be at least equal to that of a medium power welder. A current of such strength is generated an ordinary welding transformer and an inverter machine. In the first case, the structure turns out to be conditionally mobile: due to the large weight and dimensions of the transformer, its movement is difficult. Together with a compressed gas cylinder or compressor, the system becomes cumbersome.

Transformers have low efficiency, which results in increased energy consumption when cutting metal.

The circuit with an inverter is somewhat simpler and more convenient, and even more profitable in terms of energy consumption. The welding inverter will produce a fairly compact cutter that will cut metal up to 30 mm thick. Industrial plants cut metal sheets of the same thickness. A plasma cutter on a transformer can cut even thicker workpieces, although this is not required so often.

pros plasma cutting visible just on thin and ultra-thin sheets.

• Smooth edges.
• Line accuracy.
• No metal spatter.
• The absence of overheated zones near the interaction between the arc and metal.

A homemade cutter is assembled on the basis of an inverter welding machine of any type. It doesn’t matter what the number of operating modes is, you only need a direct current of more than 30 A.

Plasma torch

The second most important element is the plasmatron. A plasma cutter consists of a main and an additional electrode, the first is made of a refractory metal, and the second is a nozzle, usually copper. The main electrode serves as the cathode, and the nozzle serves as the anode, and during operation this is the current-conducting part being processed.

If we consider the plasmatron direct action, the arc occurs between the workpiece and the cutter. Indirect plasma torches cut with a plasma jet. The inverter device is designed for direct action.

The electrode and nozzle are consumables and are replaced as they wear out. In addition to them, the housing has an insulator that separates the cathode and anode units, and there is also a chamber where the supplied gas vortexes. In a nozzle, conical or hemispherical, a thin hole is made through which gas escapes, heated to 3000-5000°C.

Gas enters the chamber from a cylinder or is supplied from a compressor through a hose, which is combined with power cables, forming a package of hoses and cables. The elements are connected in an insulating sleeve or connected by a harness. Gas enters the chamber through a straight pipe, which is located on top or on the side of the vortex chamber, which ensures the movement of the working medium in only one direction.

The principle of operation of the plasma torch

Gas entering under pressure into the space between the nozzle and the electrode passes into the working hole and is then released into the atmosphere. When the oscillator is turned on - a device that generates a pulsed high-frequency current - a preliminary arc appears between the electrodes and heats the gas in the limited space of the combustion chamber. Since the heating temperature is very high, the gas turns into plasma. In this state of aggregation, almost all atoms are ionized, that is, electrically charged. The pressure in the chamber rises sharply, and the gas rushes out in a hot stream.

When brought to the part plasmatron, a second, more powerful arc occurs. If the oscillator current is 30-60 A, the working arc occurs at a force of 180-200 A. It additionally heats the gas, which accelerates under the influence of electricity to 1500 m/s. The combined effect of high temperature plasma and speed of movement cuts the metal along the finest line. The thickness of the cut is determined by the properties of the nozzle.

An indirect plasma torch works differently. The role of the main anode in it is played by the nozzle. Instead of an arc, a plasma jet erupts from the cutter, cutting non-conductive materials. Homemade equipment of this type works extremely rarely. Due to the complexity of the plasma torch design and fine adjustments, it is almost impossible to make it in artisanal conditions, although drawings are not difficult to find. It works under high temperatures and pressures and becomes dangerous if done incorrectly!

Oscillator

If you don’t have time to assemble electrical circuits and search for parts, take factory-made oscillators, for example, VSD-02. The characteristics of these devices are most suitable for working with an inverter. The oscillator is connected to the plasmatron power circuit in series or in parallel, depending on what the instructions for a particular device dictate.

Working gas

Before you start making a plasma cutter, consider the scope of its application. If you have to work exclusively with ferrous metals, you can get by with just one compressor. Copper, brass and titanium require nitrogen, and aluminum is cut in a mixture of nitrogen and hydrogen. High-alloy steels are cut in an argon atmosphere; here the machine is also designed for compressed gas.

Transporting the device

Due to the complexity of the device design and the numerous components that make it up, the plasma cutting machine is difficult to place in a box or portable case. It is recommended to use a warehouse cart to move goods. The trolley will compactly accommodate:

• inverter;
• compressor or cylinders;
• cable and hose group.

Within a workshop or workshop there will be no problems with moving. When the device needs to be transported to any site, it is loaded into a passenger car trailer.

Plasma cutting is widely used in various industries: mechanical engineering, shipbuilding, advertising, utilities, metal structures and other industries. In addition, a plasma cutter can also be useful in a private workshop. After all, with the help of it you can quickly and efficiently cut any conductive material, as well as some non-conductive materials - plastic, stone and wood. You can cut pipes, sheet metal, make a shaped cut or make a part simply, quickly and conveniently using plasma cutting technology. The cut is performed using a high-temperature plasma arc, which requires only a power source, a torch and air to create. To make working with a plasma cutter easy and the cut to be beautiful and smooth, it doesn’t hurt to learn the operating principle of a plasma cutter, which will give you a basic understanding of how you can control the cutting process.

A device called a “plasma cutter” consists of several elements: power supply, plasma cutter/plasma torch, air compressor And cable-hose package.

Power supply for plasma cutter supplies a certain current to the plasmatron. May be a transformer or inverter.

Transformers They are heavier, consume more energy, but are less sensitive to voltage changes, and they can be used to cut workpieces of greater thickness.

Inverters lighter, cheaper, more economical in terms of energy consumption, but at the same time they allow cutting workpieces of smaller thickness. Therefore, they are used in small industries and private workshops. Also, the efficiency of inverter plasma cutters is 30% greater than that of transformer ones, and their arc burns more stable. They are also useful for working in hard-to-reach places.

Plasma torch or whatever they call it "plasma cutter" is the main element of the plasma cutter. In some sources you can find a mention of a plasma torch in such a context that one might think that “plasma torch” and “plasma cutter” are identical concepts. In fact, this is not so: a plasma torch is directly a cutter with which the workpiece is cut.

The main elements of a plasma cutter/plasma torch are nozzle, electrode, cooler/insulator between them there is a channel for supplying compressed air.

The plasma cutter diagram clearly demonstrates the location of all plasma cutter elements.

Inside the plasma torch body there is electrode, which serves to excite an electric arc. It can be made of hafnium, zirconium, beryllium or thorium. These metals are suitable for air plasma cutting because during operation, refractory oxides are formed on their surface, which prevent the destruction of the electrode. However, not all of these metals are used because the oxides of some of them can be harmful to the operator's health. For example, thorium oxide is toxic, and beryllium oxide is radioactive. Therefore, the most common metal for the manufacture of plasmatron electrodes is hafnium. Less commonly, other metals.

Plasma torch nozzle compresses and forms a plasma jet, which escapes from the output channel and cuts the workpiece. The capabilities and characteristics of the plasma cutter, as well as the technology for working with it, depend on the size of the nozzle. The dependence is as follows: the diameter of the nozzle determines how much air volume can pass through it in a unit of time, and the width of the cut, the cooling rate and the operating speed of the plasma torch depend on the volume of air. Most often, the plasma torch nozzle has a diameter of 3 mm. The length of the nozzle is also an important parameter: the longer the nozzle, the more accurate and better the cut. But you need to be more careful with this. A nozzle that is too long will break down faster.

Compressor for a plasma cutter it is necessary for air supply. Plasma cutting technology involves the use of gases: plasma-forming and protective. Plasma cutting machines, designed for currents up to 200 A, use only compressed air, both to create plasma and for cooling. This machine is sufficient for cutting workpieces 50 mm thick. An industrial plasma cutting machine uses other gases - helium, argon, oxygen, hydrogen, nitrogen, as well as their mixtures.

Cable-hose package connects the power source, compressor and plasmatron. The electric cable supplies current from a transformer or inverter to initiate an electric arc, and the hose carries compressed air, which is necessary for the formation of plasma inside the plasma torch. We will describe in more detail what exactly happens in the plasmatron below.

As soon as the ignition button is pressed, the power source (transformer or inverter) begins to supply high-frequency currents to the plasmatron. As a result, a pilot electric arc appears inside the plasma torch, the temperature of which is 6000 - 8000 °C. The pilot arc lights up between the electrode and the nozzle tip for the reason that it is difficult to form an arc between the electrode and the workpiece being processed immediately. The pilot arc column fills the entire channel.

After the pilot arc occurs, compressed air begins to flow into the chamber. It breaks out of the pipe, passes through an electric arc, as a result of which it heats up and increases in volume by 50 - 100 times. In addition, the air is ionized and ceases to be a dielectric, acquiring conductive properties.

The plasma torch nozzle, narrowed to the bottom, compresses the air, forms a flow from it, which escapes from the nozzle at a speed of 2 - 3 m/s. The air temperature at this moment can reach 25,000 - 30,000 °C. It is this high-temperature ionized air that is in this case plasma. Its electrical conductivity is approximately equal to the electrical conductivity of the metal being processed.

At the moment when the plasma escapes from the nozzle and comes into contact with the surface of the metal being processed, the cutting arc is ignited, and the pilot arc goes out. The cutting/working arc heats up the workpiece being processed at the cutting site - locally. The metal melts, a cut appears. Particles of just molten metal appear on the surface of the metal being cut, which are blown away from it by a stream of air escaping from the nozzle. This is the simplest plasma metal cutting technology.

Cathode spot The plasma arc must be located strictly in the center of the electrode/cathode. To ensure this, the so-called vortex or tangential supply of compressed air is used. If the vortex feed is disrupted, then the cathode spot moves relative to the center of the electrode along with the plasma arc. This can lead to unpleasant consequences: the plasma arc will burn unstably, two arcs may form simultaneously, and in the worst case, the plasma torch may fail.

If you increase the air flow, the speed of the plasma flow will increase, and the cutting speed will also increase. If you increase the diameter of the nozzle, the speed will decrease and the width of the cut will increase. The speed of the plasma flow is approximately 800 m/s at a current of 250 A.

Cutting speed is also an important parameter. The larger it is, the thinner the cut. If the speed is low, the cutting width increases. If the current increases, the same thing happens - the width of the cut increases. All these subtleties relate directly to the technology of working with a plasma cutter.

Plasma cutter parameters

All plasma cutting machines can be divided into two categories: manual plasma cutters and machine cutting machines.

Manual plasma cutters are used in everyday life, in small industries and in private workshops for the manufacture and processing of parts. Their main feature is that the plasma torch is held in the hands of the operator, he guides the cutter along the line of the future cut, holding it in weight. As a result, the cut is even, but not perfect. And the productivity of such technology is low. To make the cut more even, without sagging and scale, a special stop is used to guide the plasma torch, which is placed on the nozzle. The stop is pressed against the surface of the workpiece and all that remains is to guide the cutter, without worrying about whether the required distance is maintained between the workpiece and the nozzle.

For a manual plasma cutter, the price depends on its characteristics: maximum current, thickness of the workpiece being processed, and versatility. For example, there are models that can be used not only for cutting metals, but also for welding. They can be distinguished by their markings:

• CUT - cutting;
• TIG - argon arc welding;
• MMA - arc welding with a stick electrode.

For example, the FoxWeld Plasma 43 Multi plasma cutter combines all of the listed functions. Its cost is 530 - 550 USD. Characteristics related to plasma cutting: current strength - 60 A, workpiece thickness - up to 11 mm.

By the way, the current strength and the thickness of the workpiece are the main parameters by which a plasma cutter is selected. And they are interconnected.

The higher the current, the stronger the plasma arc, which melts the metal faster. When choosing a plasma cutter for specific needs, you need to know exactly what metal will have to be processed and what thickness. The table below shows how much current is needed to cut 1 mm of metal. Please note that processing non-ferrous metals requires high amperage. Keep this in mind when you look at the characteristics of a plasma cutter in a store; the thickness of the ferrous metal workpiece is indicated on the device. If you plan to cut copper or other non-ferrous metal, it is better to calculate the required amperage yourself.

For example, if you need to cut copper 2 mm thick, then you need to multiply 6 A by 2 mm, we get a plasma cutter with a current strength of 12 A. If you need to cut steel 2 mm thick, then multiply 4 A by 2 mm, you get a current strength of 8 A. Only Take a plasma cutting machine with a reserve, since the specified characteristics are maximum, not nominal. You can only work on them for a short time.

CNC plasma cutting machine used in manufacturing plants for the manufacture of parts or processing of workpieces. CNC stands for Computer Numerical Control. The machine operates according to a given program with minimal operator participation, which eliminates the human factor in production as much as possible and increases productivity significantly. The cutting quality of the machine is ideal; no additional edge processing is required. And most importantly - figured cuts and exceptional precision. It is enough to enter the cutting diagram into the program and the device can make any intricate shape with perfect accuracy. The price of a plasma cutting machine is significantly higher than that of a manual plasma cutter. First, a large transformer is used. Secondly, a special table, portal and guides. Depending on the complexity and size of the device, the price can be from 3000 USD. up to 20,000 USD

Machine plasma cutting machines use water for cooling, so they can work the entire shift without interruption. The so-called PV (on duration) is 100%. Although for manual devices it can be 40%, which means the following: the plasma cutter works for 4 minutes, and it needs 6 minutes to cool down.

It would be most reasonable to purchase a ready-made, factory-made plasma cutter. In such devices, everything is taken into account, adjusted and works as perfectly as possible. But some “Kulibina” craftsmen manage to make a plasma cutter with their own hands. The results are not very satisfactory, since the quality of the cut is poor. As an example, we will give a stripped-down version of how you can make a plasma cutter yourself. Let us immediately make a reservation that the diagram is far from ideal and only gives a general concept of the process.

So, a transformer for a plasma cutter must have a falling current-voltage characteristic.

Example in the photo: the primary winding is from below, the secondary winding is from above. Voltage - 260 V. Winding cross-section - 45 mm2, each bus 6 mm2. If you set the current to 40 A, the voltage drops to 100 V. The inductor also has a cross-section of 40 mm2, wound with the same bus, about 250 turns in total.

To operate, you need an air compressor, of course, a factory-made one. In this case, a unit with a capacity of 350 l/min was used.

Homemade plasma cutter - operation diagram.

It is better to purchase a factory-made plasma torch; it will cost about 150 - 200 USD. In this example, the plasma torch was made independently: a copper nozzle (5 cu.) and a hafnium electrode (3 cu.), the rest is “handicraft”. Due to this, the consumables quickly failed.

The circuit works like this: there is a start button on the cutter, when it is pressed, the relay (p1) supplies voltage to the control unit, the relay (p2) supplies voltage to the transformer, then releases air to purge the plasma torch. The air dries the plasma torch chamber from possible condensation and blows out all excess, it has 2 - 3 seconds for this. It is with this delay that the relay (p3) is activated, which supplies power to the electrode to ignite the arc. Then the oscillator is turned on, which ionizes the space between the electrode and the nozzle, as a result, the pilot arc lights up. Next, the plasma torch is brought to the workpiece and the cutting/working arc lights up between the electrode and the workpiece. The reed switch switches off the nozzle and ignition. According to this scheme, if the cutting arc suddenly goes out, for example, if the nozzle gets into a hole in the metal, then the reed switch relay will turn on the ignition again and after a few seconds (2 - 3) the pilot arc will light up, and then the cutting arc. All this is provided that the “start” button is not released. Relay (p4) releases air into the nozzle with a delay, after the “start” button is released and the cutting arc goes out. All these precautions are necessary in order to extend the life of the nozzle and electrode.

Making a plasma cutter yourself at home makes it possible to save a lot, but there is no need to talk about the quality of the cut. Although if an engineer takes on the work, the result may be even better than the factory version.

Not every enterprise can afford a CNC plasma cutting machine, because its cost can reach 15,000 - 20,000 USD. Quite often, such organizations order plasma cutting work to be carried out at special enterprises, but this is also expensive, especially if the volume of work is large. But you really want your own new plasma cutting machine, but you don’t have enough money.

In addition to well-known specialized factories, there are enterprises that produce plasma cutting machines, purchasing only profile parts and assemblies, and producing everything else themselves. As an example, we will tell you how engineers make CNC plasma cutting machines on a production floor.

Components of a do-it-yourself plasma cutting machine:

• Table 1270x2540 mm;
• Belting;
• Step parts;
• Linear guides HIWIN;
• System that controls the height of the THC flame;
• Control block;
• The terminal stand in which the CNC control unit is located is separate.

Machine characteristics:

• The speed of movement on the table is 15 m/min;
• The accuracy of setting the plasma torch position is 0.125 mm;
• If you use a Powermax 65 machine, the cutting speed will be 40 m/min for a 6 mm workpiece or 5 m/min for a 19 mm thick workpiece.

For a similar metal plasma cutting machine, the price will be about 13,000 USD, not including the plasma source, which will have to be purchased separately - 900 USD.

To manufacture such a machine, components are ordered separately, and then everything is assembled independently according to the following scheme:

• The base for welding the table is being prepared, it must be strictly horizontal, this is very important, it is better to check with a level.
• The machine frame is welded in the form of a table. Square pipes can be used. The vertical “legs” must be reinforced with jibs.

• The frame is coated with primer and paint to protect it from corrosion.

• Supports for the machine are being manufactured. The material of the supports is duralumin, the bolts are 14 mm, it is better to weld the nuts to the bolts.

• The water table is welded.

• Fastenings for the slats are installed and the slats are installed. For slats, metal is used in the form of a 40 mm strip.
• Linear guides are installed.
• The table body is covered with sheet iron and painted.
• The portal is installed on the guides.

• A motor and end inductive sensors are installed on the portal.
• The guide rails, rack and pinion and Y-axis motor are installed.

• The guides and motor are installed on the Z axis.
• A metal surface sensor is installed.

• A tap is installed to drain water from the table, and limiters for the portal are installed so that it does not move off the table.
• Cable channels Y, Z and X are installed.

• All wires are hidden in corrugation.
• A mechanized burner is installed.

• Next, the CNC terminal is manufactured. First, the body is welded.
• A monitor, keyboard, TNS module and buttons for it are installed in the CNC terminal housing.

That's it, the CNC plasma cutting machine is ready.

Despite the fact that the plasma cutter has a fairly simple device, you still shouldn’t start making it without serious knowledge of welding and extensive experience. It’s easier for a beginner to pay for a finished product. But engineers who want to implement their knowledge and skills at home, as they say “on the knee,” can try to create a plasma cutter with their own hands from start to finish.

The technology of various metal products is used with equal success in everyday life and in large industrial production. Using special equipment, you can easily cut non-ferrous metals, as well as work efficiently with stainless steel, aluminum and other alloys. Cutting non-ferrous metals is carried out using special plasma cutters, which are at the same time easy to use, functional and reliable. Let's tell you more about this equipment and talk about how to make a plasma cutter with your own hands from an inverter.

Industrial plasma cutters are productive equipment that allows for the most accurate cutting of metals with different refractoriness indices. Such industrial plasma cutters are designed primarily for operation under conditions of increased loads and are equipped with CNC, which makes it possible to manufacture parts in a serial manner.

If you need a plasma cutter for domestic use, as well as for the use of such equipment in construction, then such a cutter you can make it yourself from a simple welding inverter. Subsequently, self-made equipment will be distinguished by its versatility in use and will allow you to effectively cut non-ferrous metals and thick sheet steel.

Making such a cutter with your own hands from an inverter will not be particularly difficult. You can easily find diagrams for the implementation of such devices on the Internet and, using the calculations obtained, make such an easy-to-use device. We can recommend that you make plasma cutters based on compact welding inverters, which will significantly simplify the design and guarantee the necessary efficiency of such devices.

Homemade plasma cutting machines are not equipped with CNC, so it will be impossible to use such equipment for work that is fully controlled by automation. You must understand that using such homemade plasma cutters it will be impossible to make two perfectly accurate parts.

A homemade plasma cutter will consist of the following elements:

• Plasmatron.
• DC source.
• Compressor or gas cylinder.
• Oscillator.
• Power cables.
• Connection hoses.

Principle of operation

The operating principle of such equipment is extremely simple:

1. The current source used, and in our case it is an inverter, generates voltage and supplies it through cables to the plasmatron.
2. The plasma torch contains two electrodes, between which a high-temperature arc is excited.
3. Through specially twisted channels under high pressure, a stream of air or gas is supplied to the working area with a ignited arc.
4. A work cable is pre-connected to the product being cut, which closes to the surface being cut and provides the ability to work with metal.

DC power supplies

Plasma cutting technology will invariably require high operating current power, the performance of which should be at the level of semi-professional and professional inverter welding machines. It is not recommended to use transformer welding machines as a power source, since such devices are bulky and inconvenient to use. But an inverter will be an excellent choice, since such devices combine compact dimensions and provide high-quality electric current.

Schemes and drawings of a plasma cutter with your own hands are simple, while the costs of manufacturing such equipment are significantly reduced. A hand-made compact plasma cutter made from a welding inverter will be able to cope with cutting metal whose sheet thickness will reach 30 mm. If we talk about the advantages of such home plasma cutters made using an inverter, then we note the following:

• No metal sparks.
• Smooth edges.
• Line accuracy.
• Overheating problems resolved.

Important: making a homemade plasma cutter based on an inverter is not difficult. It is only necessary that the device generate an electric current with a force of at least 30 Amps.

The current source used must meet the following requirements:

• Power supply from a network with a voltage of 220 Volts.
• Ability to operate with a power of 4 kW.
• The idle speed should be 220 Volts.
• The current adjustment range is in the range of 20−40 Amperes.

Plasma torch design

The plasma torch is the second most important element of a metal cutter. Let's take a closer look at the design of the plasma torch and the principle of its operation. It consists of a main and auxiliary electrode. The main electrode is made of refractory metals, and the auxiliary electrode, which has the shape of a nozzle, is usually made of copper.

In a plasma torch, the cathode is the main electrode made of a refractory metal, and a copper electrode-nozzle is used as an anode, which makes it possible to provide high-quality electric current and a high-temperature arc for cutting metal.

The completed plasma torch is responsible for creating and maintaining an arc that is located between the workpiece and the cutter. The thickness of the cut, as well as the temperature created by such a cutter, will depend on the shape and design of the nozzle. The nozzle used can be hemispherical or conical, providing an operating temperature of 30,000 degrees Celsius.

During operation of the plasma torch, the main electrode and nozzle may wear out, which leads to a deterioration in the quality of metal cutting. If these elements become so worn, they should be replaced with new ones, which will ensure excellent quality working with metal.

The plasma torch is supplied with working gas from a cylinder, using special heavy-duty gas hoses that can withstand high pressure. In each specific case, depending on the material being worked with, the gas used, which is necessary for cutting the metal, may differ.

The working gas is supplied through special channels, and the presence of numerous turns in the supply tube makes it possible to provide the necessary air turbulence, which, in turn, guarantees a high-quality cutting plasma arc that will have the correct shape. This improves the quality of metal cutting and welding and minimizes the thickness of the seam.

Oscillator

A special feature of plasma cutters is the fact that To start work, preliminary ignition of the arc is required, only after this gas is supplied to the plasmatron, the arc is created at the required temperature and the metal is cut. An oscillator is used as such a kind of starter, which serves to pre-ignite the arc. The implementation scheme of the oscillator is not difficult.

On the Internet you can find functional and electrical diagrams of oscillators, which will not be difficult to complete. It is only necessary to use high-quality electrical circuits and capacitors, which will be suitable in their parameters to the electric current generated by the inverter. Depending on its type, such a torch can be connected to the plasma torch power circuit in series or in parallel.

Working gas

Even before choosing a specific design for manufacturing a plasma cutter, you should decide on the scope of use of such equipment. If you plan to use the device exclusively for working with ferrous metals, you can exclude gas cylinders from the circuit and use only a compressor with compressed air. If you plan to use such equipment for brass, titanium and copper, then you need to choose a plasma cutter with a nitrogen cylinder. Aluminum cutting is performed using a special gas mixture with hydrogen and nitrogen.

Let's figure out how plasma cutting of metal is done with our own hands. After turning on the inverter, the generated electric current enters the plasma cutter onto the electrode, and the oscillator ignites the electric arc. Its temperature can initially be 6-8 thousand degrees. Immediately after the arc is ignited, air or gas is supplied to the nozzle under high pressure, through which an electric charge passes. The air flow is heated and ionized by an electric arc, after which its volume can increase hundreds of times, and the gas and air itself begins to conduct electric current.

A plasma cutter produces a thin jet of plasma, the temperature of which can reach 30,000 degrees. Subsequently, such a high-temperature plasma jet is supplied to the metal being processed, which makes it possible to cut heavy-duty metal elements.

One of the features of using plasma cutting is the fact that the metal being processed is cut and melted exclusively at the point where it is exposed to the plasma flow. It is extremely important to correctly position the plasma impact spot, which should be located strictly in the center of the working electrode. If this requirement is neglected, the air-plasma flow is disrupted, which deteriorates the quality of metal cutting.

The quality of work with such a plasma cutter will also depend on the air flow rate. It is recommended that all work be carried out with a current of 250 Amperes, while the speed of the air stream will be 800 meters per second. This will allow you to easily work with metals with different refractoriness characteristics, ensuring high-quality cutting without thermal effects on the structure of the alloy.

A plasma cutter is a special device that allows you to quickly, efficiently and effectively cut metal of various structures. You can either purchase plasma cutters that have already been manufactured in a factory, or make them yourself. You can easily find suitable schemes for making plasma cutters from an inverter or transformer welding machine, which will allow you to make such equipment yourself, saving on buying it in a store.

Plasma cutting is actively used in many industrial fields. However, a plasma cutter is quite capable of being useful to a private master. The device allows you to cut any conductive and non-conductive materials with high speed and quality. The technology of work makes it possible to process any parts or create shaped cuts, which is carried out by a high-temperature plasma arc. The flow is created by basic components - electric current and air. But the benefits of using the device are somewhat overshadowed by the price of factory models. To provide yourself with the opportunity to work, you can create a plasma cutter with your own hands. Below we present detailed instructions with the procedure and list of equipment that is needed.

What to choose: transformer or inverter?

Due to the presence of features and parameters of plasma cutting devices, it is possible to divide them into types. Inverters and transformers have gained the most popularity. The cost of the device of each model will be determined by the declared power and operating cycles.

Inverters are lightweight, compact in size and consume minimal electricity. Disadvantages of the equipment include increased sensitivity to voltage changes. Not every inverter is able to function within the specific conditions of our electrical network. If the device’s protection system fails, you must contact a service center. Also, inverter plasma cutters have a rated power limitation of no more than 70 amperes and a short period of switching on the equipment at high current.

A transformer, traditionally, is considered more reliable than an inverter. Even with a noticeable drop in voltage, they lose only part of the power, but do not break. This property determines the higher cost. Plasma cutters based on a transformer can operate and be switched on for a longer period of time. Similar equipment is used in automatic CNC lines. The negative aspect of a transformer plasma cutter will be its significant weight, high energy consumption and size.

The maximum metal thickness that a plasma cutter can cut is from 50 to 55 millimeters. The average power of the equipment is 150 - 180 A.

Average cost of factory devices

The range of plasma cutters for manual cutting of materials is now truly huge. Price categories are also different. The price of devices is determined by the following factors:

• Device type;
• Manufacturer and country of production;
• Maximum possible cutting depth;
• Model.

Having decided to explore the possibility of purchasing a plasma cutter, you need to be interested in the cost of additional elements and components for the equipment, without which it will be difficult to fully operate. Average prices for devices, depending on the thickness of the metal being cut, are:

• Up to 6 mm – 15,000 – 20,000 rubles;
• Up to 10 mm – 20,000 – 25,000;
• Up to 12 mm – 32,000 – 230,000;
• Up to 17 mm – 45,000 – 270,000;
• Up to 25 mm – 81,000 – 220,000;
• Up to 30 mm – 150,000 – 300,000.

Popular devices are “Gorynych”, “Resanta” IPR-25, IPR-40, IPR-40 K.

As you can see the price range is wide. In this regard, the relevance of a homemade plasma cutter is increasing. Having studied the instructions, it is quite possible to create a device that is in no way inferior in technical specifications. You can select an inverter or transformer at a price significantly lower than the prices presented.

Operating principle

After pressing the ignition button, the source of electricity starts, supplying high-frequency current to the working tool. An arc (pilot) occurs between the tip located in the cutter (plasma torch) and the electrode. Temperature range from 6 to 8 thousand degrees. It is worth noting that the working arc is not created instantly; there is a certain delay.

Then compressed air enters the cavity of the plasmatron. This is what a compressor is designed for. Passing through the chamber with a pilot arc on the electrode, it is heated and increases in volume. The process is accompanied by ionization of the air, which transforms it into a conductive state.

Through a narrow plasma torch nozzle, the resulting plasma flow is supplied to the workpiece. The flow speed is 2 – 3 m/s. Air in an ionized state can heat up to 30,000°C. In this state, the electrical conductivity of air is close to the conductivity of metal elements.

After the plasma contacts the surface being cut, the pilot arc is switched off and the working arc begins to operate. Next, melting is carried out at the cutting points, from which the molten metal is blown with supplied air.

Differences between direct and indirect devices

There are various types of devices that differ in operating principles. In direct acting equipment, the operation of an electric arc is assumed. It takes on a cylindrical shape and is directly connected to the gas stream. This equipment design makes it possible to provide a high arc temperature (up to 20,000°C) and a highly efficient cooling system for other components of the plasma cutter.

In indirect-acting devices, operation is assumed to be less efficient. This determines their lower distribution in production. The design feature of the equipment is that the active points of the circuit are placed on special tungsten electrodes or a pipe. They are used more often for heating and spraying, but are practically not used for cutting. Most often used in car repairs.

A common feature is the presence in the design of an air filter (extends the life of the electrode, ensures quick start-up of the equipment) and a cooler (creates conditions for long-term operation of the device without interruption). An excellent indicator is the ability of the device to operate continuously for 1 hour with a 20-minute break.

Design

With the proper desire and skill, anyone can create a homemade plasma cutter. But in order for it to function fully and effectively, certain rules must be followed. It is advisable to try on an inverter, because It is he who is able to ensure a stable current supply and stable arc operation. As a result, there are no interruptions and electricity consumption will be significantly reduced. But it is worth considering that an inverter-based plasma cutter can cope with a thinner metal thickness than a transformer.

Required components

Before starting assembly work, it is necessary to prepare a number of components, materials and equipment:

1. Inverter or transformer with suitable power. To eliminate error, it is necessary to determine the planned cutting thickness. Based on this information, select the right device. However, taking into account manual cutting, it is worth choosing an inverter, because... it weighs less and consumes less electricity.
2. Plasma torch or plasma cutter. There are also some peculiarities of choice. It is better to choose direct action for working with conductive materials, and indirect action for non-conductive materials.
3. Compressed air compressor. It is necessary to pay attention to the rated power, because it must cope with the load imposed and match the other components.
   Cable hose. Required for connecting all components of the plasma cutter and supplying air to the plasma torch.

Selection of power supply

The operation of the plasma cutter is ensured by the power supply. It generates the specified parameters of electric current and voltage and supplies them to the cutting unit. The main supply unit can be:

• Inverter;
• Transformer.

It is necessary to approach the choice of power supply taking into account the features of the devices described above.

Plasma torch

A plasma torch is a plasma generator. This is a working tool in which a plasma jet is formed that directly cuts materials.

The main features of the device are:

• Creation of ultra-high temperature;
• Simple adjustment of current power, start and stop of operating modes;
• Compact dimensions;
• Reliability of operation.

Structurally, the plasma torch consists of:

• Electrode/cathode containing zirconium or hafnium. These metals are characterized by a high level of thermionic emission;
• The nozzle is basically isolated from the electrode;
• A mechanism that swirls plasma-forming gas.

The nozzle and electrode are consumables of the plasma torch. If a plasma cutter processes a workpiece up to 10 millimeters in size, then one set of electrodes is consumed within 8 hours of operation. Wear occurs evenly, which allows you to change them at the same time.

If the electrode is not replaced in a timely manner, the cutting quality may be impaired - the geometry of the cut changes or waves appear on the surface. The hafnium insert in the cathode gradually burns out. If it has a production of more than 2 millimeters, then the electrode can burn and overheat the plasmatron. This means that electrodes replaced at the wrong time will lead to rapid failure of the remaining elements of the working tool.

All plasmatrons can be divided into 3 volume groups:

• Electric arc - has at least one anode and cathode, which are connected to a direct current power source;
• High-frequency - there are no electrodes and cathodes. Communication with the power supply is based on inductive/capacitive principles;
• Combined - operates when exposed to high-frequency current and arc discharges.

Based on the arc stabilization method, all plasmatrons can also be divided into gas, water and magnetic types. Such a system is extremely important for the operation of the instrument, because it forms a compression of the flow and fixes it on the central axis of the nozzle.

Currently, various modifications of plasma torches are available for sale. You may need to study the offers and buy a ready-made one. However, it is quite possible to make a homemade one at home. This requires:

• Lever. It is necessary to provide holes for wires.
• Button.
• An appropriate electrode designed for the current.
• Insulator.
• Flow swirler.
• Nozzle. Preferably a set with different diameters.
• Tip. Splash protection must be provided.
• Distance spring. Allows you to maintain a gap between the surface and the nozzle.
• Nozzle for removing carbon deposits and chamfering.

Work can be carried out with one plasma torch due to replaceable heads with different diameters that direct the plasma flow to the part. It is necessary to pay attention that they, like the electrodes, will melt during operation.

The nozzle is secured with a clamping nut. Directly behind it there is an electrode and an insulator that prevents the ignition of the arc in the wrong place. Next, a flow swirler is placed to enhance the arc effect. All elements are housed in a fluoroplastic casing. You can do some things yourself, but others will have to be purchased at the store.

The factory plasma torch will allow you to work without overheating for a longer time due to the air cooling system. However, for short-term cutting this is not an important parameter.

Oscillator

An oscillator is a generator that produces high-frequency current. A similar element is included in the plasma cutter circuit between the power source and the plasma torch. Capable of acting according to one of the following schemes:

1. Creation of a short-term impulse that promotes the formation of an arc without touching the surface of the product. Externally, it looks like a small lightning bolt supplied from the end of the electrode.
2. Support DC voltage with a high voltage value superimposed on the welding current. Ensures the preservation of stable arc maintenance.

The equipment allows you to quickly create an arc and start cutting metal.

For the most part they have a similar structure and consist of:

• Voltage rectifier;
• Charge storage unit (capacitors);
• Power unit;
• Pulse creation module. Includes an oscillatory circuit and a spark gap;
• Control block;
• Step-up transformer;
• Voltage monitoring device.

The main task is to modernize the incoming voltage. The frequency and voltage level increase, reducing the period of action to less than 1 second. The work sequence is as follows:

1. The button on the cutter is pressed;
2. In the rectifier, the current is leveled out and becomes unidirectional;
3. Charge accumulates in capacitors;
4. Current is supplied to the oscillatory circuit of the transformer windings, increasing the voltage level;
5. The pulse is controlled by a control circuit;
6. The pulse creates a discharge on the electrode, igniting an arc;
7. The impulse ends;
8. After stopping cutting, the oscillator purges the plasma torch for another 4 seconds. Due to this, cooling of the electrode and the treated surface is achieved.

Depending on the type of oscillator, it can be used in different ways. However general characteristic is to increase the voltage to 3000 - 5000 volts and frequency from 150 to 500 kHz. The main differences are in the intervals of action of the high-frequency current.

For use in a plasma cutter, it is advisable to use an oscillator for non-contact ignition of the arc. Similar elements are used to work in argon welders. The tungsten electrodes in them will quickly become dull if they come into contact with the product. Including an oscillator in the apparatus circuit will allow you to create an arc without making contact with the plane of the part.

Using an oscillator can significantly reduce the need for expensive consumables and improve the cutting process. Properly selected equipment in accordance with the planned work allows you to improve its quality and speed.

Electrodes

Electrodes play an important role in the process of creating, maintaining an arc and direct cutting. The composition contains metals that allow the electrode not to overheat and not prematurely collapse when working with an arc at high temperatures.

When purchasing electrodes for a plasma cutter, it is necessary to clarify their composition. Beryllium and thorium contents create harmful fumes. They are suitable for work in appropriate conditions, with adequate protection for the worker, i.e. additional ventilation is required. Because of this, for application in everyday life it is better to buy hafnium electrodes.

Compressor and cable - hoses

The design of most homemade plasma cutters includes compressors and hose lines to direct air to the plasma torch. This design element allows you to heat the electric arc up to 8000°C. An additional function is to purge the working channels, clearing them of contaminants and removing condensate. In addition, compressed air helps cool the components of the device during long-term operation.

To operate the plasma cutter, it is possible to use a conventional compressed air compressor. Air exchange is carried out by thin hoses with suitable connectors. An electric valve is located at the inlet, which regulates the air supply process.

An electrical cable is placed in the channel from the apparatus to the burner. Therefore, it is necessary to place a hose with a large diameter here, which can accommodate the cable. The passing air also has a ventilation function, as it is able to cool the wire.

The mass must be made of cable with a cross-section of 5 mm2. There must be a clamp. If there is poor ground contact, switching the working arc to the standby arc will be problematic.

Scheme

Now you can find many schemes using which you can assemble a high-quality device. The video will help you understand the symbols in detail. A suitable schematic drawing of the equipment can be selected from those presented below.

Assembly

Before starting the assembly process, it is advisable to clarify the compatibility of the selected components. If you have never assembled a plasma cutter with your own hands before, you should consult with experienced craftsmen.

The assembly procedure assumes the following sequence:

1. Prepare all assembled components;
2. Electrical circuit assembly. In accordance with the diagram, an inverter/transformer and an electrical cable are connected;
3. Connecting the compressor and air supply to the apparatus and plasma torch using flexible hoses;
4. For your own safety net, you can use the source uninterruptible power supply(UPS), taking into account the battery capacity.

Detailed equipment assembly technology is presented in the video.

Checking the plasma cutter

After all nodes are connected into a single structure, it is necessary to test for functionality.

Please note that testing and working with the plasma cutter must be carried out in protective clothing using personal protective equipment.

It is necessary to turn on all the units and press the button on the plasma torch, supplying electricity to the electrode. At this moment, an arc with a high temperature should form in the plasmatron, passing between the electrode and the nozzle.

If the assembled plasma cutting equipment is capable of cutting metal up to 2 cm thick, then everything is done correctly. It should be noted that a homemade device made from an inverter will not be able to cut parts with a thickness of more than 20 millimeters, since there is not enough power. To cut thick products, you will need to use a transformer as a power source.

Advantages of a homemade device

The benefits provided by an air plasma cutting machine are difficult to overestimate. It is capable of cutting sheet metal accurately. After work, there is no need to further process the ends. The main advantage is the reduction in work time.

These are already compelling reasons for assembling the equipment yourself. The circuit is not complicated, so anyone can cheaply remake an inverter or semi-automatic device.

In conclusion, let us draw your attention to the fact that it is necessary for an experienced specialist to work with a plasma cutter. It's best if it's a welder. If you have little experience, we recommend that you first study the technology of working with photos and videos, and then begin to complete the assigned tasks.

Factory plasma cutting machine. Our task: to make an analogue with your own hands

Making a functional plasma cutter with your own hands from a serial welding inverter is not as difficult as it might seem at first glance. In order to solve this problem, it is necessary to prepare all the structural elements of such a device:

• plasma cutter (also called a plasma torch);
• a welding inverter or transformer that will act as a source of electric current;
• a compressor, with the help of which a jet of air will be created, necessary for the formation and cooling of the plasma flow;
• cables and hoses for combining all structural elements of the device into one system.

Plasma cutters, including homemade ones, are successfully used to perform various jobs both in production and at home. Such a device is indispensable in situations where it is necessary to perform an accurate, thin and high-quality cut of metal workpieces. Some models of plasma cutters, due to their functionality, allow them to be used as a welding machine. This welding is performed in an argon shielding gas environment.

When choosing a power source to complete a homemade plasma torch, it is important to pay attention to the current strength that such a source can generate. Most often, an inverter is chosen for this, providing high stability to the plasma cutting process and allowing for more economical energy consumption. Differing from a welding transformer in its compact dimensions and light weight, the inverter is more convenient to use. The only disadvantage of using inverter plasma cutters is the difficulty of cutting too thick workpieces with their help.

When assembling a homemade device for performing plasma cutting, you can use ready-made diagrams that are easy to find on the Internet. In addition, there is a video on the Internet on how to make a plasma cutter with your own hands. When using a ready-made diagram when assembling such a device, it is very important to strictly adhere to it, and also pay special attention to the correspondence of the structural elements to each other.

Schemes of a plasma cutter using the example of the APR-91 device

As a donor when considering a fundamental electrical diagram we will use APR-91.

Power section diagram (click to enlarge)

Plasma cutter control circuit (click to enlarge)

Oscillator circuit (click to enlarge)

Elements of a homemade plasma cutting machine

The first thing you need to find to make a homemade plasma cutter is a power source in which an electric current with the required characteristics will be generated. Most often they are used in this capacity, which is explained by a number of their advantages. Due to its technical characteristics, such equipment provides high stability of the generated voltage, which has a positive effect on the quality of cutting. Working with inverters is much more convenient, which is explained not only by their compact dimensions and low weight, but also by ease of setup and operation.

Due to their compactness and light weight, plasma cutters based on inverters can be used to perform work even in the most inaccessible places, which is impossible for bulky and heavy welding transformers. A huge advantage of inverter power supplies is that they have high efficiency. This makes them very energy efficient devices.

In some cases, a welding transformer can serve as a power source for a plasma cutter, but its use is fraught with significant energy consumption. It should also be taken into account that any welding transformer is characterized by large dimensions and significant weight.

The main element of the apparatus designed for cutting metal using a plasma jet is a plasma cutter. It is this element of equipment that ensures the quality of cutting, as well as the efficiency of its implementation.

To form an air flow that will be converted into a high-temperature plasma jet, a special compressor is used in the design of the plasma cutter. Electric current from the inverter and air flow from the compressor are supplied to the plasma cutter using a cable and hose package.

The central working element of the plasma cutter is the plasma torch, the design of which consists of the following elements:

• nozzles;
• the channel through which the air stream is supplied;
• electrode;
• an insulator that simultaneously performs a cooling function.

The first thing that needs to be done before manufacturing a plasma torch is to select the appropriate electrode for it. The most common materials used to make electrodes for plasma cutting are beryllium, thorium, zirconium and hafnium. When heated, refractory oxide films are formed on the surface of these materials, which prevent the active destruction of the electrodes.

Some of the above materials, when heated, can emit compounds hazardous to human health, which should be taken into account when choosing the type of electrode. Thus, when beryllium is used, radioactive oxides are formed, and thorium vapors, when combined with oxygen, form dangerous toxic substances. The completely safe material from which electrodes for plasmatrons are made is hafnium.

The nozzle is responsible for the formation of the plasma jet, thanks to which cutting is performed. Its manufacture should be given serious attention, since the quality of the work flow depends on the characteristics of this element.

The most optimal is a nozzle with a diameter of 30 mm. The accuracy and quality of the cut depends on the length of this element. However, you should also not make the nozzle too long, since this contributes to its destruction too quickly.

As mentioned above, the design of a plasma cutter necessarily includes a compressor that forms and supplies an air flow to the nozzle. The latter is necessary not only for the formation of a jet of high-temperature plasma, but also for cooling the elements of the apparatus. The use of compressed air as a working and cooling medium, as well as an inverter that generates an operating current of 200 A, allows you to effectively cut metal parts whose thickness does not exceed 50 mm.

In order to prepare the plasma cutting machine for operation, it is necessary to connect the plasma torch to the inverter and air compressor. To solve this problem, a cable-hose package is used, which is used as follows.

• The cable through which electric current will be supplied connects the inverter and the plasma cutter electrode.
• A hose for supplying compressed air connects the compressor outlet and the plasmatron, in which a plasma jet will be formed from the incoming air flow.

Features of the plasma cutter

To make a plasma cutter using an inverter for its manufacture, you need to understand how such a device works.

After turning on the inverter, electric current from it begins to flow to the electrode, which leads to the ignition of an electric arc. The temperature of the arc burning between the working electrode and the metal tip of the nozzle is about 6000–8000 degrees. After the arc is ignited, compressed air is supplied to the nozzle chamber, which passes strictly through an electric discharge. The electric arc heats and ionizes the air flow passing through it. As a result, its volume increases hundreds of times, and it becomes capable of conducting electric current.

Using a plasma cutter nozzle, a plasma jet is formed from a conductive air flow, the temperature of which actively increases and can reach 25–30 thousand degrees. The speed of the plasma flow, due to which metal parts are cut, at the exit from the nozzle is about 2–3 meters per second. At the moment when the plasma jet comes into contact with the surface of the metal part, an electric current from the electrode begins to flow through it, and the initial arc goes out. The new arc that burns between the electrode and the workpiece is called cutting.

A characteristic feature of plasma cutting is that the metal being processed melts only in the place where it is exposed to the plasma flow. That is why it is very important to ensure that the plasma exposure spot is strictly in the center of the working electrode. If you neglect this requirement, you may encounter the fact that the air-plasma flow will be disrupted, which means the quality of the cut will deteriorate. In order to meet these important requirements, a special (tangential) principle of air supply to the nozzle is used.

It is also necessary to ensure that two plasma flows do not form at once instead of one. The occurrence of such a situation, which is caused by non-compliance with the modes and rules of the technological process, can provoke failure of the inverter.

An important parameter for plasma cutting is the air flow speed, which should not be too high. Good cutting quality and speed of execution are ensured by an air jet speed of 800 m/sec. In this case, the current supplied from the inverter apparatus should not exceed 250 A. When performing work in such modes, one should take into account the fact that in this case the air flow used to form the plasma flow will increase.

It’s not difficult to make a plasma cutter yourself if you study the necessary theoretical material, watch a training video and select all the necessary elements correctly. If you have such a device in your home workshop, assembled on the basis of a serial inverter, you can perform high-quality not only cutting, but also plasma welding with your own hands.

If you don’t have an inverter at your disposal, you can assemble a plasma cutter using a welding transformer, but then you’ll have to put up with its large dimensions. In addition, a plasma cutter made on the basis of a transformer will not have very good mobility, since it is difficult to move it from place to place.