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How to make a good plasma cutter from an inverter with your own hands. How to make your own plasma cutter from an inverter Do-it-yourself plasma cutter from a resanta inverter

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 plasma cutting machine, 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

When considering the electrical circuit diagram, we will use APR-91 as a donor.

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 with an inverter and an 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.

Increasingly, small private workshops and small enterprises use plasma metal cutting devices instead of grinders and other devices. Air plasma cutting allows you to perform high-quality straight and shaped cuts, align the edges of sheet metal, make openings and holes, including shaped ones, in metal workpieces and other more complex work. The quality of the resulting cut is simply excellent; it turns out smooth, clean, practically free of scale and burrs, and also neat. Air plasma cutting technology can process almost all metals, as well as non-conductive materials such as concrete, ceramic tiles, plastic and wood. All work is performed quickly, the workpiece is heated locally, only in the cutting area, so the metal of the workpiece does not change its geometry due to overheating. Even a beginner without welding experience can handle a plasma cutting machine or, as it is also called, a plasma cutter. But so that the result does not disappoint, it still does not hurt to study the device of a plasma cutter, understand its operating principle, and also study the technology of how to operate an air plasma cutting machine.

Design of an air plasma cutting machine

Knowledge of the design of a plasma cutter will allow you not only to carry out work more consciously, but also to create a home-made analogue, which requires not only more in-depth knowledge, but also preferably engineering experience.

An air plasma cutting machine consists of several elements, including:

  • Power supply;
  • Plasma torch;
  • Cable-hose package;
  • Air compressor.

Power supply for a plasma cutter, it serves to convert voltage and supply a certain current strength to the cutter/plasma torch, due to which an electric arc lights up. The power source can be a transformer or an inverter.

Plasma torch- the main element of an air plasma cutting machine, it is in it that the processes take place due to which plasma appears. The plasma torch consists of a nozzle, an electrode, a housing, an insulator between the nozzle and the electrode, and air channels. Elements such as the electrode and nozzle are consumables and require frequent replacement.

Electrode in the plasma torch it is the cathode and serves to excite the electric arc. The most common metal from which electrodes for plasmatrons are made is hafnium.

Nozzle has a cone-shaped shape, compresses the plasma and forms a plasma jet. Escaping from the nozzle exit channel, the plasma jet touches the workpiece and cuts it. The dimensions of the nozzle affect the characteristics of the plasma cutter, its capabilities and the technology of working with it. The most common nozzle diameter is 3 - 5 mm. The larger the diameter of the nozzle, the greater the volume of air per unit time it can pass through. The width of the cut depends on the amount of air, as well as the operating speed of the plasma cutter and the cooling rate of the plasma torch. The most common nozzle length is 9 - 12 mm. The longer the nozzle, the more accurate the cut. But a nozzle that is too long is more susceptible to destruction, so the optimal length is increased by a size equal to 1.3 - 1.5 times the nozzle diameter. It should be taken into account that each current value corresponds to the optimal nozzle size, which ensures stable arc burning and maximum cutting parameters. Reducing the nozzle diameter to less than 3 mm is not advisable, since the service life of the entire plasma torch is significantly reduced.

Compressor supplies compressed air to the plasmatron to form plasma. In air plasma cutting machines, air acts as both a plasma-forming gas and a protective gas. There are devices with a built-in compressor, as a rule, they are low-power, as well as devices with an external air compressor.

Cable-hose package consists of an electrical cable connecting the power source and the plasmatron, as well as a hose for supplying air from the compressor to the plasmatron. We will consider below what exactly happens inside the plasma torch.

Operating principle of air plasma cutting machine

The air plasma cutting machine operates according to the principle described below. After pressing the ignition button, which is located on the handle of the plasma torch, high-frequency current begins to be supplied to the plasma torch from the power source. As a result, the pilot electric arc lights up. Due to the fact that the formation of an electric arc between the electrode and the workpiece directly is difficult, the nozzle tip acts as the anode. The temperature of the pilot arc is 6000 - 8000 °C, and the arc column fills the entire nozzle channel.

A couple of seconds after the pilot arc is ignited, compressed air begins to flow into the plasma torch chamber. It passes through a duty electric arc, is ionized, heated and increases in volume by 50 - 100 times. The shape of the plasma torch nozzle is narrowed downwards, due to which the air is compressed and a flow is formed from it, which escapes from the nozzle at a speed close to sound - 2 - 3 m/s. The temperature of the ionized heated air escaping from the nozzle outlet can reach 20,000 - 30,000 °C. The electrical conductivity of the air at this moment is approximately equal to the electrical conductivity of the metal being processed.

Plasma This is precisely what is called the heated ionized air escaping from the plasma torch nozzle. As soon as the plasma reaches the surface of the metal being processed, the working cutting arc is ignited, at this moment the pilot arc goes out. The cutting arc heats up the workpiece at the point of contact, locally, the metal begins to melt, and a cut appears. The molten metal flows onto the surface of the workpiece and solidifies in the form of drops and small particles, which are immediately blown away by the plasma flow. This method of air plasma cutting is called a sharp plasma arc (direct arc), since the metal being processed is included in the electrical circuit and is the anode of the cutting arc.

In the case described above, the energy of one of the near-electrode arc spots, as well as the plasma of the column and the torch flowing from it, is used to cut the workpiece. Plasma arc cutting uses a direct current arc of straight polarity.

Plasma arc cutting of metal is used in the following cases: if it is necessary to produce parts with shaped contours from sheet metal, or to produce parts with straight contours, but so that the contours do not have to be processed additionally, for cutting pipes, strips and rods, for cutting holes and openings in details and more.

But there is also another method of plasma cutting - plasma jet cutting. In this case, the cutting arc lights up between the electrode (cathode) and the nozzle tip (anode), and the workpiece is not included in the electrical circuit. Part of the plasma is removed from the plasma torch in the form of a jet (indirect arc). Typically, this cutting method is used to work with non-metallic, non-conductive materials - concrete, ceramic tiles, plastic.

The air supply to the direct-acting and indirect-acting plasmatrons is carried out differently. Plasma arc cutting requires axial air supply (direct). And for cutting with a plasma jet you need tangential air supply.

Tangential or vortex (axial) air supply to the plasmatron is necessary to ensure that the cathode spot is located strictly in the center. If the tangential air supply is disrupted, the cathode spot will inevitably shift, and with it the plasma arc. As a result, the plasma arc does not burn stably, sometimes two arcs light up at the same time, and the entire plasma torch fails. Homemade air plasma cutting is not capable of providing a tangential air supply. Since to eliminate turbulence inside the plasma torch, specially shaped nozzles and liners are used.

Compressed air is used for air plasma cutting of the following metals:

  • Copper and copper alloys - no more than 60 mm thick;
  • Aluminum and aluminum alloys - up to 70 mm thick;
  • Steel up to 60 mm thick.

But air should absolutely not be used to cut titanium. We will consider in more detail the intricacies of working with a manual air plasma cutting machine below.

How to choose an air plasma cutting machine

To make the right choice of a plasma cutter for private household needs or a small workshop, you need to know exactly for what purpose it will be used. What workpieces will you have to work with, from what material, what thickness, what is the load intensity of the machine and much more.

An inverter may well be suitable for a private workshop, since such devices have a more stable arc and a 30% higher efficiency. Transformers are suitable for working with workpieces of greater thickness and are not afraid of voltage surges, but at the same time they weigh more and are less economical.

The next gradation is plasma cutters of direct and indirect action. If you plan to cut only metal workpieces, then a direct-action machine is needed.

For a private workshop or home needs, it is necessary to purchase a manual plasma cutter with a built-in or external compressor, designed for a certain current.

Plasma cutter current and metal thickness

Current strength and maximum workpiece thickness are the main parameters for choosing an air plasma cutting machine. They are interconnected. The higher the current the power source of the plasma cutter can supply, the thicker the workpiece can be processed using this device.

When choosing a machine for personal needs, you need to know exactly how thick the workpiece will be processed and from what metal. The characteristics of plasma cutters indicate both the maximum current strength and the maximum metal thickness. But please note that the thickness of the metal is indicated based on the fact that ferrous metal will be processed, and not non-ferrous or stainless steel. And the current strength indicated is not the nominal, but the maximum; the device can operate at these parameters for a very short time.

Different metals require different amounts of current to cut. The exact parameters can be seen in the table below.

Table 1. Current required for cutting various metals.

For example, if you plan to cut a steel workpiece with a thickness of 2.5 mm, then a current strength of 10 A is required. And if the workpiece is made of non-ferrous metal, for example, copper 2.5 mm thick, then the current strength must be 15 A. In order for the cut to be of high quality , it is necessary to take into account a certain power reserve, so it is better to purchase a plasma cutter designed for a current of 20 A.

The price of an air plasma cutting machine directly depends on its power - the current output. The higher the current, the more expensive the device.

Operating mode - ON duration (DS)

The operating mode of the device is determined by the intensity of its load. All devices indicate a parameter such as on-time or duty cycle. What does it mean? For example, if PV = 35% is indicated, this means that the plasma cutter can be operated for 3.5 minutes, and then it must be allowed to cool for 6.5 minutes. The cycle duration is 10 minutes. There are devices with PV 40%, 45%, 50%, 60%, 80%, 100%. For domestic needs, where the device will not be used constantly, devices with a duty cycle of 35% to 50% are sufficient. For CNC machine cutting, plasma cutters with duty cycle = 100% are used, as they ensure continuous operation throughout the entire shift.

Please note that when working with manual air plasma cutting, there is a need to move the plasma torch or move to the other end of the workpiece. All these intervals count towards the cooling time. Also, the duration of activation depends on the load of the device. For example, from the beginning of a shift, even a plasma cutter with a duty cycle of 35% can work for 15 - 20 minutes without a break, but the more often it is used, the shorter the continuous operation time will be.

Do-it-yourself air plasma cutting - working technology

We have chosen the plasma cutter, familiarized ourselves with the principle of operation and the device, and it’s time to get to work. To avoid making mistakes, it won’t hurt to start by familiarizing yourself with the technology of working with an air plasma cutting machine. How to comply with all safety measures, how to prepare the device for work and select the correct current strength, and then how to ignite the arc and maintain the required distance between the nozzle and the surface of the workpiece.

Take care of your safety

Air plasma cutting involves a number of hazards: electric current, high plasma temperatures, hot metal and ultraviolet radiation.

  • It is necessary to work in special equipment: dark glasses or a welder's shield (glass darkening class 4 - 5), thick gloves on your hands, thick fabric pants on your feet and closed shoes. When working with a cutter, gases can be generated that pose a threat to the normal functioning of the lungs, so you must wear a mask or respirator over your face.
  • The plasma cutter is connected to the network via an RCD.
  • Sockets, work stand or table, and surrounding objects must be well grounded.
  • Power cables must be in perfect condition and windings must not be damaged.

It goes without saying that the network must be designed for the voltage indicated on the device (220 V or 380 V). Otherwise, following safety precautions will help avoid injuries and occupational diseases.

Preparing the air plasma cutting machine for operation

How to connect all the elements of an air plasma cutting machine is described in detail in the instructions for the device, so let’s immediately move on to further nuances:

  • The device must be installed so that there is access to air. Cooling the plasma cutter body will allow you to work longer without interruption and less often turn off the device for cooling. The location should be such that drops of molten metal do not fall on the device.
  • The air compressor is connected to the plasma cutter through a moisture and oil separator. This is very important, since water or drops of oil that get into the plasma torch chamber can lead to failure of the entire plasma torch or even its explosion. The pressure of air supplied to the plasmatron must correspond to the parameters of the device. If the pressure is insufficient, the plasma arc will be unstable and will often go out. If the pressure is excessive, some elements of the plasma torch may become unusable.
  • If there is rust, scale or oil stains on the workpiece you are going to process, it is better to clean and remove them. Although air plasma cutting allows you to cut rusty parts, it is still better to play it safe, since when the rust is heated, toxic fumes are released. If you plan to cut containers in which flammable materials were stored, they must be thoroughly cleaned.

In order for the cut to be smooth, parallel, without scale and sagging, it is necessary to correctly select the current strength and cutting speed. The tables below show the optimal cutting parameters for various metals of various thicknesses.

Table 2. Force and cutting speed using an air plasma cutting machine for workpieces made of various metals.

At first it will be difficult to select the cutting speed; experience is required. Therefore, at first you can follow this rule: it is necessary to drive the plasma torch in such a way that sparks are visible from the back of the workpiece. If no sparks are visible, it means the workpiece is not cut all the way through. Please also note that moving the torch too slowly negatively affects the quality of the cut; scale and sagging appear on it, and the arc may burn unstably and even go out.

Now you can begin the cutting process itself.

Before igniting the electric arc, the plasma torch should be purged with air to remove any accidental condensation and foreign particles. To do this, press and then release the arc ignition button. So the device switches to purge mode. After about 30 seconds, you can press and hold the ignition button. As has already been described in the principle of operation of the plasma cutter, a pilot (auxiliary, pilot) arc will light up between the electrode and the nozzle tip. As a rule, it burns for no longer than 2 seconds. Therefore, during this time it is necessary to light the working (cutting) arc. The method depends on the type of plasmatron.

If the plasma torch is direct-acting, then it is necessary to make a short circuit: after the formation of a pilot arc, you must press the ignition button - the air supply stops and the contact closes. Then the air valve opens automatically, a stream of air escapes from the valve, ionizes, increases in size and removes a spark from the plasmatron nozzle. As a result, a working arc lights up between the electrode and the metal of the workpiece.

Important! Contact ignition of the arc does not mean that the plasma torch must be applied or leaned against the workpiece.

As soon as the cutting arc lights up, the pilot arc goes out. If you fail to light the working arc the first time, you must release the ignition button and press it again - a new cycle will begin. There are several reasons why the working arc may not ignite: insufficient air pressure, incorrect assembly of the plasma torch, or other problems.

During operation, there are also cases when the cutting arc goes out. The reason is most likely a worn electrode or failure to maintain the distance between the plasma torch and the surface of the workpiece.

Distance between plasmatron torch and metal

Manual air plasma cutting is fraught with the difficulty that it is necessary to maintain the distance between the torch/nozzle and the metal surface. When working with your hand, this is quite difficult, since even breathing confuses your hand, and the cut turns out uneven. The optimal distance between the nozzle and the workpiece is 1.6 - 3 mm; to maintain it, special distance stops are used, because the plasma torch itself cannot be pressed against the surface of the workpiece. The stops are placed on top of the nozzle, then the plasma torch is supported by the stop on the workpiece and the cut is made.

Please note that the plasma torch must be held strictly perpendicular to the workpiece. Permissible deviation angle 10 - 50 °. If the workpiece is too thin, the cutter can be held at a slight angle, this will avoid severe deformation of the thin metal. Molten metal should not fall on the nozzle.

It is quite possible to do the work with air plasma cutting yourself, but it is important to remember about safety precautions, as well as the fact that the nozzle and electrode are consumables that require timely replacement.

The operating principle of most plasmatrons with a power ranging from several kW to several megawatts is practically the same. An electric arc burns between a cathode made of a refractory material and an intensively cooled anode.

A working fluid (WM) is blown through this arc - a plasma-forming gas, which can be air, water vapor, or something else. Ionization of the RT occurs, and as a result, we obtain the fourth aggregate state of matter, called plasma.

In powerful devices, an electric magnet coil is placed along the nozzle; it serves to stabilize the plasma flow along the axis and reduce wear of the anode.

This article describes the second design, because The first attempt to obtain stable plasma was not particularly successful. Having studied the Alplaza device, we came to the conclusion that it is probably not worth repeating it one by one. If anyone is interested, everything is very well described in the instructions included with it.

Our first model did not have active anode cooling. The working fluid was water vapor from a specially constructed electric steam generator - a sealed boiler with two titanium plates immersed in water and connected to a 220V network.

The cathode of the plasmatron was a tungsten electrode with a diameter of 2 mm, which quickly burned out. The diameter of the anode nozzle hole was 1.2 mm, and it constantly became clogged.

It was not possible to obtain stable plasma, but there were still glimpses, and this stimulated the continuation of experiments.

In this plasma generator, a steam-water mixture and air were tested as a working fluid. The plasma output was more intense with water vapor, but for stable operation it must be overheated to a temperature of several hundred degrees so that it does not condense on the cooled plasmatron components.

Such a heater has not yet been made, so experiments so far continue only with air.

Photos of the insides of the plasmatron:

The anode is made of copper, the nozzle hole diameter is from 1.8 to 2 mm. The anode block is made of bronze and consists of two hermetically sealed parts, between which there is a cavity for pumping coolant - water or antifreeze.

The cathode is a slightly sharpened tungsten rod with a diameter of 4 mm, obtained from a welding electrode. It is additionally cooled by the flow of the working fluid supplied under pressure from 0.5 to 1.5 atm.

And here is a completely disassembled plasmatron:

Power is supplied to the anode through the cooling system tubes, and to the cathode through a wire attached to its holder.

Launch, i.e. The arc is ignited by twisting the cathode feed knob until it comes into contact with the anode. Then the cathode must be immediately moved to a distance of 2..4 mm from the anode (a couple of turns of the handle), and the arc continues to burn between them.

Power supply, connection of air supply hoses from the compressor and cooling system - in the following diagram:

As a ballast resistor, you can use any suitable electric heating device with a power of 3 to 5 kW, for example, select several boilers connected in parallel.

The rectifier choke must be designed for a current of up to 20 A; our example contains about a hundred turns of thick copper wire.

Any diodes designed for a current of 50 A and above, and a voltage of 500 V are suitable.

Be careful! This device uses transformerless mains power.

The air compressor used to supply the working fluid is a car one, and a car glass washer is used to pump the coolant through a closed circuit. Power is supplied to them from a separate 12-volt transformer with a rectifier.

A little about plans for the future

As practice has shown, this design also turned out to be experimental. Finally got stable operation within 5 - 10 minutes. But there is still a long way to go to complete perfection.

Replaceable anodes gradually burn out, and it is difficult to make them from copper, and even with threads; it would be better without threads. The cooling system does not have direct contact of the liquid with the replaceable anode, and because of this, heat transfer leaves much to be desired. A more successful option would be with direct cooling.

The parts were machined from semi-finished materials at hand; the design as a whole was too complex to be repeated.

It is also necessary to find a powerful isolation transformer; without it, using the plasmatron is dangerous.

And finally, some more pictures of the plasmatron when cutting wire and steel plates. Sparks fly almost a meter :)



Modern inverter welding machines cover most of the needs for producing permanent joints of metal workpieces. But in some cases, a device of a slightly different type will be much more convenient, in which the main role is played not by an electric arc, but by a flow of ionized gas, that is, a plasma welding machine. Purchasing it for occasional use is not very cost-effective. You can make such a welding machine with your own hands.

Equipment and components

The easiest way to make a microplasma welding machine is on the basis of an existing inverter welding machine. To complete this upgrade, you will need the following components:

  • any inverter welding machine for TIG welding with or without a built-in oscillator;
  • nozzle with a tungsten electrode from a TIG welder;
  • argon cylinder with reducer;
  • a small piece of tantalum or molybdenum rod with a diameter and length of up to 20 mm;
  • fluoroplastic tube;
  • copper tubes;
  • small pieces of copper sheet 1-2 mm thick;
  • electronic ballast;
  • rubber hoses;
  • pressure lead;
  • clamps;
  • wiring;
  • terminals;
  • car windshield wiper reservoir with electric pump;
  • rectifier power supply for the electric windshield wiper pump.

Work on fine-tuning and manufacturing of new parts and assemblies will require the use of the following equipment:

  • lathe;
  • electric soldering iron;
  • soldering torch with cylinder;
  • screwdrivers;
  • pliers;
  • ammeter;
  • voltmeter.

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Theoretical basis

A plasma welding machine can be one of 2 main types: open and closed. The main arc of an open-type welding machine burns between the central cathode of the torch and the workpiece. Between the nozzle, which serves as the anode, and the central cathode, only a pilot arc burns to excite the main one at any time. A closed-type welding machine has only an arc between the central electrode and the nozzle.

It is quite difficult to make a durable one according to the 2nd principle. When the main welding current passes through the anode nozzle, this element experiences enormous thermal loads and requires very high-quality cooling and the use of appropriate materials. It is very difficult to ensure the heat resistance of the structure when making such a device yourself. When making a plasma device with your own hands, for durability it is better to choose an open circuit.

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Practical implementation

Often, when making a homemade plasma welding machine, the nozzle is machined from copper. If there is no alternative, this option is possible, but the nozzle becomes a consumable even when only a standby current passes through it. It will have to be changed frequently. If you can get a small piece of molybdenum or tantalum round timber, it is better to make a nozzle from them. Then you can limit yourself to periodic cleaning.

The size of the central hole in the nozzle is selected experimentally. You need to start with a diameter of 0.5 mm and gradually bore it to 2 mm until the plasma flow is satisfactory.

The conical gap between the central tungsten cathode and the anode nozzle should be 2.5-3 mm.

The nozzle is screwed into a hollow cooling jacket, which is connected to the central electrode holder through a fluoroplastic insulator. Coolant circulates in the cooling jacket. As such, in the warm season you can use distilled water; in winter, antifreeze is better.

The cooling jacket consists of 2 hollow copper tubes. The inner one with a diameter and length of about 20 mm is located at the front end of the outer tube with a diameter of about 50 mm and a length of about 80 mm. The space between the ends of the inner tube and the walls of the outer tube is sealed with thin sheet copper. Copper tubes with a diameter of 8 mm are soldered into the jacket using a gas torch. Coolant flows in and out through them. In addition, a terminal must be soldered to the cooling jacket to supply a positive charge.

A thread is made in the inner tube into which a removable nozzle made of heat-resistant materials is screwed. An internal thread is also cut at the extended end of the outer tube. An insulating ring made of fluoroplastic is screwed into it. The central electrode holder is screwed into the ring.

An argon supply tube of the same diameter as for cooling is soldered through the wall of the outer tube into the space between the cooling jacket and the fluoroplastic insulator.

Liquid from the windshield wiper reservoir circulates through the cooling jacket. Power is supplied to the pump of its electric motor through a separate 12 V rectifier. There is already an outlet for the supply on the tank; the liquid return can be cut through the wall or lid of the tank. To do this, a hole is drilled in the lid and a piece of tube is inserted through the pressure seal. Rubber hoses for liquid circulation and argon supply are connected to their tubes with clamps.

The positive charge is taken from the main power source. A suitable electronic ballast is selected to limit the current through the nozzle surface. The supplied electric current must have a constant value in the region of 5-7 A. The optimal current value is selected experimentally. This should be the minimum current that ensures stable combustion of the pilot arc.

The pilot arc between the nozzle and the tungsten cathode can be excited in one of two ways. Using an oscillator built into the welding machine or, in the absence of one, using a contact method. The second option requires a more complex design of the plasma torch. During contact excitation, the central electrode holder is made spring-loaded relative to the nozzle.

When the rubber button of the rod connected to the electrode holder is pressed, the sharp end of the central tungsten cathode contacts the conical surface of the rod. During a short circuit, the temperature at the contact point rises sharply, which makes it possible to initiate an arc when the cathode is pulled away from the anode by a spring. The contact must be very brief, otherwise the surface of the nozzle will burn.

Excitation of current by a high-frequency oscillator is preferable for the durability of the structure. But purchasing it or even manufacturing it makes it unprofitable for plasma welding.

During operation, the positive terminal of the welding machine is connected to the part without ballast. When the nozzle is within a few millimeters of the workpiece, electrical current is switched from the nozzle to the workpiece. Its value increases to that set on the welding machine, and the formation of plasma from argon intensifies. By adjusting the argon supply and welding current, you can achieve the required intensity of plasma flow from the nozzle.

At industrial enterprises, small workshops, during construction and repair work, a manual plasma cutter is used when it is necessary to weld or cut metal products, as well as special equipment equipped with CNC systems. To perform small-scale work, you can use a plasma cutter assembled with your own hands from an inverter, which is capable of providing high quality cuts or seams, taking into account the operations being performed.

Operating principle of a plasma cutter

When the power source is turned on, current begins to flow into the working area into the internal chamber of the plasma cutter, where the electric pilot arc between the nozzle tip and the electrode is activated. The forming arc fills the nozzle channel, where an air mixture begins to flow under high pressure, which, due to the high temperature of 6000-8000 °C, heats up greatly and increases in volume from 50 to 100 times. Due to the internal shape of the tapering nozzle, which has the shape of a cone, the air flow is compressed, heating up to an outlet temperature of 25,000 - 30,000 °C, forming a plasma jet that cuts the processed blank. Moreover, the initially activated pilot arc goes out and the working arc between the electrode and the metal product is activated. The resulting products from the effects of plasma combustion and metal melting are removed due to the force of the jet.

Fig. 1 Carrying out metal cutting operations where cutting or welding of a product is necessary, using a hand-made homemade one or a professional plasma cutter.

The optimal indicators for the workflow are:

  1. gas supply at speeds up to 800 m/sec;
  2. The current indicator can be up to 250 - 400 A.

Scheme 1. Drawing of the plasma cutting process of the workpiece.

A manual plasma cutter assembled using an inverter is mainly used for processing workpieces and is characterized by its low weight and economical power consumption.

Selection of plasma cutter components

To assemble a plasma cutter using drawings (based on an inverter), you need the following units with your own hands:

  1. pressure gas supply device - compressor;
  2. plasma cutter;
  3. electrical device - an inverter that provides current to form an electric arc;
  4. high pressure working hoses for air supply and protected electrical cable.

To supply air, we select a compressor taking into account the output volume for 1 minute. Manufacturing companies produce 2 types of compressors:

  1. piston apparatus;
  2. screw device (which has lower power consumption, is lighter, but 40-50% more expensive).

Rice. 2 Plasma cutter (device) with a cable set for the cutter and connection to the workpiece (as an anode).

Piston compressors are divided into oil and non-oil based, based on the drive principle - with a belt or direct connection of elements.
When operating compressors, a number of rules must be observed:

  1. at negative ambient temperatures, it is necessary to preheat the oil contained in the crankcase;
  2. It is necessary to regularly change the air (inlet) filter;
  3. strictly control the oil level in the crankcase;
  4. At least once every six months it is necessary to completely clean the units from foreign impurities;
  5. Upon completion of work, it is necessary to relieve pressure (using a regulator) in the system.

During repair work, products from ORLIK KOMRESSOR (Czech Republic) are often used. The ORL 11 device allows cutting workpieces using a current of 200-440 A and an air-gas flow coming under pressure.

The equipment set includes:

  1. compressor;
  2. block of main filters for the air-gas mixture;
  3. gas dryers;
  4. receiver.

At the outlet of the unit, purified air free of oil, dust and moisture arrives. An example of screw compressors is the CA series product from Atlas Copco (Sweden). The device is equipped with an automatic condensate removal system for air purification.

A plasmatron is a special device in which, using an electric current, an electric arc is formed that heats air supplied under pressure in a chamber to form a cutting plasma stream.

The cutter consists of elements:

  1. special holder with electrode;
  2. an insulating gasket separating the nozzle and the electrode assembly;
  3. plasma generation chambers;
  4. output nozzles for the formation of a plasma jet (see drawings);
  5. supply systems;
  6. tangential plasma supply elements (on some models) to stabilize the arc discharge.

According to the method of performing work (welding or cutting), cutters are divided into:

  1. Double-flow, used in reducing, oxidizing and inert environments.
  2. Gas inert (using helium, argon), reducing (hydrogen, nitrogen).
  3. Gas oxidizing (the air-gas mixture includes oxygen).
  4. Gas using a stabilizing (gas-liquid) arc.

The plasmatron cathode is made in the form of a rod or inserts made of tungsten, hafnium, and zirconium. Plasmatrons with a sleeve cathode, used for cutting using an air-gas flow under pressure, have become widespread.

To cut products in an oxidizing environment, a hollow cathode made of copper with a forced cooling system using water is used.

Rice. 3 Portable device (inverter) for plasma cutting.

Double-flow plasma cutters (inverter) are equipped with 2 coaxial nozzles, external and internal. The gas entering the internal nozzle is considered primary, and the external one is considered additional, and the gases can have different compositions and volumes.

A plasma cutter with arc stabilization due to the supply of a gas-liquid flow has a difference, which is the supply of water to the torch chamber to stabilize the state of the arc discharge.

To activate the working arc, a workpiece is used as an anode, which is connected to the inverter using clamps and a cable.

As a power plant for carrying out the plasma cutting process, a device (inverter) is used that provides the necessary current strength, which has a higher efficiency than a transformer, but the transformer’s metal processing capabilities are much higher.

Scheme 2. Drawing of the plasmatron power supply with your own hands.

Inverter advantages:

  1. the ability to uniformly change parameters;
  2. light weight;
  3. stable state of the working arc;
  4. high quality cutting or welding.

The equipment set also includes a set of high pressure hoses for connecting a stationary compressor and an electrical connecting cable.

To assemble a plasma cutter with your own hands, a device diagram is developed indicating the necessary units that meet the required characteristics, which should include all additions and changes used during assembly with the necessary calculations of the most important indicators. You can assemble a homemade plasma cutter with your own hands using ready-made blocks and assemblies produced by specialized companies; in this case, it is necessary to make accurate calculations and coordinate the output parameters of the ongoing processes.

Features of marking plasma cutters

Plasma cutters produced by industrial enterprises can be divided into 2 categories:

  1. machine cutting units;
  2. manual.

Hand cutters are more affordable if you need to do it yourself. Manufactured models have special markings:

  1. MMA - the device is designed for arc welding using an individual electrode;
  2. CUT - a device (plasma cutter) used for cutting metal;
  3. TIQ - the device is used for work where argon welding is necessary.

Manufacturing enterprises produce equipment for metal cutting:

  1. Profi CUT 40 (RT-31 burner, permissible cut thickness – 16 mm, air-gas mixture flow rate – 140 l/min, receiver volume 50 l);
  2. Profi CUT 60 (P-80 burner, permissible workpiece cutting thickness - 20 mm, air-gas mixture flow rate - 170 l/min.);
  3. Profi CUT 80 (burner R. – 80, permissible cutting thickness of the workpiece – 30 mm, air-gas mixture flow rate – 190 l/min.);
  4. Pro CUT 100 (burner A-101, permissible cutting thickness of the workpiece - 40 mm, air-gas mixture flow rate - 200 l/min.), receiver with a volume of 100 l.

Making a CNC plasma cutter with your own hands

A CNC-equipped plasma cutter must have a unified assembly using drawings made on the basis of the prepared technical specifications for the product, which include:

  1. work table;
  2. belt transmission;
  3. function control unit;
  4. step elements;
  5. linear guides;
  6. cutting height adjustment system;
  7. CNC control unit;

Scheme 3. Drawing of an inverter device for plasma cutting.

Drawings of all plasma cutter blocks can be purchased taking into account the required power and installation characteristics and financial capabilities, or you can do it yourself if you have experience and knowledge.

To complete and assemble a CNC machine, it is necessary to manufacture a number of elements using drawings:

  1. table base for welding;
  2. a durable frame is assembled and then painted;
  3. support posts are attached;
  4. the water table is assembled;
  5. fastenings and the slats themselves are installed;
  6. linear guides are mounted;
  7. the table cover is installed;
  8. guides are installed together with the portal;
  9. the portal is equipped with a motor and signal sensors;
  10. the guides, the Y guide motor and the positioning control rack are mounted;
  11. a guide equipped with a motor is mounted;
  12. a metal surface signal sensor is mounted;
  13. a tap is installed to remove water from the table;
  14. connecting cables-channels X.Z.Y are laid;
  15. the wires are insulated and covered with cladding;
  16. the working cutter is mounted;
  17. The CNC device is assembled and installed.

Carrying out operations for the manufacture and assembly of a CNC plasma torch should only be carried out in the presence of qualified specialists. The device diagram (drawings) must include all the necessary elements to ensure high quality of work and safety of metal cutting. Equipping enterprises with CNC equipment can increase labor productivity and the complexity of operations. Make production processes performed using CNC equipment more economical by increasing labor productivity and reducing the processing speed of products.

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