About the secrets of assembling a plasma cutter with your own hands from an inverter. Do-it-yourself plasma cutter from an inverter

Plasma welding is a modern advanced technology. Until recently, its application applied only to industry. This welding was carried out using special equipment. Now a do-it-yourself plasma welding machine has become a reality.

Plasma welding has a number of undeniable advantages over other types of welding. Possession of technology allows you to expand the possibility of welding metal joints at home. The device can also be used for spot welding (Fig. 1).

A homemade welding machine, including a spot welding machine, consists of the following main parts: a welding current source, a plasma torch, a compressor or gas cylinder and a cooling system.

Figure 1. Design of a plasma welding machine.

When using an open type device (the most common design), a current source is also used to form a pilot arc.

As a current source for the welding arc, it is best to use a standard inverter for low-power electric arc welding. Such an inverter supplies direct current to the welding zone, due to which the main arc is ignited between the plasma torch nozzle and the part being welded. The inverter power can be minimal, since the arc power is significantly enhanced by the plasma flow (Fig. 2).

Making an auxiliary current source

The current source for the pilot arc is assembled independently. It includes a diode bridge rectifier, an output transformer (choke) and a ballast (load) resistor. The following parts are recommended: diodes for a current of 50 A and an operating voltage of up to 500 V; resistor with power up to 5 kW. Due to the ballast resistor, the voltage on the primary winding of the transformer is about 100 V at a current of no more than 20 A.

Figure 2. Plasma generator design.

The transformer is selected so that the voltage on the secondary winding is about 20 V. You can use any 110/24 V transformer with a power of 1.6 kW (for example, OSM type). Any heating element or assembly of several heaters can be used as a ballast resistance.

The auxiliary source is assembled in a metal panel. A transformer is installed at the bottom of the shield. If the ballast is made from heaters, then they should be placed separately in a metal frame. A contact block is installed in the shield, onto which the ends of the secondary winding of the transformer are brought out, and a cable is connected to supply current to the plasmatron.

Selection of gas source and cooling system

As a source of plasma-forming gas, a car compressor can be used to supply compressed air with a capacity of up to 50 l/min. If water steam is used instead of gas, a standard small steam generator should be installed. In this case, only distilled water should be used.

Cooling of the anode of the plasma torch can be based on an automobile windshield wiper system. If possible, it is better to provide cooling from the water supply through rubber hoses.

What does it look like?

The plasma torch consists of two main blocks - anode and cathode. The anode block includes an anode, made in the form of a nozzle, and a housing for attaching the anode, in which it is necessary to place a cooling jacket (tubes, coil). A screw is attached to the anode body to supply power.

Figure 3. Plasmatron diagram.

The cathode block consists of the following main parts: block body, cathode holder, cathode. A tungsten welding electrode with a diameter of 4 mm, which is combined with a shank, is used as a cathode. The top of the shank is terminated by an adjusting screw with an insulated handle. The cathode is fixed in the cathode holder. The cathode holder consists of several sections.

The lower section is a pointed tube of small diameter that acts as a guide for the cathode. The middle section is a bushing with an external thread for mounting on the body and an internal channel for the passage of the electrode. The upper section is a tube for attaching the electrode. Its internal diameter corresponds to the diameter of the cathode tail. The cathode holder is installed inside the housing, which is made of a polymer pipe. The casing of the cathode block has a hole and a corresponding fitting for supplying plasma-forming gas. Gas is supplied through a tube located in the space between the bottom of the holder and the housing. The holder has a screw for connecting electrical power. A hole is drilled in the housing for the passage of a wire (cable) (Fig. 3).

Making an anode block

The anode is made as a copper cap (in the form of a hat). The total length of the anode is 10-15 mm. The lower end part (side) has a diameter of 20-25 mm and a length of 3-4 mm. The cylindrical part is 15-20 mm in diameter. A hole with a diameter of 1.8-2 mm is drilled in the center of the anode along its entire length. A thread is cut on the cylindrical part of the anode to screw it into the housing.

It is advisable to make the body of the anode block from bronze, but it can also be made from steel, in the form of two cylinders (pipes), between which a cooling jacket is located. The cylinders are welded (soldered) together. The outer diameter of the outer cylinder is recommended 50-80 mm. But the sizes of the cylinders can be any, taking into account the found pipes. The main condition: the housing must consist of two cylinders that fit into each other, while the internal diameter must be equal to the diameter of the cylindrical part of the anode, and the cooling coil tubes must be located between the cylinders. Case length – 30-60 mm.

The cylinder is threaded at both ends. At the lower end, the thread is cut inside and is intended for fastening the anode, at the upper end - inside the outer cylinder for connection to the cathode block. A threaded hole is made on the outer cylinder to install a screw to connect the cable.

Manufacturing of the cathode block

The body of the cathode block is made of a polymer or textolite pipe with a diameter equal to the inner diameter of the outer cylinder of the anode block. An external thread is cut at the lower end of the pipe for connection to the body of the anode block. A thread is cut inside the housing to screw in the cathode holder. Body length 7-10 cm.

The cathode holder is made of bronze or steel and has different diameters in different areas. The lower section, 15-20 mm long, is made in the form of a pointed tube with a diameter of 8-10 mm and an internal diameter of 5-5.5 mm.

The middle section, 20-25 mm long, has a diameter equal to the internal diameter of the cathode block housing. In this area, a thread is cut for mounting on the body.

The diameter of the internal channel must be at least 5 mm. The upper section, 30-40 mm long, has a diameter of 10-15 mm. The internal diameter of this area is 6-7 mm. On the upper section of the holder, an internal thread is cut for attaching the electrode. From the outside, in the upper part, a thread is cut to a length of 20-25 mm to install a lock nut. This holder is best made on a lathe.

The cathode is made from a standard tungsten welding electrode with a diameter of 4 mm. Its end becomes pointed. A tungsten rod 40-50 mm long is firmly connected to the cathode shank, on which a thread is cut for fastening to the upper section of the cathode holder. Shank length 40-60 mm, diameter 6-7 mm. The upper part of the shank goes into an adjusting screw (of any shape), which, in turn, has a handle made of insulating material. The cathode is twisted into the internal channel of the holder so that its pointed end extends 5-10 mm from the lower (guide) section of the holder. By rotating the knob, the position of the cathode can be changed.

To limit and control the longitudinal movement of the cathode, a lock nut installed on the holder is used.

A hole is drilled in the body of the cathode block at the level of the lower section of the holder and a fitting is installed to supply plasma-forming gas. Gas is supplied through a tube located in the space between the bottom of the holder and the housing. The holder has a screw for connecting electrical power. A hole is drilled in the upper part of the case for the passage of wires (cables).

Plasma torch assembly

First, the cathode block is assembled in the following sequence. The electrode is screwed into the holder. The holder is then screwed into the housing. A wire is connected to the holder screw, which is led out through a hole in the housing. The cathode body is screwed into the anode body. The anode is screwed into the anode housing from below. The electrode is additionally twisted so that the rod rests against the anode. The locking nut on the holder is adjusted to this position of the electrode.

Assembling the welding machine

Assembling the welding machine includes the following operations. One of the cores of the welding cable from the inverter is connected to the contact screw of the anode block of the plasma torch, the second is fixed to the part being welded. A cooling hose is connected to the fitting in the anode block, and a hose from the compressor is connected to the fitting of the cathode block. The cable from the auxiliary arc power transformer is secured to the contact screws of the anode and cathode blocks of the plasma torch. When the pilot arc is ignited, the cathode touches the anode and then quickly withdraws by 2-3 mm.

Necessary tools and equipment.

When making a homemade welding machine, you must use the following tool:

welding machine;
electric drill;
Bulgarian;
milling cutter;
file;
hacksaw for metal;
vice;
emery wheel;
pliers;
screwdriver;
wrenches;
chisel;
hammer;
calipers;
tap;
die;

Plasma welding is a modern, effective type of welding. A homemade welding machine will help you perform almost any welding work, including working as a welding machine for spot welding.

A plasma cutting machine is a fairly popular piece of equipment that allows cutting any metals in many areas of production. Plasma cutters are used not only in enterprises. Recently, they have begun to appear in home workshops. But, since almost every workshop already has welding machines, it would be wiser not to buy a ready-made plasma cutter, but to make one from an inverter with your own hands.

In some cases, a plasma cutter is an indispensable tool for processing metal products, since the temperature of the plasma leaving its torch reaches 25-30 thousand degrees. Thanks to these characteristics, the scope of application of plasma cutters is quite extensive:

production of various types of metal structures;
laying of pipelines;
fast cutting of any metals, including high-alloy heat-resistant steels containing titanium, nickel and molybdenum, the melting point of which is above 3000°C;
shaped cutting of thin-sheet materials (conductive) due to high cutting accuracy.

In addition, plasma cutters (as an alternative to laser cutters) are used as part of automatic lines at large enterprises for cutting parts of various configurations from sheet materials.

It is necessary to distinguish between concepts such as plasma cutting and plasma welding. The latter is available only on expensive, professional equipment, the cost of which starts from 100 thousand rubles.

Inverter or transformer

There are various methods, as well as drawings and diagrams, according to which you can make a plasma cutter. For example, if it is made on the basis of a transformer welder, then the plasma cutter diagram provided below is suitable, which describes in detail what parts are needed to manufacture this module.

If you already have an inverter, then in order to convert it into a plasma cutter, you will need a little modification, namely adding an oscillator to the electrical circuit of the device. It is connected between the inverter and the plasma torch in two ways, as shown in the following figure.

The oscillator can be soldered independently according to the diagram provided below.

If you make a plasma cutter yourself, then choosing a transformer as a current source is not recommended for several reasons:

the unit consumes a lot of electricity;
The transformer is heavy and inconvenient to transport.

Despite this, the welding transformer also has positive qualities, for example, insensitivity to voltage changes. It can also cut thick metal.

But advantages of an inverter plasma cutting machine in front of the transformer unit there is:

light weight;
high efficiency (30% higher than that of a transformer);
low electricity consumption;
High-quality cutting thanks to a more stable arc.

Therefore, it is preferable to make a plasma cutter from a welding inverter than from a transformer.

Typical plasma cutter design

To assemble a device that will make air plasma cutting of metals possible, you will need to have the following components available.

Power supply. Required to supply electric current to the burner electrode. The power source can be either a transformer (welding) that produces alternating current, or an inverter-type welding unit, the output of which is direct current. Based on the above, it is preferable to use an inverter, and with an argon welding function. In this case, it will have a connector for connecting the hose package and a place to connect the gas hose, which will simplify the modification of the device.
Plasma torch (cutter). It is a very important piece of equipment that has a complex design. In a plasma torch, a plasma jet is formed under the influence of an electric current and a directed air flow. If you decide to assemble a plasma cutter with your own hands, then it is better to purchase this element ready-made on Chinese websites.
. Required for effective arc ignition and stabilization. As mentioned above, it is soldered according to a simple scheme. But if you are not strong in radio, then this module can be bought in China for 1,400 rubles.
Designed to create an air flow entering the burner. Thanks to it, the plasma torch is cooled, the plasma temperature rises and the molten metal is blown away from the cut site on the workpiece. For homemade work, any compressor that is usually connected to a spray gun is suitable. But to remove water vapor from the air pumped by the compressor, you will need to install a filter drier.
. Through it, current flows into the burner, facilitating the ignition of the electric arc and ionization of gases. Compressed air is also supplied to the burner through this hose. You can make a hose cable yourself by placing an electrical cable and an oxygen hose inside, for example, a water hose of a suitable diameter. But it’s still better to buy a ready-made hose package, which will have all the elements for connecting to the plasmatron and to the unit.
Ground cable. It has a clamp at the end for attaching to the metal being processed.

Assembling the device

After all the necessary elements have been prepared, you can begin assembling the plasma cutter:

connect a hose to the inverter through which air will be supplied from the compressor;
connect the hose package and ground cable to the front side of the inverter;
Connect the torch (plasma torch) to the hose package.

After assembling all the elements, you can begin equipment testing. To do this, connect the ground cable to the part or metal table on which it is placed. Turn on the compressor and wait until it pumps the required amount of air into the receiver. After the compressor automatically turns off, turn on the inverter. Bring the torch close to the metal and press the start button to create an electric arc between the torch electrode and the workpiece. Under the influence of oxygen, it will turn into a stream of plasma, and metal cutting will begin.

In order for a homemade plasma cutter from a welding inverter to work effectively and for a long time, you should listen to the advice of specialists related to the operation of the device.

Recommended to have a certain number of gaskets which are used to connect hoses. Their presence should especially be checked when the unit has to be transported frequently. In some cases, the absence of the necessary gasket will make the device impossible to use.
Because the cutter nozzle is exposed to high temperatures, it will wear out and fail over time. Therefore, you should worry about purchasing spare nozzles.
When selecting components for a plasma cutter, you should consider how much power you want to get from the unit. First of all, this concerns the choice of a suitable inverter.
When choosing an electrode for a burner, if you make it yourself, you need to give preference to a material such as hafnium. This material does not emit harmful substances during heating. But it is still strongly recommended to use ready-made cutters manufactured at the factory, in which all parameters for air flow swirl are observed. A homemade plasmatron does not guarantee high-quality cutting and quickly breaks down.

As for safety rules, work should be carried out in special clothing that protects against splashes of hot metal. You should also wear chameleon welding goggles to protect your eyes.

Plasma cutters are widely used in enterprises working with non-ferrous metals. Unlike ordinary steel, which can be cut with a propane-oxygen flame, stainless steel or aluminum cannot be processed in this way, due to the greater thermal conductivity of the material. When attempting to cut with a conventional flame, a wide part of the surface is exposed to heat, which leads to deformation in this area. A plasma cutter is capable of point heating of metal, producing cutting with a minimum cutting width. When using filler wire, the machine can, on the contrary, weld non-ferrous types of steel. But this equipment is quite expensive. How to assemble a plasma cutter yourself from a welding inverter? On what principle does the device work? What is the equipment layout? Is it possible to make a cutter gun yourself, or is it better to buy this item? The following discusses the answers to these questions, including a topical video.

You can make a plasma cutter from an inverter with your own hands if you have a good understanding of the operating principle of the device and the elements involved in the process. The essence of the functioning of the plasma cutter is as follows:

The current source generates the necessary voltage, which is supplied through cables to the torch torch (plasma torch).
The plasma torch contains two electrodes (cathode and anode), between which an arc is excited.
The air flow, supplied under pressure and special twisted channels, directs the electric arc outward, while simultaneously increasing its temperature. Other models use a liquid that evaporates and creates release pressure. The resulting high-temperature ionized flame (as it looks externally) is plasma.
A ground cable, pre-connected to the product, helps close the arc on the surface being cut, which makes it possible for the plasma cutter to operate.
When welding is performed, the supplied gas can be argon or other inert mixtures that protect the weld pool from the external environment.

The temperature of the arc, due to acceleration by air flow, can reach 8000 degrees, which allows you to instantly and precisely heat the required section of the metal, performing cutting, and without overheating the rest of the product.

Plasma cutters differ in power and configuration. Small models are capable of cutting metal about 10 mm thick. Industrial machines work with steels up to 100 mm thick. Often these are large machines on brackets, onto which steel sheets are fed by hoists. A plasma cutter made at home will be able to cut stainless steel and other metals up to 12 mm. They can make shaped cuts in sheet iron (circles, spirals, wave-like shapes), as well as welding alloy steel with filler wire.

The simplest homemade plasma cutter should have four component parts:

power supply;
plasmatron;
compressor;
mass.

Current source

Assembling the product must begin by finding a suitable power source. Industrial models use powerful transformers that produce high current and are capable of cutting thicknesses over 80 mm. But at home you don’t have to work with such values, and such a transformer will make a lot of noise.

As a current source, you can take a regular inverter, which costs four times less than the simplest plasma cutting machine. It will outperform the transformer by producing a stable voltage at a high frequency. Thanks to this, the stability of the arc and the required cut quality will be ensured. The inverter will also be convenient due to its small size, in case of on-site work with a plasma cutter. Light weight will make it easier to transport the device to the desired location.

The plasma cutter from the inverter, in finished form, must meet a number of key requirements:

powered by 220V network;
operate at a power of 4 kW;
have a current adjustment range from 20 to 40 A;
idle 220V;
nominal operating mode 60% (with a cycle of about 10 minutes).

To achieve these parameters, the product must be equipped with additional equipment, strictly according to the scheme.

Plasma cutter circuit and its operation

How to make a plasma cutter is well shown in some videos on the network. There you can also find important diagrams according to which the device is assembled. To read symbols, basic electrical engineering skills and the ability to understand symbols are required.

The plasma cutter circuit ensures that the device can actually perform the work. This happens as follows:

The plasma torch has a process start button. Pressing the button turns on the relay (P1), which supplies current to the control unit.
The second relay (P2) supplies current to the inverter, and at the same time connects the solenoid valve that purges the burner. The air flow dries the burner chamber and frees it from possible scale and debris.
After 3 seconds, the third relay (P3) is activated, powering the electrodes.
Simultaneously with the third relay, an oscillator is started, ionizing the air between the cathode and anode. An arc called a pilot arc is excited.
When the flame is brought to a product connected to ground, an arc is ignited between the plasma torch and the surface, called the working one.
The reed switch relay cuts off the supply of current that operates for ignition.
The material is being cut or welded. If contact with the surface is lost (the arc hits an already cut place), then the reed switch relay is activated again to ignite the pilot arc.
After turning off the button on the plasma torch, any type of arc goes out, and the fourth relay (P4) starts a short-term supply of purge air to remove burnt elements from the nozzle.

Plasma torch assembly

Plasma cutting and welding is performed with a torch (plasma torch). It can have various modifications and sizes. It is quite difficult to build a model that runs on water at home, so it is worth purchasing such a “gun” in a store.

It is much easier to make a plasmatron with an air system. Homemade versions of the plasma cutter are most often just like this. To assemble it yourself you will need:

handle with holes for cables (can be used from an old soldering iron or toys);
start button;
special electrode;
insulator;
flow swirler;
nozzles for different metal diameters;
splash-proof tip;
distance spring to maintain the gap between the nozzle and the surface;
nozzles for removing chamfers and carbon deposits.

Welding and cutting with the same device can be carried out on different thicknesses of metal thanks to the replaceable elements of the plasma torch head. For this purpose, a variety of nozzles are provided, differing in the diameter of the outlet opening and the height of the cone. It is they who direct the formed plasma jet to the metal. Nozzles are purchased separately in the store. It is worth buying several pieces of each type, because they will melt, which will require replacement over time.

The nozzles are secured with a special clamping nut, the diameter of which allows the nozzle cone to pass through and clamp its wide part. Immediately behind the nozzle there is an electrode and an insulating sleeve that prevents the arc from igniting in an unintended place. Afterwards, there is a mechanism for twisting the air flow, which enhances the effect of the arc. All this is placed in a fluoroplastic case and covered with a metal casing. Some of these items can be made yourself, while others are better purchased at the store.

A store-bought plasma torch may also have an air cooling system, which will allow the device to operate longer without overheating. But if cutting will be carried out for a short time, then this is not necessary.

Electrodes used

Electrodes play an important role in ensuring the arc burning process and cutting with a plasma torch. Beryllium, hafnium, thorium and zirconium are used in their manufacture. Due to the formation of a refractory surface film, the electrode rod is not subject to overheating and premature destruction when working at high temperatures.

When buying electrodes for a homemade plasma cutter, you should find out what material they are made of. Beryllium and thorium produce hazardous fumes and are suitable for use in special environments that provide adequate protection to the welder. Therefore, for home use it is better to purchase hafnium electrodes.

Compressor and cable hoses

Most homemade plasma cutters include a compressor and air supply paths to the burner in their design. This is an important part of the device, allowing the temperature of the electric arc to develop up to 8000 degrees, and ensuring the cutting process. Additionally, the compressor blows through the channels of the equipment and the plasma torch, draining the system of condensate and removing debris. The possibility of compressed air passing through the burner helps to cool the working parts.

You can install a simple compressor in your plasma torch, which is used when painting with a spray gun. Connection to the device is made with a thin hose and an appropriate connector. An electric valve is installed at the inlet to regulate the air supply to the system.

The channel from the plasma cutter to the torch already contains an electrical component (a cable for powering the electrode), so a thicker hose is used, for example from an old washing machine, inside which the electrical wire is placed. The supplied air will simultaneously cool the cable. The mass is made from wire with a cross-section of more than 5 mm square, with a clamp at the end. If the ground contact is poor, the pilot arc will not be able to switch to the working arc. Therefore, it is important to buy a clamp that is strong and reliable.

It is quite possible to assemble a plasma cutter at home using a video and purchased components. A working inverter and circuit will serve as the basis for realizing the goal. And the above tips will help you better understand the process and purpose of each element in the assembly.

Plasma cutting is a method of processing metal empty parts with a plasma stream. This method allows you to cut metal because it is enough to be done in such a way that the material is electrically conductive. Compared to similar methods, plasma cutting of metals allows for a faster and higher-quality process without the use of massive rollers and special additives.

In this way, it is possible to process a variety of metal sheets, pipes of different diameters, shaped and sorted products. During processing, a high-quality cut is obtained, which requires minimal cleaning effort. Even with the help of this technology, various imperfections can be eliminated from the metal surface such as bulges, seams and irregularities and prepare for welding, drilling and other operations.

Plasma cutting of sheet metal is an extremely effective method.

Unlike other methods, it can be used to process ferrous and non-ferrous metals. For this reason, there is no need to prepare the surface and clean it of contaminants, which could make it difficult to ignite the arc. In the industry, the main competitor to this method is laser processing, which has even greater precision but also requires significantly more expensive equipment.

At home, there are no equivalent competitors to the plasma device.

Quality of plasma cutting of metals

Plasma cutting technology

Plasma cutting is carried out using a special device, which has dimensions similar to those of a conventional welding machine. At first these devices were large in size, but as they were improved they became smaller.

The device is connected to a 220V power supply for household appliances and 380V for industrial applications.
During the production process, cutting is carried out using CNC machines, which consist of one or more torches with mechanisms for moving them.

The machine can implement measures according to a specific program, which greatly facilitates the work of several sheets in the same cut.

To create a plasma jet, you need to connect the system to a compressor or air line.

The compressed air supplied to the device must be free of dirt, dust and moisture. For this purpose, air filters and dehumidifiers are installed in front of the device. Without such devices, wear of electrodes and other elements will accelerate faster. Liquid-cooled plasma torches also require plumbing.

Manual cutting of steel pipe

Circular cutting of steel pipe
self-propelled vehicle

Air plasma cutting technology achieves quality edges (no sucking or grating) and no warping (also on low-thickness sheets).

This allows subsequent welding of the cleaned metal without pre-treatment.

Manual cutting of metals on a sample

Essence of Plasma Sheet

Plasma cutting of steel in everyday life is carried out with devices along which the length of pipes reaches 12 m.

Manual devices have a cutting head equipped with a motorized handle. Such devices use air cooling because it is simpler in design and does not require additional refrigeration units. Water cooling is used in industrial installations where plasma cutting of steel sheets is more efficient, but the cost of the devices is higher.

Oxygen plasma technology

Oxygen plasma cutting requires a special electrode and nozzle, which has a significant temperature effect as a consumable. First, an auxiliary arc begins, which is excited by the discharge caused by the DC generator. Thanks to the arc, a plasma torch 20-40 mm long is created. When the torch touches the metal, a working arc appears and the auxiliary bow is turned off.

How to make a plasma welding machine with your own hands?

Thus, the plasma acts as a guide between the device and the workpiece. Arisen arc is self-sufficient, creating plasma due to the ionization of air molecules.

Plasma cutting using working fluid at temperatures up to 25000 ° C.

Plasma cutting of large diameter pipes and other tanks

Plasma cutting and welding can be done in workshops and workshops, as well as outdoors.

This method may not be as efficient as a gas power plant for renovation and construction work without a central system for electricity and compressed air. In this case, a sufficiently strong generator is required to provide power to the device and the compressor.

Similar to gas flame cutting, this method can be used to process empty pieces of different sizes and shapes.

Plasma cutting of large diameter pipes does not create any problems: it is performed manually or using self-propelled machines. The fixed burner rotates outside the tube. The use of self-propelled machines ensures precise and smooth cutting. Work with formed and sorted rolled products can also be automated in industrial settings.

Advantages of using SIBERIAN devices:

Versatility (can be applied to any metal, including non-ferrous and refractory metals);
Cutting speed;
High quality surface after cutting;
Economics (using compressed air);
Almost complete absence of thermal deformations on the product to be reduced;
Mobility rather than heavy weight of air-cooled units;
Easy to use.

Arc ignition devices

Devices for the initial ignition of the arc are divided into two classes: ignition of the arc from a short circuit and by breakdown of the electrode-product gap with high-voltage pulses.

Ignition by short circuit is carried out by short-term contact of the electrode and the product and their subsequent separation. The current through the microprotrusions of the electrode heats them to the boiling point, and the field that arises when the electrodes are separated provides the emission of electrons sufficient to initiate the arc.

With this ignition, transfer of electrode material into the weld is possible. To eliminate this undesirable phenomenon, ignition should be carried out at a low current not exceeding 5-20A. The ignition device must provide a low short-circuit current, maintain the current at this level until the arc is formed, and only then smoothly increase to the operating level.

(UDG-201, ADG-201, ADG-301).

Basic requirements for gap ignition devices (arc exciters or oscillators):

1) must ensure reliable arc initiation;

2) must not endanger the safety of the welder and equipment.

Exciters can be designed to initiate a DC or AC arc. In the latter case, a number of specific requirements are imposed on the exciters related to the moment of ignition of the arc. The circuit diagram of the OSPZ-2M oscillator is shown in Fig.

Rice. 5.5. Schematic diagram of the OSPZ-2M oscillator. F1 – fuse; PZF – noise protection filter; TV1 – step-up transformer; FV – spark gap; Cg – capacitor of the oscillatory circuit; Cn – decoupling capacitor; TV2 – high voltage transformer; F2 – fuse.

Capacitor Cr is charged from the voltage of the secondary winding of step-up transformer TV1.

After charging it to the breakdown voltage of the spark gap FV, an oscillatory circuit is formed, consisting of a capacitor Cr and the primary winding of a high-voltage transformer TV2. The oscillation frequency of this circuit is approximately 500 - 1000 kHz. From the secondary winding, this voltage with a frequency of 500 - 1000 kHz and a value of about 10,000 V is supplied to the electrode-product gap through a separating capacitor Cn and fuse F2.

In this case, a spark appears in this gap, which ionizes the gap, as a result of which an electric arc is excited from the power source. After the arc is excited, the oscillator automatically turns off.

Please note that the oscillator has high voltage.

It is not dangerous for humans due to the low power of the source. However, if the source circuit contains semiconductors (diodes, thyristors, etc.), then their breakdown by the oscillator voltage is possible.

To avoid this, the oscillator must be connected to the source using protection systems (Fig. 5.6).

How to make a plasma cutter with your own hands from an inverter?

Connection diagram of the oscillator to the power source.

The choke is protected by DZ for the high frequency of the oscillator, has a very large inductive reactance and does not allow the oscillator voltage to pass to the source.

The protective capacitor SZ, on the contrary, has a very low resistance for high frequency, protecting the source from the high frequency and high voltage voltage of the oscillator. The decoupling capacitor Cp protects the oscillator from the power supply voltage.

Recommendations. Typical mistakes of the MTP operator during plasma cutting and ways to avoid them

Using consumables until they fail

If you look at a number of parts of the same type that were cut out using this approach, you can unmistakably identify those parts for which the nozzle or electrode was already “on the way.”

The use of heavily worn nozzles and electrodes can not only lead to defects when cutting the part, but also cause expensive repairs to the flame cutter and even the plasma cutting machine, during which the plasma cutting machine will be idle.

Failure of nozzles and electrodes can be easily prevented by several signs indicated by worn consumables. An experienced operator will always tell you when it is time to change the electrode by the sound of cutting and the color of the arc flame (when the zirconium insert burns out, it acquires a greenish tint), as well as the need to reduce the height of the plasma torch when punching.

Also, one of the best ways to assess the condition of cutter parts is the quality of the cut. If the quality of the cut suddenly begins to deteriorate, then this is a reason to check the condition of the nozzle and electrode. A reasonable approach is to keep a log of the average electrode or nozzle operating time from replacement to replacement. The nozzle and electrode can withstand different amounts of piercing depending on the cutting current, material type and thickness.

For example, when cutting stainless steel, consumables need to be replaced more frequently.

Once you have determined from such a log the average lifetime of the electrode for each specific type of cut-out part, you can perform a planned replacement of nozzles and electrodes without leading to defects in the cut-out parts or breakdown of the flame cutter.

Replacing nozzles and electrodes too frequently

Among the used nozzles and electrodes, you can often find those that can still be used for cutting.

Excessively frequent replacement of consumables is also very common among operators of CNC metal cutting machines, and especially plasma cutting machines.

When replacing a nozzle or electrode, the operator must clearly know what to look for. The nozzle requires replacement in the following situations:

1. If the nozzle is deformed from the outside or inside.

This often happens when the punching height is too low and the metal is not cut through. Molten metal hits the outer surface of the nozzle or protective cap and deforms it.

2. If the nozzle outlet is shaped differently from a circle. With a high piercing height, if the movement begins before the metal is cut, then the arc deviates from the perpendicular to the sheet and passes through the edge of the nozzle hole.

To determine whether the electrode is worn out, you need to look at the silver-colored metal insert at the end of the copper electrode (usually an alloy of zirconium, hafnium or tungsten). In general, an electrode is considered operational if this metal exists at all and the depth of the hole in its place does not exceed 2 mm for air plasma or oxygen plasma cutting. For plasma cutting in a protective gas environment (nitrogen or argon), the hole depth can reach 2.2 mm. The swirler needs to be replaced only if a careful inspection reveals clogged holes, cracks, arc marks, or severe wear.

Swirlers are especially likely to be replaced prematurely. The same applies to protective caps, which only need to be replaced in case of physical damage. Very often the protective caps can be cleaned with sandpaper and reused.

Using incorrect plasma settings and consumables

The choice of consumables for plasma cutting depends on the type of metal being cut (steel, copper, brass, stainless steel, etc.), its thickness, the set arc current on the plasma cutting machine, plasma-forming and protective gases, etc.

The Plasma Cutting Machine Operator's Reference Guide describes which consumables to use for different cutting process conditions. The modes and recommendations regarding plasma cutting settings specified in the operator's manual should be followed.

The use of consumables (nozzles, electrodes) that do not correspond to the current plasma cutting mode usually leads to accelerated failure of the consumables and to a significant deterioration in the quality of the flame cut.

It is very important to perform plasma cutting of metal with exactly the arc current for which the consumables used are designed. For example, you should not cut metal with a 100-amp plasma if the plasma cutter has a 40-amp nozzle, etc.

The highest cut quality is achieved when the current on the plasma cutting machine is set to 95% of the rated cutting current for which the nozzle is designed. If the plasma cutting mode is set to a low arc current, the cut will be slagged, and there will be a significant amount of burr on the reverse side of the cut parts; the flame cut will be of unsatisfactory quality.

If the current set on the plasma cutting machine is too high, the life of the nozzle will be significantly reduced.

Incorrect plasma cutter assembly

The flame cutter must be assembled in such a way that all its parts fit tightly together, and there is no impression of “looseness”.

The tight fit of the plasma torch parts ensures good electrical contact and normal circulation of air and coolant through the plasma cutter. When replacing consumables, you should try to disassemble the plasma cutter on a clean surface so that dirt and metal dust generated during plasma cutting do not contaminate the plasma torch.

Cleanliness when assembling/disassembling a plasma cutter is very important and yet this requirement is often not met.

Failure to perform regular scheduled maintenance of the plasma torch

A plasma cutter can run for many months, even years, without proper maintenance.

However, the gas and coolant passages inside the plasma cutter must be kept clean, and the nozzle and electrode seats must be checked for contamination or damage. Dirt and metal dust must be removed from the plasma cutter. To clean the plasma torch, use a clean cotton cloth and electrical contact cleaner or hydrogen peroxide.

Cutting metal without checking the pressure of the plasma gas or the supply of coolant to the plasma cutter

The flow and pressure of plasma gas and coolant should be checked daily.

If the flow rate is insufficient, the torch parts will not be cooled properly and their life will be reduced. Insufficient coolant flow due to a worn pump, clogged filters, or insufficient coolant is a common cause of plasma cutter failures.

Constant pressure of the plasma gas is very important for maintaining the cutting arc and for a quality cut. Excessive pressure of the plasma-forming gas is a common cause of difficult ignition of the plasma arc, despite the fact that all other requirements for settings, parameters and the plasma cutting process are fully satisfied. Too high pressure of the plasma-forming gas causes rapid failure of the electrodes.

The plasma-forming gas must be cleared of impurities, because its cleanliness has a strong influence on the service life of consumables and the plasma torch as a whole. Compressors supplying air to plasma cutting machines tend to contaminate the air with oils, moisture and fine dust particles.

Punching at a low plasma torch height above the metal

The distance between the workpiece and the plasma torch nozzle cut has a huge impact on both the quality of the cut and the service life of consumables.

Even small changes in the height of the plasma cutter above the metal can significantly affect the bevels on the edges of the parts being cut. The height of the plasma cutter above the metal during piercing is especially important.

A common mistake is punching when the height of the plasma torch above the metal is insufficient. This causes molten metal to splash out of the piercing hole and onto the nozzles and protective caps, destroying these parts.

This significantly degrades the quality of the cut. If piercing occurs when the plasma cutter touches the metal, arc retraction may occur.

If the arc is “pulled” into the plasma torch, then the electrode, nozzle, swirler, and sometimes the entire cutter are destroyed.

The recommended piercing height is 1.5-2 times the thickness of the metal being cut by the plasma. It should be noted that when punching a sufficiently thick metal, the recommended height is too high, the pilot arc does not reach the surface of the metal sheet, therefore, it is impossible to start the cutting process at the recommended height. However, if the punching is carried out at a height at which the plasma cutter can ignite an arc, then splashes of molten metal may fall on the plasma torch.

A solution to this problem may be the use of a technological technique called “jumping”. When processing the command to turn on the cutting, the plasma cutting is turned on at a low height, then the cutter rises up to a given jump height, at which the metal splashes do not reach the cutter.

After punching has been completed, the cutter is lowered to the piercing height and begins to move along the contour.

Plasma cutting of metal at too high or too low a speed

The discrepancy between the plasma cutting speed and the selected mode significantly affects the quality of the cut. If the set cutting speed is too low, the cut parts will have a large amount of flash and various metal deposits along the entire length of the cut on the lower part of the edge of the parts.

Slow cutting speeds can cause larger kerf widths and large amounts of metal spatter on the top surface of parts. If the cutting speed is set too high, the arc will bend back, causing distortion of the cut edges, a narrow cut, and small beads of burr and flash at the bottom of the cut edge.

The burr formed at high cutting speeds is difficult to remove. With the correct cutting speed, the amount of burr, flash and metal sagging will be minimal. The surface of the flame cut edge at the correct speed should be clean and machining should be minimal. At the beginning and end of the cut, the arc may “deviate” from the perpendicular.

Homemade plasma cutter from an inverter welding machine: diagram and assembly procedure

This occurs because the arc cannot keep up with the torch. Deflection of the arc leads to the fact that it cuts into the side surface of the nozzle, thereby violating its geometry. If you are cutting from an edge, the center of the nozzle hole must be exactly in line with the edge of the part. This is especially important in combined machines that use both a punching head and a plasma cutter.

Arc deflection can also occur when the plasma torch, when cutting is turned on, passes through the edge of the sheet, or if the lead out line intersects the old cut. Fine adjustment of timing parameters is necessary to reduce this effect.

Mechanical damage or breakdown of the plasma cutter

Collisions between the cutter and the sheet metal, cut parts, or edges of the cutting table can completely damage the cutter. Collisions between the cutter and the cut parts can be avoided if the control program specifies idle passes around, rather than over, the cut parts.

For example, the ProNest optimal cutting program produced by MTC-Software has such a feature, which allows you to minimize the risk of plasma torch failure and save significant money. Torch height stabilizers also provide some protection against metal collisions. However, if only a torch height sensor based on arc voltage is used, then “pecks” may occur at the end of the cut, because The arc voltage changes as a result of its “deflection” and the cutter moves down to compensate.

CNC systems use a multi-level system of protection against collisions with metal. Used as a touch sensor that measures the resistance between the antenna around the torch and the sheet, a capacitive sensor and an arc voltage sensor. This allows you to take full advantage of each sensor type. Also, to protect the cutter, you can use “brittle” brackets, which will break faster in the event of a collision than a plasma cutter.

Thus, a competent plasma cutting machine operator can save his business a huge amount of money, time and overhead costs on plasma cutting.

The result of the work of a good equipment operator will be increased profitability of plasma cutting and increased profit for the enterprise as a whole.

At the present stage of development of construction equipment, diamond cutting and concrete drilling are most often used.

However, other technologies for cutting high-strength materials, for example, plasma cutting technology for concrete, are not excluded.

This technology was developed and patented at the end of the 20th century.

Do-it-yourself plasma cutter from an inverter for plasma cutting of metal (7 photos + 2 videos)

But equipment that works on this principle has only now begun to be used.

What is the principle of plasma cutting based on? Very simple. Due to the effect of heat generated by a compressed plasma arc, even dense material, including concrete and reinforced concrete, melts. Then a jet of hot plasma very quickly removes the molten mass.

It is thanks to the acquisition of electrically conductive properties by inert gases, as well as their transformation into plasma, that plasma cutting of concrete is carried out.

After all, plasma is nothing more than an ionized gas heated to ultra-high temperatures, formed when an instrument is connected to a specific source of electricity.

A plasma torch is a special technical device that generates plasma, compresses an electric arc and blows plasma-generating gas into it.

It should be noted that this technology is becoming increasingly popular among specialists in industrial materials processing.

The difference between plasma cutting of concrete and oxygen lance cutting is that during the cutting process the material melts very intensively and is rapidly removed from the cut furrow.

During processing, the temperature reaches 6000°C.

The powder lance used in plasma cutting increases the heat to 10,000 - 25,000°.

Specialists use two different concrete cutting technologies to operate the equipment: plasma jet cutting and plasma-arc cutting technology.

How are they different?

The fact that the cutting arc lights up when cutting with a plasma jet between the electrode and the generating tip of the installation, but the object of influence is located outside the electrical circuit.

A high-speed plasma jet comes from the plasmatron and it is its powerful thermal energy that cuts reinforced concrete, as well as other high-strength materials.

With the plasma arc cutting method, a plasma arc ignites between a non-consumable electrode and the plane of the material being cut. The cutting process occurs due to the action of several components: the energy of the near-electrode arc spot, as well as the plasma column and the torch escaping from it.

Plasma arc cutting is considered the most effective by practitioners and is often used in metal processing.

Plasma jet cutting technology is mainly used to process non-conductive materials.

Do-it-yourself plasma cutting - working technology

Safety precautions when working with a plasma lamp

Plasma cutting involves a number of hazards: electrical current, high plasma temperatures, hot metals and ultraviolet radiation.

Safety precautions when working with plasma cutting:

Preparing the air and plasma cutting machine for operation

How to connect all the elements of the air and plasma cutting device is described in detail in the instructions for the device, so immediately start adding additional shades:

The device must be installed in such a way that air is accessible.
Cooling the plasma cutter body allows you to work longer without interruption and reduce the need to turn off the cooling device less often. The location should be such that there are no drops of molten metal on the device.
The air compressor is connected to the plasma torch through a moisture-oil separator. This is very important because water entering the plasmatron chamber or oil droplets can lead to the destruction of the entire plasma or even its explosion. The air pressure transmitted 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 parts of the plasma lamp may become useless.
If rust, mask or oil is applied to the workpiece, it should be better cleaned and removed. Although air cutting is plasma and can cut out brown parts, it is best to forget that toxic fumes are released when the rust is heated.
If you plan to cut into tanks that store flammable materials, they should be thoroughly cleaned.
If you want a smooth, parallel cut without dross or pitting, you must select the correct flow rate and cutting speed.
The following tables show the optimal cutting parameters for different metals of different thicknesses.

Table 2. Plasma cutting power and cutting speed for blank parts of various metals.

Air plasma cutting parameters

The first time you select the burner speed it will be difficult, you need experience.

Thus, this principle can be initially controlled: the plasma torch must be controlled so that the sparks are visible from the back of the workpiece. If no sparks are visible, the workpiece will not cut. Also note that operating the knife too slowly will negatively affect the quality of the cut, there are dimensions and bark on it, and the armpit can also be unstable to burn and even come out.

Plasma cutting

You can now continue the cutting process.

Before ignition of the electric arc, the plasmatron must be bubbled with air to remove accidental condensation and foreign particles.

To do this, press and release the ignition button. Thus, the device enters the cleaning method. After about 30 seconds, you can press and hold the ignition button.

As already described in the principle of operation of a plasma lamp, an auxiliary (pilot, pilot) arc lights up between the electrode and the tip of the nozzle. Typically it will not light for more than 2 seconds. Therefore, during this time it is necessary to illuminate the working (cutting) arc. The method depends on the type of plasma lamp.

If the plasma flash works directly, it is necessary to make a short circuit: after forming the length of the turn, you must press the ignition button - the air supply will stop and the contact will close.

The air valve then automatically opens, a stream of air flows out of the valve, ionizes, increases in size, and drains the spark from the plasma lamp nozzle. Therefore, a working arc lights up between the electrode and the metal of the part.

Important! Contact arc ignition does not mean that the plasma torch should be applied or applied to the workpiece.

Plasma flame ignition

Once the indicator lights up, the light will go off.

If the working arc cannot be turned on for the first time, you must release the ignition button and press it again - a new cycle begins.

Features of producing a plasma lamp with your own hands from a converter: circuit, working stages, equipment

There are several reasons why the working arc may not be illuminated: insufficient air pressure, insufficient assembly of the plasma lamp, or other damage.

There are also cases when the cutting blade is turned off.

The reason will most likely be wearing the electrode or ignoring the distance between the plasma fuel and the workpiece surface.

Distance between lamp and metal

To learn more:

Plasma metal cutting with remote shutdown

Manual pneumatic plasma cutting involves the problem of observing the distance between the torch/nozzle and the metal surface.

When working with the hand, this is quite difficult, as breathing gets out of control and the cutting turns out to be uneven. The optimal distance between the nozzle and the workpiece is 1.6-3 mm; special spacers are used for observation, since the plasma itself cannot be pressed against the surface of the workpiece.

The ladders are located at the top of the nozzle, then the plasmatron mounted on the workpiece and cutting.

Keep in mind that the plasma lamp must be firmly perpendicular to the workpiece. Permissible deviations from 10 to 50 °. If the workpiece is too thin, the cutter can be held in a small corner, which will prevent severe deformation of the thin metal.

Melted metal should not fall into the nozzle.

You can master working with plasma cutting yourself, but it is important to remember safety measures, but also that the nozzle and electrode are consumables that require timely replacement.

Operating principle of the burner

The operation of a plasma welding and cutting apparatus (plasma cutter) is based on the use of plasma, the fourth state of matter, as a cutting or welding tool.

To obtain it, high temperature and gas under high pressure are required. When an electric arc is created between the anode and cathode of the burner, a temperature of several thousand degrees is maintained in it.

Plasma formation

If you pass a gas stream through an arc under such conditions, it will ionize, expand in volume several hundred times and heat up to a temperature of 20-30 thousand °C, turning into plasma. High temperature almost instantly melts any metal.

Unlike a cumulative projectile, the process of plasma formation in a plasmatron is adjustable.

The anode and cathode in a plasma cutter are located at a distance of several millimeters from each other. The oscillator generates a pulsed current of high magnitude and frequency, passes it between the anode and the cathode, which leads to the occurrence of an electric arc.

After this, gas is passed through the arc, which is ionized. Since everything happens in a closed chamber with one exit hole, the resulting plasma rushes out at tremendous speed.

At the output of the plasma cutter torch, it reaches a temperature of 30,000 ° and melts any metal. Before starting work, a ground wire is connected to the workpiece using a powerful clamp.

When the plasma reaches the workpiece, an electric current begins to flow through the mass cable and the plasma reaches maximum power. The current reaches 200-250 A. The anode-cathode circuit is broken using a relay.

cutting

When the main arc of the plasma cutter disappears, this circuit turns on again, preventing the plasma from disappearing. Plasma plays the role of an electrode in electric arc welding; it conducts current and, due to its properties, creates an area of high temperature in the area of contact with the metal.

The contact area between the plasma jet and the metal is small, the temperature is high, heating occurs very quickly, so there is virtually no stress or deformation of the workpiece.

The cut is smooth, thin and does not require further processing. Under the pressure of compressed air, which is used as a plasma working fluid, the liquid metal is blown out and a high-quality cut is obtained.

When using inert gases with a plasma cutter, you can carry out high-quality welding without the harmful effects of hydrogen.

DIY plasma torch

When making a plasma cutter from a welding inverter with your own hands, the most difficult part of the work is the production of a high-quality cutting head (plasma torch).

Tools and materials

If you make a plasma cutter with your own hands, it is easier to use air as a working fluid. For production you will need:

Plasma cutter consumables in the form of nozzles and electrodes should be purchased at a welding equipment store. They burn out during the cutting and welding process, so it makes sense to purchase several pieces for each nozzle diameter.

The thinner the metal to be cut, the smaller the plasma cutter torch nozzle hole should be. The thicker the metal, the larger the nozzle opening. The most commonly used nozzle is the one with a diameter of 3 mm; it covers a wide range of thicknesses and types of metals.

Assembly

The plasma cutter torch nozzles are attached with a clamping nut. Directly behind it there is an electrode and an insulating sleeve, which does not allow an arc to occur in an unnecessary place in the device.

Then there is a flow swirler that directs it to the desired point. The entire structure is placed in a fluoroplastic and metal case. A pipe for connecting an air hose is welded to the outlet of the tube on the plasma cutter torch handle.

Electrodes and cable

The plasma torch requires a special electrode made of refractory material. They are usually made from thorium, beryllium, hafnium and zirconium. They are used due to the formation of refractory oxides on the surface of the electrode during heating, which increases the duration of its operation.

When used at home, it is preferable to use electrodes made of hafnium and zirconium. When cutting metal, they do not produce toxic substances, unlike thorium and beryllium.

The cable from the inverter and the hose from the compressor to the plasma cutter torch must be laid in one corrugated pipe or hose, which will ensure cooling of the cable in case of heating and ease of operation.

The cross-section of the copper wire must be selected at least 5-6 mm2. The clamp at the end of the wire must ensure reliable contact with the metal part, otherwise the arc from the pilot arc will not transfer to the main arc.

The compressor at the outlet must have a reducer to obtain normalized pressure at the plasma torch.

Options for direct and indirect action

The design of a plasma cutter torch is quite complex; it is difficult to do at home, even with various machines and tools, without a highly qualified worker. That's why the manufacture of plasma torch parts must be entrusted to specialists, or even better, buy it in a store. The direct action plasma torch torch was described above; it can only cut metals.

There are plasma cutters with indirect action heads. They are also capable of cutting non-metallic materials. In them, the role of the anode is played by the nozzle, and the electric arc is located inside the plasma cutter torch; only the plasma jet comes out under pressure.

Despite the simplicity of the design, the device requires very precise settings; it is practically not used in amateur production.

Inverter modification

To use an inverter power source for a plasma cutter, it needs to be modified. You need to connect an oscillator with a control unit to it, which will serve as a starter that ignites the arc.

There are quite a few oscillator circuits, but the principle of operation is the same. When the oscillator is started, high-voltage pulses pass between the anode and cathode, which ionize the air between the contacts. This leads to a decrease in resistance and causes an electric arc.

Then the gas electric valve is turned on and under pressure air begins to pass between the anode and cathode through an electric arc. Turning into plasma and reaching the metal workpiece, the jet closes a circuit through it and the mass cable.

A main current of approximately 200 A begins to flow through the new electrical circuit. This triggers the current sensor, which turns off the oscillator. The functional diagram of the oscillator is shown in the figure.

Functional diagram of the oscillator

If you have no experience working with electrical circuits, you can use a factory-made oscillator of the VSD-02 type. Depending on the connection instructions, they are connected in series or in parallel to the plasmatron power circuit.

Before making a plasma cutter, you must first determine what metals and what thickness you want to work with. A compressor is sufficient to work with ferrous metal.

Cutting non-ferrous metals requires nitrogen; high-alloy steel requires argon. In this regard, you may need a trolley for transporting gas cylinders and reduction gears.

Like any equipment and tool, a welding machine with a plasma head requires certain skill from the user. The movement of the cutter should be uniform, the speed depends on the thickness of the metal and its type.

Slow movement results in a wide cut with jagged edges. Moving quickly will result in the metal not being cut through in all places. With proper skill, you can get a high-quality and even cut.