Welding is a simple and reliable way to connect permanent metal. Welding work is carried out using special equipment, ranging from microelectronics to heavy construction.
Today, welding is carried out using direct and alternating voltage. In AC welding installations, the main element is a transformer of any structure. And in welding devices with constant flow energy they use power rectifier blocks. Correctly selected electric welding electrodes are the key to quality work.
Alternating voltage gets its name because the flow of electrons continuously changes the direction of its movement. During a welding process using alternating current, the arc continuously "jumping". This happens due to regular deviation from the axis of the welding arc. Of course, this affects the quality of the resulting seam. As a result, the scar is wide, and metal droplets form at the junction. If the arc goes out, the ignition can be restarted by increasing the voltage.
With all this, equipment for alternating electric welding has its advantages:
Transformers continue to enjoy their popularity.
Welding machines permanently support 2 operating modes - the process of connecting with direct and reverse polarity. When using such installations, it is necessary to regularly monitor their operating mode, since some metals are seized in direct polarity, while others are seized in reverse polarity.
Most widely used straight polarity. The welded crater is deep and narrow. The heat supply decreases, the passage speed increases. It is used for cutting metal, has a stable arc, resulting in a high-quality connection. Used when working with steel, thickness from 4 mm. Most materials are welded using straight polarity.
Reverse polarity is used to join thin metals of medium thickness. The electric welding seam is not deep, but wide enough. With this polarity, you cannot use electrodes that are sensitive to overheating.
The main advantages of constant voltage welding are:
Electrodes conditionally do not differ. But constant power flow is not suitable for AC connection. Electric welding materials that are designed for alternating periods are also successfully used for electric welding using direct electricity. Experts call the resulting electrodes universal.
Universal electrodes are characterized by:
A feature of universal electric welding electrodes is the ability to make a connection of metal products, even if there is large distance between metal parts. They are excellent for electric welding short seams and spot tack welding.
Comparing welding with direct and alternating voltage, devices with a constant flow of energy have more advantages. Welding materials are saved, since spattering is minimal. The constant is simple and easy to use and is used for thin-walled products. Exposure to weather conditions does not affect arc stability, ensuring high performance. All areas of the structure are boiled, as a result the specialist receives a high-quality and neat scar.
The variable device provides good connection quality, simplicity and convenience of the welding process. Equipment that operates on this type of voltage is much cheaper.
The main difference between alternating and direct electricity is that the electrode is supplied with current or alternating frequency during operation. 50 Hz or constant. The design of a constant flow welding machine has rectifiers in the form of diodes, which rectify the electricity at the output and create a constant-sign pulsating value. Modern semiconductor rectifiers guarantee high performance and high efficiency. Consequently, better welding will be achieved using a constant flow. As practice has shown, alternating electrodes are a thing of the past.
Welding current is the most important parameter on which a quality connection depends. The diameter of the electrode must be selected taking into account the thickness of the metal. And based on its diameter, electricity is set. This information can be found on the packaging. There are no exact and specific voltage settings - each master is guided by his own feelings and sets the desired voltage parameter.
Special stores have a very wide selection of electrodes for arc welding. When purchasing, pay attention to the quality of the product and the presence of a license.
In the twentieth century, the AC welder was the most common metal welding device in construction and industry. This is explained by the simplicity of the design of the device.
In short, it is a power step-down transformer, the secondary winding of which has several terminals. Depending on what kind of metal needs to be welded, what thickness, what electrode, the welder chooses one or another output of the secondary winding.
Welding machines operating using alternating current are divided into the following types:
In the international classification, electric arc welding is designated MMA-AC or MMA-DC, in the case of manual electric welding with single electrodes, and argon welding with non-consumable electrodes is TIG.
The size and shape of a regular welding machine looked like a household washing machine on wheels, only even heavier. The closed magnetic circuit was located vertically. Below was the primary winding of the transformer.
The secondary winding was movable. It was attached to the nut of a vertical screw with a tape thread. On the housing cover there was an eye bolt with a handle.
When the handle was rotated, the nut with a secondary winding moved along the screw, changing the magnetic flux passing through the coils. Thus, the welding electric current was adjusted.
To move the apparatus, there was a handle on the lid; to connect the wires of the welding chain, there was a clamp on the side wall. All walls had slotted holes for cooling the transformer.
Speaking about such devices in the past tense, it means that now most people use AC and DC welding inverters. Welding equipment based on a power transformer is practically not used.
In order for the weld to be of high quality, a steeply falling current-voltage characteristic of the transformer is required. This is achieved in two ways. First option: in a transformer with normal magnetic leakage and a separate reactive coil (choke), the welding process is adjusted by changing the gap in the choke core.
Second option: adjustment is carried out by changing the gap between the primary and secondary coils. In this case, a change in the electric current over a wide range does not lead to a change in the arc voltage, which has a positive effect on the quality of the seam.
In resistance welding machines at the time of the welding process, in low-power devices the welding current reaches 5000-10000 A, in powerful devices it reaches 500 kA. Therefore, high demands are placed on transformers.
They are step-down transformers with a number of design features:
Resistance welding machines are mostly single-phase with armor-type cores. Since the quality of welding strongly depends on the duration of the welding pulse, the switching equipment is quite complex - a price to pay for accuracy.
The devices experience heavy mechanical loads, up to 400 starts per minute, so they are subject to additional requirements for structural strength.
Low-power resistance welding machines have a welding current of up to 5000 A, weigh about 20 kg and weld metal up to 2.5 mm thick. Widely used at home and small workshops.
Inverters are sometimes called DC welding machines because during their operation, the first stage is the conversion of alternating voltage to direct current.
Inverters are actively replacing transformer-based devices due to their light weight, compact size and high performance.
The welding inverter consists of a high-voltage rectifier diode bridge and a low-pass filter, a frequency generator in the range of 30-70 kHz, high-voltage power switches, an isolation capacitor and a step-down transformer. It performs the function of a low-frequency alternating current to high-frequency converter.
A voltage of 220 V 50 Hz is supplied to the rectifier bridge, where it is rectified, the filter reduces ripple and is supplied to electronic switches made on bipolar transistors with an insulated gate or field-effect transistors.
At the output of the keys, thanks to a control unit based on a frequency generator, a signal with a frequency of 30-70 kHz is obtained. Passing through the separating capacitor, the electric current gets rid of the constant component and enters the primary winding of the step-down transformer.
The output of the secondary winding produces high-frequency alternating current, which is used for welding. Essentially, AC welding inverters are designed as switching power supplies without a rectifier unit at the output.
Due to the rapid transition through zero, AC inverter welding machines have a stable, uniform arc, which has a positive effect on the quality of the seam.
Using an inverter allows you to get a small-sized device with high power. A disadvantage of the inverter can be considered its high sensitivity to voltage surges.
Manual arc welding with alternating current works on the basis of a power transformer, which has a simple, reliable and inexpensive design. It can work in almost any conditions and for a long time without interruption.
The disadvantages include the low productivity of welding work and the need for constant removal of slag. The welding seam is worse than that produced by DC welding.
Argon welding using an alternating current machine with non-consumable electrodes produces a weld of the highest quality, allows you to weld large-section metal, and there is no spatter.
The disadvantages include the need to use additional equipment in the form of gas cylinders and low productivity.
Electrodes for welding with alternating current have been developed for a long time and have a wide variety. When using inverters, it was necessary to create new electrodes due to the specifics of high-frequency alternating current.
The most widely used electrodes are the ANO, OZS, and MR brands. They are used for welding carbon and low alloy steels. They ensure easy ignition of the electric arc and uniform maintenance of it, and easy removal of slag. Can be used for AC and DC welding machines.
The main feature of alternating current welding is the change in the polarity of the current flowing through the electric arc. Due to the fact that at a frequency of 50 Hz the time of transition through zero is quite long, the arc almost goes out and turns out to be uneven.
This often leads to porosity of the seam and a decrease in its quality. When using high-frequency alternating electric current, this disadvantage is practically overcome.
The use of constant allows you to obtain welds of higher quality due to the uniform release of heat in the weld pool. With direct current, the arc starts at lower voltage and is easier for the welder to maintain.
Once upon a time, welding transformers were popular; they remained in the memory of experienced welders due to the instability of welding current, operating parameters, significant weight and dimensions. The popularity of the equipment at that time was explained by the lack of alternative options. A DC welding machine is a modern, cost-effective assistant when it comes to welding, surfacing metals using direct current or a stick electrode. Popular models of the equipment in question deserve the attention of potential consumers and ordinary interested people.
The choice of a suitable welding device that satisfies all professional or domestic needs is directly related to high-quality preliminary information to the potential buyer. First of all, you should know about the most common models of welding equipment. Below are the best selling ones.
In order for the choice to be accurate and definite, you will need a researcher of the most popular options for welding equipment, descriptions, technical characteristics, welding current parameters, advantages, features and benefits. Below are the sources of welding current and descriptions of them with accompanying characteristics.
The ARC-200A equipment is an excellent choice for a person who wants to get all the delights of direct current when joining metals. For a person who has made a choice in favor of the DC machine in question, all sorts of advantages of the modern welding process become possible. The device of this model is designed for joining and surfacing metals using direct current. They work using a coated piece electrode
Compactness, energy saving, the possibility of mating steels in domestic and industrial conditions, simple ignition of an electric arc, useful functionality - all these modern and high-tech welding advantages are ready to be offered by the equipment in question. The device is equipped with automatic protection against current and voltage overloads. Due to its compactness and low weight, the device can be used in confined spaces, when welding work on hard-to-reach metal structures is required.
Industrial-style welding transformers are critical equipment. Of course, the characteristics, parameters and set of functions are somewhat different than in the case of household appliances, since industrial needs
Welding transformers, which provide the opportunity to take advantage of the delights of direct current, are useful assistants in everyday life, on a construction site, in the manufacturing sector, agriculture, etc. Thanks to the stability of the electric arc and the effect of direct current, the inverter in question helps to carry out high-quality, reliable, accurate and along with this, durable seams and connections. 
KAISER NBC-250 is a portable type of equipment. Its purpose is welding under direct current conditions, and the work can be done with rutile, cast iron electrodes in the MMA mode. Electrode diameter limits can vary from 1.6 to 5 millimeters. The device in question is an inverter with a single-phase connection.
The device has thermal protection that blocks the possibility of overheating. The body of the device, as well as all its components, are made of high-quality materials, in accordance with European Union standards (welding inverter transformers of this series are manufactured in China, but despite this, the quality requirements are somewhat different). This model has INVERTER technology, which controls current parameters, thereby ensuring stability of the arc, which, in turn, improves the quality of the connecting process.
A standard set of functions, including anti-sticking of the electrode and hot start, help minimize the likelihood of the electrode sticking to the working surface of the metal being welded, as well as simplify the start of the work process. The forced cooling system prevents the inverter from overheating, which some welding transformers do not have. Simplicity of operation, compactness and lightness make the device even more attractive for workers operating equipment in various conditions and spatial positions.
There are special industrial welding transformers, as already mentioned, that operate using direct current. Their characteristics are somewhat different, since the industry needs to process metals of large thickness.
Deca MMA Mastro 50 EVO is an inverter-type device designed for the production of joints and seams using electric arc and argon arc welding. The inverter allows you to use arc stability and other advantageous parameters obtained through direct current. It is possible to work with positive as well as negative cathodes. It is worth noting that it is possible to perform connecting work in an argon-arc environment using a tungsten electrode.
The equipment has reduced dimensions and low weight, and all this became possible thanks to inverter technology. A set of inverter functions, including hot start, simplify ignition of the electric arc and stabilize its combustion. It is possible to connect copper, steel, nickel, as well as stainless steel, etc. We are ready to offer the owner of the equipment anti-stick electrode and easy arc ignition with functionality that is not available in outdated welding transformers. The diffusion of the cathode material with the metal of the workpiece being connected is increased in the device.
Modern transformers allow the use of inverter technologies, which improve productivity, control arc characteristics, and much more. This makes it possible to improve the quality of the seam and connection. The internal components of the welding device in question comply with European quality standards, since all the manufacturer’s welding transformers are manufactured in Italy.
It is not advisable to dispute the advantages of direct current in combination with modern inverter technologies, because they are obvious and understandable. The main thing that is needed to clearly understand and identify quality equipment is knowledge regarding the characteristics of advantages and disadvantages and much more. etc.
Welding is the joining of two materials by melting. Using high temperature, the edges of the materials being joined are melted and mixed together, forming a uniform weld seam. Very often, with the exception of some types of welding, the electrode material is also involved in this process. High temperatures are achieved through an electric arc between the electrode and the material being welded, an electron beam, a laser beam, gas welding and the same methods that cause melting of the metal.
Most connections are made to metal parts, but recently welding has begun to be widely used to connect products made of plastic, ceramics, and combinations of these materials.
Naturally, the welding process itself is unsafe. It is necessary to observe special safety precautions to avoid electric shock, burns of both the body and various parts of the body, both infrared and ultraviolet radiation, as well as splashes from molten metal.
There are several sources for creating an electric arc and maintaining it. These are transformer sources, inverters, rectifiers. There are also welding units that operate on the principle of an internal combustion engine.
The largest application of these machines is in welding transformers, as well as DC inverter welding machines. If you look at an inverter, it uses high-frequency currents in its operation, while working due to the power electronics built inside, as well as a small-sized transformer - converter. The advantages of this device include its compactness, weight; for domestic use it is quite small, up to 5 kg, as well as energy consumption, which is quite low.
Welding inverter The disadvantages include the price, which is higher than that of welding transformers, especially professional welding machines with a DC inverter, and special requirements for ambient temperature and humidity. It reacts to voltage drops in the network and its repair is quite expensive compared to the total cost.
If we consider, its advantage will be the simplicity of the design. The transformer, which is the basis of the device, provides the network voltage to that required for welding. It is powered by alternating current from the network, and we receive either direct or alternating current, depending on the operation scheme of the device. They have a low cost, and if they break down, they are not difficult to repair.
Welding transformer The devices are divided by power, by the number of workstations connected to one transformer and by voltage, and by network: single-phase or three-phase.
Another necessary part of the transformer design is a choke for a DC welding machine, which is used as an amplifier in electrode devices and in semi-automatic machines.
Choke for DC welding machine, diagram. It is also called an inductor. This part improves the operation of the transformer and is a special wire that is wound around a ferromagnet core. To explain it more simply, the voltage supplied to the output coil increases, and smoothly, the current strength. If you change the polarity, the current decreases, again smoothly, without jumps. This is very important for the uniform burning of the electric arc and, accordingly, for the quality of welding, as well as protection against voltage fluctuations in the network.
The efficiency of the inductor is determined by such a parameter as inductance. It is measured in a value such as Gn. (Henry), which means that through a choke having an inductance of 1 H, at a voltage of 1 V, only 1 A of current can pass through 1 second.
The number of turns on the coil and induction are interrelated according to the principle of direct proportion. Very often, a choke is made by hand, especially since there are enough diagrams on the Internet, as well as descriptions of how to do it. Therefore, it is not necessary to calculate the number of turns or square them.
These welding machines have different welding arcs. Hence the difference in the electrodes used. This should be taken into account when purchasing electrodes. But this is not the only difference; the main difference lies in the design of the welding transformer itself.
AC Welding Machine As described above, the welding transformer has a core in the form of a closed magnetic circuit under its body, as well as both primary and secondary windings. Electric current passes through the primary winding, magnetizing the core. The resulting magnetic flux on the secondary winding produces alternating current, the voltage of which directly depends on how many turns are wound on the secondary winding. This produces alternating current. If we compare a DC welding transformer, its design contains a rectifier, which makes the current constant.
Transformer circuit Welding itself with alternating and direct current, when compared, shows that the latter provides a higher quality weld due to the fact that the current value is stable, does not have zero values, and the arc burns constantly. The result is good melting of the edges, while the number of defects in the weld itself is reduced, which improves the quality of the seam. In addition, the spattering of molten metal itself is significantly reduced, which reduces the cost of cleaning the seam after cooling.
If you consider buying a welding machine, of course, you choose from two categories: for welding at home and for welding in industrial conditions, for professionals. For work in an apartment, house, or garage, household models of step-down transformers are best suited. They can be with several chokes or with one or two rheostats. The main thing in choosing is a single-phase device with 220 V, although there are those that have switching over networks, 220 or 380 volts.
Ammeter for measuring current The greater the current the device produces, the higher its price, since the greater the thickness of the metal it can weld.
If the goal is to buy a DC welding machine for home use, we can recommend a current value from 50 to 160 A, not higher. When choosing, you need to know basically what kind of work will be carried out and with what metal, how often the equipment will be used and how much money you can spend on the purchase of both the equipment itself and on the required components, and especially personal protective equipment for welding.
Household welding machine More often used is a machine for manual arc welding with a consumable electrode, which is coated with flux, the so-called MMA welding.
Types of electrodes for manual arc welding. As an option, non-consumable electrode welding is also used, or is also called: TIG welding, but at home it is not used very often, but this method is suitable for welding thin sheet steel, for example, for car repairs, aluminum parts.
The price for a DC welding machine, for example, Zubr, Fubag, Resanta, Antika - 3300 rubles - 3800 rubles.
If we consider imported equipment, we can suggest the German KRÜGER device, it costs from 5,500 rubles.
Welding machine diagram Of course, you can make a DC welding machine yourself. This will not be difficult for a specialist if there is access to the materials from which it can be made. Instead of a body, you can use a frame as a basis. You also need a power source that has high power. All instructions can be found on the Internet.
Homemade welding machine To work in auto repair shops, in various workshops of small enterprises, devices with large output currents are needed; they must operate from a network with three-phase current. The device itself contains from 6 to 12 diodes, which are connected in parallel and in series in the electrical circuit.
Diagram of a professional welding machine with additional functions This industrial DC welding machine allows you to weld metals of various thicknesses. A good machine can be used for both welding and metal cutting. You can also connect two or three workstations to them and work simultaneously.
The three-phase device has switching for both 220 and 380 volts. They are most applicable in enterprises, since the quality of the connection when used is high.
Mostly 380 volt DC welding machines are used. These are not used in everyday life due to the fact that there is practically no 380 volts in the house. The standard welding current used is 300 A. All industrial devices have a significant weight, so they are installed on wheels. Their weight can reach 100 kg, they all have short circuit protection.
What is AC welding? Welding work is a special type of work with metal, which is intended for fastening metal structures. Currently, according to the type of current, welding can be done using direct and alternating electric current. Let's take a closer look at welding using alternating electric current.
The first and perhaps the most basic advantage of AC welding is the production of a high-quality weld. The strength of the entire structure depends on the quality of the weld, and the effect of strength itself is achieved due to the fact that the arc does not have any deviations from the original axis, and this, in turn, is the key to a high-quality and ultra-reliable weld.
The second advantage is that less expensive equipment can be used. Devices that generate alternating electric current will be discussed below.
All equipment designed for AC welding can be divided into the following categories:
In addition, it should be added that these devices have their own abbreviations and allow welding with direct or alternating current. Arc welding with stick electrodes is designated as MMA, and argon welding as TIG.
In addition, welding methods are divided into the following types:
Let's look at the main pros and cons of TIG. Regardless of the type of current supply, this type of welding has the following advantages:
It is quite natural that where there are advantages, there are also disadvantages. The disadvantages of the above method are as follows:
Now we should say a few words about the MMA method. Its advantages are:
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Electrodes designed for AC welding have been used in this industry for quite some time, when DC welding was very expensive. Therefore, we had to look for compromise options, albeit reducing the quality of the final result.
This situation arose largely due to the fact that rectifier elements, which were designed for high welding currents, until recently were bulky, expensive and inefficient units. The situation has changed for the better relatively recently. This became possible thanks to the availability of small-sized, highly efficient semiconductor rectifiers of the latest generation. Well, after inverters were invented, RDS became available to a wide range of users. Below are the main brands of electrodes that allow inverter welding.
The most popular electrodes used for alternating current welding are AHO, O3C and MP.
These types differ not only in the type of coating, but also in the chemical composition. For example, electrodes marked MP-3 and ANO-6 have a special rutile coating; it is basic and ilmenite, respectively. Well, all the others, brands MR-3S, OZS-12, OZS-6, OZS-4, ANO-6, ANO-4, ANO-21, have an ordinary rutile coating. It should be noted that these electrodes are used for welding carbon, low-carbon and low-alloy steels. One of the main features of these electrodes is that they are perfect for welding using direct electric current.
