Welding machines – types and description

Recommendation points

• Welding transformer
• Welding rectifier
• Welding generator
• Welding inverter
• Semi-automatic welding
• DIY welding machine
• How to choose a welding machine

In this article: types of welding machines, their principle of operation, characteristics, GOSTs; the cost of welding machines; how to make a welding machine with your own hands; selection criteria for a welding machine.

Among all construction equipment, the welding machine occupies a special place, if only because not a single construction site can do without it – there is simply no other way to reliably connect metal structures and pipes. What could replace a welded joint? Fastening with anchors, bolts or rivets, connecting pipes with clamps – all these and similar methods provide either a temporary solution to the problem or are not applicable for many reasons. Welding machines are of different designs and types – transformers, rectifiers, inverters, generators, semiautomatic devices – this article will help you understand this variety..

Welding transformer

Its task is to lower the voltage from the electrical network to the required level (below 141 V) and adjust the welding current to the desired values.

The design of any transformer must comply with GOST 95-77, it includes a steel magnetic circuit (core) and two windings in isolation – primary (connected to the network) and secondary (connected to the electrode holder and the welding object). In transformers of the popular TDM series, the primary winding is rigidly connected to the core, the secondary winding coils are removed from the primary coils (there are two of them for each winding) at a certain distance. Arc ignition requires a voltage on the secondary winding in the range of 55-60 V, for most electrodes used in manual welding, 50 V is sufficient.

By turning the screw with a knob, the secondary winding coils connected to the core are moved vertically – the welding current is adjusted to the required parameters. When the windings approach (the handle is rotated clockwise), the inductive resistance and the magnetic flux of leakage decrease, the welding current increases, and its decrease is achieved by reverse rotation. Adjustment range of welding current: with parallel connection of coils in both windings – 65-460 A, with serial connection – 40-180 A. The handle on the transformer cover is designed to switch the current ranges.

What happens in the welding transformer when it is connected to the AC mains? The flow of alternating current into the primary winding causes magnetization of the core. Having passed through the secondary winding, the magnetic flux of the core induces in it an alternating current of a lower voltage than that supplied to the primary winding. With more turns on the secondary winding, the voltage will be higher, with less – the voltage will be lower.

The value of the welding current is regulated by means of a controlled inductive reactance that changes the magnetic leakage flux. There are two ways to change the welding current: movable coils (as in TDM transformers), magnetic shunts or turn (step) regulation; addition of a reactive coil to the transformer design. The choice of the control method depends on the magnetic dissipation in this transformer: with increased dissipation, the first control method is used; at normal – the second.

The efficiency of welding transformers is low – rarely exceeds the 80% barrier, their weight is impressive. When carrying out welding work with this equipment, it is difficult to achieve a high quality of the seam, except that the use of special stabilizing electrodes that can improve the weld seam. However, the disadvantages of welding transformers are compensated by the low price (from 6,000 rubles) and their unpretentiousness.

Welding rectifier

This machine requires a DC connection. The rectifier design includes a valve block, a transformer and a choke (in some models) – performance in accordance with GOST 13821-77. The most widespread are multiphase rectifiers – their dimensions are much smaller than those of transformers, so they are easier to use in welding. Valves in the design of rectifiers can be silicon or selenium – the first type is smaller, but requires additional cooling. The efficiency of selenium valves is lower, but they are more resistant to overloads than silicon.

Adjustment of the welding current in the rectifier is carried out in three ways: by increasing / decreasing the distance between the windings; using a saturation throttle; transformer windings, divided into sections. The circuits according to which welding rectifiers are assembled are three-phase bridge and single-phase bridge with full-wave rectification. Assembly according to the first scheme is more common, because the rectifier built on it contains a smaller number of valves in the design – while the welding arc burns more steadily.

The welding rectifier is extremely unstable to overheating – it is necessary to constantly monitor the health of the blower fans, otherwise the welding machine will burn out. The cost of a welding rectifier – from 12,000 rubles.

Welding generator

It consists of two main elements – a direct current generator and an asynchronous motor, installed in one housing (the generator armature and the rotor of the engine are mounted on a common shaft). Technical requirements for the design of welding generators are given in GOST 304-82.

Welding generators are created according to several schemes, among which two are the most popular. The first – the excitation winding is independent, demagnetization occurs through the serial winding. The power supply of such a generator is carried out through a rectifier with selenium valves from an alternating current network – a magnetic flux is formed that induces a voltage on the generator brushes, which causes the arc to be excited. By changing (switching) the number of turns on the serial winding, the welding operator adjusts the welding current to the required characteristics.

The second most popular welding generator circuit – the excitation winding is parallel, the demagnetization winding is serial. The magnetic poles of these generators require ferromagnetic steel – they must have residual magnetism. A gasoline (diesel) engine is used as a power source.

In terms of their characteristics, welding generators are far from ideal – they are expensive (average price – from 50,000 rubles), have a complex design, their efficiency is low (0.7), high power consumption (5 kW / h per kg of molten metal). However, in the field you cannot do without them – only gasoline (diesel) welding generators will provide the ignition and stability of the arc in the absence of a power grid..

Welding inverter

This welding unit is built on transistor electrical circuits. GOST for the device and operating parameters of welding inverters in Russia has not been developed – each manufacturer develops its own technical specifications (technical conditions). The principle of its operation is as follows: alternating current from the mains enters the rectifier (being converted into direct current), then into the power module, where the direct current again becomes alternating, but with a higher frequency. The next stage is a high-frequency transformer, from where the rectified voltage is directed to the welding arc.

The design of the welding inverter is different from the device of welding transformers and rectifiers – it does not have a power transformer. Its work is based on voltage inversion (phase shift) – current amplification is performed in a cascade and controlled by a microprocessor. The resulting welding current has an almost ideal value, which has a qualitative effect on welding work. The electrical blocks of the power circuits of welding inverters are built on MOSFET (MOS – metal / oxide / semiconductor) or IGBT (bipolar transistor, gate insulated).

Advantages of the welding inverter: low weight (no more than 10 kg) and dimensions; high efficiency – 85-90%; the microprocessor monitors the slightest changes in voltage and current (sticking of the electrode during welding is completely excluded); “Fine” adjustment of the welding current in a wide range.

Disadvantages: high sensitivity to dust, to welding overloads (for example, to attempts to cut metal of impressive thickness), high cost – from 9,000 rubles.

Semi-automatic welding

Performed according to the conditions of GOST 18130-79. Consists of a power source (usually a welding inverter or rectifier), a control unit, a feed mechanism and the welding wire itself (d from 0.6 to 2.0 mm), a cylinder with an active gas (carbon dioxide – MAG-welding or argon – MIG- welding). To work on this welding machine, the electrode holder (like the electrodes themselves) is not used – the working tool here is a torch through which the wire is fed. By the way, about the wire for welding semiautomatic devices – stainless, steel, flux cored and aluminum wires are used (it is better if with depletion). Flux cored wire is also made of steel, but it can be welded with it without creating a shielding gas atmosphere.

The supply of shielding gas to the object of the weld allows for the displacement of oxygen, preventing it from oxidizing the weld, thereby greatly improving the welding characteristics.

Advantages of a semiautomatic welding machine: achieving a strong weld seam up to several meters long, easy and safe welding of thin metal (any grades of steel and aluminum alloys). The control unit allows you to save the preset welding modes, with their subsequent activation.

Disadvantages: the need for bulky gas cylinders, high consumption of an expensive inert gas (on average, MIG welding will require an argon flow of 9 l / min).

The average cost of a semiautomatic welding machine is 11,000 rubles. (220 V) and 20,000 rubles. (380 V).

DIY welding machine

The design of most homemade welding machines requires certain skills and specific materials to create them. Meanwhile, the simplest device for welding in everyday life can be arranged without knowledge of electrical engineering – you only need ordinary car batteries (used ones will also do).

So, four 12-volt batteries or two 24-volt ones are connected in series by electric cables with crocodile clips, a cable with a holder of welding electrodes is connected to the “-” of the extreme battery, the “+” of the other extreme battery is connected through a cable and a clamp to the workpiece … That’s it – simple and effective! Such a do-it-yourself welding machine has several advantages: a smooth welding seam (there are no voltage surges), independence from the mains during the welding process. Finally, upon completion of welding, the batteries can be used for their intended purpose – for a 3 mm electrode, a current of 90-120 A is required, i.e. it does not require even 60% of the standard battery load.

For permanent use of the welding machine from batteries, you will need a 54-volt charger (if there are four batteries) and a charging current of 5 A (if the battery capacity is 55 Ah. !) – its level will decrease due to evaporation.When using maintenance-free batteries, no action is required.

How to choose a welding machine

First of all, do not rely on the impressive weight of the proposed device. Modern welding machines have two to three times less weight compared to “heavy” transformers. The kilograms that make up the weight of the welding machine are especially noticeable with frequent movement from one object of work to another – if such movement is supposed, then you should choose the lightest welding device.

What network will the device be powered from? In production, most often it is 380 V, in everyday life – 220 V. It should be noted right away that if the voltage in the network is abrupt, then it is better to choose a welding inverter, because any other welding machine will simply burn out.

What metal will be welded? For non-ferrous metal or cast iron, a welding rectifier or generator is required, because it requires a constant current. For welding on thin metal of the car body, a semiautomatic device is better suited. Welding ferrous metal is acceptable with a simple welding transformer.

When choosing a specific model, pay attention to how long this device can work without the threat of overheating – in the passport, these data will be indicated under the abbreviation “PV” (duration of inclusion) or “PVR” (duration of operation). In Russia and the CIS, the standard is 5 minutes, in Europe – 10 minutes. Those. the passport value “PV” of 20% for a domestic welding machine means that you can work with it 5 x 20% = 1 minute, after which the device needs a four-minute break; for imported goods, the same 20% means 10 x 20% = 2 minutes of work and 8 minutes of “rest”. The lower the welding current, the higher the “PV” value (less the machine overheats) and vice versa. The optimal value will be “PV” 15-20% (at home), 60% (at work).

Output parameters of the welding machine – the higher the voltage and output current, the thicker the metal it can work with. On the other hand, at high parameters, the windings of the apparatus heat up faster, i.e. the built-in thermostat will shut it off faster, so there will be fewer actual duty cycles and more downtime. It will be correct to stop here on a device with output parameters that exceed the required by 30%.