How to make a welder from a change to a constant. Welding machine from "break" to "permanent"

Inverters are widely used by home and garage craftsmen. However, welding with such an apparatus requires certain skills from the operator. You need the ability to "hold the arc."

In addition, the arc resistance is a variable value, so the quality of the seam directly depends on the qualifications of the welder.

All these problems fade into the background if you work with a semi-automatic welding machine.

Design features and principle of operation of the semiautomatic device

A distinctive feature of this welder is that instead of replaceable electrodes, a wire is continuously fed into the welding zone.

It provides constant contact and has less resistance than arc welding.

Due to this, a zone of molten metal is instantly formed at the point of contact with the workpiece. The liquid mass glues the surfaces, forming a high-quality and durable seam.

With the help of a semi-automatic device, any metals are easily boiled, including non-ferrous and stainless steel. You can learn the welding technique on your own, there is no need to sign up for courses. The device is very easy to operate, even for a novice welder.

In addition to the electrical part - a high-power current source, the semi-automatic device has a continuous welding wire feed mechanism and a torch equipped with a nozzle to create a gaseous environment.

They work with ordinary copper-plated wire in a protective inert gas (usually carbon dioxide). To do this, a cylinder with a gearbox is connected to a special inlet fitting on the body of the semiautomatic device.

In addition, a semi-automatic machine can be brewed in a self-protective environment, which is created using a special coating on welding wire. In this case, inert gas is not used.

It is the ease of operation and versatility of the semiautomatic device that makes the unit so popular among amateur welders.

In many kits, the two-in-one function is implemented - and a semiautomatic device in a common case. An additional tap is made from the inverter - a terminal for connecting the holder of replaceable electrodes.

The only serious drawback is that a high-quality semi-automatic device costs significantly more. simple inverter. With similar characteristics, the cost differs by 3-4 times.

This article begins a new section "Tools and fixtures", and the article will be somewhat unusual, that is, it will not be about what and how to make, but rather what not to do.

Thanks to the amazing productivity of the inhabitants of the "Celestial Empire" and affordable cost, welding machines - "inverters" have firmly established themselves in the garages of many car owners. And for good reason: small size, light weight, wide and smooth current adjustment range, “soft” arc, low power consumption make this welding machine an invaluable assistant in many cases, but not always, a car “tin” is often too gentle for welding with an electrode . And then in the inquisitive minds of motorists, thoughts begin to be born: what if we add a burner, wire broaching and convert the “inverter” into a “semiautomatic” at low cost. I must say right away that this option will not work, nor will such an additive be added to a conventional welding machine on a transformer. Why? Read on.

Semiautomatic torch and welding wire

Not to be unfounded: I have a welding machine in the garage direct current on a transformer, also a few years ago I made a semi-automatic device on my own (also a transformer, which I successfully use), and this year I purchased an inverter welding machine (it’s hard to carry the transformer myself). I decided to test this possibility "empirically", especially since everything you need is available, and no costs are needed. I turned off the transformer in the "semiautomatic device", applied power from the "inverter", tried it ... To be honest - I tried it on different modes, regulated the current, changed the wire feed speed, cooked with gas and without ... a normal seam did not come out, it turned out to put it mildly "shit".

Now for some theory. Without this, in any way, but I will try to be as simple and concise as possible.

Types or types of welding.

MMA (ManualmetalArc). The most common type of welding is manual welding with stick electrodes coated with flux, by the way, this technology was developed by our compatriot N.G. Slavyanov.

TIG (TungstenInertGas). Welding with a non-consumable (tungsten or graphite) electrode in a shielding inert gas (argon-arc welding). Invented by N.N. Benardos.

MIG (MechanicalInertGas). Mechanized supply of electrode material (semi-automatic or automatic) in an inert gas environment (argon, helium).

MAG (MechanicalActiveGas). Mechanized supply of electrode material (semi-automatic or automatic) in an active (carbon dioxide) gas environment. which interests us the most. By the way, alloyed wire (we use copper-plated wire) was also invented by our compatriots K.V. Lyubavsky and N.M. Novozhilov.

Now let's see how the power sources differMMAAndMAG,and why they cannot be used one instead of the other.

First, consider the conditions for the existence electric arc used in welding. In the above graph, it is noticeable

that the current-voltage characteristic of the arc (CVC) has three pronounced sections:

descending section- which corresponds to a low current density,
horizontal section– with average current density
ascending section- which corresponds to a high current density.

So, at manual weldingMMA the process of arc burning occurs in the middle section of the CVC, preferably in its first third, while the arc ignites easily, keeps stable, the seams are smooth and the metal does not spatter (at the same time, fluctuations of the electrode (welder's hand) and changes in the arc length practically do not cause a change in the welding current If the current density rises and the burning point of the arc shifts to the ascending section, then the arc becomes unstable, “hard”, the metal splashes, the seams come out torn and uneven.

When welding semi-automaticMAG the arc point should be located at the beginning of the ascending section of the I–V characteristic, with a high current density, while the welding process will self-regulate.

Each type of welding must correspond to the power source of the welding machine, be it an inverter or a transformer. For clarity, another graph,

which depicts external current-voltage characteristics of power sources of welding machines.

Curve 1 corresponds to the steeply falling I-V characteristic of the power supply, which is almost ideally suited for manual DC welding MMA, curve 2 - gently dipping current-voltage characteristic, curve 3 — rigid V-characteristic, providing self-regulation when welding with thin wire MAG.

Output: DC manual welding power source is designed and manufactured with steeply falling CVC , which absolutely not suitable for welding wire electrode in semi-automatic mode . With regard to the inverter power source, alteration and reconfiguration of the control unit is required, but if you are not very strong in electronics, then it is better not to climb into a well-established mechanism.

A do-it-yourself semiautomatic device from an inverter can be made without much difficulty if you have the appropriate technical knowledge. To make a semiautomatic device with your own hands, you will need to prepare a certain list of mechanisms, devices, tools and materials that are part of the unit.

The semiautomatic device from the inverter includes an inverter and a welding torch.

Preparation for manufacturing and design features

Home craftsmen have developed various schemes for designing semiautomatic devices from an inverter.

The most common device scheme involves required list tools and materials:

welding inverter, which has the ability to deliver a working current of about 150 A;
a feed mechanism that feeds the electrode wire into the welding zone;
burner;
flexible hose;
working bobbin with electrode wire, which has changes in the device;
device control unit.

The inverter should be about 150 A.

Particular attention should be paid to the feed mechanism. Using this structural element, the electrode wire is fed to the burner through a flexible hose. The ideal wire feed speed corresponds to the rate of wire melting. The indicator of the wire feed speed, which is provided by the feeder, has a significant impact on the process of work and the quality of the welding seam using a semi-automatic welding machine.

When designing a semiautomatic device, it is necessary to provide for the possibility of changing the speed of feeding the electrode wire into the welding zone. The ability to change the electrode material feed rate allows you to work with consumables of various diameters and from different materials. Most often at work welding semi-automatic wire sizes 0.8 mm, 1 mm, 1.2 mm and 1.6 mm are used. The wire is wound on special coils installed in the welding device.

If the wire feed is carried out fully automatically, this significantly reduces the time required for welding workpieces.

The semi-automatic control unit is equipped with a channel for adjusting and stabilizing the working current. Operating current parameters are controlled by the microcontroller in pulse-width mode. The voltage on the capacitor largely depends on the pulse-width parameter of the current. The voltage on the latter directly affects the strength of the working welding current.

Choosing a transformer for the inverter and assembling the unit

Before self-designing a semiautomatic device, you need to decide on the type and power welding transformer, which is planned to be installed in a semiautomatic device. It should be remembered that when using wire for the welding process minimum size 0.8 mm working welding current should be 160 A. The power of the welding transformer to obtain such a current should be 3 kW. When choosing a transformer, you should pay attention to the fact that the toroidal core transformer has a lower weight compared to other types of devices.

When manufacturing a transformer, several subtleties must be taken into account. The transformer must be wrapped with a copper strip with dimensions (40 mm - width and 30 mm - thickness). Before using the copper strip, it is first wrapped with thermal paper. Use for winding ordinary copper wire not possible, because it is very hot.

The secondary winding of the transformer is made of three layers of tin. The layers of tin are isolated from each other with the help of a fluoroplastic tape. At the exit, the ends are soldered together to increase conductivity. In the case where the transformer is installed, a fan is mounted for blowing in order to increase the cooling of the system components during the operation of the device.

Adjustment of the current in the device can be carried out in two ways: on the primary and secondary windings. The implementation of the adjustment in the first way requires the use of a thyristor adjustment circuit. This method of regulation has certain disadvantages, which are eliminated by including a relay and some switching elements in the circuit.

When applying current regulation in the secondary winding, a high ripple occurs, to reduce which a thyristor circuit is used. The use of switching circuits leads to an increase in the weight of the structure and the cost of the installation. For this reason, the use of primary current regulation is considered more acceptable.

To smooth out ripples, a smoothing inductor and a capacitor with a capacity of about 50,000 uF are built into the secondary winding circuit. This configuration of the device allows you to smooth out voltage ripples when choosing any current control scheme.

As a gearbox for wire feed, you can use a gearbox from a VAZ windshield wiper.

Setting up a semi-automatic inverter

When assembling a semi-automatic inverter with your own hands, it is required for power switches, input and output rectifiers to ensure good cooling by using radiators. A thermal sensor is also required in the housing. After the installation of the power part of the device, it is connected to the control unit of the device.

The finished device can be connected to the network. After the indicator lights up, an oscilloscope is connected to the device and the correct operation is checked. Bipolar pulses should have a frequency of 40-50 Hz, and the time between them is corrected by changing the input voltage. The normal time interval between pulses should be 1.5 µs.

The pulses that the oscilloscope registers must have rectangular fronts with a duration of no more than 500 ns.

After checking the inverter, it is connected to a household electrical network. When connecting the device, the indicator should show 120 A. If this indicator is not reached, it is necessary to check the correct assembly of the device.

After testing the device at idle, the device is tested under load. For this purpose, it is required to include a load in the form of a 0.5 Ohm rheostat in the welding wire circuit, which is capable of withstanding a current of more than 60 A. With this load, the current is controlled using a voltmeter.

After assembling the unit, its performance is checked. To do this, click on the start button. Immediately after this, carbon dioxide begins to flow, after a few seconds the current is turned on, the supply of the electrode wire begins. When the device is turned off, the supply of the working current and the electrode wire is first stopped, and only after a few seconds the electrovalve is closed, which ensures the supply of carbon dioxide to the welding area. As a valve to ensure the supply of carbon dioxide, you can use the valve for supplying water to the rear window of a VAZ car.

Rules for using the welding inverter and the use of the unit

After starting the inverter, the current required for operation is set using the controller. When correct setting at the output of the device electric current is 120 A. Using the control unit, if necessary, the current strength can be changed in the range from 20 to 160 A. When using the unit, the temperature of its heating should be controlled. The heating temperature should not exceed 75º C. To control it, a temperature sensor should be installed in the device. If the temperature rises above the set maximum, the device should be switched off and allowed to cool down. To improve cooling, the unit provides for the installation of several fans.

Semi-automatic welding, made on the basis of an inverter, is used to carry out the procedure for precise welding of products from various types become. In addition, the device is used for welding thin metal blanks. The use of a semi-automatic device is common during automotive repair work body.

After the manufacture of semi-automatic welding from an inverter for the home, this unit becomes an indispensable device used in household for execution a large number various welding jobs.

A semi-automatic welding machine is a fairly popular device among professional and home craftsmen, especially those involved in body repair. This unit can be purchased ready-made. But many owners of inverter welding machines are wondering: is it possible to convert the inverter into a semiautomatic device so as not to buy another welder? Making a semiautomatic device from an inverter with your own hands is a rather difficult task, but with strong desire quite feasible.

To assemble the unit, you will need the following items:

inverter welding machine;
burner, as well as a special flexible hose, inside which a gas pipeline passes, a wire guide, power cable and electrical control cable;
mechanism for uniform automatic wire feed;
control module, as well as a motor speed controller (PWM controller);
protective gas cylinder (carbon dioxide);
solenoid valve for cutting off gas;
coil with electrode wire.

To assemble a homemade semi-automatic from welding inverter, the latter must produce a welding current of at least 150 A. But it will have to be slightly upgraded, since the current-voltage characteristics (CV) of the inverter are not suitable for welding with electrode wire in a shielding gas environment.

But more on that later. First you need to make the mechanical part of the semiautomatic device, namely the wire feed mechanism.

Wire feed mechanism

Since the feeder will be placed in a separate box, it is ideal for this purpose. computer system case. In addition, you do not need to throw away the power supply. It can be adapted to the operation of the broach mechanism.

First, you need to measure the diameter of the wire spool or, having outlined it on paper, cut out a circle and insert it into the body. There must be enough space around the reel to accommodate other components (power supply, hoses and wire feeder).

The wire pulling device is made from a windshield wiper mechanism from a car. Under it, it is necessary to design a frame that will also hold the pressure rollers. The layout must be drawn on thick paper in real scale.

Advice! The connector for connecting the burner hose and the hose with the burner itself can be made by hand. But it would be better to buy ready kit which has an affordable price.

The feeder should be installed in the housing so that the connector is in a convenient location.

In order for the wire to be fed evenly, all components must be fixed exactly opposite each other. The rollers must be centered in relation to the hole for the inlet fitting, which is located in the connector for connecting the hose.

as roller guides use suitable diameter bearings. on them with lathe a small groove is machined along which the electrode wire will move. For the body of the mechanism, you can use plywood 6 mm thick, textolite or durable sheet plastic. All elements are fixed on the basis, as shown in the following photo.

Used as primary wire guide axially drilled bolt. The result is something like a wire extruder. At the inlet of the fitting, a cambric reinforced with a spring is put on (for rigidity).

The rods on which the rollers are fixed are also spring-loaded. The clamping force is set using a bolt located below, to which the spring is attached.

Advice! If for some reason you do not have the opportunity to make a wire pulling mechanism with your own hands, then you can buy it in China. There are 12 V and 24 V mechanisms on sale. In this case, since a PSU is used from a computer, a device powered by 12 V is required.

The basis for fixing the bobbin can be made from a small piece of plywood or textolite and trimmed plastic pipe suitable diameter.

Mechanics control scheme

To achieve good quality seam when welding, it is necessary to ensure that the wire is fed at a certain and constant speed. Since the motor from the wiper is responsible for the feed rate of the equipment, a device is needed that can change the speed of rotation of its armature. Suitable for this turnkey solution, which is also available in China and is called

Below is a diagram from which it becomes clear how the speed controller is connected to the engine. The regulator of the controller with a digital display is displayed on the front panel of the case.

Next, you need to install relay controlling the gas valve. It will also control the start of the engine. All of these elements must be activated by pressing the start button located on the burner handle. In this case, the gas supply to the place of welding should be ahead (by about 2-3 seconds) of the start of the wire feed. Otherwise, the arc will ignite in the environment atmospheric air, and not in a shielding gas environment, as a result of which the electrode wire will melt.

A delay relay for a homemade semiautomatic device can be assembled based on the 815th transistor and capacitor. To get a pause of 2 seconds, a 200-2500 uF capacitor will be enough.

Advice! Since the power comes from a computer PSU that outputs 12 V, instead of self-manufacturing module, you can use an automotive relay.

It is placed in any place where it will not interfere with the operation of moving parts, and is connected to the circuit according to the diagram. You can use an air valve from GAZ 24 or buy a special one designed for semiautomatic devices. The valve is responsible for automatic feed shielding gas to the burner. It turns on after pressing the start button located on the semi-automatic burner. The presence of this element significantly saves gas consumption.

But as already noted, the current-voltage characteristics (CVC) of the inverter are not suitable for the full operation of the semiautomatic device. Therefore, in order for the semi-automatic prefix to work in tandem with an inverter, small changes are required to be made to its electrical circuit.

Changing the I-V characteristic of the inverter

There are many schemes to change the I-V characteristic of an inverter, but the easiest way to do this is as follows:

assemble the device using throttle from fluorescent lamp according to the scheme below;

to connect the assembled device, you will need to assemble another block according to the following scheme;

In order to prevent the inverter from triggering the overheating sensor, an optocoupler must be soldered (in parallel) to it, as shown in the following diagram.

But if the welding current is controlled in the inverter with a shunt, then you can collect a simple circuit of three resistors and a mode switch as shown below.

As a result, the conversion of a welding inverter into a semiautomatic device will cost 3 times cheaper than an already finished unit. But of course, for self assembly the device will need to have certain knowledge in the radio business.

The advantages of DC welding machines over their "alternating current counterparts" are well known. This includes soft arc ignition, the ability to connect thin-walled parts, less metal spatter, and the absence of non-welding areas. There is not even an annoying (and, as it turned out, harmful to people) cod. And all because there is no main inherent in welding machines alternating current feature - intermittent arcing when the sinusoid of the supply voltage flows through zero

Rice. 1. Graphs explaining the process of welding on alternating (a) and direct (b) current.

Turning from graphs to real designs, it should also be noted: in AC machines, powerful transformers are used to improve and facilitate welding (the magnetic circuit is made from a special electrical iron with a steeply falling characteristic) and a deliberately overestimated voltage in the secondary winding, reaching up to 80 V, although 25-36 V is enough to support the burning of the arc and the deposition of metal in the welding zone. By reducing the voltage transformed into the secondary circuit to 36 V, it is possible to lighten the weight of the “welder” by 5-6 times, bring its dimensions to the size of a portable TV while improving other performance characteristics.

But how to ignite an arc with a low-voltage winding?

The solution was to introduce a diode bridge with a capacitor into the secondary circuit. As a result, the output voltage of the modernized "welder" was increased by almost 1.5 times. The opinion of experts is confirmed in practice: when the 40-volt DC barrier is exceeded, the arc easily ignites and burns steadily, allowing even thin body metal to be welded.

Rice. 2. Fundamental circuit diagram DC welding machine.

The latter, however, is easily explained. With the introduction of a large capacity into the circuit, the characteristic of the welding machine also turns out to be steeply falling (Fig. 3). The initial increased voltage created by the capacitor facilitates the ignition of the arc. And when the potential on the welding electrode drops to U2 of the transformer (working point "A"), a process of stable arc burning with metal deposition in the welding zone will occur.

Fig.3. Volt-ampere characteristic of the welding machine at direct current.

The "welder" recommended by the author can be assembled even at home, based on an industrial power transformer 220-36 / 42 V (these are usually used in systems for safe lighting and powering low-voltage factory equipment). After making sure that the primary winding, containing, as a rule, 250 turns of insulated wire with a cross section of 1.5 mm2, is intact, the secondary ones are checked. If their condition is not important, everything (with the exception of a working network winding) is deleted without regret. And in the vacated space, a new secondary winding is wound (until the “window” is filled). For the recommended 1.5 kVA transformer, this is 46 turns of a 20 mm2 copper or aluminum bus with good insulation. Moreover, a cable (or several insulated single-core wires twisted into a bundle) with a total cross section of 20 mm2 is quite suitable as a bus.

The choice of the cross section of the electrodes depending on the power of the transformer.

The rectifier bridge can be assembled from semiconductor diodes with a working current of 120-160 A, installing them on heat sinks-radiators 100x100 mm. It is most convenient to place such a bridge in the same housing with a transformer and a capacitor, bringing to the front textolite panel a 16-ampere switch, an “On” signal light eye, as well as “plus” and “minus” terminals (Fig. 4). And to connect to the electrode holder and the "ground" use a segment single core cable of the corresponding length with a section for copper 20-25 mm2. As for the welding electrodes themselves, their diameter depends on the power of the transformer used.

Rice. 4. Homemade welding machine for DC welding.

And further. When testing, it is recommended, by disconnecting the device (10 minutes after welding) from the network, to check the thermal conditions of the transformer, diode bridge and capacitor. Only after making sure that everything is in order, you can continue to work. After all, an overheated "welder" is a source of increased danger!

Of the other requirements, it is worth noting, I think, that the welding machine must be equipped with a spark-protective mask, gloves and a rubber mat. The place where they are performed welding work, equipped according to the requirements fire safety. In addition, it is necessary to ensure that there are no rags or other combustible materials nearby, and the connection of the “welder” to the network must be carried out in compliance with electrical safety rules through a powerful plug connector of the electrical panel at the entrance to the building.

V.Konovalov, Irkutsk
Mk 04 1998