We assemble a DC welding machine with our own hands. Converting the inverter into a semiautomatic welding machine Welding machine as variable to constant

Inverters are widely used by home and garage craftsmen. However, welding with such a machine requires certain skills from the operator. The ability to "keep the arc" is required.

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 the principle of operation of the semiautomatic device

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

It provides permanent 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 semiautomatic device, any metals, including non-ferrous and stainless steel, are easily boiled. You can master 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 semiautomatic device has a continuous welding wire feed mechanism and a torch equipped with a nozzle for creating a gas atmosphere.

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

In addition, the semiautomatic device can be welded in a self-shielding environment, which is created using a special spraying on the welding wire. In this case, no inert gas is used.

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

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

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

Any welder knows about the advantages of a semiautomatic device over manual electric welding. Due to its high prevalence and low cost, MMA inverters are in the arsenal of many craftsmen. But with MIG welding, it's a different matter - these devices are more expensive. But, there is a way out - you can make a semiautomatic device from an inverter with your own hands. If you delve into this issue, the matter will not be so difficult.

There are fundamental differences between MMA and MIG welding. To operate a semiautomatic device, you need carbon dioxide (or a mixture of carbon dioxide with argon) and an electrode wire, which is fed to the welding place through a special hose. Those. the very principle of semiautomatic welding is more complicated, but it is universal and its use is justified. What is needed for the semiautomatic device to work:

wire feeder;
burner;
hose for supplying wire and gas to the heating pad;
constant voltage current source.
And to turn welding inverter in a semiautomatic device, you will need a tool, time and desire.

Preparation

Making a semiautomatic welding machine at home begins with work planning. There are two options for making MIG welding from an inverter:

Completely make a semiautomatic welding machine with your own hands.
To remake only the inverter - the feeder is purchased ready-made.

In the first case, the cost of parts for the feeder will be about 1000 rubles, excluding work, of course. If the factory semiautomatic device includes everything in one case, then the homemade one will consist of two parts:

Welding inverter.
Drawer with wire feeder and wire spool.

First, you need to decide on the case for the second part of the semiautomatic device. It is desirable that it be light and roomy. The feed mechanism must be kept clean, otherwise the wire will be fed in jerks, in addition, the spools must be changed periodically and the mechanism must be adjusted. Therefore, the drawer must be easy to close and open.

The ideal option is to use the old system unit:

neat appearance - it does not really matter, but it is much more pleasant when the insides of the homemade product do not stick out and the semiautomatic device from the MMA inverter looks good;
lightweight, closes;
the body is thin - it is easy to make the necessary cutouts;
the gas valve and wire feed drive are powered by 12 volts. Therefore, a power supply from a computer will do, and it is already built into the case.

Now you need to estimate the size and location of future parts in the case. You can cut out approximate layouts from cardboard and check their relative position. After that, you can start working.

The best option for electrode wire is a 5 kg spool. Her external diameter 200 mm, inner - 50 mm. For the axis of rotation, you can use sewer PVC pipe. Its outer diameter is 50 mm.

Burner

A homemade semiautomatic device must be equipped with a burner. You can do it yourself, but it's better to buy ready-made kit, which includes:

Burner with a set of tips of different diameters.
Delivery hose.
Euro plug.

A normal burner can be purchased for 2-3 thousand rubles. Moreover, the device is homemade, so you don't have to chase expensive brands.

What to look for when choosing a kit:

what welding current the torch is designed for;
hose length and stiffness - the main task hose, ensure free wire feed to the torch. If it is soft, any bend will slow down the movement;
springs near the connector and burner - they prevent the hose from breaking.

Feeder

The electrode wire must be fed continuously and evenly - then the welding will turn out to be of good quality. The feed rate must be adjustable. There are three options for how to make a device:

Buy a fully assembled mechanism. Expensive, but fast.
Buy feed reels only.
Do it yourself.

If the third option is chosen, you will need:

two bearings, guide roller, tension spring;
wire feed motor - a wiper motor will do;
metal plate for fastening the mechanism.

One pressure bearing - it must be adjustable, the second serves as a support for the roller. Manufacturing principle:

holes are made on the plate for the motor shaft and for fastening the bearings;
the motor is attached to the back of the plate;
a guide roller is put on the shaft;
bearings are fixed at the top and bottom;

The bearings are best placed on metal strips - one end is bolted to the base plate, and a spring with an adjusting bolt is attached to the other.

The made mechanism is placed in the housing so that the rollers are in line with the connector for the torch, i.e. so that the wire does not break. A rigid wire alignment tube must be installed in front of the rollers.

Implementation of the electrical part

For this you will need:

two car relays;
diode;
PWM regulator for the engine;
capacitor with transistor;
solenoid valve idle move- to supply gas to the burner. Any VAZ model will do, for example, from an eight;
wires.

The control circuit for wire and gas feed is quite simple and is implemented as follows:

when the button on the burner is pressed, relay no. 1 and relay no. 2 are activated;
relay # 1 turns on the gas supply valve;
relay # 2 works in tandem with a capacitor and turns on the wire feed with a delay;
wire pulling is done with an additional button bypassing the gas supply relay;
to remove self-induction from solenoid valve, a diode is connected to it.
It is necessary to provide for the connection of the burner to power cable from the inverter. To do this, next to the euro connector, you can install a quick connector and connect it to the burner.

The semiautomatic device has the following sequence of work:

The gas supply is switched on.
With a short delay, the wire feed starts up.

Such a sequence is necessary so that the wire immediately enters the protective environment. If you make a semiautomatic device without delay, the wire will stick. To implement it, you need a capacitor and a transistor through which the motor control relay is connected. Operating principle:

voltage is applied to the capacitor;
it is charging;
current is supplied to the transistor;
the relay turns on.

The capacitance of the capacitor must be selected so that the delay is about 0.5 seconds - this is enough to fill the weld pool.

After assembly, the mechanism needs to be tested, and the manufacturing process can be seen in the video.

Alteration of the inverter

To make a semiautomatic device from a conventional inverter with your own hands, you will have to slightly alter its electrical part. If you connect the MMA inverter to the assembled case, you will be able to cook. But at the same time, the quality of welding will be far from the factory semiautomatic device. It's all about the CVC - current-voltage characteristics. The electric arc inverter produces a falling characteristic - the output voltage is floating. And for the correct operation of the semiautomatic device, a rigid characteristic is required - the device maintains a constant voltage at the output.

Therefore, in order to use your inverter as a current source, you need to change its I – V characteristic (current-voltage characteristic). For this you will need:

toggle switch, wires;
variable resistor and two constants;

It is quite easy to get a hard response on an inverter. To do this, you need to place a voltage divider in front of the shunt that controls the welding current. Fixed resistors are used for the divider. Now you can get the required millivolts, which will be proportional to the output voltage, and not the current. There is only one minus in this scheme - the arc is too hard. To mitigate this, you can use a variable resistor that connects to the divider and the output of the shunt.

The advantage of this approach is that there is an adjustment of the arc stiffness - such a setting is available only in professional semiautomatic devices. And the toggle switch switches the inverter between MMA and MIG modes.

Thus, converting an MMA inverter into a semiautomatic device, although not an easy task, is quite realizable. As a result, we get a device that is not inferior to the factory ones in terms of its characteristics. But at the same time it is much cheaper. The cost of such an alteration is 4-5 thousand rubles.

This article begins a new heading "Tools and devices", and the article will be somewhat unusual, that is, it will not be about what and how to make, but on the contrary, what is not worth doing.

Thanks to the stunning labor productivity of the inhabitants of the "Celestial Empire" and the affordable cost, welding machines - "inverters" are firmly established 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, an automobile "tin" is often too delicate for electrode welding ... And then in the inquisitive minds of motorists, thoughts begin to arise: what if you add a burner, a wire drawer and, at low cost, convert the "inverter" into a "semiautomatic device". I must say right away that this option will not work, and such an additive will also not work for a conventional welding machine on a transformer. Why? Read on.

Semi-automatic torch and welding wire

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

Now a little theory. There is nothing without it, but I will try to be as simple and short as possible.

Types or types of welding.

MMA (ManualMetalArc). The most common type of welding is manual MMA welding, by the way, this technology developed by our compatriot N.G. Slavyanov.

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

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

MAG (MechanicalAktiveGas). 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 figure out what is the difference between power supplies.MMAandMAG,and why they cannot be used one instead of the other.

To begin with, consider the conditions for the existence of an 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:

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

So, with manual weldingMMA the arc burning process occurs in the middle section of the I - V characteristic, it is better in its first third, while the arc ignites easily, keeps stable, the seams are smooth and the metal is not splashed (at the same time, oscillations 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 increases and the arc burning point shifts to the ascending section, then the arc becomes unstable, "hard", the metal splashes, the seams come out torn and uneven.

When welding semiautomaticMAG the point of the arc should be located at the beginning of the ascending section of the I - V characteristic, with high density current, while self-regulation of the welding process will occur.

Each type of welding must have a corresponding power source for the welding machine, be it an inverter or a transformer. For clarity, one more graph,

which depicts external volt-ampere characteristics of power sources of welding machines.

Curve 1 corresponds to the steeply dipping current-voltage characteristic of the power supply, which is almost ideal for manual welding on direct current MMA, curve 2 - gently dipping volt-ampere characteristic, curve 3 — rigid current-voltage characteristic, providing self-regulation when welding with a thin wire MAG.

Output: The DC manual power source is designed and manufactured with steeply dipping current-voltage characteristic which absolutely not suitable for welding work 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 semiautomatic welding machine is a functional device that can be purchased ready-made or made from. It should be noted that the manufacture of a semi-automatic device from an inverter device is not an easy task, but it can be solved if desired. Those who set such a goal should study well the principle of operation of a semiautomatic device, see thematic photos and video, prepare everything necessary equipment and accessories.

What is required to convert an inverter into a semiautomatic device

To remake the inverter, making a functional semiautomatic welding machine out of it, you must find the following equipment and additional components:

inverter machine capable of generating a welding current of 150 A;
a mechanism that will be responsible for feeding the welding wire;
the main working element is the burner;
a hose through which the welding wire will be fed;
a hose for supplying shielding gas to the welding area;
a spool of welding wire (such a spool will need to undergo some alterations);
an electronic unit that controls the operation of your homemade semiautomatic device.

Special attention should be devoted to the alteration of the feeder, due to which the welding wire is fed into the welding zone, moving along flexible hose... In order for the weld to be of high quality, reliable and accurate, the wire feed speed through the flexible hose must match the wire melt speed.

Since when welding using a semiautomatic device, wire from different materials and of various diameters, its feed rate must be regulated. It is this function - the regulation of the welding wire feed speed - that the feeder of the semiautomatic device should perform.

Internal layout Wire spool Wire feeder (view 1)
Wire feeder (view 2) Fastening the welding arm to the feeder Construction of a homemade torch

The most common wire diameters used in semiautomatic welding are 0.8; 1; 1.2 and 1.6 mm. Before welding, the wire is wound on special coils, which are attachments of semi-automatic devices, fixed to them with the help of simple structural elements. In the process of welding, the wire is fed automatically, which significantly reduces the time spent on such a technological operation, simplifies it and makes it more efficient.

The main element of the electronic circuit of the semiautomatic device control unit is a microcontroller, which is responsible for regulating and stabilizing the welding current. It is from this element of the electronic circuit of the semiautomatic welding machine that the parameters of the operating current and the possibility of their regulation depend.

How to remake an inverter transformer

In order for the inverter to be used for a self-made semiautomatic device, its transformer must be subjected to some alterations. It is not difficult to do such a rework with your own hands, you just need to adhere to certain rules.

In order to bring the characteristics of the inverter transformer in accordance with those required for a semiautomatic device, it should be wrapped with a copper strip, on which a winding made of thermal paper is applied. It must be borne in mind that for these purposes you cannot use an ordinary thick wire, which will be very hot.

The secondary winding of the inverter transformer also needs to be redone. To do this, you need to do the following: wind a winding consisting of three layers of tin, each of which must be insulated with fluoroplastic tape; the ends of an existing winding and made by hand to solder together, which will increase the conductivity of currents.

The design used for its inclusion in the semiautomatic welding machine must necessarily provide for the presence of a fan, which is necessary for effective cooling of the device.

Setting up the inverter used for semi-automatic welding

If you decide to make a semiautomatic welding machine with your own hands using an inverter for this, you must first de-energize this equipment. To prevent such a device from overheating, its rectifiers (input and output) and power switches should be placed on the radiators.

In addition, in that part of the inverter housing where the heatsink is located, which heats up more strongly, it is best to mount a thermal sensor, which will be responsible for turning off the device if it overheats.

After all the above procedures have been completed, you can connect the power section of the device to its control unit and connect it to electrical network... When the mains indicator is on, an oscilloscope should be connected to the outputs of the inverter. With the help of this device it is necessary to find electrical impulses with a frequency of 40-50 kHz. The time between the formation of such pulses should be 1.5 μs, which is regulated by changing the voltage applied to the input of the device.

It is also necessary to check that the pulses reflected on the oscilloscope screen have rectangular shape, and their front was no more than 500 ns. If all the checked parameters correspond to the required values, then the inverter can be connected to the mains. The current coming from the output of the semiautomatic device must have a strength of at least 120 A. If the current strength is less, this may mean that a voltage is supplied to the equipment wires, the value of which does not exceed 100 V. In such a situation, do the following: test the equipment by changing the current strength (in this case, it is necessary to constantly monitor the voltage on the capacitor). In addition, the temperature inside the device should be constantly monitored.

After the semiautomatic device has been tested, it is necessary to test it under load. To make such a check, a rheostat is connected to the welding wires, the resistance of which is at least 0.5 Ohm. Such a rheostat must withstand a current of 60 A. The strength of the current that is supplied to the welding torch in such a situation is controlled using an ammeter. If the current strength when using a load rheostat does not correspond to the required parameters, then the resistance value this device are selected empirically.

How to use a welding inverter

After starting the semiautomatic device, which you assembled with your own hands, the indicator of the inverter should display a current value equal to 120 A. If everything is done correctly, then this will happen. However, the inverter display may show eights. This is most often caused by insufficient voltage in the welding leads. It is better to immediately find the cause of such a malfunction and quickly eliminate it.

If everything is done correctly, the indicator will correctly show the strength of the welding current, which is regulated using special buttons. The range of adjustment of the operating current, which is provided, is in the range of 20-160 A.

How to control the correct operation of the equipment

So that the semiautomatic welding machine, which you assembled with your own hands, will serve you long time, it is better to constantly monitor temperature regime inverter operation. To carry out such control, it is necessary to press two buttons simultaneously, after which the temperature of the hottest radiator of the inverter will be displayed on the indicator. The normal operating temperature is one that does not exceed 75 degrees Celsius.

If this value is exceeded, then, in addition to the information displayed on the indicator, the inverter will start emitting an intermittent sound signal, which should be immediately noted. In this case (as well as in the event of a breakdown or short circuit of the temperature sensor) electronic circuit the device will automatically reduce the operating current to 20A, and the buzzer will beep until the equipment returns to normal. In addition, an error code (Err) displayed on the display of the inverter may indicate a malfunction of the equipment made by hand.

Most welding machines, especially homemade ones, are very far from perfect. We offer a scheme for fine-tuning a homemade welding machine from "break" to "constant" with your own hands and you can use any type of electrodes ( see fig. 1).

Rice. 1 Diagram of a welding machine with a high-efficiency inductive-capacitive filter that smooths out the ripple of the rectified voltage.

Let's "walk" through the scheme.

Choke L.

The core for it is taken from the choke of 1N400N37-110 city lighting lamps. When removing the old windings, it is necessary to preserve the cardboard spacers, which provided a gap between the main and closing parts of the core (Fig. 2).

When reassembled, they are reinstalled. The new winding is wound on only one side rod - three layers of copper bus with a cross section of 4x6 mm, located evenly along the entire length of the core. The beginning of the choke winding is connected to the capacitor bank C1 ... C6, and the end of the winding is connected to the "+" terminal (fig. 1).

Rectifier and filter capacitor bank.

Diodes U01 ... U04 type D161-320 or similar, designed for an average rectified current - above 250 A and reverse voltage - not less than 200 V, are mounted on standard cast radiator-coolers, which must be isolated from each other and from the welding body apparatus with textolite plates. Capacitors 31 ... 56 - electrolytic, type K50-3 or K50-7 two-section 250/290 (150 + 150 microfarads). The total capacity of the capacitor bank is 1800 microfarads. It is most convenient to install them in one row on a textolite plate 4 ... 6 mm thick.

Regulator of welding current P ("ballast rheostat").

Made from one section of limiting resistance overhead crane DEK-256 (fig. 3).

This resistance represents ceramic pipe with a curly spiral groove on outer surface, in which is laid a bus made of material with high resistivity, with a cross section of about 20 mm2.