Time relay circuit for resistance welding. Home tool: do-it-yourself resistance spot welding

Spot welding machines are not used as often in everyday life as arc welding machines, but sometimes it is impossible to do without them. Considering that the cost of such equipment starts from $450-$470, the profitability of its purchase is questionable.

The way out of this situation is resistance spot welding with your own hands. But, before we tell you how to make such a device yourself, let's look at what spot welding is and the technology of its operation.

Briefly about spot welding

This type of welding is contact (thermomechanical). Note that this category also includes seam and butt welding, but it is not possible to implement them at home, since complex equipment will be needed for this purpose.

The welding process includes the following steps:

• the parts are combined in the required position;
• they are secured between the electrodes of the device, which press the parts;
• heating is performed, as a result of which, due to plastic deformation, the parts are firmly connected to each other.

A production spot welding machine (such as the one shown in the photo) is capable of performing up to 600 operations within a minute.

Process technology

To heat the parts to the required temperature, a short-term pulse of high-power electric current is applied to them. As a rule, the pulse lasts from 0.01 to 0.1 seconds (the time is selected based on the characteristics of the metal from which the parts are made).

When pulsed, the metal melts and a common liquid core forms between the parts; until it hardens, the welded surfaces must be held under pressure. Due to this, as it cools, the molten core crystallizes. A drawing illustrating the welding process is shown below.

Designations:

• A – electrodes;
• B – parts to be welded;
• C – welding core.

Pressure on the parts is necessary so that, when pulsed, a sealing belt is formed along the perimeter of the molten metal core, preventing the melt from flowing outside the zone where welding occurs.

To provide better conditions for crystallization of the melt, the pressure on the parts is gradually removed. If it is necessary to “forge” the welding site in order to eliminate inhomogeneities inside the seam, increase the pressure (do this at the final stage).

Please note that to ensure a reliable connection, as well as the quality of the seam, it is first necessary to treat the surfaces of the parts in the places where welding will take place. This is done to remove oxide film or corrosion.

When it is necessary to ensure reliable connection of parts with a thickness of 1 to 1.5 mm, capacitor welding is used. The principle of its operation is as follows:

• the capacitor block is charged with a small electric current;
• the capacitors are discharged through the parts being connected (the pulse strength is sufficient to ensure the required welding mode).

This type of welding is used in those areas of industry where it is necessary to connect miniature and subminiature components (radio engineering, electronics, etc.).

Speaking about spot welding technology, it should be noted that it can be used to connect dissimilar metals together.

Examples of homemade designs

There are many examples on the Internet of creating machines that produce spot welding. Here are some of the most successful designs. Below is a diagram of a simple spot welder.

For implementation we will need the following radio components:

• R – variable resistance with a nominal value of 100 Ohms;
• C – capacitor designed for a voltage of at least 25 V with a capacity of 1000 μF;
• VD1 – thyristor KU202, the letter index can be K, L, M or N, you can also use PTL-50, but in this case the capacitance “C” must be reduced to 1000 μF;
• VD2-VD5 – diodes D232A, foreign analog – S4M;
• VD6-VD9 – D226B diodes, they can be replaced with a foreign analogue 1N4007;
• F – 5 A fuse.

It is necessary to make a digression to tell how to make the TR1 transformer. It is made on the basis of Sh40 iron, with a set thickness of 70 mm. For the primary winding you will need PEV2 wire Ø0.8 mm. The number of turns in the winding is 300.

To make a secondary winding, you will need a Ø4 mm stranded copper wire. It can be replaced with a tire, provided that its cross-section is at least 20 mm 2. The number of turns of the secondary winding is 10.

Video: do-it-yourself resistance welding

As for TR2, any of the low-power transformers (from 5 to 10 W) will be suitable for it. In this case, winding II, used to connect the backlight lamp “H”, should have an output voltage within 5-6 V, and winding III – 15 V.

The power of the manufactured device will be relatively low, ranging from 300 to 500 A, maximum pulse time up to 0.1 sec (provided that the ratings “R” and “C” are the same as in the diagram shown). This is quite enough for welding steel wire Ø0.3 mm or sheet metal if its thickness does not exceed 0.2 mm.

Let us present a diagram of a more powerful device, in which the welding electric current of the pulse will be in the range from 1.5 kA to 2 kA.

We list the components used in the circuit:

• resistance ratings: R1-1.0 kOhm, R2-4.7 kOhm, R3-1.1 kOhm;
• capacitances in the circuit: C1-1.0 µF, C2-0.25 µF. Moreover, C1 must be designed for a voltage of at least 630 V;
• VD1-VD4 diodes - D226B diodes, replacement with a foreign analogue 1N4007 is allowed, instead of diodes you can install a diode bridge, for example, KTs405A;
• thyristor VD6 - KU202N, it must be placed on a radiator with an area of ​​at least 8 cm2;
• VD6 – D237B;
• F – 10 A fuse;
• K1 is any magnetic starter that has three pairs of working contacts, and the winding is designed for ~220 V, for example, you can install PME071 MVUHLZ AC3.

Now we’ll tell you how to make transformer TR1. The LATR-9 autotransformer, such as shown in the photograph, is used as a basis.

The winding in this autotransformer has 266 turns, it is made with copper wire Ø1.0 mm, we will use it as the primary. We carefully disassemble the structure so as not to damage the winding. We dismantle the shaft and the movable roller contact attached to it.

Next, we need to isolate the contact track; for this purpose, we clean it from dust, degrease it and varnish it. When it dries further, we insulate the entire winding using varnished cloth.

As a secondary winding we use copper wire with a cross-sectional area of ​​at least 80 mm 2. It is important that the insulation of this wire is heat resistant. When all conditions are met, we make a winding of three turns.

Setting up the assembled device comes down to calibrating the scale of the variable resistor that regulates the pulse time.

We recommend that before starting welding, you experimentally establish the optimal time for the pulse. If the duration is excessive, the parts will be burned, and if it is less than necessary, the strength of the connection will be unreliable.

As already written above, the device is capable of delivering a welding electric current of up to 2000 A, which allows you to weld steel wire Ø3 mm or sheet steel, the thickness of which does not exceed 1.1 mm.

- a very useful skill.

If any inverter model is available for free sale, a person planning to weld at home has a choice - purchase a ready-made device or make it himself.

In this article, we will look at what it is, demonstrate an instructional video on resistance welding, give step-by-step instructions on how to carry out resistance welding yourself, and how you can make a homemade resistance welding machine with your own hands from a microwave and used car batteries.

Owners of private houses, motorists and others need welding work.

At home or in a small workshop, using a welding inverter to connect metal parts is quite possible.

The principle of its operation is that, with the help of an electric current, the metal is heated, melted and solidified, forming a weld.

To fix and prevent shifting, the parts to be welded are compressed using electrodes through which an electric current is supplied.

To work at home, powerful power sources will be required, which affects the overheating of household wiring.

Before carrying out work, you should check the quality of the wiring and, if possible, replace it with a new one.

In resistance spot welding, two workpieces are joined along the surface of adjacent edges.

This technology is suitable for thin sheets, small parts and metal rods up to 5 mm thick.

Three types of surface connections are used: using resistance, intermittent reflow or continuous reflow.

For resistance welding, prepared workpieces or sheets are fixed and heated with welding current until melting.

The method is applicable for the following metals:

• low carbon steel;
• non-ferrous metal;
• connections of copper with brass and steel.

Due to strict temperature requirements and the absence of impurities at the joints, this method is rarely used.

When continuously melting a workpiece, pliers or other part clamps are used, they are connected with the current turned on, after melting the edges of the parts being connected, upsetting is carried out and the current supply is turned off.

This method is most applicable for pipes with thin walls. It is permissible to connect workpieces of different structures.

The main advantage is the high speed of work, the serious disadvantage is the leakage and waste of metal along the weld.

Intermittent melting occurs with alternating tight and loose contact of the workpieces while the current is on.

The clamping pliers ensure closure of the welding line at the point of contact of the workpieces until they reach a temperature of 900-950 degrees Celsius.

This method is used if the initial power of the device is not enough to ensure continuous reflow.

Thus, resistance welding consists of the following steps:

• Preparing surfaces for joining (cleaning, leveling the contour).
• Aligning edges and fixing workpieces under the welding machine.
• Supply of electric current.
• Warming up and melting of the edges of parts under its action.
• Upsetting and turning off the current.

The resistance welding methods discussed above differ in the fixation of workpieces and the supply of current; in general, the welding process is similar.

For home resistance welding, you can design a homemade machine.

Its main operating components are a welding clamp and a voltage supply unit on capacitors, to the low-voltage winding of which an electrode is connected.

The second wing of the clamp serves as a support or is connected (depending on the mounting of the device) with a larger workpiece.

Video instructions for resistance spot welding are presented above.

Microwave welding machine

You can make a device for resistance spot welding yourself using a transformer from a microwave.

When making such a welding device, you need to weigh what will be cheaper - buy an inverter or make it yourself, using a transformer from an unnecessary microwave.

The transformer is the most expensive part of our future homemade device. All other consumables - wires, casing and base on which the mounting will be made - will be available in almost any workshop.

We will need a transformer power of at least 1 kW. Using a welding machine using such a transformer, it is possible to spot weld sheets up to 1 mm.

Doubling the transformer power will allow you to work with sheets up to 1.8 mm thick. The transformer of a modern microwave oven can have a power of up to 3 kW.

If necessary, two or three transformers can be used. This circuit will increase the power of the supplied current.

It is necessary to remove the transformer from the metal casing and get rid of the shunts for limiting the current and the secondary winding.

The microwave oven uses high voltage, so there are fewer loops on the primary winding of the transformer than on the secondary winding.

Because of this, a potential difference appears. Our task is to change the secondary winding, adapting it for resistance welding purposes.

Thoroughly clean the transformer of any residual secondary wiring and shunts, using a wire brush or long narrow object (such as a screwdriver) if necessary.

Only the primary winding will remain intact; we will make the secondary winding again.

Considering the high voltage, we take multi-core electrical wiring with a cross-section of at least one square.

If a circuit of two or more transformers is used, then the conclusions of all secondary windings from them are combined into one.

When one transformer is used, the housing for it can be adapted from the same microwave oven, reducing the width and length.

For a transformer system, the casing can be made from an iron sheet, providing it with an insulating layer. The secondary winding is formed by 2-4 turns of wire.

However, the thick layer of insulation in which the wire is packed will not allow it to bend along the coil.

Therefore, we remove the wire from the insulation and we can use ordinary flexible electrical tape as an insulating coating.

With two or three loops of wire we will achieve a voltage of 2 W.

To supply current to the welding site, we create a lever mechanism, one lever of which is rigidly fixed to the main surface (for the convenience of resistance welding, the transformer in the casing can be secured to the same surface using clamps).

The second lever will compress the parts when lowered. We insert the switch into the primary winding circuit and install it on the upper lever.

This will allow you to simultaneously compress the part and allow current to flow. In this case, pliers are not used, and the tips themselves are pre-soldered to the wires to prevent oxidation.

When spot welding, we will use copper rods with a thickness greater than the diameter of the wire. During operation, they need to be sharpened and replaced if necessary.

During operation, the part is clamped using levers between two electrodes and current is started.

Battery welding machine

When welding with an electric welding machine, household electrical networks are subject to significant overload.

Prolonged resistance welding can lead to melting of electrical wiring or failure of household appliances. The welding machine can be powered from an autonomous power supply.

This role can be played by a portable station (a generator running on gasoline or diesel), which is very expensive, or you can make a power source yourself.

You will need several car batteries; used ones are quite acceptable. Ideally, they will be of the same capacity.

Then the current strength will be calculated as 1/10 of the battery capacity. If devices of different power are assembled, then the smallest capacity will be needed for the calculation.

Let's make a circuit of series-connected batteries, fastening the corresponding “pluses” and “cons” using wires and wire cutters or, even better, cigarette wires.

You can also use any pliers. From the free “minus” we bring the wire to the electrode, which we clamp in pliers, and from the free “plus” to the working plate, it is recommended to install a rheostat in the circuit.

The resulting welding machine for spot welding from car batteries is ready and can be used away from a source of electricity.

You can make a homemade charging device for it. This option can be successfully used by experienced welders and is not recommended for gaining welding skills.

As shown in the article, homemade resistance spot welding is quite accessible. We reviewed the options and technology of resistance welding.

The information provided will help you gain initial resistance welding skills and create a welding inverter for spot welding yourself using available tools.

Resistance welding is increasingly used not only in manufacturing plants, but also in home workshops and garages, where it can be successfully used for various metal-related work. Serial equipment for performing such a technological operation is quite expensive, but a device for contact welding can be made with your own hands from an old microwave.

One of the options for a resistance welding machine from a microwave oven

To manufacture equipment for contact welding at home, you will need the following components, accessories and tools:

• a transformer that can be removed from an old microwave oven (if you need a high-power device, you will need two such transformers);
• thick copper wire or small diameter wiring harness;
• levers that will be used as clamps;
• lever of the required length;
• a reliable base on which the welding machine will be installed;
• clamping clamps;
• Screwdriver Set;
• cables and winding materials;
• electrodes made of copper, due to which welding will be performed.

Transformer assembly

The main element of any resistance welding machine is a transformer, which can be taken from an old but working microwave. In order for a homemade welding device to be able to connect steel sheets up to 1 mm thick, a transformer with a power of at least 1 kW is required. If you need a more powerful resistance welding machine, you will need two transformers.

Step-up transformer from a microwave oven

To make equipment for contact welding with your own hands, you need to take not the entire transformer from the microwave, but only its magnetic circuit and primary winding. The secondary winding is carefully removed from the transformer, and the shunts that are located on both sides are removed from it.

We cut off the secondary winding with a chisel (chisel) or saw it off with a hacksaw.

Shunts are removed

The new winding for the microwave transformer is made from stranded wire with a cross-section of at least 100 mm 2 (or a diameter of more than 1 cm). It will be enough to make 2-3 turns. If the wire has too thick insulation, you can remove it and replace it with fabric insulating tape. If two transformers are used at once, then the secondary winding for them is made common, but it is very important to correctly connect the leads from their primary windings.

The next stages of making resistance welding from a microwave with your own hands are the installation of controls, the manufacture and connection of electrodes, the installation of the internal part of the equipment in a reliable case, which can also be taken from broken household appliances.

Another great video on the topic:

Selecting Electrodes

The electrodes of equipment for spot welding perform several functions simultaneously: compression of the sheets being joined, supply of current to the welding zone, and subsequent heat removal. Important parameters when choosing an electrode are its shape, dimensions, etc. It is these parameters that directly determine how high-quality the welded joint will be. The geometric shape of the electrodes can be straight or curly, but preference is given to straight models, as they provide better access to the welding area.

When choosing electrodes for a microwave welding machine, you can simply refer to the corresponding GOST (14111-90), which already specifies all possible diameters of these elements (10, 13, 16, 20, 25, 32, 40 mm).

The diameter of the copper rods that will be used as electrodes must be greater than or equal to the diameter of the working wires. To avoid active oxidation of the electrodes during operation, they are connected to the working wires by soldering. The electrodes of a resistance welding device (including one made from a microwave) actively wear out during operation, so they must be regularly sharpened, giving them the shape of a sharpened pencil using a file.

Bottom electrode installed

How to operate a homemade welding machine

Despite the fact that resistance welding is a fairly simple technological operation, it must be properly controlled to achieve the required quality of the joint. It is for these purposes that a homemade microwave oven should be equipped with appropriate controls. The main ones are a switch and a lever, with the help of which the required compression force of the electrodes and connected parts is ensured.

The quality of the resulting connection directly depends on the compression force, so it is advisable to make the lever for the welding machine longer. It is very important that the equipment for resistance welding from the microwave is securely fixed to the surface of the workbench. Clamps are used for these purposes.

You can increase the force transmitted by the electrodes not only using a lever, but also using a lever-screw mechanism, which can also be equipped with a home-made device. It is most convenient to attach such a mechanism directly to the lever so that manipulating it does not take additional time. In addition, this arrangement of controls will free up the operator’s second hand, which can be used to hold the parts being connected.

A special feature of working with a resistance welding machine is that current can be supplied to the electrodes only when they are in a compressed state. If you turn on the current before compressing them, they will spark the moment they come into contact with the parts, and this will lead to their burning and rapid failure.

The switch, also related to the controls for contact welding (including those made from a microwave), must be installed in the primary winding circuit. If you neglect this recommendation and install it in the secondary winding circuit, through which a significant current flows, the switch will create additional resistance, which will lead to welding of the electrodes together.

For a homemade welding machine with a microwave transformer, you need to provide a simple cooling system, also made by yourself. An ordinary fan can be used as such a system. Using this device it will be possible to cool the transformer itself, electrodes and other conductive elements. Of course, such cooling will not be very effective, and you will still have to take regular breaks in work necessary to independently cool all heating elements of the equipment.

The welding process performed on a home-made machine is practically no different from a similar technological operation carried out on serial equipment. The first stage of this process is the compression of the parts, during which they undergo plastic deformation at the site of the future connection. In the second stage, current is supplied to the welding zone, passing through copper electrodes.

This stage is characterized by the formation of a liquid welding core, expansion of the weld pool and plastic deformation and sedimentation of the metal of the parts at the connection point. At this moment, molten metal begins to splash out of the weld pool. After the current supply to the connection zone is stopped, it begins to cool, which is accompanied by crystallization of the molten metal.