Do-it-yourself timer circuit for contact welding. Do-it-yourself welding (contact, spot): schemes, calculation, manufacturing. Description of the process of self-assembly of spot welding

The need for a welded joint of metal parts among motorists often arises, and not everyone has bulky and expensive welding machines. The way out is a point contact. A spot welding machine costs from $200, but independent production fixtures from parts of failed home appliances will require minimal cost. A tight seam cannot be achieved by spot welding, but the strength of the joint is high.

Spot welding belongs to the category of so-called contact welding.

Types of welding

Welding is a process in which parts are joined by melting using a local heating method. This is the most durable type of fusion of materials, since the bond occurs at the interatomic level. Almost any material can be welded, but in the automotive business, this procedure is resorted to in order to obtain a strong mechanical connection of metals or alloys. To melt metal, a high temperature is needed: for steel above 1300 ° C, for copper - 1000 ° C, for aluminum - 660 ° C. Energy sources to achieve such temperatures can be different:

• electric arc;
• gas flame;
• ultrasound;
• electron beam;
• laser.

Spot welding uses an electric arc to melt and join materials. Depending on the type of energy used, three types of welding are distinguished:

• mechanical, in which the thermal energy of friction of the part is used;
• thermal, when materials are melted from a high temperature achieved by gas combustion or high current strength;
• thermomechanical: a combination of high temperatures and pressure on the parts leads to the melting and merging of the material.

Machine nail welding

The type of connection is also determined by the type of alloy.

Features of spot welding

Do-it-yourself spot welding has a number of advantages over other types:

• profitability;
• ease of implementation;
• the strength of the obtained compounds.

The quality of the welded joint depends on several components, primarily on the material from which the electrodes are made. It is recommended to use copper rods for these purposes - they are durable, have high electrical and thermal conductivity. An important parameter is the cross section of the electrode. It should be two to three times smaller in diameter than the spot weld.

Spot (spotter) can be made independently - the spot welding scheme is quite simple. To make resistance welding, you need a transformer with a power of more than 1 kW. Often, an element of a failed microwave oven is used for these purposes. The size of the transformer should allow making 2-3 turns of the winding with a thick cable, and the cable length should be 1.5 m.

On the transformer, the secondary winding is replaced, leaving the primary untouched. The new secondary winding is made with an insulated aluminum wire with a diameter of 1–2 mm, to which the tips are attached. A powerful wire will provide a current of 1000 A.

Making a device with your own hands

After the transformer is ready, the primary winding is connected to a power source and the voltage on the secondary winding is determined (it turns out 2–2.8 V).

To the body, the parts of which can be made of wood or chipboard, a transformer is mounted in series, a cable with a switch, and grounding is made.

After the installation of the housing is completed, welding "pliers" are mounted. It is better to make electrodes from copper wire, and fix them in duralumin holders on wooden bars. The polished “sting” of an old unnecessary soldering iron is suitable for the role of electrodes.

The cable is connected to the electrodes using four terminals. The two upper ones are bent towards each other - electrodes are inserted into them, and the lugs of the secondary winding cable are connected to the two lower ones.

The lower electrode is often fixed in a stationary state, the upper one moves. welding is connected to the network through a 20 A automatic switch.

A welding choke is used to regulate the current strength - without it, it will be maximum. Connect the inductor to the secondary winding, it adds resistance and reduces the current strength.

The contact welding machine can be equipped with a fan that acts as a cooling system.

An example of using the device by a professional

Home-made spot welding works from a network with a voltage of 220 V.

Advice. To increase several transformers, but this entails a voltage drop in the network. Therefore, do-it-yourself resistance welding is carried out using home-made devices, the power of which is limited - it provides a current strength of 1000–2000 A.

The quality of do-it-yourself welding depends on several conditions:

• pressure on the metal - the clamping force must be sufficient;
• electrode diameter;
• current flowing through the electrode;
• the pressing time should be longer than the welding time (press the electrodes a little longer than the current flows).

Some types and features of contact welding

Depending on the size and shape of the heated area, contact welding can be of three types.

1. Spot welding - the material is “sewn” with single high-temperature “pricks”, the seam is leaky.
2. Seam - the melted edges of the parts are interconnected to obtain a sealed seam. An example of this type of connection of parts is the soldering of a metal tank for liquid. In fact, a seam connection consists of many points overlapping each other.
3. Butt joint - the connection area is wide, one part is “put on” on another, at the joints a complete fusion of parts into a homogeneous element is formed. This type of connection is most often welded pipes.

The operation of the device on the car body

Do-it-yourself spot welding does not require complex fixtures, you do not need a special table for welding, but safety precautions when carrying out welding procedures are mandatory.

Spot Welding Procedure

Before welding, the parts are cleaned to remove dust, corrosion elements, paint or oil residues - these interferences degrade the quality of the connection. The thickness of the steel in the welded parts is not more than 3 mm.

Prepared metal parts are clamped with electrodes.

Current is applied to the electrodes, the point contact affects the metal - it heats up to the melting point at the point of contact with the electrodes.

It does not require adjustment of the current value in the process, visual control is sufficient. They are guided by the heating time, which is 0.5–3 seconds (no more than five): the speed of current passing through a part 1 mm thick during the operation of the device is 0.1–1 second, and the thickness of the parts to be welded does not exceed 3 mm. On request, the spot welding machine can be equipped with a time relay.

An example of the work of a professional welder

The current power sufficient for welding parts 1 mm thick is 3–5 kW. The current strength (on copper electrodes) should be from 50 A per 1 surface. At lower values, proper heating does not occur, the metal does not melt, and fusion becomes impossible.

Then the current is turned off, and the compression of the parts by the electrodes is increased.

In the place where the current is applied and the parts come together under the pressure of the electrodes, contact and bonds of atoms are formed - the welded joint is ready.

Over time, the electrodes melt, so the contact cone must be periodically ground to keep the tip sharp.

WATCH THE VIDEO INSTRUCTIONS

Contact spot welding creates a strong connection of metal parts. It is necessary to use a welded joint in an automaker repeatedly, so the craftsmen recommend purchasing or making welding machine independently from improvised materials. It will also be useful for repairing household appliances, manufacturing metal objects, connecting electrical cables.

The process of contact welding is based on heating the junction with electric current while simultaneously exposing it to high pressure. In industry, contact welding has found wide application in making cruciform joints and joints of reinforcement of reinforced concrete or steel structures, connecting copper and wires,. At home, resistance welding is possible with your own hands using a special apparatus, which you can also do yourself. After that, the device can be used for.

Device device

AKS contains two functional units - a power supply unit and an external welding gun. The power supply assembly consists of an electronic relay assembled on a VS1 thyristor and a powerful Tr2 welding transformer. An electrode is connected to one terminal of its secondary low-voltage winding using a welding cable. The second output during welding must be securely connected to the most massive of the parts to be welded. The primary winding of the transformer Tr2 is connected to the network using a diode bridge on VD5 ... VD8 and a thyristor VS1 included in its diagonal. A low-power auxiliary transformer Tr1 feeds the thyristor control network and the backlight (winding II). Drawing No. 1 - Pistol AKS

The welding gun is assembled from two parts of the same size and shape, cut out of textolite, getinaks or other durable insulating material. A lamp holder (pos. 28), an adapter (pos. 2) and a SA5 microswitch are attached to the front. In the back there is a backlight switch SA5, fixed between the plates with M2 screws and holders (pos. 27). The plates are interconnected by screws screwed into the lamp holder, adapter and spacer bars. Between the plates there is a welding cable connected to the adapter using a locking screw (pos. 9). The control wires are fixed on the welding cable and switch the SA2, SA5 switches and PSU elements. Replacement electrodes (pos. 3) are attached to the hole in the adapter M8 and secured with a lock nut (pos. 10). On the base without insulating gaskets, the second output of the secondary winding of the transformer Tr2 is mounted. The cable connected to this output is supplied with a clamp of any type, for fastening to one of the parts to be welded. The recommended type of clamp is a clamp.

Production of AKS

In order to assemble the contact welding machine with your own hands, you should use the following recommendations. The dimensions of the power supply are determined by the dimensions of Tr2, so the assembly should begin with it. The design of the transformer does not really matter. The determining parameter is the cross section of the magnetic circuit, which should not be less than 60 cm2. Any magnetic circuit can be used. The primary winding, containing 160 - 165 turns, should be wound on a round frame made of electric cardboard with a PETV wire with a diameter of 1.62 ... 1.7 mm and placed on one of the sides of the magnetic circuit, insulating it from it with wooden wedges. The secondary winding contains 4.5 turns of a 5.2 x 17.5 mm PBU copper bus. You can use another bus or wire, but the cross section must not be less than 90 mm2. Drawing No. 2 - AKS pistol

Then the ends of the secondary winding busbar must be bent into a loop for subsequent bolting of welding cables to them. Before winding, the tire is insulated along the entire length with a tape of fluoroplast or similar material in one layer. You can use tape on a cotton basis, folded in 2 - 3 layers. The same tape must be isolated from each other by all layers of the primary winding. Her conclusions are fixed with cotton tape. The plates of the magnetic circuit must be assembled “overlapping”, that is, overlapping the joint with the short one with a long plate, and so on.

Drawing No. 3 - transformer TP2

The magnetic circuit screed must be made with corners and M8 bolts. First, a preliminary screed is performed to straighten the plates. After that, the upper part of the magnetic circuit must be removed and frames with windings placed on it. Then the plates of the upper part must be put in place and the final screed of the plates must be performed. Frames relative to the magnetic circuit must be fixed with wooden wedges.

Examination

Then you need to perform an electrical check Tr2 - turn on the 220 V network and measure the voltage on the secondary winding. It should be equal to 41 V, and the windings should not overheat. Drawing No. 4

After manufacturing Tr2, taking into account its real dimensions, it is necessary to calculate the dimensions of the casing and base and cut it out of sheet steel. Details of an electronic relay can be placed on a board made of sheet getinax or textolite 3–5 mm thick.

Auxiliary transformer

The finished transformer Tr1 can be of any type and must provide voltage values ​​​​of 6 and 10-15 V on the secondary winding. Homemade Tr1 can be made on the basis of any type of magnetic circuit with a cross section of 1 cm2. The primary winding should contain 8000 turns of PETV - 2 wire with a diameter of 0.06 mm, the secondary - 800 turns of the same wire, winding III - 200 turns of PETV - 2 wire with a diameter of 0.2 mm. The windings between themselves and the magnetic core should be insulated with several layers of fluoroplastic tape. As welding wires, you can use wires of the KOG-2 type with a main core diameter of 90 mm2 and four auxiliary cores. Transformer diagram TR-1

1. transformer winding
2. thyristor heatsink
3. thyristor
4. top plate
5. bar
6. carrying handle
7. adjustment block
8. potentiometer (R12)
9. welding cable terminal
10. fixing bolt;
11. bottom plate
12. cable winder
13. network cable

Drawing No. 5 - electrical circuit diagram

Welding Gun Assembly Sequence

It is recommended to start creating a welding gun with the manufacture of electrodes and an adapter (see drawing). Overlays are cut out of a sheet of vinyl plastic or textolite, the dimensions of which can be changed at the hand of the owner of contact welding with their own hands. Channels for wires leading to the backlight are drilled in the lamp holder. Using M2 screws and two holders, the microswitch is attached to the plates.

The spacer bars can be bent from the Plexiglas strip in place, taking into account the location on the escutcheons (pos. 2, 6, 7 and 28) and the welding cable passing through the handle. The pads are fastened with M5 screws screwed into the spacer bars and adapter. The end of the welding cable is soldered and inserted into the adapter hole with fixation with a locking screw. For a more reliable fixation of the overlays, it is recommended to use adhesive mastics “Monolith” or “Garant”. The sharp edges of the overlays must be blunted, and the handle should be wrapped with electrical tape.

If the assembly is done correctly, then the AKC starts working immediately. To evaluate how the assembled resistance welding works, you can do in the following way. To a steel bar cleaned from the surface with several sheets up to 10 - 12 mm wide, and then tear it off with pliers. At the connection points, holes (so-called tears) with a diameter of 0.5 - 0.8 mm should remain. With possible deviations, you should adjust the duration with a tuning resistor R1. The check must be carried out both with parallel and series connection of capacitors, which is selected by switches SA3 and SA4. Specification for AKS drawings

AKC operation

The master working with AKS should be on a rubber mat and use goggles and rubber gloves. The “earth” cable must be connected to the part to which another part is to be welded. Then you need to turn on the ACS, attach the parts to be connected to each other, press them tightly with the electrode of the welding gun and press the SA5 button. After 1 - 1.5 seconds, the electrode can be removed from the point and installed on the next one. If necessary, you can turn on the backlight.

is a very useful skill.

If any inverter models are available for sale, a person planning to weld at home has a choice - to purchase a ready-made device or make it yourself.

In this article, we will look at what it is, show a training video on resistance welding, give step by step instructions how to independently carry out contact welding and how you can make a home-made contact welding machine with your own hands from a microwave and used car batteries.

Owners of private houses, motorists and not only need welding.

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

Its principle of operation is that electric current the metal is heated, melted and solidified, forming a weld.

To fix and prevent shifting, the parts to be welded are compressed by means of electrodes through which an electric current is applied.

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 connection are used: with the help of resistance, intermittent reflow or continuous reflow.

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

The method is applicable to the following metals:

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

Due to stringent requirements for temperature regime and the absence of impurities at the junctions, this method is rarely used.

With continuous melting of the workpiece, pliers or other clamps of the part are used, they are connected with the current turned on, after melting the edges of the parts to be joined, precipitation is carried out and the current is turned off.

This method is most suitable for pipes with thin walls. It is possible to connect workpieces of different structure.

Main plus - high speed work, a serious minus is leakage and waste of metal along the weld.

Intermittent melting occurs when alternately dense and loose contact of the workpieces during the switched on current.

Clamping pliers ensure the closing 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:

• Preparation of surfaces for joining (cleaning, leveling the contour).
• Aligning the edges and fixing the workpieces under the welding machine.
• Supply of electric current.
• Heating and melting under its action of the edges of parts.
• Draft and power off.

The methods of resistance welding 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 home-made apparatus.

Its main working units 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 attachment of the apparatus) to a workpiece that has a larger size.

Video instruction for resistance spot welding is presented above.

microwave welding machine

A device for spot welding can be made independently using a microwave transformer.

In the manufacture of such a welding device, you need to weigh what will be cheaper - to buy an inverter or do it yourself using a transformer from an unnecessary microwave oven.

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

We need a transformer power of at least 1 kW. With the help of a welding machine using such a transformer, it is realistic to do spot welding of sheets up to 1 mm.

Doubling the power of the transformer will allow you to work with sheets up to 1.8 mm thick. The transformer of a modern microwave oven can be 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 required to remove the transformer from the metal casing and get rid of shunts for current limiting and secondary winding.

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

This results in a potential difference. Our task is to change the secondary winding, adapting it to the purposes of resistance welding.

Thoroughly clean the transformer from the remnants of the secondary wiring and shunts, if necessary, use a metal brush or a long narrow object (for example, a screwdriver).

Only the primary winding will remain intact, we will do the secondary again.

Given the high voltage, we take stranded 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 reduced to one.

When a single 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 of iron sheet, provided 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 be bent around the coil.

Therefore, we take the wire out of 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 watts.

To supply current to the place of welding, we create a lever mechanism, one lever of which is rigidly fixed on the main surface (for the convenience of contact welding, a transformer in the casing can also be fixed on the same surface with the help of clamps).

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

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

When spot welding, we will use copper rods with a thickness greater than the diameter of the wire. In the process of work, they need to be sharpened and, if necessary, changed.

In the course of work, the part is clamped with the help of levers between two electrodes and a current is started.

Battery welder

When welding with an electric welding machine, household electrical networks suffer a significant overload.

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

In this capacity, a portable station (a generator running on gasoline or diesel) can act, which is very expensive, or you can make a power source yourself.

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

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

Let's make a chain of series-connected batteries, fastening the corresponding "pluses" and "minuses" with wires and wire cutters, or, even better, lighter wires.

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

The resulting car battery spot welding machine is ready and can be used away from a power source.

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

As shown in the article, homemade spot welding is quite affordable. We considered the options and technology of contact welding.

The information provided will help you get the basic skills of contact welding and ensure the creation of a welding inverter for spot welding on your own from improvised means.

Once I was puzzled by the creation of spot welding with my own hands to connect 18650 batteries. First, a 555 timer was assembled, then on a pic16f628a microcontroller. A self-made firmware was written for him, control of the encoder with pressing, from 0.01 sec to 10 sec and up to 10 pulses. But this spot welding machine was sold a long time ago and I needed to weld 18650 batteries with something. To do this, this timer was ordered on aliexpress for $ 11.14 or about 700 Russian rubles.
Arrived a little less than a month.
Let's see what he is.

What is contact welding?
We take a large trance so that the traffic jams in the apartment do not knock out (from the microwave, for example). We cut off the secondary, the primary remains at 220. We choose a shunt. Instead of thousands of turns of the old secondary, we stuff 2-5 turns of thick wire. For welding batteries, 3-5 turns with a section of 35 mm are possible. For thicker plates and wire 2 turns with a section of 70-120mm. We finish thick wires. We attach electrodes to the ends of the wire, depending on the task. And if you apply 220 volts to the primary trance, then a current will flow in the secondary in the region of 1000A, which heats up the place of contact of the electrodes with the metal. If it is thick iron or wire, then the shutter speed is usually long, a few seconds, and you can simply apply 220 volts to the trance through an automatic machine or any other manual method. If you cook round lithium batteries, then there are thin plates of 0.1-0.3 mm and very short shutter speeds are needed, while they must be the same for repeatability of results. Burning batteries is unacceptable, depressurization of a can - a can to be thrown away. Here, to replace an automaton or a button, in order to accurately set a short shutter speed, this timer is used.
For those who have little idea what it is and what it is eaten with, you can read:

Packed well, a cardboard box and inside a board under several layers of polyethylene foam. If you play football with a box, then nothing will be damaged.
Inside board with good quality.

Controller microcircuit from STMicroelectronics STM8S003F3, Schmitt trigger 74hc14d, optocoupler moc3021 and pc817, triac BTA41600B, stabilizer lm317k diodes and other piping.








Power triac it is desirable to fasten to the radiator through thermal paste. You can screw it directly onto the contact welding body, but then this must be done through an insulator. Mica gasket and insulator on the fastening screw. The board is divided into two parts by a white strip - the part that is closer to the triac is under a dangerous voltage of 220 volts. The Chinese characters near this band are just talking about it. Most of the resistance welding board is low voltage and safe.

Deciphering the inscriptions near the LEDs in order from the knobs of the regulators:
- State. Lights up when powered.
- Status. Flashes normally and lights up when DC voltage is connected. When powered by constant voltage, the board will not work.
- Pedal. Goes out when the pedal is pressed.
- Trigger. It shines while the triac is open and welding is in progress.

The remote display of the timer for spot welding contains several LED seven-segment indicators, a TM1650 seven-segment LED driver, and a harness to it.

For contact welding, in addition to this timer board, you need:

- Supply transformer for alternating voltage 9-12v. From a constant payment does not work. Does not see network pulses. The second LED from the left should blink, it does not blink from a constant. A large transformer power is not needed, only logic is powered from it. Cell phone charger won't work. The same seller has a ready-made suitable trans. You need to choose the 220v version, it costs less than $ 6 or 370 rubles.
- Pedal or button. Something that will close the contacts on the board. Normally open.
The finished pedal from the seller costs about the same.
- Contact welding transformer. The power part is. Well, if you are interested in such a board, then you probably know what it is. This is a transformer with a primary winding for 220V and a secondary winding for low voltage (1-6V) and high current (100-1000A). This current cooks.
This timer switches the primary, that is, it gives voltage to the primary winding of the welding power transformer. Similarly, instead of this timer, you can simply put a switch - when the switch is turned on, welding will cook while the switch is on. But for welding 18650 batteries, a very short pulse (0.01-0.1 sec) is needed, otherwise the metal of the battery is burned through. You also need the constancy of the results, that is, all exposures of spot welding must be strictly the same. Such conditions - exposures in a fraction of a second and repeatability of exposures - cannot be realized manually, so I bought this spot welding timer.
The same seller has a pedal and a trance, a power transformer for spot welding can be taken from a microwave oven or a larger one. The transformer is heavy, it is expensive to order from China. You can look for a non-working microwave or an old one at a flea market for little money. Or ask at home appliance repair shops.

Timer operation:

We connect the power transformer (change 9-12V) and the pedal to the corresponding terminal blocks, the wires going to the microwave power transformer are soldered. There are two knobs on the board - the left one for adjusting the welding time delay, the right one for adjusting the current. On the remote display you can see the numbers, similarly showing on the left - the time delay and on the right - the current. The welding time delay is adjustable from 1 to 50, 1 is one network period, that is, 0.02 seconds. That is, the timer can set shutter speeds up to 50 * 0.02 = 1 second. The welding current is adjustable from 30 to 99.

When the pedal is pressed, the microcontroller monitors the voltage in the 220 volt network, at the peak or bottom of the sinusoid it gives a signal to the triac. While the thyristor is open, current flows through the primary of the welding transformer and welding is in progress. The board works as an electronic switch, a key.
With a time value of 1 on the display and a current value of 99, the timer turns on the triac for 20 ms, for one network period. If you need less, then you can reduce the current with the right regulator and the controller will open the triac not to a full sinusoid, but only to a part of it.


I took oscillograms from the secondary winding of the welding transformer at different current values ​​​​and shutter speeds, they can be seen in the photo below:






my oscilloscope is not of super quality, amateur, so I give a photo from Ali's reviews - how it should look on the oscilloscope screen:

The point of adjusting the current is that if the transformer is too powerful for welding 18650 batteries and other similar ones, and the time delay of 0.02 seconds is too long and burns through the plate or batteries, then you can still lower the current - the pulse will become weaker and the batteries will not burn through.
I tried to weld a nickel plate at a shutter speed of 1 and currents from 30 (rightmost) to 99 (to the left), the result is clearly visible. This can be seen in the photo below.
Plate 8 mm wide, 0.15 mm thick.

The last two welding tests I tried to do at a slow shutter speed and low current. With a shutter speed of 10 and 30 and a current of 30, the plate heats up, even changes color, but does not weld. For welding thin nickel plates, a short high current pulse is better than a long low current pulse.

The last points on the left, one of them is through, were made just at shutter speeds of 10 and 30 and a low welding current value of 30.
All this can be clearly seen in the video version of the review below:

In general, I liked the resistance welding board, there are 50 time settings from 0.02 sec to 1 sec, and at the same time another 70 current gradations. The board controller monitors the mains periods and starts the timer at the maximum or minimum period of the sine wave, which guarantees the same welding results and excellent welding repeatability of 18650 batteries.
I recommend this timer for creating do-it-yourself spot welding from a microwave oven.
If you need a more powerful welder, a spotter for welding cars, then the seller has the same timer with a more powerful 100A triac, it will be cheaper than buying a 100A triac and a board separately. I plan to buy +103 Add to favorites Liked the review +101 +161

Spot welding machines are not as often used 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 do-it-yourself contact spot welding. But, before telling you how to make such a device yourself, let's look at what spot welding is and how it works.

Briefly about spot welding

This type of welding refers to 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 required for this purpose.

The welding process includes the following steps:

• parts are combined in the required position;
• fix them between the electrodes of the apparatus, which press the parts;
• heating is carried out, as a result of which, due to plastic deformation, the parts are firmly connected to each other.

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

Process Technology

In order to heat the parts to the required temperature, a short-term impulse of a 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).

With a pulse, the metal melts, and a common liquid core forms between the parts, until it hardens, the surfaces to be welded must be kept under pressure. Due to this, cooling, the molten core crystallizes. A drawing illustrating the welding process is shown below.

Designations:

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

The pressure on the parts is necessary so that, with a pulse, a sealing belt is formed along the perimeter of the core of the molten metal, which does not allow the melt to flow out of the zone where welding takes place.

To provide the best conditions for the crystallization of the melt, the pressure on the parts is removed gradually. 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 in order to ensure a reliable connection, as well as the quality of the seam, it is first necessary to process 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 required to ensure a 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:

• a block of capacitors is charged with an electric current of small force;
• capacitors are discharged through the parts to be connected (the impulse strength is sufficient to ensure required mode welding).

This type of welding is used in those industries 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

On the Internet there are many examples of the creation of machines that produce spot welding. Here are some of the most successful designs. Below is a diagram of a simple spot welding device.

For implementation, we need the following radio components:

• R - variable resistance with a nominal value of 100 Ohm;
• C - a 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 uF;
• VD2-VD5 - diodes D232A, foreign analogue - S4M;
• VD6-VD9 - diodes D226B, they can be replaced by a foreign analogue 1N4007;
• F - 5 A fuse.

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

To make the secondary winding, you will need a stranded copper wire Ø4 mm. 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 do. At the same time, on winding II, used to connect the backlight lamp "H", there must be an output voltage in the range of 5-6 V, and windings III - 15 V.

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

Let's give a diagram of a more powerful apparatus, 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 uF, C2-0.25 uF. 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 put a diode bridge, for example, KTs405A;
• thyristor VD6 - KU202N, it must be placed on a radiator with an area of ​​at least 8 cm 2;
• 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 will tell you how to make a TR1 transformer. The autotransformer LATR-9 is taken as a basis, such as shown in the photo.

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

Next, we need to isolate the contact track, for this purpose we clean it of dust, degrease it and varnish it. When it dries out additionally, we isolate the entire winding using varnished cloth.

As a secondary winding, we use a 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 them a winding of three turns.

Setting up the assembled device is reduced to grading the scale of a variable resistor that regulates the pulse time.

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

As already mentioned above, the device is capable of delivering a welding electric current with a power 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.