How to use resistance welding correctly

Basic nuances of working with spot welding

04.04.2018

How to determine welding quality

The spot welding method is in great demand in modern industry. Approximately half of all metal structures today are made using this method.

Spot welding is used in almost all industries, mechanical engineering, automotive industry, aircraft manufacturing, construction work, manufacturing of various household items, etc. This is explained by the simplicity and versatility of this method.

However, there are some nuances that need to be taken into account when working with spot welding so that the quality of the products remains at a high level. It is these nuances that we will talk about in this article.

Basic methods for performing SPOT welding

This method is ideal for welding metal sheets or assembling cabinet products. In this case, the thickness of the material that can be processed by this method should be in the range of 0.1-6.0 mm. There is also professional industrial equipment that allows you to work with steel sheets up to 2 cm thick.

There are several most popular spot welding methods that are used in the work. The main difference between them is the supply of electric current to the surface to be welded. You can consider these methods with examples.

Example No1. It is required to connect two metal parts. There are no difficulties, so it is most convenient to use the two-way method. The elements need to be clamped between the electrodes, while applying some force. In this case, electric current is supplied from both sides at once.

Most often, this option is used when connecting small parts of metal structures, if the connection is open or flanged. The advantage of this method is the excellent quality of the weld, which is obtained thanks to the double-sided clamping. The result is a strong connection. The disadvantages include the limited size of parts that can be connected in this way. The problem is that the parameters of the products are limited by the length of the pliers used to clamp the material.

Example No2. The connected elements are part of a closed structure. It will not be possible to supply current from both sides. In this option, you will have to work using the one-sided welding method.

This method can be used when welding parts of any size. The dimensions of the metal structure do not affect the quality of work, however, the depth of the seam is still limited, since the current is supplied only from one side. Professionals use a special copper gasket, which must be installed in the place where the electrodes will be. This spacer helps make the connection stronger.

When welding on one side, you need to pay attention to the thickness of the elements being connected. If one of them is thicker than the other, then electric current is supplied to the thicker part. When welding, the electrodes should not be placed too close to each other, otherwise the metal may spatter.

Advantages of using the one-way method:

• high performance;
• relatively low energy consumption;
• low deformation of the product (the connection is made symmetrically).

The downside is that it is not always possible to clamp the elements with the required force, so the quality of the connection is slightly lower than when using the two-way method.

Welding modes

Spot welding equipment can operate in “hard” and “soft” modes. The hard mode has a high current strength and a short period of operation, while the soft mode has a low current strength and a longer welding time.

Main factors of work:

• The clamping force is needed not only to ensure that the elements contact each other, but also to deform them, which prevents metal from getting into the gap at the joint. The force depends on both the thickness of the elements and the type of metal;
• the thickness and type of metal also affect the required current;
• welding time affects the size of the joint;
• The diameter of the electrodes used determines the size of the connection point.

Before work, it is important to correctly select all these parameters for each specific case. Even a slight deviation will negatively affect the quality of the connection.

As a specific example, consider the connection of low-carbon steel elements. This material is most often used in the manufacture of industrial metal structures and fasteners.

If you plan to weld parts with a total thickness of up to five mm, then a cycle with one electric current pulse and a constant clamping force is optimal. To weld thicker parts, several pulses will be required.

Possible problems during operation

The quality of the resulting joint depends not only on the method used, but also largely on the material from which the welded elements are made.

In enterprises where it is often necessary to work with materials that conduct heat well (copper, aluminum billets), other nuances that affect the quality of the connection must be taken into account. We must not forget that parts made of such metals quickly remove the supplied thermal energy, so to weld them you need to use high-density electric current (up to 300 A/sq.mm).

Another problem is that aluminum particles stick to the electrode during welding. To prevent this, you need to carefully and thoroughly clean the surface of the workpiece before working. Spot welding aluminum alloy products is much easier than welding pure aluminum parts. This is caused by the lower resistance of the material.

In order to qualitatively connect aluminum parts using spot welding, you need to know the exact value of the current strength and operating time. Even small deviations from the established parameters will cause defects, which will certainly affect the quality of work. Poorly welded products differ several times in strength from those made in compliance with all the rules.

How to determine welding quality

If the connection was made correctly, then there should be a crater on one of the elements, and on the other there will be the “core” of the connection itself. If at least one of these signs is not present, then the welding was done poorly. In this case, the work must be done again, increasing the force of pressing the parts against each other or the welding time.

The main indicator of joint quality is the size of the weld core. The optimal diameter of the connection point should be approximately three times the thickness of the smaller part, with an error of 20-80 percent. If the core is less than this indicator, then the connection is not made well enough, there are parts that are poorly welded together. If the diameter is too large, metal has spilled out between the elements.

A high-quality connection is the key to a long service life of the manufactured element. Welding parts when assembling metal structures is one of the most critical stages of work; the strength and reliability of the finished product depends on it.

Source: http://s-awangard.ru/articles/osnovnye_nyuansy_raboty_s_tochechnoy_svarkoy/

What is spot welding. Operating principle and features

28.05.2018

For more than 150 years, people have known a method of joining metals called spot welding. This method made it possible to automate and mass produce cars, agricultural machinery, airplanes and thousands of household products. Thanks to its relatively simple principle of operation, spot welding comes into the everyday life of ordinary amateur craftsmen, car mechanics, and tinsmiths.

Operating principle of spot welding

Resistance welding technology works quite simply - the parts are tightly compressed and a powerful electrical impulse is applied through the shortest distance. The metal heats up and a molten core forms at the point of contact.

Since the parts are compressed, diffusion of metals occurs. The current is turned off, the point cools down, and the metal crystallizes. The welded point turns out to be strong; when you try to break the connection, the material next to the point bursts.

The operating principle of welding machines is to generate this impulse and tightly compress the parts.

In order for the current pulse to heat the metal well, it must be of high strength and low voltage. Industrial devices have the following characteristics: the voltage at the contacts is only 1 - 3 Volts, and they are capable of delivering a current of 10 - 15 kiloamperes.

Spot welding machine design

Any spot welding machine consists of two blocks:

• power supply;
• clamping pliers.

To obtain a powerful discharge at a low voltage, you will need an induction type transformer. The ratio of the primary and secondary windings allows you to obtain an electrical impulse sufficient to melt the metal.

Clamping pliers consist of two copper or graphite contacts located on different arms and a clamping mechanism. Clamps come with different drives:

• Mechanical. They consist of a powerful spring and a lever, the compression of metals occurs due to muscular force. They are used in homemade or household devices, do not provide adequate control over the degree of compression, and have low productivity.
• Pneumatic. Most popular for portable hand-held devices, they are easily adjusted by changing the pressure in the air line. The disadvantage is that they are relatively slow and do not allow pressure changes during the welding process.
• Hydraulic. Not so popular, the hydraulic drive is also slow, but has a greater range of settings due to the use of adjustable bypass valves.
• Electromagnetic. The most “lightning-fast” ones, they are used both on hand-held devices and on large stationary ones. They allow you to regulate the compression of metals during the welding process, which allows you to achieve penetration and the absence of “splashes” of metal.

Resistance spot welding pliers

Complication of the design is possible by using liquid cooling circuits on loaded devices, using various current and pressure control systems, and robotic movement of electrodes.

Where is it used?

Spot welding is used to join various structural metals and alloys. Features of the technology - environmental friendliness, speed, reliability, ease of automation - allow it to be widely used in:

• automotive industry for body assembly;
• jewelry making for joining parts;
• microelectronics for soldering microcircuits;
• production of welded reinforcement frames for monolithic slabs;
• production of housings, parts of consumer goods.

Source: https://svarkaprosto.ru/tehnologii/chto-takoe-tochechnaya-svarka

Spot welding modes, parameters

Spot welding in production

The spot welding mode is set by the following basic parameters: current strength or density, heating time, pressure, diameter of the working part of the electrode. In addition, the pre-compression time of the electrodes tсж, the forging time tnp, the shape of the working part of the electrode and the material for its manufacture are often specified . Modes of special types of spot welding have some additional parameters.

Soft modes are characterized by low current strength and long heating time; for hard modes, the current strength is high and heating time - the mode option must be made taking into account the specific production conditions and requirements for the welding joint.

Spot welding

Welding in soft modes is accompanied by the formation of a wide heating zone, which facilitates the deformation of the metal and allows us to limit ourselves to not very high requirements for the accuracy of straightening workpieces, as in hard modes.

Exact. welding

Hard modes provide higher performance and less power consumption. Due to the fact that the surface of the parts under the electrodes heats up relatively less under harsh conditions, the electrodes heat up less and, despite the increase in pressure, their consumption decreases.

The depth2 of indentation at the welding site and warping of the product are noticeably reduced.

In general, hard modes are advisable, first of all, in mass production, where the gain in productivity and energy consumption will fully compensate for the additional costs associated with the acquisition, operation and power supply of more powerful equipment.

Current strength and density

As the thickness of the sheets being welded increases, the current strength should increase. For welding low-carbon steels of medium thickness on serial machines, the approximate selection of current strength l can be carried out according to the following relationship:

l=6500qa,

Where q is the thickness of the sheets being welded in mm.

When welding sheets of different thicknesses, the choice of parameters is made under the condition that there is sufficient heating and deformation of the thinner sheet. Therefore, in the given relationship and in subsequent ones, the value of q is related to a thinner sheet.

Current density I for hard modes is selected within the range of 120 - 360 d/Lm*, for soft modes 80 - 160 A mm2.

With increasing sheet thickness, the density is then/? decreases. When the metal of the parts being welded has increased thermal and electrical conductivity, the current density should increase. Thus, when welding aluminum or its alloys, the current density sometimes reaches 1000 A/mm2 and higher. As mentioned earlier, the current density should be selected higher when, for some reason, the pressure is assumed to be increased.

Resistance spot welding

Heating time

Like current, heating time (tcs) increases with increasing part thickness. Approximately for welding low-carbon steel at hard conditions, the heating time can be selected according to the ratio

tce — (0.1 -f-0.2) q sec.,

where q is the thickness of the thinner sheet in mm.

It is not recommended to take a shorter heating time, since random, even minor errors in the operation of the time regulator can cause serious deviations from the required heating and welding quality.

For welding sheets up to 3 mm thick in soft modes, the heating time can be selected according to the ratio.

I = (0.8×1) q sec.

Heating for too long can cause overheating of the metal in the welding zone.

For welding metals with high thermal conductivity, the welding time is assumed to be short (at high current strength); when welding hardening steels, on the contrary, in order to avoid the formation of hardening cracks during rapid cooling, the heating time often has to be increased (with a corresponding decrease in current).

Spot welding progress

Pressure

The choice of pressure (P) is made depending on the thickness, condition and material of the workpieces, as well as on the nature of the adopted heating mode.

For welding low-carbon steel, the pressure depending on the thickness is selected according to the formula

P=(60×200)q kg.

where q is the thickness in mm.

The specific pressure has a limit of 3x10 kg/mm2.

Mild hot-rolled steel can be coupled at lower pressures. Cold-rolled steel, which has received increased work hardening, requires a slight increase in pressure (by 20-30%). When the workpieces are poorly straightened and have warping, then before tightly squeezing the sheets in the Siamese area, it is necessary to straighten them under the electrodes.

The total force required in this case must be increased, especially for larger thicknesses. So, for sheets with a thickness of 3-6 mm, this additional force alone is 100-400 ke.

For the same reason, the force should also increase when the points are located in those places of the welded unit where squeezing the sheets is difficult (near the ribs and other stiffeners, and at the places where the parts meet at a radius, etc.).

The specific pressure increases with the strength of the metal being welded. When welding low-alloy steels, it can be 120-160% of the specific pressure for low-carbon steel; when welding austenitic and heat-resistant steels and alloys, it increases by 2-3 times.

• Electrode diameter. The electrode diameter (d) determines the current density, specific pressure and degree of cooling intensity of the surface of the part.
• The diameter of the electrode has a relatively small effect on the electrical resistance of the welding zone, only at the final stage of heating, when complete contact of the surfaces of the electrode and the part is achieved.
• Therefore, during prolonged heating, the influence of the electrode diameter is more pronounced. The diameter of the electrode increases with the thickness of the parts.
• For thicknesses up to 3 mm, the diameter of the electrode is calculated using the following formula:

D=2q+3mm,

where q is the thickness of the thinner sheet.

For parts with greater thickness, the calculation is carried out using the formula

Changing the diameter of the electrode is often used to equalize the heat when welding parts that are unequal in thickness or type of metal.

During the welding process, under the influence of strong heat and heavy mechanical load, the working part of the electrode changes with the formation of a mushroom-shaped thickening, and the surface becomes contaminated with metal oxides. An increase in the actual diameter of the electrode at constant current and compression force means a decrease in current density and specific pressure.

As a result, the heating intensity in the welding contact is greatly reduced, and metal compaction becomes more difficult and welding may be of poor quality. In addition, contamination of the surface of the electrodes can cause an increase in contact resistance, overheating and even melting of the surface of the sheets. It is generally believed that wear-related increases in diameter by more than 10% are no longer acceptable.

Such electrodes must be cleaned with a file, a special device, or sharpened.

Pre-compression time

The pre-compression time is understood from the start of applying pressure to the start of heating. It must be sufficient so that the compression mechanism has time to bring the electrodes together and develop pressure to a given value. This parameter does not have a direct effect on thermal processes during welding. To improve performance, this parameter should be reduced as much as the speed of the compression mechanism allows.

Forging time

The forging time (tnp) is determined by the duration of the already welded point being under the compressive influence of the electrodes. This parameter affects the cooling rate of the metal after welding, since after heating, under conditions of close contact between the electrodes and the part, heat from the welding zone is transferred especially quickly to the electrodes.

When welding hardening steels, accelerated cooling can cause cracks and forging time should therefore be reduced.

However, in all cases, the pressure should not be released before some time necessary for complete hardening and strengthening of the core. Otherwise, the sheets deformed during welding, trying to elastically return to the initial position, can destroy the core that has not yet cooled. With increasing thickness, the forging time increases, since the volume of heated metal and the cooling time increase.

We also recommend that you familiarize yourself with:

Flash butt welding mode parameters.

Source: http://svarak.ru/kontaktnaya-svarka/rezhimyi-tochechnoy-svarki-parametryi/

Types and features of resistance welding

One of the welding methods used in mass production and domestic conditions is called contact welding. The essence of resistance welding is the combination of heating the site of the future welded joint with a strong electric current with mechanical pressure exerted on metal surfaces.

The method is used in such areas as mechanical engineering, aircraft manufacturing, and the creation of microcircuits. Of course, in industrial settings, powerful and large welding machines are used.

However, manual resistance welding is also possible; machines, including homemade ones, for such work can be found in automobile workshops and construction sites.

Distinctive features

Industrial resistance welding machines are complex systems consisting of many components. And the most important of them are electrodes. They are the ones who directly interact with the metal surfaces being welded.

As real practice shows, copper electrodes are best suited for the contact method. This is the peculiarity of the process.

A mandatory component of machines and devices for resistance welding is a regulator. It is with its help that the sequence of operations is ensured, their duration is set, and the phases of the welding current are smoothly adjusted.

It is also impossible to imagine modern welding machines without relays and transformers - electricity converters. The conversion is fundamentally important, since it requires a current of high strength, but low voltage - from 1 to 16 Volts.

Its reduction to the required parameters occurs precisely with the help of a welding transformer. You can clarify in advance the optimal voltage and electric current for a specific metal thickness in the instructions for the welding machine - this data must be there.

In addition to everything, modern welding machines have quite a lot of electronics that automate certain work processes. This makes managing them as convenient and simple as possible.

Advantages and disadvantages

Resistance welding has many advantages, which predetermined its prevalence. First of all, it is worth noting the high speed that this method provides.

One weld point can be created in literally one tenth of a second. Having made a simple calculation, it is easy to see that in a minute a professional welder using this method can create up to 600 connections.

Contact electrodes wear out slowly and have a fairly long service life. The process of welding by contact method is quite simple - even beginners, performers with low qualifications, can carry out such work, set the desired welding mode and control its execution.

The described welding method does not require any consumables: no inert gas, no flux, no additives. This is also why the risk of fire when working using the contact method is minimal.

Resistance welding does not have a negative impact on human health or the environment. And this characteristic gives the right to call this welding environmentally friendly.

Contact methods certainly have their disadvantages. For example, such a disadvantage is the high cost of equipment. In addition, contact welding requires high current (from 1000 Amperes). This means that power from power plants or other sources of electricity must be powerful.

Speaking about the disadvantages of resistance welding, many note that its results are subject to fairly strict official requirements. Such welding is considered to be of high quality only when the dimensions of the welded joint - core diameter, depth of dent and penetration, amount of overlap, distance between weld points - fall under GOST 15878-79.

Despite the fact that this standard was introduced back in the Soviet Union, it is still valid today and applies to all contact welded joints obtained by melting metal.

Varieties of the modern method

There are four current types of connections that occur when parts come into close contact:

• point;
• at the joint (butt);
• suture;
• embossed.

In some specific cases, combined methods of welding metal parts are possible - seam-butt, relief-point and others.

In addition, resistance welding can be double-sided or single-sided . In the first option, the electrodes are applied to two surfaces of the product, for example, above and below.

However, in hard-to-reach and inconvenient places, it is problematic to connect two electrodes at once; therefore, one-sided resistance welding is used. It is considered less efficient than two-way, but still provides an acceptable connection.

Point connection

Resistance spot welding is the most popular and common on this list. It involves connecting metal products at one or more small points.

There is no need to worry about the destruction of such a connection. When properly executed, it is indeed very reliable. The point method is used by craftsmen both for joining very thin parts (up to 0.02 micrometers) of electrical appliances, and for welding metal sheets up to 20 mm thick.

The quality of work here is determined by the structure and size of the resulting points. And these parameters directly depend on the shape and dimensions of the contact surface of the electrodes selected for operation.

Relief method

Relief welding is often used in the automotive industry to connect brackets with sheet elements (in particular, brackets are attached to the car hood and door hinges to the cab using the relief method), as well as for fixing standard fasteners - studs, bolts, nuts.

Regardless of the type of welding, the surfaces of the workpieces must be cleaned of dirt, corrosion, fuels and lubricants. However, relief welding requires additional preparation of products. Quite complex in shape (for example, round or oblong) protrusions must be made on them using special equipment.

Suture method

When seam welding, a seam is created at the junction of parts, consisting of welded zones overlapping each other. All necessary operations in this case must be carried out on specialized devices with one or more electrode rollers that will press, roll and weld metal products.

The acceptable thickness of the sheets to be welded is in the range from 0.2 to 3 mm. When creating objects and objects for which the tightness of connections is important (barrels, water pipes, gasoline tanks), experts recommend using suture technology.

Docking

Butt contact welding, like relief welding, involves preliminary processing of the welded edges (ends).

Interestingly, there are as many as three variants of the butt method - with resistance, with continuous and with intermittent reflow. Resistance welding involves pre-joining and compressing parts, after which electricity is supplied to them, which heats the metal to a plastic state.

With the last two methods, the parts are first heated strongly and then connected. The difference is as follows. With continuous melting, the metal product is heated steadily throughout the entire welding procedure, and with intermittent melting, the part is either heated or allowed to cool.

This is done in order to save equipment resources. Interestingly, under the influence of electrodynamic forces, liquid metal, as well as oxides and contaminants, are ejected from the joint area - the result is a very clean connection.

Designation on drawings

In some situations, a professional diagram or drawing with the correct resistance welding symbol may be needed.

According to current standards, there may be several such designations. If we are talking about a visible continuous seam, then it is marked with a main line, and other similar elements - with a thin line. As for the continuous hidden seam, it should be indicated by a dashed line.

Visible weld points in the drawing are marked with a “+” sign, while hidden ones are not marked in any way. Leader lines can extend from all visible and hidden solid seams or weld points.

Only on these lines or under them can you write conventional symbols, numbers and letters, and indicate the numbers of state standards. For example, the designation of resistance spot welding on the extension line must contain a large letter “K” (it indicates the type of welding - contact) and a small letter “t” (the letter indicates a specific method of work - spot).

All key information about connections necessary for drawings and diagrams can be taken from GOST or other reliable sources.

Source: https://svaring.com/welding/vidy/kontaktnaja-svarka

Do-it-yourself resistance welding machine from an inverter, microwave-based equipment

Inverters on the market are presented in a huge range, so everyone, if necessary, can choose the most suitable equipment for carrying out welding work at home. An alternative to this choice is resistance welding from an inverter.

Below you will learn what resistance welding is, how to make a device based on a microwave or battery, and how to use it correctly.

Everyone may need to do welding work at home during renovations. The inverter can be useful for installing metal parts or in a mini-workshop at home.

The operating principle of the inverter is as follows:

• the metal is heated by electric current;
• it then melts and solidifies after forming a weld;
• to secure the parts and protect them from moving apart, the parts are compressed by electrodes through which current flows.

To carry out home welding work, you need a powerful power source, and this can lead to overheating of household wires. Check the quality of your wiring in advance and replace it if necessary.

During spot welding, you need to connect two workpieces along adjacent edges. This will be required when installing small parts made of thin material, in particular, metal rods up to 0.5 cm thick.

Connection options

When resistance welding, surfaces can be joined in the following ways:

• continuous reflow;
• intermittent;
• resistance.

When working using melting, you need to connect parts or sheets of metal or heat them with current until melting occurs. This technology is relevant for the following types of work:

• processing of non-ferrous metal or low-carbon steel;
• installation of copper, steel or brass.

However, this method is not particularly popular due to the fact that there are strict temperature requirements, and also because there should be no impurities .

When continuously melting workpieces, welding pliers and other clamps will be required. The parts are connected when the current is on. When the edges of the parts melt, precipitation will occur, and the current landing will turn off. Thin-walled pipelines are installed in this way, but it is also possible to connect workpieces that differ in structure. The key advantage of the method is efficiency. But there is a risk that metal will leak out along the welding seam and cause waste.

Intermittent reflow is performed with sequential tight or loose contact. Using clamping pliers, the welding line is closed in the area where the workpieces are joined so that the temperature rises to 900-950 degrees. This method is used if the initial power of the device for continuous reflow is insufficient.

Resistance welding solves the following problems:

• the surface for installation is prepared (the contours are cleaned and leveled);
• the edges of the workpieces are connected and secured with clamping parts;
• turns on the current source;
• the edges of the workpieces heat up and melt when the device is running;
• upsetting is performed and the current is turned on.

These types of welding processes differ little from each other in technology, but they differ in the current supply and fastening of parts.

To weld parts using the spot method for domestic needs, you can make the device yourself. Its key mechanisms are:

• clamp;
• device for supplying voltage to capacitors. In it, an electrode is attached to the low-voltage winding.

The second clamping wing is a support wing and can be mounted with large parts.

DIY microwave equipment

You can make a device for carrying out welding work using the contact method with your own hands; the key part in it is a transformer from a microwave oven .

To make such a device, you will need to perform preliminary calculations of the profitability of this device compared to purchasing a ready-made inverter.

For a homemade device, the most expensive part is the transformer, but consumables (such as a base for fastening parts or a casing with wires) can be taken from a service center.

A transformer with a power of 1 kW is suitable for the manufacture of welding equipment for joining sheets up to 1 mm thick. If its power is twice as large, then it will be suitable for processing sheets up to 1.8 mm thick. Many microwave ovens are equipped with a 3 kW transformer.

To increase the current capacity, 2 or 3 transformers may be required. The transformer itself is pulled out of the protective casing, the shunts are removed along with the secondary winding. Since the voltage in a microwave oven is high, there are fewer loops on the primary winding of the device compared to the secondary. In order to remove the potential difference, the secondary winding is removed and adapted to work with spot welding.

The work looks like this:

• thoroughly clean any remaining shunts, as well as the secondary winding. You may probably need a long narrow object or a metal brush;
• the secondary winding will need to be made new, but the primary winding will remain in its original form. You will need stranded wires with a cross-section of at least 1 square;
• for the secondary winding you will need to make up to 4 turns of wiring with a voltage of 2 W, however, bending it along the coil will not work due to the thick insulation. Accordingly, the wire will need to be cleaned and then wrapped with electrical tape.

The outputs of the secondary windings are combined when using a circuit based on several transformers. And if you use one transformer, you can reduce the microwave body in width and length.

For several transformers, the casing is made on the basis of an iron sheet, which is covered with electrical tape.

To supply current to the area being welded, you need to create a lever device. One lever is firmly attached to the main surface, and while lowering, the second will put pressure on the workpiece.

Insert the switch into the primary winding circuit and install it on the upper lever, thanks to this it will be possible to start current and compress the part at the same time. In this case, pliers will not be needed; you will need to solder the tips to the wiring in advance in order to prevent oxidation.

For resistance welding, copper rods with a thickness greater than the size of the wiring are used, which will be replaced or sharpened during operation. During operation, the part will be clamped between the electrodes by levers, then the current will start.

During welding with the use of electrical devices, a huge load is placed on household networks . As a result of long spot welding, wires may melt or household equipment may break. Accordingly, the device can be powered from an autonomous source. For example, a portable generator that runs on gasoline or diesel fuel. You can purchase such a generator or make it yourself.

You will need several batteries from used cars. In this case, the current calculation will be 1/10 of the battery capacity. When using batteries of different power, the calculation can be done using the smallest capacity.

You will need to create a circuit of batteries connected in series. The “pros” and “cons” are fastened with wire cutters, wires or wiring for the cigarette lighter, or any pliers. The wire is brought out from the free “minus” to the electrode and clamped with pliers. A rheostat is placed in the circuit from the free “plus” towards the working plate.

When the equipment is ready, additional charging equipment can be made.

Features of a homemade welding machine

Resistance welding is not too complicated technologically , but in order to achieve the desired quality of the connection, it must be managed correctly. Therefore, a homemade microwave-based device will need to be equipped with special controls. The key ones are the lever, the switch, as well as the lever through which the compression force is exerted on the electrodes and the parts that are connected.

The quality of the connection directly depends on the compression force; accordingly, the lever for the device should be as long as possible. It is important that the welding equipment can be securely fixed to the surface of the work table using clamps.

The force transmitted by the electrodes can be increased not only with a lever, but also with a lever-screw mechanism, which can also be attached to a homemade device. It is best to attach it directly to the lever so that manipulations are quick. This placement will also free up your other hand so you can support the parts.

The peculiarity of working with a spot welding machine is that current can be supplied to the electrodes only when they are compressed. And if the current supply is turned on before compression, the electrodes will spark when they come into contact with parts, which will lead to burning and failure.

The switch for controlling welding will need to be placed in the primary winding circuit. And if it is installed in the secondary winding circuit, through which a significant current passes, then additional resistance will be created, and as a result, the electrodes will be welded to each other.

Also, a homemade microwave-based device will need to be equipped with a simple cooling system, which you can also make yourself. For such a system, you can take a regular fan, with which you can cool the electrodes, transformer, and other conductive elements. Naturally, this cooling is not very effective, and you will need to take regular breaks so that all the heating elements of the equipment can cool down on their own.

Above we discussed the features of assembling equipment for spot welding with your own hands . This method is available to everyone, since the materials for the work are not too expensive, and spot welding skills can be mastered very quickly.

Source: https://tokar.guru/svarka/oborudovanie-dlya-kontaktnoy-svarki-svoimi-rukami.html

Resistance spot welding

Owners of garages, cottages or private houses periodically carry out plumbing work. More often they are associated with car body repairs or restoration of sewerage and water supply systems. And a welding device is an indispensable device, without which it is impossible to carry out such procedures. It may seem that using this tool will require certain skills, but practice shows that everything is much simpler.

Spot welding

Features and principle of spot welding

The essence of the technology is to connect two metal sheets, mostly not very thick. But here, instead of the usual seam, connecting points are applied. This uniqueness allows the thinnest alloys to be bonded together without deformation. It should be noted that spot welding is used not only in households, but also in large-scale industry.

The density of the finished product will depend on the following parameters:

• shape and size of electrodes;
• duration of exposure to voltage on the object;
• surface cleanliness;
• electricity intensity.

Spot welding diagram

You can fasten ferrous and non-ferrous iron, which is included in the list of significant materials in automobile aviation and shipbuilding plants.

The main advantages of the technique are: high productivity (up to 10 rivets per second), there is no need to use auxiliary means, decent sanitary conditions during operation, spot welding can be used at home.

The fastening of the elements occurs due to the strong temperature effect at the point of contact of the contacts.

During the reaction, there is a short-term melting followed by cooling of the workpiece. This is the main principle of electric spot welding. However, before starting any manipulations, it is recommended to carefully study the operating technique.

Electric arc spot welding principle

Process technology

Before each operation, you need to thoroughly clean the surface from dirt, rust and other elements. If this is not done, there is a high probability of getting a fragile connection. Then both objects are tightly connected by planes and clamped between two electrodes. Afterwards, electricity is passed through them, which will connect the objects in a given place.

Purchasing such equipment will be expensive, but anyone can construct it from available materials. A simple spot welding diagram would be a great choice to experiment with and understand the ins and outs of the assembly. It is also easy to create a unit from household appliances that have become unusable. For example, do-it-yourself resistance welding is often made from damaged microwave ovens.

Spot Welding Process

Homemade device from a microwave oven

The task of this stage is to design a convenient housing and remove the transformer from the microwave oven. If the homemade design turns out well, spot welding will be fun. It is recommended to use wood as a material.

The product should be in the form of tongs, with the bottom bar being stationary and the top bar moving vertically. Cords from the transformer are carried to both parts, which are connected to copper rods (they are fixed at the end of the unit).

Also, for convenience, a button is connected to the cable, pressing which will supply a charge to the spiers.

Microwave welding machine

The device for spot welding is almost done, a few things remain to be done: a wire with a plug is connected to the secondary winding, an additional switch is mounted, the bare wires are well insulated. However, you do not need to start using it immediately, and the resistance spot welding machine must be tested on unwanted workpieces. Also, to avoid injury, the transformer should be properly prepared.

This part is the most significant because it is responsible for increasing the output voltage. To perform its functions efficiently, it must have an acceptable transformation rate. A do-it-yourself spot welding machine can be dangerous due to high current. To avoid this modification is carried out:

• gain access to the primary winding (cut off the side cover with a grinder) and carefully remove it;
• remove the secondary skein (you don’t have to worry about damaging it, since it won’t be useful in the future);
• clean the core from glue and paper;
• Using a rubber hammer, hammer the primary back in.

Assembling a spot welding machine with your own hands

Next, take a thick cable with a large cross-section, high-quality insulation and behind the previously installed copper lugs. It is wound on top of the first skein so that both ends come out from one side, and everything is put back together. At this point, the welding machine, or rather its main part, is ready for use.

Creation of electrodes

These parts must have high resistance to severe overheating. Copper rods with a cross section of at least 15 mm are perfect here. You can make several contacts that will have different thicknesses. In this way, they can be replaced in accordance with the work being carried out.

Another option is to use two soldering iron tips. These parts can withstand high heat perfectly and will last a long time.

Creation of electrodes

Controls

There are only two control systems: a switch and a charge button. The first is mounted in the primary winding circuit to provide auxiliary resistance. As for the feed, this system is attached to the upper tong. This creates additional convenience. However, energy must be supplied after the spiers have fully touched. Otherwise, a spark will occur that can burn the contacts.

Source: https://stankiexpert.ru/spravochnik/svarka/kontaktnaya-tochechnaya-svarka.html

Features of spot welding

Spot welding is a type of resistance welding. It differs from other types of welding in that the part is connected not by a long weld, but by one or more welding points. This is the main feature of this type of welding joint. Doing spot welding with your own hands is not at all difficult. Industry, construction and households have been using spot welding since 1877. The main thing is to study the main nuances and aspects of this type.

articles

• Concept of spot welding
• Spot Welding Technology
• Possible defects
• Advantages and disadvantages of the method
• Spot welding machine
• Spot Welding Equipment

Concept of spot welding

Resistance welding is the process of forming a permanent welded joint by heating the metal with an electric current passing through it, coming from the electrodes, and plastic deformation of the joint zone under the action of a compressive force.

This type of connection is made according to the following parameters:

• exposure time – 0.2-2.0 seconds;
• high current during operation - more than a thousand amperes;
• low mains voltage – 2-5V;
• the compressive force of the joint is up to several hundred kilograms;
• minimal melting zone allowing spot welding.

Spot welding in industry is used much more often than other types of contact methods (seam, butt). This popularity is associated with a wide range of applications and very favorable parameters of the process itself.

The strength of the bond depends on many factors. Firstly, the area of ​​the point surface, that is, the point (core) itself. Secondly, the strength of the welding current and the time it affects the parts. Thirdly, the compression forces of the parts being welded. This method is used for products of different strengths and thicknesses, for example, from 0.01 to 20-30 millimeters. As a rule, this method is used when joining parts “overlapping”.

Spot Welding Technology

The technology of this type of resistance welding is as follows: the parts that need to be connected to each other are installed in the required position and secured so that they do not move out during welding.

  Next, on both sides, current is supplied to these parts through electrodes, thereby creating a high temperature at the points of contact between the material and the electrodes - the metal begins to melt. In this case, a welding core is formed (similar to a weld pool in other cases).

Its diameter usually ranges from a few millimeters to 1.5-2 centimeters.

Low quality steel may be able to be joined without melting the core, but the joint will still be considered poor quality. Experts recommend that beginners learn and get better at these kinds of preparations.

Let's look at the step-by-step instructions and all stages of the process of joining parts:

• The preparatory stage, which includes three main aspects:
• preparing parts for fusion. In this case, the edges are sanded for adhesion to remove paint residue or oil stains. After this, they must be fixed (for this, a hand vice or clamps are used) for soldering between the electrodes;
• preparing the workplace in accordance with all norms, rules and safety requirements;
• welder training. Before starting work, be sure to wear a special suit and mask to protect your eyes from sparks that can cause burns.
• A direct welding process in which the metal melts under the influence of high temperatures created by electrodes. To do this, the master fixes the part between the electrodes and supplies a current, due to which energy is generated that melts the metal. When the core appears, the current is removed, and the parts are tightly pressed together, the welding core crystallizes (solidifies) and forms a spot weld.

Due to the simplicity of the process, in order to perform precision welding with your own hands, you do not need to be a highly qualified welder. The main thing is to understand the very essence of welding. Heating is carried out due to the pulse generated by the welding current. It melts the metal (pointwise) and forms the so-called welding core. Then the impulse disappears, and the product remains under pressure for a few more seconds. During this time it has time to harden and hold together.

Important: compression occurs at the moment the pulse is applied in order to avoid splashing.

Possible defects

If you decide to weld at home, then you should familiarize yourself with possible defects and their origin in order to avoid such mistakes. Let's look at the most common defects that can happen during spot welding:

• complete or partial lack of penetration may occur due to poor-quality electrodes, which should be replaced with new ones, low current strength, or excessive compression. This oversight can be examined in two ways: during an external inspection or when using a special device for welding control (radiation or ultrasonic;
• cracks during welding can occur due to high current or poorly cleaned products, which, due to the resulting resistance, violates the temperature regime of welding;
• Breaks at the edges during overlap welding most often occur due to the fact that the craftsman places the weld point too close to the edge of the part. That is, it is necessary to calculate so that the overlap is enough for a high-quality connection;
• internal splash is a defect in which the molten metal “crawls out” beyond the core and creates a gap between the workpieces. The main reason for this error is a long pulse or too much current, causing the core to melt excessively. To avoid this, it is important to install the electrodes evenly and control the current strength. To set up the device, it is recommended to try several points on the rough material;
• external splash is a defect in which the molten mass “climbs” out. It occurs as a result of insufficient compression of parts. That is, there is no forging moment that allows joining the workpieces.
• Indentations from the electrode are left due to the small diameter of the electrode or excessive compression. Due to incorrectly installed conductors, the melting zone may increase, causing defects;
• Burn-through is the most common mistake that novice welders make when doing any type of welding. It happens for several reasons: low compression force of the electrodes, contaminated surface of the workpiece or the tip of the conductor;
• core displacement occurs due to incorrectly installed electrodes in relation to the workpiece;
• External and internal cracks are caused by a strong current and a long pulse, or from untimely forging efforts.

Advantages and disadvantages of the method

We figured out how to do spot welding. Now let's look at the main advantages and disadvantages that characterize this type of connection. The advantages of this method include the following factors:

• in comparison with other types and technologies, this method is considered the most “cultural” and hygienic method;
• there is no need to use additional materials in the process - gases, fluxes, and so on;
• no waste and slag;
• welding without gas does not release harmful substances that harm the health of the worker;
• high level of efficiency;
• the ability to use high-performance multi-point machines, assembly and welding flow machines, units and robotic resistance welding complexes;
• high quality connections in a short period of time.

If you follow the rules and regulations for working with spot welding, then you can get a high-quality connection that is neat and reliable. According to statistics, it is much easier for beginners to learn spot welding than to get the hang of laying out different types of seams.

In addition to the advantages, there are also a number of disadvantages that you need to familiarize yourself with:

• it is very difficult to implement reliable bonding when melting different metals, or rather, almost impossible;
• when a strong impulse is applied, metal splashes;
• the complexity of the design of the welding head and the compression mechanism when welding several points simultaneously;
• complication of the design of electrodes and their operation, especially in multi-point welding.

Spot welding machine

The spot welding machine looks like this and includes the following parts:

• current transformer;
• welding clamp;
• turning on and off relay;
• electrode compression mechanism;
• regulator of current supply strength and duration.

Those devices that are intended for home and household use may not have a power regulator. Then the master himself regulates the compression force of the conductors and the time of exposure to the part, based on his experience and relying on his skills.

During operation, it is very important to monitor the condition of the electrodes. If their diameter increases, then the level of heat at the site of impact on the core decreases. The diameter of the electrode must match the diameter of the weld point. Typically, conductors are made of heat-resistant materials - copper, bronze. But under the influence of high temperature, over time they lose their shape, so it is important to change them in a timely manner.

Spot Welding Equipment

Considering the equipment, the following classification can be made:

• by method of movement - mobile, suspended, stationary;
• according to the method of mechanization - manual and automatic;
• according to the location of the electrodes - parallel and opposite each other.

For production purposes it is necessary to use high-quality equipment. Homemade spot welding, which you can make yourself from any electrical appliance, is also perfect for home use. The video below explains in detail how to build a welding machine yourself.

Source: http://home.nov.ru/osobennosti-tochechnoj-svarki/

Spot welding what to cook

Resistance spot welding is one of the most popular welding methods. It allows you to quickly and efficiently join thin metals. In this article we will tell you what spot welding is, what the technology of resistance spot welding is and what defects can result if welding is performed incorrectly.

general information

Spot resistance welding is one of the types of resistance welding. In addition to spot welding, there are also butt, seam and other types of resistance welding, but it is spot welding that is most widespread, so we’ll talk about it in this article. Spot resistance welding is used in many areas: from construction to aircraft manufacturing. For example, when constructing modern airliners, millions of points are located on the hull, forming a strong seam.

The principle of operation is simple: using an electric discharge, the metal is heated at a certain point to its melting point. At the same time, the two parts are pressed against each other with a certain force. Under the influence of temperature and mechanical load, the parts are connected to each other. A very aesthetic and reliable seam is formed.

Multi-spot welding differs from other types of resistance welding in several ways.

First of all, the spot method allows you to significantly reduce welding time (one “point” of the seam is formed in a fraction of a second), while the work uses high values ​​of welding current (more than 1000 amperes), also sets a low voltage (no more than 10 watts), the melting zone small (from a few mm to 1-2 centimeters), a significant mechanical load is used, which can reach up to several hundred kilograms.

In most cases, spot welding is used when thin sheet metal or rod materials need to be overlapped. Spot welding is capable of joining metal with a thickness of 1 millimeter to 3 centimeters, but such indicators are redundant and in practice you will not have to weld parts thicker than 5-7 millimeters. For this reason, spot welding is great for auto body work.

Advantages and disadvantages

The great popularity of do-it-yourself spot welding is due to many advantages. To work, you do not need electrodes, wire, fluxes, and so on. And this saves not only time, but also finances.

Also, the deformation of the metal is insignificant and only in places of “points”; the spot welding machine is very convenient to work with, even a beginner can cope with this task. The seam itself turns out very neat, the workflow is cheaper than analogues, and it can be easily automated.

It is multi-point welding that can perform a huge amount of work, forming up to several hundred weld “points” per minute.

The disadvantages are minor and few. Seams made by spot welding do not have such good tightness as connections made using electrodes, for example. There may also be excess voltage in the area where the “point” is formed; this needs to be monitored.

Welding technology

Resistance spot welding technology consists of three stages, which we will describe in detail. First, the parts are prepared (we will talk about this in more detail later). Then the parts are placed under the tip of the welding machine and are subjected to compression, as a result the surface of the metal is deformed and a small depression is formed - a dot.

Then an electric current is applied, the metal heats up, melts and a so-called liquid core is formed at the “point”. Gradually, the current penetrates through the entire core, and it increases in size. The "spot" becomes part of the weld.

And thanks to the preliminary deformation of the parts, the metal does not spatter during melting and the seam is neat and does not need to be cleaned.

Then the current supply is stopped, the metal cools and crystallizes. The liquid core becomes molten. But there is a nuance: when cooled, the core may decrease slightly in size and residual stress is formed.

It is undesirable and can be dealt with using different methods. We recommend that before completing the welding process, press the parts harder against each other in order to properly heat them and make the seam more uniform.

Otherwise, do-it-yourself spot welding is very simple and does not require highly qualified welders.

Metal preparation

Do-it-yourself spot welding, like any other welding method, requires preliminary preparation of the metal. To do this, you need to clean the areas of the future seam from dirt, corrosion and oxide film (if any).

If this is not done, power will be lost during welding and the degree of wear on the welding machine will increase. To clean the metal, use the sandblasting method, an angle grinder with a wire brush or sandpaper.

You can also etch a small part in a special solution.

Pay special attention to the preparation of aluminum and its alloys. There is a thick oxide film on the surface of this metal, which prevents complete heating and welding of the part. So remove it thoroughly before starting work. This is especially important if particularly important structures are to be welded.

Welding equipment

To do your own spot welding, you will need equipment. You can use a device operating on direct or alternating current, a capacitor-type device, or equipment operating at a low frequency.

All these types differ in the power electrical circuit and the shape of the welding current. Also, each type has its own pros and cons, do not listen to those who tell you about the superiority of this or that equipment.

In our practice, we use a device that runs on alternating current; this is the most common option. You can choose another type of equipment.

Pay attention to modern TIG LORCH welding, it is very technologically advanced.

Source: https://ravon-r2.ru/tochechnaja-svarka-chem-varjat/

Do-it-yourself resistance welding

Resistance welding is the joining of two parts into one whole, which occurs by heating at the welding site with a powerful short-term flow of electricity.

In this case, the parts are simultaneously compressed at the heating site until plastic deformation occurs. In industry, this type of connection is used quite widely, but recently craftsmen are increasingly using it in home workshops.

Moreover, this method can be used to weld not only metals that are identical to each other, but also metals that are different in composition.

Welding aluminum using resistance spot welding

This method is good for repairing tools, including garden tools, and for repairing larger parts, such as a car body. Resistance welding is especially successfully used when joining aluminum, which has its own welding characteristics.

It is also good to cook mesh for fencing.

When resistance welding, there is less risk of burning through a thin sheet of metal. At the junction of the parts at the point of their contact, the metal melts under the influence of current.

Compression of this place promotes the transition of metal from one part to another. Then the current supply is stopped and the metal crystallizes, forming a single whole.

Companies that produce such equipment are very sensitive to increased demand, which is why you can now find household welding appliances on sale. They cost from 12,000 rubles and not everyone can afford them.

While specialists have learned to make such devices themselves.

What do-it-yourself resistance welding from a microwave looks like?

The transformer is removed from the microwave oven; it is better if it has a power higher than 700 W. In the transformer we use the secondary winding, removing it so that the primary remains intact. As a result, we need to have a current of at least 500 A. To do this, we strengthen the primary winding by winding an insulated wire around it in the gap, the thickness of which is about 1 cm. You get 2-3 turns.

We wind the winding with a thick wire

If we had a transformer power of about 1000 W, such a modification would be enough to weld plates 3 mm thick.

The current at the time of welding can increase to 1500 A. To work in an apartment, you don’t need more, and there will be voltage surges. If you have a private house, then the power can be increased.

To increase power, two transformers can be installed in parallel, then the welding current doubles. It is necessary to pay attention to the fact that there is no connection in antiphase. To do this, make sure that the direction of the turns on the secondary winding is the same.

Double transformer connection diagram.

Here are diagrams No. 1 and No. 2 for resistance welding, made with your own hands from two microwave ovens.

It is only necessary that the secondary windings of the transformer have the same number of turns.

You can also assemble a time relay for resistance welding with your own hands, guided, for example, by the following diagram.

Do-it-yourself time relay for contact welding, the simplest circuit

You can assemble a relay using a very simple scheme

Even a beginner can assemble this circuit.

Next in the question of how to do resistance welding with your own hands is the question of electrodes. Using copper wire for this, you need to pay attention that its thickness must correspond to the diameter of the wire that comes from the transformer, and the length of the wires must be of a minimum length.

Example of electrode installation

As an option, you can use a tip from a used soldering iron. During the production process, the electrodes will need to be sharpened and then completely replaced. Compression pliers for resistance welding, which can be made with your own hands or used from other equipment, may have a different design at the welding site, but the pressure for a household appliance will be sufficient up to 30 kg. Moreover, the longer the lever, the less effort needs to be applied to it.

Pliers for compressing the welding area

As you can see, making equipment for resistance and spot welding with your own hands is not at all difficult.

Making your own resistance welding on capacitors

It makes sense to assemble capacitor contact welding with your own hands if the work involves welding non-ferrous metals or welding a small part to a larger one, which is important for home craftsmen. Such a device has high voltage during operation.

Capacitors are batteries assembled in a certain way. The current passage time is very short, literally 0.1 seconds, but an arc is formed at a temperature sufficient to melt the metal. The welding site is compressed by the device, resulting in an excellent weld.

By type they are either transformer or transformerless.

We assemble the device according to the scheme from capacitors

Compared to a device made from a microwave, such a device does not consume much electricity. In addition, it does not require forced cooling. The operating speed with the dense welding current generated is quite decent.

The seams are neat, which is very important when welding thin or non-ferrous metal.

We manufacture the device as follows. Let's take the simplest scheme, for example the following.

The most basic scheme of resistance welding on capacitors for DIY production

We pass the primary winding through a rectifier, diode bridge and connect it directly to the voltage source.

A signal passes from a thyristor (a semiconductor device), which has a start button, to the bridge panel. The capacitor is connected through a thyristor to the rectifier bridge and to the primary winding.

To charge it, we turn on a special additional circuit that has a diode bridge and a transformer.

The capacitance of the capacitor, which is the source of the pulse, should be in the range from 1000 to 2000 μF, and the primary winding should be made of wire, a little less than 1 cm, approximately 0.8 cm, we wrap it in 300 turns. The core is made from a Sh40 transformer measuring 7 cm.

To make the secondary winding, we use a copper busbar; 10 windings will be enough.

Using capacitors, the choice of which is limited only by power - 10V, as well as voltage 15V.

Then we make the clamp and electrodes, as indicated in the previous article, only in sizes appropriate for this device.

Option for manufacturing clamping pliers for resistance welding

Do-it-yourself resistance welding device on capacitors is ready

Making a device for resistance welding from an inverter with your own hands

You can make contact welding yourself using a welding inverter. At the same time, we obtain low power consumption at the output with sufficient basic performance indicators.

A diagram according to which you can make a resistance welding machine from a converter with your own hands

It becomes possible to weld thin sheets at a fairly low price of the machine, which ultimately results in a simple design that is not difficult to work with.

There are also disadvantages.

The whole design is not entirely reliable, since it is made without calculations. Therefore, it cannot be used as professional equipment, and besides, the adjustment range is small.

The case itself is weak and has no protection from shock, moisture, etc.

We assemble the device, for example, according to the diagram below. You can change it slightly, but the principle of connecting the power section, switch, control circuit, and protection. The inverter uses a transformer and a power supply. You need a control system and the switch itself

A welding transformer and a thyristor starter are connected in the first winding.

The secondary winding is not needed, it is removed, there is no need to stand on ceremony with it, you can use a hammer and chisel.

Next, the primary winding is reinforced by winding the second layer with wire 2-3 cm thick. It must be insulated. This can be either special insulating paper or special varnish. As in the first case, the correct direction of the windings is important. We check everything using an ordinary voltmeter.

We check the current strength, it should not be higher than 2000 A.

We choose electrodes slightly smaller than the thickness of the cable. In composition, it can be copper, a copper alloy with the addition of chromium, or with copper tips.

Connect electrodes for resistance welding with your own hands using either soldering or using bolts and nuts. Soldering is used for low-power equipment. When connecting electrodes to a cable with bolts, it is advisable to use copper bolts.

Example of electrode connection

The manufacture of such a device is always justified and advisable.

Source: http://themechanic.ru/kontaktnaja-svarka-svoimi-rukami/