What is spot welding

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 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/

Types of spot welding and areas of its application

Spot welding is a type of resistance welding, during which parts are to be joined in separate places (points), limited in size by heating the electrodes. They transmit compressive force and conduct electric current. The position of the dots depends on how the electrodes are positioned in the spot welding machine being used. It is possible to weld one or two or several points at a time.

By means of resistance spot welding, products from non-ferrous or ferrous metals, both of the same type and of dissimilar ones, are traditionally welded.

These can be blanks of different or equal thicknesses, machined or forged products, rolled or pressed sheets.

Spot welding is the most effective, at an affordable price, for welding components of agricultural machinery, automobile and tractor elements, railway cars, microelectronics parts, refrigerators and household items.

Features of spot welding

When welding using this method, the products overlap. They are then clamped with a certain force between a pair of copper electrodes connected to a transformer and conducting electric current to the welding site. When the transformer for spot welding is turned on, with the help of a short-term pulsed current, the workpieces are heated with the appearance of a molten section or core of the point at the place of their contract.

The surfaces of the products being welded, in contact with the copper of the electrodes, do not heat up as quickly as their internal layers. Therefore, heating continues until the outer layers reach a state of plasticity with the formation of a volumetric point of the metal and a melt state in the inner layers.

After turning off the current, it is necessary to maintain the gain for a certain time, which is necessary for the normal crystallization of materials subjected to melting and the prevention of such shrinkage defects as loose cracks.

After turning off the supply of currents and removing the pressure, you can see the result of the action of the spot welding machine - the resulting cast point of the welded joint.

Based on the location of the electrodes relative to the products to be connected, such welding can be performed on one side or be double-sided. In the latter case, two or more workpieces are clamped by the electrodes of the spot welding unit.

The one-sided welding method involves the distribution of current between the lower and upper parts. In this case, part of the current conducted through the lower workpiece produces heating. To increase this current, a special copper spacer is used.

One-sided welding allows you to connect products at two points at once at the same time.

How to prepare the elements?

The preparation of workpieces for processing by a resistance spot welding machine occupies an important place, since the stability of operations and the quality of the resulting joints depend on it. The product for welding is straightened, cleaned, adjusted, tacked or assembled in a special device.

A significant thickness of oxide film is removed using special rollers with helical notches, flame heating, shot blasting, shot blasting or vacuum-fractional processing, and capping the welding zone.

Workpieces made of low-carbon steel must be degreased with gasoline, acetone or other oil solvents, followed by etching, brushes, abrasive and grinding devices. The treated surfaces are also passivated.

The workpieces can be cleaned only at the overlap or completely. After mechanical cleaning procedures, oxides and dust with abrasive particles should be removed from them. Products coated with metal are usually not subjected to stripping; they are tacked by conventional welding. Small-sized components and workpieces can be welded without tacks by firmly fixing them in spot welding pliers. On large products, tacking by arc welding and subsequent cutting out of tack areas is possible.

Spot Welding Equipment

The most important parameters of the impact mode of spot welding machines are the time of current flow with its density, as well as the compression force. The choice of these characteristics is determined by taking into account the characteristics of the equipment used using technology maps, tables of approximate modes and experimental work. This welding is carried out in both soft and hard modes.

The first is characterized by a relatively low current density and a significant duration of the welding cycle at low pressure. It is most often used for welding low-alloy or carbon steel. The harsh modes of a spot welding machine are characterized by a high current density, significant pressure, and a short welding cycle.

It is suitable for welding work with copper, aluminum alloys and corrosion-resistant steels.

Spot Welding Technology

It is better to weld joints of dissimilar materials using soft conditions. In this case, it is easier to obtain a reliable connection due to the ability to adjust the parameters. Increasing heating with decreasing heat transfer into the material contributes to the symmetry of the core location. This is achieved due to the smaller thermal conductivity and diameter of the electrodes.

Spot welding schemes provide for the implementation of the entire process in four stages. In the first, the parts to be connected are clamped between the electrodes for spot welding. The second stage involves heating the joint with the current turned on to the melting temperature with the formation of a cast point core.

At the third and fourth stages, the compression force increases with the current turned on to form structures at the weld point, followed by the release of the electrodes from the force. Using this welding method, stamp-welded joints are produced. It is also indispensable in joining individual stamped products with spot welds.

Both of these significantly increase work productivity and simplify the processes of producing entire welding units.

The need to remove damaged parts during repair work necessitates the need for drilling spot welds. It is used whenever you need to carefully drill out the point connections between a faulty part and the main product. One way to remove welds is by punching and drilling with a thin metal drill.

Using a special drill for spot welding eliminates the need for these operations. In this case, not only is there no need for punching and pre-drilling, but also there are no through holes left on the second sheet of the metal joint from remote weld points.

The principle and technology of such drilling is convenient to use in bodywork and any other work when it is necessary to replace an element attached with bolts, self-tapping screws or factory spot welding.

Source: https://promplace.ru/svarka-metallov-staty/tochechnaya-svarka-1531.htm

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/

How to make a spot welding machine: resistance welding technology and assembly diagrams

Spot welding is a subtype of resistance welding. In this type of welding, metal elements are fastened in one or more places.

This surface welding method has high production technology and a variety of applications in various industrial fields, and can be used in the production of electronic devices, automobiles, ships, aircraft and other industrial production fields.

When using this type of welding, a very high strength of connection between structural parts is achieved. The degree of strength at the junction is determined by the efforts to squeeze the surfaces of the fastened elements and the physical force of the device's electric current.

In modern production, different versions of these devices are used, from stationary machines to easily transportable devices. As an example, the picture shows a photo of a manual spot welding machine.

Hardware Features

This type of welding is based on the method of heating a metal part (plate) with an electric current pulse. To ensure the welding effect, the parts (elements) are strongly pressed together.

At the point of greatest compression, parts are spot welded by passing an electric charge between the electrodes of the device. At the point of contact, a molten point of metal no larger than twelve mm in size is formed.

Spot welding methods

This type of welding is conventionally divided into two methods: soft and hard.

Soft mode. In this mode, when welding, the parts are gradually heated using a low current. It takes about three seconds to weld metal surfaces in this mode.

In this mode, the power consumption of the machine (device) is reduced. The mode is usually used when welding metals with hardening properties.

Hard mode. It is determined by a short duration of high electric current and powerful squeezing of the welded elements at the welding point. The density of consumed electric current in this mode reaches 300A per 1mm2. The welding process takes up to one and a half seconds.

The main disadvantage of this method is the large demand for electricity (machines) and large overloads of the industrial network. The advantage is minimal time for welding surfaces.

This mode is usually used when welding surfaces with good thermal conductivity, high-alloy steel or bonding surfaces of different thicknesses.

Welding options

Types of spot welding are determined by the number of joint pixels formed at a time. The following types are used in production: single-point, two-point and multi-point types.

The single-point type is used when joining several sheets, while the quality of welding decreases with each layer of sheets (parts). The two-point type of welding is used when connecting parts with wide surfaces.

The multi-point type is used to fasten various stamped structures. It can be bilateral or unilateral, it all depends on the placement of the electrodes in relation to the nodes being fastened.

This type of welding can also differ in the cycles of electrical pulses. The cyclicity depends on the thickness of the parts being welded.

For a metal surface up to five millimeters thick, one pulse of electric current is sufficient, but for large thicknesses, several short-term electrical pulses are necessary. When welding metal elements of great thickness and hardness, cycles with increased compression are used.

Welding methods

There are several methods for spot welding:

Spot - welding of elements occurs in one or many places. It is used in instrument making, the automotive industry, and the construction of sea, river and aircraft vessels.

Provides welding of steel sheets up to twenty millimeters thick.

Relief method - structural elements are welded in one or several prepared places. The difference between this method and the previous one is due to the shape of the fastened elements at the welding site.

Seam method - the welded elements are fastened with a series of welding seams. A seam can consist of individual weld pixels or overlapping ones. Used for the manufacture of various tanks requiring a high degree of tightness.

Docking - elements are welded along the adjacent contact area under high temperature. They are used in laying pipelines and making anchor chains for ships.

Design Features

Greater spot welding capabilities are in demand in industrial production. For their implementation, production machines and hand-held portable units have been created.

When solving problems of welding metal elements, you need to remember that this process depends on the metal from which the product is made and its density.

Requirements for technology for performing this type of work:

• ensuring low voltage, no more than 10W;
• ensuring a short transit time of the electrical pulse at the welding point;
• providing high electric current at the welding site;
• ensuring a minimum melt area in places where the structure is fastened;
• ensuring high quality weld strength.

A modern spot welding machine can have different designs. In modern production, transformer or capacitor spot welding machines are used.

Transformer machines must carry out high-temperature heating of the surfaces being welded. The performance of welding equipment in everyday life can be ensured by an electric current of up to 5 kiloamperes, and in industrial equipment from three hundred to five hundred kiloamperes.

Industrial machines use powerful transformers. The main disadvantage of such devices is the lack of a uniform load, which leads to large overloads of the industrial network and frequent breakdowns.

Capacitor machines load electrical networks measuredly. The use of capacitors in machine tools allows you to avoid sudden overloads of the industrial electrical network.

Manual capacitor welding machines have minimal dimensions and are widely used to solve everyday problems. Their advantages are small dimensions and operability when connected to a household power supply.

Advantages:

• there is no need to purchase welding materials;
• ease of manufacture;
• ease of operation;
• cleanliness and neatness of seams or weld points;
• compliance with environmental requirements;
• min power consumption;
• high performance.

We make the welding ourselves

This type of welding tool is not a cheap tool. It is more practical to make a spot welding machine with your own hands.

The main element of such a device is a transformer (used in various household appliances). To provide the necessary electric current for this type of work, it is necessary to rewind its windings. During the creation of the 1st winding, intermediate terminals are also prepared. The wire on the windings must be impregnated with varnish and wrapped with special paper.

The components of the device are selected according to the parameters of the transformer. Its design depends on the parts (surfaces) to be worked on. Electrical elements must be designed with a high degree of reliability.

Pincers can be of two types: stationary and remote. Stationary ones are simpler to manufacture; they are firmly fastened together and reliably insulated. Remote ones are more suitable for use when performing various types of work. They can be easily installed and removed. It is convenient to bring them to the place of direct welding.

When using external pliers, it is necessary to ensure their reliable connection to the device itself and their waterproofing. To make electrodes, you can use copper rods, bronze or an old soldering iron tip.

The electrical diagram for connecting such a device can be easily found on the Internet.

Safety precautions

To ensure their own safety, the worker must know and comply with the safety instructions for spot welding:

• To prevent electric shock, ground the unit;
• Before starting work, be sure to check its serviceability;
• use personal protective equipment for hands, eyes and body;
• exclude high voltage supply to the device controls
• use only wires of the specified cross-section in the device;
• carry out work in a room with well-equipped ventilation or use special masks to protect the respiratory system.
• locks and toggle switches (buttons) for turning on or off must be in working order, clearly visible and easily accessible;
• During work, the area of ​​the clamping mechanisms must be covered with a shield.

Compliance with these safety measures will ensure the health of the employee and others and will allow the required amount of work to be completed accurately and on time.

Photo instructions on how to make a spot welding machine

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How resistance spot welding machines work

One of the fusion methods is resistance spot welding. Its essence lies in tightly connecting two parts at a certain point and passing electric current through the point of contact.

Spot resistance welding machines are in demand in many industries. For everyday use, they learned to make them with their own hands, using transformers or a system of capacitors.

Process phases

Three phases can be distinguished in the spot welding process. In the first phase, compression of the workpieces occurs, which leads to plastic deformation at the point of contact. For this purpose, the resistance welding machine is equipped with special pliers or other similar devices.

In the second phase, current is supplied to the contact area, which causes the metal to melt at the connection point and form a molten core. While the current passes, the core expands to its maximum. The compression of the joined products causes the appearance of a dense belt around the liquid core, which prevents the spreading of the molten metal.

In the third phase, the welding current is turned off, the metal cools and crystallizes. To relieve stress during cooling, the clamping force is maintained for some time.

The requirements for welded joints are determined by the state standard - GOST 15878-79. About. What electrodes can be used in a resistance spot welding machine are described in GOST 14111-90. They are made from copper or bronze alloyed with chromium, cadmium, zirconium.

Types of equipment

When resistance spot welding, the machine can produce current of different types and frequencies. Based on these distinctive features, welding equipment is divided into four classes:

• resistance spot welding on alternating current;
• low-frequency resistance welding;
• capacitor type devices;
• DC welding.

There are multi-point resistance welding machines for welding meshes in production. In such devices, welding occurs simultaneously at several points. Any equipment has its advantages, but single-point AC devices have become the most popular.

AC operation

A resistance welding machine operating on alternating current is a transformer with two electrodes in the secondary winding. Copper is used as a material for resistance spot welding electrodes. Parts are placed between the electrodes and pressed against each other using a special device.

In the primary winding there is a thyristor module, through which the supply voltage of 220 V or 380 V is supplied to the winding. By applying a control signal to the thyristor, you can obtain the required current duration for resistance spot welding. By changing the opening angle of the thyristor, you can adjust the shape of the signal that arrives at the secondary winding.

In the case of using several primary windings, a set of transformation ratios can be obtained by combining their connection. As a result, several levels of voltage and current are obtained in the secondary winding. This allows the resistance spot welding machine to operate in different modes.

To control the equipment, there is an additional unit that has a relay, a control panel and a controller circuit.

Equipment on capacitors

A resistance spot welding machine may consist of a capacitor charging unit, a large battery of capacitors, a control unit and electrodes with a workpiece clamping mechanism.

The principle of contact welding lies in the initial rather long accumulation of electrical energy on the plates of capacitors and its instant release when creating an artificial short circuit through the point of contact.

The ability to accumulate charge in a capacitive battery allows the use of equipment of lower power compared to other welding machines.

Due to the constant battery capacity, a normalized energy release per welding pulse is obtained, which allows you to obtain a stable result regardless of changes in the mains voltage and other network characteristics.

Capacitor resistance welding lasts for milliseconds, resulting in a powerful release of energy in a small contact area. This allows it to be used when welding alloys with high thermal conductivity such as copper, as well as metals with different thermal characteristics.

Capacitor resistance spot welding machines with a rigid characteristic and fast discharge are widely used in radio electronics and instrument making.

When calculating the required energy for welding a particular joint, you can use the formula:

W = C*U2/2,

where C is the capacity in farads, W is the energy in watts; U is the charging voltage in volts. By including an active variable resistance in the charging circuit, you can regulate the amount of charging current, charging time and power consumption.

Where is the method used?

A feature of resistance spot welding is a brief impact on the products being joined (from a few milliseconds to several seconds), a welding current of several thousand amperes and a voltage of 1 to 2-3 volts. In this case, a force at the welding point is required from tens to hundreds of kilograms. A small contact area leads to a small area of ​​metal melting.

Thanks to these features, spot welding is used when welding metals with a thickness of a few microns to 20-30 mm. These capabilities have ensured its use in radio electronics, instrument manufacturing, the aviation and automotive industries, construction and many other industries.

It is impossible to imagine auto repair shops without resistance spot welding machines. They are indispensable when removing dents. All cars and airplanes are created using resistance welding. Almost all lithium batteries in laptops are connected using single-sided resistance spot welding.

Pros and cons of technology

The technology has become widespread due to the simplicity and ease of use of welding equipment and high productivity. The device can provide several hundred welds per minute with low energy consumption, and does not emit any harmful substances into the atmosphere.

The technology is easy to automate. Welding does not require welding wire, additives or fluxes. The connection is strong and without residual deformations.

The only drawback is the leaky connection of the products. The device operates intermittently, making connections at individual points, so we are not talking about tightness.

Possible defects

In spot welding, the strength of the joint is such that fractures occur in the base metal, since the weld spots are thick. Welding time and clamping force are critical. If you calculate them incorrectly, the device will cook with defects.

There are three main types of defects:

• deviations of the cast zone from the optimum, its displacement from the point of contact;
• incomplete penetration at the point of contact:
• change in the physical and chemical properties of the metal at the welding point.

The most dangerous thing is the lack of a cast area. Thermal bonding occurs, in which the connection can withstand minor loads. Under variable loads and temperature changes, the connection breaks.

Strength is compromised by high pressure on the electrodes of the resistance welding machine, which causes dents. Strength is also weakened by metal splashes.

Causes of defects

Lack of penetration is often caused by low current or worn-out contact pad of the electrodes. The low current may be due to the spacing between the weld spots being too small, causing excessive shunting. Defects are determined by visual inspection and the use of special equipment.

External cracks appear from too high a pulse current of the device, weak compression, contamination of the welding area, which changes the parameters of the welding circuit. The defect is detected by visual inspection using a magnifying glass.

In case of deep dents from the electrode, it is necessary to deal with its contact part. Perhaps the reason is that the radius of curvature of the contact pad is too small and the clamping force is too large. The defect is determined visually.

The reason that during internal splashing metal flows into the area between the workpieces may be the excess of the welding current of the machine, the welding time and the lack of compression. The defect is determined by special instruments and can also be detected visually due to loose connections of parts.

External splash occurs when the duration and current strength are exceeded, the pressure is low and the electrodes are misaligned. This can be seen with the naked eye.

Internal cracks arise from a combination of reasons such as excessive current, duration of exposure, contaminated surface, insufficient compression and lack of forging influence during the crystallization process. Defects are detected using special equipment.

Core displacement occurs due to improper installation of the electrodes of the contact welding machine and their contamination. The cause of burn-through is insufficient pressure of the connected products and their contamination.

Defects are eliminated by repeating the welding process. If it is impossible to weld, for example, reheating the product is unacceptable, then it is better to drill out the defective area and install a rivet.

Source: https://svaring.com/welding/apparaty/apparat-kontaktnoj-tochechnoj-svarki

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

Spot welding

Kashtanovy lane 8/14 51100 Magdalinovka village

Nikolaenko Dmitrij

Spot welding Spot welding ( 1 vote, average: 5 out of 5)

Spot welding is a process of joining metals by heating, passing current through it and deforming the molten zone under pressure. In this case, heating occurs only at a given point. This type of connection belongs to the category of pressure welding. The first mention of this method of joining metals dates back to 1877, it was proposed by the Russian inventor Benardos N.N.

Spot welding is also a type of resistance welding. With this method, two electrodes located on two opposite sides conduct an electric current with a force of 1-200 kA. Joining metals in this way is very popular. Approximately 30% of welded joints occur this way and this percentage is currently increasing.

Spot welding finds its application in mechanical engineering, aviation industry, and instrument making.

Resistance spot welding technology

The technology of resistance spot welding is determined by the strength of the connection, the size and structure of the weld spot. This mainly depends on the following factors:

• — size of the surface of the welding electrode;
• — the strength of the supplied current;
• — flow time through the workpiece;
• — state of the workpiece surface and the magnitude of the compression force.

Resistance spot welding technology has different modes of joining metals.

1. Soft mode.

The welding time is slightly longer. Moderate currents smoothly heat the metal surface with a moderate current, not exceeding 100 A/mm2 on the working surface. Current flow is usually from 0.5 sec. up to 3 sec. During this mode, power consumption is much less than during hard mode. Welding machines are cheaper because they do not require a large network load. The welding zone is not subjected to strong hardening, and therefore steels prone to hardening are welded using this mode.

2. Hard mode.

With this mode, the welding time is much less than with soft. This is facilitated by greater use of current. Its density is 120-300 A/mm2 when welding steel. The pressure of the welding electrodes is 3-8 kg/mm2 and the current flow is usually 0.1-1.5 sec.

Welding machines for this mode experience a significant network load, and therefore electricity consumption is much higher. A significant advantage of this mode is increased productivity and reduced welding time. In this way, high-alloy steels, parts of unequal thickness, and workpieces of different names are connected.

Metals with high thermal conductivity, such as aluminum and copper, as well as their alloys, are excellent for welding.

Thus, resistance spot welding technology makes it possible to connect different metals with sufficient strength and speed of welding work.

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Source: https://metallsmaster.ru/tochechnaya-svarka/

Resistance spot welding: what it is, where it is used, general characteristics, pros and cons

The most common type of resistance welding is spot welding (SW).

With its help, sheet metal of small thicknesses is quickly and efficiently joined.

In this article we will describe what TS is, the methods and shortcomings of such work if performed incorrectly.

Introduction

TS is one of the types of contact welding; there are also butt, seam and their derivatives. However, it is spot welding that deserves widespread use; it will be discussed further.

Spot welding is applicable everywhere. For example, when assembling modern ships, the hull has an innumerable number of points that form a reliable seam.

Its principle is to heat and weld the product by superimposing elements. Next, the electrodes are pressed against the latter and a large current is passed through them.

This means that an electrical discharge at a point heats the metal to its melting point. This way the details merge together. As a result, the seam has an acceptable appearance and high reliability.

Spot welding has its differences from other resistance welding methods. Firstly, this welding method significantly saves welding time (it takes a small fraction of a second to create one point). To work with the vehicle:

1. They use a fairly high current of 1000A;
2. Set low voltage to 10 W;
3. The melting halo is from a couple of millimeters to one or two centimeters;
4. A mechanical load is applied, reaching 100 kg.

Spot welding is often used in tasks involving connecting rod elements or sheets of thin metal. This type of welding is characterized by the combination of both millimeter and centimeter metals, but not more than 3 cm.

In practice, you have to tie workpieces no thicker than 5-7mm. TC is widely used for body construction.

Advantages and disadvantages

The popularity of cooking yourself using the spot method is due to the advantages of the TC. It does not require electrodes, wire, etc. This allows you to increase your time for other work and saves your money.

The following positive features include:

• minor deformation;
• ease of use of the welding unit.

Even a person doing TS for the first time can do everything. The result will please you - a neat and strong seam, a cheap workflow, and almost completely automated.

And the possible amount of work will be staggering, because in just one minute you can create several hundred weld points.

There are a small number of disadvantages, namely: low tightness compared to seams created using electrodes.

And one more drawback is the need to constantly monitor the voltage in the area of ​​the welding point.

TC process

Let us now move on to the spot welding process, which consists of only 3 stages. The first, preparatory (we will consider separately later in the article).

The second, weldable: after the parts are prepared, they are placed under the tip of the welding machine, then compressed. As a result of metal deformation, we obtain a depression in the form of a point.

We apply current, the part heats up, then melts, and a liquid center forms in the recess. Over time, the current passes through the entire center and increases the size of the point.

This point forms the place to be welded. Since the metal was previously deformed, the process does not create metal splashes, and the seam ultimately looks natural without stripping.

The third stage is the final one. We stop the current supply, the heating of the metal stops, and the point crystallizes. The liquid center is now part of the part.

Please note that as it cools, the center slightly reduces its size and thereby creates residual stress.

It needs to be removed; there are several ways to do this. We recommend pressing the elements harder before finishing welding, then the seam becomes more uniform. Do-it-yourself TS is simple and can be done by a person without high qualifications.

Preparatory stage

Various methods of welding metal, incl. and TS, first provide for the preparation of the metal. First, clean the welding area:

• from pollution;
• from corrosion;
• from the oxide film.

Without cleaning, power is lost and leads to more wear on the welding unit. We recommend using the following cleaning methods:

• sandblasting;
• grinder with a metal brush;
• sandpaper;
• special solutions (for small elements).

Particular attention should be paid to the preparation of aluminum and its derivatives. There is a dense oxide film on the surface. It serves as a barrier to high-quality heating and welding of parts. Therefore, it is imperative to remove the bar before starting welding.

The importance lies in the fact that a structure created without removing the film will not have sufficient strength.

Welding units

For spot welding, you must first of all have a welding machine. You can operate equipment with both direct and alternating current; capacitor type or at low frequency.

All types of welding machines differ in the form of the current being welded and the power electrical circuit. They have their positive and negative sides. There is no specific machine that will suit every welder.

We recommend operating the device with alternating current; according to statistics, this is the more commonly used option. Depending on the required work, choose the type of units.

Vehicle defects

If you have the knowledge and experience of the vehicle, the result will be of good quality. Considering the simplicity of working with it, mastering the basics is quite easy.

But if you allow mistakes or work to be done by a person who does not have at least a little experience, marriage is possible. It is formed on the workpieces themselves, and not in the welding place.

There are several types of defects. Eg:

• the center is ultimately huge;
• the center is ultimately very small;
• the center is shifted to the right or left of the joint.

Also, when the interval between the points is large, the seam is not continuous. And if the parameters on the unit are incorrectly selected, the parts are severely deformed. The worst defect is not a cooked center, but the absence of one.

The part can withstand small loads, but after a while it will still break. Such a defect is not immediately noticeable, but it can appear, for example, due to temperature changes (warm workshop - cold street).

You can make mistakes and this will not cause a breakdown, but this is not luck. Corrosion is already forming in that very place of an unchecked center or other deformation, although it is not yet visible at first glance. It's all a matter of time before the structure completely collapses.

To perform the TS correctly, we recommend:

• place the welding point in the middle of the joint;
• control the size of the cast center;
• make sure there is no slag or cracks;
• don't put too much tension.

More practice and you'll get the hang of it. Only experience will help you understand the intricacies of spot welding.

Let's summarize

Spot welding is convenient and easy to use. Does not involve the use of wire or flux. There is a wide selection of welding machines.

Both manual and automatic work also have different budgets. On the Internet you can find a detailed video about creating a vehicle with your own hands.

To construct it you will not need any special knowledge; about 15 minutes of your time will be enough and the unit will be ready. Good luck!

Source: https://prosvarku.info/tehnika-svarki/vse-o-tochechnoj-svarke

Description of the spot welding process

Spot welding is considered one of the variants of resistance welding. It is very common and has its own characteristics, as well as scope of application. A separate advantage is the ability to use it at home. Spot welding requires fulfillment of all mandatory working conditions, which will eliminate possible defects and negative consequences.

Scope of spot welding

Spot welding is used in various fields. It is used in the following areas:

• light and heavy industry;
• mechanical engineering;
• space technology;
• construction;
• instrument making;
• electronics;
• jewelry work with precious metals.

Wherever the connection of small parts is required, the point mating technique is used. Any process involving mini parts or miniature elements requires a careful approach, which can be achieved using spot welding.

The liquid dot technique is mainly used for soldering parts with a thickness ranging from 0.05 to 6 mm. The range varies from 10-30 microns.

For welding, parts are made of sheet aluminum, stainless steel, and other elements, including forged ones.

The choice of spot welding method, which can be either single or multi-point, is determined by the type of metal, the nature of the parts and various factors in the production process.

At home, as in the production process, different methods are used for different quality of parts and points, as well as depending on the current supply.

Spot welding device

For spot welding, a standard scheme is used. The device itself requires the use of mains power or a power supply with a voltage of 220 v. The basis will be a transformer that reduces the voltage. Optimally, this is 10-12 V. The current strength varies from 300 to 500 A. Such parameters allow you to do everyday work.

The principle is to change the voltage level and redistribute it into several storage devices - capacitors. The design also includes a pair of diodes and a special diode bridge. The process is regulated by a time relay or its equivalent. With its help, current is transmitted to welding equipment.

Cooling is done by water cooling or air cooler.

If power amplification is required, additional transformers are used.

If the car needs welding, then to repair the body you will need to do the following:

• we assemble a circuit or use a purchased mechanism;
• connect to the network via a transformer;
• mark on the body where soldering is required;
• We use a welding gun and carry out the procedure;
• disconnect from the network and let the fresh seam cool.

Typically, such repair work is performed semi-automatically. Each type of device is used in certain conditions.

For full operation, the device will need to be assembled as shown in the drawings.

In the latter case, a homemade spotter is shown.

Spot welding devices can have different prices. For example, professional equipment costs more than several hundred thousand rubles. The price of manual options varies within several thousand. These options include manual “Caliber”.

A homemade device can be used at home, but is not used for professional work, since it is difficult to meet the basic requirements, including GOST 15878-79.

Advantages and disadvantages

Spot welding has several advantages in the form of pros, but there are also disadvantages. Main advantages:

• ability to work with thin materials. Gas or laser welding is unable to accurately work with very small parts, but spot welding gives good results;
• high speed of the process. When the equipment is stationary, sheets or other elements can be moved very quickly and welded at the required points;
• the current strength is sufficient for a reliable and durable connection that can withstand significant loads;
• the internal connection does not allow for large and unsightly seams, which gives an aesthetic appearance;
• the ability to use when using various metals, including non-ferrous and expensive ones;
• The absence of filler material allows for significant cost savings. The copper electrode has a long service life. It is for this reason that the technology is common in large enterprises;
• there is no need to study for a long time. The method is simple and accessible to anyone.

Among the shortcomings, several points also stand out. The first is the importance of the structure with which the work is done. All basic elements must be present, including the control board.

It is problematic to connect thick products using spot contact welding. This is another disadvantage that can be solved by increasing the power, but this consumes more electricity.

Among the most common shortcomings are defects during operation due to poor quality of the metal. That is why it is necessary to follow a step-by-step action plan, which will prevent disruptions in work.

How to Spot Weld

Welding work always begins with preparing the equipment. Each version of the welding device has its own characteristics. If you have purchased equipment, then you should follow the operating instructions.

Additionally, the designation and marking will tell you. For example, MTs have a direct stroke of the electrode, and MTP is a suspended version. Any device must be completely ready for operation and not require repair.

This affects the quality of the process, so the condition of the equipment must be monitored.

Next comes the preparatory stage, which includes the following actions:

• preparation of the workplace and equipment;
• preparing parts and cleaning them from additional deposits and other things that could interfere with the fusion process;
• Next, we fix the parts in the required position. To do this, you can use a vice or similar machine, as well as tongs;
• The welder wears special clothing and a mask, which should protect against possible burns.

After preparation, the device is turned on and the process of welding the two elements is carried out. The metal melts under the influence of electrodes and the temperature created by them. After the appearance of the core, the current stops flowing, and the parts are compressed together. After compression, the core hardens and forms a weld point. The impulse force solders the material.

This procedure can be performed by a welder of any level. The main thing is not to miss the moment of soldering and keep the parts under pressure for a few seconds.

DIY spot welding

Before assembling a homemade spot welding machine, you will need to select a type. You can assemble both a manual model from available materials and a large stationary model with your own hands. First of all, you will need to choose the power of the device and its purpose. For those who work at home or in their garage, an inverter assembly is suitable. The inverter model also has a certain set of spare parts that will be required during assembly.

When choosing, you will also need to take into account that there is one-sided and two-sided welding. Before assembling the device, all basic parameters must be determined and the necessary drawing must be created. Welding can be capacitor based, supercapacitor based and pneumatic.

The procedure for creating homemade equipment is as follows:

• We make the choice and all the features of the procedure we require and the location of the equipment;
• after choosing the type of welding, we select the best option that suits the requested main parts;
• if necessary, we purchase the required elements;
• we assemble equipment based on a drawing that we make in advance;
• We check it at work.

It would be optimal to work with high-quality material, which will show the presence of defects in the device.

Each homemade device is unique, but has basic parts that cannot be replaced. Such elements include a transformer. You can use spare parts from other welding machines or similar ones, but it will be important to make sure that all parts are in good condition. If connected correctly and all requirements are met, the welder will receive a home-made device that will allow him to carry out work at home.

The spot type of welding process refers to resistance welding. It can be varied and has several types. Various devices can be used for the procedure, since the technology itself is very simple. No lengthy preparation is required to use the equipment and weld parts using liquid dots. An additional advantage is the absence of expensive elements, which allows the method to be used on a wide scale.

Source: https://svarkaspec.ru/svarka/vidy-svarki/tochechnaya-svarka.html