Contact spot welding.

Electrodes designed for contact welding, are made from metal rods whose diameter ranges from 12 to 40 mm. Their working surface is either flat or spherical. To connect the workpieces together into a rather complex structure, they use electrodes that have an offset surface - the so-called shoe products. Such products are secured using a special shank having a cone of 1:10 or 1:5.

You can also find electrodes on sale that have a cylindrical surface, thanks to which they will be fixed to work in special structures with a conical thread. In addition to them, products are produced with a replaceable working part - it is installed on the cone using a standard union nut or simply pressed.

Electrodes for resistance welding of relief type in their shape will directly depend on the method of connection and the final shape of the product. In most cases, the size of the working surface of a given electrode does not play a special role. This is due to the fact that the contact area and the selected welding current directly depend on what shape the workpieces will have at the points of contact.

There are also electrodes for connecting elements with very complex topography. Suture equipment uses products that are a disk with a flat work surface. Moreover, these products may even have asymmetrical bevels. Such discs are fixed to the equipment by veneering or pressing.

Inside the electrodes themselves there are certain cavities through which coolant will circulate during the welding process. Electrodes for resistance spot welding are solid, so in this case the so-called external cooling is used.

To ensure that the electrode material is consumed to a minimum, the roller is made replaceable. The electrode itself is made from a special alloy based on a metal such as copper. The result is a product that has virtually no resistance to electric current, is an excellent heat conductor, and is resistant to even quite high temperatures. In addition, when hot, this electrode will retain its original hardness, and interaction with the workpiece metal will be minimal.

Types of resistance welding equipment

The main feature of this technology is the connection of workpieces over the entire area. Optimal heating is achieved through reflow using a welding machine. However, in some cases they resort to heating due to the resistance of the part to the passage of electric current.

Resistance spot welding can occur either with metal melting or without this technological feature of the process. Resistance welding can be used to connect metal elements whose cross-section is in the range from 1 to 19 mm, and in most cases resistance welding is used, since the consumption of electrode material will be significantly lower, and the final connection is much more durable. This welding is used when performing fairly precise work, for example, in the process of producing rails to create a railway track.

Features of resistance spot welding

This technology is perfect for connecting metal elements together, and the connection is carried out both at one and at several points on these workpieces. It is very popular not only in industry (in particular, it is often used in agriculture, during the construction of aircraft, road transport and so on), but also in everyday life.

The principle of operation of this method is quite simple: electric current, when passing through parts that are in direct contact with each other, very much heats up their edges. The heating is so strong that the metal begins to quickly melt, and the workpieces are immediately compressed with considerable force. As a result of this, a welded joint is formed.

Equipment designed to use this technology is designed to connect sheets, rods and other metal products together. The key advantages of this method are the following:

• Absence of a welded joint in the traditional sense;
• There is no need to use filler material, gas or flux;
• The equipment is very easy to use;
• The speed of work is quite high.

The main and only drawback of this method is that the seam is completely unsealed.

What are electrodes for resistance welding made of?

The material from which the electrodes will be made is selected depending on the requirements for the operating conditions of the product. It is worth noting that the electrodes must be able to withstand compression, temperature changes, exposure to high temperatures, and stress that will be generated inside the electrode itself, which is under serious load.

In order for the products to be of the highest quality, it is necessary that the electrode retains the original shape of its working surface, which will be in direct contact with the parts to be connected. Melting of this consumable material accelerates its wear.

Usually copper is taken as the main element, and other elements are added to it - magnesium, cadmium, silver, boron, and so on. The result is a material that excellently resists even very severe physical stress. Electrodes with tungsten or molybdenum coating practically do not wear out during operation, which is why they have recently gained the greatest popularity. However, they cannot be used for welding products made of aluminum and other materials with a soft structure.

The design of the electrodes must have a shape and dimensions that provide access to the working part of the electrode to the place where parts are welded, be adapted for convenient and reliable installation on the machine, and have high durability of the working surface.

The simplest to manufacture and operate are straight electrodes, made in accordance with GOST 14111-69 from various copper electrode alloys, depending on the grade of metal of the parts being welded.

Sometimes, for example, when welding dissimilar metals or parts with a large difference in thickness, in order to obtain high-quality connections, the electrodes must have a fairly low electrical thermal conductivity (30...40% of copper). If the entire electrode is made from such metal, it will heat up intensely from the welding current due to its high electrical resistance. In such cases, the base of the electrode is made of copper alloy, and working part from a metal with the properties necessary for the normal formation of joints. Working part 3 can be replaceable (Fig. 1, a) and secured with a nut 2 on base 1. The use of electrodes of this design is convenient, as it allows you to install the desired working part when changing the thickness and grade of the metal of the parts being welded. The disadvantages of an electrode with a replaceable part are the possibility of using it only when welding parts with good approaches and insufficiently intensive cooling. Therefore, such electrodes should not be used in heavy welding conditions at high speeds.

Rice. 1 . Electrodes with a working part made of another metal

The working part of the electrodes is also made in the form of a soldered (Fig. 1, b) or pressed-in tip (Fig. 1, c). The tips are made of tungsten, molybdenum or their compositions with copper. When pressing a tungsten tip, it is necessary to grind its cylindrical surface in order to ensure reliable contact with the base of the electrode. When welding parts made of stainless steel with a thickness of 0.8...1.5 mm, the diameter of the tungsten insert 3 (Fig. 1, c) is 4...7 mm, the depth of the pressed part is 10...12 mm, and the protruding part is 1.5...2 mm. With a longer protruding part, overheating and a decrease in the durability of the electrode are observed. The working surface of the insert can be flat or spherical.

When designing electrodes, special attention should be paid to the shape and dimensions of the seating part. The most common is a conical landing part, the length of which should be at least. Electrodes with a shortened cone should only be used when welding using low forces and currents. In addition to the conical fit, electrodes are sometimes fastened to threads using a union nut. This connection of electrodes can be recommended in. multi-point machines, when it is important to have the same initial distance between the electrodes, or in clamps. When using shaped electrode holders, electrodes with a cylindrical seat are also used (see Fig. 8, d).

When spot welding parts with complex contours and poor approaches to the joint, a wide variety of shaped electrodes are used, which have a more complex design than straight ones, are less convenient to use and, as a rule, have reduced durability. Therefore, it is advisable to use shaped electrodes when welding is generally impossible without them. The dimensions and shape of the shaped electrodes depend on the size and configuration of the parts, as well as the design of the electrode holders and consoles of the welding machine (Fig. 2).

Rice. 2. Various types of shaped electrodes

During operation, shaped electrodes usually experience a significant bending moment from off-axis application of force, which must be taken into account when selecting or designing electrodes. The bending moment and the usually small cross-section of the cantilever part create significant elastic deformations. In this regard, mutual displacement of the working surfaces of the electrodes is inevitable, especially if one electrode is straight and the other is shaped. Therefore, for shaped electrodes, the spherical shape of the working surface is preferable. In the case of shaped electrodes that experience large bending moments, deformation of the conical seating part and the electrode holder socket is possible. The maximum permissible bending moments for shaped electrodes made of Br.NBT bronze and electrode holders made of heat-treated bronze Br.Kh are, according to experimental data, for electrode cones with a diameter of 16, 20, 25 mm, respectively, 750, 1500 and 3200 kg× cm. If the conical part of the shaped electrode experiences a moment greater than permissible, then the maximum diameter of the cone should be increased.

When designing complex spatial shaped electrodes, it is recommended to first make a model of them from plasticine, wood or easily machined metal. This allows you to establish the most rational dimensions and shape of the shaped electrode and avoid alterations when manufacturing it directly from metal.

In Fig. 3 shows some examples of welding assemblies in places with limited access. Welding of the profile with the shell is performed using a lower electrode with an offset working surface (Fig. 3, a).

Rice. 3. Examples of using shaped electrodes

An example of using an upper electrode with oblique sharpening and a lower, shaped one is shown in Fig. 3, b. The angle of deviation of the electrode holder from the vertical axis should not be more than 30°, otherwise the conical hole of the electrode holder will be deformed. If it is impossible to install the upper electrode with a slope, then it can also be shaped. The shaped electrode is bent in two planes to reach a hard-to-reach welding spot (Fig. 3, c-e). If the machine does not have or has limited horizontal movement of the consoles for welding the parts shown in Fig. 3, e, two shaped electrodes with equal projections are used.

Sometimes shaped electrodes perceive very large bending moments. To avoid deformation of the conical seating part, the shaped electrode is additionally secured to the outer surface of the electrode holder using a clamp and a screw (Fig. 4, a). The strength of shaped electrodes with a long reach increases significantly if they are made of composite (reinforced) electrodes. For this purpose, the main part of the electrode is made of steel, and the current-carrying part is made of a copper alloy (Fig. 4, b). The connection of current-carrying parts to each other can be made using soldering, and with a steel console - using screws. A design option is possible when a shaped electrode made of a copper alloy is supported (reinforced) with steel elements (bars), which should not form a closed ring around the electrode, since currents will be induced in it, increasing the heating of the electrode. It is advisable to fasten shaped electrodes that experience large moments in the form of an elongated cylindrical part for installation in a machine instead of an electrode holder (see Fig. 4, b).

Rice. 4. Electrodes that perceive a large bending moment:

a - with reinforcement for the outer surface of the electrode holder;

b - reinforced electrode: 1 - steel console; 2 - electrode; 3 - current supply

In most cases, spot welding uses internal cooling of the electrodes. However, if welding is performed with electrodes of small cross-section or with high heating, and the material being welded is not subject to corrosion, external cooling is used in the tongs. The supply of cooling water is carried out either by special tubes or through holes in the working part of the electrode itself. Great difficulties arise when cooling shaped electrodes, since it is not always possible to supply water directly to the working part due to the small cross-section of the cantilever part of the electrode. Sometimes cooling is performed using thin copper tubes, soldered to the side surfaces of the cantilever part of the shaped electrode of a sufficiently large size. Considering that shaped electrodes are always cooled worse than straight electrodes, it is often necessary to significantly reduce the welding rate, preventing overheating of the working part of the shaped electrode and reducing durability.

When using pliers for welding in hard-to-reach places, as well as the need to frequently replace electrodes, use the electrode mounting shown in Fig. 5. This fastening provides good electrical contact, convenient regulation of electrode extension, good stability against lateral displacement, and quick and easy removal of electrodes. However, due to the lack of internal cooling in such electrodes, they are used when welding at low currents (up to 5...6 kA) and at a low speed.

Rice. 5. Methods for attaching electrodes

For ease of operation, electrodes with several working parts are used. These electrodes can be adjustable or rotary (Fig. 6) and significantly simplify and speed up the installation of electrodes (aligning working surfaces).

Rice. 6. Multi-position adjustable (a) and surface (b) electrodes:

1 - electrode holder; 2 - electrode

The electrodes are installed in electrode holders, which are fixed to the cantilever parts of the welding machine, transmitting compression force and current. In table For reference, the dimensions of straight electrode holders of the main types of spot welding machines are given. Electrode holders must be made of sufficiently strong copper alloys with relatively high electrical conductivity. Most often, electrode holders are made of Br.Kh bronze, which must be heat-treated to obtain the required hardness (HB not less than 110). In the case of welding steels, when low currents (5...10 kA) are used, it is advisable to make electrode holders from Br.NBT bronze or silicon-nickel bronze. These metals ensure long-term preservation of the dimensions of the conical mounting hole of the electrode holder.

Table. Dimensions of electrode holders for point machines in mm

The most common are straight electrode holders (Fig. 7). Inside the cavity of the electrode holder there is a tube for supplying water, the cross-section of which should be sufficient for intensive cooling of the electrode. With a tube wall thickness of 0.5...0.8 mm, its outer diameter should be 0.7...0.75 of the diameter of the electrode hole. In the case of frequent changes of electrodes, it is advisable to use electrode holders with ejectors (Fig. 7, b). The electrode is pushed out of the seat by hitting the striker 5 with a wooden hammer, which is connected to a stainless steel tube - ejector 1. The ejector and striker are returned to their original lower position by a spring 2. It is important that the end of the ejector hitting the end of the electrode does not have damage on its surface, otherwise the seating part of the electrode will quickly fail, jamming when it is removed from the electrode holder. It is convenient for operation to make the end of the electrode holder 1 in the form of a replaceable threaded bushing 2, in which the electrode 3 is installed (Fig. 7, c). This design makes it possible to make sleeve 2 from a more resistant metal and replace it when worn and install an electrode of a different diameter, and also to easily remove the electrode when jammed by knocking it out with a steel drift from inside the sleeve.

Rice. 7. Straight electrode holders:

a – normal;

b – with ejector;

c – with replaceable sleeve

If shaped electrodes are more often used when welding parts that have small dimensions of the elements being connected, then for larger sizes it is advisable to use special shaped electrode holders and simple electrodes. Shaped electrode holders can be composite and provide installation of electrodes at different angles to the vertical axis (Fig. 8, A). The advantage of such an electrode holder is the easy adjustment of the electrode extension. In some cases, the shaped electrode can be replaced with electrode holders shown in Fig. 8, b. Also of interest is the electrode holder, the tilt of which can be easily adjusted (Fig. 8, c). The design of an electrode holder bent at an angle of 90° is shown in Fig. 30, g, it allows you to attach electrodes with a cylindrical seat. A special screw clamp ensures quick fastening and removal of the electrodes. In Fig. Figure 9 shows various examples of spot welding using shaped electrode holders.

Rice. 8. Special electrode holders

Rice. 9. Examples of the use of various electrode holders

When spot welding large-sized components such as panels, it is advisable to use a four-electrode rotating head (Fig. 10). The use of such heads allows you to quadruple the operating time of the electrodes before the next stripping, without removing the panel to be welded from the working space of the machine. To do this, after each pair of electrodes is contaminated, electrode holder 1 is rotated 90° and secured with stopper 4. Swivel head It also makes it possible to install electrodes with different shapes of the working surface for welding a unit with parts changing, for example, stepwise, in thickness, as well as to provide mechanization of stripping the electrodes with special devices. The rotating head can be used when spot welding parts with large differences in thickness and is installed on the side of the thin part. It is known that in this case the working surface of the electrode in contact with a thin part quickly wears out and is replaced by turning the head with a new one. It is convenient to use a roller as an electrode on the side of a thick part.

Rice. 10. Rotating electrode head:

1 – rotary electrode holder; 2 – body; 3 – electrode; 4 – stopper

When spot welding, the axes of the electrodes must be perpendicular to the surfaces of the parts being welded. To do this, welding of parts that have slopes (smoothly varying thickness), or are manufactured using overhead machines, in the presence of large-sized components, is performed using a self-aligning rotary electrode with a spherical support (Fig. 11, a). To prevent water leakage, the electrode has a seal in the form of a rubber ring.

Rice. 11. Self-aligning electrodes and heads:

a - rotary electrode with a flat working surface;

b - head for two-point welding: 1 - body; 2 - axis;

c - plate electrode for welding mesh: 1, 7 - machine consoles; 2-fork; 3 - flexible tires; 4-swinging electrode; 5 - welded mesh; 6 - bottom electrode

On conventional spot machines, welding of steel parts of relatively small thickness can be performed at two points at once using a two-electrode head (Fig. 11, b). Uniform distribution of forces on both electrodes is achieved by rotating the housing 1 relative to axis 2 under the action of the compression force of the machine.

To weld a mesh of steel wire with a diameter of 3...5 mm, plate electrodes can be used (Fig. 11, c). The upper electrode 4 swings on an axis to evenly distribute forces between the connections. The current supply for the purpose of its uniformity is carried out by flexible busbars 3; fork 2 and the swing axis are isolated from the electrode. When electrodes are up to 150 mm long, they can be non-oscillating.

Rice. 12. Sliding wedge electrodes inserts

When welding panels consisting of two skins and stiffeners, there must be an electrically conductive insert inside that absorbs the force of the machine electrodes. The design of the insert must ensure its tight fit to the inner surface of the parts being welded without a gap, in order to avoid deep dents on the outer surfaces of the parts and possible burns. For this purpose, a sliding insert shown in Fig. 12. The movement of the wedge 2 relative to the stationary wedge 4, ensuring their compression to the welded parts 3, is synchronized with the operation of the machine. When electrodes 1 and 5 are compressed and welding occurs, air from the pneumatic drive system of the machine enters the right cavity of the cylinder 8 mounted on the front wall of the machine and moves the wedge 2 through the rod 7, increasing the distance between the working surfaces of the wedges. When raising electrode 1, the air leaves the right one and begins to enter the left cavity of the cylinder 8, reducing the distance between the surfaces of the wedges, which allows the panel to be welded to be moved relative to the electrodes of the machine. The wedge insert is cooled by air that enters through tube 6. The use of such an insert allows you to weld parts with an internal distance between them of up to 10 mm.

Electrodes for resistance welding are designed to supply current to the elements, compress them and remove the generated heat. This part is one of the most important in the equipment, since the ability to process the unit depends on its shape. The stability of the electrode determines the level of welding quality and the duration of continuous operation. Electrodes can be shaped or straight. The production of direct type elements is regulated in the GOST 14111–77 standard.

Shaped parts are characterized by the fact that their axis is offset relative to the cone (seating surface). They are used for welding assemblies and elements of complex shapes that are difficult to reach.

Design Features

Electrodes intended for resistance welding include a cylindrical part, a working part and a landing part. In internal cavity element there is a special channel, which is designed to supply water that cools the electric holder.

The working part has a spherical or flat surface. Its diameter is selected in accordance with the thickness of the products being processed and the material used. The strength of the electrode is ensured by the middle part.

The landing part must have a conical shape so that the part is securely fixed in the electrical holder. It must be processed with a cleanliness of at least class 7.

Custom part properties are affected by distance from the very bottom of the cooling channel to the working edge: service life, stability, etc. If this distance is small, then the element will be cooled much more efficiently, but it will be able to withstand a much smaller number of regrinds.

Inserts based on molybdenum and tungsten are placed inside copper parts. Products made in this way are used for welding anodized or galvanized steel.

Production materials

The stability of electrodes is the ability of elements not to lose their shape and size, as well as to resist the transfer of material from welded elements and electrodes. This indicator is determined by the material and design of the welding electrode, as well as the operating conditions and mode. Wear of parts depends on the characteristics of the working tool (angle of the working surface, diameter, material, etc.). Melting, excessive heating, oxidation during operation of the electrode in a corrosive and/or humid environment, displacement or misalignment, compression deformation and other factors significantly increase the wear of working elements.

The tool material must be selected in accordance with the following rules:

1. Its level of electrical conductivity should be comparable to pure copper;
2. Effective thermal conductivity;
3. High degree of mechanical resistance;
4. Easy to cut or high pressure;
5. Resistance to cyclic heating.

Compared to 100% copper, its alloys are more resistant to mechanical loads, which is why copper alloys are used for such products. Alloying a product with zinc, beryllium, chromium, magnesium, zirconium does not reduce electrical conductivity, but significantly increases strength, and silicon, iron and nickel increase its hardness.

Choice

In the process of selecting suitable electrodes for spot welding, special attention should be paid to the size and shape of the working element of the product. You should also take into account the characteristics of the material being processed, its thickness, the shape of the welding units and the welding mode.

Resistance welding tools have different working surfaces:

1. Flat;
2. Spherical.

Products with a spherical working surface are not particularly sensitive to bevels, which is why they are often used on suspended and radial installations, as well as for shaped electrodes with a deflection. Manufacturers from the Russian Federation recommend this particular type of electrode for processing light alloys, as they help prevent the appearance of undercuts and dents during spot welding. However, this problem can also be prevented if you use flat electrodes with an enlarged end. And electrodes equipped with hinges can even replace spherical-type electrodes, but they are recommended for welding metal sheets whose thickness does not exceed one and a half millimeters.

Dimensions of the working element tools are selected in accordance with the type and thickness of the materials being processed. The results of a study conducted by experts from the French company ARO showed that the required diameter can be calculated using the following formula:

del = 3 mm + 2t, where “t” is the thickness of the sheets to be welded.

It is more difficult to calculate the required tool diameter when the thickness of the sheets is different, when welding materials different types and welding of a whole “package” of elements. It is clear that to work with parts of different thicknesses, the diameter of the product must be selected relative to the thinnest metal sheet.

When welding a set of elements, the diameter should be selected based on the thickness of the external elements. For welding materials of various types, the metal alloy with the minimum electrical resistivity has the least penetration. In this case, you should use a device made of material with increased thermal conductivity.

RX cutters manufactured by SINTERLEGHE according to patent EP2193003 allow you to:

Sharpen electrodes of various tip shapes using one cutter

Divide the chips of removed material between the upper and lower electrodes

Reduce consumables costs due to high strength and hardness of blade material

You can use SINTERLEGHE developments to work with other manufacturers of sharpening machines (see picture)

As a result of testing to confirm the patent EP2193003 for RX cutters, the following results were achieved:

Reducing the cost of purchasing electrodes by 50%

Reducing the amount of welding spatter

Improving the quality and appearance of welding points

Reducing the number of line stops to replace electrodes

Reducing the number of cutter models used

Reduced cutting costs

Reduced electricity consumption

DIMENSIONS OF ELECTRODES AFTER SHARPENING

The RX SINTERLEGHE cutter (patent EP 2193003) can be used when using sharpening machines from other manufacturers:

Germany: Lutz - Brauer - AEG - Wedo

Italy: Sinterleghe - Gem - Mi-Ba

France: AMDP - Exrod

USA: Semtorq, Stillwater

Japan: Kyokuton - Obara

Used everywhere. They are used for welding aluminum, stainless steel, non-ferrous metals and many other materials. A combination of tungsten electrode + shielding gas is a good choice for those who want to achieve high-quality welded joints.

But any welder will tell you that for a decent result, it is not enough to know only welding technology. You also need to remember little tricks that will simplify and even improve the result of your work. One of these tricks is sharpening the electrode. In this article we will briefly explain why it is needed and how you can sharpen a tungsten electrode yourself.

Tungsten is one of the most refractory metals used for the manufacture of electrodes. The melting point of tungsten is more than 3000 degrees Celsius. In normal welding conditions such temperatures are not used. Therefore, tungsten electrodes are called non-consumable. When used, they practically do not change in size.

But despite this, tungsten electrodes can still become shorter. During the welding process (for example, when igniting an arc or when forming a seam), the electrode can grind off the metal surface. In most cases it's not that bad. But sometimes a blunt electrode causes lack of penetration.

How to solve this problem? Very simple: sharpen it. The sharpened tungsten electrode regularly performs its function, forming high-quality, durable seams.

How to sharpen an electrode

Sharpening a tungsten electrode can be done in a variety of ways. This can be an abrasive wheel, chemical sharpening, sharpening with a special paste, or mechanical sharpening. The latter is performed using special devices. They can be either portable or stationary.

The sharpening shape can be spherical or conical. Spherical shape is more suitable for welding DC, and conical - for welding alternating current. Some welders note that they do not notice much difference when welding with electrodes with different shapes sharpening. But our experience has shown that there are still differences. And if you weld professionally, the difference will be obvious.

The optimal length of the sharpened part can be calculated using the formula Ø*2 . That is, if the diameter of the electrode is 3 mm, then the length of the sharpened part should be 6 mm. And so on by analogy with any other diameter. After sharpening, dull the end of the electrode slightly by tapping it on a hard surface.

Another important parameter is the sharpening angle of the electrode. It will depend on how much welding current you use.

So, when welding at a low value of welding current, an angle of 10-20 degrees will be sufficient for sharpening. The optimal angle is 20 degrees.

A sharpening angle of 20-40 degrees is a good option when welding using average values ​​of welding current.

If you use large currents, the sharpening angle can be from 40 to 120 degrees. But we do not recommend sharpening the rod more than 90 degrees. Otherwise, the arc will burn unstably and it will be difficult for you to form a seam.