Electrodes used for spot welding. Electrode material for contact welding

Electrodes intended for contact welding are made from metal rods, the diameter of which 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 working 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 fairly 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 extremely popular not only in industry (in particular, it is often used in agriculture, in the construction of aircraft, automobile 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.

Most of the metal products that surround us are made using resistance welding. There are different types of welding, but contact welding allows you to create fairly strong and aesthetically beautiful seams. Since the metal is not welded using the traditional method, this process requires resistance welding electrodes.

Resistance welding is only possible for welding two metal parts superimposed on one another; they cannot be joined end-to-end using this method. At the moment when both parts are clamped by the conductive elements of the welding machine, an electric current is briefly supplied, which melts the parts directly at the point of compression. This is mainly possible due to current resistance.

Electrode designs

Electrodes are also used to work with electric arc welding, but they are fundamentally different from the conductive elements for contact welding, and are not suitable for this type of work. Since at the time of welding the parts are compressed by the contact parts of the welding machine, electrodes for resistance welding are able to conduct electric current, withstand compression loads and remove heat.

The diameter of the electrodes determines how firmly and efficiently the parts will be welded. Their diameter should be 2 times thicker than the welded joint. According to state standards, they range in diameter from 10 to 40 mm.

The metal being welded determines the shape of the electrode used. These elements, which have a flat working surface, are used for welding conventional steels. The spherical shape is ideal for joining copper, aluminum, high carbon and alloy steels.

The spherical shape is most resistant to combustion. Due to their shape, they are able to make a larger number of welds before sharpening. In addition, the use of this form allows you to weld any metal. At the same time, if you weld aluminum or magnesium with a flat surface, dents will form.

The electrode seat is often cone-shaped or threaded. This design avoids current losses and effectively compresses parts. The landing cone can be short, but they are used with low forces and low currents. If a threaded fastener is used, it is often through a union nut. Threaded fastening is especially important in special multi-point machines, since the same gap between the claws is required.

To perform welding deep into the part, electrodes of a curved configuration are used. There is a variety of curved shapes, so if you are constantly working in such conditions, it is necessary to have a selection of different shapes. However, they are inconvenient to use, and they have lower durability compared to straight ones, so they are used last.

Since the pressure on the shaped electrode is not along its axis, it is subject to bending during heating, and this must be kept in mind when choosing its shape. In addition, at such moments, it is possible that the working surface of the curved electrode may shift in relation to the flat one. Therefore, in such situations, a spherical working surface is usually used. Non-axial load also affects the seat of the electrode holder. Therefore, if there is excessive load, you need to use electrodes with an increased cone diameter.

When welding deep into a part, you can use a straight electrode if you tilt it vertically. However, the angle of inclination should be no more than 30°, since with a greater degree of inclination, deformation of the electrode holder occurs. In such situations, two curved conductive elements are used.

Using a clamp at the point where the shaped electrode is attached allows you to reduce the load on the cone and extend the service life of the welding machine seat. When developing a shaped electrode, you must first make a drawing, then make a test model from plasticine or wood, and only then begin its manufacture.

In industrial welding, cooling of the contact part is used. Often this cooling occurs through an internal channel, but if the electrode is of small diameter or increased heating occurs, then the coolant is supplied externally. However, external cooling is allowed provided that the parts being welded are not susceptible to corrosion.

The most difficult thing to cool is the shaped electrode due to its design. To cool it, thin copper tubes are used, which are located on the side parts. However, even under these conditions, it does not cool well enough, so it cannot cook at the same pace as a straight electrode. Otherwise, it overheats and its service life is reduced.

Welding in the depths of a small part is carried out with shaped electrodes, and with large parts it is preferable to use shaped holders. The advantage of this method is the ability to adjust the length of the electrode.

During contact welding, the axis of the two electrodes should be 90° relative to the surface of the part. Therefore, when large-sized parts with a slope are welded, rotary, self-aligning holders are used, and welding is performed with a spherical working surface.

Steel mesh with a diameter of up to 5 mm is welded with a plate electrode. Uniform load distribution is achieved by free rotation of the upper conductive contact around its axis.

Although the spherical shape of the working surface is the most stable of the other shapes, it still loses its original shape due to thermal and power loads. If the working surface of the contact increases by 20% of the original size, then it is considered unusable and must be sharpened. Sharpening of resistance welding electrodes is carried out in accordance with GOST 14111.

Electrode materials for resistance welding

One of the decisive factors in the quality of a weld is tensile strength. This is determined by the temperature of the weld point and depends on the thermophysical properties of the conductor material.

Copper in its pure form is ineffective because it is a very ductile metal and does not have the necessary elasticity to recover to its geometric shape between welding cycles. In addition, the cost of the material is relatively high, and with such properties, the electrodes would require regular replacement, which would make the process more expensive.

The use of hardened copper was also not successful, since a decrease in the recrystallization temperature leads to the fact that with each subsequent weld point the wear of the working surface will increase. In turn, alloys of copper with a number of other metals turned out to be effective. For example, cadmium, beryllium, magnesium and zinc added hardness to the alloy during heating. At the same time, iron, nickel, chromium and silicon allow it to withstand frequent heat loads and maintain the pace of work.

The electrical conductivity of copper is 0.0172 Ohm*mm 2 /m. The lower this indicator, the more suitable it is as an electrode material for resistance welding.

If you need to weld elements from different metals or parts of different thicknesses, then the electrical thermal conductivity of the electrode should be up to 40% of this property of pure copper. However, if the entire conductor is made of such an alloy, it will heat up quite quickly, since it has high resistance.

By using composite construction technology, significant cost savings can be achieved. In such designs, the materials used in the base are selected with a high electrical conductivity, and the outer or replaceable part is made of heat and wear-resistant alloys. For example, metal-ceramic alloys consisting of 44% copper and 56% tungsten. The electrical conductivity of such an alloy is 60% of the electrical conductivity of copper, which allows heating the weld point with minimal effort.

Depending on the working conditions and assigned tasks, alloys are divided into:

1. Difficult conditions. Electrodes operating at temperatures up to 500 o C are made of bronze, chromium and zirconium alloys. For welding stainless steel, bronze alloys alloyed with titanium and beryllium are used.
2. Average load. Welding of carbon, copper and aluminum parts is usually carried out using electrodes made of alloys, in which the grade of copper for the electrodes is capable of operating at temperatures up to 300 o C.
3. Lightly loaded. Alloys, which include cadmium, chromium and silicon-nickel bronze, are capable of operating at temperatures up to 200 o C

Electrodes for spot welding

The spot welding process explains itself from its name. Accordingly, a mini welding seam is one point, the size of which is determined by the diameter of the working surface of the electrode.

Electrodes for resistance spot welding are rods made of alloys based on copper. The diameter of the working surface is determined by GOST 14111-90, and is manufactured in the range from 10-40 mm. Electrodes for spot welding are carefully selected because they have different properties. They are made with both spherical and flat working surfaces.

Electrodes for spot welding with your own hands can theoretically be made, but you need to be sure that the alloy meets the stated requirements. In addition, you need to maintain all sizes, which is not so easy at home. Therefore, when purchasing factory-made conductive elements, you can count on high-quality welding work.

Spot welding has a lot of advantages, including an aesthetic weld spot, ease of operation of the welding machine and high productivity. There is also one drawback, namely the lack of a sealed weld seam.

Electrodes for seam welding

One of the varieties of resistance welding is seam welding. However, electrodes for seam welding are also an alloy of metals, only in the form of a roller.

Rollers for seam welding are of the following types:

• without bevel;
• with a bevel on one side;
• with bevel on both sides.

The configuration of the part being welded determines what shape of roller should be used. In hard-to-reach places, it is unacceptable to use a roller with a bevel on both sides. In this case, a roller without bevels or with a bevel on one side is suitable. In turn, a roller with a bevel on both sides presses the parts more efficiently and cools faster.

The use of roller welding helps to achieve hermetically sealed welds, which allows them to be used in the manufacture of containers and tanks.

So, resistance welding allows you to produce high-tech seams, but in order to achieve a high-quality result, you need to carefully follow the values ​​​​indicated in the tables. Which welding option you choose, spot or seam welding, depends on your needs.

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 a copper alloy, and the working part is made of metal with the properties necessary for the normal formation of connections. 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-d). 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 a shaped electrode of a fairly 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, the electrode holder 1 is rotated 90° and secured with a stopper 4. The rotating head also makes it possible to install electrodes with different shapes of the working surface for welding an assembly 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.

Spot welding, thanks to the advent of compact hand-held machines such as BlueWeldPlus, is becoming popular not only for industrial applications, but also in everyday life. The weak point of this technology is electrodes for resistance welding: their low durability in many cases scares off the consumer.

Reasons for the fragility of resistance electric welding electrodes

The resistance welding process consists of the following stages:

1. Preliminary preparation of the surface of the parts to be joined - it must not be easily cleaned of contaminants and oxides, but also very smooth in order to eliminate unevenness in the resulting electric field voltage.
2. Manual or mechanical clamping of welded products - with increasing clamping force, the intensity of diffusion and the mechanical strength of the weld increase.
3. Local melting of metals in the pressing zone by the heat of an electric current, resulting in the formation of a welding joint. Pressing the electrodes at this stage prevents the formation of welding spatter.
4. Switching off the current and gradually cooling the weld.

Thus, the material of electrodes for contact welding undergoes not only significant thermal stresses, but also mechanical loads. Therefore, a number of requirements are placed on it - high electrical conductivity, high thermal resistance (including from constant temperature fluctuations), increased compressive strength, low heat capacity coefficient. A limited number of metals have this complex of properties. First of all, it is copper and alloys based on it, however, they do not always meet production requirements.

Due to the constant increase in the energy characteristics of products, many brands direct consumers to use only “their” branded electrodes, which is not always observed. As a result, the quality of welds produced using this technology decreases, and confidence in the resistance electric welding process itself is undermined.

These problems can be overcome in two ways: by improving the types and designs of welding electrodes for spot welding, and by developing new materials used for the manufacture of such electrodes. For private users, the price of the issue is also important.

Electrode materials

According to GOST 2601, the criterion for the quality of a finished seam is its tensile or shear strength. It depends on the intensity of thermal power in the electrical discharge zone, and therefore is associated primarily with the thermophysical characteristics of the electrode material.

The use of copper electrodes is ineffective for two reasons. Firstly, copper, being a highly plastic metal, does not have sufficient elasticity to completely restore the geometric shape of the electrodes during the period between operating cycles. Secondly, copper is very scarce, and frequent replacement of electrodes also causes high financial costs.

Attempts to use harder, strengthened copper are not successful: for cold-worked material, in parallel with an increase in hardness, the recrystallization temperature decreases, therefore, with each working cycle, the wear of the working end of the electrode for contact welding will increase. Therefore, copper alloys with the addition of a number of other metals have found practical use. In particular, the introduction of cadmium, beryllium, magnesium, zinc and aluminum into a copper alloy changes the thermal conductivity slightly, but improves the hardness when heated. The resistance of the electrode to dynamic thermal loads is increased by iron, nickel, chromium and silicon.

When selecting the optimal material for welding electrodes for resistance welding, they are guided by the specific electrical conductivity of the alloy. The less it differs (downward) from the electrical conductivity of pure copper - 0.0172 Ohm mm 2 /m, the better.

The most effective resistance to wear and deformation is shown by alloys containing cadmium (0.9...1.2%), magnesium (0.1...0.9%) and boron (0.02...0.03%).

The choice of material for spot welding electrodes also depends on the specific tasks of the process. Three groups can be distinguished:

1. Electrodes designed for resistance welding under harsh conditions (continuous alternation of cycles, surface temperatures up to 450…500ºС). They are made from bronzes containing chromium and zirconium (Br.Kh, Br.KhTsr 0.6-0.05. This group also includes nickel-silicon bronzes (Br.KN1-4), as well as bronzes additionally alloyed with titanium and beryllium (Br.NTB), used for spot welding of stainless and heat-resistant steels and alloys.
2. Electrodes used at contact temperatures on the surface up to 250…300ºС (welding of conventional carbon and low-alloy steels, copper and aluminum products). They are made from copper alloys of the MS and MK grades.
3. Electrodes for relatively light operating conditions (surface temperatures up to 120…200ºС). The materials used are cadmium bronze Br.Kd1, chromium bronze Br.X08, silicon-nickel bronze Br.NK, etc. Such electrodes can also be used for roller contact electric welding.

It should be noted that in descending order of electrical conductivity (relative to pure copper), these materials are arranged in the following sequence: Br.HTsr 0.6-0.05→MS→MK→Br.Kh→Br.Kh08→Br.NTB→Br .NK →Br.Kd1→Br.KN1-4. In particular, heating an electrode made of Br.KhTsr 0.6-0.05 bronze to the required temperature will occur approximately twice as fast as one made from Br.KN1-4 bronze.

Electrode designs

The least resistant part of the electrode is its spherical working part. The electrode is rejected if the increase in end dimensions exceeds 20% of the original dimensions. The design of the electrodes is determined by the configuration of the surface being welded. The following versions of the instrument are distinguished:

1. With a cylindrical working part and a conical landing part.
2. With conical landing and working parts, and a transition cylindrical section.
3. With a spherical working end.
4. With a beveled working end.

In addition, electrodes can be solid or composite.

When making it yourself (or re-sharpening), it is recommended to maintain the following size ratios at which the tool will have maximum durability:

• To calculate the electrode diameter d, use the dependence P = (3...4)d 2, where P is the actually necessary compression of the electrodes during the resistance electric welding process. In turn, the recommended values ​​of upsetting pressure, at which the highest quality joints are obtained, is 2.5...4.0 kg/mm ​​2 of the area of ​​the resulting weld;
• For electrodes with a conical working part, the optimal taper angle varies from 1:10 (for a tool with a working part diameter of up to 30...32 mm) to 1:5 - in the opposite case;
• The choice of cone angle is also determined by the greatest compression force: with maximum forces, it is recommended to take a taper of 1:10, as it ensures increased longitudinal resistance of the electrode.

The main forms of electrodes for resistance welding are established by GOST 14111, therefore, when using certain size ratios, you should take into account the dimensions of the mounting space for the tool for a specific model of resistance welding machine.

Significant savings in material come from the use of composite structures. At the same time, materials with high electrical conductivity values ​​are used to manufacture the body, and the removable working part is made of alloys with high hardness and wear resistance (including thermal). In particular, metal-ceramic alloys from the Swiss company AMRCO grades A1W or A1WC, containing 56% tungsten and 44% copper, have a similar combination of properties. Their electrical conductivity reaches 60% of the electrical conductivity of pure copper, which determines low heating losses when welding. Recommended materials can also be bronze alloys with additions of chromium and zirconium, as well as tungsten.

Electrodes for resistance welding of light alloys, where significant clamping force is not required, are made with a spherical working part, and for the contact jaws of electric spot welding machines it is advisable to use silicon bronze.

The mechanical characteristics of the electrodes must be within the following limits:

• Brinell hardness, HB – 1400...2600;
• Young's modulus, GPa – 80…140;
• Limit bending moment, kgsm – not lower than 750...800.

Electrode structures should always be hollow to ensure efficient cooling.

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