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

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

Tungsten is one of the most refractory metals used to make electrodes. The melting point of tungsten is over 3000 degrees Celsius. Under normal welding conditions, these temperatures are not used. Therefore, tungsten electrodes are called non-consumable. When applied, they practically do not change in size.

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

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

How to sharpen an electrode

Sharpening of the tungsten electrode can be carried out 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 with the help of special devices. They can be both portable and stationary.

The sharpening shape can be spherical or conical. The spherical shape is more suitable for DC welding, and the conical shape is more suitable for AC welding. Some welders note that they do not notice a big difference when welding with electrodes with different sharpening shapes. But our experience has shown that there are differences. And if you are a professional welder, the difference will be obvious.

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

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

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

A sharpening angle of 20-40 degrees is a good option when welding with medium welding currents.

If you use high currents, then 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 unstable and it will be difficult for you to form a seam.

This table clearly shows the importance of electrode maintenance. This is important not only to maintain the quality of the welded joint, which is of paramount importance, but also to reduce unnecessary stress on the welding equipment. After examining the tabular data, you can draw your own conclusions.

TIP PROFILE

WELD SPOT

REQUIRED CURRENT, A

RESULT

CORRECT MAINTENANCE OF ELECTRODES FOR RESISTANCE SPOT AND RELIEF WELDING

Projection welding electrodes

To ensure the precise alignment required for good contact and quality of welded joints, the electrodes for projection welding should be located directly on the center line of application of pressure. In addition to the appearance of poor-quality welded joints, insufficient alignment of the electrodes can lead to damage to their surfaces [Fig. one].

Another serious cause of poor welding is the non-parallelism of the electrode surfaces. It entails uneven pressure on the electrodes, which causes molten metal to slosh out of the weld area during the welding cycle. In the event that welding has gone through the bearing part of the electrode, the reliefs are damaged, and the insulation may burn out. In addition, non-parallelism leads to biting of the electrode tips by their bearing parts during welding, resulting in a burn on the workpiece at the point of contact with displaced reliefs, and a shift relative to the mating parts of the welding equipment is possible [Fig. 2].

SHOULD
... keep a supply of electrodes on the machine to minimize downtime due to electrode replacement,
... grind the electrodes on lathe,
...use special Grade 3 copper for the electrode tips.
DO NOT DO IT
... file the electrodes (an uneven surface will result in either partial welding or metal splashing out of the welding zone),

Spot welding electrodes

In contact spot welding, the thermal concentration depends on the size and shape of the electrode tips. Welding is carried out over the entire area under the tip of the electrode through which the current passes. Tips of small diameter spot welding electrodes break down or wear down much faster than their relief welding counterparts and therefore need to be sharpened regularly to maintain proper contact [fig. 3].

SHOULD
... keep a supply of electrodes on the machine,
... periodically grind the electrodes on specialized machine,
... to change the diameter of the tips when working with different thicknesses of the welded metal.
DO NOT DO IT
... file the electrodes (an uneven surface will lead to lack of penetration),
... store electrodes in places where damage to their surfaces is possible,
... use an adjustable wrench to remove the electrodes.

1. To ensure perfect alignment, the surfaces and axes of the electrodes must be parallel. This can be tested by inserting a piece of charcoal and a sheet of clean white paper between the electrodes and running the electrodes in test mode. The resulting print on paper will show the size and uniformity of the plane of contact between the two surfaces.

2. Use a water jacket if necessary and keep it as close to the welding surface as possible.

3. Keep the material to be welded clean: free of oil, film, dirt and other foreign matter.

4. Follow the prescribed welding procedure.

WELDING ELECTRODES AND HOLDERS

High electrode durability and good spot weld quality are not possible without proper care of the electrodes. From 3 to 10% of the welder's working time is spent on electrode maintenance. Proper care of the electrodes allows one pair of electrodes to make 30 ... 100 thousand weld points, while the consumption of the electrode alloy is only 5 ... 20 g per thousand welded points.

Electrode Care point machines consists of two operations - stripping the electrodes directly on the machine and filling the removed electrode on a lathe or a special machine.

The frequency of stripping depends mainly on the material to be welded. When welding steel with a well-prepared surface, in some cases it is possible to do without stripping, in others the required stripping is carried out after welding several hundred points. When welding aluminum alloys, electrode cleaning is required after 30 ... The same phenomenon is observed when welding other materials with a lower melting point, such as, for example, magnesium.

Stripping should be carried out in such a way that, without removing a large amount of metal, a clean electrode surface is obtained. To simplify this operation and facilitate working conditions when stripping the electrodes, special devices are used.

The simplest device is shown in Fig. 1. It is a spatula with double-sided recesses into which sandpaper. The spatula is inserted between the compressed electrodes, and when rotated around the axis of the electrodes, it cleans their contact surfaces.

Rice. 1. Device for manual stripping of electrodes:

1 - skin; 2 - spherical recess.

Instead of such a spatula, you can use a steel plate for stripping electrodes with a flat contact surface or a piece of rubber for stripping electrodes with a spherical working surface. Electrodes with a flat contact surface are cleaned simultaneously or alternately, with a spherical one - simultaneously, with a small compressive force. After stripping, traces of abrasive dust are removed with a dry rag.

The desire to mechanize the process of cleaning the contact surface of the electrodes led to the creation of devices with an electric or pneumatic drive. On fig. 2 shows a pneumatic machine for stripping electrodes.

Rice. 2. Angle pneumatic electrode stripping machine

The need for cleaning the contact surface is determined visually, according to the state of the surface of the product to be welded, but attempts are known to determine the moment of cleaning with the help of special devices.

With the help of software control, not only the installation of the welded unit, welding current and welding time is carried out, but also a signal is given about the need to clean the electrodes.

It is proposed to determine the moment of stripping the electrodes by comparing the brightness light beam reflected from the contact surface of the electrode, with the brightness of the beam reflected from the surface of the standard. This method also makes it possible to stop the welding process under the action of a signal, the magnitude of which increases with contamination. working surface electrode.

Filling the working part of a worn electrode in order to restore its original shape can be done in several ways. The least quality is refilling with a small file. It is recommended to use special filling stations for these purposes. An example of a manual primer is shown in fig. 3.

Rice. 3. Manual electrode filler:

1 - body; 2 - screws. 3 - incisors; 4 - handle.

It is also recommended to use special pneumatic fillers equipped with a face mill, the profile of the cutting part of which corresponds to the profile of the working part of the electrode. A special cutter is inserted into the chuck of a conventional hand drill and allows you to simultaneously process the conical and flat surfaces of the working part of the electrode.

A good way to thread electrodes is threading on lathes with a gauge check.

With a large number of refillable electrodes, it is advisable to use special machines of the type.

To quickly change the electrodes without damage, it is recommended to use turnkey flattened electrodes or use special pullers.

The simplest puller (Fig. 4) is a screw clamp of a special design.

Rice. 4. Puller of the simplest design:

1 - body; 2 - dies; 3 - clamping screw.

Recovery of worn electrodes for spot welding has not previously been practiced. Behind recent times the technology of restoration of electrodes of spot welding machines by arc surfacing has been developed. The hardness, electrical conductivity and resistance of the regenerated electrodes correspond to the properties of electrodes made from rods. Application of the method of recovery of the electrode by surfacing for only one multi-point machine allows saving up to 500 kg of bronze per year.

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

The simplest for manufacturing and operation are straight electrodes, made in accordance with GOST 14111-69 from various copper electrode alloys, depending on the metal grade 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 joints, the electrodes must have a sufficiently low electrical and thermal conductivity (30 ... 40% of copper). If the entire electrode is made of such a metal, then it will intensively heat up 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 joints. The working part 3 can be replaceable (Fig. 1, a) and fixed with a nut 2 on the base 1. The use of electrodes of this design is convenient, as it allows you to set the desired working part when changing the thickness and grade of the metal of the parts to be welded. The disadvantages of an electrode with a replaceable part are the possibility of using it only when welding parts with good approaches and insufficient cooling. Therefore, such electrodes should not be used in heavy welding at a high pace.

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 tip (Fig. 1, c). Tips are made of tungsten, molybdenum or their compositions with copper. When pressing a tungsten tip, it is necessary to grind it cylindrical surface for the purpose of reliable contact with the base of the electrode. When welding stainless steel parts 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 resistance of the electrode are observed. The working surface of the insert can be flat or spherical.

Particular attention in the design of electrodes should be given to the shape and dimensions of the landing part. The most common conical landing part, the length of which should be at least. Short cone electrodes should only be used when welding using low forces and currents. In addition to the conical fit, sometimes the electrodes are fastened to the thread with a union nut. Such connection of electrodes can be recommended c. multi-point machines, when it is important to have the same initial distance between the electrodes, or in clamps. When using figured electrode holders, electrodes with a cylindrical landing part are also used (see Fig. 8, d).

When spot welding parts of a complex contour and poor approaches to the junction, a wide variety of figured 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 figured electrodes when welding is generally not feasible without them. The dimensions and shape of the curly electrodes depend on the dimensions 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

Curly electrodes during operation usually experience a significant bending moment from the off-axis application of force, which must be taken into account when choosing or designing electrodes. The bending moment and the usually small section of the cantilever create significant elastic deformations. In this regard, the mutual displacement of the working surfaces of the electrodes is inevitable, especially if one electrode is straight and the other is shaped. Therefore, for figured electrodes, the spherical shape of the working surface is preferable. In the case of shaped electrodes experiencing large bending moments, deformation of the conical landing part and the electrode holder socket is possible. The maximum permissible bending moments for figured electrodes made of bronze Br.NBT and electrode holders made of heat-treated bronze Br.X 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 the allowable one, then the maximum diameter of the cone should be increased.

When designing complex spatial figured electrodes, it is recommended to pre-make their model from plasticine, wood, or easily processed metal. This makes it possible to establish the most rational dimensions and shape of the shaped electrode and avoid alterations in its manufacture immediately from metal.

On fig. 3 shows some examples of welding knots in places with limited access. Welding of a profile with a shell is performed with a lower electrode with a displaced working surface (Fig. 3, a).

Rice. 3. Examples of the use of curly electrodes

An example of using the upper electrode with oblique sharpening and the lower one, curly, is shown in fig. 3b. 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 is deformed. If it is impossible to install the upper electrode with an inclination, then it can also be curly. The shaped electrode is bent in two planes to reach a hard-to-reach welding spot (Fig. 3, cd). If there is no or limited horizontal movement of the consoles for welding parts shown in fig. 3e, two shaped electrodes with the same projections are used.

Sometimes shaped electrodes perceive very large bending moments. To avoid deformation of the conical seating part, the shaped electrode is additionally fixed to the outer surface of the electrode holder with a clamp and a screw (Fig. 4, a). The strength of figured electrodes with a long overhang increases significantly if they are made composite (reinforced). For this, 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 done by soldering, and with a steel console - by screws. A variant of the design is possible, when the curly copper alloy electrode is reinforced (reinforced) with steel elements (slats), 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 figured electrodes experiencing 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 lead

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 heat, 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 curly electrodes, since it is not always possible to bring 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 figured electrode of a sufficiently large size. Given 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 clamps for welding in hard-to-reach places, as well as the need for frequent replacement of electrodes, the electrode fastening shown in fig. 5. Such fastening provides good electrical contact, convenient adjustment of the electrode extension, good stability against lateral displacements, quick and easy removal of the electrodes. However, due to the lack of internal cooling in such electrodes, they are used for welding at low currents (up to 5 ... 6 kA) and at a low rate.

Rice. 5. Ways of fixing electrodes

For ease of use, electrodes with several working parts are used. These electrodes can be adjustable or swivel (Fig. 6) and greatly simplify and speed up the installation of electrodes (combination of working surfaces).

Rice. 6. Multiposition adjustable (a) and surface (b) electrodes:

1 - electrode holder; 2 - electrode

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

Table. Dimensions of electrode holders for spot machines in mm

The most common are direct 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 change 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 spring 2. It is important that the end of the ejector that strikes the end of the electrode does not have damage on its surface, otherwise the landing part of the electrode will quickly fail, jamming when it is removed from the electrode holder. Convenient for operation is the execution of the end of the electrode holder 1 in the form of a replaceable threaded sleeve 2, in which the electrode 3 is installed (Fig. 7, c). This design makes it possible to manufacture bushing 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 in case of jamming by knocking it out with a steel punch from inside the bushing.

Rice. 7. Straight electrode holders:

a - normal;

b - with ejector;

c - with a replaceable sleeve

If shaped electrodes are more often used when welding parts that have small dimensions of the elements to be connected, then for large sizes it is advisable to use special shaped electrode holders and simple electrodes. Figured 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 figured electrode can be replaced by the electrode holder shown in Fig. 8, b. Of interest is also the electrode holder, the slope of which can be easily adjusted (Fig. 8, c). The design of the electrode holder bent at an angle of 90° is shown in fig. 30, d, it allows you to fix the electrodes with a cylindrical landing part. A special screw clamp ensures quick attachment and removal of the electrodes. On fig. 9 presented various examples spot welding using curly electrode holders.

Rice. 8. Special electrode holders

Rice. 9. Application examples of various electrode holders

When spot welding large assemblies such as panels, it is advisable to use a four-electrode rotary head (Fig. 10). The use of such heads makes it possible to quadruple the operating time of the electrodes until the next cleaning, without removing the welded panel from the working space of the machine. To do this, after contamination of each pair of electrodes, the electrode holder 1 is rotated by 90° and fixed with a stopper 4. The swivel head also makes it possible to install electrodes with a different shape of the working surface for welding an assembly with a variable, for example, stepwise thickness of parts, and also to provide mechanization of electrode cleaning with special devices. The swivel head can be used for spot welding of parts with a large difference 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 wears out quickly and is replaced by a new one when the head is turned. It is convenient to use a roller as an electrode on the side of a thick part.

Rice. 10. Rotary electrode head:

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

In spot welding, the axes of the electrodes must be perpendicular to the surfaces of the parts to be welded. To do this, welding of parts with slopes (smoothly changing thickness), or manufactured using hanging machines, in the presence of large-sized units, is performed using a self-aligning rotary electrode with a spherical support (Fig. 11, a). The electrode is sealed with a rubber ring to prevent water leakage.

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

On conventional spot machines, welding of steel parts of relatively small thickness can be carried out with 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 the axis 2 under the action of the compression force of the machine.

For mesh welding steel wire with a diameter of 3 ... 5 mm, plate electrodes can be used (Fig. 11, c). The top electrode 4 swings on the axis for even distribution of forces between the joints. The current supply for the purpose of its uniformity is carried out by flexible tires 3; fork 2 and the swing axis are isolated from the electrode. With electrode lengths up to 150 mm, they can be made non-swinging.

Rice. 12. Sliding wedge electrode inserts

When welding panels consisting of two skins and stiffeners, there must be an electrically conductive insert inside, which perceives the force of the machine's electrodes. The design of the insert should ensure its tight fit to the inner surface of the parts to be welded without a gap, in order to avoid deep dents on the outer surfaces of the parts and possible burns. For this purpose, the sliding insert shown in fig. 12. The movement of the wedge 2 relative to the fixed wedge 4, which ensures their compression to the parts to be welded 3, is synchronized with the operation of the machine. When the electrodes 1 and 5 are compressed and welding takes place, air from the pneumatic drive system of the machine enters the right cavity of the cylinder 8 fixed 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 electrode 1 is raised, air leaves the right cavity and begins to flow into the left cavity of the cylinder 8, reducing the distance between the surfaces of the wedges, which allows you to move the welded panel relative to the machine electrodes. The wedge insert is cooled by air that enters through tube 6. The use of such an insert makes it possible to weld parts with an internal distance between them of up to 10 mm.

k-svarka.com

Connection of parts by resistance spot welding

• 27th of December
• 77 views
• 13 rating

• Spot welding electrodes
• Spot welding parameters
• Possible defects and their causes

Spot welding is a method in which parts are overlapped at one or more points. When an electric current is applied, local heating occurs, as a result of which the metal is melted and seized. Unlike electric arc or gas welding no filler material is required: it is not the electrodes that melt, but the parts themselves. Enveloping with an inert gas is also not necessary: ​​the weld pool is sufficiently localized and protected from the ingress of atmospheric oxygen. The welder works without a mask and gloves. This allows better visualization and control of the process. Spot welding provides high productivity (up to 600 dots/min) at low cost. It is widely used in various industries economy: from instrument making to aircraft building, as well as for domestic purposes. No car repair shop can do without spot welding.

Scheme of spot welding.

Spot welding equipment

The work is carried out on a special welding machine called a spotter (from the English Spot - a point). Spotters are stationary (for work in workshops) and portable. The unit operates from a 380 or 220 V power supply and generates current charges of several thousand amperes, which is much more than that of inverters and semi-automatic devices. The current is applied to a copper or carbon electrode, which is pressed against the surfaces to be welded by pneumatics or a hand lever. There is a thermal effect lasting a few milliseconds. However, this is enough for reliable docking of surfaces. Since the exposure time is minimal, the heat does not spread further through the metal, and the weld point cools quickly. Details from ordinary steels, galvanized iron, stainless steel, copper, aluminum are subject to welding. The thickness of the surfaces can be different: from the thinnest parts for instrumentation to sheets with a thickness of 20 mm.

General form pinpoint welding machine.

contact- spot welding can be carried out with one electrode or two from different sides. The first method is used for welding thin surfaces or in cases where it is impossible to press on both sides. For the second method, special pliers are used to clamp parts. This option provides a more secure hold and is more commonly used for thick-walled workpieces.

According to the type of current, spot welding machines are divided into:

• working on alternating current;
• operating on direct current;
• low frequency devices;
• capacitor type devices.

The choice of equipment depends on the features technological process. The most common devices are alternating current.

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Scheme of a home-made apparatus for spot welding.

Spot welding electrodes are different from arc welding electrodes. They not only provide current to the surfaces to be welded, but also perform a clamping function, and are also involved in heat removal.

The high intensity of the working process necessitates the use of a material that is resistant to mechanical and chemical influences. Most of all, the requirements are met by copper with the addition of chromium and zinc (0.7 and 0.4%, respectively).

The quality of the weld point is largely determined by the diameter of the electrode. It should be at least 2 times the thickness of the parts to be joined. The dimensions of the rods are regulated by GOST and are from 10 to 40 mm in diameter. Recommended electrode sizes are shown in the table. (Picture 1)

For welding ordinary steels, it is advisable to use electrodes with a flat working surface, for welding high-carbon and alloy steels, copper, aluminum - with a spherical one.

Spherical tip electrodes are more durable: able to produce more points before resharpening.

In addition, they are universal and suitable for welding any metal, but using flat ones for welding aluminum or magnesium will lead to the formation of dents.

Spot welding in hard-to-reach places is performed with curved electrodes. A welder who is faced with such working conditions always has a set of different figured electrodes.

To ensure reliable current transfer and clamping, the electrodes must be tightly connected to the electrode holder. To do this, their landing parts are given the shape of a cone.

Some types of electrodes are threaded or mounted on a cylindrical surface.

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The main parameters of the process are current strength, pulse duration, compression force.

The amount of heat generated, the heating rate, and the size of the welded core depend on the strength of the welding current.

Along with the current strength, the amount of heat and the size of the nucleus are affected by the duration of the pulse. However, when a certain moment is reached, a state of equilibrium sets in, when all the heat is removed from the welding zone and no longer affects the melting of the metal and the size of the core. Therefore, increasing the duration of the current supply beyond this is impractical.

The compression force affects the plastic deformation of the welded surfaces, the redistribution of heat over them, and the crystallization of the core. High compression force reduces drag electric current, going from the electrode to the parts to be welded and in the opposite direction. Thus, the current strength increases, the melting process accelerates. A connection made with a high compressive force is characterized by high strength. At high current loads, compression prevents splashes of molten metal. In order to relieve stress and increase the density of the core, in some cases, an additional short-term increase in the compression force is performed after the current is turned off.

Allocate soft and hard welding mode. In soft mode, the current strength is less (current density is 70-160 A / mm²), and the pulse duration can be up to several seconds. Such welding is used to connect low carbon steels and more common at home, when work is carried out on low-power devices. In hard mode, the duration of a powerful pulse (160-300 A / mm²) is from 0.08 to 0.5 seconds. Details provide the maximum possible compression. Rapid heating and rapid cooling allow the welded core to maintain anti-corrosion resistance. Hard mode is used when working with copper, aluminum, high-alloy steels.

The choice of optimal parameters requires taking into account many factors and testing after calculations. If the performance of trial work is impossible or impractical (for example, with one-time welding at home), then you should adhere to the modes described in the reference books. The recommended parameters for current strength, pulse duration and compression for welding ordinary steels are given in the table. (Picture 2)

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Cyclograms of resistance spot welding processes.

High-quality resistance spot welding provides a reliable connection, the service life of which, as a rule, exceeds the service life of the product itself. However, a violation of technology can lead to defects that can be divided into 3 main groups:

• insufficient dimensions of the welded core and deviation of its position relative to the joint of parts;
• mechanical damage: cracks, dents, shells;
• violation of the mechanical and anti-corrosion properties of the metal in the area adjacent to the weld point.

Consider specific types of defects and their causes:

1. Lack of penetration can be caused by insufficient current strength, excessive compression, wear of the electrode.
2. External cracks occur with too much current, insufficient compression, dirty surfaces.
3. Breaks at the edges are due to the close location of the core to them.
4. Electrode dents occur when electrodes are too small, improperly installed, over-compressed, too high current, and too long.
5. The splash of molten metal and its filling of the space between the parts (internal splash) occurs due to insufficient compression, the formation of an air cavity in the core, and misaligned electrodes.
6. An external splash of molten metal onto the surface of parts can be caused by insufficient compression, too high current and time modes, contamination of surfaces, and skewed electrodes. The last two factors are Negative influence on the uniformity of current distribution and the melting of the metal.
7. Internal cracks and cavities occur due to excessive current and time regimes, insufficient or delayed forging compression, and contamination of surfaces. Shrinkage cavities appear at the moment of core cooling. To prevent them, forging compression is used after the current supply is stopped.
8. The reason for the irregular shape of the core or its displacement is the skew or misalignment of the electrodes, the contamination of the surface of the parts.
9. Burn-through is the result of contaminated surfaces or insufficient compression. To avoid this defect, the current must be applied only after the compression is fully secured.

To detect defects, visual inspection, radiography, ultrasound, capillary diagnostics are used.

At test work control over the quality of the weld point is carried out by the gap method. The core should remain completely on one part, and on the second - a deep crater.

Correction of defects depends on their nature. Apply mechanical cleaning of external splashes, forging during deformation, heat treatment to relieve stress. More often, defective points are simply digested.

expertsvarki.ru

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

Reasons for the fragility of resistance welding electrodes

The contact welding process consists of the following stages:

1. Preliminary preparation of the surface of the parts to be joined - it should not be easily cleaned of dirt and oxides, but also very smooth in order to eliminate the unevenness of the resulting electric field voltage.
2. Manual or mechanical clamping of the workpieces to be welded - with an increase in the clamping force, the intensity of diffusion and mechanical strength increase weld.
3. Local melting of metals in the pressing zone by the heat of an electric current, as a result of which a welded joint is formed. The clamping of the electrodes at this stage prevents the formation of welding spatter.
4. Switching off the current and gradual cooling of 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 imposed on it - high electrical conductivity, high thermal resistance (including from constant temperature fluctuations), increased values ​​of compressive strength, low heat capacity coefficient. A limited number of metals have such a complex of properties. First of all, it is copper, and alloys based on it, however, they do not always satisfy production requirements.

In connection with constant increase energy characteristics of manufactured spot welding machines, many trade marks orient the consumer to the use of only "their", branded electrodes, which is not always observed. As a result, the quality of welds obtained using this technology decreases, and confidence in the process of contact electric welding itself is undermined.

These problems are 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 also matters.

Electrode materials

According to GOST 2601, the criterion for the quality of the finished seam is its tensile or shear strength. It depends on the intensity of the thermal power in the electric 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 ductile metal, does not have sufficient elasticity to completely restore the geometric shape of the electrodes between work cycles. Secondly, copper is very scarce, and frequent replacement of electrodes causes high financial costs.

Attempts to use harder, hardened copper are not successful: for work-hardened material, in parallel with an increase in hardness, the recrystallization temperature decreases, therefore, with each work cycle, the wear of the working end of the resistance welding electrode will increase. So practical use received copper alloys with the addition of a number of other metals. In particular, the introduction of cadmium, beryllium, magnesium, zinc and aluminum into a copper alloy does not significantly change the thermal conductivity, but improves the hardness when heated. The stability of the electrode against dynamic thermal loads is increased by iron, nickel, chromium and silicon.

When selecting the optimal material for welding electrodes for contact welding, they are guided by the indicator of the specific electrical conductivity of the alloy. The less it differs (downward) from the electrical conductivity of pure copper - 0.0172 Ohm mm2 / m, the better.

The most effective resistance to wear and deformation is shown by alloys, which include 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 in 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. 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 ordinary carbon and low alloy steels, copper and aluminum products). They are made from copper alloys of grades MS and MK.
3. Electrodes for relatively light operating conditions (surface temperatures up to 120 ... 200ºС). Cadmium bronze Br.Kd1, chromium bronze Br.Kh08, silicon nickel bronze Br.NK, etc. are used as materials. Such electrodes can also be used for roller contact electric welding.

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

Electrode designs

The least resistant place of the electrode is its spherical working part. The electrode is rejected if the increase in the dimensions of the butt exceeds 20% of the primary dimensions. The design of the electrodes is determined by the configuration of the surface to be welded. There are the following versions of the tool

1. With a cylindrical working part and a conical landing part.
2. With a conical landing and working part, and a transitional cylindrical section.
3. With a spherical working end.
4. With bevelled working end.

In addition, the electrodes can be solid and composite.

When self-manufacturing (or regrinding), it is recommended to maintain the following ratios of sizes, in which the tool will have maximum durability:

• To calculate the electrode diameter d, the dependence Р = (3…4)d2 is used, where Р is the actual required compression of the electrodes during the resistance electric welding process. In turn, the recommended values ​​of the upsetting pressure, at which the highest quality joints are obtained, is 2.5 ... 4.0 kg / mm2 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 up to 30 ... 32 mm) to 1:5 - otherwise;
• The choice of the cone angle is also determined by the greatest compression force: at maximum effort, it is recommended to take a taper of 1:10, as providing an increased longitudinal resistance of the electrode.

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

Significant savings in material can be achieved through the use of composite structures. At the same time, materials with high electrical conductivity values ​​are used to manufacture the case, and the removable working part is made of alloys with high hardness and wear resistance (including thermal). In particular, ceramic-metal 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 the low heating losses during welding. Bronze alloys with additions of chromium and zirconium, as well as tungsten, can also be recommended materials.

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

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

• Brinell hardness, HB - 1400 ... 2600;
• Young's modulus, GPa – 80…140;
• Ultimate bending moment, kgcm - not less than 750 ... 800.

Electrode designs should always be hollow to ensure efficient cooling.

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Technology and devices of spot welding

What is spot welding? This is a contact method for connecting workpieces at one or more points. The formed connection looks like a rivet.

Advantages of the method:

• welding of metals of different alloys (from expensive to cheap);
• strength and aesthetic appearance of the connection;
• high speed (performance);
• economy in the consumption of materials;
• low qualification of the worker.

Disadvantages: the seam is not tight, stress concentration in the joint area.

Point technology has become widespread in industry and in everyday life. It is connected both by small parts in instrument making and large steel sheets in various industries.

Technology Sequence

The whole process can be described as follows:

1. The prepared parts are placed between two electrodes and compressed with a certain force;
2. an electric current is applied to the electrodes;
3. heating and melting of the metal occurs at the point of contact;
4. power is turned off (forging) - crystallization of the core of the melt;
5. the compression is removed from the parts.

Forging can be carried out with or without increased compression.

The shape and dimensions of the point connection depend on the strength of the electric current, the process time, the electrodes, the compression force and the cleanliness of the surface of the workpieces. The diameter of the welded rivet can be from 3 to 12 mm.

Preparation of blanks for welding

The material is cleaned only at the point of contact of the electrodes with the surface. For this, brushes, circles, sandblasting tools and etching solutions are used.

Without cleaning - the electrodes wear out faster, the quality of the bonding of the material is lame and the consumption of electricity increases.

Spot welding equipment

Spot welding machines are:

• with alternating current;
• with direct current;
• condenser type machines;
• low frequency devices.

Each spot welding machine has its pros and cons.

On sale there are different models of devices, for all occasions

AC equipment is more popular. The device includes - power transformer, thyristor module, step-down transformer, logic controllers, relays, control unit, etc.

What is capacitor welding? The technology is simple: when charging, energy is gradually accumulated in the capacitor, which, when consumed, generates a large current pulse.

Due to this, less controlled power from the mains is consumed during welding. This technology perfectly connects metals with good thermal conductivity (silver, aluminum - copper alloys).

Note: point bonding can be performed in soft and hard modes.

With a soft process, the workpieces are heated with a moderate current from 0.5 to 3 seconds. The method is used to connect products prone to hardening.

The hard method is applicable to high alloy steels, aluminum and copper alloys. Warm-up time 0.1 - 1.5 sec.

Cost of equipment

The industry supplies various spot welding machines to the market - the price is very different from the power and purpose of the machines. There are manual portable models and powerful machines for workshop work.

For example, BlueWeld Plus 230 823226 manual spot welding guns can be purchased for 40,000 rubles.

Spotters. The TELWIN DIGITAL CAR SPOTTER 5500 (400) device will cost 66,000 rubles.

Specifications Telvin

Now, in online stores you can buy Chinese spot welding for hint batteries (from 7,000 rubles).

Photo of a Chinese device for batteries

We must pay tribute to our craftsmen who assemble a variety of devices for point connection with their own hands. Of course, in other publications we will talk about this and even about home-made spot welding with an inverter.

Video: how to make a spot welding machine yourself.

electrodes

Electrodes for spot welding must fulfill their function - this is the compression of metal products and the supply of current to them.

different shape electrodes

The tip plays an important role at the electrode. For example, thin ones wear out very quickly and need to be sharpened. The best shape is a cone.

How to extend the life of electrodes:

• buy only branded products;
• use a separate electrode for each alloy;
• under severe welding conditions, use the correct tips;
• use transparent hoses for water control.

Know: a filed electrode leads to poor welding. Also, store them in special places to avoid damage.

Simple and high-quality electrodes are straight, which correspond to GOST 1411-69, they are made from special copper alloys. Often, the working part of the electrode is replaceable, which allows you to set the desired size based on the alloy and thickness of the workpieces to be welded.

The fastening of the working part is carried out with a nut, solder or pressing on a cone. The conical working part has become more widespread.

Tips come in flat and spherical shapes. A spherical surface is used for all machines and alloys, while a flat surface is not suitable in all cases.

When spot welding for hard-to-reach places, electrodes of different configurations are sometimes used. Having less wear resistance than direct counterparts.

P.S. We got acquainted with the technology of spot welding (contact), learned the advantages and disadvantages of this type of connection, what devices and electrodes are used to perform the process.

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Welding performed in a shielding gas environment (helium or argon) requires tungsten electrodes, which are classified as non-consumable. Due to its refractoriness, the tungsten electrode can withstand high temperatures and a long uninterrupted service life. Currently, this welding material has a fairly extensive classification, where there is quite a large number of types divided by brands.

Marking and characteristics of tungsten electrodes

Marking of tungsten electrodes is stipulated by international standards. Therefore, it is easy to choose them for the required purpose in any country, no matter where you are. It is the marking that reflects both the type of the selected electrode and its chemical composition.

The marking begins with the letter "W", which stands for tungsten itself. In its pure form, the metal is present in the product, but the characteristics of such an electrode are not very high, because it is too refractory element. Alloying additives help to improve the welding qualities.

• Pure tungsten rod is designated "WP". The tip of the rod is green. We can say that it belongs to the category of tungsten electrodes for welding aluminum and copper with alternating current. The content of tungsten in the alloy is not less than 99.5%. The disadvantage is the limitation in the thermal load. Therefore, the sharpening of the tungsten electrode (its end) "WP" is made in the form of a ball.
• "C" is cerium oxide. Bar with a gray tip. It is this additive that allows you to use the electrode when working with any type of current (direct or alternating), maintains a stable arc even at low current. Content - 2%. By the way, cerium is the only non-radioactive material from a series of rare earth metals.
• "T" - thorium dioxide. A rod with a red tip. Such electrodes are used for welding non-ferrous metals, low-alloy and carbon steels, stainless steel. It is a commonly used electrode in welding work. argon welding. It has one drawback - the radioactivity of thorium, so it is recommended that welding be carried out in open areas and in well-ventilated rooms. The welder must follow the safety precautions. Note that thoriated tungsten electrodes for argon arc welding hold their shape well at the highest currents. Even the “WP” brand (pure tungsten) cannot cope with such loads. Content - 2%.
• "Y" is yttrium dioxide. Bar with a dark blue tip. With its help, critical structures are usually welded from different metals: titanium, copper, stainless steel, carbon and low alloy steels. Work is carried out only on direct current (direct polarity). The yttrium additive increases such an indicator as the stability of the cathode spot at the end of the electrode itself. This is the reason why it can operate within a fairly wide range of welding current. Content - 2%.
• "Z" - zirconium oxide. A rod with a white tip. It is used for argon welding of aluminum and copper with alternating current. This type of electrode provides a very stable arc. At the same time, the element is quite demanding on the cleanliness of the welding joint. Content - 0.8%.
• "L" - lanthanum oxide. There are two positions here: WL-15 and WL-20. The first bar with a golden tip, the second with a blue one. Welding with a tungsten electrode with the addition of lanthanum oxide is the ability to use both alternating current and direct current. Let's add here the ease of starting the arc (initial and re-ignition), this type has the smallest wear on the end of the rod, a stable arc at the highest current, low tendency to burn through, the carrying capacity is twice as high as that of a pure tungsten rod. The content of lanthanum oxide in WL-15 is 1.5% and in WL-20 is 2%.

The classification by digital marking is as follows. The first numbers after the letters indicate the content of alloying additives in the alloy. The second group of numbers, separated from the first by a hyphen, is the length of the tungsten rod. The most common size is 175 mm. But on the market you can also find 50 mm lengths, 75 and 150. For example, WL-15-75 is an electrode with lanthanum oxide, which contains 1.5% of the additive. The length of the bar is 75 mm. Its tip is golden.

Methods for sharpening tungsten electrodes

Sharpening of tungsten electrodes is the most important component of a properly conducted welding process. Therefore, all welders involved in welding in an argon environment carry out this operation very carefully. It is on the shape of the tip that it depends on how the energy transmitted from the electrode to the two metals being welded will be correctly distributed, what will be the pressure of the arc. And the shape and dimensions of the weld penetration zone, and, accordingly, its width and depth, will already depend on these two parameters.

Attention! The parameters and form of sharpening are selected from the type of electrode used and from the parameters of the two metal blanks being welded.

• The working end of WP, WL electrodes is a sphere (ball).
• A bulge is also made on WT, but with a small radius. Rather, they simply indicate the roundness of the electrode.
• The rest of the types are sharpened under the cone.

When an aluminum joint is welded, a sphere forms on the electrode by itself. Therefore, when welding aluminum, there is no need to sharpen the electrode.

What sharpening errors can lead to.

• The sharpening width is very different from the norm, that is, it can be very wide or very narrow. In this case, the probability of non-penetration of the seam greatly increases.
• If asymmetric sharpening is carried out, then this is a guarantee of the deviation of the welding arc to one side.
• The sharpening angle is too sharp - the service life of the electrode is reduced.
• The sharpening angle is too obtuse - the depth of penetration of the seam decreases.
• The marks left from the abrasive tool are not located along the axis of the bar. Get an effect like a wandering arc. That is, the stable and uniform burning of the welded arc is disturbed.

By the way, there is a simple formula that determines the length of the sharpened area. It is equal to the diameter of the bar, multiplied by a constant factor - 2.5. There is also a table that indicates the ratio of the diameter of the electrodes to the length of the end to be sharpened.

It is necessary to sharpen the end of the tungsten rod across, like a pencil. You can sharpen on an electric emery or on a grinder. To achieve uniform metal removal throughout the sharpening zone, you can fix the bar in the drill chuck. And rotate it at low speeds of the power tool.

Currently, manufacturers of special electrical equipment offer a machine for sharpening non-consumable tungsten electrodes. A convenient and accurate option to make high-quality sharpening. The machine includes:

• Diamond disk.
• Dust filter.
• Setting the revolutions of the working shaft.
• Sharpening angle setting. This parameter varies between 15-180°.

Research, to find the optimal sharpening angle, is carried out constantly. In one research institute, a test was conducted where a WL tungsten electrode was tested for the quality of the weld by sharpening it at different angles. Several angular dimensions were chosen at once: from 17 to 60°.

The exact parameters of the welding process were determined:

• Welded two metal sheets of corrosion-resistant steel with a thickness of 4 mm.
• Welding current - 120 amperes.
• Speed ​​- 10 m / h.
• Welding position is lower.
• The consumption of inert gas is 6 l/min.

The results of the experiment are as follows. An ideal seam was obtained when a bar with a sharpening angle of 30 ° was used. At an angle of 17°, the shape of the weld was tapered. At the same time, the welding process itself was unstable. The resource of the cutting electrode decreased. At large sharpening angles, the pattern of the welded process also changed. At 60°, the weld width increased, but its depth decreased. And although the welding process itself has stabilized, it cannot be called high-quality.

As you can see, the sharpening angle plays an important role in the welding process. It doesn't matter if stainless steel, steel or copper electrodes are used. In any case, you need to properly sharpen the bar, because the consequences can be extremely negative. Description of bars by color and chemical characteristics helps to make the right choice, and at the same time choose the shape of sharpening.