Machines and tools for sharpening electrodes for resistance spot welding Sinterleghe. Contact welding equipment (electrode holders and electrodes for spot welding)

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 the 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. The 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 portable ones include a manual machine for sharpening tungsten electrodes, and the stationary ones include a machine for sharpening tungsten electrodes. In our opinion, the use of such devices gives the best result.

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.

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 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 sectors of the economy: from instrument making to aircraft construction, as well as for domestic purposes. No car repair shop can do without 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.

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 characteristics of the technological process. The most common devices are alternating current.

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Spot welding electrodes

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.

For 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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Spot welding parameters

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. A high clamping force reduces the resistance of the electric current flowing from the electrode to the parts to be welded and vice versa. 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.

Distinguish between soft and hard. 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 is 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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Possible defects and their causes

A well-made point 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, contaminated surfaces, and skewed electrodes. The last two factors have a negative impact on the uniformity of current distribution and metal melting.
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.

During test work, the quality control of the weld point is carried out by the rupture 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.

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

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

Electrode designs

Electrodes are also used to work with electric arc welding, but they are fundamentally different from conductive elements for resistance welding, and are not suitable for this type of work. Since at the time of welding the parts are squeezed by the contact parts of the welding machine, the resistance welding electrodes are able to conduct electric current, withstand the compression load 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 come in diameters from 10 to 40 mm.

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

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

The electrode seat is often cone-shaped or threaded. This design avoids current loss and effectively performs compression of parts. The landing cone can be short, but they are used at low forces and low currents. If a threaded fastener is used, then 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 in the depth of 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 a lower resistance than straight ones, so they are resorted to last.

Since the pressure on the shaped electrode is not along its axis, it is subject to bending during heating, and this must be remembered when choosing its shape. In addition, at such moments, it is possible to shift the working surface of a curved electrode in relation to a 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, with excessive load, it is necessary to use electrodes with an increased cone diameter.

When welding in the depth of a part, a straight electrode can be used if it is tilted 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.

The use of a clamp at the point of attachment of the figured electrode allows to reduce the load on the cone and extend the service life of the seat of the welding machine. When developing a curly electrode, you must first make a drawing, then make a trial model from plasticine or wood, and only after that proceed with its manufacture.

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

The hardest thing is to cool the figured electrode because of its design. For its cooling, 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 the service life is reduced.

Welding in the depth of a small part is done 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 must be 90 about in relation 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 distribution of the load is achieved by free rotation around its axis of the upper conductive contact.

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

Materials of electrodes for contact welding

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

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

The use of hardened copper was also unsuccessful, 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, copper alloys with a number of other metals proved 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 you to withstand frequent thermal loads and keep 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 and 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, then it will heat up quickly enough, since it has a high resistance.

Using the technology of composite structures, you can achieve tangible cost savings. 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, cermet 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 tasks, alloys are divided into:

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

Spot welding electrodes

The process of spot welding explains itself from its own 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. Spot welding electrodes are carefully selected because they have different properties. They are made with both spherical and flat working surfaces.

Do-it-yourself spot welding electrodes can theoretically be made, but you need to be sure that the alloy meets the stated requirements. In addition, you need to withstand all sizes, which is not so easy at home. Therefore, when purchasing factory conductive elements, you can count on high-quality welding work.

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

Seam welding electrodes

One of the varieties of resistance welding is seam welding. However, seam welding electrodes 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;
• beveled on both sides.

The configuration of the part to be welded determines which roller shape 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 tight welds, which allows them to be used in the manufacture of containers and reservoirs.

So, contact welding allows you to produce high-tech seams, but in order to achieve a high-quality result, you must carefully follow the values ​​\u200b\u200bindicated in the tables. Which welding to choose, spot or seam, depends on your needs.

Electrodes (rollers) are a tool that makes direct contact between the machine and the parts to be welded. Electrodes in the welding process perform three main tasks:
- compress details;
- bring the welding current;
- they remove the heat released during welding in the electrode-electrode section.
The quality of the resulting welded joints directly depends on the shape of the working surface of the electrodes in contact with the parts. The wear of the working surface, the associated increase in the contact area between the electrode and the part, leads to a decrease in the current density and pressure in the welding zone, and, consequently, to a change in the previously obtained parameters of the cast zone and the quality of the joints.
An increase in the working surface of a flat electrode during its wear reduces the size of the cast zone to a greater extent when welding ductile metal than when welding high-strength metal (Fig. 1a). The wear of the spherical working surface of the electrode, installed on the side of a thin part, reduces its penetration (Fig. 1b, c).
Basic requirements for electrodes:
- high electrical conductivity of welding
- maintaining the shape of the working surface in the process of welding a given number of points or meters of a roller seam.
In spot and roller welding, the electrodes are heated to high temperatures as a result of the release of heat directly in the electrodes and its transfer from the parts to be welded.

Rice. 1. Dependence of the dimensions of the cast zone on changes in the working surface of the electrodes:
a - thickness 1 + 1 mm: 1 - steel Kh18N10T; 2 - steel VNS2
b, c - when the spherical surface of the electrode is worn from the side of a thin part

The degree of heating of the electrodes depends on the welding mode used and the thickness of the parts to be welded. For example, when spot welding corrosion-resistant steel, with an increase in the thickness of parts from 0.8 + 0.8 to 3 + 3 mm, the ratio of heat released in the electrodes to the total heat released during welding increases from 18 to 40%. According to the results of direct measurements, the temperature of the working surface of the electrodes when welding single points of samples with a thickness of 1.5–2 mm is: 530°C for ZOHGSA steel, 520°C for Kh18N9T steel, 465°C for OT4 titanium and 420°C for VZh98 alloy. At a pace (speed) of welding 45 points per minute, the temperature increased and amounted to 660, 640, 610 and 580°C, respectively.

Tab. 1
Properties of metals for electrodes and rollers

Metal grade electrodes and rollers	specific electrical resistance, Ohm mm 2 /m	Maximum electrical conductivity, % of electrical conductivity copper	Minimum hardness according to Brinell kgf/mm 2	Temperature softening, about C	Welding materials
Karmium bronze Br.Kd-1 (MK)	0,0219	85	110	300	brass, bronze
Chrome Karmium Bronze Br.HKd-0.5-0.3	0,0219	85	110	370	Brass, bronze, low alloy steels, titanium*
Chrome bronze Br.X	0,023	80	120	370	Brass, bronze, low alloy steels, titanium*
Chromium Zirconium Bronze Br.HTsr-0.6-0.05	0,023	80	140	500	Low alloy steels, titanium
Alloy Mts4	0,025	75	110	380	Corrosion-resistant, heat-resistant steels and alloys, titanium*
Bronze Br.NBT	0,0385	50	170	510	Corrosion-resistant, heat-resistant steels and alloys, titanium

* For metal with a thickness of 0.6 mm or less

For electrodes and rollers, special copper alloys are used, which have high heat resistance and electrical conductivity (Table 1). The best metal for electrodes and rollers used in welding corrosion-resistant, heat-resistant steels and alloys and titanium is Br.NBT bronze, which is produced in the form of heat-treated rolled plates and cast cylindrical blanks. It is especially expedient to make curly electrodes from Br.NBT bronze, because to ensure the required hardness, work hardening is not required, which is necessary for cadmium copper, Mts5B alloy and Br.Kh bronze.
It is not recommended to use electrodes and rollers made of bronze Br.NBT for welding low-alloy steels, especially without external cooling, due to the possible sticking of copper to the surface of parts at the point of contact with the electrodes.
The most versatile alloy is Mts5B; it can be used for electrodes and rollers when welding all the metals under consideration. However, the Mts5B alloy is somewhat difficult to manufacture and thermomechanical processing, so it is not widely used. In addition, its durability when welding corrosion-resistant and heat-resistant steels and alloys is much lower than that of Br.NBT bronze. In spot welding of corrosion-resistant steels with a thickness of 1.5 + 1.5 mm, the resistance of electrodes made of Br.NBT alloy averages 7-8 thousand points, of bronze Br.X - 2-3 thousand points, and in roller welding - respectively 350 and 90 m seam.
Electrodes with a flat and spherical surface and rollers with a cylindrical and spherical working surface have received the greatest application for spot welding. The dimensions of the working surface of the electrodes are selected depending on the thickness of the parts to be welded; for most metals, the surface shape can be flat (cylindrical for rollers) or spherical (Table 2).

Tab. 2
Dimensions of electrodes and rollers

Thickness thin sheet, mm	electrodes			Rollers
	D	d email	R email	S	f	R email
0.3	12	3.0	15-25	6.0	3.0	15-25
0.5	12	4.0	25-50	6.0	4.0	25-30
0.8	12	5.0	50-75	10.0	5.0	50-75
1.0	12	5.0	75-100	10.0	5.0	75-100
1.2	16	6.0	75-100	12.0	6.0	75-100
1.5	16	7.0	100-150	12.0	7.0	100-150
2.0	20	8.0	100-150	15.0	8.0	100-150
2.5	20	9.0	150-200	18.0	10.0	150-200
3.0	25	10.0	150-200	20.0	10.0	150-200

Note: Dimensions D And S minimum recommended

Electrodes with a spherical working surface remove heat better, have greater resistance and are less sensitive to distortions of the axes of the electrodes when they are installed than electrodes with a flat working surface, therefore they are used when welding on hanging machines (pliers).
When welding with electrodes with a spherical working surface, the change F St. affects the dimensions of the cast zone to a greater extent than when using electrodes with a flat surface, especially when welding ductile metals. However, when decreasing I St. And t St. from the set value d And A decrease less when welding with electrodes with a spherical surface than when welding with electrodes with a flat surface.
When using spherical electrodes, the electrode-workpiece contact area at the beginning of welding is much smaller than at the end. This leads to the fact that on machines with a flat load characteristic (machines with a large Z m, tongs with cable) the current density in the electrode-part contact can be very high when turned on, which helps to reduce the resistance of the electrodes. Therefore, it is advisable to use a gradual increase i St., which provides an almost constant current density in the contact.
In spot and roller welding of copper and titanium alloys, it is preferable to use electrodes and rollers with a spherical working surface. In some cases, the use of only a spherical surface provides the required quality of joints, for example, when welding parts of unequal thickness.
In most cases, the electrodes are connected to the electrode holders using a conical seat. According to GOST 14111-90 for straight electrodes, the taper of the landing part is taken 1:10 for electrodes with a diameter D≤25mm and 1:5 for electrodes D>25 mm. Depending on the electrode diameter, the practically permissible compression force F el=(4-5)D2 kgf.
In practice, a variety of electrodes and electrode holders are used for welding various parts and assemblies. To obtain point connections of stable quality, it is better to use figured electrode holders than figured electrodes. Figured electrode holders have a longer service life, and also have better conditions for cooling the electrodes, which increases their durability.

Rice. 2. Electrodes of various designs

On fig. 2 shows some special purpose electrodes. Welding of a T-shaped profile with a sheet is performed using a lower electrode with a slot under the vertical wall of the profile (Fig. 2a, I). When welding parts of unequal thickness, when a deep dent on the surface of a thin part is unacceptable, electrode 1 can be used with a steel ring 2 on the working surface, which stabilizes the electrode-part contact area (Fig. 2a, II). The presence of copper foil 3 between the electrode and the workpiece eliminates arson in the contact ring - workpiece. To seal thin-walled tubes 3 made of corrosion-resistant steel using spot welding, electrode 1 with an elongated working surface is used (Fig. 2 a, III). Steel nozzle 2 concentrates the current and allows the tubes to be crushed without the danger of damaging the working surface. On the working surface of the electrodes 1, steel tubes 2 can be fixed, which stabilize the contact between the electrode and the part and reduce the wear of the electrodes (Fig. 2a, IV, V).
In spot welding, the axes of the electrodes must be perpendicular to the surfaces of the parts to be welded. Therefore, parts with slopes (smoothly changing thickness) should be welded using a self-aligning rotary electrode with a spherical support (Fig. 2b).
For spot welding of parts with a large ratio of thicknesses, sometimes an electrode is installed on the side of a thin part (Fig. 2c, I), the working part of which is made of metal with low thermal conductivity (tungsten, molybdenum, etc.). Such an electrode consists of a copper body 1 and an insert 2 soldered in the body. The working part of the electrode 3 is sometimes made replaceable and fixed on the body of the electrode 1 with a union nut 2 (Fig. 2c, II). The electrode provides a quick replacement of the working part when it is worn out or, if necessary, the rearrangement of the insert with a different shape of the working surface.
For roller welding, composite rollers are used, in which the base 1 is made of a copper alloy, and the working part 2 soldered to it is made of tungsten or molybdenum (Fig. 2c, III). During roller welding of long seams on parts of small thickness (0.2-0.5 mm), the working surface of the rollers wears out quickly, and therefore the quality of welding deteriorates. In such cases, the rollers have a groove in which a wire of cold-drawn copper is placed (Fig. 3), which is rewound when the rollers rotate from one coil to another. This method provides a stable shape of the working surface and multiple use of the wire electrode in roller welding of thin or coated parts.

To avoid frequent changes of electrodes, multi-electrode heads can be used to weld parts of different thicknesses on the same machine. Electrodes with a working surface of various shapes are installed in the head. When spot welding parts of unequal thickness, it is important to ensure a stable working surface of the electrode on the side of the thin part. For this purpose, a multi-electrode head 1 is used; roller 2 is installed from the side of the thick part (Fig. 4). When the working surface of the electrode is worn, it is replaced with a new one by turning the head. Multi-electrode heads also make it possible to automatically clean an electrode that is not currently welding without removing the electrodes from the welding machine.
Sometimes the electrodes supply current to the parts to be welded but are not connected directly to the welding machine. For example, it is necessary to weld thin-walled pipes of small diameter (10-40 mm) with a longitudinal roller seam. To do this, a pipe blank 1 with a copper mandrel 2 is placed between the rollers of the transverse welding machine (Fig. 5a). Seams of sufficient length can be welded in this way. For welding of box-shaped parts 1, a template electrode 2 is used, fixed on axis 3 to rotate it after welding the first seam (Fig. 5b).

Rice. 5. Mandrel electrodes used on roller machines
transverse welding:
a - welding of a thin-walled pipe;
b - casing welding;
1- details; 2 - electrodes; 3 - axis.

The resistance of electrodes and rollers depends on the conditions of their cooling. Spot welding electrodes must be internally water cooled. To do this, the electrodes on the side of the landing part have a hole into which a tube is inserted, fixed in the electrode holder. Water enters through the tube, washes the bottom and walls of the hole, and passes through the space between the inner walls of the electrode and the tube into the electrode holder. The end of the tube should have a bevel at an angle of 45°, the edge of which should be 2-4 mm from the bottom of the electrode. With an increase in this distance, air bubbles form and the cooling of the working surface of the electrode deteriorates.
The resistance of the electrodes is affected by the distance from the working surface to the bottom of the cooling channel. With a decrease in this distance, the resistance of the electrodes increases (the number of points before regrinding), but the number of its possible re-points to complete wear decreases, and thus its service life is reduced. Analyzing the influence of these two factors on the cost of the electrode metal, and therefore on the cost of the electrodes, it was found that the distance from the bottom to the working surface should be (0.7 -0.8) D (where D is the outer diameter of the electrode). To enhance the intensity of cooling during spot welding, additional water cooling of the electrodes and the welding spot can be used. In this case, water is supplied through the holes in the electrodes or separately through a special external cooling tube. Sometimes internal cooling with liquids below 0°C or compressed air is used.
In roller welding, external cooling of the rollers and the welding spot is more often used. However, this method of cooling is not suitable for welding hardening steels. If in spot welding it is easy to carry out internal cooling of the electrodes, then in roller welding this is a rather difficult task.
When operating electrodes and rollers, it is periodically necessary to clean and restore their working surface. Electrodes with a flat working surface are usually cleaned with a personal file and an abrasive cloth, electrodes with a spherical working surface - with a rubber pad 15-20 mm thick wrapped with an abrasive cloth.
The working surface of the electrodes is most often restored on lathes. To obtain a working surface of the correct shape, it is advisable to use special shaped cutters.

UNION OF SOVIET SOCIALIST REPUBLICS 1-5 V 23 K 11/10 INVENTION 4b ".,".,.;.;,: 1 ore for resistance spot welding. The purpose of the invention is to simplify the design and improve the cleanliness of the machined surface, On both ends of the tool 1, teeth 7 are located parallel to each other, Each of the teeth 7 is made with two cutting edges 8 and a supporting surface 5 between them, The device is clamped between the electrodes 4 by force , developed by the machine drive for contact welding. When the device is rotated, the cutting edges 8 cut off the metal layer, and the support surfaces 5 smooth the work area along the entire working end of the electrode. 4 il, eknoKTmo- bogoSTATE COMMITTEE ON INVENTIONS AND DISCOVERIES OF THE USSR State Committee for Science and Technology AUTHOR'S WITNESS (56) Author's certificate USSRM 490579, class. V 23 V 29/14, 1974. Sliozberg S.KChuloshnikov P. LEtrodes for contact welding, L.; Mechanical Engineering, 1972, p. 79, fig. 44 a, (54) DEVICE FOR SHARPENING ELRODS MACHINES FOR RESISTANCE WELDING (57) The invention relates to welding and can be used in the development of 1595635 A 1 The invention relates to welding and can be used in the development of equipment for resistance spot welding. improved surface finish. FIG. 1 schematically shows a device for sharpening the spherical working surface of the electrode, axial section; in fig. 2 - the same, top view; in Fig. 3 - a device for sharpening flat-conical and flat-conical with a ledge of the working surfaces of the electrode, an example of execution; in Fig. 4 - the same, top view. The device for sharpening the electrode consists of a tool 1 installed in a holder 2 with a handle 3 (Fig. 2), or the handle 3 is fixed directly on the tool 1 itself (Fig. 4), In the tool 1, a recess is made on both ends that defines the profile of the processed surface of the electrode 4 and forms a support surface 5. At the ends of the tool 1, grooves b are made, forming parallel teeth 7 on the support surface with two cutting edges 8,U of the tool 1, intended for processing electrodes with a working with a flat-conical or flat-conical surface with a ledge shape (Fig. 3 and 4), the grooves b are placed symmetrically relative to the longitudinal axis and centering blind holes 9 are made on the ends. The electrodes are sharpened as follows .. The device is clamped between the electrodes 4 installed in the electrode holders of the welding machine, welding force, while the electrodes rest on the supporting surfaces 5 on the teeth 7 of the tool 1. The device is centered on the electrodes. At the same time, sections of the supporting surface 5, taking the force from the electrodes, crush the protrusions on the surfaces and elastically deform the electrode material. Turning the device with the handle 3 around the electrodes of the edge 8 cuts off the metal layer, 5 The surface of the electrodes being processed along the entire length of the cutting edge fits snugly to the sections 5 of the supporting surface; since the cutting edge is part of the supporting surface, the sections of the supporting surface 5 sliding along the electrodes 10 under load the end face of the tooth 7, thereby achieving a high surface finish. When the cutting edge 15 is located exactly along the axis of the tool 1, the entire surface of the electrode end face is machined and smoothed. for sharpening electrodes allows you to process the working surfaces of the electrodes without readjusting the machine in terms of force. This achieves high purity and precision processing. The simplicity of the design of the device ensures low manufacturing costs when using commercial equipment 30 that, in order to simplify the design and improve the cleanliness of the machined surface, the teeth are parallel to each other, and each of the teeth is made with two cutting edges and a supporting surface between them to smooth the working surface of the electrode. Production and publishing plant "Patent", Uzhgorod, Gagarina st., 101 Order 2876 Circulation 645

Application

4440071, 03.05.1988

ENTERPRISE PYa G-4086

KRASNOV FELIX IVANOVYCH

IPC / Tags

Link code

Device for sharpening electrodes of resistance spot welding machines

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