UNION OF SOVIET SOCIALIST REPUBLICS 1)5 V 23 K 11/10 DESCRIPTION INVENTED 4b ".,".,.;.;,: 1 ore for resistance and spot welding. The purpose of the invention is to simplify the design and improve the cleanliness of the machined surface. At 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 drive of the resistance welding machine. When the device rotates, the cutting edges 8 cut off the metal layer, and the supporting surfaces 5 smooth the area being processed along the entire working end of the electrode. 4 ill., eknoKTMO-BOGO STATE COMMITTEE FOR INVENTIONS AND DISCOVERIES YAMPRI SCST USSR AUTHOR'S WITNESS (56) Author's certificate USSR 490579, class. B 23 B 29/14, 1974. Sliozberg S. K. Chuloshnikov P. LEtrodes for resistance welding, L.; Machine building, 1972, p. 79, fig. 44 a, (54) DEVICE FOR SHARPENING ELRODS OF MACHINES FOR RESISTANCE Spot 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. The purpose of the invention is to simplify the design and increasing the cleanliness of the treated surface. In FIG. 1 schematically shows a device for sharpening the spherical working surface of an electrode, axial section; in fig. 2 - the same, top view; in Fig, 3 - a device for sharpening flat-conical and flat-conical electrode working surfaces with a protrusion, an example of implementation; 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 handle 3 is attached directly to the tool 1 itself (Fig. 4), in the tool 1, at both ends there is a recess that defines the profile of the processed surface of the electrode 4 and forms the supporting surface 5. At the ends of the tool 1 there are grooves b, forming parallel teeth 7 on the supporting surface with two cutting edges 8. In tool 1, intended for processing electrodes with a working flat-conical or flat-conical surface with a protrusion shape (Fig. 3 and 4), grooves b are placed symmetrically relative to the longitudinal axis and centering blind holes 9 are made at 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 along the electrodes. At the same time, sections of the supporting surface 5, receiving the force from the electrodes, crush the protrusions on the surfaces and elastically deform the material of the electrodes. By rotating the device with handle 3 around the electrodes, edges 8 cut off the metal layer. 5 The treated surface of the electrodes along the entire length of the cutting edge fits tightly to sections 5 of the supporting surface; since the cutting edge is part of the supporting surface, sections of the supporting surface 5 sliding along the electrodes 10 under load smooth out the treated area throughout the end of the tooth 7, thereby achieving high cleanliness of the processed surface. When the cutting edge 15 is positioned exactly along the axis of the tool 1, the entire surface of the end of the electrode is processed and smoothed. The processing of flat-conical electrodes with a protrusion continues until the cylindrical protrusion at the end reaches the bottom of the cylindrical hole 9. The proposed device for sharpening electrodes allows you to process the working surfaces of electrodes without readjusting the machine in terms of force. At the same time, high purity and processing accuracy are achieved. The simplicity of the design of the device ensures a low manufacturing cost when using 30 serial equipment. Formula of invention: A device for sharpening electrodes of machines for resistance spot welding, equipped with teeth and grooves between them, 35 intended for removing chips, different from that , that, in order to simplify the design and improve the cleanliness of the processed surface, the teeth are located parallel to each other, and each 40 of the teeth is made with two cutting edges and a supporting surface between them for smoothing the working surface of the electrode. Production and Publishing Plant "Patent", Uzhgorod, Gagarina St., 101 Order 2876 Circulation 645 Subscription VNIIPI of the State Committee for Inventions and Discoveries at the State Committee for Science and Technology of the USSR 113035, Moscow, Zh-Z 5, Raushskaya embankment, 4/5
Application
4440071, 03.05.1988
ENTERPRISE PYA G-4086
KRASNOV FELIX IVANOVICH
IPC / Tags
Link code
Device for sharpening electrodes of resistance spot welding machines
Similar patents
Movement. During the reverse stroke, the right surface of the upper arm of the double-armed lever 8 and the left surface of the adjacent tooth of the rack 5 come into contact. The direction of action of the resulting reaction force of the rack tooth 5 on the lever 8 changes to the opposite, since nothing interferes in this direction change 119953 The invention relates to the field of welding, in particular to devices for sharpening micro-welding electrodes, and can find application in the instrument-making and radio engineering industries. The purpose of the invention is to improve the quality of sharpening. This goal is achieved through the use of a movable abrasive tool. In FIG. 1 shows the sharpener, general view; in fig. 2 - trajectory of movement of the sharpened end of the elec...
The end section will connect both sides of the rod.1. After this, the rod 1 is installed perpendicular to the sital plate 2 and ground to a certain value 11, determined from the relation where and. - the angle of the initial sharpening of the end; D in the linear dimension "ord" necessary for welding a specific material, Size d increases with increasing thickness of the parts being welded 111 - the height of the end section that must be ground to obtain the required end size). 1) with an increase in the angle Yu , to obtain the end size O, size 1 is increased. The sharpening device, in addition to the electrode 1 and the glass-ceramic plate 2, contains a housing 3, fixed to the handle 4 with the help of a stop 5 and nut B. A screw stop 7 is attached to the housing 3, intended for...
On the tool being sharpened, a metal cutting zone 12 is formed, on which, for safety, the axes of handles 13 are located parallel to the horizontal axis of the body, made of any durable, lightweight material, which serves to apply less force to the handles during the sharpening process. A hand tool for sharpening cutting edges works as follows .When sharpening the cutting edges of tools with a wedge-shaped blade (scythe, ax, etc.) in the field, the sharpened tool is rested with its 3 toe against any hard object or into the ground. The hand tool is taken by the handles 13 and the angular cuts 5 10 15 20 25 30 35 2 are directed to the cutting area. talla 12, Wing nut 9 releases the adjusting screw from fixation and installs it with a spherical...
We decided to separate the story about electrode holders and electrodes for spot welding into a separate article due to the large amount of material on this topic.
Electrode holders for spot welding machines
Electrode holders are used to install electrodes, regulate the distance between them, supply welding current to the electrodes and remove heat generated during welding. The shape and design of the electrode holders is determined by the shape of the unit being welded. As a rule, the electrode holder is a copper or brass pipe with a conical hole for installing an electrode. This hole can be made along the axis of the electrode holder, perpendicular to the axis or at an angle. Often, the same machine can be equipped with several options for electrode holders for each type of electrode, depending on the shape of the parts being welded. In some low-power machines, electrode holders may not be included in the package at all, since their functions are performed by welding trunks.
In standard machines, straight electrode holders are most often used (Fig. 1), as they are the simplest. Electrodes of various shapes can be installed in them. In the case of welding large parts with limited access to the welding site, it is advisable to use shaped electrode holders with simple straight-shaped electrodes. They are attached to electrode holders using a conical fit, pins or screws. The electrode is removed from the holder by lightly tapping it with a wooden hammer or a special extractor.
Electrodes for spot welding
Electrodes for spot welding are used to compress parts, supply welding current to parts and remove heat generated during welding. This is one of the most critical elements of the welding circuit of a spot welding machine, because the shape of the electrode determines the possibility of welding a particular unit, and its durability determines the quality of welding and the duration of uninterrupted operation of the machine. There are straight (Fig. 4) and shaped electrodes (Fig. 5). Some examples of the use of straight electrodes are given in Table 1. Many straight electrodes are manufactured in accordance with GOST 14111-77 or OST 16.0.801.407-87.
For shaped electrodes, the axis passing through the center of the working surface is significantly shifted relative to the axis of the seating surface (cone). They are used for welding parts of complex shapes and assemblies in hard-to-reach places.
Design of electrodes for spot welding
The electrode for spot welding (Fig. 6) structurally consists of a working part (1), a middle (cylindrical) part (2) and a landing part (3). Inside the electrode body there is an internal channel into which the cooling water supply tube of the electrode holder is inserted.
The working part (1) of the electrode has a flat or spherical surface; The diameter of the working surface d el or the radius of the sphere R el is chosen depending on the material and thickness of the parts being welded. The cone angle of the working part is usually 30°.
The middle part (2) ensures the strength of the electrode and the possibility of using extractors or other tools to dismantle the electrodes. Manufacturers use various techniques to calculate electrode sizes. In the USSR, according to OST 16.0.801.407-87, standard size ranges were established:
D el = 12, 16, 20, 35, 32, 40 mm
L = 35, 45, 55, 70, 90, 110 mm
Depending on the maximum compression force of the machine:
D el = (0.4 - 0.6)√F el (mm).
Where: F el - maximum compression force of the machine (daN).
The seating part (3) must be tapered to fit tightly into the electrode holder and prevent cooling water leaks. For electrodes with a diameter of 12-25 mm, the taper is 1:10, for electrodes with a diameter of 32-40 mm - the taper is 1:5. The length of the conical part is at least 1.25D el. The landing part is treated with a cleanliness of at least class 7 (R z 1.25).
The diameter of the internal cooling channel is determined by the flow of cooling water and the sufficient compressive strength of the electrode and is:
d 0 = (0.4 - 0.6) D el (mm).
The distance from the working surface of the electrode to the bottom of the internal channel significantly affects the operational characteristics of the electrode: durability, service life. The shorter this distance, the better the cooling of the electrode, but the less regrinding the electrode can withstand. According to experimental data:
h = (0.75 - 0.80) D el (mm).
Refractory inserts made of tungsten W or molybdenum Mo (Fig. 4g) are pressed into copper electrodes or soldered with silver-containing solders; such electrodes are used when welding galvanized or anodized steels. Electrodes with a replaceable working part (Fig. 4i) and with a ball joint (Fig. 4k) are used when welding parts made of different materials or parts of different thicknesses. The replaceable working part is made of tungsten, molybdenum or their alloys with copper and is attached to the electrode with a union nut. Steel or brass electrodes with a pressed copper shell are also used (Fig. 4h) or copper electrodes with a steel spring-loaded sleeve.
Materials for spot welding electrodes
The durability of electrodes is their ability to maintain the dimensions and shape of the working surface (end), to resist the mutual transfer of metal from the electrodes and the parts being welded (contamination of the working surface of the electrode). It depends on the design and material of the electrode, the diameter of its cylindrical part, the cone angle, the properties and thickness of the material being welded, the welding mode, and the cooling conditions of the electrode. The wear of the electrodes depends on the design of the electrodes (material, diameter of the cylindrical part, cone angle of the working surface) and welding mode parameters. Overheating, melting, oxidation when working in a humid or corrosive environment, deformation of the electrodes under high compression forces, misalignment or displacement of the electrodes increase their wear.
The electrode material is selected taking into account the following requirements:
- electrical conductivity comparable to that of pure copper;
- good thermal conductivity;
- mechanical strength;
- machinability by pressure and cutting;
- resistance to softening during cyclic heating.
Compared to pure copper, alloys based on it have 3-5 times greater resistance to mechanical loads, so copper alloys are used for spot welding electrodes with their seemingly mutually exclusive requirements. Alloying with cadmium Cd, chromium Cr, beryllium Be, aluminum Al, zinc Zn, zirconium Zr, magnesium Mg does not reduce electrical conductivity, but increases strength in a heated state, and iron Fe, nickel Ni and silicon Si increase hardness and mechanical strength. Examples of the use of some copper alloys for spot welding electrodes are given in Table 2.
Selecting electrodes for spot welding
When choosing electrodes, the main parameters are the shape and dimensions of the working surface of the electrode. In this case, it is necessary to take into account the brand of the material being welded, the combination of thicknesses of the sheets being welded, the shape of the welded unit, the requirements for the surface after welding and the design parameters of the welding mode.
There are the following types of shape of the working surface of the electrode:
- with flat ones (characterized by the diameter of the working surface d el);
- with spherical (characterized by radius R el) surfaces.
Electrodes with a spherical surface are less sensitive to distortions, so they are recommended for use on radial-type machines and suspended machines (pincers) and for shaped electrodes operating with large deflections. Russian manufacturers recommend using only electrodes with a spherical surface for welding light alloys, which avoids dents and undercuts along the edges of the weld point (see Fig. 7). But you can avoid dents and undercuts by using flat electrodes with an enlarged end. The same electrodes on a hinge help avoid distortion and therefore can replace spherical electrodes (Fig. 8). However, these electrodes are mainly recommended for welding sheets ≤1.2 mm thick.
According to GOST 15878-79, the dimensions of the working surface of the electrode are selected depending on the thickness and grade of the materials being welded (see Table 3). After examining the cross-section of the weld point, it becomes clear that there is a direct relationship between the diameter of the electrode and the diameter of the core of the weld point. The electrode diameter determines the contact surface area, which corresponds to the fictitious diameter of the resistance conductor r between the sheets being welded. The contact resistance R will be inversely proportional to this diameter and inversely proportional to the pre-compression of the electrodes to smooth out surface micro-irregularities. Research by the ARO company (France) has shown that the diameter of the working surface of the electrode can be calculated using the empirical formula:
d el = 2t + 3 mm.
Where t is the nominal thickness of the sheets being welded.
It is most difficult to calculate the diameter of the electrode when the thickness of the sheets being welded is unequal, when welding a package of three or more parts, and when welding dissimilar materials. Obviously, when welding parts of different thicknesses, the diameter of the electrode must be selected relative to the thinner sheet. Using the formula for calculating the diameter of the electrode, which is proportional to the thickness of the sheet being welded, we form a fictitious conductor with a tapering diameter, which, in turn, moves the heating spot to the point of contact of these two sheets (Fig. 10).
When simultaneously welding a package of parts, the diameter of the working surface of the electrode is selected based on the thickness of the outer parts. When welding dissimilar materials with different thermophysical characteristics, less penetration is observed in the metal with lower electrical resistivity. In this case, on the side of the metal part with lower resistance, an electrode with a larger diameter of the working surface d el or made of a material with greater thermal conductivity (for example, BrKh chromium bronze) is used.
Valery Raisky
Magazine "Equipment: market, supply, prices", No. 05, May 2005.
Literature:
- Knorozov B.V., Usova L.F., Tretyakov A.V. Metal technology and materials science. - M., Metallurgy, 1987.
- Mechanical Engineer's Handbook. T. 5, book. 1. Ed. Satele E.A. - M., Mashgiz, 1963.
The electrode material for resistance welding is selected based on the requirements determined by the specific operating conditions of the electrodes, i.e. significant heating with simultaneous compression, thermal stresses arising inside the electrode due to uneven heating, etc. Quality stability depends on maintaining the shape of the working surface of the electrode in contact with the part being welded. Typically, the durability of electrodes is assessed by the number of points welded under intensive conditions, in which the diameter of the electrode end increases to a size that requires sharpening (about 20%).
Overheating, oxidation, deformation, displacement, and melting of the electrodes during heating increase their wear. Pure copper is thermally and electrically conductive, but not heat resistant. Cold-worked copper is rarely used due to its low recrystallization temperature. Copper alloys with the addition of alloying elements are most often used. Alloying copper with chromium, beryllium, aluminum, zinc, cadmium, zirconium, magnesium, which slightly reduce electrical conductivity, increases its hardness in a heated state. Nickel, iron, and silicon are introduced into copper to strengthen the electrodes. The electrical conductivity of the alloys is estimated as a percentage compared to the conductivity of annealed copper - 0.017241 Ohm mm 2 /m.
Electrodes with tungsten and molybdenum inserts provide high resistance when welding galvanized steel. And electrode plates made of alloys with a hardness of 140–160HB are equipped with inserts made of a metal-ceramic alloy (40% Cu and 60% W) or Br.NBT bronze (see table).
Table. Electrode material for contact welding: characteristics of some alloys, main purpose.
Material for resistance welding electrodes, brand |
Minimum hardness HB |
Content of alloying elements, % mass | Tr, °С |
Main purpose |
|
| 99 Cu | 150– 300 |
Electrodes and rollers for welding aluminum alloys |
|||
| 1.0 Ag | 250– 300 | ||||
|
Bronze Br.KhTsrA 0.3–0.09 |
0.03–0.08 Zr; 0.4–1.0 Cr; | 340– 350 |
Electrodes and rollers for welding aluminum and copper alloys |
||
|
Bronze Br.K1 (MK) |
0.9–1.2 Сd | 250– 300 | |||
|
Bronze Br.H |
0.4–1.0 Cr | 350– 450 |
Electrodes and rollers for welding carbon, low-alloy steels and |
||
|
Bronze Br.ХЦр 0.6–0.05 |
0.03–0.08 Zr; 0.4–1.0 Cr; | 480– 500 | |||
|
Bronze Br.NTB |
1.4–1.6 Ni; 0.05–0.15 Ti; 0.2–0.4 Ve; | 500– 550 |
Electrodes, rollers for welding carbon, stainless steels and heat-resistant alloys |
||
|
Bronze Br.KN1–4 |
3–4 Ni; 0.6–1 Si; | 420– 450 |
Jaws for welding carbon, stainless steels and heat-resistant alloys |
||
|
Cadmium bronze Br.Kd1 (MK) |
0.9–1.2 Cd | - |
Electrodes, rollers for welding light and copper alloys |
||
|
Chrome-zirconium bronze Br.ХЦp 0.3–0.9 |
0.07–0.15 Zr; 0.15–0.35 Cr; | - | |||
|
Chrome bronze Br.X for nickel, titanium and their alloys |
0.3–0.6 Zn; 0.4–1.0 Cr; | - |
Electrodes and rollers |
||
|
Chrome-zirconium bronze Br.ХЦр 0.6–0.05 |
0.03–0.08 Zr; 0.4–1.0 Cr; | - | |||
|
Nickel-chromium-cobalt bronze Br.NKHKo |
≤ 0.5 Ni; ≤ 5.0 Co; ≤ 1.5 Cr; ≤ 2.0 Si | - | |||
|
Nickel-beryllium bronze Br.NBT |
1.4–1.6 Ni; 0.05–0.15 Ti; 0.2–0.4 Be; | - |
Electrodes, jaws, rollers for welding chemically active, refractory metals and alloys |
||
|
Chrome bronze Br.X08 |
0.4–0.7 Cr | - |
Contact jaws |
||
|
Silicon-nickel bronze Br.KN1–4 |
3–4 Ni; 0.6–1.0 Si; | - | |||
|
Silicon-nickel bronze Br.NK1.5–0.5 |
1.2–2.3 Ni; 0.15–0.5 Ti; 0.3–0.8 Si; | - | |||
Used everywhere. They are used for welding aluminum, stainless steel, non-ferrous metals and many other materials. A tungsten electrode + shielding gas combination is a good choice for those who want to achieve high-quality welded joints.
But any welder will tell you that for a decent result, it is not enough to know only welding technology. You also need to remember little tricks that will simplify and even improve the result of your work. One of these tricks is sharpening the electrode. In this article we will briefly explain why it is needed and how you can sharpen a tungsten electrode yourself.
Tungsten is one of the most refractory metals used for the manufacture of electrodes. The melting point of tungsten is more than 3000 degrees Celsius. In normal welding conditions such temperatures are not used. Therefore, tungsten electrodes are called non-consumable. When used, they practically do not change in size.
But despite this, tungsten electrodes can still become shorter. During the welding process (for example, when igniting an arc or when forming a seam), the electrode can grind off the metal surface. In most cases it's not that bad. But sometimes a blunt electrode causes lack of penetration.
How to solve this problem? Very simple: sharpen it. The sharpened tungsten electrode regularly performs its function, forming high-quality, durable seams.
How to sharpen an electrode
Sharpening a tungsten electrode can be done in a variety of ways. This can be an abrasive wheel, chemical sharpening, sharpening with a special paste, or mechanical sharpening. The latter is performed using special devices. They can be either portable or stationary.
Portable ones include a manual machine for sharpening tungsten electrodes, and stationary ones include a machine for sharpening tungsten electrodes. In our opinion, the use of such devices gives the optimal result.
The sharpening shape can be spherical or conical. The spherical shape is more suitable for DC welding, while the conical shape is more suitable for AC welding. Some welders note that they do not notice much difference when welding with electrodes with different sharpening shapes. But our experience has shown that there are still differences. And if you weld professionally, the difference will be obvious.
The optimal length of the sharpened part can be calculated using the formula Ø*2 . That is, if the diameter of the electrode is 3 mm, then the length of the sharpened part should be 6 mm. And so on by analogy with any other diameter. After sharpening, dull the end of the electrode slightly by tapping it on a hard surface.
Another important parameter is the sharpening angle of the electrode. It will depend on how much welding current you use.
So, when welding at a low value of welding current, an angle of 10-20 degrees will be sufficient for sharpening. The optimal angle is 20 degrees.
A sharpening angle of 20-40 degrees is a good option when welding using average welding current values.
If you use large currents, the sharpening angle can be from 40 to 120 degrees. But we do not recommend sharpening the rod more than 90 degrees. Otherwise, the arc will burn unstably and it will be difficult for you to form a seam.
The design of the electrodes must have a shape and dimensions that provide access to the working part of the electrode to the place where parts are welded, be adapted for convenient and reliable installation on the machine, and have high durability of the working surface.
The simplest to manufacture and operate are straight electrodes, made in accordance with GOST 14111-69 from various copper electrode alloys, depending on the grade of metal of the parts being welded.
Sometimes, for example, when welding dissimilar metals or parts with a large difference in thickness, in order to obtain high-quality connections, the electrodes must have a fairly low electrical thermal conductivity (30...40% of copper). If the entire electrode is made from such metal, it will heat up intensely from the welding current due to its high electrical resistance. In such cases, the base of the electrode is made of a copper alloy, and the working part is made of metal with the properties necessary for the normal formation of connections. Working part 3 can be replaceable (Fig. 1, a) and secured with a nut 2 on base 1. The use of electrodes of this design is convenient, as it allows you to install the desired working part when changing the thickness and grade of the metal of the parts being welded. The disadvantages of an electrode with a replaceable part are the possibility of using it only when welding parts with good approaches and insufficiently intensive cooling. Therefore, such electrodes should not be used in heavy welding conditions at high speeds.
Rice. 1 . Electrodes with a working part made of another metal
The working part of the electrodes is also made in the form of a soldered (Fig. 1, b) or pressed-in tip (Fig. 1, c). The tips are made of tungsten, molybdenum or their compositions with copper. When pressing a tungsten tip, it is necessary to grind its cylindrical surface in order to ensure reliable contact with the base of the electrode. When welding parts made of stainless steel with a thickness of 0.8...1.5 mm, the diameter of the tungsten insert 3 (Fig. 1, c) is 4...7 mm, the depth of the pressed part is 10...12 mm, and the protruding part is 1.5...2 mm. With a longer protruding part, overheating and a decrease in the durability of the electrode are observed. The working surface of the insert can be flat or spherical.
When designing electrodes, special attention should be paid to the shape and dimensions of the seating part. The most common is a conical landing part, the length of which should be at least. Electrodes with a shortened cone should only be used when welding using low forces and currents. In addition to the conical fit, electrodes are sometimes fastened to threads using a union nut. This connection of electrodes can be recommended in. multi-point machines, when it is important to have the same initial distance between the electrodes, or in clamps. When using shaped electrode holders, electrodes with a cylindrical seat are also used (see Fig. 8, d).
When spot welding parts with complex contours and poor approaches to the joint, a wide variety of shaped electrodes are used, which have a more complex design than straight ones, are less convenient to use and, as a rule, have reduced durability. Therefore, it is advisable to use shaped electrodes when welding is generally impossible without them. The dimensions and shape of the shaped electrodes depend on the size and configuration of the parts, as well as the design of the electrode holders and consoles of the welding machine (Fig. 2).
Rice. 2. Various types of shaped electrodes
During operation, shaped electrodes usually experience a significant bending moment from off-axis application of force, which must be taken into account when selecting or designing electrodes. The bending moment and the usually small cross-section of the cantilever part create significant elastic deformations. In this regard, mutual displacement of the working surfaces of the electrodes is inevitable, especially if one electrode is straight and the other is shaped. Therefore, for shaped electrodes, the spherical shape of the working surface is preferable. In the case of shaped electrodes that experience large bending moments, deformation of the conical seating part and the electrode holder socket is possible. The maximum permissible bending moments for shaped electrodes made of Br.NBT bronze and electrode holders made of heat-treated bronze Br.Kh are, according to experimental data, for electrode cones with a diameter of 16, 20, 25 mm, respectively, 750, 1500 and 3200 kg× cm. If the conical part of the shaped electrode experiences a moment greater than permissible, then the maximum diameter of the cone should be increased.
When designing complex spatial shaped electrodes, it is recommended to first make a model of them from plasticine, wood or easily machined metal. This allows you to establish the most rational dimensions and shape of the shaped electrode and avoid alterations when manufacturing it directly from metal.
In Fig. 3 shows some examples of welding assemblies in places with limited access. Welding of the profile with the shell is performed using a lower electrode with an offset working surface (Fig. 3, a).
Rice. 3. Examples of using shaped electrodes
An example of using an upper electrode with oblique sharpening and a lower, shaped one is shown in Fig. 3, b. The angle of deviation of the electrode holder from the vertical axis should not be more than 30°, otherwise the conical hole of the electrode holder will be deformed. If it is impossible to install the upper electrode with a slope, then it can also be shaped. The shaped electrode is bent in two planes to reach a hard-to-reach welding spot (Fig. 3, c-e). If the machine does not have or has limited horizontal movement of the consoles for welding the parts shown in Fig. 3, e, two shaped electrodes with equal projections are used.
Sometimes shaped electrodes perceive very large bending moments. To avoid deformation of the conical seating part, the shaped electrode is additionally secured to the outer surface of the electrode holder using a clamp and a screw (Fig. 4, a). The strength of shaped electrodes with a long reach increases significantly if they are made of composite (reinforced) electrodes. For this purpose, the main part of the electrode is made of steel, and the current-carrying part is made of a copper alloy (Fig. 4, b). The connection of current-carrying parts to each other can be made using soldering, and with a steel console - using screws. A design option is possible when a shaped electrode made of a copper alloy is supported (reinforced) with steel elements (bars), which should not form a closed ring around the electrode, since currents will be induced in it, increasing the heating of the electrode. It is advisable to fasten shaped electrodes that experience large moments in the form of an elongated cylindrical part for installation in a machine instead of an electrode holder (see Fig. 4, b).
Rice. 4. Electrodes that perceive a large bending moment:
a - with reinforcement for the outer surface of the electrode holder;
b - reinforced electrode: 1 - steel console; 2 - electrode; 3 - current supply
In most cases, spot welding uses internal cooling of the electrodes. However, if welding is performed with electrodes of small cross-section or with high heating, and the material being welded is not subject to corrosion, external cooling is used in the tongs. The supply of cooling water is carried out either by special tubes or through holes in the working part of the electrode itself. Great difficulties arise when cooling shaped electrodes, since it is not always possible to supply water directly to the working part due to the small cross-section of the cantilever part of the electrode. Sometimes cooling is performed using thin copper tubes soldered to the side surfaces of the cantilever part of a shaped electrode of a fairly large size. Considering that shaped electrodes are always cooled worse than straight electrodes, it is often necessary to significantly reduce the welding rate, preventing overheating of the working part of the shaped electrode and reducing durability.
When using pliers for welding in hard-to-reach places, as well as the need to frequently replace electrodes, use the electrode mounting shown in Fig. 5. This fastening provides good electrical contact, convenient regulation of electrode extension, good stability against lateral displacement, and quick and easy removal of electrodes. However, due to the lack of internal cooling in such electrodes, they are used when welding at low currents (up to 5...6 kA) and at a low speed.
Rice. 5. Methods for attaching electrodes
For ease of operation, electrodes with several working parts are used. These electrodes can be adjustable or rotary (Fig. 6) and significantly simplify and speed up the installation of electrodes (aligning working surfaces).
Rice. 6. Multi-position adjustable (a) and surface (b) electrodes:
1 - electrode holder; 2 - electrode
The electrodes are installed in electrode holders, which are fixed to the cantilever parts of the welding machine, transmitting compression force and current. In table For reference, the dimensions of straight electrode holders of the main types of spot welding machines are given. Electrode holders must be made of sufficiently strong copper alloys with relatively high electrical conductivity. Most often, electrode holders are made of Br.Kh bronze, which must be heat-treated to obtain the required hardness (HB not less than 110). In the case of welding steels, when low currents (5...10 kA) are used, it is advisable to make electrode holders from Br.NBT bronze or silicon-nickel bronze. These metals ensure long-term preservation of the dimensions of the conical mounting hole of the electrode holder.
Table. Dimensions of electrode holders for point machines in mm
|
Electrode holder dimensions |
MTPT-600 |
MTPT-400, MTK-75 |
MTP-300, MTP-400 |
MTK 6301, MTP-200/1200 |
MTPU-300, MTP-150/1200 MTP-200, MTP-150, MT 2507 |
MT 1607, MTP-75 MTP-100, MTPR-75 (50, 25) MTPK-25, MT 1206 |
|
Outside diameter |
||||||
|
Cone diameter for electrode |
||||||
|
Taper |
1: 10 |
1:10 |
1:10 |
The most common are straight electrode holders (Fig. 7). Inside the cavity of the electrode holder there is a tube for supplying water, the cross-section of which should be sufficient for intensive cooling of the electrode. With a tube wall thickness of 0.5...0.8 mm, its outer diameter should be 0.7...0.75 of the diameter of the electrode hole. In the case of frequent changes of electrodes, it is advisable to use electrode holders with ejectors (Fig. 7, b). The electrode is pushed out of the seat by hitting the striker 5 with a wooden hammer, which is connected to a stainless steel tube - ejector 1. The ejector and striker are returned to their original lower position by a spring 2. It is important that the end of the ejector hitting the end of the electrode does not have damage on its surface, otherwise the seating part of the electrode will quickly fail, jamming when it is removed from the electrode holder. It is convenient for operation to make the end of the electrode holder 1 in the form of a replaceable threaded bushing 2, in which the electrode 3 is installed (Fig. 7, c). This design makes it possible to make sleeve 2 from a more resistant metal and replace it when worn and install an electrode of a different diameter, and also to easily remove the electrode when jammed by knocking it out with a steel drift from inside the sleeve.
Rice. 7. Straight electrode holders:
a – normal;
b – with ejector;
c – with replaceable sleeve
If shaped electrodes are more often used when welding parts that have small dimensions of the elements being connected, then for larger sizes it is advisable to use special shaped electrode holders and simple electrodes. Shaped electrode holders can be composite and provide installation of electrodes at different angles to the vertical axis (Fig. 8, A). The advantage of such an electrode holder is the easy adjustment of the electrode extension. In some cases, the shaped electrode can be replaced with electrode holders shown in Fig. 8, b. Also of interest is the electrode holder, the tilt of which can be easily adjusted (Fig. 8, c). The design of an electrode holder bent at an angle of 90° is shown in Fig. 30, g, it allows you to attach electrodes with a cylindrical seat. A special screw clamp ensures quick fastening and removal of the electrodes. In Fig. Figure 9 shows various examples of spot welding using shaped electrode holders.
Rice. 8. Special electrode holders
Rice. 9. Examples of the use of various electrode holders
When spot welding large-sized components such as panels, it is advisable to use a four-electrode rotating head (Fig. 10). The use of such heads allows you to quadruple the operating time of the electrodes before the next stripping, without removing the panel to be welded from the working space of the machine. To do this, after each pair of electrodes is contaminated, the electrode holder 1 is rotated 90° and secured with a stopper 4. The rotating head also makes it possible to install electrodes with different shapes of the working surface for welding an assembly with parts changing, for example, stepwise in thickness, as well as to provide mechanization of stripping the electrodes with special devices. The rotating head can be used when spot welding parts with large differences in thickness and is installed on the side of the thin part. It is known that in this case the working surface of the electrode in contact with a thin part quickly wears out and is replaced by turning the head with a new one. It is convenient to use a roller as an electrode on the side of a thick part.
Rice. 10. Rotating electrode head:
1 – rotary electrode holder; 2 – body; 3 – electrode; 4 – stopper
When spot welding, the axes of the electrodes must be perpendicular to the surfaces of the parts being welded. To do this, welding of parts that have slopes (smoothly varying thickness), or are manufactured using overhead machines, in the presence of large-sized components, is performed using a self-aligning rotary electrode with a spherical support (Fig. 11, a). To prevent water leakage, the electrode has a seal in the form of a rubber ring.
Rice. 11. Self-aligning electrodes and heads:
a - rotary electrode with a flat working surface;
b - head for two-point welding: 1 - body; 2 - axis;
c - plate electrode for welding mesh: 1, 7 - machine consoles; 2-fork; 3 - flexible tires; 4-swinging electrode; 5 - welded mesh; 6 - bottom electrode
On conventional spot machines, welding of steel parts of relatively small thickness can be performed at two points at once using a two-electrode head (Fig. 11, b). Uniform distribution of forces on both electrodes is achieved by rotating the housing 1 relative to axis 2 under the action of the compression force of the machine.
To weld a mesh of steel wire with a diameter of 3...5 mm, plate electrodes can be used (Fig. 11, c). The upper electrode 4 swings on an axis to evenly distribute forces between the connections. The current supply for the purpose of its uniformity is carried out by flexible busbars 3; fork 2 and the swing axis are isolated from the electrode. When electrodes are up to 150 mm long, they can be non-oscillating.
Rice. 12. Sliding wedge electrodes inserts
When welding panels consisting of two skins and stiffeners, there must be an electrically conductive insert inside that absorbs the force of the machine electrodes. The design of the insert must ensure its tight fit to the inner surface of the parts being welded without a gap, in order to avoid deep dents on the outer surfaces of the parts and possible burns. For this purpose, a sliding insert shown in Fig. 12. The movement of the wedge 2 relative to the stationary wedge 4, ensuring their compression to the welded parts 3, is synchronized with the operation of the machine. When electrodes 1 and 5 are compressed and welding occurs, air from the pneumatic drive system of the machine enters the right cavity of the cylinder 8 mounted on the front wall of the machine and moves the wedge 2 through the rod 7, increasing the distance between the working surfaces of the wedges. When raising electrode 1, the air leaves the right one and begins to enter the left cavity of the cylinder 8, reducing the distance between the surfaces of the wedges, which allows the panel to be welded to be moved relative to the electrodes of the machine. The wedge insert is cooled by air that enters through tube 6. The use of such an insert allows you to weld parts with an internal distance between them of up to 10 mm.