Special types of contact welding. We understand the drawings of welding seams according to GOST Designation of capacitor welding cd drawing

26.04.2020

- your favorite word, hardly anyone will believe you. But if you are engaged in welding and claim the status of a high-class professional, you will have to respect this word, if not love it.

He needs not only to be respected, but to be well versed in the state standards concerning the typology of welding methods. Why? Because if you are working with something more serious than an old basin in the country, you will definitely come across working drawings, where there will be icons, letters and abbreviations in huge quantities.

That's right, without technical specifications and standard designations - nowhere. Modern welding technologies are a wide range of the most different methods with their own requirements and technical nuances. All of them fit into several standards, which we will now go through and consider in the most careful way.

Welding symbols in GOST drawings look intimidating at first glance. But if you figure it out and stock up on original versions of the three main GOSTs by types and designations, the designations will become understandable and informative, and your work will be accurate and professional.

Kinds welded joints.

First, ESKD is a Unified System Design Documentation, to put it simply - a set of various standards, according to which all modern technical drawings, including welding documentation, must be carried out.

As part of this system, there are several standards that interest us:

GOST 2.312-72 entitled "Conventional images and designations of welded joints".
GOST 5264-80 “Manual arc welding. Welded joints”, which exhaustively describes all possible types and designations welds.
GOST 14771-76 “Seams of welded joints, welding in shielding gases”.

To deal with the symbols of welding methods in engineering drawings, you need to understand their types. We offer a look at an example of the designation in the drawing:

Looks bulky and intimidating. But we will not be nervous and slowly figure everything out. There is a clear logic in this long abbreviation, let's start moving through the stages. Let's break this monster into nine components:

Now these same constituent elements by squares:

Square 1 - auxiliary signs to indicate: a closed line or field connection.
Square 2 is the standard according to which the symbols are given.
Square 3 - designation by letter and number of the type of connection with its structural elements.
Square 4 - welding method according to the standard.
Square 5 - type and dimensions structural elements according to the standard.
Square 6 - characteristic in the form of the length of a continuous section.
Square 7 - connection characteristic, auxiliary sign.
Square 8 is an auxiliary sign for describing a compound or its elements.

And now let's analyze in detail each element of our long abbreviation.

In square number 1 there is a circle - one of the additional characteristics, a symbol of a circular connection. The alternate symbol is a flag indicating a mounting option instead of a circular one.

A special one-way arrow shows the seam line. Another specific feature of welding drawings is associated with this arrow. This one-sided fletching arrow has a nice feature called "shelf". The shelf plays the role of a real shelf - all symbols can be located on the shelf if a visible connection is specified.

Or under the shelf, if this seam is invisible and located on the reverse side, i.e. from the inside. What is considered the front side, and what is the wrong side? The front side of a one-way connection is always the one that is being worked on, it's simple. But in the double-sided version with asymmetrical edges, the front side will be the one where the main joint is being welded. And if the edges are symmetrical front and back, any side can.

And here are the most popular auxiliary signs used in drawings with welding:

We disassemble squares No. 2 and 3, types of seams according to GOSTs

Two standards are closely involved in connection options: GOST 14771-76 already familiar to us and the famous GOST 5264-80 about.

What the second standard is famous for: it was written many years ago - in 1981, and it was done so competently that this document still works fine.

An example of a drawing of welds according to GOST.

Kinds welding joints the following:

C - butt seam. Welded metal surfaces are connected by adjacent ends, are on the same surface or in the same plane. This is one of the most common options, since the mechanical parameters of butt structures are very high. However, this method is quite complicated from a technical point of view, it is within the power of experienced craftsmen.

T - tee seam. The surface of one metal workpiece is connected to the end face of another workpiece. This is the most rigid design of all possible, but due to this, the tee method does not like and is not intended for loads with bending.

H - overlap seam. The surfaces to be welded are parallel offset and slightly overlap each other. The method is pretty solid. But the load transfers less than the butt options.

U - corner seam. Melting goes along the ends of the workpieces, the surfaces of the parts are held at an angle to each other.

O - special types. If there is no method in GOST, a special type of welding is indicated in the drawing.

Both standards within the framework of the EKSD are in good agreement with each other and fairly share the responsibility by type:

Variants of the image of welds in the drawings.

Connections of the manual arc method according to GOST 5264-80:

C1 - C40 butt
T1 - T9 tee
H1 - H2 lap
U1 - U10 corner

Welding joints in shielding gases according to GOST 14771-76:

C1 - C27 butt
T1 - T10 tee
H1 - H4 lap
U1 - U10 corner

In our abbreviation, in the second square, GOST 14771-76 is indicated, and in the third T3, the tee method without beveled edges is double-sided, which is just indicated in this standard.

Square No. 4, welding methods

As indicated different kinds seams.

Also in the standards there are designations of welding methods, here are examples of the most common of them:

A - automatic submerged arc without pads and pads;
Af - automatic submerged arc on a cushion;
ANDH - in an inert gas tungsten electrode without additive;
INp - method in an inert gas with a tungsten electrode, but already with an additive;
IP - method in an inert gas with a consumable electrode;
UE - the same, but in carbon dioxide.

We have in square No. 4 the designation of welding UE is indicated - this is a method in carbon dioxide with a consumable electrode.

Square No. 5, seam dimensions

These are the required seam dimensions. It is most convenient to indicate the length of the leg, since we are talking about a T-shaped version with a perpendicular union at a right angle. The leg is determined depending on the yield strength.

It should be noted that if the connection of standard dimensions is indicated on the drawing, the length of the leg is not indicated. In our drawing designation, the leg is equal to 6 mm.

Classification of welds.

Additional connections are:

SS unilateral, for which the arc or move on one side.
BS double-sided, the source of melting moves on both sides.

The third participant of our drawing and welding party - GOST 2.312-72, just dedicated to images and symbols, enters into business.

According to this standard, the seams are divided into:

Visible, which are depicted as a solid line.
Invisible, indicated in the drawings by a dotted line.

Now back to our original seam. We are able to translate this welding symbol into a simple and understandable text for the human ear:

Double-sided tee seam by manual arc welding in protective carbon dioxide with edges without bevels, intermittent with a staggered arrangement, the leg of the seam is 6 mm, the length of the welded area is 50 mm, the step is 100 mm, the bulges of the seam should be removed after welding.

state standard

UNION SSR

CONSTRUCTION ELEMENTS AND DIMENSIONS

GOST 15878-79

Official edition

USSR STATE COMMITTEE ON STANDARDS

UDC 621.791.76.052:006.354 STATE

STANDARD OF THE UNION OF THE SSR

CONTACT WELDING. WELDED CONNECTIONS

Structural elements and dimensions

resistance welding. Welded joints.

Design elements and dimensions

GOST 15873-70

By the Decree of the USSR State Committee for Standards dated May 28, 1979 No. 1926, the validity period is established

1. This standard establishes the structural elements and dimensions of design welded joints made of steels, alloys on iron-nickel and nickel bases, titanium, aluminum, magnesium and copper alloys, performed by resistance spot, projection and seam welding.

The standard does not apply to welded joints performed by resistance welding without metal fusion.

2. The following designations for contact welding methods are accepted in the standard:

/C t - point;

Kr - embossed;

K w - suture.

The following designations are accepted for structural elements of welded joints:

s and 51-thickness of the part;

d is the calculated diameter of the cast core of the point or the width of the cast zone of the weld;

h and hi - penetration value;

g and g\ - the depth of the dent;

t is the distance between the centers of neighboring points in a row;

c is the distance between the axes of adjacent rows of points in a chain arrangement;

C\ - distance between the axes of adjacent rows of points in a staggered arrangement;

Official publication Reprint prohibited

from 01.07. 1980 to 01.07. 1985

Non-compliance with the standard is punishable by law

(§) Standards Publishing, 1979

I - length of the cast zone of the seam;

f ~ the value of the overlap of the cast zones of the weld;

1\ - the length of the non-overlapped part of the seam zone with a league;

B - the amount of overlap;

and - distance from the center of the point or axis of the seam to the edge of the overlap;

n is the number of rows of points.

3. Structural elements of welded joints, their dimensions must correspond to those indicated in Fig. 1, 2, 3 and in the table. 1, 3, 5 for compounds of the Ive group of the table. 2, 4, 6^ for compounds of group B.

The connection group must be established during the design, depending on the requirements for the welded structure and especially on it. technological process welding.

4. The value of the overlap B for multi-row seams with a chain arrangement of points B ~ 2u + c (n-1); with a checkerboard arrangement of points B \u003d 2u + C\ (n-1).

5. Depending on the type of overlap of the welded joint, the amount of overlap B should be determined in accordance with Fig. four.

6. The distance from the center of the point or axis of the seam to the edge of the overlap and must be at least half the minimum overlap.

7. Welding of parts of unequal thickness is allowed; in this case, the dimensions of the structural elements should be selected according to the part of a smaller thickness.

In the case of - > 2, the minimum overlap values B at the distance

The distance between the centers of adjacent points in the row t and the distance between the axes of adjacent rows of points c should be increased by 1.2-1.3 times.

8. When welding three or more parts, the calculated diameter of the cast core of the point d should be set separately for each pair of mating parts. Through penetration of medium parts is allowed.

9. The penetration value h y hi should be for magnesium alloys from 20 to 70%, titanium --- from 20 to 95% and other metals and alloys - from 20 to 80% of the thickness of the parts.

10. With suture resistance welding the overlap of the cast zones of the sealed weld / must be at least 25% of the length of the cast zone of the weld L

In case of resistance seam welding of parts with a thickness of less than 0.6 mm, it is allowed to reduce the amount of overlap of the cast zones of the seam to values that guarantee the tightness of the weld.

11. The depth of the dent g y gi should not be more than 20% of the thickness

details. When welding parts with a ratio of -\u003e 2, in the case of using one of the electrodes with an increased flat working

surface, as well as when welding in hard-to-reach places, it is allowed to increase the depth of the dent up to 30% of the thickness of the part.

Structural elements of welded joints,

made by resistance spot welding

a-unlacquered metals; b - clad metals; c - parts of unequal thickness; 2 - dissimilar metals

Structural elements of welded joints made by contact relief welding

Ppspe gift

Structural elements of welded joints made by resistance seam welding

	Single row sh<	ev V, not less than	don't change it

St. 0.3 to 0.4
St. 0.4 to 0.6
St. 0.6 to 0.7
St. 0.7 to 0.8
Over 0.8 to 1.0
Over 1.0 to 1.3
St. 1.3 to 1.6
St. 1.6 to 1.8
St. 1.8 to 2.2
St. 2.2 to 2.7
St. 2.7 to 3.2
St 3.2 to 3.7
St. 3.7 to 4.2
St. 4.2 to 4.7
St. 4.7 to 5.2
St. 5.2 to 5.7
St. 5.7 to 6.0

connections		Single row seam B, not less than
connections		Steels, alloys on iron-nickel and nickel bases, titanium alloys	Aluminum, magnesium and copper alloys

	Over 0.3 to 0.4
	St. 0.4 to 0.5
	St. 0.5 to 0.6
	St. 0.6 to 0.8
	Over 0.8 to 1.0
	Over 1.0 to 1.3
	St 1.3 to 1.6
	St. 1.6 to 1.8
	St. 1.8 to 2.2
	St. 2.2 to 2.7
	St. 2.7 to 3.2

Note. It is allowed to reduce the dimensions t and c, while the dimension d must correspond to those indicated in the table.

Connection group		d, not less than	Single row seam B, not less than

	St, 0.3 to 0.4
	St. 0.4 to 0.6
	St, 0.6 to 0.7
	St, 0.7 to 0.8
	Sv 0.8 to 1.0
	Over 1.0 to 1.3
	St. 1.3 to 1.6
	St. 1.6 to 1.8
	St. 1.8 to 2.2
	St. 2.2 to 2.7

Continuation of the table. 3

connections		d, not less than	Single row seam B, not less than
	St. 2.7 to 3.2
	St. 3.2 to 3.7
	St. 3.7 to 4.2
	St 4.2 to 4.7
	St. 4.7 to 5.2
	St. 5.2 to 5.7
	St. 5.7 to 6.0

Table 4

Connection group		Single-row seam B, d, not less

	St. 0.3 to 0.4
	Sv 0.4 to 0.5
	St. 0.5 to 0.6
	St. 0.6 to 0.8
	Over 0.8 to 1.0
	Over 1.0 to 1.3
	St. 1.3 to 1.6
	St. 1.6 to 1.8
	St.], 8 to 2.2
	St. 2.2 to 2.7
	St. 2.7 to 3.2
	St. 3.2 to 3.7
	St. 3.7 to 4.2
	St. 4.2 to 4.7
	St. 4.7 to 5.2
	St. 5.2 to 5.7
	St. 5.7 to 6.0

				Single row seam B, not less than
Welding method			d, not less than	Steels, alloys on iron-nickel and nickel bases, titanium alloys	Aluminum, magnesium and copper alloys

		St. 0.3 to 0.4
		St. 0.4 to 0.6
		Sv 0.6 to 0.8
		Sv 0.8 to 1.0
		From 1.0 to 1.3
		("at 1.3 to 1.6
		g:in 1.6 to 1.8
		St. 1.8 to 2.2
		St. 2.2 to 2.7
		St. 2.7 to 3.2
		St. 3.2 to 3.7
		St. 3.7 to 4.0
					Table 6
				Single row seam B, not less than
Welding method	Connection group		d, not less than	Steels, alloys on iron-nickel and nickel bases, titanium alloys	Aluminum, magnesium and copper alloys

		St. 0.3 to 0.4
		St. 0.4 to 0.5
		St. 0.5 to 0.6
		Sv 0.6 to 0.8
		Over 0.8 to 1.0

Continuation of the table. 6

Welding method	Connection group		d, not less than	Single row seam B, not less than
Welding method	Connection group		d, not less than	Steels, alloys on iron-nickel and nickel bases, titanium alloys	Aluminum, magnesium and copper alloys
		Over 1.0 to 1.3
		St. 1.3 to 1.6
		St. 1.6 to 1.8
		St. 1.8 to 2.2
		St, 2.2 to 2.7
		St. 2.7 to 3.2

Types of overlapping of welded joints performed by resistance spot relief and seam welding

Editor I. V. Vinogradskaya Technical editor V. Yu. Smirnova Proofreader E. I. Evteeva

Handed over to the set 06/21/79 Signed. in the oven 08/10/79 0.75 p. l. 0.57 account -ed. l. Tyr. 30000 Price 3 kop.

Order "Badge of Honor" Publishing house of standards. Moscow, D-557, Novopresnensky per., 3. Kaluga printing house of standards, st. Moscow, 256. Zach. 1727

1. Physical basis of welding

Welding is a technological process of obtaining an inseparable connection of materials due to the formation of an atomic bond. The process of creating a welded joint proceeds in two stages.

At the first stage, it is necessary to bring the surfaces of the materials to be welded closer to the distance between the forces of interatomic interaction (about 3 A). Ordinary metals at room temperature do not bond under compression even with considerable effort. The bonding of materials is hindered by their hardness; when they come together, actual contact occurs only at a few points, no matter how carefully they are processed. The bonding process is strongly affected by surface contamination - oxides, fatty films, etc., as well as layers of absorbed impurity atoms. Due to these reasons, it is impossible to fulfill the condition of good contact under normal conditions. Therefore, the formation of physical contact between the joined edges over the entire surface is achieved either due to the melting of the material, or as a result of plastic deformations resulting from the applied pressure. At the second stage, the electronic interaction between the atoms of the joined surfaces takes place. As a result, the interface between the parts disappears and either atomic metal bonds are formed (metals are welded), or covalent or ionic bonds (when welding dielectrics or semiconductors). Based on the physical essence of the process of formation of a welded joint, three classes of welding are distinguished: fusion welding, pressure welding and thermomechanical welding (Fig. 1.25).

Rice. 1.25.

To fusion welding include types of welding carried out by fusion without applied pressure. The main sources of heat in fusion welding are the welding arc, gas flame, radiant energy sources and "Joule heat". In this case, the melts of the joined metals are combined into a common weld pool, and upon cooling, the melt crystallizes into a cast weld.

For thermomechanical welding thermal energy and pressure are used. The joining of the connected parts into a monolithic whole is carried out by applying mechanical loads, and the heating of the workpieces provides the necessary plasticity of the material.

For pressure welding include operations carried out with the application of mechanical energy in the form of pressure. As a result, the metal deforms and begins to flow like a liquid. The metal moves along the interface, carrying the contaminated layer with it. Thus, fresh layers of material come into direct contact, which enter into chemical interaction.

2. Main types of welding

Manual arc welding. Electric arc welding is currently the most important type of metal welding. The heat source in this case is an electric arc between two electrodes, one of which is the workpiece to be welded. An electric arc is a powerful discharge in a gaseous medium.

The process of ignition of the arc consists of three stages: short circuit of the electrode to the workpiece, retraction of the electrode by 3-5 mm and the occurrence of a stable arc discharge. A short circuit is performed in order to heat the electrode (cathode) to the temperature of intense electron exo-emission.

At the second stage, the electrons emitted by the electrode are accelerated in the electric field and cause ionization of the cathode-anode gas gap, which leads to the appearance of a stable arc discharge. The electric arc is a concentrated source of heat with temperatures up to 6000 °C. Welding currents reach 2-3 kA at arc voltage (10-50) V. Covered electrode arc welding is most commonly used. This is manual arc welding with an electrode coated with an appropriate composition, having the following purpose:

1. Gas and slag protection of the melt from the surrounding atmosphere.

2. Alloying of the weld material with the necessary elements.

The composition of the coatings includes substances: slag-forming - to protect the melt with a shell (oxides, feldspars, marble, chalk); forming gases CO2, CH4, CCl4; alloying - to improve the properties of the seam (ferrovanadium, ferrochromium, ferrotitanium, aluminum, etc.); deoxidizers - to eliminate iron oxides (Ti, Mn, Al, Si, etc.) An example of a deoxidation reaction: Fe2O3 + Al \u003d Al2O3 + Fe.

Rice. 1.26. : 1 - parts to be welded, 2 - weld, 3 - flux crust, 4 - gas shield, 5 - electrode, 6 - electrode coating, 7 - weld pool

Rice. 1.26 illustrates coated electrode welding. According to the above scheme, a welding arc is ignited between the parts (1) and the electrode (6). Coating (5) during melting protects the welding seam from oxidation, improves its properties by alloying. Under the influence of the arc temperature, the electrode and the workpiece material melt, forming a weld pool (7), which further crystallizes into a weld (2), the latter is covered with a flux crust (3) from above, designed to protect the weld. To obtain a high-quality weld, the welder places the electrode at an angle (15-20) 0 and moves it down as it melts to maintain a constant arc length (3-5) mm and along the weld axis to fill the groove with metal. In this case, usually the end of the electrode makes transverse oscillatory movements to obtain rollers of the required width.

Automatic submerged arc welding.

Widely used automatic consumable electrode welding under a layer of flux. The flux is poured onto the product with a layer (50-60) mm thick, as a result of which the arc burns not in air, but in a gas bubble located under the flux melted during welding and isolated from direct contact with air. This is sufficient to eliminate splashing of liquid metal and distortion of the weld shape even at high currents. When welding under a flux layer, a current of up to (1000-1200) A is usually used, which is impossible with an open arc. Thus, betting submerged arc welding can increase the welding current by 4-8 times compared to open arc welding, while maintaining good welding quality at high productivity. In submerged arc welding, the weld metal is formed due to the melting of the base metal (about 2/3) and only about 1/3 due to the electrode metal. The arc under a flux layer is more stable than with an open arc. Welding under a flux layer is carried out with a bare electrode wire, which is fed from the coil into the arc burning zone by the welding head of the machine, which is moved along the seam. Ahead of the head, a granular flux enters the weld groove through the pipe, which, melting during the welding process, evenly covers the seam, forming a hard crust of slag.

Thus, automatic welding under a flux layer differs from manual welding in the following indicators: stable quality of the seam, productivity is (4-8) times greater than in manual welding, the thickness of the flux layer is (50-60) mm, the current strength is ( 1000-1200) A, the optimal arc length is maintained automatically, the seam consists of 2/3 of the base metal and 1/3 of the arc burns in a gas bubble, which ensures excellent welding quality.

Electroslag welding.

Electroslag welding is a fundamentally new type of metal joining process, invented and developed at the PWI. Paton. The parts to be welded are covered with slag heated to a temperature exceeding the melting temperature of the base metal and electrode wire.

At the first stage, the process proceeds in the same way as in submerged arc welding. After the formation of a bath of liquid slag, the arc stops and the edges of the product are melted due to the heat released when current passes through the melt. Electroslag welding allows welding large thicknesses of metal in one pass, provides high productivity, high quality of the weld.

Rice. 1.27. :

1 - welded parts, 2 - weld, 3 - molten slag, 4 - sliders, 5 - electrode

The scheme of electroslag welding is shown in fig. 1.27. Welding is carried out with a vertical arrangement of parts (1), the edges of which are also vertical or have an inclination of not more than 30 o to the vertical. A small gap is established between the parts to be welded, where slag powder is poured. At the initial moment, an arc is ignited between the electrode (5) and the metal bar installed from below. The arc melts the flux, which fills the space between the edges of the parts to be welded and the water-cooled copper forming sliders (4). Thus, a slag bath (3) appears from the molten flux, after which the arc is shunted by the molten slag and goes out. At this point, the electric arc melting passes into the electroslag process. When current passes through the molten slag, Joule heat is released. The slag bath is heated to temperatures (1600-1700) 0С, exceeding the melting temperature of the base and electrode metals. The slag melts the edges of the parts to be welded and the electrode immersed in the slag bath. The molten metal flows down to the bottom of the slag pool, where it forms the weld pool. The slag pool reliably protects the weld pool from the surrounding atmosphere. After the heat source is removed, the weld pool metal crystallizes. The formed seam is covered with a slag crust, the thickness of which reaches 2 mm.

A number of processes contribute to improving the quality of the weld in electroslag welding. In conclusion, we note the main advantages of electroslag welding.

Gas bubbles, slag and light impurities are removed from the welding zone due to the vertical position of the welding device.

High density weld.

The weld is less prone to cracking.

The productivity of electroslag welding at large thicknesses of materials is almost 20 times higher than that of automatic submerged arc welding.

You can get seams of complex configuration.

This type of welding is most effective when joining large parts such as ship hulls, bridges, rolling mills, etc.

Electron beam welding.

The heat source is a powerful beam of electrons with an energy of tens of kiloelectronvolts. Fast electrons, penetrating into the workpiece, transfer their energy to the electrons and atoms of the substance, causing intense heating of the material being welded to the melting point. The welding process is carried out in a vacuum, which ensures high quality of the seam. Due to the fact that the electron beam can be focused to very small sizes (less than a micron in diameter), this technology is monopoly in welding micro-parts.

Plasma welding.

In plasma welding, the source of energy for heating the material is plasma - an ionized gas. The presence of electrically charged particles makes the plasma sensitive to the effects of electric fields. In an electric field, electrons and ions are accelerated, that is, they increase their energy, and this is equivalent to heating the plasma up to 20-30 thousand degrees. For welding, arc and high-frequency plasma torches are used (see Fig. 1.17 - 1.19). For welding metals, as a rule, direct action plasma torches are used, and for welding dielectrics and semiconductors, indirect action plasma torches are used. High-frequency plasma torches (Fig. 1.19) are also used for welding. In the plasma torch chamber, the gas is heated by eddy currents generated by high-frequency inductor currents. There are no electrodes, so the plasma is of high purity. A torch of such plasma can be effectively used in welding production.

Diffusion welding.

The method is based on the mutual diffusion of atoms in the surface layers of contacting materials under high vacuum. The high diffusion capacity of atoms is ensured by heating the material to a temperature close to the melting point. The absence of air in the chamber prevents the formation of an oxide film that could interfere with diffusion. Reliable contact between the surfaces to be welded is ensured by machining to a high purity class. The compressive force required to increase the actual contact area is (10-20) MPa.

Diffusion welding technology is as follows. The workpieces to be welded are placed in a vacuum chamber and squeezed with a small force. Then the blanks are heated by current and kept for some time at a given temperature. Diffusion welding is used to join poorly compatible materials: steel with cast iron, titanium, tungsten, ceramics, etc.

Contact electric welding.

In electric contact welding, or resistance welding, heating is carried out by passing an electric current of a sufficient needle through the welding site. Parts heated by electric current to a melting or plastic state are mechanically squeezed or upset, which ensures the chemical interaction of metal atoms. Thus, resistance welding belongs to the pressure welding group. Resistance welding is one of the high-performance welding methods; it can be easily automated and mechanized, as a result of which it is widely used in mechanical engineering and construction. According to the shape of the joints, there are three types of resistance welding: butt, roller (seam) and spot.

Butt contact welding.

This is a type of resistance welding, in which the connection of the parts to be welded occurs along the surface of the butt ends. The parts are clamped in sponge electrodes, then pressed against each other by the surfaces to be joined and the welding current is passed through. Butt welding connects wire, rods, pipes, strips, rails, chains, and other parts over the entire area of their ends. There are two methods of butt welding:

Resistance: plastic deformation occurs in the joint and the joint is formed without melting the metal (the temperature of the joints is 0.8-0.9 of the melting temperature).

Reflow: the parts touch at the beginning at separate small contact points through which a high density current passes, causing the parts to melt. As a result of melting, a layer of liquid metal is formed on the butt end, which, during precipitation, is squeezed out of the joint together with impurities and oxide films.

Table 1.4

Butt Welding Machine Parameters

Machine type	W,(kVA)	U slave, (B)	Welds per hour.	F,(kN)

Column designations: W - machine power, Uwork - operating voltage, productivity, F - compression force of the parts to be welded, S - area of the surface to be welded.

The heating temperature and compressive pressure in butt welding are interrelated. As follows from Fig. 1.28, the force F decreases significantly with an increase in the heating temperature of the workpieces during welding.

Seam contact welding.

A type of resistance welding, in which the elements are joined by overlapping rotating disk electrodes in the form of a continuous or intermittent seam. In seam welding, the formation of a continuous connection (seam) occurs by successive overlapping of points one after another; to obtain a sealed seam, the points overlap each other by at least half of their diameter. In practice, seam welding is used:

continuous;

Intermittent with continuous rotation of the rollers;

Intermittent with periodic rotation.

Rice. 1.28.

Seam welding is used in mass production in the manufacture of various vessels. It is carried out on alternating current with a force of (2000-5000) A. The diameter of the rollers is (40-350) mm, the compression force of the parts to be welded reaches 0.6 tons, the welding speed is (0.53.5) m / min.

Spot contact welding.

In spot welding, the parts to be joined are usually located between two electrodes. Under the action of the pressure mechanism, the electrodes tightly compress the parts to be welded, after which the current is turned on. Due to the passage of current, the parts to be welded quickly heat up to the welding temperature. The diameter of the molten core determines the diameter of the weld spot, usually equal to the diameter of the contact surface of the electrode.

Depending on the location of the electrodes in relation to the parts to be welded, spot welding can be bilateral and one-sided.

When spot welding parts of different thicknesses, the resulting asymmetrical core shifts towards a thicker part and, with a large difference in thickness, does not capture a thin part. Therefore, various technological methods are used to ensure the displacement of the core to the joined surfaces, increase the heating of a thin sheet due to overlays, create a relief on a thin sheet, use more massive electrodes from the side of a thick part, etc.

A variation of spot welding is relief welding, when the initial contact of the parts occurs along pre-prepared protrusions (reliefs). The current, passing through the place of contact of all the reliefs with the lower part, heats them up and partially melts them. Under pressure, the reliefs are deformed, and the upper part becomes flat. This method is used for welding small parts. In table. 1.5 shows the characteristics of machines for spot welding.

Table 1.5

Characteristics of Spot Welding Machines

Machine type	W,(kVA)	U slave, (B)	D,(mm)	F,(kN)	Welds per hour

Column designations: W - machine power, rab - operating voltage, D - electrode diameter, F - compression force of the parts to be welded, welds per hour - productivity.

Spot capacitor welding.

One of the common types of resistance welding is capacitor welding or welding with stored energy stored in electrical capacitors. Energy in capacitors is stored when they are charged from a constant voltage source (generator or rectifier), and then, during the discharge process, it is converted into heat used for welding. The energy stored in the capacitors can be regulated by changing the capacitance of the capacitor (C) and the charging voltage (U).

There are two types of capacitor welding:

Transformerless (capacitors are discharged directly onto the parts to be welded);

Transformer (the capacitor is discharged to the primary winding of the welding transformer, in the secondary circuit of which there are pre-compressed parts to be welded).

A schematic diagram of capacitor welding is shown in fig. 1.29.

Rice. 1.29. : Tr - step-up transformer, V - rectifier, C - capacitor with a capacity of 500 microfarads, Rk - resistance of the parts to be welded, K - key switch

In switch position 1, the capacitor is charged to voltage U0. When the switch is moved to pos. 2 the capacitor is discharged through the contact resistance of the parts to be welded. This creates a powerful current pulse.

The voltage from the capacitor is applied to the workpiece through point contacts with an area of ~ 2 mm. The resulting current pulse, in accordance with the Joule-Lenz law, heats up the contact area to the operating temperature of welding. To ensure reliable pressing of the surfaces to be welded, a mechanical stress of about 100 MPa is transmitted to the parts through the point electrodes.

The main application of capacitor welding is the joining of metals and alloys of small thicknesses. The advantage of capacitor welding is the low power consumption.

To determine the efficiency of welding, we estimate the maximum temperature in the contact area of the parts being welded (Tmax).

Due to the fact that the duration of the discharge current pulse does not exceed 10 -6 s, the calculation was carried out in the adiabatic approximation, that is, neglecting the heat removal from the current flow region.

The principle of contact heating of parts is shown in fig. 1.30.

Rice. 1.30 .: 1 - welded parts with a thickness of d \u003d 5 * 10 -2 cm, 2 - electrodes with an area S \u003d 3 * 10 -2 cm, C - capacitor with a capacity of 500 microfarads, Rk - contact resistance

The advantage of capacitor welding is the low power consumption, which is (0.1-0.2) kVA. The duration of the welding current pulse is thousandths of a second. The range of welded metal thicknesses is in the range from 0.005 mm to 1 mm. Capacitor welding makes it possible to successfully connect metals of small thicknesses, small parts and micro-parts that are poorly visible to the naked eye and require the use of optical devices during assembly. This progressive method of welding has found application in the production of electrical and aviation instruments, clockwork, cameras, etc.

Cold welding.

The connection of workpieces during cold welding is carried out by plastic deformation at room and even at negative temperatures. The formation of an inseparable connection occurs as a result of the appearance of a metallic bond when the contacting surfaces approach each other to a distance at which the action of interatomic forces is possible, and as a result of a large compression force, the oxide film breaks and clean metal surfaces are formed.

The surfaces to be welded must be thoroughly cleaned of adsorbed impurities and fatty films. Cold welding can be used for spot, seam and butt joints.

On fig. 1.31 shows the process of cold spot welding. Sheets of metal (1) with a carefully cleaned surface at the welding point are placed between punches (2) with protrusions (3). The punch is compressed with a certain force P, the protrusions (3) are pressed into the metal to their entire height until the supporting surfaces (4) of the punches rest against the outer surface of the workpieces to be welded.

Rice. 1.31.

Cold welding is used to connect wires, tires, pipes with an overlap and butt. The pressure is chosen depending on the composition and thickness of the welded material, on average it is (1-3) GPa.

Induction welding.

This method mainly welds the longitudinal seams of pipes during their manufacture on continuous mills and welds hard alloys onto steel bases in the manufacture of cutters, drill bits and other tools.

In this method, the metal is heated by passing high-frequency currents through it and compressed. Induction welding is convenient because it is non-contact, high-frequency currents are localized near the surface of the heated workpieces. Such installations work as follows. The current of the high-frequency generator is supplied to the inductor, which induces eddy currents in the workpiece, and the tube is heated. Mills of this type are successfully used for the manufacture of pipes with a diameter of (12-60) mm at a speed of up to 50 m/min. Current is supplied from lamp generators with a power of up to 260 kW at a frequency of 440 kHz and 880 kHz. Pipes of large diameters (325 mm and 426 mm) with a wall thickness of (7-8) mm are also produced, with a welding speed of up to (30-40) m/min.

Features of welding various metals and alloys

Weldability is understood as the ability of metals and alloys to form a joint with the same properties as the metals being welded, and not to have defects in the form of pore cracks, cavities and non-metallic inclusions.

During welding, residual welding stresses almost always occur (as a rule, tensile in the seam and compressive in the base metal). To stabilize the properties of the connection, it is necessary to reduce these stresses.

Welding of carbon steels.

Electric arc welding of carbon and alloy steels is carried out with electrode materials that provide the necessary mechanical properties. The main difficulty in this case lies in the hardening of the near-weld zone and in the formation of cracks. To prevent the formation of cracks, it is recommended:

1) to produce heating of products to temperatures (100-300) 0C;

2) replace single-layer welding with multilayer;

3) use coated electrodes (welding is carried out on direct current of reverse polarity);

4) temper the product after welding up to a temperature of 300 0C.

Welding of high-chromium steels.

High-chromium steels containing (12-28)% Cr have stainless and heat-resistant properties. Depending on the content of chromium and carbon, high-chromium steels are divided into ferritic, ferritic-martensitic and martensitic steels according to their structure.

Difficulties in welding ferritic steels are due to the fact that during cooling in the region of 1000 0C, precipitation of chromium carbide grains at the grain boundaries is possible. This reduces the corrosion resistance of steel. To prevent these phenomena, it is necessary:

1) apply reduced current values in order to ensure high cooling rates during welding;

2) introduce strong carbide formers (Ti, Cr, Zr, V) into steel;

3) anneal after welding at 900 0C to equalize the chromium content in the grains and at the boundaries.

Ferrite-martensitic and martensitic steels are recommended to be welded with heating up to (200-300) 0C.

Cast iron welding.

Welding of cast iron is carried out with heating up to (400-600) 0С. Welding is carried out with cast-iron electrodes with a diameter of (8-25) mm. Good results are obtained by diffusion welding of cast iron to cast iron and cast iron to steel.

Welding of copper and its alloys.

The weldability of copper is negatively affected by impurities of oxygen, hydrogen, and lead. The most common gas welding. Arc welding with carbon and metal electrodes is promising.

aluminum welding.

Welding is hindered by the Al2O3 oxide film. Only the use of fluxes (NaCl, RCl, LiF) makes it possible to dissolve aluminum oxide and ensure the normal formation of the weld. Aluminum is well welded by diffusion welding.

Spot welding is a type of contact welding. With this method, the heating of the metal to its melting point is carried out by heat, which is formed when a large electric current passes from one part to another through the place of their contact. Simultaneously with the passage of current and some time after it, the parts are compressed, as a result of which mutual penetration and fusion of the heated sections of the metal occur.

The features of contact spot welding are: short welding time (from 0.1 to several seconds), high welding current (more than 1000A), low voltage in the welding circuit (1-10V, usually 2-3V), significant force compressing the welding spot (from several tens to hundreds of kg), a small melting zone.

Spot welding is most often used for joining sheet blanks with an overlap, less often for welding rod materials. The range of thicknesses welded by it is from a few micrometers to 2-3 cm, however, most often the thickness of the welded metal varies from tenths to 5-6 mm.

In addition to spot welding, there are other types of contact welding (butt, seam, etc.), but spot welding is the most common. It is used in the automotive industry, construction, radio electronics, aircraft manufacturing and many other industries. During the construction of modern liners, in particular, several million weld points are produced.

Deserved popularity

The great demand for spot welding is due to a number of advantages that it has. Among them: no need for welding consumables (electrodes, filler materials, fluxes, etc.), slight residual deformations, simplicity and convenience of working with welding machines, accuracy of the connection (virtually no weld), environmental friendliness, efficiency, susceptibility to easy mechanization and automation, high performance. Spot welding machines are capable of performing up to several hundred welding cycles (spot welds) per minute.

The disadvantages include the lack of tightness of the seam and the concentration of stresses at the welding point. Moreover, the latter can be significantly reduced or even eliminated by special technological methods.

Sequence of processes in resistance spot welding

The whole process of spot welding can be divided into 3 stages.

Compression of parts, causing plastic deformation of microroughnesses in the chain electrode-part-part-electrode.
Switching on an electric current pulse, which leads to heating of the metal, its melting in the joint zone and the formation of a liquid core. As the current passes, the core increases in height and diameter to a maximum size. Bonds are formed in the liquid phase of the metal. At the same time, the plastic sedimentation of the contact zone continues to the final size. The compression of the parts ensures the formation of a sealing belt around the molten core, which prevents the metal from splashing out of the welding zone.
Turning off the current, cooling and crystallization of the metal, ending with the formation of a cast core. On cooling, the volume of the metal decreases and residual stresses arise. The latter are an undesirable phenomenon, which is fought in various ways. The force that compresses the electrodes is removed with some delay after the current is turned off. This provides the necessary conditions for better crystallization of the metal. In some cases, in the final stage of resistance spot welding, it is even recommended to increase the clamping force. It provides metal forging, which eliminates weld inhomogeneities and relieves stress.

At the next cycle, everything repeats again.

Basic parameters of resistance spot welding

The main parameters of resistance spot welding include: the strength of the welding current (I CB), the duration of its pulse (t CB), the compression force of the electrodes (F CB), the size and shape of the working surfaces of the electrodes (R - with a spherical, d E - with a flat shape ). For better visualization of the process, these parameters are presented in the form of a cyclogram reflecting their change over time.

Distinguish between hard and soft welding modes. The first is characterized by high current, short duration of the current pulse (0.08-0.5 seconds depending on the thickness of the metal) and high compression force of the electrodes. It is used for welding copper and aluminum alloys with high thermal conductivity, as well as high-alloy steels to maintain their corrosion resistance.

In the soft mode, the workpieces are heated more smoothly with a relatively small current. The duration of the welding pulse is from tenths to several seconds. Soft modes are shown for steels prone to hardening. Basically, it is soft modes that are used for resistance spot welding at home, since the power of the devices in this case may be lower than with hard welding.

Dimensions and shape of electrodes. With the help of electrodes, the welding machine is in direct contact with the parts to be welded. They not only supply current to the welding zone, but also transmit compressive force and remove heat. The shape, dimensions and material of the electrodes are the most important parameters of spot welding machines.

Depending on their shape, the electrodes are divided into straight and curly. The former are the most common, they are used for welding parts that allow free access of electrodes to the welded zone. Their sizes are standardized by GOST 14111-90, which establishes the following diameters of electrode rods: 10, 13, 16, 20, 25, 32 and 40 mm.

According to the shape of the working surface, there are electrodes with flat and spherical tips, characterized respectively by the values of the diameter (d) and radius (R). The contact area of the electrode with the workpiece depends on the value of d and R, which affects the current density, pressure, and the size of the nucleus. Spherical surface electrodes have greater tool life (capable of making more points before regrinding) and are less susceptible to misalignment than flat surface electrodes. Therefore, with a spherical surface, it is recommended to manufacture electrodes used in tongs, as well as figured electrodes that work with large deflections. When welding light alloys (for example, aluminum, magnesium), only electrodes with a spherical surface are used. The use of electrodes with a flat surface for this purpose leads to excessive dents and undercuts on the surface of points and increased gaps between parts after welding. The dimensions of the working surface of the electrodes are selected depending on the thickness of the metals being welded. It should be noted that electrodes with a spherical surface can be used in almost all cases of spot welding, while electrodes with a flat surface are very often not applicable.

* - in the new GOST, instead of a diameter of 12 mm, 10 and 13 mm are introduced.

The landing parts of the electrodes (places connected to the electric holder) must ensure reliable transmission of the electrical impulse and the pressing force. Often they are made in the form of a cone, although there are other types of connections - along a cylindrical surface or thread.

Of great importance is the material of the electrodes, which determines their electrical resistance, thermal conductivity, thermal stability and mechanical strength at high temperatures. During operation, the electrodes heat up to high temperatures. The thermocyclic mode of operation, together with a mechanical variable load, causes increased wear of the working parts of the electrodes, resulting in a deterioration in the quality of the connections. In order for the electrodes to be able to withstand harsh working conditions, they are made from special copper alloys with high heat resistance and high electrical and thermal conductivity. Pure copper is also capable of working as electrodes, however, it has a low resistance and requires frequent regrinding of the working part.

Welding current. The strength of the welding current (I CB) is one of the main parameters of spot welding. It determines not only the amount of heat released in the welding zone, but also the gradient of its increase in time, i.e. heating rate. The dimensions of the welded core (d, h and h 1) directly depend on I WT and increase in proportion to the increase in I WT.

It should be noted that the current that flows through the welding zone (I CB) and the current flowing in the secondary circuit of the welding machine (I 2) differ from each other - and the more, the smaller the distance between the weld points. The reason for this is the shunt current (Ish) flowing outside the welding zone - including through previously made points. Thus, the current in the welding circuit of the machine must be greater than the welding current by the value of the shunt current:

I 2 \u003d I CB + I w

To determine the strength of the welding current, you can use different formulas that contain various empirical coefficients obtained empirically. In cases where an accurate determination of the welding current is not required (which happens most often), its value is taken from tables compiled for different welding modes and various materials.

Increasing the welding time allows welding with currents much lower than those given in the table for industrial devices.

welding time. The welding time (t CB) is understood as the duration of the current pulse when performing one weld point. Together with the strength of the current, it determines the amount of heat that is released in the connection zone when an electric current passes through it.

With an increase in t CB, the penetration of parts increases and the dimensions of the core of the molten metal increase (d, h and h 1). At the same time, heat removal from the melting zone also increases, parts and electrodes are heated, and heat is dissipated into the atmosphere. When a certain time is reached, a state of equilibrium may occur, in which all the input energy is removed from the welding zone, without increasing the penetration of parts and the size of the core. Therefore, an increase in t SW is advisable only up to a certain point.

When accurately calculating the duration of the welding pulse, many factors must be taken into account - the thickness of the parts and the size of the weld spot, the melting point of the metal being welded, its yield strength, heat accumulation coefficient, etc. There are complex formulas with empirical dependencies, which, if necessary, carry out the calculation.

In practice, most often the welding time is taken according to the tables, correcting, if necessary, the accepted values in one direction or another, depending on the results obtained.

Compression force. The compression force (F CB) affects many processes of resistance spot welding: plastic deformations occurring in the joint, heat release and redistribution, metal cooling and its crystallization in the core. With an increase in F CB, the deformation of the metal in the welding zone increases, the current density decreases, and the electrical resistance in the electrode-workpiece-electrode section decreases and stabilizes. Provided that the dimensions of the core remain unchanged, the strength of the weld points increases with increasing compression force.

When welding in hard conditions, higher values of F CB are used than in soft welding. This is due to the fact that with an increase in rigidity, the power of the current sources and the penetration of parts increase, which can lead to the formation of splashes of molten metal. A large compression force is just designed to prevent this.

As already noted, in order to forge a weld point in order to relieve stress and increase the density of the core, the resistance spot welding technology in some cases provides for a short-term increase in the compression force after the electric pulse is turned off. The cyclogram in this case looks as follows.

In the manufacture of the simplest resistance welding machines for home use, there is little reason to engage in accurate parameter calculations. Approximate values for electrode diameter, welding current, welding time and clamping force can be taken from tables available in many sources. It is only necessary to understand that the data in the tables are somewhat overestimated (or underestimated, if we keep in mind the welding time) compared to those that are suitable for home devices where soft modes are usually used.

Preparation of parts for welding

The surface of the parts in the zone of contact between the parts and in the place of contact with the electrodes is cleaned from oxides and other contaminants. With poor cleaning, power losses increase, the quality of the connections deteriorates and the wear of the electrodes increases. In resistance spot welding technology, sandblasting, emery wheels and metal brushes are used to clean the surface, as well as etching in special solutions.

High demands are placed on the surface quality of parts made of aluminum and magnesium alloys. The purpose of surface preparation for welding is to remove, without damage to the metal, a relatively thick film of oxides with high and uneven electrical resistance.

Spot welding equipment

The differences between the existing types of spot welding machines are determined mainly by the type of welding current and the shape of its pulse, which are produced by their power electrical circuits. According to these parameters, resistance spot welding equipment is divided into the following types:

machines for welding with alternating current;
low-frequency spot welding machines;
capacitor type machines;
DC welding machines.

Each of these types of machines has its own advantages and disadvantages in technological, technical and economic aspects. The most widely used machines for welding with alternating current.

AC resistance spot welding machines. A schematic diagram of machines for spot welding with alternating current is shown in the figure below.

The voltage at which welding is carried out is formed from the mains voltage (220/380V) using a welding transformer (TC). The thyristor module (CT) ensures the connection of the primary winding of the transformer to the supply voltage for the required time for the formation of a welding pulse. Using the module, you can not only control the duration of the welding time, but also control the shape of the applied pulse by changing the opening angle of the thyristors.

If the primary winding is made not from one, but from several windings, then by connecting them in various combinations with each other, it is possible to change the transformation ratio, obtaining different values of the output voltage and welding current on the secondary winding.

In addition to the power transformer and thyristor module, AC spot welding machines have a set of control equipment - a power source for the control system (step-down transformer), relays, logic controllers, control panels, etc.

Capacitor welding. The essence of capacitor welding is that at first, electrical energy is relatively slowly accumulated in the capacitor when it is being charged, and then it is consumed very quickly, generating a large current pulse. This allows welding to be carried out using less power from the network compared to conventional spot welding machines.

In addition to this main advantage, capacitor welding has others. With it, there is a constant controlled consumption of energy (the one that has accumulated in the capacitor) for one welded joint, which ensures the stability of the result.

Welding occurs in a very short time (hundredths and even thousandths of a second). This gives a concentrated heat release and minimizes the heat affected zone. The latter advantage allows it to be used for welding metals with high electrical and thermal conductivity (copper and aluminum alloys, silver, etc.), as well as materials with sharply different thermal properties.

Rigid capacitor micro welding is used in the radio-electronic industry.

The amount of energy stored in capacitors can be calculated using the formula:

W = C U 2 /2

where C is the capacitance of the capacitor, F; W - energy, W; U - charging voltage, V. By changing the resistance value in the charging circuit, the charging time, charging current and power consumed from the network are regulated.

Resistance spot welding defects

With high-quality performance, spot welding has high strength and is able to ensure the operation of the product for a long service life. In case of destruction of structures connected by multi-point multi-row spot welding, destruction occurs, as a rule, along the base metal, and not along the weld points.

The quality of welding depends on the acquired experience, which is mainly reduced to maintaining the required duration of the current pulse on the basis of visual observation (by color) of the weld point.

A correctly made weld point is located in the center of the joint, has the optimal size of the cast core, does not contain pores and inclusions, does not have external and internal splashes and cracks, and does not create large stress concentrations. When a tensile force is applied, the destruction of the structure occurs not along the cast core, but along the base metal.

Spot welding defects are divided into three types:

deviations of the dimensions of the cast zone from the optimal ones, displacement of the core relative to the joint of the parts or the position of the electrodes;
violation of the continuity of the metal in the connection zone;
change in properties (mechanical, anti-corrosion, etc.) of the metal of the weld point or areas adjacent to it.

The most dangerous defect is the absence of a cast zone (lack of penetration in the form of "gluing"), in which the product can withstand the load at a low static load, but is destroyed under the action of a variable load and temperature fluctuations.

The strength of the connection is also reduced with large dents from the electrodes, gaps and cracks in the edge of the overlap, and splashing of metal. As a result of the exit of the cast zone to the surface, the anti-corrosion properties of the products (if any) are reduced.

Complete or partial lack of fusion, insufficient dimensions of the cast core. Possible reasons: low welding current, too high clamping force, wear of the working surface of the electrodes. The lack of welding current can be caused not only by its low value in the secondary circuit of the machine, but also by the electrode touching the vertical walls of the profile or by too close a distance between the weld points, leading to a large shunt current.

The defect is detected by external inspection, by lifting the edges of the parts with a punch, ultrasonic and radiation devices to control the quality of welding.

External cracks. Causes: too high welding current, insufficient compression force, lack of forging force, contaminated surface of parts and / or electrodes, leading to an increase in the contact resistance of parts and a violation of the temperature regime of welding.

The defect can be detected with the naked eye or with a magnifying glass. Effective capillary diagnostics.

Breaks at the edges of the lap. The reason for this defect is usually the same - the weld point is located too close to the edge of the part (insufficient overlap).

It is detected by external examination - through a magnifying glass or with the naked eye.

Deep dents from the electrode. Possible reasons: too small size (diameter or radius) of the working part of the electrode, excessive forging force, incorrectly installed electrodes, too large dimensions of the cast zone. The latter may be due to excess welding current or pulse duration.

Internal splash (outflow of molten metal into the gap between parts). Causes: Permissible values of current or duration of the welding pulse are exceeded - too large a zone of molten metal has formed. The compression force is low - a reliable sealing belt around the core was not created or an air cavity formed in the core, which caused the molten metal to flow into the gap. The electrodes are installed incorrectly (misaligned or skewed).

It is determined by the methods of ultrasonic or radiographic control or external examination (due to the splash, a gap may form between the parts).

External splash (outlet of metal to the surface of the part). Possible reasons: switching on of the current pulse with uncompressed electrodes, too high value of the welding current or pulse duration, insufficient compression force, distortion of the electrodes relative to the parts, contamination of the metal surface. The last two reasons lead to uneven current density and melting of the surface of the part.

determined by external examination.

Internal cracks and shells. Causes: The current or pulse duration is too high. The surface of the electrodes or parts is dirty. Small compression force. Missing, late or insufficient forging force.

Shrinkage cavities can occur during the cooling and crystallization of the metal. To prevent their occurrence, it is necessary to increase the compression force and apply forging compression at the moment of core cooling. Defects are detected by X-ray or ultrasonic testing.

Displacement of the cast core or its irregular shape. Possible reasons: electrodes are installed incorrectly, the surface of the parts is not cleaned.

Defects are detected by X-ray or ultrasonic testing.

Burn through. Causes: the presence of a gap in the assembled parts, contamination of the surface of the parts or electrodes, the absence or low force of compression of the electrodes during the current pulse. To avoid burn-through, current should only be applied after full compression force has been applied. determined by external examination.

Correction of defects. The method of correcting defects depends on their nature. The simplest is repeated spot or other welding. It is recommended to cut or drill the defective place.

If it is impossible to weld (due to the undesirability or inadmissibility of heating the part), instead of a defective weld spot, you can put a rivet by drilling out the welding spot. Other correction methods are also used - cleaning the surface in case of external splashes, heat treatment to relieve stress, straightening and forging when the entire product is deformed.

When using the content of this site, you need to put active links to this site, visible to users and search robots.

Contact welding is the process of creating a monolithic weld by melting the edges of the parts to be welded with electric current and subsequent deformation by compressive force. The technology has received special distribution in heavy industry and serves for the continuous production of the same type of products.

This technology is common in the serial connection of thin sheet metal

Today, at least one resistance welding machine is available in every plant, and all thanks to the advantages of technology:

productivity - the weld point is created no longer than 1 second;
high stability of work - once having configured the device, it can work for a long time without third-party intervention, while maintaining the quality of work;
low maintenance costs - this applies to consumables, contact electrodes serve as a working element;
the ability to work with the machine of low-skilled specialists.

Contact welding technology

Simple, at first glance, resistance welding technology consists of a number of procedures that must be completed. It is possible to achieve a high-quality connection only if all technological features and process requirements are observed.

Process essence

To begin with, it is worth understanding how this system works?

The essence of electric resistance welding is two inseparable physical processes - heating and pressure. When an electric current passes through the junction zone, heat is released, which serves to melt the metal. To ensure sufficient heat release, the current strength must reach several thousand or even tens of thousands of amperes. At the same time, some pressure is applied to the part from one or both sides, and a tight seam is created without visible and internal defects.

The joining process is associated with local heating of the workpieces with their simultaneous pressing.

With the correct organization of the process, the parts themselves are practically not subject to heat, since their resistance is minimal. As a monolithic connection is created, the resistance decreases, and with it the current strength. The electrodes of the welding machine exposed to heat are cooled by an advanced technology using water.

Surface preparation

There are many technologies that allow you to treat the surface before using resistance welding. These include:

cleaning from coarse dirt;
degreasing;
removal of the oxide film;
drying;
passaging and neutralization.

The order and the technologies themselves are determined by the specific process and type of blanks.

In general, before starting welding, the surface must:

ensure minimum resistance between the part and the electrode;
provide equal resistance throughout the contact;
The parts to be welded must have smooth surfaces without bulges and depressions.

Contact welding machines

Contact welding equipment is:

motionless;
mobile;
suspended or universal.

Divide welding according to the type of current into direct and alternating current (transformer, capacitor). According to the welding methods, there are spot, seam butt and embossed, which we will talk about below.

Equipment can be either stationary or portable.

All spot welding devices consist of three parts:

electrical systems;
mechanical part;
water cooling.

The electrical part is responsible for the melting of parts, control of work and rest cycles, and also sets the current modes. The mechanical component is a pneumatic or hydraulic system with various drives. If only a compression drive is installed, then we have a point variety, seam ones also have rollers, and butt joints have a compression system and upset products. Water cooling consists of a primary and secondary circuit, distributing fittings, hoses, valves and relays.

Contact welding electrodes

In this case, the electrodes not only close the electrical circuit, but also serve as a heat sink from the welded joint, transfer a mechanical load, and in some cases help to move the workpiece (roller electrodes).

The size and shape of resistance welding electrodes vary depending on the equipment used and the material to be welded.

Such use causes a number of stringent requirements that the electrodes must meet. They must withstand temperatures over 600 degrees, pressure up to 5 kg / mm2. That is why they are made of chrome bronze, chrome zirconium bronze or cadmium bronze. But even such powerful alloys are not able to withstand the described loads for a long time and quickly fail, reducing the quality of work. The size, composition and other characteristics of the electrode are selected based on the selected mode, type of welding and thickness of the products.

Weld defects and quality control

As with any other technology, welding joints must be subjected to strict control to detect all kinds of defects.

Almost everything is used here, and above all - external examination. However, due to the pressing of the parts, it can be very difficult to identify them in this way, so a part of the manufactured product is selected and the parts are cut along the seam to identify errors. If a defect is found, a batch of potentially defective products is sent for processing, and the apparatus is calibrated.

Varieties of resistance welding

The technology for creating a weld spot causes the division of the process into several types:

Spot welding

In this case, welding occurs at one or simultaneously at several points. The strength of the seam consists of many parameters.

The point method is the most common method.

In this case, the quality of work is affected by:

the shape and size of the electrode;
current strength;
pressure force;
the duration of work and the degree of surface cleaning.

Modern spot welding machines are capable of working with an efficiency of 600 welds per minute. This technology is used to connect parts of precision electronics, to connect the body parts of cars, aircraft, agricultural machinery and has many other areas of use.

relief welding

The principle of operation is the same with spot welding, but the main difference is that the weld itself and the electrode have a similar, relief shape. Relief is provided by the natural shape of the parts or the creation of special stampings. Like spot welding, the technology is used almost everywhere and serves as a complementary, capable of welding embossed parts. It can be used to attach brackets or support pieces to flat workpieces.

Seam welding

A multi-point welding process in which multiple welds are placed close together or overlapping to form a single monolithic joint. If there is an overlap between the points, then an airtight seam is obtained; if the points are close, the seam is not airtight. Since a seam using the distance between the points does not differ from that created by a spot seam, such devices are rarely used.

In industry, the overlapping, sealed seam is more popular, with the help of which tanks, barrels, cylinders and other containers are created.

Butt welding

Here, the parts are connected by pressing against each other, and then the entire contact plane is melted. The technology has its own varieties and is divided into several types based on the type of metal, its thickness and the desired quality of the connection.

Welding current flows through the joint of the workpieces, melts them and securely connects

The easiest way is resistance welding, suitable for low-melting workpieces with a small contact patch area. Flash and hot melt welding is suitable for stronger metals and huge cross-sections. In this way, parts of ships, anchors, etc. are welded.

Above, the most popular and used are described, but there are also such types of spot welding:

seam-butt is carried out by a rotating electrode with several contacts to close the circuit, pulling the workpiece through such an apparatus, you can get a leaky continuous seam, consisting of many weld points;
the relief-point part is welded according to the current relief, however, the seam does not consist of a continuous contact patch, but of many points;
according to the Ignatiev method in which the welding current flows along the parts to be welded, so the pressure does not affect the heating of the product and its welding.

Designation of resistance welding in the drawing

According to the existing standard for symbols, spot welding has the following designation in the drawings:

Solid seam. A visible continuous seam in the general plan of the drawing is marked with the main line, the remaining structural elements are the main thin line. The hidden welded solid seam is indicated by a dashed line.
Weld points. Visible welded joints in the general drawing are marked with a “+” symbol, and hidden ones are not marked at all.

From a visible, hidden solid seam or a visible weld point, there is a special line with a callout, on which auxiliary symbols, standards, alphanumeric characters, etc. are marked. The designation contains the letter “K” - contact and the small letter “t” - dot, indicating the method of welding and its variety. Seams that do not have a designation are marked with lines without shelves.

GOST 15878-79 Regulates the dimensions and designs of resistance welding welded joints

All basic information is presented on the leader line or below it, depending on the facing side (front or back). All necessary information about the seam is taken from the relevant GOST, which is indicated on the footnote or duplicated in the table of seams.