Classification of welded joints and seams. All types of welded joints and types of welded seams according to GOST - classification Welded seams of parts

One way to connect parts of a material is welding. The method has found very wide application in various fields. Using this relatively cheap and at the same time reliable method, permanent connections are obtained. Taking into account the types of metals, each of which has its own welding characteristics, differences in work conditions and joint requirements, various types of welds and joints are distinguished.

Welding zones

The fusion zone with partially melted grains is 0.1−0.4 mm of the main metal. When the metal in this zone warms up, its structure becomes needle-like with high fragility and low strength.

The thermal zone is divided into four sections:

The main metal zone begins from a section heated to less than 450 °C. The structure here is similar to the structure of the base metal, but the steel loses its strength due to heating. Oxides and nitrides are released along the boundary, weakening the bond of the grains. The metal in this place becomes more durable, however, it receives less ductility and toughness.

Classification of welded joints and seams

Types of seams are divided into several categories depending on their characteristics. In appearance they stand out:

• Normal.
• Convex.
• Concave.

By type, welds can be single-sided or double-sided. According to the number of passes - single-pass and multi-pass. By the number of layers: single-sided and multilayer (when welding thick metals).

There are also varieties in length:

• One-sided continuous.
• Unilateral intermittent.
• Double-sided chain.
• Double-sided chess.
• Spot welds (created by resistance welding).

Types of seams according to the force vector:

• Transverse - the force is perpendicular to the seam.
• Longitudinal - force parallel to the seam.
• Oblique - force at an angle.
• Combined - signs of both transverse and longitudinal seams.

By spatial position:

According to their functions, seams are divided into the following:

• Durable.
• Durable and dense.
• Sealed.

Width:

• Thread seams whose width practically does not exceed the diameter of the electrode.
• Widened seams are made by transverse oscillatory movements of the rod.

Special connections

Butt. The most common option, representing an ordinary connection of end surfaces or sheets. Their formation requires a minimum of time and metal. They can be done without beveled edges if the sheets are thin. For thick products, you need to prepare the metal for welding, where you will need to bevel the edges to increase the depth of welding. This is relevant for a thickness of 8 mm or more. If the thickness is more than 12 mm, double-sided butt joints and beveled edges will be required. Most often these connections are made in a horizontal position.

Tavrovoe. T-joints are T-shaped and can be single- or double-sided. They can be used to connect products of different thicknesses. If the smaller part is mounted perpendicular, the electrode is tilted up to 60° during the welding process. To carry out a simpler version of boat welding, use tacks. This reduces the likelihood of undercuts. Usually the suture is applied per pass. Today, many machines for automatic T-welding are produced.

Angular. The edges of these joints (at different angles) are often bent so that the seam lies at the required depth. Double-sided welding makes the connection stronger.

overlap. This method is used to weld sheets less than 1 cm thick. They are laid overlapping each other and boiled on both sides. There should be no moisture between them. For better bonding, the joint is sometimes welded from the end.

Seam geometry

S - thickness of the workpiece.

E - width.

B - gap between workpieces.

H is the depth of the welded area.

T - thickness.

Q is the size of the convex part.

P is the calculated height corresponding to the perpendicular line from the point of penetration to the hypotenuse of the largest right triangle inscribed in the outer part.

A is the thickness of the fillet weld, which includes the value of the convexity and the design height.

K - leg is the distance from the surface of one workpiece to the corner boundary of the other.

Q - convexity of the deposited area.

Choice

The types of seams and welded joints differ in properties, and for each case the parameters of a successful combination are selected. The first step is to evaluate the spatial position. The easier the work is, the better the quality. It is easier to make horizontal seams, so they try to position the workpieces horizontally. Sometimes, to ensure quality, a part has to be turned over several times.

Welding in one pass helps to achieve better strength than in the case of multiple passes. So, a balance is required between convenience and number of aisles.

When the pieces are thick, the edges are cut and the surface is treated to add a clean finish. Butt-joint options are the simplest; it is preferable to choose them, since fixation is easier to ensure in order to avoid distortion of the geometry of the finished parts. In addition to choosing the type, attention is also paid to the temperature regime, because the cooking zones may shift and the product will not be fully cooked or will melt.

Terms and definitions for welded structures, assemblies, connections and seams are established by GOST 2601-84.

A welded connection is a permanent connection of two or more elements (parts) made by welding. A welded joint includes a weld, an adjacent zone of the base metal with structural and other changes as a result of the thermal action of welding (heat-affected zone) and adjacent areas of the base metal.

A weld is a section of a weld joint formed as a result of crystallization of molten metal or as a result of plastic deformation in pressure welding or a combination of crystallization and deformation.

A welded assembly is a part of a welded structure in which elements adjacent to each other are welded.

A welded structure is a metal structure made from individual parts or assemblies by welding.

The metal of the parts to be joined by welding is called the base metal.

The metal supplied to the arc zone in addition to the molten base metal is called filler metal.

Remelted filler metal introduced into the weld pool or deposited onto the base metal is called weld metal.

The alloy formed by remelted base or base and deposited metals is called weld metal.

The performance of a welded product is determined by the type of welded joint, the shape and size of welded joints and seams, their location relative to the acting forces, the smoothness of the transition from the weld to the base metal, etc.

When choosing the type of welded joint, the operating conditions (static or dynamic loads), the method and conditions of manufacturing the welded structure (manual welding, automatic in factory or installation conditions), savings in base metal, electrodes, etc. are taken into account.

Types of welded joints. Based on the form of mating of the parts (elements) to be connected, the following types of welded joints are distinguished: butt, corner, T, and lap (Figure 1).

Picture 1 -

Welds are divided according to cross-sectional shape into butt (Figure 2.a) and corner (Figure 2.b). A variation of these types are cork seams (Figure 2.c) and slotted seams (Figure 2.d), made in overlap joints. Based on their shape in the longitudinal direction, continuous and intermittent seams are distinguished.

With the help of butt welds, mainly butt joints are formed (Figure 1.a), with the help of fillet welds - T-, cross, corner and lap joints (Figure 1.b - 1.d), with the help of plug and slotted seams lap joints can be formed and sometimes T-joints.

Butt welds are usually made continuous; A distinctive feature for them is usually the shape of the cutting of the edges of the parts being connected in cross section. Based on this feature, the following main types of butt welds are distinguished: with flanged edges (Figure 3.a); without cutting edges - one-sided and two-sided (Figure 3.b); with cutting of one edge - one-sided, two-sided; with a straight or curved cutting shape (Figure 3.c); with one-sided cutting of two edges; with a V-shaped groove (Figure 3.d); with two-sided cutting of two edges; X-shaped cutting (Figure 3.d). The groove can be formed by straight lines (beveled edges) or have a curved shape (U-shaped groove, Figure 3.e).

Figure 2 -

The butt connection is most common in welded structures, as it has a number of advantages over other types of connections. It is used in a wide range of thicknesses of welded parts from tenths of a millimeter to hundreds of millimeters in almost all welding methods. With a butt joint, less filler material is consumed to form a seam, and quality control is easy and convenient.

Fillet welds are distinguished by the shape of the preparation of the welded edges in cross section and the continuity of the seam along the length.

According to the cross-sectional shape, fillet welds can be without edge grooves (Figure 4.a), with one-sided edge grooves (Figure 4.b), with double-sided edge grooves (Figure 4.c). In terms of length, fillet welds can be continuous (Figure 5.a) or intermittent (Figure 5.b), with a staggered (Figure 5.c) and chain (Figure 5.d) arrangement of seam sections. T-joints, lap joints and corner joints can be made with short sections of seams - spot welds (Figure 5.e).

Figure 4 -

Figure 4 - Preparation of the edges of fillet welds of T-joints: a - without cutting the edges; b, c - with edge cutting

Plug seams in their plan form (top view) usually have a round shape and are obtained as a result of complete melting of the top and partial penetration of the bottom sheets (Figure 6.a) - they are often called electric rivets - or by melting the top sheet through what was previously done in the top sheet hole (Figure 6.b).

Figure 5 -

Figure 6 -

Slotted seams, usually of an elongated shape, are obtained by welding the top (covering) sheet to the bottom with a fillet weld around the perimeter of the slot (Figure 6. c). In some cases, the slot may be filled completely.

The shape of the edges and their assembly for welding are characterized by four main structural elements (Figure 7): gap b, blunting c, bevel angle b and cutting angle a, equal to b or 2b.

Existing methods of arc welding without cutting edges make it possible to weld metal of limited thickness (for one-sided manual welding - up to 4 mm, mechanized submerged arc welding - up to 18 mm). Therefore, when welding thick metal, it is necessary to cut the edges. The bevel angle of the edge provides a certain value for the cutting angle of the edges, which is necessary for the arc to penetrate deep into the joint and completely penetrate the edges to their entire thickness.

Figure 7 -

The standard cutting angle of the edges, depending on the welding method and type of connection, varies from (60±5) to (20±5) degrees. The type of groove and the angle of the edges determine the amount of additional metal required to fill the groove, and therefore the welding performance. For example, X-shaped cutting of edges compared to V-shaped allows reducing the volume of deposited metal by 1.6 - 1.7 times. The time required for edge processing is reduced. However, in this case it becomes necessary to weld on one side of the seam in an awkward ceiling position or to turn over the products being welded.

Bluntness c is usually (2 ± 1) mm. Its purpose is to ensure proper formation and prevent burns at the top of the seam. The gap b is usually equal to 1.5 - 2 mm, since at the accepted edge cutting angles, the presence of a gap is necessary for penetration of the top of the seam, but in some cases, with a particular technology, the gap can be equal to zero or reach 8 - 10 mm or more.

For all types of seams, complete penetration of the edges of the elements being connected and the external shape of the seam, both on the front side (strengthening the seam) and on the back side, i.e. the shape of the reverse bead, are important. In butt welds and especially one-sided welds, it is difficult to weld the blunting edges to their entire thickness without special techniques to prevent burn-through and ensure good formation of the return bead.

Welds are classified according to a number of characteristics. Based on their appearance, seams are divided into convex, normal, and concave (Figure 8). As a rule, all seams are made with slight reinforcement (convex). If joints without reinforcement are required, this should be indicated on the drawing. Fillet welds are made weakened (concave), which is also noted in the drawing. Such seams are required to improve the performance of welded joints, for example under variable loads. Butt seams are not weakened; concavity in this case is a defect. An increase in the size of the welds compared to the specified ones leads to an increase in the weight of the welded structure and excessive consumption of electrodes. As a result, the cost of welded structures increases and the labor intensity of welding work increases.

Figure 8 -

The formation of a smooth transition of the metal of the front and back rollers to the base metal is also of great importance, as this ensures high strength of the connection under dynamic loads. In fillet welds, it can also be difficult to weld the root of the seam to its full thickness, especially when welding with an inclined electrode. For these seams, a concave cross-sectional shape of the seam with a smooth transition to the base metal is recommended, which reduces the stress concentration at the transition site and increases the strength of the connection under dynamic loads.

Based on the number of layers and passes, single-layer, multi-layer, single-pass, and multi-pass seams are distinguished (Figures 9, 10).

Figure 9 -

Figure 10 - Classification of seams by the number of layers and passes: I - IV - number of layers; 1 - 8 - number of passes

Weld layer - part of the weld metal, which consists of one or more beads located at the same level of the cross-section of the weld. Bead - weld metal deposited or remelted in one pass.

When welding, each layer of a multilayer seam is annealed when the next layer is applied. As a result of this thermal effect on the weld metal, its structure and mechanical properties are improved. The thickness of each layer in multi-layer seams is approximately 5 - 6 mm.

According to the effective force, seams are divided into longitudinal (flank), transverse (frontal), combined, and oblique (Figure 11). The front seam is located perpendicular to the force P, the flank seam is parallel, and the oblique seam is at an angle.

Figure 11-

Based on their position in space, there are lower, horizontal, vertical and ceiling seams (Figure 12). They differ from each other in the angles at which the surface of the welded part is located relative to the horizontal. The ceiling seam is the most difficult to perform; the seam is best formed in the lower position. Ceiling, vertical and horizontal seams usually have to be made during manufacturing and especially during installation of large-sized structures.

Examples of designating welds by their position in space are given in Figure 13.

Figure 12

Figure 13 -

2. STRUCTURAL ELEMENTS OF WELDED JOINTS IN MANUAL ARC WELDING

Due to the importance of proper preparation of welded edges from the point of view of quality, efficiency, strength and performance of the welded joint, state standards have been created for the preparation of edges for welding. The standards regulate the shape and structural elements of cutting and assembling edges for welding and the dimensions of finished welds.

GOST 5264-80 “Seams of welded joints. Manual electric arc welding. Basic types, structural elements and dimensions" and GOST 11534-75 "Manual arc welding. Welded connections at acute and obtuse angles. Basic types, structural elements and dimensions” regulate the structural elements of edge preparation and the dimensions of the seams made during manual arc welding with a metal electrode in all spatial positions.

It is necessary to note some features of the application of standards. Due to their technological features, various methods of electric fusion welding make it possible to obtain different maximum penetration depths. By varying the basic parameters of the welding mode and the design types of edge preparation, it is possible to increase or decrease the depth of penetration and other dimensions of the weld.

For this reason, the mentioned standards regulating the structural elements of edge preparation take into account the possibility of varying the welding current, voltage, electrode wire diameter (current density) and welding speed. In cases where the welding process requires the use of high currents, high current densities and heat concentrations, increased bluntness, smaller groove angles and gap sizes are possible.

In manual arc welding, factors such as welding current, welding speed and arc voltage vary within small limits.

To ensure through penetration of the edges of the product when welding one-sided butt or fillet welds with sheet thicknesses over 4 mm, welding must be carried out along pre-cut edges. When manually welding, welders cannot significantly change the depth of penetration of the base metal, but by changing the amplitude of the transverse vibrations of the electrode, they can significantly change the width of the weld.

For sheet thicknesses of 9 - 100 mm, GOST 5264-80 for butt joints requires mandatory edge cutting and a gap, which vary in size depending on the thickness of the metal and the type of joint.

In all cases, using edge preparation standards, you should choose those types of grooves that provide the least volume and cost of edge preparation work, volume and weight of deposited metal, full thickness penetration, smooth mating shape of the outer part of the weld and minimal angular deformations.

The quality of welded joints and the efficiency of the welding process are greatly influenced by the cleanliness of the edges and the adjacent surface of the base metal, the accuracy of edge preparation and assembly for welding. Blanks for parts to be welded should be made from pre-straightened and cleaned metal. Cutting of parts and preparation of edges is carried out by mechanical processing (on press shears, edge planers and milling machines), oxygen gas and plasma cutting, etc. After using thermal cutting methods, the edges are cleaned of burr, scale, etc. (grinding wheels, metal brushes, etc. etc.).

In some cases, when welding high-alloy steels, the base metal in the heat-affected zone after cutting is also removed mechanically. Before assembling the edge, adjacent areas of the base metal (40 mm from the edge) must be cleaned of oil, rust and other contaminants using wire brushes, shot blasting or chemical etching. The parts are assembled using tack welds (short seams) 20 - 30 mm long or in special assembly devices.

2.1 Geometric parameters of the weld

Butt seam. The elements of the geometric shape of a butt weld (Figure 14) are the width of the seam - e, the convexity of the seam - q, the depth of penetration - h, the thickness of the seam - c, the gap - b, the thickness of the welded metal - S.

Figure 14 -

Weld width- the distance between visible fusion lines on the face of the weld in fusion welding.

Weld convexity

The depth of penetration (penetration) is the greatest depth of melting of the base metal in the weld cross-section. This is the depth of penetration of the welded joint elements.

Seam thickness includes weld convexity q and penetration depth (c = q + h).

Gap- the distance between the ends of the elements being welded. It is set depending on the thickness of the metal being welded and is 0 - 5 mm (large size for thick metal).

A characteristic of the weld shape is the weld shape coefficient ψш - a coefficient expressed by the ratio of the width of a butt or fillet weld to its thickness. For a butt weld, the optimal value of ψsh is from 1.2 to 2 (can vary within 0.8 - 4).

Another characteristic of the weld shape is the weld convexity coefficient, which is determined by the ratio of the weld width to the convexity ψw of the weld. The coefficient ψш should not exceed 7 - 10.

The width of the weld and the depth of penetration depend on the welding method and modes, the thickness of the elements being welded and other factors.

Corner weld. The elements of the geometric shape of a fillet weld (Figure 15) are the leg of the seam - k, the convexity of the seam - q, the estimated height of the seam - p, the thickness of the seam - a.

Fillet weld leg- the shortest distance from the surface of one of the welded parts to the fillet weld boundary on the surface of the second welded part.

Figure 15 -

Weld convexity is determined by the distance between the plane passing through the visible lines of the boundary of the weld with the base metal and the surface of the weld, measured at the point of greatest convexity.

Design fillet weld height- the length of the perpendicular lowered from the point of maximum penetration at the junction of the mating parts to the hypotenuse of the largest one inscribed in the outer part of the fillet weld of a right triangle.

Fillet weld thickness- the greatest distance from the surface of the fillet weld to the point of maximum penetration of the base metal.

If the seam is made concave, then measure the concavity of the fillet weld. It is determined by the distance between the plane passing through the visible lines of the fillet weld boundary with the base metal and the surface of the weld, measured at the point of greatest concavity.

Depending on the welding parameters and the form of preparation of the welded edges of the parts, the share of participation of the base and deposited metals in the formation of the weld can vary significantly (Figure 16).

The coefficient of the proportion of the base metal in the weld metal is determined by the formula

K = Fo/(Fo + Fe),

where Fo is the cross-sectional area of ​​the weld formed due to the melting of the base metal;

Fe is the cross-sectional area of ​​the weld formed by the deposited electrode metal.

When the proportion of participation of the base and filler metals in the formation of a weld changes, its composition may change, therefore, its mechanical, corrosion and other properties also change.

Figure 16 -

The main types and structural elements of seams of welded joints for manual arc welding are regulated by GOST 5264-80.

2.2 Weld designations

Conventional images of seams of welded joints. The main types, structural elements, dimensions and symbols of welded joints and seams in the drawings, as well as the shape and dimensions of the preparation of welded edges from various structural materials used in arc welding, are regulated by standards.

In the drawings of welded products, the conventional images and designations of seams given in GOST 2.312-72 are used.

The seam of a welded joint, regardless of the welding method, is conventionally depicted: visible - with a solid main line (Figure 17.a - 17.c), invisible - dashed (Figure 17.d). A visible single weld point, regardless of the welding method, is conventionally designated with a “+” sign (Figure 17. b).

From the image of a seam or a single point, draw a leader line with a one-way arrow indicating the location of the seam. It is preferable to make a leader line from the image of a visible seam.

It is allowed to draw the contours of individual passes onto the image of the cross-section of a multi-pass weld, and they must be designated in capital letters of the Russian alphabet (Figure 18. a).

Figure 18 -

Non-standard seams (Figure 18.b) are shown indicating the structural elements required to make the seam according to this drawing.

In cross-sectional drawings, the boundaries of the seam are drawn with solid main lines, and the structural elements of the edges within the boundaries of the seam are drawn with solid thin lines.

2.3 Symbols for seams of welded joints

Auxiliary symbols for designating welds are given in Table 1.

Table 1 - Auxiliary symbols for designating welds

Auxiliary sign	Meaning of the auxiliary sign	The location of the auxiliary symbol relative to the flange of the leader line drawn from the seam image
		from the front side		from the reverse side
	Remove seam reinforcement
	Process sagging and unevenness of the seam with a smooth transition to the base metal
	The seam should be made during installation of the product, i.e. when installing it according to the installation drawing at the place of use
	The seam is intermittent or point with a chain arrangement. Line inclination angle ≈ 60°
	The seam is interrupted or dotted with a checkerboard arrangement
	Seam along a closed line. Sign diameter 3 - 5 mm
	Seam along an open line. The sign is used if the location of the seam is clear from the drawing

In the symbol of a seam (Figure 19), auxiliary signs are made with solid thin lines. Auxiliary signs must be the same height as the numbers included in the seam designation.

The structure of the symbol for a standard seam or a single weld point is shown in Figure 19. a.

1. The first in the designation are auxiliary signs - “seam along a closed line” and “perform when installing the product” (Table 1).

2. Indicate the standard number for the types and structural elements of welded joints. For example: GOST 5264-80 - Manual arc welding.

3. Give the alphanumeric designation of the seam according to the standard for the types and structural elements of seams in welded joints. For example, a one-sided butt weld without beveled edges is designated as C2.

Figure 19 -

4. This position indicates the symbol of the welding method according to the standard for the types and structural elements of seams. The standard allows not to specify the welding method.

5. Sign and size of the leg for corner, T-joints and overlaps, for which the standard provides for an indication of the leg of the seam, for example 5.

6. In this position enter:

For an intermittent seam - the length of the welded section, the sign / or Z and the step size, for example, 50 Z 100;

For a single weld point - the size of the calculated diameter of the point;

For a resistance spot welding seam or an electric rivet weld - the size of the calculated diameter of the point or electric rivet; sign / or Z and step size, for example 10/80;

For a resistance seam welding seam - the size of the calculated seam width;

For an intermittent weld of contact seam welding - the size of the calculated width, the multiplication sign, the size of the length of the welded section, the sign / and the step size, for example 5 x 40/200.

7. In the last place of the designation there are auxiliary signs - remove the seam reinforcement, etc. (Table 1).

If the seam is non-standard, then in its symbol (Figure 19. b) from the parts discussed above, only auxiliary signs (1 and 7) and the part of the designation relating to the structural elements of an intermittent or spot weld (6) are retained. The technical requirements of the drawing or the seam table indicate the welding method by which the non-standard seam is made.

The symbol of the seam is applied:

On the shelf there is a leader line drawn from the image of the seam on the front side (Figure 20.a);

Under the shelf there is a leader line drawn from the image of the seam on the reverse side (Figure 20. b).

Figure 20 -

The front side of a one-sided seam is taken to be the one from which welding is performed. The front side of a double-sided seam with asymmetrically prepared edges is taken to be the one with which the main seam is welded. If a double-sided seam has symmetrical edges, then either side of the seam can be taken as the front side.

The designation of the roughness of the mechanically processed surface of the seam is applied on the flange or under the flange of the leader line after the symbol of the seam (Figure 20.a - 20.b), indicated in the table of seams or given in the technical requirements of the drawing, for example: parameter of surface roughness of welded seams Rz 80 µm.

If a control complex or a seam control category is installed for the seam of a welded joint, then their designation may be placed under the leader line (Figure 20). In the technical requirements or the table of seams in the drawing, a link to the corresponding regulatory and technical document is provided.

Welding materials are indicated in the technical requirements drawing or seam table. It is allowed not to specify welding materials.

If there are identical seams in the drawing, the designation is applied to one of the images, and leader lines with shelves are drawn from the images of the remaining identical seams. All identical seams are assigned the same number, which is applied:

On a leader line that has a shelf with a seam designation applied (Figure 21. a);

On the shelf there is a leader line drawn from the image of the seam, which does not have a designation, on the front side (Figure 21. b);

Under the shelf there is a leader line drawn from the image of the seam, which does not have a designation, on the reverse side (Figure 21.c).

Figure 21

It is allowed to indicate the number of identical seams on a leader line that has a shelf with a printed designation (Figure 21.a).

If all the seams in the drawing are the same and are shown on the same side, then a serial number is not assigned to the seams and they are marked only with leader lines without shelves (Figure 21.d) except for the seam on which the symbol is applied.

In a drawing of a symmetrical product, if there is an axis of symmetry in the image, it is allowed to mark with leader lines and indicate the seams of only one of the symmetrical parts of the product image.

In the drawing of a product in which there are identical components welded with identical seams, it is allowed to mark with leader lines and indicate seams only on one of the identical depicted parts.

If all the seams in this drawing are made according to the same standard, the designation of the standard is indicated in the technical requirements of the drawing (with an entry of the type: “Welds according to ...”) or in the table.

It is allowed not to mark seams in the drawing with leader lines, but to provide instructions for welding with an entry in the technical requirements of the drawing, if this entry unambiguously defines the welding locations, welding methods, types of seams of welded joints and the dimensions of their structural elements in cross section and the location of the seams.

The same requirements for all seams or a group of seams are given once - in the technical requirements or in the table.

Symbols of standard weld seams

Figure 22 shows the cross-sectional shape of the seam and the symbol of a standard butt weld, respectively. This seam has the following characteristics: a butt joint seam with a V-shaped bevel of one edge, double-sided, performed by manual arc welding during installation of the product; reinforcement removed on both sides; weld surface roughness parameter: on the front side Rz 20 µm;

Drawings depicting welded products, welded assemblies, etc., which contain the necessary data for assembly, welding and control, are called assembly drawings. Assembly drawings make it possible to determine how the product is designed and operates, what parts are included in it, what types of welded joints should be, what welding method should be used to connect the parts to each other, what kind of control should be applied to welded joints and seams, what technical requirements should match welds, etc.

Figure 22 -

When starting work, the welder must first of all study the drawing: all the inscriptions, depicted views, symbols, material of parts, technical requirements for welds.

The section of a metal structure in which different parts are combined during welding operation is called a welding joint. Welds can vary in strength. The weld joint may include a single weld. This is the place of thermal influence on the point of connection of metals. As a result of this effect, the metal melts and crystallizes when cooled. The quality of the weld is largely influenced by the characteristics of the metal at the point of thermal impact.

Type of weld points according to connection type

Butt welds are used in butt joints. They are carried out continuously. The difference is the actions to prepare the plane at the end of the section and the elements prepared for contact. This allows full access to the welding site and ensures the most efficient welding of planes to the full thickness.

Among butt seams, different types can be distinguished:

1. Single-sided and double-sided without sawing edges.
2. With one-sided or two-sided sawing of one of the edges.
3. With one-sided sawing of both edges.
4. V or X sawing.
5. Double-sided sawing of both edges.

The corner type of joints is used when welding of fillet welds is required. Fillet welds are used in the manufacture of such joints. They can be divided by continuity and by gap.

The above types can be supplemented with another variety that relates to both butt and corner ones. These are cork and slotted varieties. The slotted type is used when it is necessary to melt the upper layer, and possibly the underlying ones, to the main element. In the contact of thickened layers, slotted seams and connections are made along manufactured vents. In this form they will be called “cork” or in the case of arc welding “electric rivet”.

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Various types of welding seams

Differences in welding and types of welding seams according to their stay in space:

• welding horizontal seams;
• welding of ceiling seams;
• bottom seams.

Used for welding work located below on a flat plane. They are technically the simplest in execution. The high strength of the joints is explained by convenient conditions in which the melted metal, under its own weight, rushes into the weld pool, which is located horizontally. This work is the easiest to do and easy to follow. In overlap structures, the coal in the lower position is continuous, without producing transverse vibrations.

Horizontal welds. The process of welding horizontal points is associated with some difficulties. During cross welding on a vertical surface, molten metal may flow to the bottom edge. As a result, an undercut may appear on the upper edge. The use of this method in welding carbon points produced in a horizontal position is quite simple and does not cause any difficulties. The work itself is similar to welding work in the lower position and depends on the required seam.

Vertical welds. When welding vertical parts, the metal underneath is designed to hold the melting metal on top, but it ends up being rough and flake-like. It is much more difficult to obtain a quality connection when working downward. Welding vertical seams in a standing plane is only possible in a bottom-up orientation and vice versa.

Ceiling seams. The most difficult type of welding work to perform. During operation, the release of gases and slags is difficult, and it is also difficult to keep the melt from flowing and achieve point strength. But despite following all ceiling welding techniques, the seams are still inferior in reliability to welding seams made in other positions.

Classification of features of welded joints by outline:

• welding of longitudinal seams;
• creation of circular seams.

To perform longitudinal welding work, it is necessary to thoroughly prepare the metal at the point of intended welding. The surfaces of the parts must be cleaned of burrs, edges and irregularities. In longitudinal welding work, a seam is only possible if the required surfaces are completely cleaned and degreased.

Circumferential welds. Welding work on circles requires great care and precision; calibration of welding currents is also necessary, especially when working with small diameters.

Welding of circumferential seams varies in outline. They are:

• convex;
• concave;
• flat.

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Geometry of welds

The main geometric parameters are: width, curvature, convexity and root of the joint.

Width is the gap between visibly different faces of metal fusion. Curvature is the gap between the area flowing along the visible edges of the welding point and a certain metal at the point of extreme concavity.

To measure convexity, the gap relative to the levels is determined, flowing along the visible edges of the weld and the base metal at the point of maximum convexity. The root is the edge that is extremely distant from the profile level, which is actually its reverse side.

You can divide such seams according to dimensional standards:

• leg;
• thickness;
• design height.

In a fillet weld for fillet welding, the length from the level of the first part being welded to the edge of the seam on the next part is the leg of the fillet weld. The leg is one of the important characteristics that must be observed during welding work. In simple coal joints with a single size, the weld leg is determined by the size of its edges. In welding T-shaped structures, the leg has a fixed size, and a single dimension of materials is used. And when using T-shaped structures of different sizes in welding work, it is equal to the thickness of a thinner metal. The leg must have the correct dimensions to achieve maximum joint strength; if you use a leg that is too large, welding defects are possible.

Beginners can make it easier to work with parts by arranging them for welding “in a boat”. When welding “in a boat”, the likelihood of undercuts is reduced, and the lock will be stronger.

The thickness of a coal weld is the maximum distance from its level to the contact of the maximum penetration of the base metal.

What to remember when welding corner joints? For fillet welds, a concave level shape with a smooth transition to the base is considered favorable. This is due to the difficulty of welding the entire thickness of the root in coal seams. In most options, the leg and thickness are measured with certain patterns.

To obtain the strongest possible connection, you need to refer to many factors. They are taken into account when determining the type of connection depending on the required characteristics of the products being welded.

In order to learn how to cook well, it is not enough to master just holding the electric arc. In addition, you need to understand what types of welded joints and seams there are. Beginning welders often make serious mistakes, for example, not welding the metal. And it happens that finished parts have weak fracture resistance. What is the reason? First of all, in the wrong choice of connection type, errors in technology. Today we invite you to talk about different types of welding, types of welded joints, as well as defects!

Weld seam: definition

First, let’s define the definition of a weld seam. This is the name given to crystallized metal that was in a molten state at the time of welding.

The structure of the weld seam includes:

• deposited metal zone;
• mechanical fusion zone;
• heat affected zone;
• transition zone to the base metal.

Welded joint: what is it?

A welded joint is usually defined as a limited section of a structure that contains one or more welds. It is by the appearance of the connection that a specialist can determine the qualifications of the welder and understand what welding method was used. The welded connection also tells about the technological purpose of the structure.

Welds: classification

Experienced welders say: the classification of weld types can be based on a variety of factors, for example structural and strength, geometric and technological. If we consider the seams from the point of view of location, they can be divided into lower, inclined, horizontal and vertical.

The bottom seam can be called not only the simplest, but also the most durable. The fact is that the gravity of the metal makes it possible to better fill the gaps between the surfaces being connected. In addition, this type is the most economical. There are certain conditions, for example, the burner or electrode must be directed from top to bottom.

A horizontal seam is usually formed when the surfaces are perpendicular to the plane of the electrode. The consumption of fluxes and electrodes with this type increases significantly. If the seam is drawn slowly, drips are possible, and if it is done quickly, uncooked areas may occur.

It is much more difficult to make a high-quality vertical seam. Here, metal loss increases, unevenness increases (at the final stage of welding, the seam turns out to be thicker). This method requires a certain classification of the welder. It is usually used for welding pipes or when fastening large structures.

Welders consider ceiling welding to be the most difficult. How is it produced? The seam is applied with an intermittent arc. The current strength is small. This type is usually used when welding pipes that cannot be turned.

Welded joints: types and types

We propose to talk about what types of welded joints there are according to the types of joining surfaces. Depending on factors such as the thickness of the metal, the geometric shape of the parts, and the required tightness of the joint, welded joints can be divided into:

• T-bars;
• overlap;
• butt;
• corner.

All types of welded joints have their own purpose, which suits the specific needs of the finished elements. We invite you to consider these types in more detail!

Joint

The most common type of welded joint is a butt. It is used when welding the ends of pipes, steel sheets or any geometric shapes.

The parts that are joined end-to-end differ in the thickness of the product and the side of the seam. Several subtypes of connections can be distinguished:

• unilateral normal;
• one-sided, in which the edges are processed at an angle of 45 degrees;
• one-sided, in which one edge is processed at an angle of 45 degrees;
• one-sided, in which the edge on both parts is removed with a milling cutter;
• double-sided, which involves cutting the edges at an angle of 45 degrees on each side.

It is important to note that with this type of welded joint, the thickness of the welded surfaces plays an important role. If it is no more than 4 millimeters, then a one-sided suture is used, but if the thickness exceeds 8 millimeters, the suture must be applied on both sides. If the thickness of the product exceeds 5 mm, but the seam needs to be applied only on one side, thereby obtaining high strength, the edges should be separated. You need to do it with a file or grinder; a 45-degree bevel is enough.

Gusset

There are several corner connection options:

• one-sided - both with and without preliminary cutting;
• double-sided - regular and with cutting.

Using this connection, you can fasten two elements together at any angle. In this case, the first seam will be internal, and the second - external. This type is ideal for welding various canopies and canopies, truck bodies and gazebo frames.

If you need to connect two plates of different thicknesses, this type of welded joint, according to GOST, must be performed as follows: the thicker plate should be placed at the bottom, and the thinner should be placed on its edge. In this case, the electrode or burner should be directed at the thick part - this way there will be no burns or undercuts on the part.

Lap joint

Two plates can be welded not only end-to-end, but also overlapping - by slightly pulling one onto the surface of the second. Experts recommend using this type of welded joint where greater tensile strength is required. The seam must be placed on each side - this will not only increase strength, but also prevent the accumulation of moisture inside the finished product.

T-joint

This type is similar to a corner connection, but there are differences - the plate, attached with an edge, should not be placed at the edge of the lower base, but at a short distance.

Classification by technology and seam shape

Welders distinguish between types of welded joints based on the type of welds. The seam can be:

1. Smooth. It is achieved with optimal settings of the welding machine and with its comfortable position.
2. Convex. Such a seam can be obtained with low current and passing through several layers. A convex seam requires machining.
3. Concave. Such a seam can only be obtained with increased current strength. This type of weld has excellent penetration and does not require grinding.
4. Solid. To make a high-quality continuous seam, you need to do it continuously. This will prevent the occurrence of fistulas.
5. Intermittent. This seam should be used for products made from thin sheets.

A welder who is familiar with the main types of joints and their fundamental differences can correctly select the type of weld that can satisfy the basic requirements for strength and tightness.

Defects in welded joints: types, description, causes

Welded joints can have various effects that affect strength and sealing. It is customary to divide all types of defects into three categories:

• internal (these include lack of penetration, porosity and foreign inclusions);
• external (including cracks, undercuts, craters, sagging);
• through (here you can highlight burns and cracks).

Let's talk in more detail about each type of defect.

Cracks

This type of defect is considered the most dangerous; it can lead to rapid destruction of welded structures. Cracks are distinguished by their size (there are macro- and microcracks) and by the time of appearance (during the process of welding parts or after). The reason for the appearance of cracks is non-compliance with welding technology, incorrect choice of materials for welding, or too rapid cooling of the structure.

You can fix a crack as follows: drill out its beginning and end, remove the seam and weld it.

Undercuts

Undercuts are the depressions between the seam and the metal. The seam becomes weak due to this defect. The reason for the appearance of undercuts is an increased current value. An undercut usually occurs on horizontal seams. This defect can be eliminated by surfacing a thin weld along the undercut line.

Surges

Such a defect can appear when molten metal flows onto the base metal without forming a homogeneous compound. The reasons for the appearance of sagging are simple - the base metal is not heated, the welder uses an excessive amount of filler material. The defect can be eliminated by cutting, making sure to check for lack of penetration.

Burns

Burn-throughs are defects that manifest themselves in through penetration and leakage of liquid metal. In this case, on the other side, as a rule, a sag appears. The cause of burn-throughs is high welding current, slow movement of the electrode, insufficient thickness of the lining, and too large a gap between the edges of the metal being welded. You can fix a burn-through: just clean and weld the defect area.

Lack of penetration

Lack of penetration refers to local lack of fusion of the deposited metal with the base metal. Lack of penetration can also be called non-filling of the seam section. This type of defect reduces the strength of the seam and causes destruction of the finished structure. The reason lies in the low welding current, the presence of slag or rust on the parts being welded. To correct the error, you need to cut out the lack of fusion and weld the parts.

Craters

Depressions called craters are usually caused by a broken welding arc. If such a defect appears, it is necessary to cut it down to the base metal and carefully weld it.

Fistulas

This is the common name for cavities that reduce the strength of the seam. It is because of fistulas that cracks can form. Cutting out the defect and welding will correct the situation.

Porosity

What is porosity? These are cavities that are filled with gases. The reason for their appearance is intense gas formation inside the metal. Pore ​​sizes can be either microscopic or reaching several millimeters. To avoid porosity, the metal should be cleaned of dirt and foreign substances. It is necessary that the electrode is not wet. If a mistake has already been made, the porous zone should be cut out to the base metal and welded, following the technology.

Overheating and burnout

These defects appear as a result of high welding current or insufficient welding speed. Because of this, the finished product becomes very fragile. Burnt metal can only be cut out, and the metals can be welded again.

Welding control

Now let's look at the types of inspection of welded joints. The following methods exist:

• visual inspection;
• chemical analysis;
• transillumination with gamma rays or x-rays;
• metallographic analysis;
• ultrasonic or magnetic flaw detection;
• mechanical tests.

There is a very important rule - for reliable control, it is imperative to clean the joint from slag, scale and welding spatter!

Welds are classified according to purpose, design feature, length, position relative to the acting force and position in space.

According to their purpose, seams are divided into working and connecting, or structural. The working seams absorb design forces, their dimensions are determined by calculation. Structural, or connecting, seams are used to connect elements, attach structural parts, eliminate gaps and are used with a minimum cross-section.

Based on their design, seams are divided into butt, corner and spot.

Butt weld- This is a weld of a butt joint. Butt welds are made when connecting elements that are usually located in the same plane by filling the space between the parts with filler material. When welding elements of small thickness, for complete penetration it is enough to leave a gap between the edges equal to */3 the thickness of the metal, while the butt weld can be either on the remaining or on the removable lining.

With a large thickness of metal, in order to achieve complete penetration throughout the entire depth of the seam, it is necessary to specially process the edges of the elements being welded - to prepare the edges, and the seam may consist of one or more beads welded into the groove.

A bead is a weld metal that is deposited or remelted in a single pass. The first bead (Fig. 2.7), welded into the groove, is called the root pass or sometimes the root weld. Subsequent rollers form filling layers. With a double-sided weld, the smaller part of the double-sided seam, made first to prevent burns during subsequent welding, or applied last at the root of the seam, is called a gift seam.

Rice.

1 - root pass; 2-4 - filling layers; 5 - underwelding seam

Butt seams should have a convexity on both sides in the form of beads, having a smooth outline, and, if possible, a small height. The convexity compensates for the unevenness of the outer surface of the weld and possible weakening (pores, slag inclusions) of the inner part.

The butt weld is the main and most economical welded joint. It transmits force evenly over the entire cross-section with the lowest local stresses, which makes it especially suitable for vibration and dynamic loads.

The disadvantages of a butt weld are: production difficulties in creating a uniform gap along the entire length of the elements being connected; additional costs for edge processing; the need for precise cutting of elements.

Corner weld- This is a weld of a corner, lap or T-joint. Fillet welds are placed in the corner formed by the elements being connected, located in different planes, and can consist of one or more rollers (Fig. 2.8).

Rice. 2.8.

A normal fillet weld looks like an isosceles triangle with a slight convexity. In connections that absorb dynamic forces, fillet welds must have a concave surface. GOST allows convexity and concavity of a fillet weld up to 30% of its leg. In this case, concavity should not lead to a decrease in the value of the leg to n(the size of the fillet weld leg established during design). The design size of the leg ( To n) is the leg of the largest right-angled triangle inscribed in the outer part of the fillet weld (Fig. 2.9). With a symmetrical seam behind the leg to and any of the equal legs is accepted, with an asymmetrical seam - the smaller one.

Rice. 2.9. Design value of leg ( To„) fillet welds

Spot seam called a weld in which the connection between the welded parts is carried out by welded points. Weld point - This is an element of a spot weld, which is a circle or ellipse in plan. Spot welds are used for welding lap joints with a hole in the upper element (Fig. 2.10). The hole can have vertical walls or have a beveled edge. Spot welds have much in common with fillet welds, except that the cross-section of the weld is formed by filling a hole in the plate with weld metal. This type of weld is not widely used.

Rice. 2.10.

Based on their length, welds are divided into continuous, intermittent and tack welds.

Continuous seam - This is a weld without any gaps along its length. A continuous weld runs along the entire length of the joint, from one end to the other (2.11 , A).

Rice. 2.11.A- double-sided continuous; b- one-sided intermittent, V - double-sided chain; G - double-sided chess

Intermittent seam- this is a weld with intervals along the length (Fig. 2.11, b). On non-critical structures (welding fences, decking, etc.), the use of intermittent seams can provide a significant economic effect, and the cost of welding work can be significantly reduced. This type of weld is usually used for welding lap and T-joints. Varieties of intermittent seams are: chain intermittent seam and checkerboard intermittent seam.

Chain interrupted stitch- this is a double-sided intermittent seam, in which the gaps are located on both sides of the wall - one opposite the other (Fig. 2.11, V).

Checkerboard interrupted seam- this is a double-sided intermittent seam, in which the gaps on one side are located opposite the welded sections of the seam on the other side (Fig. 2.11 , G).

Tack- this is a short weld to fix the relative position of the parts to be welded. Structures made by welding often consist of many different elements. These elements, assembled by welding, form the final welded product. During the assembly process, it becomes necessary to attach some element to the main structure before welding it. This is achieved by applying a series of short sutures located at some distance from each other. The tacks must be strong enough to hold the element in the desired position and not break when welding the product. The number and cross-section of tacks are determined by the thickness of the metal being welded, the length of the seam, the load from cold working that the tacks will have to withstand, as well as the welding technology used.

According to their position relative to the acting force, welds are divided into flank, frontal, combined and oblique (Fig. 2.12).

A frontal butt weld transmits the applied force evenly over the entire section with the lowest local stresses. The strength of the connection does not depend on the type of cutting of the edges of the elements being welded and, if the work is carried out correctly, is almost the same. It is necessary to carefully weld the ends of the seams, especially oblique ones, without leaving under-welds or unfinished craters, which can serve as centers of stress concentration and the appearance of cracks.

Rice. 2.12. Types of welds in relation to the direction of acting

effort on them:

A- longitudinal (flank); b- transverse (frontal); V- combined; G- oblique

The frontal double-sided fillet weld of an overlap joint in most cases has an uneven load distribution. The distribution of stress along the length of the flank weld in the elastic stage of work occurs unevenly, and large overstresses occur at the extreme points.

The strength of flank seams is somewhat less than that of front seams, since their destruction occurs mainly from shearing with a slight influence of bending. The plastic properties of flank seams are insignificant, and after the first crack appears at the beginning of the seam, destruction occurs quite quickly.

When making overlap joints using only flank seams, it is necessary that the length of the seam be greater than the width of the part. If this condition cannot be met, welding is carried out along the contour using both frontal and flank seams. Welding along the contour increases the strength of the joint compared to frontal or flank seams, but the intersection of frontal and flank seams reduces it. An increased concentration of stress is created in the corners, therefore, when welding along the contour, it is advisable not to scald them (Fig. 2.13).

The following welding positions are accepted (Fig. 2.14): lower butt and “boat”; lower tee; horizontal; ceiling butt; ceiling T-bar; vertical from bottom to top; vertical from top to bottom; inclined at an angle of 45°.

Rice. 2.13.

Rice. 2.14.

Lower welding position- the position when the plane in which the seam of the welded joint is located is at an angle from 0 to 10° with respect to the horizontal plane. When welding in the lower position, the surface of the weld pool occupies a horizontal position, which creates the best conditions for the formation of a seam.

Horizontal welding position- a position in which the seam of the welded joint is located on a vertical surface and is at an angle from 0 to 10° with respect to the horizontal plane.

Vertical welding position- the seam of the welded joint is on a vertical plane at an angle of 90° ± 10° with respect to the horizontal plane.

Uphill welding- This is fusion welding in an inclined position, in which the weld pool moves from bottom to top. Downhill welding- This is fusion welding in an inclined position, in which the weld pool moves from top to bottom.

Welding in a vertical position from top to bottom and “downhill” is characterized by the fact that the direction of gravity of the liquid metal and the direction of welding coincide, the metal of the weld pool flows under the arc, which reduces the depth of penetration. When welding in a vertical position from bottom to top and “up”, the direction of gravity of the liquid metal is opposite to the direction of welding, the metal of the weld pool flows out from under the arc, thereby increasing the depth of penetration.

Inclined welding position- the plane on which the weld is located is at an angle of 45° ± 10° with respect to the horizontal plane.

Ceiling welding position- spatial position during welding, when the latter is performed from below the connection. When welding in the ceiling position, the surface of the weld pool occupies a horizontal position, and the metal of the pool is held by the forces of surface tension and arc pressure. This kind of welding is the most difficult and can only be carried out by highly qualified welders.

Welding in vertical and overhead spatial positions is used mainly in those enterprises where the products are large and cannot be rotated. The vertical welding position is more common than the ceiling position.