The main types of welds and joints. Welding seams: from simple to complex. Symbols and symbols of welds

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

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

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

A welded assembly is a part of a welded structure in which adjoining elements 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 fed into the arc zone in addition to the molten base metal is called filler metal.

The remelted filler metal introduced into the weld pool or deposited on the base metal is called the weld metal.

The alloy formed by the remelted base or base and weld metal is called the 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 for manufacturing the welded structure (manual welding, automatic in the factory or installation conditions), the economy of the base metal, electrodes, etc. are taken into account.

Types of welded joints. According to the form of mating of the parts (elements) to be joined, the following types of welded joints are distinguished: butt, corner, tee, overlapping (Figure 1).

Welded seams are subdivided according to the shape of the cross-section into butt (Figure 2, a) and corner (Figure 2, b). A variety of these types are cork seams (Figure 2, c) and slotted (Figure 2, d), performed in lap joints. According to the shape in the longitudinal direction, the seams are continuous and intermittent.

With the help of butt welds, butt joints are mainly formed (Figure 1, a), with the help of fillet welds - T-shaped, cross, corner and overlap joints (Figure 1, b-e), with the help of cork and slotted seams, overlap and sometimes tee connections.

Butt seams are usually continuous; a distinctive feature for them is usually the shape of the groove of the edges of the parts to be joined in cross-section. On this basis, the following main types of butt seams are distinguished: with flanging edges (Figure 3, a); without cutting edges - one-sided and two-sided (Figure 3, b); with cutting one edge - one-sided, two-sided; with a straight or curvilinear cut (Figure 3, c); with one-sided groove of two edges; with a V-shaped groove (Figure 3, d); with two-sided groove of two edges; X-shaped groove (Figure 3, e). The groove can be formed by straight lines (bevel edges) or have a curved shape (U-groove, Figure 3, e).

a) butt; b, c) T-shaped; d) corner; e) overlapping

Figure 1 - The main types of welded joints

a) butt; b) corner; c) cork; d) slotted

Figure 2 - Basic types welds

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

a) with flanged edges; b) without cutting edges;

c, d, e, f) with grooves

Figure 3 - Preparation of butt joint edges

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

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

Cork seams in their shape in plan (top view) are usually round in shape and are obtained as a result of complete penetration of the upper and partial penetration of the lower sheets (Figure 6, a) - they are often called electric rivets, or by melting the upper sheet through the previously made in the upper sheet hole (Figure 6, b).

a) without cutting edges; b, c) with cutting edge

Figure 4 - Preparation of the edges of fillet welds

connections

Figure 5 - Fillet welds of T-joints

Figure 6 - Cross-sectional shape of plug and

slotted seams

Slotted seams, usually of an elongated shape, are obtained by welding the upper (covering) sheet to the lower fillet weld along the perimeter of the slot (Figure 6, c). In some cases, the slot can be completely filled.

The shape of the groove and their assembly for welding is characterized by four main structural elements (Figure 7): gap b, bluntness c, bevel angle and groove angle equal to or 2 .

Existing methods arc welding without cutting edges allow welding metal of limited thickness (with one-sided manual welding - up to 4 mm, mechanized submerged arc - 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 of the groove angle, which is necessary for the arc to reach deep into the joint and to completely penetrate the edges to their entire thickness.

The standard groove angle, depending on the welding method and the type of joint, varies from 60 ± 5 to 20 ± 5 degrees. The type of groove and the value of the groove angle determine the amount of additional metal required to fill the groove, and hence the welding performance. So, for example, X-shaped groove in comparison with V-shaped groove allows to reduce the volume of deposited metal by 1.6-1.7 times. Reduces the time spent on edge processing. True, in this case, it becomes necessary to weld on one side of the seam in an inconvenient ceiling position or to turn over the products to be welded.

Bluntness is usually 2 ± 1 mm. Its purpose is to ensure correct formation and prevent burn-in at the top of the seam. The gap b is usually 1.5-2 mm, since at the accepted groove angles, the presence of a gap is necessary for penetration of the weld top, but in some cases, with one technology or another, the gap can be zero or reach 8-10 mm or more.

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

Figure 7 - Structural elements of grooving and

weld assemblies

Welds are classified according to a number of characteristics. By appearance seams are divided into convex, normal, concave (Figure 8). As a rule, all

the seams are performed with a slight reinforcement (convex). If seams without reinforcement are required, this should be indicated on the drawing. Weak (concave) fillet welds are made, which is also noted in the drawing. Such seams are required to improve the performance of welded joints, for example, under varying loads. Butt seams are not made weakened, concavity in this case is a marriage. An increase in the size of welded seams in comparison with the specified leads to an increase in the mass of the structure to be welded and excessive consumption of electrodes. As a result, the cost of welded structures increases, and the labor intensity of welding increases.

a) convex; b) normal; c) concave

Figure 8 - Classification of seams by appearance

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

According to the number of layers and passes, single-layer, multi-layer, single-pass, multi-pass seams are distinguished (Figure 9, 10).

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

Figure 9 - Classification of seams by execution: a - one-sided; b - bilateral

Figure 10 - Classification of seams by the number of layers and passes:

I-IV - number of layers; 1 ~ 8 - number of passes

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 joints is approximately 5-6 mm.

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

By position in space, lower, horizontal, vertical and ceiling seams are distinguished (Figure 12). They differ from each other in the angles at which the surface of the part to be welded is located relative to the horizontal. The most difficult to execute is the overhead seam, the seam is best formed in the lower position. Ceiling, vertical and horizontal seams usually have to be performed during manufacture and, especially, when installing large-sized structures.

a) - longitudinal (flank); b) - transverse (frontal);

c) - combined; d) - oblique

Figure 11- Classification of seams by effective force

Figure 12 - Classification of welds according to their position

in space

Examples of the designation of welds by their position in space are given in Figure 13

H - lower; P - ceiling; Пп - semi-ceiling; Г - horizontal;

PV - semi-vertical; B - vertical; L - into the boat;

PG - semi-horizontal

Figure 13 - Designation of welds by their position

A welded joint is a set of parts connected by a welded seam. In arc welding, the following types of joints are used: butt, overlap, tee and corner; in a number of cases, slotted, end connections, with linings, electric rivets are used (Fig. 56).

Butt joints. Butt joints (Fig. 56, a) are the most common, since they give the lowest natural stresses and strains during welding, as well as high strength under static and dynamic loads. They are used in sheet metal structures and when joining angles, channels, I-beams and pipes. Butt joints require least expense base and weld metal. With butt joints, careful preparation of sheets for welding and a fairly accurate fit to each other is required.

Sheets 1-3 mm thick can be butt-welded with flanging, without a gap and without filler metal (Fig. 56, b).

In manual arc welding of steel sheets 3-8 mm thick, the edges are cut at right angles to the surface, and the sheets are placed with a gap of 0.5-2 mm.

Without beveling the edges, you can butt-weld sheets up to 6 mm for one-sided and up to 8 mm for double-sided welding.

Sheets with a thickness of 3 to 26 mm with manual arc welding are butt-welded with a one-sided bevel of one or two edges. This type of edge preparation is called V-shaped. Sheets 12-40 mm thick are welded with a double-sided bevel of the edges, called X-shaped when both edges are beveled and K-shaped when one edge is bevel.

The edges are blunt in order to prevent metal leakage during welding (burn-through). A gap between the edges is left to facilitate penetration of the root of the seam (lower parts of the edges). Great importance for the quality of welding it has the preservation of the same gap width along the entire length of the seam, that is, the observance of the parallelism of the edges.

Double-sided bevel (X-shaped) has advantages over one-sided (V-shaped), since with the same thickness

In sheets, the volume of deposited metal will be almost two times less than with a one-sided bevel of the edges. Accordingly, the consumption of electrodes and electricity during welding will decrease. In addition, with two-sided bevel of the edges, less warpage and residual stresses occur than with one-sided. Therefore, sheets with a thickness of more than 12 mm are best welded with an X-shaped bevel of the edges. However, this is not always feasible due to the design and dimensions of the product.

In manual arc welding of steel with a thickness of 20-60 mm, a curvilinear U-shaped bevel of one or two edges is also used in order to reduce the volume of deposited metal, which increases welding productivity and saves electrodes. When butt welding of sheets of unequal thickness, a thicker sheet is beveled to a greater extent (Fig. 56, c).

Lap joints. Lap joints (Fig. 56, d) are mainly used in arc welding of building structures made of steel with a thickness of no more than 10-12 mm. In some cases, they are also used when welding thicker sheets (but not more than 20-25 mm). Lap joints do not require any special edge processing other than trimming. In such joints, it is recommended, if possible, to weld the sheets on both sides, since during one-sided welding, moisture can enter the gap between the sheets and cause subsequent rusting of the metal in the welded joint.

Assembly of the product and preparation of sheets for overlapping welding are simplified, but the consumption of base and weld metal is higher than for butt welding. Lap joints are less robust under alternating and shock loads than butt joints. In roller and spot contact electric welding, overlap joints are mainly used.

Corner connections. Such joints (Fig. 56, e) are used when welding along edges located at a right or other angle to each other. They are used, for example, when welding tanks, containers, vessels, pipeline flanges and other products operating under low pressure (below 0.7 kgf / cm 2), irresponsible. Sometimes corner joints are also welded from the inside. For metal 1–3 mm thick, corner joints with flanging and welding without filler metal can be used.

Tee connections. Tee joints (Fig. 56, e) are widely used in arc welding of beams, columns, racks, truss frames and other building structures. They are made without bevel and with beveled edges on one or two sides. The vertical sheet should have a fairly even cut edge. With one-sided and two-sided bevel of the edge, a gap is left between the vertical and horizontal sheets for better penetration of the vertical sheet through the entire thickness. A one-sided bevel is needed if the design of the product does not allow welding the T-joint on both sides. In joints without beveled edges, lack of penetration at the root of the seam is possible, therefore, such a seam can collapse under vibration and shock loads. T-joints with beveled edges provide the necessary strength for all types of loads.

Slotted connections. These joints (Fig. 56, g) are used when the length of a normal overlap seam does not provide sufficient strength. Slotted joints are either closed or open. The slot can be cut with oxygen, air arc and plasma cutting.

End, or side, connections. Such connections are shown in Fig. 53, h. Sheets are welded along adjacent ends.

Connections with overlays (fig. 56, i). Cover 2, overlapping the joint of sheets 1 and 3, is welded along the side edges to the surface of the sheets. These joints require additional metal consumption for the lining and therefore are used only in cases where they cannot be replaced by butt or lap joints.

Electrical rivets. With the help of electric rivets, strong, but not tight connections are obtained (Fig. 56, k). The top sheet is punched or drilled and the hole is welded so that the bottom sheet is caught. With a thickness of the top sheet up to 3 mm, it is not pre-drilled, melting the rivet with an arc when welding. Electric riveted seams are used in lap and T-joints.

The described connections are typical for rune arc welding of steel. In gas welding, submerged arc welding, welding of low-melting non-ferrous metals and in other cases, the shape of the edges may be different. Information about them is given in the following chapters when describing these welding methods.

Forms of preparation and bevel angles of edges, gaps and deviations allowed for the seams of welded joints in manual arc welding are regulated by GOST 5264-69.

Types of seams. There are the following types of welds:

1. By position in space - lower, horizontal, vertical and ceiling (Fig. 57, a). The easiest to implement is the bottom seam, the most laborious is the ceiling seam. Ceiling seams can be performed by welders who have specially mastered this type of welding. Arc welding overhead seams is more difficult than gas welding. Welding horizontal and vertical seams on a vertical surface is somewhat more difficult than welding the bottom seams.

2. In relation to the acting forces - flank, frontal, combined and oblique (Fig. 57, b).

3. In length - continuous and intermittent (Fig. 57, c). Discontinuous seams are used in cases where the joints should not be tight, and according to the strength calculation, a continuous seam is not required.

The length of the individual sections of the interrupted seam (l) is from 50 to 150 mm; the distance between the sections of the seam is usually 1.5-2.5 times the length of the section; the value of t is called the step of the seam. Interrupted welds are widely used because they provide savings in weld metal, welding time and cost.

4. By the amount of deposited metal or the degree of convexity - normal, convex and concave (Fig. 57, d). The convexity of the seam depends on the type of electrodes used: when welding with thin-coated electrodes, seams with a large convexity are obtained. When welding with thick-coated electrodes, due to the greater fluidity of the molten metal, normal seams are usually obtained.

Seams with a large bulge do not provide the strength of the welded joint, especially if it is subjected to variable fluidity of the molten metal, normal seams are usually obtained.

Seams with a large bulge do not provide the strength of the welded joint, especially if it is subjected to alternating loads and vibrations. This is due to the fact that in seams with a large bulge it is impossible to obtain a smooth transition from the bead to the base metal, and in this place a kind of "undercut" of the edge is formed, where the concentration of stresses occurs. Under the action of alternating shock or vibration loads, destruction of the welded joint may begin from this place. Seams with a large bulge are uneconomical, as they require more electrodes, time and energy to complete.

5. By the type of connection - butt and corner. Fillet welds are used when making overlap, tee, corner, with overlays, slotted, butt joints. The side to the fillet weld (fig. 58) is called the leg.

When determining the leg k in the seams shown in Fig. 58, a, the smaller leg of the triangle inscribed in the cross-section of the seam is taken; in the seams shown in fig. 58, b and c, the leg of an inscribed isosceles triangle is taken.

GOST 5264-80 allows a weld bulge e: at the lower welding position - up to 2 mm, at a different welding position - up to 3 mm. The increment of the leg (m - k) at any position of the seam is allowed up to 3 mm.

Administration Overall score articles: Posted: 2011.06.01

Welding seams- zones of welded joints, which are formed initially by molten metal, and then crystallized during cooling.

The service life of the entire weld structure depends on the quality of the welds. Welding quality is characterized by the following geometrical parameters of the weld:

Width is the distance between its edges;
The root is the inner part opposite to its outer surface;
Bulge - the largest protrusion from the surface of the metal to be joined;
Concavity - the greatest deflection from the surface of the metal being joined;
A leg is one of the equal sides of a triangle inscribed in cross section two connected elements.

What are the welds and joints, classification

Table 1 shows the main types of welded joints, grouped by cross-sectional shape.

	Welded joints and seams	Location features	Main application	Note
1	Butt	Connected parts, elements are in the same plane.	Welding of sheet metal structures, tanks and pipelines.	Saving Supplies and time for welding, bond strength. Thorough metal preparation and selection of electrodes.
2	Corner	Connected parts, elements are located at any angle relative to each other.	Welding of tanks, tanks.	The maximum metal thickness is 3 mm.
3	Overlapping	Parallel arrangement of parts.	Welding of sheet metal structures up to 12 mm.	Large consumption of material without careful processing.
4	Tauric (letter T)	The end of one element and the side of the other are at an angle	Welding of supporting structures.	Thorough processing of a vertical sheet.
5	End	The side surfaces of the parts are adjacent to each other	Pressureless vessel welding	Material savings and ease of execution

By way of execution:

Double-sided - welding from two opposite sides with the removal of the root of the first side;
Single-layer - execution in one "pass", with one weld bead;
Multilayer - the number of layers is equal to the number of "passes". It is used for large metal thicknesses.

By the degree of convexity:

Convex - reinforced;
Concave - weakened;
Normal are flat.

The convexity of the seam is influenced by the welding materials used, the modes and speed of welding, the width of the groove.

By position in space:

Lower - welding is carried out at an angle of 0 ° - the most the best option, high performance and quality;
Horizontal - welding is carried out at an angle from 0 to 60 ° require increased
Vertical - welding is carried out at an angle from 60 to 120 ° qualification of the welder;
Ceiling - welding is carried out at an angle of 120 to 180 ° - the most labor-intensive, unsafe, welders undergo special training.

By length:

Solid are the most common;
Intermittent - structural leaks.

Types of welded joints and seams in relative position:

Arranged in a straight line;
Arranged along a curved line;
Arranged in a circle.

In the direction of the acting force and the vector of action of external forces:

flank - along the axis of the welded joint;
frontal - across the axis of the welded joint;
combined - a combination of flank and frontal;
oblique - at a certain angle to the axis of the welded joint.

Types of welds according to the shape of the welded products:

on flat surfaces;
on spherical.

The types of seams also depend on the thickness of the working material and on the length of the joint itself:

short - not> 25 cm, while welding is performed using the "one pass" method;
medium - length< 100 см – используется обратно-ступенчатый способ сварки, при этом строчка разбивается на малые отрезки длиной в 100-300 мм;

All extended seams are processed in a reverse-stepped manner, from the center to the edges.

Preparation of edges for welding

To create a strong and high-quality weld, the edges of the products to be joined undergo the necessary preparation and they are given a certain shape (V, X, U, I, K, J, Y - shaped). To avoid burn-through, edge preparation can be performed with a metal thickness of at least 3 mm.

The order of preparation of edges:

Cleaning the edges of the metal from rust and dirt;
Chamfering of a certain size - depending on the welding method;
The size of the gap - depending on the type of welded joints.

Edge preparation options:

Table 2 shows the features of edge preparation depending on the thickness of the metal.

table 2

No., p / p	Metal thickness, mm	Edge preparation	Angle, α	Clearance b, mm	Blunt edges c, mm
1	3-25	Unilateral V-shaped	50	–	–
2	12-60	Double-sided X-shaped	60	–	–
3	20-60	One-sided, two-sided U-shaped	–	2	1-2
4	>60	I-shaped	–	–	–

They are used both in low-rise construction and in the construction of large houses, office and sports centers... By means of welding, 2 or more parts are connected in 1. This forms a strong and reliable seam that can last a long time without breaking or causing damage to the part as a whole.

In addition, welded joints and seams can be used both for the joint of metal parts from a homogeneous type of steel, and elements made of various alloys. With such complex work, it is necessary to choose the right welding technology, current strength, consumables (electrodes). In addition, the welder must have sufficient experience and skills to prevent burn-through of the part, avoid unnecessary stresses and deformation in further operation.

Classification of welds

All welded joints are standardized by special documentation that defines the concepts, areas and places of welding. The described terminology is applicable for technical documentation, which is attached at the end of the seams. The same concepts are indicated in the training and teaching aids for which the training of welders is carried out, as well as further training and improving their qualifications.

Weld Classification Table.

Using generally accepted abbreviations, even in the absence of documentation on the marking of the connection or a general specification, it is possible to determine which particular welded joint is made at a particular place in the building structure. The following conventions have been adopted: butt welded joints are usually denoted by the letter "C", when making an overlap - indicate "H", if T-joints are provided, then the specification is indicated by "T", corner - "U".

Basically, welding joints and seams should be divided according to several criteria:

By the appearance of the final cross-sectional shape:

Butt, that is, the parts to be welded are placed on the same plane.
Angular, when metal parts are at an angle to each other, while its value does not matter.
Slotted, if the parts superimposed on each other are mutually fused. In this case, one of the parts (upper) is completely melted, and the other part of the welded joint (lower) is only partially melted. The seam itself is a rivet. This connection is also called electro-riveted.

By configuration when welding:

straightforward character;
curvilinear appearance;
ring type.

By the duration of the welded joint:

Solid seam joints. Their length ranges from 300 mm to 1 m or more.
Which are performed intermittently. In this case, the location of the seam can be in a chain, in a checkerboard pattern, depending on the design features of the part and the requirements.

By the method of the applied welding technology:

arc welding without the use of additional means (gas, flux);
welding performed in an environment with the presence of gas (for example, argon).

By the number of welding elements applied:

unilateral;
two-way connection;
multilayer.

By the amount of metal formed as a result of fusion:

normal;
reinforced;
weakened.

There is usually no strict separation across all types of classifications. During operation, welded joints can be straight butt reinforced. That is, the combinations can be very diverse, depending on the complexity of the metal structure, the requirements of rigidity and reliability, the availability of consumables, as well as the skill of the welder.

Characteristics of welded joints

The main types of welded joints.

Depending on how it should turn out in the end, it is necessary to take into account the peculiarities of its implementation and the technology of execution.

Butt welded joints are the connection of parts by fusing together. Parts are located in the same plane and arc welding is most often used. Moreover, such seams can be used to connect parts with different edges. The processing of the weld edge depends on the sheet thickness. If, in the process of performing work, it is required to connect parts of different thicknesses, then the thicker edge should be beveled to the size of the smaller one. This ensures a secure seam.

By the type of edges that are involved in welding, butt welds can be divided into:

parts that do not have a beveled edge. They should be 3-5 mm thick;
elements that have a curved edge;
parts with an edge forming the letter "U", their thickness is 20-60 mm;
parts in which the edge looks like "X", metal thickness 12-40 mm.

Learn more about connections

Butt welds have the lowest stress value and are less prone to deformation. This leads to their frequent use. When performing a butt joint, metal consumption is minimal, the preparation itself for work must be carried out carefully and scrupulously.

Tee elements are joints of metal parts, when one of them is located perpendicular to the other. It turns out a joint in the form of the letter "T". With this type, the seam itself can be located both on one of the sides, and on two. It all depends on the requirements of rigidity, technical and constructive ability to perform work. T-systems are used to assemble frames for trusses, various types of columns, racks. In addition, such a connection is good for welding beams.

Corner joints are performed in cases where the elements in the structure will not carry significant stresses. For example, when welding tanks, tanks. To ensure the required reliability and strength, the thickness of the metal to be welded should not exceed 1-3 mm. When corner joining, the parts are applied to each other at the required angle and welded. The magnitude of the angle does not matter. The seam is made double-sided solid so that moisture cannot penetrate into it.

Lap joints are formed when parts are parallel to each other. In this case, the seam is located on the side surfaces of the metal elements. Metal edges do not need additional processing, unlike the butt method. The consumption of both the base and the weld metal will be significant.

The thickness of the structure itself with such processing is no more than 12 mm. To exclude the penetration of moisture into the connection itself, it must be made double-sided.

Seams for T-shaped, overlapping, corner joints can be made in the form of small segments, that is, by the point method. If it is necessary to make preliminary surfacing, then they are performed in a round shape. Those. are formed when one of the parts is completely melted and partly the other.

Additional points

Known methods of performing arc welding without additional processing of edges can be produced with a metal thickness of 4 mm for manual work, 18 mm for mechanized work. Therefore, if it is required to weld parts of considerable thickness using a manual arc technique, then the edges must be additionally processed.

The elements of the geometry of the connection include the gap that is present between the elements, the angle of groove, bevel and the deviation of the parts involved in welding in relation to each other. The bevel angle determines the groove angle, which is decisive for ensuring the necessary arc access to the entire seam depth, which means that the seam itself is fully completed. The value of the angle, depending on the type of connection and the processing method, mainly ranges from 20-60 ° with a tolerance of 5 °. The gap is 0-4 mm.

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

Weld seam: definition

To begin with, let's decide on the definition of a welded (welding) seam. This is the name given to crystallized metal, which was in a molten state at the time of welding.

The structure of the weld 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 a limited area of a structure that contains one or more welds. It is by the appearance of the joint that the specialist can determine the qualifications of the welder, understand which welding method was used. The welded joint also tells about the technological purpose of the structure.

Weld seams: classification

Experienced welders say: a variety of factors can be taken as the basis for classifying the types of seams, 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 to be joined. In addition, this type is the most economical. Exist certain conditions, so, for example, the torch or electrode must be directed from top to bottom.

A horizontal weld is usually formed when the surfaces are perpendicular to the plane of the electrode. The consumption of fluxes and electrodes in this type increases significantly. With a slow seam lead, drips are possible, and with a fast one - poorly welded places.

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

Ceiling welding is considered the most difficult for welders. How is it produced? A seam is applied with an intermittent arc. The current strength is small. This type is usually used when welding pipes that cannot be cranked.

Welded joints: types and types

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

T-shaped;
overlap;
butt;
corner.

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

Joint

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

Parts that are joined end-to-end differ in the thickness of the product, on the side of the seam. Several subtypes of connections can be distinguished:

unilateral usual;
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 cutter removes the edge on both parts;
double-sided, which involves trimming the edges at an angle of 45 degrees on each side.

It is important to note that with this type of welded joint big role plays the thickness of the surfaces to be welded. If it is not more than 4 millimeters, then a one-sided seam is used, but if the thickness exceeds 8 millimeters, the seam must be applied on both sides. If the thickness of the product exceeds 5 mm, however, the seam needs to be applied only on one side, while obtaining high strength, the edges should be divided. You need to carry it out using a file or grinder, a 45-degree bevel is enough.

Gusset

There are several options for the gusset:

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

With the help of such a connection, two elements can be fastened together at any angle. In this case, the first seam will be internal, and the second will be external. This type is ideal for welding various canopies and canopies, bodies trucks and frames of arbors.

If you need to connect two plates with different thicknesses, this type of welded joint according to GOST must be performed as follows: a thicker plate should be placed at the bottom, and a thin one should be placed on it with an edge. At the same time, the electrode or torch should be directed to the thick part - so there will be no burns or undercuts on the part.

Lap joint

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

T-joint

This type is similar to the corner joint, but there are also differences - the edge-attached plate should not be positioned from the edge of the lower base, but at a short distance.

Classification by technology and seam shape

Welders distinguish between types of welded joints according to the type of welded seams. The seam can be:

Smooth. It is achieved at optimal settings welding machine and in a comfortable position.
Convex. Such a seam can be obtained with a low current strength and passing through several layers. A raised seam requires machining.
Concave. Such a seam can be obtained only with an increased current strength. This weld is characterized by excellent penetration and does not require grinding.
Solid. To make a high-quality continuous seam, you need to do it continuously. This will prevent fistula from developing.
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 seam that can satisfy the basic requirements for strength and tightness.

Defects of welded joints: types, description, reasons

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

internal (these include lack of penetration, porosity and foreign inclusions);
external (among them cracks, undercuts, craters, slugs);
through (burn-throughs and cracks can be distinguished here).

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

Cracks

This type of defects 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), by the time of occurrence (during the welding of parts or after). The reason for the appearance of cracks is non-compliance with the welding technology, the wrong choice of materials for welding, too fast cooling of the structure.

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

Undercuts

Undercuts are called indentations 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 is usually formed on horizontal seams. Such a defect can be eliminated by surfacing a thin seam along the undercut line.

Influx

Such a defect can appear when the 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. You can eliminate the defect by cutting, be sure to check for lack of fusion.

Burns

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

Lack of penetration

Lack of fusion is called local lack of fusion of the deposited metal with the base metal. Can be called lack of penetration and incomplete section of the seam. This type of defect reduces the strength of the seam, it becomes the cause of the destruction of the finished structure. The reason lies in the underestimated welding current, the presence of slag or rust on the parts to be welded. To fix the error, you need to cut out the lack of fusion and weld the parts.

Craters

The depressions, called craters, are usually caused by the breaking of the welding arc. If such a defect appears, it is necessary to cut it out to the base metal and weld it thoroughly.

Fistulas

So it is customary to call cavities that reduce the strength of the seam. It is because of the fistula that cracks can form. Cutting 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. The pore sizes can be both microscopic and up to several millimeters. To avoid the appearance of porosity, the metal should be cleaned from dirt and foreign matter. 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, observing the technology.

Overheating and burnout

These defects appear as a result of high welding current or insufficient welding speed. This makes the finished product very fragile. Burnt metal can only be cut out, and the metals can be re-welded.

Welding control

Now let's consider the types of welded joints inspection. There are the following methods:

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

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