Classification of welded joints and seams

Basics of welding - the classification of welded joints and seams

The classification of welded joints and seams

Welded connection as a structural element called the plot structure in which some of its elements are joined by welding. In the welded joint are welded joint, the adjacent area of the base metal to structural and other changes as a result of the welding thermal (heat affected zone) and the adjacent parts of the base metal. weld metal is crystallized, which was in the process of welding in the molten condition. separation of these concepts is necessary because the weld seam as a connecting portion connected elements defines the geometric shape, continuity, stability and other properties of the metal in the place of welding. The properties of welded joints is determined by properties of the weld metal and base metal zone, adjacent to the seam, restructured, and in many cases with altered properties - heat-affected zone. Must take into account some of the base metal adjacent to the heat-affected zone and determining the stress concentration at the junction of the weld metal to base metal plastic deformation in the second heat-affected zone, thus affecting the nature and distribution of forces acting in the welded joint. The form interface welded elements are the following basic types of welds: Butt (Fig. 1 a), T-(Fig. 1, b and c), angle (Fig. 1d), overlap (Fig. 1 d). Welds divided by the cross-sectional shape in the Butt (Fig. 2a) and angle (Fig. 2b). A variety of these types of joints are cork (Fig. 2c) and the welt (Fig. 2d), performed in the lap joints. The shape of the longitudinal seams distinguish continuous and discontinuous. With the help of butt welds in the main form butt joints (Fig. 1a), with fillet welds - T, cross, corner, and overlap of the compound (Fig. 1b-d) , with cork and slash joints can be formed by overlap and sometimes T-joints. Butt joints tend to perform continuous, the hallmark for them is usually a form of cutting edges of the joined parts in cross section. On this basis distinguish the following basic types of butt welds: Flare the edges (Fig. 3a), without cutting edges - one-sided and bilateral (Fig. 3b), with one edge of butchering - unilateral, bilateral, with a straight or curved shape cuts (Fig. 3, e) with one-sided edges of butchering two, with a V-shaped cut (Fig. 3d), with two edges of butchering two-way, X-shaped cut (Fig. 3e). Cutting can be formed by straight lines (edges beveled) or have a curved shape (U-shaped cutting, Fig. 3, e). Corner joints are distinguished by the form of preparation welded edges in cross section and the continuity of the seam along the length. The shape cross-section of joints may be no cutting edges (Fig. 4a), with one-sided butchering edge (Fig. 4b), with bilateral cutting edges (Fig. 4c). By the length of fillet welds may be continuous (Fig. 5a) and intermittent (Fig. 5b), with a checkerboard (Fig. 5c) and chain (Figure 5d) is the joint-Niemi segments. Fillet, lap and corner joints may be performed by segments of the small extent of seams - seams point (Fig. 5e). cork joints in shape in plan (top view) usually have a round shape and are the result of complete melting of the upper and lower partial melting sheets - they are often called plug lap joint, or by penetration through the top sheet of pre-done on the upper sheet of the hole. welt seams, usually of elongated form, obtained by welding the upper (covering) of the sheet to the bottom fillet weld around the perimeter of the slot. In some cases, the slot can be filled and completely. form cutting edges and assembly welding is characterized by four main structural elements: the gap b, a blunting of the angle beta and bevel angle cutting edges alfa, beta or equal to 2 beta Existing methods of arc welding without cutting edges can be welded metal thickness for a limited one-sided welding hand - up to 4 mm, mechanized submerged arc - up to 18 mm). Therefore, the welding of thick metal edge to carve. The angle of bevel angle provides a certain amount of cutting edges that need to access the arc into the compound and complete penetration on all edges of their thickness. Standard corner cutting edges, depending on the method of cooking and type of connections varies from 60 ± 5 to 20 ± 5 degrees . Type and size of cutting angle cutting edges determine the amount needed to fill the additional metal cutting, and hence the productivity of welding. For example, the X-shaped cutting edge in comparison with the V-shaped to reduce the amount of weld metal in the 1.6 - 1.7 times. Reduced time to process the edges. However, in this case there is a need to weld on one side 1VA in an uncomfortable position, or turn over the overhead workpiece. Dullness is usually from 2 ± 1 mm. Its purpose is to provide the correct formation and prevent burn marks in the top of the seam. The gap b is usually equal to 1.5-2 mm, since the angles of cutting edges taken a gap is necessary for the top seam penetration, but in some cases, a technology gap may be zero or up to 8-10 mm or more. to all types of joints are important edges of a complete penetration of connected elements and the external form of the joint as a front side (the so-called joint gain) and on the reverse side, ie the form of so-called reverse roller. In the butt, especially the joints is difficult to boil thoroughly one-sided edge blunting at full depth without special techniques that prevent burn-through and provide a good reverse bead formation. Also important are the formation of a smooth transition of the metal front and rear rollers to the base metal, as it provides high bond strength under dynamic loads. In the corner seams as it is difficult to boil the root of the weld to the whole of its thickness (see Fig. A, b and c), especially when welding electrode inclined. For these joints is recommended to the concave shape of the cross section of the seam with a smooth transition to the base metal, which reduces stress concentration at the junction and increases the bond strength under dynamic loads.

See also:
Weld Seams and Joints
Laser Welding
Classification of welded joints and seams

Weld Seams and Joints

geometry of the weld seam
weld classification
the effect of welding parameters on the shape and size of weld

Weld - a crystallized metal, which is in the process of welding is in the molten state.

Welded joints - a limited area of construction, containing one or more welds.

Types of welds
Depending on the shape of the cross section welds can be

• butt;
• angle;
• slotted

Types of welded joints
Depending on the nature of the workpiece interface the following types of welded joints:

• butt joints;
• corner joints;
• T-joints;
• lap joints;
• Mechanical connections.

Butt joint is welded to the two elements adjacent to each other and the end surfaces located on a surface or in the same plane.

Figure. Butt welds: no bevel the edges with a curved bevel edges, with V-shaped bevel edge, with the X-shaped bevel edge

Angular coupling is welded to the two elements, placed at an angle and welded to the junction with their edges.

T-joints is called a weld, which abuts the end face of one element at an angle and attached to the lateral surface of another element.

Figure. Corner and fillet welds: no bevel edge, with a bevel edge, with two single edge bevels

Lap connection is placed parallel to the weld and partially overlapping elements.

Mechanical connection is a welded joint in which the side surfaces of the elements adjacent to each other.

Figure. Lap welds without the bevel edge and face welds

Weld seams and joints:
geometry of the weld seam
weld classification
the effect of welding parameters on the shape and size of weld

Effect of welding parameters on the shape and size of weld

The main mode of arc welding parameters are:

• size, density, polarity and welding current generation;
• arc voltage;
• welding speed;
• cross-sectional area (diameter) wire (electrode).

More Options:

• thickness and composition of the electrode surface;
• Departure wire;
• position of the electrode and welding products;
• grain size of the welding flux and its composition.

From these parameters depend on the shape and size of the seam, its chemical composition. In shape and size also affects the weld welding technique.

With the increase of welding current increases the depth of penetration and weld width is almost unchanged.

With the increase of arc voltage rises sharply joint width, depth of penetration is reduced. It also decreases and convexity (height gain) seam. When welding with direct current (in particular, reverse polarity) joint width will be much greater than when welding with alternating current with the same voltage value.

With increasing welding speed decreases joint width and the depth of penetration at first increases (up to a speed of 40-50 m / h) and then decreases. When the welding speed of more than 70-80 m / h are possible undercuts on both sides of the joint due to insufficient heating of the base metal.

With decreasing diameter of the wire (ceteris paribus) increases the current density in the electrode, which leads to an increase in the depth of penetration and the convexity of the joint, but it reduces the width of the seam. Thus, with decreasing diameter of the wire can get deeper penetration with a constant current intensity or the same penetration at lower amperage.

With increasing emission of wire diameter of 3 mm from the current supply mouthpiece reduces the depth of penetration that can lead to baffle edge in the seam. Increasing the departure of wire 5 mm in diameter from 60 to 150 mm has no effect on the shape of the weld.

See also:
Defects in welded joints and seams

Weld seams and joints:
geometry of the weld seam
weld classification
the effect of welding parameters on the shape and size of weld

Weld Classification

Welds in appearance are divided into

• normal (flat);
• convex (Reinforced), and
• concave (or weakened).

Welds in appearance

Convex weld better with a static (constant) loads, but they are uneconomical. Normal and concave joints are better suited for dynamic and alternating loads, as through a more seamless transition from the base metal to the weld reduced the likelihood of stress concentrations that lead to the destruction of the joint.

The implementation of welds may be unilateral or bilateral.

implementation of welds

By the number of layers of welding is a single-layer and multilayer, the number of passes - one pass and multipass.

Multi-layer suture is used for welding of thick metal, and also to reduce the heat-affected zone. Passage - a single heat source moving in one direction during welding or surfacing. Roller is part of the weld metal, which was naplavlena in one pass. layer of weld - the weld metal consisting of one, two or more cylinders, which are placed on a level cross-section of the seam.

Depending on the length of welds are continuous and discontinuous. Butt joints are usually made ​​continuous. Fillet welds can be made

• continuous;
• intermittent one-way;
• bilateral chain;
• bilateral chess;
• and can be dotted.

Fillet welds

In the direction of acting force welds are divided into

• longitudinal (flank) - the direction of acting force parallel to the axis of the weld;
• transverse (frontal) - the direction of acting force perpendicular to the axis of the weld;
• Combination - a combination of longitudinal and transverse joints;
• Skew - the direction of the current effort is placed at an angle to the axis of the weld.

On the situation in the area seams are divided into:

• lower (H);
• "The boat" (A);
• horizontal (H);
• polugorizontalnye (Pg);
• semi-vertical (PV);
• vertical (V);
• polupotolochnye (PP);
• Ceiling (R).

By appointment welds are

• strong;
• tight (sealed);
• firmly-tight.

Depending on the conditions of the weldment joints are divided into

• workers, intended for direct loads;
• non-business (or binder connectors), used only to connect parts of the weldment.

As the width of the welds are divided into

• needles with a seam width equal to or slightly greater than the diameter of the electrode, are performed without transverse vibrational motions of the welding electrode;
• broadened, which operates with transverse vibrational motion of the electrode.

Weld seams and joints:
geometry of the weld seam
weld classification
the effect of welding parameters on the shape and size of weld

The Geometry of the Weld

The main geometric parameters of butt weld :

main geometric parameters of butt weld

• S - thickness of the weld metal;
• E - the width of the weld;
• q - bulge butt weld (height gain) - maximum height (depth) between the surface of the weld location and level the surface of the welded parts;
• H - depth of penetration (depth of penetration) - the maximum depth of melting of base metal;
• t - thickness of the seam, t = q + h;
• b - a gap.

The main geometric parameters of fillet welds:

main geometric parameters of fillet welds

• k - a leg fillet weld - the shortest distance from the surface of one of the parts being welded to the border fillet weld on the surface of the second work piece;
• q - the convexity of the joint;
• p - the estimated height of the fillet weld - the length of the perpendicular line drawn from the point of maximum penetration at the site of conjugation of welded parts to the hypotenuse of the largest right triangle inscribed in the outer part of the fillet weld;
• a - thickness of the fillet weld, a = q + p.

The aspect ratio of the seam - the ratio of width to its thickness.

K n = E / t

The value of the weld shape is usually in the range of 0.5 to 4. The optimal value is between 1.2 and 2.

The coefficient of convexity of the joint - the ratio of width to its convexity.

K y = E / q

The value of the convexity of the weld should not exceed 7-10.

Factor share of the base metal in the weld metal :

K a = F a / (F a + F e ) ,

where F a - cross-sectional area of the molten base metal, F e - cross-sectional area of weld electrode metal.

base metal in the weld metal

The root of the weld seam is a part which is furthest from his face. Podvarochny seam - lower part of the bilateral joint performed in advance to prevent burn-through in the future the main seam welding or placed in the least to the root of the weld.

root of the weld

Weld seams and joints:
geometry of the weld seam
weld classification
the effect of welding parameters on the shape and size of weld