How to choose a weld leg

Weld leg during welding: definition and calculation methods

Home comfort September 3, 2017

In the construction industry, when welding massive metal structures, serious loads arise at the joints, which, if the technology is not followed, carries the risk of structural collapse.

This is relevant in the shipbuilding and mechanical engineering industries (when installing large-sized automatic machines), and during the construction of massive buildings. A high-quality connection must be initially calculated to avoid possible future deformations.

The easiest way to check the correctness of the weld line is to find out the leg of the seam.

The leg of a weld seam is the leg of a conventional triangle that fits into the cross section. There is no single figure that would become an indicator of a reliable and high-quality seam when determining its leg.

The larger the size of an isosceles triangle that can be inserted instead of a seam, the greater the load it can withstand. Often this characteristic depends on the type of metal and the stress limit it can withstand.

Increasing the leg has the opposite effect - the part is deformed and will not be able to work in the desired mode.

How to determine the size of the leg?

To determine the optimal welded joint, it is necessary to calculate the seam, as well as determine the leg of the seam during welding. The following factors are taken into account:

thickness of metal blanks;
position of parts relative to each other;
type of seam used for joining.

For each product, the leg is selected individually, but here we are talking only about working with heavy loads. For private use of welding, delicate calculations are not needed, but professionals still take into account the properties of the metal and try to make the seam strong without harming the parts.

Specify the leg of the seam along the edge if two parts have the same thickness. If it is different, then the leg is determined by the thinner metal. It is important to choose and calculate its size correctly. After all, the maximum power that the part can resist depends on this.

The leg of the weld is determined by the standardization system GOST 5264-80.

The leg of the weld during welding is equal to the thickness of the sheets with an overlap connection, but it should not exceed 4 mm. If this parameter is greater, then you should take 40% of the metal thickness and add 2 mm. This way you can determine the maximum value of the seam leg.

How to choose a leg?

The leg of the seam is determined when welding reinforcement in the same way as when connecting any other elements of metal structures. The size depends on several parameters, including the position of the workpieces, their length and thickness.

Professionals use templates that welders have already developed before them. The main parameter is the length of the weld, because it affects the strength of the future structure. Material consumption and the possibility of deformation are the main dangers when making long seams.

Much depends on the type of seam that will be used to connect the parts.

Butt weld

A butt weld involves the following technology - connecting two butt welding elements (that is, placing the parts with the ends of the surfaces in the same or different planes). There are more than 30 types of butt joints, all of them are provided for by GOST. In this case, a dependence is made on the thickness of the elements being welded, equipment and welding technology.

If the structure will be subject to alternating stress, then this joining method is the most reliable. Various parts can be joined and welded. This can be not only sheets of metal, but also pipes, angles, and channels. To weld two sheets, they do not even need to be in contact with each other - welding is carried out with a minimum distance between the two workpieces.

Lap joint

An lap joint is a welding method where the parts are parallel and their edges overlap each other. Unlike a weld, there are only two types of lap joints. The ends of the products can be welded on both sides or on one.

There is also a connection using an additional pad, which is welded to two parts, connecting them at the desired angle. Overlapping parts are welded using two types of seams - end and frontal.

The welding mode for this connection can be higher, since there is no danger of burning through the surfaces.

Gusset

Welding of two parts, the edges of which are located at an angle relative to each other, occurs using the corner joint method. The standard distinguishes up to 10 types of such joints.

Sometimes, for the strength and reliability of the weld, a special metal lining is used, which allows for better joining of elements and makes the structure more reliable. It is rare to see this type of connection in load-bearing structures, so calculations for such seams are not performed.

However, if this type of welding is necessary, calculations are made by analogy with a T-joint and the type of seam must be taken into account.

T-welded connection

Often there is a need to connect elements that are located in different planes. The best solution in this case is a T-joint, where the end of one workpiece adjoins the other at a right or other angle. The types of such connections vary within 9 types provided for by GOST.

A T-joint requires deep penetration at the joint; the seam is usually made by automatic welding or the edges are prepared in advance, for example, with a fillet weld, which can be made manually, or a butt weld. The type of seam used to make the connection affects its calculation.

Here, the fact is taken into account that the welding site, pre-treated, will be much stronger than the base metal.

Seam quality control

In any of the seams, you should not forget about the weld leg when welding, the formula of which is not complicated and consists of determining the thickness of the metal. If it is less than 4 mm, then the leg is taken equal to it, but if more, then in the range of 40% - 45% of the thickness with an increase of 2 mm. Formula for calculating the leg: T = S cos 45º, here T is the desired leg, and S is the hypotenuse or the width of the seam bead.

It is not difficult to control the connection of workpieces; visual and instrumental methods (using instruments) are used. A tool has been developed that determines the leg of a weld during welding. How to measure the seam of interest with it? To do this, you need to attach the device to two parts of the workpiece, and point the middle at the seam, then write down the indicators and carry out a simple calculation. Usually the seam is convex, but this is the most unreliable option. After all, it is in this form that tension is concentrated.

The ideal option is a concave seam, which is quite difficult to obtain. Here you need to maintain the welding speed, as well as ensure proper operation of the welding machine. Experienced craftsmen will be able to make such a seam. But more often it is obtained mechanically, simply by cutting off the unnecessary part of the seam.

Source: https://monateka.com/article/246269/

How to choose a leg?

Much depends on the type of seam that will be used to connect the parts.

Lap joint

There is also a connection using an additional pad, which is welded to two parts, connecting them at the desired angle. Overlapping parts are welded using two types of seams - end and frontal.

THIS IS INTERESTING: How to cut a round hole in metal

The welding mode for this connection can be higher, since there is no danger of burning through the surfaces.

T-welded connection

Here, the fact is taken into account that the welding site, pre-treated, will be much stronger than the base metal.

The geometric parameters of the weld, along with the correctly selected mode, have a significant impact on strength, as well as durability. In the case of joining two parts end-to-end, the main geometric characteristic is the width of the seam bead. In the case of fillet welding, the leg takes its place.

Weld leg

What is a weld leg

The cross section of the corner suture bead is an isosceles right triangle. The hypotenuse runs along the surface of the suture material, and the legs run from the edges of the weld joint to the top of the corner.

The dependence of strength on the size of the leg is not linear. If the value is too small, the strength will be insufficient due to the small cross-sectional area; if the length is too large, the excessive amount of deposition can cause deformation of the workpiece metal. In addition, an overestimated value leads to increased consumption of welding materials and electricity. In addition, the unit cost of welding work is increasing.

During the design and technological preparation of production, the optimal value of this parameter is selected. If parts of different thicknesses are connected, the seam leg is selected according to the thinner part.

After welding, it is necessary to check whether the dimensions of the actual connection correspond to the design ones. For this purpose, special sets of templates are used - cathetometers.

Weld geometry

The geometry of the butt joint is completely described by the following set of parameters:

width;
thickness;
gap between workpieces;
deepening the welding zone;
elevation of the surfacing area above the plane of the workpiece.

When welding at an angle, a modified set of parameters is used:

weld leg;
thickness of the surfacing zone, equal to the sum of the calculated height and elevation;
elevation of the surfacing zone;
design height.

Geometric parameters of the weld seam

The calculated height is the length of the segment restored perpendicular to the hypotenuse of the roller from the point of maximum penetration.

Properties

Having gained an idea of the geometric parameters, you can understand the properties of the welded joint. The main properties are:

uniformity of weld bead surfacing;
uniformity of surfacing;
penetration depth.

Uniformity means the constancy of geometric parameters along the suture line, first of all:

height of suture material;
its width.

If in any place the width turns out to be less than the design one, then during operation of the product under external load mechanical stresses will concentrate. At this point, structural failure is most likely.

Uniformity is the absence of welding defects, such as porosity or inhomogeneity of the suture material.

Uniform weld seam

Compliance with the design welding depth, its constancy ensures a given area of fusion of the workpieces, which guarantees the ability of the structure to withstand heavy loads.

Selecting a weld leg

Determination of the length of the weld leg during welding is carried out for each specific product. Should be considered:

thickness of welded workpieces;
their material;
one-sided connection or two-sided (on how many sides will the corner be welded);
characteristics of electrodes or wire.

The length must be sufficient to ensure the specified welding strength. Extending the length is also unacceptable.

Overestimation leads to increased consumption of materials, increased labor intensity, and also makes the structure heavier. To facilitate the selection of length, based on practical experience as well as scientific research, standard templates have been developed for each type of welded joint.

How to measure

To check the quality of the work performed, it is necessary to measure its main parameters. Measurements are carried out using sets of specially calibrated plates - cathetometers. They are applied alternately perpendicular to the line of suture material until a complete fit is achieved.

Cathetometer

If a cathetometer is not at hand, measurements can be made using a caliper and a square. The square is applied to one of the parts so that its top rests against the top of the welding bead. The caliper probe is lowered from behind the square to the other top of the roller. The reach of the probe will be equal to the desired length.

The accuracy of such measurements will be somewhat lower, and it will take much more time to check the welded joint, especially a long one.

Why do you need a calculation?

It would seem, why even bother with calculating and measuring the leg of the welding seam? Weld more metal - the welding will take centuries. This approach has the right to exist only when welding the frame of a fence around a summer cottage. If the surfacing height is too high, the opposite effect can occur:

If the surfacing thickness is exceeded, the heating zone and the volume of molten metal expand unreasonably. Parts may be bent.
The increased consumption of welded materials and excess of planned labor intensity will make welding work economically ineffective, especially when producing large series of products.
When welding parts of different thicknesses, the length is selected according to the thin part to avoid its deformation.

Underestimating the length or too narrow a bead will not provide sufficient welding reliability. Therefore, calculation is extremely important for creating durable and economical connections.

How to make a calculation

In practice, approximate calculation rules are used. According to them, the thickness of a thinner workpiece is taken as the parameter value.

The exact calculation is performed using the formula:

Т=S×cos(α),

where T is the fillet weld leg;
S is the width of the roller between the parts;
α is the angle between the plane of the part and the hypotenuse of the roller section.

In most cases, the angle is taken to be 45°, its cosine is 0.7.

and the formula simplifies:

T= 0.7×S.

After carrying out the work, be sure to check the dimensions of the actual suture material for compliance with the calculated ones. Determination of the leg of the weld is carried out using a cathetometer or caliper.

, please select a piece of text and press Ctrl+Enter.

Source: https://respect-kovka.com/kak-vybrat-katet-svarnogo-shva/

Selecting a weld leg - Metalworker's Handbook

In the production of metal structures and heavy vehicles, welded joints must withstand high loads. The weld will be of high quality only if all parameters are accurately calculated before starting work. One of the important indicators is the seam leg (K).

This is one of the sides of the largest conditional triangle with equal sides, which can be inscribed in the cross section of the connection (GOST R ISO 17659-2009, which came into force on July 1, 2010). It can be measured or calculated based on the dimensions of the elements being welded.

When choosing the length of the side of the triangle, the dimensions of the workpieces, position and type of joint are taken into account. The selection is carried out for each element, but general principles are taken into account. In the household, you can use a template to measure.

In order for the connection to be strong enough, both identical sides of the triangle must have the same length (if the elements are located at an angle of 90°).

Connections can be:

butt (without beveled edges, with one-sided, with V-shaped, X-shaped, curved bevel);
end;
overlap;
corner (angle from 30°, one-sided, two-sided without beveled edges, with one or two bevels);
T-shaped (acute or straight angle, one-sided, two-sided, without beveled edges, with one or two bevels).

THIS IS INTERESTING: How to clean a copper distiller

Calculation of the length of the leg of the weld depending on the thickness of the metal is possible for three types of welds: fillet, T, and overlap.

Calculation of the length of the weld leg, based on the thickness of the metal, is required in industrial production, since the strength of the weld, the consumption of welding wire, and its diameter depend on this indicator (the longer the side of the triangle, the thicker the wire).

Important! If the side of the triangle is too long, the volume of liquid metal increases (due to the large heating area) and the consumption of the additive increases, and the finished product may become deformed.

The leg is also important if elements of different sizes are welded (calculations are made based on the smaller figure).

Calculation formula

The volume of deposited material is equal to the square of the leg. For example, if K increases by 1 mm at a junction length of 10 mm, wire consumption increases by 20%.

For overlapping materials with a thickness of up to 4 mm K=4. If the figure is greater, you need to take 40% of the thickness and add 2 mm.

Corner welded joints are:

normal (without convexity or concavity) - K is equal to the thickness of the metal;
concave - K=0.85;
convex - K= s×cos45°, where s is the width of the junction, cos45°=0.7071;
special (the triangle is not isosceles).

When calculating the length of the weld leg depending on the thickness of the metal, the formula is not enough - the welding method and the fluidity of the metal being welded are important.

The obtained result must be checked against the requirements of GOST 11534-75 and GOST 5264-80 or reference materials.

When carrying out welding work in the household, it is enough to establish the side of the triangle that exceeds the thickness by 1-1.5 mm, or determine the indicator from the table. There are rules that must be followed at all times. K must be less than the thickness of the thinnest element multiplied by 1.2. The length of the junction should be less than K*4.

Calculation of the leg for a 1m seam

In practice, all calculations are quite conditional, as they are based on the following premises:

the load is distributed evenly along the entire length of the deposited filler;
destruction is possible only through an additive layer equal to 0.7 K.

The purpose of design calculations is to determine the optimal weld size for a certain elongation and axial stress.

The optimal length of the deposited filler for tensile load is determined by the formula:

L= F/ρ*[ρ], where

L – length of the junction;

F – planned actual load on the connection;

ρ – permissible load on the connection.

Optimal length for axial stress:

L=F/0.7K*ρ

From this formula we can derive a formula for calculating K for a deposited filler length of 1 m:

K= 0.7*L*ρ

K=0.7*ρ

This means that K completely depends on the magnitude of the permissible load.

Permissible loads in compression, tension and shear for various welding methods are determined in special tables.

When developing design documentation:

select the welding method, type of welding, brand of electrode (wire);
determine the standard permissible load;
calculate the length of the joint for tension and axial stress;
create a connection drawing;
specify the technical characteristics and dimensions of the elements being welded.

When developing design documentation for welding, determining the exact size of the weld leg from the thickness of the metal and the optimal length of the weld is carried out in order to improve the quality of the work and minimize its cost. It is important to obtain strong and reliable connections at minimal cost. This indicator is especially important at large industrial enterprises that produce metal structures that must withstand increased loads during operation.

Source: https://ssk2121.com/vybor-kateta-svarnogo-shva/

Calculation of weld leg

Welds have different characteristics. For example, the width, thickness or height of the reinforcement. And these characteristics directly depend on the type of connection: straight or fillet weld. Using such characteristics, you can easily calculate the weld leg. This is a very useful calculation, it will allow you to improve the quality of your work and more.

But what is a weld leg? How to measure the leg of a seam by its width? And why is it necessary to measure the leg at all? In this article we will try to briefly answer these questions and tell you how to calculate the leg of a weld based on the thickness of the metal. Beginners will only need to read this material to understand the essence.

general information

The leg of the welding seam is the leg of a triangle, which we can fit into the longitudinal section. Enter, of course, conditionally. But why bother calculating the leg of a fillet weld (or any other type of joint, be it straight, butt or lap)? Of course, you can purchase a special mechanical ruler for this, but we recommend learning how to do the calculations yourself. This will improve your professional skills.

Using calculations, you can literally measure the strength characteristics of your seam.

You can't just make a weld leg larger to solve the problem of a weak joint (although at first glance you might even think that the weld is strong enough).

Many beginners believe that they can simply increase the surfacing and there will be no problems, but this is a big mistake. The more metal you deposit, the hotter the part gets, and overheating can cause the metal to warp.

The calculation is also necessary from a financial point of view. You will be able to calculate the cost of work down to the penny and you will not have to increase the number of components, electricity and effort to make a seam that is too thick or wide. Calculations are also useful in cases where there are significant differences in the thickness of the parts being welded. For example, you are welding a thin metal part to a thick metal part. In such cases, it is necessary to calculate a part made of thin metal.

Having made the calculations, you simply cannot make the seam too narrow. And this is especially important if you need to weld an important metal structure that is subject to increased requirements.

Especially if you need to make a lot of fillet welds, which are more susceptible to deformation than others. In appearance, your connections may seem quite strong, but in fact, a responsible structure may simply not withstand the mechanical load during operation.

In a word, calculating the leg is really important. Well, we will tell you how to make the calculation further.

How to calculate a weld leg

There are a huge number of formulas with which you can calculate the leg of a seam. Along with them, there are various types of seams: butt, T, lap, corner, and each type has its own subtypes. It turns out that there is a formula for each type of seam, and there are about a dozen of them (taking into account all the features, of course). We will not be able to reveal them all within the framework of this article, so we will tell you how to calculate the leg by the width of the seam, since this is the most popular and frequently used formula.

T is our leg

Source: https://svarkaed.ru/svarka/poleznaya-informatsiya/rasschet-kateta-svarnogo-shva.html

Seam length depending on metal thickness

Calculation of legs based on metal thickness

In order for the connection to be strong enough, both identical sides of the triangle must have the same length (if the elements are located at an angle of 90 o).

Connections can be:

butt (without beveled edges, with one-sided, with V-shaped, X-shaped, curved bevel);
end;
overlap;
corner (angle from 30°, one-sided, two-sided without beveled edges, with one or two bevels);
T-shaped (acute or straight angle, one-sided, two-sided, without beveled edges, with one or two bevels).

THIS IS INTERESTING: How to choose a metal lathe

Calculation of the length of the leg of the weld depending on the thickness of the metal is possible for three types of welds: fillet, T, and overlap.

The leg is also important if elements of different sizes are welded (calculations are made based on the smaller figure).

Welded joints

The quality of construction and installation work largely depends on the degree of responsibility and conscientiousness of the direct participants in the construction process.

In an effort to maximize profits and follow the path of minimizing all possible costs, contractors often give preference to the labor of low-skilled welders.

In addition, in order to save money, outdated and worn-out equipment is used to perform certain types of construction work.

This situation cannot but have a significant negative impact on the quality of welding work, which causes a significant number of detected defects.

The photograph clearly shows a chain of pores, and the leg of the seam on the right gradually disappears

Pores may or may not extend to the surface of the weld; they are arranged in a chain or in groups. Pores are an unacceptable defect for welded seams of products; compared to cracks, pores are not as dangerous, but their presence is undesirable.
Cracks are microscopic, incision-like discontinuities that arise in the temperature range of metal crystallization. Cracks can develop when the metal cools in a solid state. In relation to the weld axis, cracks are divided into longitudinal and transverse. Longitudinal cracks can be located along the axis of the seam at the junction. Cracks are one of the main types of welding defects. The presence of cracks in the welded joint is not allowed, as they can cause destruction of the product.

Unauthorized changes in the design of units - the use of additional overlays, the extension of embedded or mounting ties using, among other things, butt seams, the replacement of corners on ties made of plates connected by fillet welds (poorly resistant to fracture), the extension of load-bearing beams using unauthorized butt joints, etc. .

Reinforcement is welded into the butt seam of the structure, which leads to increased gaps between the parts being welded.

Increased gaps between welded parts. The main reason is incorrect assembly of the unit, excessive displacement of the embedded parts in the plane and out of the plane. The defect leads not only to a decrease in the actual length of the seam, but also to a change in the working conditions of the seam for the worse, i.e. to the appearance of bending stresses in addition to shear stresses.

Defects in weld formation, their origin is associated with a violation of the welding regime, improper preparation for welding, malfunction of welding equipment and other general reasons. Due to incorrect selection of the welding mode, deviations of the mode parameters from the specified ones, improper preparation of the product for welding, or malfunction of the equipment, defects may occur in the welded joint - lack of fusion, undercuts, sagging and burns.

Undercuts of the base metal affect not only the strength, but also the durability of the connection (weakening of the section + stress concentrator). Main causes of the defect:

incorrect position of the electrode;
high current during welding (as a rule, metal flows off vertical surfaces, leaving an undercut);
leaving the outlet crater unmelted;
wrong welding direction.

Reduced seam leg.

The main reasons are haste when making a weld, incorrect position of the electrode (metal is deposited on one edge of the parts being welded, which leads to a significant difference between the legs of the same seam, while measurements are taken along the smallest leg), high current during welding (metal flows off from a vertical surface to a horizontal one, which leads to a significant difference between the legs), an increased gap between the welded edges. At the same time, having already prepared mounting ties of a fixed length, it is impossible to ensure the required length of the seam. It’s disappointing that designers often show welds in their drawings along the contour of the part’s contact, without specifying the minimum length of the seam to ensure the required joint strength.

No vertical weld seam.

Based on detection methods, defects are divided into external and internal. Above we discussed external defects located on the surface of the welded joint and detectable with the naked eye. The presence of gaps, uneven welding seams, the presence of rust, loose seams and other defects indicate poor quality work. Welded joints are checked using a magnifying glass with sixfold magnification, and their current dimensions are compared with acceptable standards.

Internal defects are those that do not extend to the surface of the welded joint and are observed using special equipment, such as ultrasonic equipment.

Ultrasonic devices allow you to quickly and accurately carry out ultrasonic testing along the weld line without transverse scanning, including over long distances, which significantly reduces the time for preparing the heat-affected surface of welded joints.

You can check welding using a vacuum method, which consists of soaping the seam and placing a vacuum frame on it. Then air at atmospheric pressure passes through the seam defects, if any, and bubbles appear.

The permeability of welded seams can be checked by staining them with phenolphthalein. If there are defects, red-violet or black spots form on the seam. Ideal welding seams should be fine-scaled in appearance, dense along the entire length, and should not have accumulations or chains of pores, sagging, burns, narrowings or breaks.

Cracks in weld joints can be identified by sanding them with coarse sandpaper. If defects are found, they must be eliminated, otherwise the metal structure is not allowed for further use.

We conduct professional examination of welding works

The Expertise Laboratory is pleased to offer you its services in detecting defects in welding seams. We employ qualified employees who, using modern equipment, will quickly give an opinion on the quality of welding work, and also describe all the technical characteristics of the metal structure sample under study.

All mechanical tests and chemical examinations in our construction laboratory are carried out legally with strict compliance with GOST and established standards. The test results are always reliable and 100% accurate. A team of experienced specialists has been working in the field of construction expertise for many years, so errors and inaccuracies in the inspection process are completely excluded.

The cost of our services is reasonable and affordable for every potential client.

Source: https://labexp.ru/help/articles/kachestvo_svarnykh_soedineniy/

How to calculate the leg of a weld - Machine tools, welding, metalworking

In the construction industry, when welding massive metal structures, serious loads arise at the joints, which, if the technology is not followed, carries the risk of structural collapse.

The easiest way to check the correctness of the weld line is to find out the leg of the seam.

Increasing the leg has the opposite effect - the part is deformed and will not be able to work in the desired mode.

Weld leg during welding: definition and calculation methods

How to determine the size of the leg?

How to choose a leg?

Butt weld

Lap joint

Gusset

T-welded connection

Seam quality control

How to choose a leg?

Lap joint

T-welded connection