Everything you need to know about welded metal structures: what is their classification, types and types

08/29/2019 Author: VT-METALL

Issues discussed in the material:

• What is the technology of automatic welding of metal structures
• What is the technology of semi-automatic welding of metal structures
• What are the features of welding aluminum metal structures
• What defects are possible when welding metal structures?

For a long time, metal structures have been connected to each other by welding. This technology is used not only by amateurs at home, but also by professionals on an industrial scale. Welding techniques are constantly being improved, so at present the result shown by the technology of welding metal structures (regardless of their dimensions) is much higher than a couple of decades ago.

Requirements for welding metal structures

The following requirements for the installation of metal structures and welding apply to a greater extent to professional workers, but if a person wants to develop in this business, then it would be a good idea to familiarize yourself with the following information.

For certain types of metal structures, special types of materials are used from which elements of the correct geometric shape are made. It is also important that the strength and weldability characteristics comply with those required by SNIP II 23-81 and GOST 27772-88. This document also contains sections devoted to diagrams of how seams are created correctly and how their quality affects the stability and durability of the entire structure. The complexity of the work depends on the number and shape of the parts.

Download GOST 27772-88

Also an important point is the qualifications of the employee. Since there are types of welding of metal structures that can only be assembled by workers who have long been familiar with this craft, the work of beginners is simply not acceptable. A more detailed list of such structures is regulated by document RD 15.132-96 of the Ministry of Fuel and Energy of the Russian Federation.

Example of welding metal structures

Also, according to GOSTs of the Russian Federation, welding of critical metal structures must be controlled.

Download GOST 5264-80

When is welding required?

Welding work allows you to quickly restore parts while maintaining their strength. Many manipulations can be carried out without disassembling and unscrewing threaded connections, which can become sour over time. Using welding, you can quickly restore a part and do not have to wait for a spare part from the store. This is very convenient, because the equipment does not stand idle and quickly returns to work.

Welding work is carried out in the following cases:

• presence of traces of deep corrosion on parts;
• cracks in metal structures, signs of deformation;
• Additional upgrades are being carried out, for example, fasteners for a winch or attachments;
• scheduled repairs are required to eliminate defects in the body or metal structures.

It is better to entrust welding work to professionals - the master will perform high-quality welding without oxide and slag, which allows you to achieve high strength and rigidity of the structure. For additional protection against corrosion, the metal is treated with polymer paint.

Classic technology

Classic technology for welding metal structures is based on time-tested methods such as gas-fire and electric welding. In both options, suture methods are divided into:

• Auto.
• Semi-automatic
• Manual.

The automatic method is based on the absence of human physical labor. A special robotic device, depending on the work being carried out, is switched to the correct mode and performs the work, thereby replacing a person. Such units have limitations commented on in their instructions. It is most profitable to use such machines in mass production by companies whose products require a large number of connections.

The manual method implies the presence of physical human labor. This includes control of the welding electrodes and joint formation. Most often, the manual method means:

• Using standard flux welding.
• Soldering of metal structures with a gas welding device.
• Arc welding.

The latter method is popular when working at home for your own needs, or in a small enterprise, since large-scale production will have large costs for maintaining this method of welding structures.

Semi-automatic welding

Semi-automatic - involves manual processing of seams, but the supply of the electrode itself is carried out automatically, which increases labor productivity. And in combination with the human factor and the automatic welding method, the robotic joining method is very popular and has gained development among both amateurs and professionals in this field.

Classical methods for metal structures

Regardless of the method of connecting the rental, there are three modes of performing work:

• auto;
• semi-automatic;
• manual.

Let's take a closer look at them.

Auto

This method reduces human participation in the process to a minimum . The operator’s function is to control the production process, as well as adjust the input parameters, if necessary. Used in large-scale enterprises.

Semi-automatic

The welder's task is to determine the optimal speed of the arc, as well as adjust the direction . The supply of filler material is carried out automatically, according to pre-configured parameters.

Manual

In this case, all operations are performed by the hands of a welder . There are several ways to create a permanent connection. In addition to electric welding, you can perform metal soldering manually, as well as work with gas welding equipment.

Types of welding for assembling metal structures

A major issue is the type of welding used to join the seams. The grade of the steel profile, its composition and thickness are not the only things that matter in the issue of successful seam processing. The type of welding also has a big influence.

The mechanization of production has influenced the choice of shop welding in favor of those based on flux-cored wires or an automatic process that is performed in an environment of inert gases or in layers of flux. The difference in the methods is that the first of them mainly applies to joints of fillet welds located under the ceiling or vertical joints, while the second option is suitable for joining parts in lower positions.

Previously, a very common type of connection was electroslag welding, which is currently practically not used, due to the fact that research by specialists in this field has shown the unreliability of metal structures erected in this way, and that at negative temperatures it loses its strength characteristics.

Manual arc welding

Based on these facts, it can be concluded that in work areas and even in open areas, work can be carried out using any type of welding. It is curious that foreign companies, whose enterprises are equipped with modern automatic machines, still pay more attention to manual arc welding of metal structures. Japan can serve as a serious example, significant enterprises of which use more than 60% of manual welding for the construction of important metal structures.

How to choose electrodes

The main element in metal welding technology is electrodes, which are available in various versions: consumable and non-consumable.

For a beginning student, in order to be able to make high-quality connections of metal structures, it is recommended that in the first approaches only use universal rods with a thickness of 3-4 mm.

Before installation, experts insist on choosing the right type of electrodes and type of metal. The classification distinguishes several types: rutile, basic, acidic, cellulose.

• Cellulose electrodes are intended for welding with alternating current, where it is necessary to obtain a strong seam, for example, when installing load-bearing structures. These electrodes can be used to cook using any method.
• Acidic electrodes are cooked using alternating and direct currents. The only drawback to using such electrodes is the formation of toxic fumes. Therefore, working with them indoors is prohibited.
• Mixed electrodes are used for pipeline welding. This method shows excellent results in a ceiling position.

Temperature conditions of the welding process

Air temperature has a great influence on the choice of the technology used to create a seam and on its quality.

The fact is that it is impossible to carry out work on the construction of metal structures if the temperature of the workpieces themselves drops below - 18 ° C. In such conditions, the temperature must be monitored by measuring the area where the two parts join. And if it turns out to be below critical, the workpieces themselves undergo heat treatment before creating the seam. Not the entire element is heated, but only at a short distance from the edge, equal to the thickness of the workpiece, or at a distance of at least 75 mm in any direction.

If a seam must be created between parts made of different alloys, then both are heated according to the temperature regime of the strongest of them (in terms of material strength). Do not forget also that the heating temperature depends on some characteristics of the material itself.

As an example, use steel grade A514, the blade of which, with a thickness exceeding 40 mm, requires heating to 210 °C. Thicker parts made from this steel are heated to 235 °C.

Prices for welding work

Today, metal structures are actively used in construction. Therefore, the question of the price of welding for work when installing metal structures is very important for many.

Welding structures - features

The very concept of welding applies not only to products made of metal alloys, but also to products made of polymers, that is, for example, plastic. After all, this concept implies a thermal processing process in which two or more parts are combined into a single component.

The work itself is divided into two steps - assembly and connection. The first one has the greatest labor intensity.

After all, in order for the quality of the erected metal structure to be durable, it is necessary that all the stated requirements for the workpieces and the material from which they were made were observed until the end of the work.

Welding work

From an objective point of view, more than half of the entire work period is spent on the assembly of the future metal structure.

How to make welds correctly

To perform a weld correctly, firstly, you need to familiarize yourself with the regulatory welding and design documentation. The necessary design documentation is presented in the form of a basic set of drawings of the KM brand, and KMD (metal structures, metal detailing structures). In the album of the KM section you will receive general information about the metal welded structures of the construction site (or part of it):

• General form;
• composition of structures (how many beams, columns, trusses, braces, etc. parts);
• main connection points;
• instructions for performing work;
• information about loads on structures;
• specification of rolled metal.

In the KMD section you will find:

• detailed drawings of each metal element;
• detailed components for connecting elements;
• updated specification of rolled metal products.

Read the notes and instructions for performing work on the drawings. It may contain important points, without which the manufactured metal structure will not meet the requirements applied to it.

Assembly and welding of elements must be carried out only if there is a documented technology for welding work for this structure.

Documentation is carried out in the form of technological maps and (or) a production project (PPSD) for welding work. They reflect in detail all questions about the process and materials.

Ensuring Correct Assembly

Ensuring high-quality completion of work is also based on correct adherence to a certain list of rules for the assembly of metal structures:

• When selecting the parts that will make up the metal structure, you should adhere to the drawings that were outlined when drawing up the project. Otherwise, the minimal losses will be a discrepancy in the appearance of the structure, and in the worst case, it will not be able to perform the functions assigned to it.
• Based on the project plan, each element must be in its place.
• The width of the gaps plays an important role in the construction of structures. If they end up having larger dimensions than they were supposed to, then this fact will greatly affect the strength of the product. But in turn, too small gaps can negatively affect the proper operation of moving parts.
• Any structure has corners, the level of which must be controlled using special tools. Where this is required, the angles must be exclusively straight, otherwise this will greatly affect the position of the structure and cause it to skew, or even lead to complete destruction.
• Butt joints must be provided with gaps with sufficient space for permissible backlash of elements.
• Throughout the construction of the entire structure, these points must be taken into account. Especially in the case of automatic welding, because with manual technology the worker can control and adjust the direction of the part, which is almost impossible to do when using automatic devices. But at the same time, robotic intervention in welding virtually eliminates errors caused by the human factor.

Electrode installation

There are two cables in the structure of the inverter, in the first there is a clothespin - clamp, in the second - a holder for the electrode. Before turning it on, you need to unscrew the head on the handle near the screw holder, install the electrode, and after fixing, screw the head into place.

During the entire welding procedure, it is necessary to hold the electrodes in relation to the coating being welded at an angle of 70-80 degrees, the welding line should be at 90 degrees. This arrangement will create a high-quality, durable seam.

Positive aspects of welding

In addition to reducing working time and quality, welding has a positive effect on other characteristics:

• Due to the fact that during the welding process only two elements are involved, excluding the influence of other factors, the final soldering in mass does not differ in any way from the original version, which in turn allows saving the amount of material.
• Due to its characteristics, welding is almost completely devoid of restrictions in work due to the material thickness factor. All responsibility for this shifts only to the use of certain equipment.
• A variety of modern welding machines make it possible to carry out joining work with almost any material without loss of seam strength, even taking into account the factor of manipulating such a complex material as aluminum.
• A significant positive aspect of using welding is saving money and working time.
• The heavier the type of welding, the more complex the type of structure can be. It also makes it possible to use elements made by stamping or cast in molds. In this case, the material from which they are made does not play a special role.
• Welding units presented on today's market are quite affordable, and if you use the right technique, you can increase the production speed factor.
• If there is an opportunity, as well as the desire of the enterprise, to erect structures in the assembly of which non-standard materials will be used, welding will help to easily carry out this task.
• Welding is more than applicable even for working with very small parts.
• Welding for the purpose of repairing or bringing mechanisms into working condition is also very appropriate.
• When welding is used, each structure will have absolute tightness. Of all the available methods of connecting joints, welding has the highest reliability indicator for this parameter.

Possible defects

1. Swells. They appear when metal leaks onto poorly heated ends of the workpiece. Often found on horizontal seams. They are removed with a hammer, then the connections are checked for integrity.
2. Burnout. The part is melted through, there are metal streaks on the reverse side. The causes of the defect may be low speed or poor edge processing, too much flame power and increased clearance. Corrected by cutting and subsequent filling.
3. Lack of penetration. A very dangerous situation that must be eliminated when installing metal structures . The cause may be the presence of dirt, scale or rust, as well as incorrectly selected flame power. All damaged areas are cut down and re-welded.
4. Cracks. They are formed due to incorrect placement of seams or incorrect conditions. Errors in the location of joints destabilize the entire structure, creating excessive stress, which leads to destruction. The cracks are completely cleaned out and digested. To prevent the crack from spreading, holes are made at its ends.
5. Porosity. Appears if gases do not have time to escape from the metal before it cools. This reduces the reliability of the seam. The reason may be poor edge processing, the presence of any contamination at the processing site and incorrect choice of flame strength. Such seams are completely eliminated and covered.
6. Burnout. Due to the appearance of oxidized grains, the quality of such seams is low. The resulting film prevents reliable adhesion. The defect cannot be corrected because such metal is very fragile.

Subject to the requirements of the project and the technology of working with the type of metal, welded joints are characterized by high strength. At the same time, the resulting structures are much lighter than cast ones or those made using rivet installation. The connection method allows you to save up to 20% of material compared to other methods. Welding also allows you to work with any materials, controlling or adjusting the shapes of finished structures if necessary.

Welded joints and their types

Welded joints are classified according to the presence of one of the following characteristics:

• Location of connection of 2 parts.
• Type of weld used.
• Welding technologies used in connection.
• The environmental conditions under which the process itself was carried out
• According to the thickness of the parts.
• The grade of alloy from which the parts are made.

Aluminum weld

Regarding the first point of the plan, the details, according to their geometric location, have four types of connections:

• Butt joint, single-plane connection of two workpieces.
• Overlapping, when the workpieces are welded by placing the edge of one part on the edge of another.
• Corner joints - joining parts at a certain angle.
• T-joint. Welding when a part is adjacent to another end plane.

Butt joints are made by welding along the thickness of the element or when creating a seam on the lead strips. If the welding process is carried out outside the workshop room, then the connection can be organized by one-sided welding, with further welding of the base of the seam, which implies filling the space between the elements, carried out along one of the edges.

The work based on output pads is radically different from the previous one. The lining should be adjacent to the edge of the parts being joined - this is it. The resulting space should measure no more than 6 mm. This condition applies to the manual welding method. If the work is performed mechanically. Then it should not exceed 15 mm. The pads are selected based on the thickness parameter so that the part does not burn through during the working process.

Titanium weld

In erected structures based on butt joints, blanks made of different thicknesses are often combined. In this case, a processing method is used in which the angle of inclination of steel with greater thickness is reduced, which should correspond to 1/8 of the inclination of stretched metal workpieces, or 1/5 for compressed elements.

Types of connections

1. Tavrovoe. The edge of the workpiece is leaned against the end of the other.
2. Overlapping. The parts are arranged so that their edges overlap.
3. Butt. The parts are located in the same plane, their edges touch.
4. Angular.

In practice, the last two types of connections are most often encountered. They are used to fix beams, racks and trusses. During butt installation, the seam is welded throughout the entire thickness of the part. It is also possible to use welding technology with special linings installed near the edges of the workpieces. In the semi-automatic mode, the distance between the parts is 1.6 cm, in the manual mode - 0.7 cm. If you need to connect workpieces of different sizes, then make a groove in a larger part.

The load on corner joints is higher than on butt joints. This imposes a number of requirements on the welding of metal structures with the following options:

1. Loaded frames cannot have a one-way joint. A suture is required on both sides, which reduces stress concentration in the upper lobe.
2. If it is impossible to make a weld on both sides, they try to reduce the volume of deposited metal. In this case, the edges are not cut.
3. When the structure is statically loaded, an incomplete seam is applied, cutting the edges of both workpieces.
4. It is recommended to replace corner joints with T-joints where possible.

Welded components in metal structures

All structures made of metal are supported on a base of welded joints, which are the basis of butt joints. When developing a project, engineers must take into account convenient conditions for high-quality work in these units. These include:

• The condition is that the nodes be welded with a corner or butt joint.
• The lower welding position has priority.
• Mainly use mechanized or fully robotic welding to ensure the quality of the work performed.

There are many subspecies among connecting nodes, most of which have different requirements. A good example would be a beam assembly. In it, the greatest attention is concentrated on the distance between the welds, since it should not be shorter than the thickness of the thickest steel element divided by 10 that is part of this assembly.

Metal welded trusses

Welded steel trusses are a flat lattice system of metal elements that allows you to span large spans of buildings and structures. A truss is a structural element of a building that serves to support the roofing system (purlins, decking, roofing pie) and transfer the load from it to columns or walls.

Metal trusses are often used in the construction of industrial buildings, since the technological process often does not allow the installation of intermediate racks. Also, steel trusses are most widely used in the construction of social and administrative buildings. Such as: shopping centers, cinemas, stadiums, swimming pools and many others.

It is such buildings that are characterized by the presence of large free internal space. The metal welded truss consists of:

• Knots of the upper belt.
• Raskosov.
• Stoeck.

Braces, in turn, are divided into supporting and ordinary. Support braces are located at the point where the truss is supported. They carry heavy loads, so their cross-section is often larger than that of ordinary braces (or the grade of steel is higher). Farms can be homogeneous or combined. Because they can combine elements made from different grades of steel.

It is combined metal structures that are an effective solution; their use is most rational in cases where the loads on the elements are significantly different. The braces, as well as the truss posts, are connected to the lower as well as the upper chord directly or using gussets. Their elements can be made from:

• Square pipe.
• Rectangular pipe.
• Round pipe.
• Corner.
• Various profiles.

Steel trusses are the most common solution. Trusses are developed for a specific construction project or selected according to a series, having performed the appropriate calculations.

Truss drawings are developed in the KM and KMD section, where basic instructions for the production and installation of structures are also prescribed.

How to weld metal structures with your own hands?

Professional welders will confirm that a modern master must be able to manufacture any type of metal structures.
Moreover, there are truly many types; enterprises and individuals often order the production of thick-walled structures. Therefore, any self-respecting welder should know how welded structures are manufactured. In this article, we will briefly describe what types of welded metal structures there are, what the technology for welding metal structures is, and what features should be taken into account in order for your work to be appreciated.

Types of metal structures

There are different types of welded structures. The most popular are beams. Welding of I-beams is the most frequently requested service. Remember that the beams must be rigidly connected to each other. This is the basic requirement.

The second type is columns. Columns must withstand compression well. In general, column welding is as popular a service as I-beam welding. There are also lattice metal structures. To weld lattice structures, you need to make sure that they can withstand significant tension. This type includes a mesh of reinforcement, a metal frame or a truss.

Additionally, shell metal structures are distinguished. Often these are pipelines and various containers. The main requirement for them is absolute tightness and resistance to high pressure. Don't forget about metal frame structures. These include train sets and car bodies. The main requirement is resistance to permanent dynamic loads.

As you understand, each type has its own requirements. They definitely need to be taken into account. You cannot do work “at random”, based only on your own considerations. It is necessary to take into account the environment in which the metal structure will be used and the loads it must withstand.

Metal structure welding technology

The manufacturability of welded structures is not that complicated. Everything is simple here: the technology for connecting parts for a particular metal structure depends on the welding method you choose. For example, you will be welding metal structures with a semi-automatic machine. To do this, you need a semi-automatic device, protective gas in cylinders, filler wire and electrodes.

This approach is appropriate regardless of what kind of structural welding you need. You may be tasked with welding I-beams or box structures. In any case, rely on the features of the welding method you choose. However, there are some tips that are suitable for any type of welding of metal structures. We will share them in detail below.

Selecting a welding method

Now that you know the classification of welded structures, it will be easier for you to choose the type of welding. I can say with confidence that the assembly of metal structures can be carried out using any equipment.

For example, welding of building structures is often performed using a semi-automatic machine. This is not surprising, because semi-automatic welding of metal structures is simple and convenient, it saves time and resources.

We recommend choosing a welding method based on your skills, working conditions and quality requirements.

Welding mode selection

To properly weld metal structures, you need to set up your welding machine. Simply put, select the welding mode. There is only one recommendation: try to maintain the golden mean. There is no need to set the current too high in hopes of getting the job done faster. And you don’t need to cook at low current simply for fear of ruining the seam.

Welding critical metal structures (for example, I-beams) requires maximum concentration and experience from you. Therefore, rely on your own strength and set the settings recommended by GOST for each welding method. As for speed, try to weld about 20 meters of seam per hour. This is the average value.

Temperature selection

Welding of structures must be carried out at a metal temperature of at least 17 degrees Celsius. This is especially important if you plan to manufacture welded structures with increased requirements for the quality of seams (for example, the welding of beams mentioned above). Warm up the area of ​​the future seam to 20 degrees before starting work.

Selecting the type of welded connection

In most cases, butt and corner joints are chosen for welding metal structures. Let's talk about each of them in more detail.

The butt seam must be welded evenly along the entire length and thickness of the metal. This is the optimal method. You can also weld a seam on one side, and then weld the root of the seam on the other side. This is especially true if lattice structures are to be assembled and welded.

With fillet welds everything is more complicated. They are more susceptible to deformation than butt joints, since they are not able to withstand such large loads. If you have the opportunity to replace the fillet weld with a T-weld, then do so. It is also prohibited to use a one-sided fillet weld when connecting thick-walled structures. Double-sided stitching is required.

Assembly and welding of metal structures also requires an understanding of the loads the product will be subject to. If there is a lot of static load, then cut the edges in a K-shape.

Welding Features

Firstly, before work you must have drawings of welded structures on hand. It would be even better if there was a full-fledged package with technical documentation. Technicians must determine which type of welding is best suited and select the optimal types of welded joints.

Welded metal structures contain many components, and each has its own requirements. For example, when welding joints of metal structures, the distance between the seams should be no more than 10 times the thickness of the metal profile itself. This is especially important when connecting beam structures. There is one more feature.

Professionals often use the terms local strength and fragility. Local strength is the nodes to which stiffeners were welded, for example. And fragility means holes in metal profiles, unwelded seams, large gaps between parts, and so on.

It is believed that if both of these shortcomings are noticed in a design, then the product can no longer be called durable.

Therefore, if you have to manufacture welded structures, try to avoid the “sores” mentioned above. Even if you decide that a lower-quality seam can be made in an uncritical area, then you are mistaken. Ultimately, it is this error that will lead to the destruction of the entire structure. Welding of structures does not forgive even minor defects.

Instead of a conclusion

The manufacturability of welded structures lies only in the variety of welding methods. The direct welding process (also known as the technological process) and the production of welded metal structures is not as difficult as it might seem at first glance.

How to cook properly

After turning on the welding machine, the heat energy is redistributed in the direction from the electrode to the metal structure, as a result of the influence of the current, a high-voltage voltage is formed, the metal heats up to high temperatures, thereby acquiring a semi-liquid phase. In connection with this, an effect appears - a weld pool. The electrode substance enters into a chemical-physical bond with the metals, excess slag is formed, which turns into a durable surface that protects the seam.

To correctly form an arc between the adjacent electrodes, you need to turn on the equipment and run the electrode across the metal coating at an angle of 60 degrees until sparks form, then lift the holder at a distance of 5 mm from the part, resulting in the formation of an electric arc, which must be present from the very beginning of the process until completion of work. To maintain tension in the arc, it is recommended to maintain a distance of 5 mm and follow an equal speed throughout the melting section.

As a result of the contact of two differently charged elements, where the minus is the electrode, the plus is the metal structure, a high-voltage flow of current energy is formed, which melts the product, which makes it possible to obtain a strong connection. The welding process should not stop for a minute. This rule must be followed to ensure that the seam is even.

A similar option for welding metal structures is forging. The method is often used by the basics, first-class masters. Screws and bolts are required. This method is performed if the characteristics of the metal are not suitable for welding.

It should be remembered that welding is considered a hazardous activity where eye protection is important. Without a mask, even a highly qualified master will not be able to get the desired result. Compliance with the conditions of work performance is a secondary, important factor where it is necessary to strictly adhere to all requirements.