Development of assembly-welding process BelAZ 75570 front axle beams

Introduction

Currently, welding has taken a leading place among technological processes in the manufacture and construction of a large number of steel structures of hazardous industries controlled by technical supervision bodies. Oil and gas pipelines, steam and hot water pipelines, high pressure boilers, oil storage tanks, cracking and synthesis columns, handling equipment; steel construction and bridge-building structures, components of space and water ships, components of reactors, electronic devices and much more are produced using modern welding methods.

The Republic of Belarus currently employs many heavy industry enterprises, including engineering, where welding has become widespread.

However, there are many problems with the use of a weld joint:

1. Still about 80% of all welding is manual arc. In second place in terms of use is the most universal method of welding and at the same time quite productive - mechanized welding in protective gases (semi-automatic in protective gases) [3, p. 6].

2. The qualification of welders, both produced by initial vocational education organizations and working at enterprises and often having quite high grades (from 3rd to 6th), in most cases is at a low level that does not meet the requirements of modern production. This is due to the low level of theoretical training, insufficient qualification of practical training instructors, lack of criteria and methods for objective assessment of the qualification of welders, as well as the fuzziness of the requirements of ETKS, the lack of necessary technological documentation for welders and the low requirement on the part of monitoring services for the quality of welding [3, p. 7].

3. Currently, the market offers a wide variety of types and brands of welding equipment of foreign and domestic production. At the same time, there are no objective criteria and methods for their comparative assessment according to technological, operational, ergonomic and other characteristics, which makes it difficult for consumers to choose the optimal option that is most effective for specific production conditions [3, p. 6].

4. There is a constant shortage of welders, especially highly skilled welders, which in some cases can be compensated by an increase in productivity due to an increase in the level of mechanization and automation of welding [3, page 6].

5. Expensive imported welding materials, in particular electrodes for manual arc welding, are widely used in production, while domestic manufacturers produce similar materials that are not inferior in technological properties, cost and quality to foreign ones [3, p. 6].

6. In a number of industries, especially small and medium-sized enterprises, insufficient attention is paid to the health, safety and working conditions of welders, which makes this specialty unattractive and heavy [3, p. 7].

The application of welding in engineering enterprises also includes all these problems. One of the solutions to these problems is automation and robotization of welding production, the use of waste-free and resource-saving production, the development of new technologies that allow improving the quality of welded joint, labor protection, production culture, etc.

Due to the introduction of these measures into welding production, as well as new equipment, it is necessary to change or compose new technological processes that will meet the growing needs of consumers.

Purpose and characteristics of the product. Its structural and technological analysis

Selects the shape of the parts to be welded.

When designing, the dimensions and shape of the welded elements from the position of their processability should be chosen based on the use of high-performance automatic welding methods; performing welding in a lower position; free access to the front and root parts of the seam; heating (or cooling) and subsequent thermal or mechanical treatment, if necessary; minimizing weld lengths and mass of base and build-up metals, etc.

In this case, sheet metal is used as billets for the beam. It is better to apply a U-shaped profile. This will reduce the length of the seams by 2 times, and therefore reduce welding strains and stresses, as well as reduce the manufacturing time of the beam.

Selects the welding method and type.

For welding of the front axle beam, mechanized welding in the environment of protective gases is used. The protective medium is M21 gas according to STB EN 439. This gas is the most versatile of all mixtures for carbon structural steels. It consists of 82% argon and 18% carbon dioxide. Suitable for almost all types of materials [5]. When welding the welding wire of 1.2 Sv08G2S About GOST 224670 is used.

This type of welding ensures the necessary operational properties and protection of the welding bath from environmental influences and at the same time ensures the necessary production rate. [4, t.2, p. 107].

However, the disadvantage of this method is the improper selection of welding materials. Svish8G2S wire is used for welding of 09G2S steel with a sufficient small metal thickness (the number of passes up to two) otherwise there is a high probability of cold cracks [4, t.2, p. 107]. At present, properties of new gas mixtures have been investigated, which give increased protection of welding bath at high production rates, higher mechanical properties of built-up metal, and also allow saving welding materials [6].

For welding of this article, it is more advisable to use automatic welding in the environment of protective gases, using a more efficient mixture of gases .

Direction of process improvement over existing version

After structural and technological analysis and process analysis, the need to change the process becomes apparent:

Application of more efficient welding methods in protective gases for welding .

Automation of production.

The use of stamped blanks will reduce the number of seams, and thereby reduce their length. This will reduce welding strains and stresses and increase production speed.

In connection with the use of a more efficient welding method in the environment of protective gases and the use of stamped blanks, there is a need for the use of new welding materials, as well as the calculation of modes.

Product Workpiece, Assembly and Welding Specification

The article blanks must undergo the following control operations before welding:

- checking the availability of the certificate, completeness of the data given in it and compliance of this data with the requirements of the standard, technical specifications or design documentation;

- check of presence of marking and compliance of its certificate or passport data;

- inspection of metal and structural elements for detection of surface defects and damages.

In the absence of a certificate or incomplete certificate data, the use of this metal can be allowed only after testing confirming the compliance of the metal with all standards.

During the tests, the chemical composition, physical properties are detected, and the weldability of steel is also determined.

Structural elements that do not have a factory passport cannot be allowed for further production.

At all parts coming to the installation site, before the start of assembly, the master (or other responsible person) must check the presence of stamps, markings, as well as certificates of the manufacturer confirming the compliance of the parts with their purpose. If there are no marks, markings or part certificates, no further processing is allowed. When preparing butt joints for welding, it is necessary to check their compliance with drawings and requirements of NDT. You should also check:

- compliance of shape, dimensions and quality of edge preparation with the required requirements (machining of chamfers for welding and dimensions of edges are checked with special templates);

- quality of grinding of surfaces of welded parts;

- correctness of transitions from one section to another;

-conformance of minimum actual thickness of parts prepared for welding with set tolerances.

Immediately prior to assembly, the welded edges and adjacent parts surfaces shall be cleaned to metallic gloss and degreased, and the weld joint clearance shall be checked depending on the metal thickness and in accordance with GOST. The width of the cleaned areas, counting from the cutting edge, must be at least 20 mm. When assembling a joint, it is necessary to provide for the possibility of free shrinkage of the weld metal during welding; do not assemble the joint with interference.

Welding of structures shall be carried out by welders who have undergone theoretical and practical training and have certificates establishing their qualifications and the nature of the work to which they are admitted.

It can be performed only after acceptance of the assembly CTC for welding. Surfaces to be welded shall be thoroughly cleaned of rust, dirt, oil, moisture.

Welding of structures shall be carried out in accordance with the process that establishes the sequence of assembly and welding works, welding method, welding equipment, power supply, accessories and auxiliary equipment, welding materials, welding procedure, welding modes, etc.

The design drawings shall have such an arrangement, and the process shall be such as to apply welds so that the shrinkage stresses and deformations of the structural elements are minimal.

Prevent alignment of craters in one section. Each subsequent pass must be superimposed after careful cleaning from the slag of the previous pass.

Welding shall be performed at positive temperature.

In the area where the work is carried out, the voltage of the supply network is allowed to fluctuate within ± 10%.

Substantiation of article material selection, material consumption per article

Steel 09G2S is used for various parts and elements of welded steel structures operating at temperature from 70 to + 425 0С. This steel has the required technological and mechanical properties, at a low price .

328 kg of metal is required to make the front axle beam. The metal for making the beam is supplied in the form of sheet and U-shaped rolled stock with a thickness of 16 mm.

Welding Technology

Selection and technical justification of welding method.

The choice of welding method depends on: the thickness of the workpieces by welding, the length and position of the joints, the possibility of automation of production, etc.

For joints with a length of more than a meter, it is more advisable to use automatic welding under a flux layer (beam length 2100 mm). However, due to the fact that the dimensions and design technology do not allow for the production of a weld joint, the use of a lining or a flux pad, such welding is not advisable .

The use of electron beam welding is also not advisable. Using ELS for a T-section requires edge flanging.

Therefore, in this case, it is more appropriate to use automatic welding in a mixture of protective gases. This welding can be performed in all spatial positions and provides sufficiently high properties of the weld metal and protection of the molten metal at low costs for welding equipment and materials.

Tacks, process inserts and pads are carried out by mechanized welding in the environment of protective gases.

Economic justification of welding method selection.

Welding in a mixture of protective gases is the most cost-effective method among melting welding. In the automation of this welding, the main economic costs are associated with the purchase of a welding machine, a welding column and new welding materials (helium gas). At the same time, there are savings in welding wire (up to 20%) and protective gases, which leads to a decrease in the cost of production .

Also, the use of automatic welding eliminates the need for a highly paid skilled welder, which also reduces the cost of production.

The high welding speeds that automatic welding can achieve increase the production rate and therefore the number of products produced, which leads to an increase in the budget of the enterprise.

Thus, the use of this method allows:

1. Reduce the cost of production.

2. Increase the rate of production without compromising the quality of products.

Selection and justification of welding materials.

The main criterion for selecting the welding wire is the chemical composition of the base metal and the weld metal, and ensuring the strength of the weld metal is equal to or greater than that of the base metal.

For welding in the environment of protective gases of steel 09G2S, Sv8G2S and Sv8XG2S are used as welding wire. However, the welding wire Sv00G2S is used in single or double-layer welding, so the use of this wire is not advisable, since the thickness of the welded blanks is large [4, i.e., page 107].

The protective gas will be a mixture of gases M12 (2) according to STB EN 439 (Helishield H101). The inert gas mixture includes: Ar + 38% He + 2% CO2. Gas mixture M12 (2) is recommended for welding materials over 9 mm thick.

Argon is heavier than air, so it easily displaces it from the welding zone. This provides reliable protection for the welding bath. Also, the use of argon allows the jet transfer of metal, which provides less spattering of the molten metal. Helium increases the rate of welding and penetration, as well as the spattering of molten metal. The addition of carbon dioxide leads to a decrease in the cost of the mixture of gases, but also leads to an increase in the spattering of molten metal.

Thus, this mixture ensures the formation of small droplets during the transfer of molten metal, a low level of spraying of metal, increases the welding speed, and increases penetration. In this case, an even surface of the seam is formed. All this determines the savings of welding wire and the improvement of weld joint performance

Design, calculation and description of process equipment

Selection of installation bases and development of theoretical layout of parts and assemblies.

Basing refers to a certain position of parts in the product relative to each other or the product relative to the appliance, technological welding equipment (welding arc, torch flame, contact machine electrodes). When designing, operating assembly devices, you most often have to deal with installation bases.

In this case, a basing scheme is required that will deprive all components of six degrees of freedom, since the tool will previously rotate about its axis to provide a convenient welding position.

The front axle beam is a part consisting of three parts: a box beam and two tips. In turn, the box beam consists of their U-shaped profile and sheet.

Select the bottom face as the primary datum for the U-shaped profile. This will ensure deprivation of 3 degrees of freedom (movement in one direction, and rotation around 2 axes). Deprivation of 3 more degrees of freedom is carried out by pressing the side of the U-shaped to the stops (movement in two directions and rotation around the 3rd axis).

The sheet is installed on the beam and pressed by pressing devices - this will ensure deprivation of 4 degrees of freedom (movement in two directions, and rotation around 2 axes). Deprivation of another 2 degrees of freedom provides bars of square or round cross-section welded to the sheet (movement in one direction and rotation around the 3rd axis).

The tips are installed on the lower face, inserted into the expansion pin and installed in the beam. Installation on the lower face provides deprivation of 3 degrees of freedom (as in previous cases), and the expansion finger is another 2 degrees (movement in two directions). Installation of the tip in the beam will ensure deprivation of the last degree of freedom (rotation around the 3rd axis).

Selection and justification of the type of mounting and pressing elements.

For welding of this article, an accessory is required that will provide rigid fixation of the part and its rotation to ensure welding in the lower position.

Assembly and welding device consists of base (frame or housing), fixing (mounting) elements, clamps, turning devices, auxiliary parts and devices.

The base of the fixture is an element that combines all parts of the fixture into one structure. Support and guide parts, stops and supports are located on the base, which determine the position of the installed parts, bushings, bosses, bracket and other retainers.

The base perceives the mass of the product and all the forces arising in the process of assembly, tack, welding, bunting. In this case, it must ensure the accuracy of the placement of the installation parts (as in a static state), as well as the absence of displacements and vibrations at any turns, i.e., have sufficient rigidity and strength.

The base of the device should be technological, have a rational, structural design, have a possibly lower mass and be compact.

In this case, the base of the device is welded, from sheet rolled. It is a welded frame. Holes and rotation of base around axis are provided for access to welding of seams located on lower face in base. The upper face of the base follows the contour of the lower face of the part, and at the ends of the base there are flanges with holes for attachment to the contactor and the post.

Installation parts (supports, stops, pins, prisms, installation cones) form the basic surfaces of the devices and ensure the correct orientation of the parts in them in accordance with the rule of six support points.

Supports of accessories are divided into main and auxiliary. The main supports determine the position of the part in space, depriving it of all or several degrees of freedom (as a rule, they are rigidly fixed in the housing of the device by pressing or welding), auxiliary ones are designed to give the part additional rigidity and stability, for example, in cases when the part may overturn or due to low rigidity deform.

Main supports of assembly-welding devices can be support pins with flat, spherical and notched heads.

Large-sized parts with machined base planes are installed on plates, and small and medium-sized parts - on pins. Adjustable screw supports can be used as main and auxiliary supports. Auxiliary supports do not affect part basing accuracy.

The base of the accessory is used as supports.

Stops and clamps are installed to fix parts. Rectangular bars, pins, ribs, etc. can be used as stops and clamps arranged along the contour of the part to be mounted. The abutments may be permanent, pivoting, folding, diverting or detachable with a corrugated, spherical or flat base surface. Clamps come with a mechanical, pneumatic, hydraulic, etc. drive.

To fix the parts, we use pneumatic branch stops and clamps to automatically fix the part in the accessory.

Process Section

Synchronizing operations.

In the manufacture of welded structures, a certain sequence of assembly and welding of parts and assemblies is observed. This sequence depends on the configuration of the part, assembly, the possibility of welding taking into account the technological capabilities of the selected welding method. For this reason, the accepted sequence of assembly and welding operations may be the only possible, since only in this case the specified accuracy, strength of the structure is observed, the usual execution of operations is ensured, the required release of products at high economic performance.

In the manufacture of welded structures, schemes are possible: sequential assembly and welding, complete assembly of the entire structure with its subsequent welding, parallel-sequential assembly and welding.

In the course design, a scheme with full assembly and welding was adopted as the basic one, since welding with a serial or parallel-serial design is impossible. The required accuracy is achieved by using rigid fixation of the part elements in the accessory.

Development, description of methods of quality control of welded joints and organization of technical control.

When welding the front axle beam, welding is used in a mixture of gases according to, therefore, the following defects can occur in all welds: pores, non-holes, burns, undercuts, slag inclusions, as well as various deformations that distort the shape of the product. A visual inspection method is used to check the joints for the presence of non-holes, burns, undercuts, cracks, burrs. If there are irregularities, an ultrasonic control method is used.

Quality control is a multi-stage operation that begins with quality control of procurement and assembly work and ends with control of welds on the finished product.

Quality of preparation and assembly of blanks for welding, quality of made joints during welding and quality of finished welds are checked by external inspection. External control is in many cases quite informative, it is the cheapest and most operational method of control.

External inspection is carried out on a material that can be rejected in the presence of dents, burrs, scale, oxides, rust, etc. We determine the quality of preparation of edges for welding and assembly of blanks, their purity, compliance of gaps with permissible values, correctness of their preparation, etc. Strict control of blanks and assembly in many ways ensures high quality of welding of the console.

Observation of the welding process allows to prevent defects in time. The welding mode, gas protection of the arc, correct application of rollers in multi-layer seams, etc. are visually monitored.

Inspection of finished products is performed by magnifying glass or without it for cracks, undercuts, fistula, burning, flares, non-roasting of seam root and edges. During inspection defects in the form of seams, distribution of flakes, the nature of metal distribution in the reinforcement of the seam, the amount of meniscus, weave, etc. are determined. The appearance of the seam surface is characteristic for each welding method, as well as for the spatial position in which welding is carried out. Unevenness, flakiness, different width and height of the seam indicate fluctuations in arc power, its frequent breaks and combustion stability .

When welded in protective gases, the outer surface of the seams should be smooth, shiny, without flakes and in the form of a strip of molten metal.

For visual inspection method the following equipment is used:

- UHS3 templates;

- elbow USh225, GOST 374977;

- SHD1630 line GOST 802675.

Product quality control according to GOST 1546779 is defined as a check of compliance of product quality indicators with installation requirements. At the same time, at all stages of the product manufacturing technology, it is necessary to check the quality of the control operations themselves: metrological verification of devices, control of compliance with modes, qualification and condition of operators, etc.

The high quality of the connections depends primarily on the level and state of the production process. Detection of defects serves as a signal not only to the rejection of products, but also to the prompt correction of technology. The main impact of control is on production technology, ensuring through prompt feedback the prevention of defects and scrap of products.

Quality control of welding work begins even before the welder begins welding the product. The quality of the base metal, welding materials, billets entering the assembly, the state of the welding equipment and the quality of the assembly, as well as the qualification of welders are checked. All these activities bear the names of pre-inspection.

In the process of welding, the appearance of the seam, its geometric dimensions are checked, the article is measured, continuous monitoring of the serviceability of the welding equipment and the execution of the technological process is carried out. Specifying an operation makes up the monitoring.

The last check step is to check the welding quality of the finished product.

Methods for correcting weld defects.

If invalid external or internal defects are detected, remove them. If this is not possible, then the whole product is married.

External defects are removed by embossing with provision of smooth transitions in places of samples. External defects can be corrected by grinding without subsequent brewing of their sampling places only while maintaining the minimum permissible wall thickness of the part in the place of maximum brewing depth. Defects on the back of the seam are removed along the entire length of the seam flush with the base metal.

Removal of buried external and internal defects (defective areas in joints from aluminum, titanium and their alloys should be carried out only by mechanical method - by grinding with abrasive tool or cutting, as well as by cutting with subsequent grinding.

Cracks, non-cracks in the root of the seam, internal non-cracks, slag inclusions, fistulas and internal pores are corrected by embroidery, cutting or arc stitching.

Surface pores located at low depth are removed by welding.

Undercuts are eliminated by welding of thread seam along entire length of defect. However, this leads to an increase in the consumption of welding materials.

Build-ups and unevenness of seam shape are corrected by mechanical treatment of defect along the whole length. Seam craters brew. Burns in stitches are cleaned and brewed.

The corrected welds should be inspected. If defects are again detected, then they are corrected. The number of corrections of the same defect depends on the category of responsibility of the structure and should not exceed three.

Proposals for industrial implementation.

The industrial implementation of the developed project of automation of the beam welding section of the front axis of the BelAZ - 75570 quarry dump truck can be carried out at the BelAZ plant in Zhodina in order to improve the existing technological process for the production of the beam of the front axis of the BelAZ 75570 quarry dump truck.

It is also possible to implement the automated site developed in the project at other mechanical engineering enterprises for the production of similar or related products.

Safety of the design object.

Patent law establishes strict criteria for the protection of objects, the emergence of exclusive rights to inventions, utility models and industrial designs is associated with the receipt of a security document - a patent, contains a special procedure for concluding license agreements providing for their mandatory state registration.

Objects of industrial property rights.

The right of industrial property extends to:

1) inventions;

2) useful models;

3) industrial designs;

4) selection achievements;

5) topologies of integrated circuits;

6) undisclosed information, including secrets of production (know-how);

7) company names;

8) trademarks and service marks;

9) geographical indications;

10) other objects of industrial property and means of individualization of participants in civil turnover, goods, works or services in cases provided by law.

Legal protection of invention, utility model, industrial design

The right to invention, utility model, industrial design is protected by the state and certified by patent.

Conditions of legal protection of invention of utility model, industrial design

1. The rights to invention, utility model and industrial design are protected subject to the issuance of a patent.

2. The invention in any field of the art provides legal protection if it relates to a product or method, is novel, has an inventive level and is commercially applicable.

3. A useful model to which legal protection is provided is recognized as a technical solution related to devices, which is new and industrially applicable.

4. The industrial model, which is provided with legal protection, is recognized as the artistic or artistic design solution of the product, which determines its appearance and is new and original.

5. The requirements for the invention, the utility model, the industrial model, in which the right to obtain a patent arises, and the procedure for issuing it to the patent authority is established by law.

Right to use invention, utility model, industrial design

1. The patent holder has the exclusive right to use patented inventions, utility model, industrial design.

The exclusive right to use the invention, utility model, industrial design includes the right to use the invention, utility model, industrial design at its discretion, if this does not violate the rights of other persons, and also includes the right to prohibit the use of the invention, utility model, industrial design to other persons.

The exclusive right to use the patented invention, which is a method of producing a product, extends to the product directly obtained by this method. At the same time, the new product is considered obtained by a patented method, until it is proved otherwise.

2. Other persons, non-patent holders, are not entitled to use the invention, utility model, industrial design without the permission of the patent holder, except when the use in accordance with this Code or other law is not recognized as a violation of the rights of the patent holder.

Conclusion

During the course project, the technology for assembling and welding the front axle beam BelAZ 75570 was developed. Optimal selection of welding materials, equipment and welding modes was made. The accessory for assembly and welding of the beam is designed.

The use of automation made it possible to increase labor productivity, the quality of welding operations and, as a result, reduce the likelihood of formation of defects during welding. And also reduce the harm during welding.

The main direction of improving the process of welding the front axle beam is to replace semi-automatic welding in the environment of protective gases with automatic welding without reducing the strength of the joints.

The use of automatic welding in combination with a welding column reduces labor intensity and allows you to automate the welding process.