Blanks and blank production. Electronic textbook for the course "Fundamentals of Mechanical Engineering Technology"

Blank production in mechanical engineering

Blank production in mechanical engineering

Blank production in mechanical engineering

Blank production in mechanical engineering

Blank production in mechanical engineering

Blank production in mechanical engineering

Blank production in mechanical engineering

10. Blank production in mechanical engineering

11. Blank production in mechanical engineering

12. Blank production in mechanical engineering

13. Blank production in mechanical engineering

14. Blank production in mechanical engineering

15. Blank production in mechanical engineering

16. Blank production in mechanical engineering

17. Blank production in mechanical engineering

18. Blank production in mechanical engineering

19. Blank production in mechanical engineering

20. Blank production in mechanical engineering

21. Blank production in mechanical engineering

22. Blank production in mechanical engineering

23. Blank production in mechanical engineering

24. Blank production in mechanical engineering

25. Blank production in mechanical engineering

26. Blank production in mechanical engineering

27. Blank production in mechanical engineering

28. Blank production in mechanical engineering

29. Blank production in mechanical engineering

30. Blank production in mechanical engineering

31. Blank production in mechanical engineering

32. Blank production in mechanical engineering

33. Blank production in mechanical engineering

34. Blank production in mechanical engineering

35. Blank production in mechanical engineering

36. Blank production in mechanical engineering

37. Blank production in mechanical engineering

38. Blank production in mechanical engineering

39. Blank production in mechanical engineering

40. Blank production in mechanical engineering

41. Blank production in mechanical engineering

42. Blank production in mechanical engineering

43. Blank production in mechanical engineering

44. Blank production in mechanical engineering

45. Blank production in mechanical engineering

46. ​​Blank production in mechanical engineering

47. Blank production in mechanical engineering

48. Blank production in mechanical engineering

49. Blank production in mechanical engineering

50. Blank production in mechanical engineering

51. Blank production in mechanical engineering

52. Blank production in mechanical engineering

53. Blank production in mechanical engineering

54. Blank production in mechanical engineering

55. Blank production in mechanical engineering

56. Blank production in mechanical engineering

57. Selecting the type of blanks.

58. Selecting the type of blanks.

59. Selecting the type of blanks.

60. Selecting the type of blanks.

61. Selecting the type of blanks.

62.

68. Selecting the type of blanks.

1. Types and forms of production and methods of organizing its preparation

1.1 Types of production

In engineering production, there are three main types: mass, serial and single. The belonging of production to one or another type is determined by the degree of specialization of jobs, the range of production objects, the form of movement of these objects through jobs.

The degree of job specialization is characterized by the coefficient of fixing operations, which is understood as the number of different operations performed at one workplace during the month:

K Z.O,=O/R, (1.1)

where ABOUT- the number of various operations performed at the workplaces of the site or workshop during the month;

R- the number of jobs on the site or in the shop.

If only one operation is assigned to the workplace, regardless of its load, then K Z.O.= 1, which corresponds to mass production. At 1< Kz.o,< 10 производство является крупносерийным, при 10 < Kz.o< 20 - среднесерийным, при 20 < Kz.o< 40 - мелкосерийным, при Kz.o> 40 - single.

Example. On a site of 15 workplaces, one operation was performed at 1, 2, 3, 7, 10, and 13 workplaces during the month; on the 4th, 5th and 12th - two each; on the 6th, 8th, 9th and 11th - three each and on the 14th and 15th - four each.

From here

Consequently, the production at the site is large-scale.

Mass production characterized by the continuous production of a limited range of products at highly specialized workplaces. A product is a product of the final stage of production. Mass production allows you to mechanize and automate the entire process and organize it more economically.

Specifications of various types of blank production

Mass production characterized by the manufacture of a limited range of products in batches (series), repeating at certain intervals, and a wide specialization of jobs. The division of mass production into large-, medium- and small-scale production is conditional, since in various branches of engineering with the same number of manufactured products in a series, but with a significant difference in their size, complexity and labor intensity, production can be attributed to different types. In terms of the level of mechanization and automation, large-scale production is approaching mass production, and small-scale production is approaching a single one.

Single production is distinguished by the manufacture in single quantities of a wide range of non-repeating or repeating at indefinite intervals of products at workplaces that do not have a specific specialization (except professional). In unit production, a significant percentage of technological operations are performed manually.

Technical characteristics of various types of blank production according to the main features are presented in Table. 1.1. Increasing the degree of specialization of workplaces, the continuous and direct movement of production objects through them, i.e. the transition from single to serial and from serial to mass production, allows the wider use of special equipment and technological equipment, advanced technological processes, advanced methods of organizing labor and in in the end - to increase labor productivity, reduce the cost of production, improve its quality.

1.2 Production and technological processes

According to GOST 14.004-83, the totality of all actions of people and production tools necessary for this production for the manufacture or repair of manufactured products, is called production process. When implementing production process materials and semi-finished products are converted into finished products that correspond to their official purpose. The production process covers: preparation of means of production and maintenance of jobs; receipt and storage of materials and semi-finished products; all stages of manufacturing machine parts; transportation of materials, blanks, parts, parts and finished products, assembly of parts and products; technical control, testing and certification of products at all stages of production; dismantling of assembly units and products (if necessary); container manufacturing; packaging of finished products and other activities related to the manufacture of manufactured products. The production process is carried out in space and time when the objects of production interact with the instruments of production.

The area required for the production process is called production area. The calendar time required to carry out a recurring production process is called production cycle.

According to GOST 3.1109-82, a part of the production process that contains purposeful actions to change the state of the object of labor is called technological process. During the implementation of the technological process, there is a consistent change in the shape, size, properties of the material or semi-finished product in order to obtain a product that meets the specified technical requirements. The technological process has its own structure and is carried out at the workplace.

Technological operation- a complete part of the technological process, performed at one workplace and covering all sequential actions of the worker (or group of workers) and equipment for the manufacture of the workpiece or its processing (one or more at the same time). Part of the production area of ​​the workshop, where one or more performers of work and a piece of equipment or part of the conveyor serviced by them, as well as equipment and production items, are located. workplace. Modern production of mechanical engineering products is unthinkable without technological equipment and tooling.

Technological equipment- these are production tools in which materials or blanks, means of influencing them and energy sources are placed to perform a certain part of the technological process. Examples of process equipment are foundry machines, presses, machine tools, furnaces, electroplating baths, washing and sorting machines, test benches, marking plates, etc. Technological equipment- these are the tools of production used in conjunction with technological equipment and added to them to perform a certain part of the technological process. Examples of tooling are tools, dies, fixtures, molds, gauges, patterns, molds, core boxes, etc.

The launch of products into production can be carried out continuously (for a long time) and one-time (single copies and batches). A group of blanks of the same name and size, launched into production simultaneously or continuously for a certain period of time, is called production batch. Technological processes in mass and large-scale production are characterized by the release cycle. Release stroke- this is the time interval through which the release of a workpiece or product of a certain name, size and design is periodically performed. The concept of “output cycle” is widely used in mass and large-scale production of blanks, where there is a high level of mechanization and automation of production (special equipment, conveyors, etc.). If the workpiece in this enterprise is the final product of production (for example, in a steel mill), then in this case it is a product of this plant.

1.3 Principles, forms and methods of organization of production

The results of the production and economic activities of the enterprise, the economic indicators of its work depend on the correct organization of the production process: the cost of production, profit and profitability of production. Basic principle rational organization manufacturing process is specialization.

Specialization- one of the forms of division of labor, which consists in the fact that the enterprise as a whole and its individual divisions manufacture products of a limited range. Reducing the range of manufactured products at each workplace, site, workshop and plant leads to an increase in the output of products of the same name, to an improvement in economic indicators through the use of special and more productive equipment, an increase in the degree of mechanization and automation of all processes, the acquisition of work skills by workers, improvement of the organization of labor, organization of in-line production, etc. The reduction in the range of products produced is facilitated by the standardization, normalization and unification of products and their components.

With regard to blank production, the principle of specialization can be easily traced against the background of various types of production. Yes, under the conditions single production in the structure of a machine-building plant, one foundry is most often provided, in which blanks from cast iron, steel and non-ferrous alloys are produced in various departments using a variety of equipment. In the conditions of serial and mass production, the structure of the plant may have separate independent workshops: steel, iron foundry, non-ferrous casting. A large concentration of production of the same type of blanks leads to the creation of factories specializing in the production of blanks from certain materials, a certain weight category, complexity and other features. Therefore, in our country there are steel, iron foundry, forging and stamping plants, etc. The US engineering industry, for example, is characterized by the fact that back in the 50s of the current century, blank production was mainly separated from mechanical assembly. Compliance with the principle of specialization significantly affects the forms and methods of organizing technological processes.

Forms and methods of organizing technological processes depend on the established procedure for performing operations, the location of technological equipment, the number of products and the direction of their movement during manufacture. There are two forms of organization of technological processes: group and flow.

The foundation group form organization of production - grouping of manufactured blanks according to homogeneous design and technological features. It is characterized by the unity of technological equipment and the specialization of jobs.

inline form characterized by the specialization of each workplace, the coordinated and rhythmic execution of all operations of the technological process based on the release cycle, the placement of workplaces in a sequence corresponding to the sequence of technological operations. The flow form of production is realized in the form of a production line. Production lines, on which blanks are manufactured alternately, in batches, are called variable-flow lines. They are typical for serial production and are used in the manufacture of structurally similar blanks with the corresponding readjustment of equipment and tooling. If all processes on the production line are automated, then the production line is called automatic.

1.4
The concept of unified system technological preparation of production

In the early seventies of the current century, a Unified system of technological preparation of production(ESTPP). ESTPP - established state standards a system for organizing and managing the technological preparation of production, which provides for the widespread use of advanced standard technological processes, standard technological equipment and equipment, means of mechanization and automation of production processes, engineering and management work.

Technological preparation of production(TPP) should ensure the full technological readiness of the enterprise to produce products of the highest quality category in accordance with the specified technical and economic indicators, i.e., at minimal labor and material costs. Full technological readiness is understood as the presence at the enterprise of a complete set of technological documentation and technological equipment that ensures the production of products. TPP includes the solution of many tasks that can be grouped into the following main functions: ensuring the manufacturability of the product design; development of technological processes; design and manufacture of technological equipment; organization and management of the CCI.

One of the prominent places in the ECTPP is the design of blanks and technological processes for their production.

1.5 Purpose and development trend of procurement production

The main purpose of blank production is to provide machine shops with high-quality blanks.

In mechanical engineering, blanks are used that are obtained by casting, forming, welding, as well as from plastics and powder materials (Table 1.2). Modern blank production has the ability to form blanks of the most complex configuration and the most diverse sizes and accuracy.

An approximate structure for the production of blanks in mechanical engineering

At present, the average labor intensity of procurement work in mechanical engineering is 40 ... 45% of the total labor intensity of machine production. The main trend in the development of blank production is to reduce the labor intensity of mechanical processing in the manufacture of machine parts by increasing the accuracy of their shape and size.

test questions

1. What are the types of production? List their main features.

2. What is meant by production and technological processes?

3. What is meant by technological equipment and equipment?

4. What are the forms of organization of technological processes?

5. Give the definition of ECTPP and describe its purpose.

6. What is the purpose and trend of development of procurement production?

7. What blanks are used in mechanical engineering?

2. Basic concepts about blanks and their characteristics

2.1 Procurement, basic concepts and definitions

blank, according to GOST 3.1109-82, the subject of labor is called, from which a part is made by changing the shape, size, surface properties and (or) material.

There are three main types of blanks: machine-building profiles, piece and combined. Machine-building profiles are made of a constant section (for example, round, hexagonal or pipe) or periodic. In large-scale and mass production, special rolled products are also used. Piece blanks are obtained by casting, forging, stamping or welding. Combined workpieces are complex workpieces obtained by joining (for example, welding) separate, simpler elements. In this case, it is possible to reduce the mass of the workpiece, and use the most suitable materials for more loaded elements.

Workpieces are characterized by their configuration and dimensions, the accuracy of the obtained dimensions, the state of the surface, etc.

Forms and dimensions of the workpiece largely determine the technology of both its manufacture and subsequent processing. Dimensional accuracy workpiece is the most important factor affecting the cost of manufacturing a part. In this case, it is desirable to ensure the stability of the dimensions of the workpiece over time and within the limits of the manufactured batch. The shape and dimensions of the workpiece, as well as the condition of its surfaces (for example, the chill of iron castings, the layer of scale on forgings) can significantly affect subsequent machining. Therefore, for most workpieces, preliminary preparation is necessary, which consists in the fact that they are given such a state or appearance in which they can be machined on metal-cutting machines. This work is carried out with particular care if further processing is carried out on automatic lines or flexible automated complexes. Pre-processing operations include cleaning, straightening, peeling, cutting, centering, and sometimes processing of technological bases.

2.2 Allowances, overlaps and dimensions

Machining allowance- this is a layer of metal removed from the surface of the workpiece in order to obtain the shape and dimensions of the part required according to the drawing. Allowances are assigned only to those surfaces whose required shape and dimensional accuracy cannot be achieved by the accepted method of obtaining a workpiece.

Allowances are divided into general and operational. Total allowance for processing- this is a layer of metal necessary to perform all the necessary technological operations performed on a given surface. Operating allowance- this is a layer of metal removed during one technological operation. The allowance is measured along the normal to the surface in question. The total allowance is equal to the sum of the operating ones.

The size of the allowance significantly affects the cost of manufacturing the part. An overestimated allowance increases the cost of labor, the consumption of material, cutting tools and electricity. An underestimated allowance requires the use of more expensive methods for obtaining a workpiece, complicates the installation of the workpiece on the machine, and requires a higher qualification of the worker. In addition, it is often the cause of marriage during machining. Therefore, the assigned allowance should be optimal for given production conditions.

The optimal allowance depends on the material, dimensions and configuration of the workpiece, the type of workpiece, the deformation of the workpiece during its manufacture, the thickness of the defective surface layer, and other factors. It is known, for example, that iron castings have a defective surface layer containing shells, sand inclusions; forgings obtained by forging have scale; forgings obtained by hot forging have a decarburized surface layer.

The optimal allowance can be determined by the calculation and analytical method, which is considered in the course "Mechanical Engineering Technology". In some cases (for example, when machining technology has not yet been developed), allowances for processing various types of workpieces are selected according to standards and reference books.

Rice. 2.1. Allowances, laps and dimensions of the bearing housing (a), plugs (b) and shaft (in): BUT eag, B zag, IN zag, D zag, D′ zag, D″ zag - the original dimensions of the workpiece; A det, B det, IN det, D" det, D"det, - dimensions of the finished part; D 1 , D 2 , ABOUT" 1 , ABOUT" 1 , - workpiece operating dimensions

The actual layer of metal removed in the first operation can vary widely, since in addition to the operating allowance, it is often necessary to remove the overlay.

lap- this is an excess of metal on the surface of the workpiece (in excess of the allowance), due to technological requirements to simplify the configuration of the workpiece to facilitate the conditions for its production. In most cases, the overlap is removed by machining, less often it remains in the product (forging slopes, increased radii of curvature, etc.).

In the process of converting a workpiece into a finished part, its dimensions acquire a number of intermediate values, which are called operating dimensions. On fig. 2.1 details of various classes show allowances, laps and operating dimensions. Operating dimensions are usually affixed with deviations: for shafts - minus, for holes - plus.

2.3 Construction materials

The role of structural material in the technological process of manufacturing machine parts is extremely high. On the one hand, the structural material should ensure the manufacture of blanks and parts at the lowest production costs. The share of the cost of materials in the cost of engineering products is relatively high (for example, in the machine tool industry it is 60% of the total cost, in the manufacture of locomotives and wagons - 70 ... 75%) and tends to increase. On the other hand, right choice structural material should provide the details of its high performance properties, its durability and maintainability. When choosing a structural material, it is necessary to take into account its operational, technological and economic properties.

Performance properties of the material must ensure that the parts reliably perform their functions. From this point of view, his choice is made on the basis of calculations, experiments or operating experience of similar parts. Data on the choice of grades of materials for the manufacture of parts operating under certain conditions are usually given in reference books.

Technological properties(fluidity, ability to plastic deformation, weldability) is an important factor that determines the possibility and efficiency of processing a given material by the selected technological method. When designing a part, the designer must imagine from the very beginning how it will be manufactured, starting from the receipt of the workpiece and ending with finishing.

Technological properties of the material can determine in advance the subsequent technology for manufacturing blanks. For example, if the machine bed is made of gray cast iron, then the workpiece can only be obtained by casting. Cast iron cannot be pressure treated. It is practically not weldable (at least when creating new structures) and almost does not allow repair by surfacing. Cast blanks of frames require additional processing (natural aging, low-temperature annealing, etc.) to stabilize their shape and dimensions.

Economic efficiency used structural material can be estimated by its cost and scarcity. The economic efficiency of a structural material should not be reduced to its low cost. The choice of material is significantly influenced by the cost-effectiveness of the methods for manufacturing blanks and their subsequent processing, which is determined by the technological properties of this material. In addition, with the current trend to increasingly use higher quality and, therefore, more expensive materials, it is necessary to consider how their use will affect the reduction in weight and cost of the part in in general, to increase its service life and maintainability.

2.4 Quality of blanks

The quality of industrial products is a set of properties that determine its suitability to satisfy certain needs in accordance with its purpose. Some of the most important indicators of the quality of machines are:

1) operational, which determine the technical level of the machine (its perfection), its reliability, aesthetic and other characteristics;

2) production and technological, which characterize mainly the manufacturability of the design of the machine and its elements;

3) economic, which characterize the cost of manufacture, operation and repair of the machine.

The quality of the workpiece in most cases is assessed by its accuracy and the quality of the surface layer.

2.4.1 Workpiece accuracy

Under workpiece accuracy its compliance with the requirements of the drawing and technical conditions for its manufacture is understood. The deviation of a real workpiece from the requirements of the drawing (or standard) is called error. Errors are inevitable at all stages of the manufacture of the workpiece, so it is almost impossible to produce an absolutely accurate workpiece.

The accuracy of blanks is characterized by both geometric (shape and size deviations) and physical and mechanical properties (for example, strength, hardness, elasticity, electrical conductivity, etc.). The first group of indicators was studied in the course "Interchangeability, standardization and technical measurements". The second group is ensured by the correct choice of material and the stability of the blank manufacturing technology.

For each method of manufacturing blanks, a distinction is made between achievable and economic accuracy. The accuracy that can be achieved in this type of production by a highly skilled worker under the most favorable conditions is called achievable. Economic Accuracy achieved with this technological method under normal production conditions. When designing technological processes, the technologist should focus on the average economic accuracy, which is stipulated in reference literature.

2.4.2 The quality of the surface layer of blanks

The quality of the surface layer of workpieces is the totality of all the service properties of the surface layer of the material as a result of the impact on it of one or several successively applied technological processes. The surface layer of the blank is qualitatively different from the material of the core of the blank.

The quality of the surface layer is characterized by two groups of parameters: geometric(waviness, roughness, submicroroughness) and physical and mechanical(chemical composition; microstructure; microhardness; magnitude, sign and depth of propagation of residual stresses, etc.).

The quality of the surface layer is determined by the properties of the material and the manufacturing technology of the workpiece. For example, after hot stamping, there will be scale on the surface of the workpiece. The surface roughness of the blank obtained by cold stamping is significantly lower than that of the blank obtained by hot stamping, but its surface layer has a work hardening. If the workpiece has undergone chemical-thermal treatment, its surface layer has a different chemical composition and structure than the base.

The geometric parameters of the quality of the surface layer and the accuracy of the workpiece are interrelated in a certain sense. For example, if the billet is produced by casting into sand molds, then micro- and macro-roughnesses do not allow obtaining high dimensional accuracy. When choosing the type of workpiece and the technology of its production, it is necessary to know the accuracy and quality of the surface layer of the workpiece, which can be obtained in this case.

2.5
Manufacturability of blanks

2.5.1 Basic concepts of manufacturability

Manufacturability of the product design, according to GOST 14.205-83, is a set of design properties that determine its adaptability to achieve optimal costs in production, operation and repair for given quality indicators, output volume and work conditions. Manufacturability testing is mandatory at all stages of product creation.

Manufacturability issues must be addressed in a comprehensive manner, starting from the stage of designing a workpiece and choosing a method for its manufacture and ending with the process of machining and assembling the entire product. A workpiece worked out for manufacturability should not complicate subsequent machining. Manufacturability, as a rule, is laid down at the design stage, therefore a high level of technological training is required from the designer.

Manufacturability is a relative concept. One design of the workpiece can be manufacturable for a given type of production and completely non-technological for another. Manufacturability also depends on the production capabilities of a given enterprise (factory). The development of the production base of the enterprise (for example, the introduction of CNC machines, automated equipment) changes the requirements for manufacturability. production workpiece manufacturability

The procedure and rules for ensuring manufacturability are established by state standards. Modern trends are that the development of a design for manufacturability is increasingly shifting to the stage of development of design documentation. This requires business and creative cooperation of designers and technologists both in choosing the type of workpiece and in developing the technology for its subsequent processing.

2.5.2 Manufacturability indicators

There are two types of manufacturability indicators: qualitative and quantitative.

Qualitative assessment("good - bad", "permissible - unacceptable") is obtained by comparing two or more options for blanks. The criterion in this case is the reference data and experience of the technologist and designer. Usually such an assessment is made at the stage of preliminary design and always precedes a quantitative assessment.

Quantitative indicators make it possible to objectively and fairly accurately assess the manufacturability of the compared structures. The choice of indicators depends on the purpose of the part (blank), type of production and operating conditions. For each detail, choose their own, the most characteristic indicators. In relation to blanks, the labor intensity of manufacturing, the technological cost and the metal utilization factor are most often used as indicators of manufacturability.

The complexity of manufacturing the workpiece represents the total time spent on the production of the workpiece for all technological operations. The components of the norms of time for the performance of work on individual operations are given in the relevant reference books.

In the early stages of design, approximate methods for estimating the complexity. For example, the "weight method" labor intensity is estimated by the labor intensity of a typical workpiece, similar in shape, accuracy and manufacturing technology:

where T etc, T type - the complexity of the designed and standard blanks, respectively; G etc, G type - the mass of the designed and standard blanks, respectively.

To assess manufacturability, the ratio of the labor intensity of machining to the labor intensity of obtaining a workpiece is also used T fur / T zag. The smaller this ratio, the more technologically advanced the workpiece (the volume of machining is reduced). Attitude T fur / T zag also depends on the type of production (for a single production it is maximum).

Technological production cost It is used to select the best variant of the procurement in the conditions of one production method (workshop, plant). In general terms, for one part, it consists of the following elements:

C etc. = M + 3 + I.o + C about, (2.2)

where M is the cost of consumable basic materials, rubles / piece; 3 - wages of production workers, rubles / piece; And acting - compensation for wear and tear of equipment, rubles / piece; C about - the costs associated with the maintenance and operation of equipment during the manufacture of one part, r./pc.

All cost elements are interconnected. For example, a change in the type of workpiece causes a change in the cost of machining. A change in the structural material may cause a change in the range of process equipment. From the compared options, choose the one for which the technological cost is minimal, regardless of the individual components.

Metal utilization rate- this is a dimensionless quantity, determined by the ratio of the mass of the product to the mass of the consumed metal:

TO i.m =G d /G p , (2.3)

where G d is the mass of the finished part;

G p - the mass of the entire metal used, including the mass of sprues, flash, scale, rejects, etc.

Distinguish coefficient K c.g metal output, suitable in procurement workshops, and weight accuracy factor K w.t.:

TO c.g = G s / G p, (2.4)

where G 3 - mass of the workpiece;

K w.t = G d / G s. (2.5)

Ceteris paribus, higher values ​​are more favorable. K them. To assess the effect of workpiece manufacturability on the metal utilization factor, it must be remembered that

TO i.m = TO c.g TO v.t. (2.6)

2.5.3 Ensuring the manufacturability of blanks at the design stage

The task of ensuring the manufacturability of blanks should be solved taking into account the interaction of all services of the plant (designers, technologists, workers technical supply etc.) and specific production conditions (availability of certain equipment, materials, areas at the plant). Ways to improve manufacturability largely depend on the type of production, batch size, type of workpiece and other factors. Therefore, only some recommendations for improving the manufacturability of blanks are given below.

1. It is desirable that the outlines of the workpiece are a combination of the simplest geometric shapes.

2. The shape and dimensions of individual elements of the workpiece (fillets, slopes, etc.) must be unified.

3. Dimensional accuracy and surface roughness of workpieces must be economically justified.

4. It is desirable to use as much as possible methods for obtaining blanks that do not require subsequent chip removal (Fig. 2.2).

5. If it is impossible to do without mechanical processing, it is necessary to strive to reduce it as much as possible by reducing the number and length of the processed surfaces (Fig. 2.3).

The design of the part should allow for the possibility of its manufacture as a composite of two or more parts (Fig. 2.4).

Rice. 2.2. Stud made by cutting (o) and rolling (b)

Rice. 2.3. Examples of reducing the volume of machining by reducing the length of the machined surfaces (a) and reducing their number (b)

Rice. 2.4. One-piece (o) and composite construction (b) details

test questions

1. What is a blank? How are blanks classified?

2. What is overlap and allowance; in what cases are they appointed and how are they determined?

3. How does the material affect the choice of how to obtain the workpiece? Give examples.

4. What types of indicators characterize the quality of the workpiece?

What is the achievable and economic accuracy of a workpiece? How does the specified accuracy affect the cost of the workpiece and finished part?

What is meant by the quality of the surface layer of the workpiece and what factors affect it?

7. What is meant by workpiece manufacturability and by what indicators is it evaluated?

8. How is the manufacturability of blanks ensured at the design stage?

All types and grades of materials that make up the finished machine-building product, before turning into it, undergo a series of successive structural and parametric transformations during the production process. In the general case, the scheme for the transformation of raw materials into a finished product is shown in Fig. 6.1.

Rice. 6.1.

The processes of obtaining blanks are closely related to the subsequent dimensional processing. The labor intensity of the latter largely depends on the accuracy of the workpieces and the approximation of their configuration to the configuration of finished parts. Therefore, mechanical engineering technology is developing in the direction of an integrated process for manufacturing parts, including the preparation of a workpiece and subsequent dimensional processing. The maximum approximation of the geometric shapes and dimensions of the workpiece to the dimensions and shape of the finished part - the main task prefabrication production.

The definition of the concept of a part and an assembly unit was given in Ch. 2. Let us supplement them with the concepts of a semi-finished product and a blank.

Semifinished- a structural material that has passed one or more stages of processing (sheet, pipe, rod, profile, etc.), intended for the manufacture of blanks and parts. A semi-finished product is an intermediate link in the chain from materials to finished products.

blank- a subject of production, from which, by changing the shape, size, properties of the surface or material, the structural elements of the product are made. Parts blanks include: casting, stamping, rolling, forging, etc.

The procurement processes for converting semi-finished products into blanks include: cutting, cutting, straightening, etc.

Edit- an operation associated with the elimination or reduction of local and general deformations of the workpiece. Rolled steel straightening precedes its cutting into cut-to-length billets, which in some cases are also straightened. Editing reduces the allowance for subsequent machining of the workpiece. It is performed on straightening rolls, presses, stretching straightening machines, straightening and sizing machines, etc. (Fig. 6.2).

Rice. 6.2.

but - for a bar, pipes; b - for sheet

Shown in fig. 6.2, but the machine is designed for straightening any bar: cold-drawn, hot-rolled, smooth or corrugated, as well as cutting it to size. On fig. 6.2, b shows a machine for straightening large-sized sheet material.

cutting rolled blanks are usually carried out along the stop on band saws, cutting hacksaws, circular saws, etc.

At present, the average labor intensity of procurement work in mechanical engineering is 40–45% of the total labor intensity of the production of mechanical engineering products. The main trend in the development of blank production is to reduce the labor intensity of mechanical processing in the manufacture of machine parts by increasing the accuracy of their shape and size.

The choice of a rational type of blanks (material, method of manufacture, constructive form) is one of the most important factors in the struggle for the economical use of machine-building materials and the reduction in the cost of parts. It is determined by the functional requirements for the part, the nature of production, and economic feasibility. There is a universal technological classification of methods for manufacturing blanks and parts, which allows, as a first approximation, to start choosing.

Based on the structural forms, overall dimensions, grade of material and the required number of manufactured parts per unit of time, the method for obtaining the workpiece is determined. In this case, they are based only on the technological properties of this material, such as the possibility of casting, stamping, compressibility, weldability, machinability. The choice of the method for obtaining the workpiece is schematically shown in Fig. 6.3.

Rice. 6.3.

In the process of manufacturing blanks and parts, different kinds energy: mechanical, thermal, acoustic, electrical, magnetic, light, chemical, radiation, etc. and their combinations: electromagnetic, electrothermal, electrochemical; thermomechanical, etc.

The energy fields used are divided into stationary and non-stationary, wave, impulse, etc.

Machining allowance- this is a layer of material removed from the surface of the workpiece in order to obtain the shape and dimensions of the part required according to the drawing. Allowances are assigned only to those surfaces whose required shape and dimensional accuracy cannot be achieved by the accepted method of obtaining a workpiece.

Allowances are divided into general and operational. General allowance for processing is a layer of material necessary to perform all technological operations performed on a given surface. One-ration allowance - this is a layer of material removed during one technological operation.

The allowance is measured along the normal to the surface in question. The total allowance is equal to the sum of the operating ones. As an example, in fig. 6.4 shows the total allowance for the processing of blanks (rolled products, forgings, castings).

Rice. 6.4.

but - from rental; b - forgings; in - castings

In addition to the allowance, blanks are often formed with an overlap.

lap- this is an excess of material on the surface of the workpiece in excess of the allowance, due to technological requirements to simplify the configuration of the workpiece to facilitate the conditions for its production. In most cases, it is removed by subsequent machining, less often it remains in the part, for example, in the form of stamping slopes, increased rounding radii, etc.

All blanks, regardless of the methods of their production, must have a minimum allowance, and therefore, their geometric dimensions must approach the geometric dimensions of the finished parts, but at the same time ensure the quality specified in the working documentation (in terms of dimensions and surface roughness). Providing a minimum allowance increases the utilization of the material and reduces the complexity of further processing.

Blanks in the process of their formation must also meet the following requirements:

• the chemical composition, structure and grain size of the material must be the same throughout the volume of the workpiece to ensure the stability of the mechanical and physical properties of the material of the workpiece;
• all surfaces must be free of pits, cracks, junctions and mechanical damage that could lead to the release of low-quality parts;
• the surfaces used as bases in the first operation of their processing must be clean, free of burrs, sprue residues, profits, scale and other defects, otherwise this will lead to significant installation errors during further processing or assembly;
• all internal stresses must be removed through the use of heat treatment (firing).

It is expedient to use combined methods for the manufacture of complex and large workpieces. Usually they are divided into separate elements, manufactured by progressive methods, followed by their connection by welding or soldering. Examples of blanks: stamped elements connected by spot or seam welding or soldering into one complex blank; elements obtained by gas cutting from rolled sheets (or castings), connected by seam welding into large-sized blanks (fundamental rings of hydraulic turbines, frames of stationary internal combustion engines); stamped or machined blanks cast into one complex blank (diaphragms steam turbines with filled blades); medium-sized castings connected by thermite welding into one large and complex workpiece.

Fundamentals of technology in mechanical engineering

In mechanical engineering, three main technological stages should be distinguished:

Billet production carried out in two ways:

plastic deformation method;

casting method.

Production of blanks by plastic deformation methods. Various blanks are used to obtain parts. Metal blanks are made by casting, rolling, forging, stamping and other methods.

Plastic deformation methods are used to produce workpieces from steel, non-ferrous metals and their alloys, as well as plastics, rubber, many ceramic materials, etc. The widespread use of plastic deformation methods is due to their high productivity and high quality of manufactured products.

An important task of the technology is to obtain blanks that are as close as possible in shape and size to the finished parts. Workpieces obtained by plastic deformation methods have minimal machining allowances, and sometimes do not require it at all. The structure of the metal workpiece and its mechanical properties after plastic deformation are improved.

Metal forming is based on plastic deformation. This method is used to produce blanks and products weighing from several grams to hundreds of tons from metals and alloys. Metal forming includes: rolling, forging, stamping, pressing and drawing. This is one of the progressive and widespread methods for obtaining blanks for machine parts.

Metal forming is based on the plasticity of the material being processed. Plasticity is the ability of a material to change its shape irreversibly and without collapsing under the influence of external forces. When processing by pressure, the shape of the workpiece changes without changing its mass. Only those materials that have plasticity in a cold or heated state can be subjected to pressure treatment. For example, cast iron cannot be pressure treated. The plasticity of alloys depends on their composition, deformation temperature (the higher the temperature, the greater the plasticity; however, the deformation temperature should not exceed 0.4 Tm), the degree of deformation (with increasing degree of deformation, the plasticity decreases).

Plastic deformation of solids occurs as a result of the displacement of atoms along the crystallographic planes, in which the largest number of atoms is located. As a result of distortion of the crystal lattice - hardening during deformation in a cold state - the properties of the crystal change: hardness, strength, brittleness increase; reduced plasticity, viscosity, corrosion resistance, electrical conductivity. To restore the plastic properties, to eliminate hardening, decrystallization annealing is performed, after which the material acquires its previous properties. In this case, the material from the unstable state of hardening gradually passes into a stable, equilibrium state.

Rolling is the most common forming method. About 90% of all steel being smelted and most of the non-ferrous metals and alloys are subjected to rolling. The essence of rolling is the plastic deformation of the workpiece between the rotating rolls of the rolling mill.

Rolled metal is used directly in the construction of machines, equipment mechanisms, it is used to make metal constructions bridges, trusses, beds, riveted and welded products, reinforced concrete structures, etc.; it also serves as a blank for machine shops, as well as for subsequent forging and stamping.

The geometric shape of the cross section of a rolled product is called its profile, the set of profiles of different sizes is called the assortment. The range of rolled products is very diverse and is divided into five groups:

1. Long products, which are divided into two subgroups:

a) profiles of a simple geometric shape (rectangle, square, circle, etc.);

b) profiles of complex shaped geometric shapes (channel, rail, I-beam, etc.).

2. Sheet metal, which is also divided into two subgroups:

a) thin sheet (for steel with a thickness of 0.2 - 4 mm; for non-ferrous metals - 0.05 - 2 mm);

b) thick sheet (4 - 60 mm for steel and up to 25 mm for non-ferrous metals). Sheet metal with a thickness of less than 0.2 mm is called foil.

3. Pipe rolling is divided into:

a) seamless pipes (for steel with a diameter of 30 - 650 mm);

b) welded pipes (for steel with a diameter of 10 -1420 mm).

4. Periodic rental. The profiles of this group of rolled products are a blank, the geometric shape and cross-sectional area of ​​​​which periodically changes along its length. Periodic rolling is used as a blank for subsequent stamping.

5. Special rental. This includes wheels, rings, tires, ball bearings and other finished products.

The main technical and economic indicators of rolling production include: metal consumption per 1 ton of finished products; hourly productivity of the rolling mill; rolling speed; total power of the main drives (kW); output per unit of power of the main drives; yield of good rolled products (%); fuel consumption per 1 ton of suitable rolled products (thousand cal.), energy (kWh); product quality; the cost of production by types of assortment; labor productivity. These technical and economic indicators characterize the presence and use of labor tools - the main one in its value and specific gravity part of the fixed assets of the enterprise. Metal consumption per 1 ton of products is calculated by the formula:

where a, b And c- loss of metal during rolling, respectively, for waste, cutoffs and scrap, t;

G- weight of finished rolled products, t;

K p-expenditure coefficient characterizing the amount of metal consumed per 1 ton of suitable rolled products.

Rolling speed can be determined by the formula:

where D is the diameter of the rolls, mm;

n is the number of revolutions of the rolls per minute.

Rolling mill hourly output R:

where 3600 is the number of seconds in 1 hour;

T- rolling period, s;

IN- mass of ingots, t.

In the structure of the cost of rolling production, about 90% are the costs of metal. From this we can conclude that the most effective factors for reducing the cost of production in the rolling industry are: reduction of metal losses in processing stages; production of rolled products with minus deviations; decline in marriage recycling of waste.

Forging and die forging are widely used metal forming methods. These are methods of manufacturing products called forgings. Forging is the only possible way to manufacture large items weighing more than 250 tons, such as hydro generator shafts, turbine disks, ship engine crankshafts, rolling mill rolls, etc.

Forging is called "free" because the metal, plastically deformed under the action of the strikers of a hammer or press, moves freely in the direction where it experiences the least resistance.

Special Shapes not used for forging. The billet, which is an ingot, profile or periodic rolling, is placed on a slab (anvil). The alternation in a certain sequence of main and auxiliary operations is the free forging process. Free forging operations include: upsetting, piercing, broaching, bending, cutting, twisting, etc.

When receiving products by volumetric stamping, special equipment is used - stamps. Stamps are a metal mold that has a cavity, the dimensions and configuration of which correspond to the dimensions and configuration of the future part.

Forging has a number of advantages over forging. Die forging can produce forgings of complex configuration, higher dimensional accuracy and surface quality. The machining allowance is significantly (3-4 times) lower than for forging, and, consequently, there is less metal loss into chips and less volume of subsequent processing. In addition, stamping is many times more productive than forging. Therefore, it is more economically expedient to use volumetric stamping in serial and mass production.

The maximum weight of forgings obtained by die forging is 3 tons.

In addition to volumetric stamping, there is a sheet. The initial workpiece for sheet stamping is sheet metal. For the manufacture of parts from thin-sheet rolled products, cold stamping is used, with a thick-sheet initial workpiece (more than 10 mm thick), hot stamping is used.

Sheet stamping produces a wide range of parts such as washers, rings, cups, brackets, bushings, fasteners, car lining, etc. from mild, stainless and other steels; as well as from alloys based on copper, aluminum, magnesium, etc. Sheet forging operations include: cutting, cutting along the contour, punching holes, bending, drawing, crimping, flanging, etc.

The advantages of sheet stamping are: high productivity (30,000 - 40,000 parts per shift from one stamp), high dimensional accuracy and surface quality of the parts obtained, wide possibilities for process automation.

The process of drawing also belongs to the processing of metals by pressure. Drawing is the process of plastic formation of the workpiece by pulling it through the hole of the drawing die or drawing board of the drawing bench. As a result, the workpiece to be processed acquires a cross section, the size and shape of which corresponds to the size and shape of this hole.

The initial workpiece for drawing is rolled and extruded metal. Drawing is a cold type of pressure treatment, during which the workpiece is hardened. To remove hardening, decrystallization annealing is carried out. By drawing a wire with a diameter of up to 0.001 mm, bars of various profiles are obtained.

Technological processes for obtaining blanks by casting methods. Casting is one of the most important and widespread methods of manufacturing blanks and machine parts. Casting receive blanks of various configurations, mass sizes from various metals and alloys - cast iron, steel, aluminum, copper, magnesium and other alloys.

Casting is the simplest and cheapest, and sometimes the only way to obtain products.

The casting process consists in the fact that the molten metal is poured into a pre-prepared casting mold, the cavity of which, in size and configuration, corresponds to the shape and dimensions of the future workpiece. After cooling and solidification, the workpiece (or part) is removed from the mold. Foundry products are called castings.

Molds can be single (for the manufacture of one casting) and permanent (multiple use).

To obtain high-quality castings, casting alloys must have certain properties: good fluidity, low shrinkage, low segregation (heterogeneity of the chemical composition of the alloy and structure along the thickness of the casting).

Depending on what form (permanent or one-time) the metal is poured into and how the pouring takes place, there is one or another casting method. At present, up to 60% of iron and steel castings are produced by casting into sand-clay molds. To obtain castings of high dimensional accuracy, good quality surfaces and the best structure of the metal, special casting methods are used (in a chill mold, under pressure, by a centrifugal method, according to investment models, etc.).

The technological process of obtaining castings in sandy-clay disposable molds includes a number of lengthy operations associated with the preparation of molding and core sands, the manufacture of pattern equipment, cores, their drying, molding, etc. Despite the fact that at present the labor-intensive operations of this method are mechanized and automated, it still remains a relatively low-productivity and labor-intensive casting method. Therefore, casting in sand-clay molds is mainly used in single and pilot production, as well as in cases where the product is impossible or difficult to obtain by other methods.

At enterprises producing castings in mass quantities, automatic and semi-automatic production lines have been created. The disadvantage of casting in sand-clay molds is also the low dimensional accuracy and poor surface quality of the castings, which necessitates mandatory subsequent machining. And this leads to the loss of metal in chips and lengthens the technological cycle of manufacturing the product.

Die casting is one of the most common methods for obtaining castings in metal permanent molds. The chill mold is made of cast iron, steel, aluminum. By design, chill molds are one-piece and detachable.

Detachable molds, consisting of two parts with a horizontal or vertical parting plane, are most widely used. To increase labor productivity during mold casting, multi-position carousel-type machines are used, at a certain position of which one of the operations is sequentially performed.

The advantages of die casting compared to sand-clay casting are: higher dimensional accuracy and surface quality of castings; better mechanical properties, which is associated with an increased cooling rate of the casting and obtaining a finer structure; higher performance.

Injection molding is a high-performance method for obtaining castings of high dimensional accuracy from non-ferrous metal alloys (aluminum, zinc, copper, magnesium). The essence of the method is to fill a metal mold with molten metal under piston pressure.

Castings are produced on semi-automatic injection molding machines. Piston machines with a hot cold (horizontal or vertical) pressing chamber are used. Hot chamber reciprocating machines are used to make small castings from magnesium and zinc alloys. Cold chamber machines are mainly used for casting body parts from aluminum and copper alloys.

Centrifugal casting is a productive method for manufacturing castings with surfaces of bodies of revolution, with a central hole - pipes, bushings, etc., as well as shaped casting parts.

The essence of the method is to fill a rotating mold with molten metal. Under the action of centrifugal forces, the liquid metal is thrown to the walls of the mold and solidifies. The result is a dense casting structure without shrinkage cavities. Non-metallic inclusions collect on the inside of the casting and elongate during further machining.

Castings from cast iron, steel and non-ferrous metals and alloys are made by centrifugal method on centrifugal casting machines with horizontal and vertical axis of rotation. Small-height shaped castings are produced on machines with a vertical axis of rotation. On machines with a horizontal axis of rotation, cast-iron and steel pipes, bushings and other parts with a hole are made.

The advantages of centrifugal casting are: high productivity, cost-effectiveness (no expenses are required for the preparation of the molding sand, the manufacture of cores, etc.) and the quality of the resulting castings.

Investment casting is used to obtain castings of high dimensional accuracy and surface quality from any casting alloys. With its help, it is possible to obtain products of complex configuration with thin sections. However, the technological process of this casting method is characterized by high labor intensity and high cost of the materials used. The investment casting process includes the following operations:

Making a model - a casting standard from an easily machined alloy (aluminum);

Making a mold according to a metal standard, in which a model is pressed from low-melting materials (paraffin, stearin, polystyrene, wax, etc.);

Manufacture of the shell by repeated application of a refractory composition to the model - a ceramic suspension with quartz sand, followed by drying (hot air treatment) at a temperature of 150 - 200 ° C to remove the fusible model;

Calcination of the resulting mold in a furnace at 800-850 °C; form filling.

The casting is cleaned from the remnants of the ceramic coating by leaching followed by washing in hot water. The high cost of castings obtained by this method makes it possible to use this method only for the manufacture of products of a particularly complex configuration from hard-to-machine and refractory materials in mass or large-scale production.

Shell casting is used in mass and large-scale production for the manufacture of shaped castings from steel, cast iron, aluminum and copper alloys.

The essence of the method is that a molding sand (quartz sand and 6–7% bakelite synthetic resin) is poured onto the surface of a metal model preheated to 200°C, attached to a model plate, then they are all calcined together at a temperature of 300°C for 1 - 2 min. The resin melts and hardens irreversibly, forming a sand-resin shell 5 - 8 mm thick.

Shell half-moulds are assembled, fastened and filled with liquid metal. These half-moulds are made on one-, two- and four-position machines with semi-automatic or stomatic control.

Casting in shell molds ensures high dimensional accuracy of the casting, low surface roughness, and high-quality metal structure. To select a casting method when receiving blanks, it is necessary to take into account all the factors that affect the technical and economic indicators of the process.

Workpiece processing It is carried out mainly mechanically and, regardless of its type, consists in removing an excess layer of metal from the treated surface.

Machining. Technological process of processing construction materials cutting consists in removing a metal layer (machining allowance) from a workpiece with a cutting tool to give it (the workpiece) the required dimensional accuracy and surface quality. Steel, non-ferrous metal alloys, plastics, ceramics, composite materials, rubber, wood, glass, etc. are widely used as structural materials.

Processing of workpieces of machine parts by cutting is carried out in the mechanical shops of machine-building plants. Blanks for machine shops are: rolled products (round, square, strip, etc.), forgings, stampings and castings.

The choice of workpiece depends on the material, size and shape of the part, its working conditions, type of production. When designing a machine, the designer determines the type of the most rational workpiece, as close as possible in shape and size to the finished part, since the size of the allowance for subsequent machining affects labor and financial costs in the manufacture of the part as a whole. Reducing the amount of allowance for machining is one of the most important factors in increasing labor productivity in mechanical engineering.

Among the main indicators of the quality of a part in mechanical engineering are its dimensional accuracy and surface roughness, since these indicators significantly affect the nature of dynamic processes in the machine and its mechanisms, especially if the machine operates at high speeds, at high workloads, temperatures, etc. The reliability and durability of the product depend on the accuracy of processing the quality of the surface of parts.

The accuracy of machining parts is the degree to which the shape, dimensions and position of the machined surface correspond to the requirements of the drawing and specifications.

The surface quality of the parts is determined by the combination of microroughnesses on the surface of the parts, as well as the physicochemical properties of the surface layer of the part.

The main methods of material processing by cutting are: turning, planing, drilling, milling and grinding.

First, the workpiece is fixed in a certain way on the machine. Then a cutting tool (cutter, drill, cutter, grinding wheel, etc.) is brought to it, which removes a layer of material from the workpiece - an allowance. Moreover, no matter what tool is used for cutting, the essence of the process remains unchanged, only the processing conditions change.

The essence of the cutting process lies in the occurrence of elastic-plastic deformations under the action of the cutting tool, as a result of which the plastically deformed layer of metal cut off is separated in the form of chips.

Thus, for the implementation of the cutting process, it is necessary to have relative movements between the tool and the workpiece, which are called cutting movements. The process of machining parts by cutting is characterized by the elements of the cutting mode, the main of which are cutting speed, feed and depth of cut.

The elements of the cutting mode for turning are: cutting speed V - the path traveled by the machined surface of the workpiece per unit time:

( m/min),

where D- workpiece diameter, mm;

P- the number of revolutions of the workpiece per minute.

Submission - path traveled cutting blade cutter relative to the machined surface of the workpiece in one of its revolutions S, mm/rev.

Depth of cut - the thickness of the cut metal layer from the machined surface of the workpiece in one pass of the cutter, mm:

where D- diameter of the processed surface of the workpiece, mm;

d- diameter of the machined surface of the workpiece, mm.

The time during which the machining allowance is removed is called machine or main time Tm:

where L- tool path in feed direction, mm;

P- the number of revolutions of the workpiece per minute;

S- the amount of allowance for machining, mm;

t- cutting depth, mm;

h- machining allowance, mm.

Reduction of machine time due to the reduction of values L, h or increase the parameters of the cutting process n,S,t is an important factor in increasing labor productivity.

The time required for processing one workpiece Tsht (piece time):

where T m - machine time;

T in- auxiliary time required for installation and removal of the workpiece, supply and withdrawal of tools, etc.;

T about- time of maintenance of the equipment of the workplace, maintenance of tools and devices in working condition;

T p- the time of breaks for rest of the worker, related to one workpiece.

decline T m And T wt leads to increased productivity.

Turning- the process of processing metals by cutting the outer, inner and end surfaces of bodies of revolution of cylindrical, conical, spherical and shaped shapes, as well as the process of cutting external threads on workpieces, boring holes.

Turning tools are turning tools. The types of turning are as follows:

Rough turning - peeling, cutting off and trimming the ends of the workpiece; semi-finish turning;

Fine turning;

Fine turning;

Boring.

Planing- a rough low-performance type of machining with a large thickness of the cut metal layer.

This method mainly processes large heavy workpieces and planes horizontal and inclined planes, shaped and cylindrical surfaces of keyways. Tool - planing cutters.

drilling blind and through holes are obtained in a solid material, and pre-formed holes are machined to increase their size, improve accuracy and reduce surface roughness. In addition, threading is performed in the holes. Drilling tools are: drills, countersinks, reamers, taps, etc.

Milling- a high-performance cutting method carried out with a multi-blade tool called a milling cutter. Milling is used for both coarse and fine machining. This method processes the horizontal planes of workpieces, vertical planes, combined surfaces, ledges and rectangular grooves, shaped grooves and shaped surfaces.

grinding is the process of machining the surfaces of parts with abrasive tools. The removal of the allowance from the workpiece during grinding is carried out by a huge variety of miniature cutters - abrasive grains connected by a bond (grinding wheel) so that there is space between them to accommodate chips.

The grinding process is characterized by high cutting speeds and a small thickness of the cut metal layer. Each grain of the grinding wheel cuts off very thin chips, but since a large number of grains are involved in the work at the same time, and the cutting speed is high, a large amount of metal is cut off per unit time.

A large amount of heat is released in the cutting zone, and fine particles of the material being processed, when burned, form a beam of sparks.

Grinding is a finishing method of processing that allows achieving high dimensional accuracy of the part and low roughness of the machined surface. In many cases, grinding is an operation that is difficult to replace with any other processing.

For example, processing of hardened steels, iron castings, cleaning of rolled products, final processing of workpieces with a minimum allowance for machining without pre-treatment with a blade tool is carried out by grinding.

assembly production - the final stage of machine-building production, in which the results of all previous work done by designers and technologists to create machines or mechanisms are accumulated.

The performance of the product, its reliability, performance and durability depend on the quality of the assembly. In a number of cases, assembly is the most labor-intensive process: for many machines, instruments, and devices, the assembly labor intensity is from 40 to 60% of the total manufacturing labor intensity. The technological assembly process consists in the coordination and subsequent connection of parts into assembly units, mechanisms, machines as a whole in accordance with the technical requirements.

Detail is the simplest assembly unit. A characteristic feature of the part is the absence of any connections: the part is made from a single homogeneous piece of material. Two or more parts connected to each other in some way form node.

The node included directly in the product is called a group. A node included in a group is called a subgroup of the first order, and a node included in a subgroup of the first order is called a subgroup of the second order, and so on. The product, depending on its complexity, can be divided into a greater or lesser number of assembly units.

The initial data for the design of the assembly process are the following documents:

Assembly drawings of the product with a specification of assembly units and parts arriving for assembly;

Specifications for acceptance and testing of products;

Manufacturing program.

All operations of the assembly process are divided into:

Preparatory - associated with the re-preservation of parts, their cleaning, supply to the assembly site;

Actually assembly operations - coordination of parts relative to each other, contact with their base planes, connection into nodes, groups, mechanisms, products;

Auxiliary operations - fitting, adjustment;

Control and testing.

Assembly work is carried out at the assembly sites and in the assembly shops of factories. Features of manufactured products, labor intensity, duration of the production cycle, production volume are the determining factors in the organization of the assembly process. In single and small-scale production, assembly is carried out in assembly shops, assembly areas; in mass production - on-line or conveyor lines. Assembly in mass production is characterized by complete interchangeability, the absence of finishing work and the selection of parts, which creates the conditions for automating the assembly and increasing its productivity.

The main types of assembly are: stationary assembly and movable assembly.

At stationary assembly the product is stationary, and the assembler teams move from one product to another and perform assembly operations. All parts and components in accordance with the assembly kit are supplied to the workplace. At mobile assembly of products are forcibly moved from one post to another, each of which performs a certain assembly operation. The movement of the product can be continuous or intermittent. With the continuous movement of the product, the assembler performs the operation during the movement of the conveyor, the speed of which must ensure the execution of the assembly operation at this workplace and correspond to the assembly (release) cycle: t in \u003d t 0. With periodic movement, the assembly operation is performed while the conveyor is stopped. Stop duration tr should correspond to the time of the assembly operation. The build cycle in this case: t B = t p + t n , where tp- the time of moving the product from one workplace to another.

From point of view organizational forms assembly is divided into concentrated and differentiated.

When assembled according to the principle of concentration operations, the entire technological process of product assembly is performed by one assembler or one team of assemblers. This is a low-productivity assembly process that requires a high qualification of the assembler, a large number of complex tools and fixtures. It is used in single and pilot production, in the assembly of unique products.

Differentiated Assembly subdivided into general and nodal. When assembling according to the principle of differentiation of operations, the assembly of a unit or machine is carried out at several workplaces, to which assembly units are supplied. Movable differentiated assembly is used in series and mass production.

To assess the technical and economic efficiency of the assembly process, the following indicators are used:

1. Productivity of the workplace - the number of units or products assembled in 1 hour:

where t sat- the time limit for the assembly operation.

2. The amount of costs for the assembly process of a unit or product (shop cost From Sat):

where C o- the costs associated with the performance of one operation;

m- the number of assembly operations.

The cost of performing one operation includes:

main wages collectors for this operation;

Deductions for depreciation of equipment, fixtures, tools related to one operation;

Shop overheads, also charged to one operation.

3. Assembly labor intensity factor - By Sat, which is equal to the ratio of the complexity of assembly t sat to the complexity of manufacturing parts included in this product t out:

where t c6- time spent on assembling a unit or product;

t ed.- the time spent on the manufacture of parts for this unit or product for all types of processing, starting from the workpiece.

The lower this indicator, the more perfect the assembly process. Have the most efficient assembly processes By Sat ≤ 0,2.

A feasibility study of various assembly methods allows you to choose the most effective in economic terms process option. The efficiency of assembly operations, the quality of products and their cost largely depend on the design features of the assembled product and the degree of automation of the assembly process. Simplification of the design of the product while reducing its functional value, the use of universal self-adjusting automatic assembly machines with adaptive technological equipment for feeding, locating and aligning the relative position of various connected parts before they are assembled into a product are the main ways to improve assembly processes.

Classification of methods for obtaining blanks

There are four types of blanks in mechanical engineering - coiled (wire or tape rolled into a riot), bar (rods, strips, rods), piece (castings, forgings, piece from bars) and powder (pressed powders, granules, tablets) to obtain plastic, metal-ceramic and ceramic parts.

A very large number of parts can be obtained from long length coil blanks, a smaller number from bar blanks and only one part from piece blanks. Parts small in size and weight are expediently made from coil and bar blanks.To obtain a high material utilization rate, it is necessary to use piece blanks that are close in shape and size to the finished part. From powders and granules, piece blanks or finished parts are obtained, further processing of which is almost not required.

The main methods for manufacturing blanks are shown in Figure 1.

Choosing the right method for obtaining a workpiece means determining a rational technological process for obtaining it, taking into account the material of the part, the requirements for the accuracy of its manufacture, technical conditions, operational characteristics and serial production. Mechanical engineering has big amount ways to get details. The maximum approximation of the geometric shapes and dimensions of the workpiece to the dimensions and shape of the finished part is the main task of blank production. The shape, dimensions and brand of the material of the part specified by the designer largely determine the manufacturing technology. Thus, the choice of the type of workpiece occurs in the design process, since when calculating parts for strength, wear resistance, or when taking into account other indicators of operational characteristics, the designer proceeds from the physical and mechanical properties of the material of the part.

The cost of manufacturing a part is influenced by design, production and technological factors. The extent to which the influence of the factors of the first and second groups is taken into account in the workpiece makes it possible to judge the manufacturability of the workpiece.

Other casting methods are also used: continuous, electroslag, burning, melt stamping, etc.

Opportunities: blanks weighing up to 250 tons of a simple form; on hammers in backing rings and dies up to 10 kg, while the wall thickness of the workpiece reaches 3-2.5 mm, accuracy

Sheet forming operations include straightening (straightening), shaped (embossed) stamping, flanging, forming, crimping, distribution.

Metal alloys (steel of various grades, non-ferrous metal alloys, as well as bimetallic ones) and non-metallic materials (textolite, pressboard, rubber, felt) are produced by stamping methods. According to the type of blanks, metal materials can be divided into rolled (over 300 mm wide), tapes, sheets, strips, wire and round rolled products (in coils), bars and rolled products of various sections. Non-metallic materials are usually supplied in the form of sheets or strips.

In conditions of mass and large-scale production, it is economically feasible to obtain blanks that are closest in shape and size to finished parts. In this case, the cost of blanks increases, but the amount of machining is significantly reduced.

In conditions of single and small-scale production, workpieces are far in size and shape from the finished part, i.e., they have significant allowances for machining. Of the many possible ways to obtain the workpiece, it is necessary to choose the economically viable one.

The final choice of method is established on the basis of calculations:

• A) the cost of the method for obtaining initial blanks;
• B) the cost of the machining process itself.