Drawing up a technological map of the assembly of resistors. Rules for constructing technological assembly schemes. Designations of devices and devices
Modern electrical equipment in its work uses numerous technological processes that proceed according to various algorithms. An employee involved in its operation, maintenance, installation, adjustment and repair must have reliable information about all their features.
Providing ongoing events in a graphical form with the designation of each element in a certain, standard way, greatly facilitates this process, allows you to transfer the ideas of developers to other specialists in an understandable form.
Purpose
Electrical circuits are created for electricians of all specialties, have different design features. Among the methods of their classification, division into:
fundamental;
mounting.
Both types of schemes are interconnected. They complement each other's information, are performed according to uniform standards that are understandable to all users, and have differences in purpose:
circuit diagrams are created to show the principles of operation and interaction of the constituent elements in the order of their operation. They demonstrate the logic inherent in the technology of the applied system;
wiring diagrams are made as drawings or sketches of parts of electrical equipment, according to which the assembly and installation of the electrical installation is carried out. They take into account the location, layout of the components and display all the electrical connections between them.
Wiring diagrams are created on the basis of the circuit diagrams and contain all the necessary information for the installation of an electrical installation, including the implementation of electrical connections. Without their use, it is impossible to create high-quality, reliable and understandable for all specialists electrical connections of modern equipment.
The protection panel shown in the photograph is connected by numerous cables to measuring current and voltage transformers, power executive equipment, hundreds of meters apart. It is possible to assemble it correctly only according to a well-prepared wiring diagram.
How wiring diagrams are created
First, the developer creates a circuit diagram that shows all the elements he uses and how to connect them with wires.
An example of a simple connection of a DC motor to a power circuit using a contactor K, and two buttons Kn1 and Kn2 demonstrates this method.
Powerful power normally open contacts of the contactor 1-2 and 3-4 allow you to control the operation of the electric motor M, and 5-6 is used to create a self-retaining circuit of the A-B winding energized after pressing and releasing the Kn1 "Start" button with a closing contact 1-3.
Button Kn2 "Stop" with its NC contact removes power from the winding of the contactor K.
The positive voltage potential “+” is supplied to the electric motor through the wire marked with the number “1” and “-” - “2”. The rest of the wires are marked with the numbers "5" and "6". The way they are marked may be different, for example, with the addition of letters and symbols.
In this way, all the contacts of the windings, switching devices and connecting wires are shown on the circuit diagram. Other information necessary for the work may also be indicated.
After the circuit diagram is created, a wiring diagram is developed for it. It depicts the elements that are involved in the work. Moreover, both all existing contacts of switching devices, buttons (example Kn1 and Kn2), contactors and relays, and only those used in the case under consideration (example contactor K) can be shown to simplify perception.
All mounting units are numbered with an individual number assigned to each position. For example, our diagram shows:
01 - terminal block for connecting power circuits;
02 - motor contacts;
03 - contactor;
04 - button "Start";
05 - Stop button.
The contacts of buttons, relays, starters and all electrical elements of the circuit are numbered on the body of each device or indicated by a specific position in the technical documentation.
Images of wires are made with straight lines and marked in the same way as in the circuit diagram. In the considered version, they were assigned numbers 1, 2, 5, 6.
During the assembly of complex circuits, it is convenient to work immediately with wiring and circuit diagrams. They supplement general information that can be difficult to keep in memory.
At the same time, it should be understood that the ideas depicted on paper should be implemented on real equipment and just as well, clearly read, and be informative. For this purpose, any element is signed, marked, marked.
Designations of devices and devices
On the front side of the panels, control cabinets, inscriptions are made explaining to the operating personnel the purpose of each electrical device, and for switching devices - the position of the switching element corresponding to each mode.
Keys and buttons are signed according to the action, for example, "Start", "Stop", "Test". The signal lights indicate the nature of the acting signal, for example, "Blinker not up".
On the reverse side of the panel, against each element, there is a sticker (usually round) with a fraction indicating the mounting position according to the diagram above and a short designation according to the installation diagram below, for example, 019 / HL3 - for an alarm lamp.
Wire designations
When installing equipment, each end of the wire is put on tubing signed with light-resistant and indelible ink, indicating the accepted marking. They are connected to the indicated terminals. When only the numbers "0", "9" are found in the designation. “6”, then after them they put a dot, excluding the incorrect reading of the information when considering the inscription on the reverse side.
For simple equipment, this technique is sufficient.
On complex and branched systems add the return address of the end. It consists of two parts:
1. first, the numbering of the reference designation of the element connected on the reverse side is numbered;
For example, on terminal 2 of the Kn2 button, a wire with a cambric, signed 5-04-3, must be connected. This inscription is deciphered:
5 - wire marking according to the assembly and circuit diagram;
04 - the number of the mounting unit of the "Start" button;
3 - terminal No. Kn1.
The alternation sequence, as well as the use of brackets or other designation separators, may vary, but it is important to do it the same way in all sections of the electrical installation. Marking must be carried out in strict accordance with the working drawings and wiring diagram.
For information: earlier, the marking of the ends of the wires was performed:
putting on porcelain tips with the application of symbols with oil paints;
hanging aluminum tokens with minted information;
fixing cardboard tags with ink or pencil inscriptions;
in other available ways.
The wiring diagram can supplement or replace the wire connection table. She points out:
marking of each wire;
the beginning of its connection;
reverse end;
brand, type of metal, cross-sectional area;
other information.
Cable designations
A mandatory element of each electrical installation is a cable magazine created for each individual connection in complex areas or one common for several simple ones. It contains complete information about each cable connection.
For example, with sectioned power buses and switches that control the operation of 25 overhead power lines, a mounting connection is created for each overhead line. It is assigned an individual number, which is indicated in the documentation and on the equipment.
Line No. 19 from this outdoor switchgear is given an operational dispatching name for the main settlement of power supply and an installation designation, for example, 19-SL, which is affixed to all equipment, including the secondary cable networks of this overhead line at the substation.
In addition to the cable belonging to the line, in the cable magazine and on the equipment, its attribute is indicated by purpose, for example:
alarms;
blocking;
other secondary devices.
measuring circuits of current or voltage;
automation or control scheme;
When installing electrical circuits, cable lines of various lengths can be used. At the entrance to the panel or cabinet, their number can be quite large. All of them are marked at both ends, as well as at the transitions through the walls of the building and other building structures.
A tag is hung on the cable with information indicating its belonging, purpose, brand, composition of cores. When cutting it, each wire is marked. On the tips connected to the electrical circuit, information about the cable accessory, the number of the switched terminal on the terminal block and the designation of the chain is applied.
Free cable cores that are in reserve, as well as workers, must be called and marked. However, in practice this requirement is rarely implemented.
Features of the designation of individual elements on wiring diagrams
According to local conditions, they sometimes deviate from generally accepted rules, facilitate the drawing of diagrams and the installation of electrical circuits without compromising their reading from nature.
Most often this manifests itself when:
hinged mounting of parts directly on the contact outputs of relays and devices;
installation of short, clearly visible jumpers.
Hanging mounting
An example of installing diodes VD4 and VD5 in parallel with the terminals of the A-B windings of relays K3 and K4 is shown in a fragment of the wiring diagram.
In this situation, they are mounted directly, without marking and signatures.
Jumpers
The same fragment shows the installation of a jumper between the terminals of the same name A of the windings of the same relays.
The installation of electrical equipment is carried out according to the principle and wiring diagrams, created according to uniform rules. It must meet the requirements of visibility, accessibility, information content so that repairs and maintenance work are carried out quickly and efficiently.
Guidelines
To the laboratory work on the discipline
"Technology of mechanical engineering"
GOAL OF THE WORK
1. To study and practically master the methodology for developing the assembly process.
2. Draw up an assembly flow chart.
3. Develop a route assembly process
and set time limits for operations.
BASIC INFORMATION
Assembly- often the final stage of the production of a product, characterized by the complexity and variety of operations performed, high labor intensity and cost. The labor intensity of assembly work in various branches of machine and instrument making and in different types of industries is 20 ... 70% of the total labor intensity of manufacturing the product. Manual labor predominates in assembly shops. On average, about 25% of assembly work is mechanized, and the level of automation currently does not exceed 10 ... 15% of assembly work.
The initial data for the development of the technological process are as follows: assembly drawings of the product as a whole and its individual components with specifications and drawings of parts; technical conditions (technical requirements) for products and assemblies; the volume (quantity) of assembled products with an indication of the period of their release; production conditions for assembly work.
Assembly process development sequence:
1. Establish an appropriate organizational form of the frill, determine the tact and rhythm of the assembly, depending on the volume of the assembly.
2. Conduct a study of the product, technological control-analysis of assembly and working drawings of parts and specifications (technical requirements) from the standpoint of working out manufacturability.
3. Carry out a dimensional analysis of the assembled products and establish rational methods for ensuring the required accuracy of the closing links of the assembly dimensional chains.
4. Draw up diagrams of the general and nodal assemblies of the product. Determine the appropriate degree of division of the product into assembly units (assemblies) and the sequence of connection of all assembly units and parts.
5. Develop the assembly process. If necessary, it is divided into several operations. Set the content of operations and technological modes of assembly. The most productive, economical methods of connecting, checking the position and fixing the assembly units and parts that make up the product are determined, including methods for monitoring and testing the product.
6. Install (develop) the necessary equipment and equipment (devices, tools).
Perform standardization of assembly operations.8. Prepare technological documentation.
The study of the assembled product is completed by dividing it into assembly units (assemblies) and drawing up technological assembly schemes. The breakdown of the product into assembly units and the preparation of assembly diagrams are the initial and critical stages in the development of the ruffle technology. In a visual form, they reflect the composition and assembly route of the product as a whole and its component parts.
The basic principles that a technologist should be guided by when breaking down a product into assembly units and developing assembly schemes are as follows:
The assembly unit should not be too large in size and weight and consist of a significant number of parts and interfaces, but at the same time, excessive crushing into assembly units is also irrational;
An assembly unit must be singled out as a special unit if, in the process of its assembly, testing, running-in, special locksmith refinement, fitting, etc. is required;
The assembly unit, when subsequently mounted in the machine, should not be disassembled (if this cannot be avoided, then disassembly must be provided for in the technology);
Assembly units should also include fasteners, threaded connections in order to reduce the number of individual parts supplied directly to the overall assembly;
Assembly units should be approximately the same in terms of labor intensity;
The assembly should begin with the installation at the workplace (stand, conveyor) of the base part or the base assembly unit, to which the rest of the parts and assembly units will be sequentially attached;
The assembly should begin with parts that have dimensions that are included as constituent links in that dimensional chain, with the help of which the most important task is solved;
The assembly sequence is determined by the possibility and convenience of attaching parts;
Each previously mounted part or assembly unit should not interfere with subsequent assembly;
Parts or assembly units that perform the most critical functions or that are common links in parallel-connected dimensional chains should preferably be mounted first;
During the assembly process, it is necessary to ensure a minimum number of reinstallations.
Technological assembly schemes- this is a graphic representation of the corresponding assembly units and parts, presented in the order of their mounting (installation) in the assembled machine. Various options for drawing up assembly diagrams are possible. Let's consider one of them.
Graphically, on assembly diagrams (Fig. 1), product elements (parts, assembly units) are depicted as rectangles divided into three parts, in which the name, position number and number of elements are entered. Designation of parts is accepted in accordance with assembly drawings and specifications. To designate an assembly unit, the letters "Sb." and base part number. The assembly designation is preceded by the number of the assembly unit of the corresponding order. For example, 2 Sat.5 is an assembly unit of the second order (second stage) with base part No. 5. The element from which the assembly begins is called the base element. The process of general and nodal assembly is depicted in the diagram as a horizontal line from the base element to the assembled object. From above, in the order of the installation (mounting) sequence, the parts are located, and the nodes are located below. For structurally complex products, assembly diagrams are compiled for each assembly unit separately, and simple ones are combined. In this case, the assembly lines of assembly units (assemblies) of different stages can be horizontal and vertical.
Assembly schemes, in addition to parts and assembly units, may contain inscriptions explaining the specific features of assembly work (operations): joining elements (by pressing, soldering, rolling), fixing (by screwing, using glue, varnishes, paints and compounds), machining (drilling, deployment), use of technological details, control, adjustment, etc. The possibility of simultaneous installation of several components of the product is reflected by a common point (A, B, etc.).
Additional work, which includes partial or complete disassembly of the components during assembly, is also reflected in the diagram with an explanatory inscription. Technological assembly schemes for the same product can be compiled in several versions, which will differ in the structure and sequence of assembly elements. The accepted option depends on the organizational form of the assembly. The correctness of the assembly diagrams is checked by disassembling the product.Rice. 1. Technological assembly schemes:
a - general; b - nodal (assembly unit)
The construction of technological schemes for disassembling products is based on the same principles. The only difference is that the construction of the scheme begins with the product, and not with the base part or assembly unit.
On fig. 2 shows a sketch of the assembly unit, and in fig. 4 its technological scheme of assembly.
Fig.2. Assembly unit sketch (Sat.11 - Hub)
In practice, assembly flow diagrams represent the development of a project for the assembly process.
The technological process of assembling a product in its final form is predetermined by the type of production, i.e., the volume of output of assembled products, the complexity of assembly, and the organizational forms of assembly. With large assembly volumes, the technological process is developed in detail and with the greatest possible differentiation of assembly operations. With a small volume of output, they are limited to compiling a route (sequence) of assembly operations.
Assembly operations are designed on the basis of assembly schemes. The content of assembly operations should be set in such a way that a homogeneous and technologically complete operation is performed at each workplace, and with the in-line method, the complexity of the operation should be equal to or slightly less than the assembly cycle, or a multiple of it. When designing an assembly operation, they specify the content of technological transitions and determine the scheme for basing and fixing the base element; choose equipment, fixtures, cutting and assembly (working), control and measuring tools; set the operating modes, the norm of time and the category of work, perform the necessary technological calculations (determine the pressing force; torques when tightening bolts, studs, etc.) and justifications.
The composition of the technological process includes, if necessary, preparatory, fitting, adjusting, control, and other work (operations and transitions).
The technological processes of frilling are recorded in route and operational maps drawn up in accordance with ESTD standards.
An example of a routing technological process for assembling a hub is presented in Table 1.
Table 1
| operation number | the name of the operation | Content of operation and transitions |
| Pulley assembly (1Sb.8). | 1. Fix the pulley 8 in the fixture 2. Install the ring 10. 3. Lubricate and install the bearing 9. 4. Wipe and install the sleeve 12. 5. Lubricate and install the bearing 9. | |
| Pulley installation (1Sb.8). | 1. Fix the hub 11 in the fixture. 2. Install the pulley (1Sb.8) on the hub 11. 3. Wipe and install the compensation ring 7. 4. Install the retaining ring 3. | |
| Flange assembly (1Sb.5). | 1. Attach flange 5 to the fixture. 2. Install cover 1. 3. Fasten cover with screws 2. 4. Install gasket 6. | |
| Flange installation (1Sb.5). | 1. Install the flange (1Cb.5). 2. Fix the flange (1Sb.5) with screws 4. | |
| Control | 1. Check the ease of rotation of the pulley 8. 2. Check the runout of surface B relative to surface A. |
The norm of time for performing an assembly operation is set according to formulas and standards.
Let's define as an example the rate of piece-calculation time for the assembly operation 025 - "Assembly of the flange". The operation is performed under mass production conditions. The sketch of the assembly unit is shown in fig. 3. The list of assembled parts is given in Table. 2. With regard to serial production, we apply the standards. The analysis of standards allows us to divide the operation into the following settlement complexes:
1. Fitting the flange into the fixture. The working conditions are in accordance with the regulations. According to map 7, estimated operational time = 0.304 min.
table 2
Fig.3. Sketch of the assembly unit of the first order (1 Sat.5 - Flange)
Practical work No. 1
Development of a technological scheme for disassembly and assembly of CE
Objective
1. To study the concepts of the technology of disassembly and assembly of assembly units.
2. Learn to develop a technological scheme for disassembling and assembling the CE and arrange it in the form of a technological scheme.
Initial data
The initial data for the development of the technological scheme of assembly (disassembly) are:
Assembly drawing of the product with specification;
Specifications for assembly (disassembly) indicating the fit of mating parts, product test modes, technological instructions for the selection of parts, assembly, control and adjustment of interfaces or CE;
Repair program.
In addition to the documentation, it is desirable to have a sample of the product, on which it would be possible to perform trial disassembly or assembly according to the developed technological scheme.
1. Examine the assembly drawing and the assembly specifications attached to it.
2. Development of a structural-technological scheme for dismantling CE.
The development of CE as a whole is carried out in a certain sequence, which is determined by the design of the product, as well as the program of the repair enterprise and its uniformity in relation to the types and brands of machines being repaired.
When developing a disassembly scheme, the task is to divide a given node into constituent elements in such a way that disassembly can be carried out
the largest number of these elements independently of one another (in parallel).
Such a division makes it possible, when organizing repair work, to reasonably assign certain repair work to specific performers.
The disassembly scheme is built so that the corresponding assembly units are presented in it in the order in which it is possible to remove these elements when disassembling the assembly. CE and details are depicted in the diagram in the form of rectangles indicating the index, name and number of elements. The rectangle depicting the assembly unit for greater clarity can be distinguished by marking its outline with a double line (Fig. 1).
In the diagram, the rectangles characterizing the assembly units are recommended to be placed on the left, and the details on the right along the line.
The beginning of the disassembly is the assembly unit, and the end is the base part. For example, consider the input shaft of a car gearbox (Fig. 2).
Figure 2. Vehicle gearbox input shaft assembly
1 - input shaft; 2 - nut; 3 - retaining ring; 4 - ball bearing
radial single row; 5 - retaining ring; 6 - roller 8x20.
The report gives a brief description of the disassembly. Disassembly of the node in question is carried out in the following sequence:
Unscrew the ball bearing nut 2, remove the circlip 3, remove the ball bearing 4, remove the circlip 5 and remove the rollers from the roller bearing 6.
An example of a disassembly flow chart is shown in Figure 3.
The number of jobs is determined by the program of a particular repair company and the complexity of performing the listed operations.
 |
Fig.3. Technological scheme of disassembly of the primary shaft assembly
Disassembly must be carried out in the strict sequence provided for by the technological regulations. The basic techniques and principles of disassembly are as follows:
Assembly units are disassembled directly at the place of general disassembly, as well as at the places of their repair and assembly in accordance with the technological scheme.
First, remove parts that can be easily damaged (injection tubes, rods, levers, rods, etc.). Then, separate assembly units are dismantled, which are disassembled at other workplaces.
When removing large parts fixed with a large number of bolts, in order to avoid the appearance of cracks, all bolts and nuts are first released half a turn and only after that they are unscrewed.
Rusted connections are moistened with kerosene before unscrewing.
After disassembly, fasteners are placed in mesh baskets for subsequent washing. It is not allowed to use a chisel and a hammer to loosen bolts, nuts, fittings, etc., as this may damage them. Shaped nuts and fittings are unscrewed with special keys.
Pressed parts are removed under pressure or with the help of pullers and fixtures. In some cases, fittings, bushings and axles can be pressed out with special punches with copper tips and hammers with copper bikes.
When the bearing is pressed out of the housing, the force is applied to the outer ring, and from the shaft to the inner one. It is forbidden to use a percussion instrument.
It is advisable to place the removed parts on racks and devices for transportation to the sink, so as not to damage the work surfaces.
It is impossible to disassemble parts that are processed as an assembly during manufacture (caps of main bearings with blocks, etc.). In addition, it is forbidden to remove parts that are subject to joint balancing, as well as worn-in pairs of parts suitable for further work (bevel gears of the final drive, gears of oil pumps, etc.). Parts that are not subject to maintenance are marked, tied with wire - re-connected with bolts and placed in a separate container or kept complete in other ways.
3. Construction of a technological scheme for the assembly of CE.
The assembly flow diagram, as well as the disassembly flow diagram, is an auxiliary technological document (not included in the number of mandatory technical documentation documents, which graphically shows:
The sequence of connection of parts and assembly units included in the product;
The composition of the assembly units included in the product;
Performing operations not related to the attachment of parts and assembly units (control, adjustment, filling of oil or working fluids, painting, packaging, etc.)
The technological scheme of assembly is intended for:
Disclosure of the structure of the product and the possibility of using a nodal assembly;
Formalization and algorithmization of the development of the assembly process;
Evaluation of product design from a technological point of view.
For the design of the assembly process, the most acceptable form of the assembly flow chart is the scheme that provides the ranking of assembly units by levels and orders. When compiling such a technological assembly scheme, a number of formalization descriptions and designations are also used.
1. Assembly units (CE) included in the product have different orders, ranging from 0 to N. SEO - assembly unit of zero order, is
items that do not require assembly, These include parts, bearings, products that come to the assembly from the side (purchased or assembled in other departments).
2. The order of an assembly unit is always one more than the maximum order of its constituent elements.
When determining the order of an assembly unit, consider the following:
When connecting any next part to an assembly unit, the order of the assembly unit does not increase (Fig. 4a, b).
The assembly unit moves to the next level only after the assembly units of the same order are connected (Fig. 4c).
The rules for determining the order of assembly units in general can be written as:
Fig 4. Scheme of formation of the order of assembly units
To describe assembly units in a ranked technological assembly scheme, a rectangle is used, shown in Fig. one.
3. The following formalization designations for actions related to the assembly of product elements are used in the assembly flow chart:
Attaching an assembly unit (Fig. 5a) is indicated by an arrow at a given assembly level with transition numbering;
Attaching an assembly unit with additional actions (Fig. 56);
Actions not related to attaching an assembly unit and providing for adjustment, measurement, testing, filling with working means, balancing, painting, packaging and others (Fig. 5c);
Intermediate disassembly when using adjustment with a fixed compensator (Fig. 5d).
General assembly line 7 8 9
https://pandia.ru/text/80/171/images/image006_26.jpg" width="1078" height="640">
Rice. 6. Technological scheme of the assembly of the shaft of the primary gearbox
4. Drawing up a list of transitions of the nodal and general assembly.
The list of transitions must begin with the listing of transitions of the general assembly.
The list of transitions of the nodal assembly is expressed in the enumeration of assembly transitions in the sequence of installation of assembly units of the corresponding order on the general assembly with their disclosure up to the first order CE. 7.
Rice. 7. Structural diagram of compiling a list of transitions of the nodal and general assembly
General Assembly
1. _____________________________
2. _____________________________
Assembly CE2
Assembly CE11.
1. __________________________________________
2.______________________________________
Assembly CE12.
1.__________________________________________
2.______________________________________
The description of the route assembly technology is considered on the example of the primary gearbox shaft assembly technology.
General Assembly
1. Install the input shaft.
2. Lubricate the hole along the rollers with grease.
3. Install rollers.
4. Install retaining ring 5.
6. Install retaining ring.
7. Screw on and tighten the nut.
8. Punching the retaining ring.
Any electronic device, household appliance, even furniture in our homes are made on the basis of specially drawn up drawings. In which individual elements are drawn first, and then the assemblies of these parts are shown, ways of fastening and arranging them relative to each other are shown. People working in the assembly of products must be able to read the drawings, because they serve as a kind of guide on how to assemble the designer's plan, as well as what material and what method to make the necessary parts.
Basic concepts
The concept of "assembly drawing" means an engineering document that depicts a component unit with the necessary dimensions and technical requirements for its manufacture, as well as quality control. Such a drawing is made during the development of documentation for the product. It should give a complete picture of the location in the finished product relative to other details. The assembly drawing is carried out in accordance with the requirements of GOST 2.102-68 "Types and completeness of design documents".
Detail - a product made according to the requirements of ESKD from one material and without the use of assembly operations.
Part drawing - a designer's document, where there is an image of the part, all the necessary dimensions to make it, and its coating is prescribed in the technical requirements, if necessary.
What should the drawing contain?
Any assembly drawing of a part must contain the following:
How the assembly part is located in the finished product relative to other elements;
How is the fastening of parts to each other;
Overall dimensions - they will show what length, height and width the product should have;
Mounting dimensions - show the main dimensions of all the elements that are needed for the installation of the product;
Connecting dimensions - show the dimensions of the connection points with other parts or assembly units;
Reference dimensions - indicated on the drawing from reference books (for standard sizes of threads, nuts, etc.);
The maximum permissible deviations in the manufacture, according to which the quality control of the product will be carried out;
Methods for attaching parts to each other, an indication of all connections and methods for their implementation;
The positions of each part in the assembly, taken out in the specification;
The scale at which the drawing is made;
Product weight.
Basic rules for making assembly drawings
The execution of the assembly drawing is done in accordance with the requirements of GOST 2.109-73. If it is necessary to designate rotating or moving parts of the product, then it is allowed to show them either in the extreme or in the intermediate position. In this case, the required dimensions must be specified. If reading the assembly drawing becomes difficult, then some parts can be shown separately by making the necessary signatures indicating positions.
When performing sections or cuts on the same part, it is necessary to maintain the same slope of the lines and the distance between them when hatching.
If the cut is made at the junction of two different parts, then the hatching at the cut site of each of them is applied in different directions or with different distances between the inclined lines.
If necessary, the drawing indicates the roughness, permissible deviations from the norm for some specific parts or holes. There are also a number of standard parts for which you can not produce separate drawings, but if there is a lack of necessary information, they are placed on the assembly drawing field.
If the joining of individual parts must be ensured by fitting or selection, then appropriate signatures are made.
Specifying part positions
All components of the assembly unit are numbered according to GOST 2.109-73.
Each component, as well as the materials used, standard products must have their own serial number, which is assigned to them when drawing up the specification for this assembly drawing.
All positions in the drawing are indicated by leader lines that are drawn from each individual part or material. The end of the line, which is located on the image of the part itself, thickens with a dot. The line itself and the leader shelf are depicted as a continuous thin line. The positions indicate all visible details. Positions of invisible parts are indicated on additional views or sections.
Position inscriptions are made parallel with respect to the main inscription in the drawing frame. Also, the positions should be placed outside the contour of the parts, they can be grouped.
If the same part is present on the assembly drawing several times, then its position is put only once, and in brackets next to the number it is indicated how many times it is repeated on the drawing.
Position numbers are indicated in a font that is 2 sizes larger than in the specifications and frame.
Crossing of lines when placing positions is not allowed, and they should not have the same direction as the hatch lines.
Simplifications and symbols in the drawings
When performing an assembly drawing, you can use valid symbols and simplifications.
On the drawings, you can not show chamfers, grooves, fillets, small protrusions, recesses, etc., as well as some gaps if they are small.
If in the drawing it is necessary to depict those parts of the product that are closed with a lid or shield, then the latter may not be shown. An inscription is also added indicating which position detail is not shown.
If the same component (wheel, support) is used several times in the product, it is allowed to show its image only once.
Soldering, gluing or welding spots can be shown as uniform surfaces. In this case, the boundaries between the sections of different parts are left.
Also, according to GOST 2.315-68, fastener details are shown in a simplified way.
Specification
This is a design document, which prescribes the full composition of the assembly product in accordance with GOST 2.108-68. This document is executed on A4 format separately for each assembly. It sequentially signs all the components of the assembly unit.
Based on the general case, the specification is made up of the following sections in succession: documentation, assembly parts, parts, standard products, other products, materials, kits.
It is not necessary that all sections be present in every specification. If one of them is not filled out, it is simply not registered. The name of the section is written, skipping two lines from the last entry of the previous one, in the middle of the column - the name, underlined by a thin straight line.
Items are listed in alphabetical order. The numbering of positions goes from the first section through the entire document. Also, in the corresponding column, GOST or the designation of an individual part and their number in this assembly are indicated.
The sequence of execution of assembly drawings
An assembly drawing is either made from a finished product, or first a sketch of the parts is made in programs such as SolidWorks, Kompas 3D, and only then the drawings themselves are created from them.
Before you start drawing, you need:
To study the details, the principle of operation of the product and its purpose;
Determine the order in which the finished product will be assembled;
Make a plan with the designation of all components;
Select the most informative images for placement on the drawing field, make the minimum number of additional views and cuts;
Based on the size of the selected image, the number of views and sections, choose the most appropriate format size;
Fill in the frame of the drawing;
Complete the outline of all images, check the work done;
Apply all dimensions, position numbering, sign everything;
Write technical requirements for the manufacture of parts according to this drawing;
Fill out the specification.
Below are the simplest examples of assembly drawings.
How to read assembly drawings
Reading assembly drawings implies, first of all, a preliminary study of information about how the product is arranged and how it works.
Understand the principle of operation and what this product is intended for, based on the inscriptions in the frame of the document;
Determine what components the product consists of according to the specification;
Understand why each individual detail is needed, its features of location and work in relation to other elements;
Determine the sequence in which the product will be disassembled and assembled (reading the main inscription in the frame, the contents of the drawing and its features, correlating information in the specification and on the drawing field);
Examine the description of the finished product or its analogue;
Find out how the individual parts are attached to each other.
General arrangement drawing detailing
Detailing an assembly drawing is a rather painstaking and difficult job. Having only a general assembly of the part, it is necessary, on the basis of this drawing and specification, to make drawings of all parts, and choose the most convenient angle for their implementation and applying all the necessary sizes and designations.
What size a separate part will be, they will find out based on the scale of the general drawing and the size of this part on it. The dimensions of the standard parts are taken from the standards reference, not from the drawing data.
Detailing an assembly drawing usually consists of three stages:
Reading an assembly drawing that has a general view;
Defining the shapes of individual parts;
Drawing of every detail.
BASICS OF ASSEMBLY OF MACHINERY AND EQUIPMENT
General provisions
Assembly is the final stage in the manufacture or repair of a product (machine, equipment, their individual mechanisms or units), which largely determines its technical and operational characteristics.
The assembly process consists in connecting parts into assembly units (assemblies), and assembly units and individual parts into mechanisms (assemblies) and machines, ensuring that the requirements established by technical documentation for accuracy, force interaction of parts, guaranteed gaps or tightness, etc.
When drawing up an assembly unit diagram, the concepts of “base part” and “base assembly unit” are used. The assembly of the assembly unit begins with the base part, and the assembly of the product begins with the base assembly unit.
For a better representation of the sequence of acquisition and assembly of the product, it must be divided into its component parts: complexes, assembly units, parts.
Based on the types of products, the assembly of nodes (nodal assembly), complexes and products (general assembly) are distinguished. Most of the assembly work in the manufacture and repair of machinery and equipment is carried out at the general assembly.
The assembly process is carried out in compliance with the geometric and kinematic relationships between the parts, the nature of the landings in their joints, specified by the design documentation, and ensuring the required assembly accuracy.
Assembly accuracy is understood as the degree of correspondence between the actual and design values of the parameters of the relative location of mating parts or assembly units. It depends on the accuracy of the parts and assemblies received for assembly, as well as the quality of the assembly work.
A feature of the assembly of machines during repair in comparison with their manufacture is the use of three groups of parts: those that were in operation, but have acceptable wear and tear and are suitable for further use without restoration; remanufactured parts; new parts in the form of spare parts. The difference in the accuracy of parts necessitates additional fitting and control operations.
Given that the labor intensity of assembly work can reach 35-45% of the total labor costs, the use of progressive types and forms of assembly organization, improvement of assembly processes, in particular, in the direction of increasing the level of mechanization through the widespread use of universal and special devices and equipment, is of economic importance.
Principles of organization and types of assembly production
The organization of the machine assembly process is based on the following basic principles:
– ensuring the high quality of the assembled product, which guarantees its necessary durability and reliability in operation;
- minimum assembly cycle;
- the use of mechanization tools that provide increased productivity and safe conditions for performing assembly work, etc.
The ways of implementing these principles largely depend on the specific types of assembly used at a given enterprise and its technical equipment.The main types of assemblyin the manufacture and repair of machinery and equipment are as follows.
pre-assembly, in which the assembled components or the product as a whole are subject to disassembly, for example, to determine the size of a fixed compensator.
intermediate assembly, performed to solve certain technological problems, in particular, to prepare a prefabricated part for machining. For example, pre-assembly of a gearbox housing with a cover is necessary for subsequent joint processing of holes for bearings, etc. in them.
Assembly for welding, providing with the help of a special device the relative position of the workpieces before welding, necessary to ensure the required accuracy of the product. This type of assembly is the main one in the manufacture of metal structures.
final assembly, as the final stage of obtaining this product in the process of its manufacture or repair without its subsequent disassembly. In some cases, after the final assembly of the product, its partial disassembly (dismantling) is performed in order to prepare individual parts for packaging for delivery to the consumer. The final assembly (installation) and installation of the product in this case is performed at the place of use.
According to the mobility of the assembled product, the assembly is divided into stationary and mobile, and according to the organization of production - into non-flow, group and flow.
Non-threaded stationary assemblycharacterized by the fact that the entire process of assembling the product and its assembly units is carried out at one assembly position: at the assembly site of the workshop, stand, etc. The basic parts of the product must be installed in the same position as in the place of its operation. This contributes to the achievement of high assembly accuracy, especially large products with insufficiently high structural rigidity. All parts, assemblies and components with this form of assembly are delivered to this position, and all assembly work is performed by one team of fitters sequentially. In this regard, the disadvantages of this method are: limited opportunities to reduce the duration of the overall assembly cycle due to the sequential execution of assembly operations, as well as the need for highly skilled workers capable of performing the entire range of assembly operations.
Non-flow stationary assembly with dismemberment of assembly workinvolves the allocation of the nodal and general assembly. Thanks to this, the assembly of various machine components can be performed simultaneously (in parallel), which can significantly reduce the repair time compared to non-linear stationary assembly. This form of assembly organization is especially effective in the presence of specialized sections or workplaces equipped with appropriate technical means for the manufacture (repair) of machine components - electrical equipment, hydraulic equipment, etc., as it provides better organization of labor, improved quality and reduced assembly costs due to specialization workers.
The use of a nodal assembly provides for the division of the product design into technological assembly units that can be assembled independently of each other. This condition must be ensured when designing or upgrading a product, while testing it for manufacturability.
Non-threaded movable assemblycharacterized by the sequential movement of the assembled product from one position to another with the distribution between them of the operations of the assembly process. The movement of the product to be assembled may be free or forced by means of a conveyor or similar devices. The assembly can be performed both on the conveyor and near it. The duration of work at each position may be different, which necessitates the creation of interoperational backlogs. Therefore, non-flow movable assembly is cost-effective in mass production.
In-line assembly differs in that all operations of the process are performed synchronously for the same period of time - a cycle, or a multiple of it. In the second case, the operation is performed in parallel at several workplaces. In this case, the interoperational movement of the assembled product can be carried out manually or using a conveyor having a continuous or periodic movement. In-line assembly reduces the duration of the production cycle and reduces the interoperational backlog of parts, makes it possible to reduce the labor intensity of assembly by 35-50% due to the mechanization of assembly operations and the specialization of workers. It is cost-effective with a sufficiently large number of assembled products. The design of the assembled product must be highly technological in order to exclude, if possible, fitting work. If necessary, they must be executed outside of the thread.
In-line stationary assemblyis one of the forms of in-line assembly and is used in the assembly of heavy, bulky and inconvenient for transportation products. It differs in that all products are assembled at permanent places without moving, and workers move from one product to another after periods of time equal to the tact and perform the operations assigned to them.
Types of assembly work
The assembly process consists of two main parts: preparation of parts for assembly and actual assembly operations. The preparatory work includes: fitting and fitting work performed if necessary (sanding, scraping, etc.) with accuracy control using universal or special measuring tools, as well as fitting parts in place to obtain the required assembly accuracy; cleaning and washing parts; lubrication of mating parts, if required by specifications.
Before assembly, some parts are subjected to balancing (static or dynamic), completed by size groups and by weight (for example, pistons of internal combustion engines).
The actual assembly work includes the process of connecting mating parts and assemblies with ensuring their correct relative position and a certain fit.
Assembly work, therefore, is divided into main and auxiliary. When performing basic assembly work, the required movable or fixed connections are created. Obtaining any connection includes the relative orientation of the assembled parts and giving them the required relative movement using assembly fixtures and process equipment. The purpose of auxiliary work is to prepare parts for the main assembly work, select the necessary tools for assembly, control its quality, preserve and package the assembled product, etc.
Thus, the assembly process includes a variety of works that can be attributed to the following types:
- preparatory work - bringing parts and assembly units into the condition required by the assembly conditions: re-preservation, cleaning, washing, sorting into size groups, picking, packing, transportation, etc .;
- fitting work to ensure the possibility of assembling joints: straightening, drilling and reaming of holes in the assembly, calibrating smooth and threaded holes, cleaning, filing, scraping, grinding the surfaces of parts, etc.;
- actual assembly work - obtaining, in accordance with the drawing, demountable or non-separable connections of parts, assembly units and products by screwing, pressing, riveting, soldering, and other methods;
- adjustment work to ensure the required accuracy of the relative position and relative movement of parts in assembly units;
- control work performed during the assembly process and after its completion in order to verify the compliance of assembly units and products with the requirements established by the technical documentation;
- dismantling - partial disassembly of the assembled product to ensure the possibility of its delivery to the consumer.
Assembly Accuracy Methods
When assembling machines, errors in the mutual arrangement of parts and assemblies, non-observance of the required gaps or interferences in the mating are possible.
The reasons for these errors can be: deviations in the size, shape and location of the surfaces of mating parts during manufacture; inaccurate installation and fixation of the relative position of parts during assembly; poor quality of fit and regulation of the position of mating parts; non-observance of the assembly operation mode, for example, when tightening screw connections; errors in the manufacture and adjustment of assembly equipment and technological equipment, etc.
The specified assembly accuracy can be obtained by various methods: complete interchangeability; incomplete (partial) interchangeability; group interchangeability (selective assembly); adjustment; fitting or fabrication of the part in place and the use of compensating materials. The choice of a specific method depends on the number of similar machines being manufactured or repaired, the system adopted for organizing production and its technical equipment, the qualifications of the workers, as well as the design features of the units and the machine as a whole.
Consider these methods to ensure the accuracy of the assembly.
Complete interchangeability methodcharacterized by suitability for assembling any part, assembly or assembly of a given batch without additional processing and fitting. Assembly using the method of complete interchangeability is the simplest and least time-consuming, since the required clearance or interference in the connection is provided with a given accuracy without additional time. However, with complete interchangeability, a higher accuracy of manufacturing parts is required, which is associated with an increase in the cost of manufacturing, the need to use a large number of precision fixtures, tools and instrumentation.
The use of the method of complete interchangeability is advisable when assembling simple connections from a small number of parts, for example, the shaft-sleeve type, since with an increase in the number of parts, the requirements for the accuracy of their processing become more stringent, which is not always technically achievable or economically feasible.
Method of incomplete interchangeabilityconsists in the fact that the tolerances on the dimensions of the parts that make up the dimensional chain are deliberately expanded to reduce their cost. Therefore, the required assembly accuracy is achieved not for all connections of parts, but for a pre-installed part of them. The remainder of the connections require disassembly and reassembly.
The use of the method of incomplete interchangeability is advisable if the additional costs of disassembly and assembly work are less than the costs of manufacturing mating parts with the method of complete interchangeability.
Group interchangeability method(selective assembly or selection) is characterized by the fact that the required gaps or tightness in the joints are obtained by assembling parts belonging to one of the size groups into which they are pre-sorted. At the same time, within each group, the required assembly accuracy is achieved by the method of complete interchangeability. This ensures high assembly accuracy without increasing the accuracy of part manufacturing.
A significant advantage of this method is that without reducing the assembly accuracy compared to the method of complete interchangeability, it is possible to expand the tolerances for all parts as many times as the number of groups the parts are divided into, and thereby reduce the accuracy of their processing. Due to the division of parts into size groups, the assembly accuracy by the group interchangeability method can even be significantly higher than with the full interchangeability method. Therefore, this method is widely used in the production of high-precision products (bearings, plunger pairs, etc.). However, this method is associated with an additional operation of sorting parts into size groups, the need to create and store large stocks of parts, which increases the volume of work in progress, material and labor costs. Therefore, the method of group interchangeability is cost-effective in conditions of large-scale and mass production.
With the adjustment methodthe required assembly accuracy is achieved by changing the size or position of the compensating link. In practice, this is ensured by moving (Fig. 6.1, a) or selecting the size A 2 (Fig. 6.1, 6) compensator to obtain the required size of the closing link (gap) АƩ
In the assembly design according to Fig. 6.1, and the compensator is the sleeve 2, the movement of which in the axial direction achieves the required clearance in the connection - the size АƩ of the master link. After that, the sleeve is locked with screw 1.
In the node in Fig. 6.1, b, the necessary clearance is provided by the thickness A 2 ring K, which in this case is a compensator. Its thickness is selected according to the results of measuring the actual size of the closing link (gap).
The main advantage of movable compensators in comparison with selectable ones is the ability to adjust the assembly assembly accuracy without disassembling it with minimal time. Adjusting screws, threaded bushings, wedges, eccentrics, parts made of elastic materials, etc. can serve as movable compensators, some of them are shown in Fig. 6.2.
Rice. 6.1 Schemes for ensuring assembly accuracy by adjustment methods (a, 6) and fitting (c)
Rice. 6.2. Structural varieties of movable compensators: a - rod with a threaded connection; b - adjusting ring with a locking screw; c - wedge device; g - split conical bushing; e - ring made of elastic material
Assembly by the adjustment method has the following advantages: universality (the method is applicable regardless of the number of links in the chain, the tolerance for the master link and the volume of production of parts); ease of assembly with high accuracy; lack of fitting work; the possibility of periodic adjustment of the connection during the operation of the machine to restore its accuracy.
Fit method (machining the part in place) consists in the fact that the required assembly accuracy is achieved by changing the size of one of the parts (compensator) by cutting off a certain layer of material from it. The most common fitting methods are turning, grinding, filing, scraping, and lapping. All other parts are processed to tolerances that are economically acceptable for this production. The compensator can be one of the main parts of the connection (Fig. 6.1, c) or a specially provided part (gasket, ring, etc.). For example, if in the design according to Fig. 6.1, b, the gap is provided not by selecting the thickness of the ring, but by cutting off a metal layer from it, then the assembly accuracy will be ensured by the fitting method.
On fig. 6.1, the specified gap is achieved by fitting the thickness of part 1, in the manufacture of which allowance Z is provided for fitting work.
The fitting method is used when assembling products with a large number of links, while all parts with the exception of the compensator can be manufactured to economical tolerances, however, additional costs for fitting the compensator are required. The efficiency of the method largely depends on the correct choice of the compensating link, which should not belong to several related dimensional chains.
A common feature of fitting and adjustment methods is the use of a compensator with a change in its position or dimensions to ensure assembly accuracy. With both methods, the parts being assembled are produced to extended, economically achievable manufacturing tolerances, but additional time is required to fit or adjust the dimensions of the master link to ensure the required accuracy of the product. At the same time, pre-assembly, checking the correct position of the mating parts and determining the work to fit the compensator is often necessary to perform the fitting. Then, after disassembly, the compensator is adjusted. Only after that is the final assembly. All this significantly increases the overall complexity of the assembly and its cost, since the fitting operation is performed by highly qualified workers.
When carrying out the regulation, the need for reassembly is eliminated and the complexity of the assembly is reduced. However, the introduction of special parts (compensators) complicates the design of the product. Methods of regulation and fitting are typical for single and small-scale production.
Assembly with compensating materials. With this method, the required accuracy of the closing link of the dimensional chain is achieved by using a compensating material introduced into the gap between the mating surfaces of the assembled parts. This method is being used more and more widely due to the creation of modern polymeric materials, in particular, in the assembly of threaded connections, bearing assemblies, joints and assemblies based on planes.
Assembly design steps
The design of the assembly process is the most important stage in the technological preparation of the assembly production, which, in addition to the development of standard technological documentation, also includes the design and manufacture of non-standard equipment, special equipment, planning and other work. The initial data for the development of the assembly process are: assembly drawings of the assembled product; specifications; technical requirements for individual components and for the product as a whole; release program, etc. Therefore, the development of the assembly process is preceded by a detailed acquaintance with the design of the product, the interaction of its parts, the technical conditions for the manufacture, acceptance and testing of the product, the existing technical base of the assembly production.
The assembly process, as part of the manufacturing process, consists of a set of operations that ensure serial connection, mutual orientation, fitting and fixing of parts and assemblies to obtain a finished product that meets the established requirements. It also includes operations related to checking and ensuring the accuracy of the relative position of the assembled parts and assemblies, the correct functioning of individual mechanisms, systems and the machine as a whole, as well as operations for cleaning, painting and preserving the product or its individual parts.
It is known that assembly processis a complete part of the technological process performed at one workplace by one or more workers continuously on one assembly unit or on a set of simultaneously assembled units, andassembly transition- this is a completed part of the operation, performed by the same method using the same tools and fixtures.
The assembly process is designed taking into account the technical and organizational achievements of production in the field of assembly technology, resource saving, mechanization and automation of work, creation of favorable working conditions, etc. taking into account specific conditions and type of assembly production. Designedassembly process, as a document, includes: a description of the composition and sequence of operations and transitions of the product assembly; technical and economic calculations of labor, material and energy costs, the amount of equipment and tooling required, the number of production workers, production area, labor intensity and cost of assembling the product.
The design of the assembly process includes the following main steps:
- analysis of the manufacturability of the product design from the standpoint of assembly and adjustment;
- dimensional analysis of the design of the assembled product with the performance of appropriate calculations, the choice of a rational method for ensuring the required assembly accuracy, determining the probable scope of fitting and adjustment work;
- substantiation of the degree of differentiation and form of organization of the assembly process;
- division of the product into assembly units (groups and subgroups), setting the sequence of connection of all assembly units and parts of the product, drawing up a diagram of the general assembly and nodal assemblies of the product, assembly maps;
- determination of the content of technological assembly operations, selection of methods for monitoring and testing the product and technical regulation of assembly work;
- substantiation of the accepted version of the assembly process;
— preparation of technological documentation;
— selection and quantification of standard equipment; design of technological equipment, fixtures, locksmith, cutting and instrumentation tools that are missing for organizing the assembly; design, if necessary, of the assembly site.
Consider the content of the main of these stages.
Dimensional analysisdesign of the assembled product is associated with determining the conditions for obtaining the necessary clearances or interferences. These tasks are solved on the basis of dimensional chains
The use of the method of dimensional chains in the assembly of machines allows:
- according to the given tolerances of all the constituent links of the assembled assembly, calculate the tolerance of the closing link;
- according to the given tolerance of the closing link (usually called the initial one in this case), find the most rational values of the tolerances of the component links;
- based on the general requirements for the assembly being assembled, establish a rational combination of the tolerance of the closing link and the tolerances of the remaining links.
The efficiency of the assembly process depends significantly on the degree of its differentiation (dismemberment into operations). The degree of in-depth design of the technological process depends on the product release program: in single and small-scale production, a simplified version is developed without detailing the content of operations.
Differentiation of technological processes of assemblyIt is typical mainly for serial and mass production. It allows you to divide the process into operations with a duration equal to or a multiple of the set build cycle. This increases productivity and creates organizational conditions for the mechanization and automation of manual assembly processes. However, excessive differentiation of the assembly process leads to a decrease in labor productivity due to an increase in time losses for auxiliary operations associated with the transportation and reinstallation of the assembled product. Therefore, the degree of differentiation of the assembly process must be economically justified.
For pilot, single and partially small-scale production, typical for the manufacture and repair of technological equipment, it is inherent to perform all the operations of the nodal and general assembly at a few or even at one workplace. The disadvantages of a concentrated assembly are the cycle time due to the sequential execution of operations; complexity of their mechanization.
Separation of the product into assembly unitsinitials. When dividing a product into assembly units, it should be taken into account that, from the point of view of performing its functions, it is divided into assembly units (aggregates, assemblies, mechanisms) and parts that are its structural elements in accordance with the design documentation. From a technological point of view, the machine is divided into assembly elements, which may not coincide with the structural ones. Assembly elements are parts, components and assemblies that can be assembled separately from other elements of the machine and then installed on it.
The most complex, time-consuming and responsible stage in the development of the assembly process isdetermination of the composition, content and sequence of operations and transitions. Here it is necessary to take into account the type of production (single, serial, mass), the availability and convenience of performing work, the rational sequence of installation of the component parts of the product, the possibility of using universal or common technological equipment to perform a number of assembly operations, and other factors. The assembly sequence of a product or its component is conveniently represented graphically in the form of a so-called assembly diagram, which, for greater clarity, is supplemented with an assembly drawing of the product.
Drawing up assembly diagrams. To develop a technological assembly scheme, the product is divided into constituent elements (parts, assemblies), each of which is depicted in this diagram as a rectangle divided into three parts. The name of the element is indicated in the upper part, its designation (index) in the lower left part, and the number of identical elements in the lower right part. The indexes of the elements correspond to the numbers of parts and assemblies in the drawings and specifications. The assembly diagram should also indicate the base part (base unit), assembly units and the finished product. Let's consider the sequence of drawing up the technological scheme of the assembly using the example of the assembly of the tension roller (Fig. 6.4, b):
- on the left side of the assembly scheme (Fig. 6.4, a) the base part (roller axis) is depicted in the form of a rectangle, on which the entire product will be assembled;
- on the right side of the diagram, the assembled product (tension roller) is also depicted in the form of a rectangle;
Rice. 6.4. Assembly diagram (a) assembly unit (b): 1 - roller axis; 2 - oil deflector; 3 - roller housing; 4 - bearings; 5 - washer; 6— nut; 7 - oiler
- rectangles denoting the base part and the assembled product are connected by a straight line;
- below and above this line, parts and nodes are shown in the form of rectangles in the sequence of their installation on the base part.
The sequence of installation of the component parts of the product is determined based on the content of the assembly operations. Assembly schemes are developed for the product as a whole and for each of its nodes.
The scheme of the general assembly of a product containing several nodes of a higher (first) order and individual parts is shown in fig. 6.5. On fig. 6.6 shows a diagram of the nodal assembly of the base unit of this product, which in turn consists of several units of the second and third order and individual parts. Similar assembly schemes are compiled for nodes of all orders.
Rice. 6.5. Scheme of the general assembly of the product
If necessary, control operations are indicated on the assembly diagrams, additional inscriptions are made that determine the content of assembly and control operations, for example, “heat”, “press”, “adjust the gap”, “control the gap”, etc.
Technological schemes for assembling the same product can be developed in several versions with different sequences of operations. The optimal variant is chosen from the condition of ensuring a given assembly quality, efficiency and productivity of the process for a given product release program.
Drawing up flow charts for assembly is advisable for any type of production, since they greatly simplify the design of assembly processes and facilitate the assessment of the design of the product in terms of its manufacturability. On the basis of general and nodal assembly schemes, assembly technological processes are developed and technological, route and operational assembly maps are compiled. An assembly route chart is a document containing a description of the assembly process by operations. Route maps are used, as a rule, in small-scale and single-piece production. The assembly operating map contains a more detailed description of operations broken down by transitions. In serial and mass production, operational assembly cards are developed separately for each assembly operation.
Rice. 6.6. Scheme of the nodal assembly: DB - base part; D - detail
Design of assembly operations. Assembly operations are designed on the basis of technological assembly schemes. When developing the content of assembly operations, it should be taken into account that with the in-line assembly method, the complexity of the operation should be equal to (somewhat less than) the assembly cycle or a multiple of it. For each assembly operation, the content of technological transitions is specified, the scheme for locating and fixing the base element (part, assembly) is determined, technological equipment, fixtures, working and measuring tools are selected, operating modes, time standards and work categories are set. At the same time, the necessary technological calculations are performed, confirming the validity of the choice of equipment, technological equipment and operating modes. These include: determination of the pressing force when assembling joints with an interference fit or during riveting, heating or cooling temperatures when assembling parts with thermal effects, etc.
Rationing of assembly work is carried out according to time standards, which are established by the experimental static method and the trial assembly method, using the timing of individual operations.
Efficiency markof the developed variants of the technological assembly process is carried out on the basis of absolute and relative indicators. Absolute indicators include the cost of individual operations and the assembly process as a whole, the laboriousness of assembling units and the entire product. Relative indicators - the load factor of each assembly place, the labor input coefficient of the assembly process (the ratio of the labor input of the assembly to the labor input of manufacturing the parts included in the assembled product). The coefficient for single and small-scale production is approximately 0.5, for serial 0.3-0.4. The lower this coefficient, the higher the level of mechanization of assembly work. With a large proportion of purchased parts and assemblies in the composition of the assembled product, it is advisable to use the cost coefficient of the assembly process instead of the labor input coefficient, which is equal to the ratio of the assembly cost to the manufacturing cost.
Technological documentationassembly processes includes assembly drawings, process flow diagrams for assembly and general assembly, route and operational assembly maps. The assembly route map contains a list of assembly operations indicating data on equipment and tooling, time standards, work category and estimated time standards for technological transitions.
To implement the developed assembly process, the necessary technological equipment and fixtures are designed: test benches, fixtures, special metalwork tools and measuring instruments, etc. The final stage in the design of the assembly process is the development of the layout of the assembly site. The main ways to improve the technical and economic efficiency of assembly processes are the mechanization and automation of assembly operations based on modern technological equipment and the rational organization of production.
Picking parts and assembly units
The picking of parts and assembly units is a part of the production process that is carried out before assembly and consists in the formation of assembly kits to ensure the continuity and rhythm of the process of assembling products of the required quality. An assembly kit is a group of product components that must be submitted to the workplace to assemble the product or its component.
The set includes the following works:
- accumulation, accounting and storage of new, restored and fit without repair parts, assembly units and components, filing applications for missing components;
- selection of parts for individual connections without fitting and fitting of other parts;
- selection of component parts of the assembly kit (a group of parts, assembly units and components necessary for the assembly of the product) according to the nomenclature and quantity;
- selection of mating parts by repair dimensions, size groups, by weight;
— transportation of assembly kits to assembly posts prior to the commencement of assembly work.
Parts are delivered to the picking department from the troubleshooting department and from spare parts warehouses.
Sorting of parts provides for their layout according to their belonging to machine models, units, assemblies. Sorting characteristics are formed on the basis of specifications for assembly and testing. For specific products, parts are sorted by size, size groups, weight and other quality parameters.
The picking of parts is carried out by individual (piece), group and mixed methods. When choosing a picking method, the method used to ensure assembly accuracy is taken into account.
Individual selection methodconsists in the fact that a second part of this interface is selected for one part of a certain size, taking into account the provision of the required clearance or interference. The disadvantage of individual selection is the high labor intensity. This method is expedient for individual and small-scale production and repair of machines.
Essence group (selective) methodselection lies in the fact that mating parts made with relatively wide tolerance fields are sorted into several size groups with narrowed tolerance fields. In group picking, the size tolerance field of the mating parts is divided into several intervals, and the parts are sorted according to the measurement results into size groups in accordance with these intervals. Dimensional groups of parts are marked with numbers, letters or paints.
Parts are divided into dimensional groups based on the condition for ensuring the required limit values of group gaps or interferences. In this case, the number of groups, as a rule, is not more than five, since an increase in the number of groups leads to an increase in the stock of parts in the picking department. The number of parts in groups, if possible, should be the same for each of the mating parts. Group picking is used to select parts of exact mates (plunger pairs, pistons and piston pins, etc.). It provides high accuracy of their assembly from parts with wide tolerances for the dimensions of the mating surfaces. To determine the deviations of the dimensions of parts from the nominal values, appropriate universal or special tools, instrumentation and fixtures are used. For example, gears are selected on the device for a comprehensive check of the gearing, the readings of which depend on the deviation of the center distance, pitch error, eccentricity and other deviations of the gearing parameters.
Details of a certain size group are sent for assembly in a special container with the designation of the group number. At the assembly site of units and assemblies, there are specialized racks for storing kits.
At mixed staffingparts, both methods are used: for parts of less critical connections, an individual method is used, and for critical connections, a group method.
To avoid imbalance, some parts are selected by weight (for example, pistons of internal combustion engines). The picking of parts may be accompanied by fitting and fitting work.
Large-sized parts and assembly units (beds, frames, gearbox housings, etc.) are usually delivered to the assembly sites, bypassing the picking area.
When picking, for each assembled product, a picking card is filled out, which indicates:
- the number of the workshop, section, workplace where assembly operations are performed and where the component parts come from;
- designations of parts, assembly units, materials of components;
- consumption rates of materials and components, etc.
The picking department should be equipped with the necessary control and measuring instruments and tools, equipment and locksmith tools to perform fitting work, and the workplaces should be equipped with technical documentation corresponding to their specialization.
The efficiency of assembly work is estimated by the time of formation of optimal sets of parts of the required range and quality and their delivery to the assembly sites. High-quality picking reduces labor intensity and improves assembly accuracy.
Completion of interfaces consists in the selection of pairs of jointly working parts, when connected during the assembly process, the required clearance or interference is formed. Individual (piece) and group (selective) methods for selecting mated parts are used.
The acquisition of components and assemblies consists in preparing the sets necessary for their assembly from selected pairs, individual parts and assemblies that are not disassembled during the repair of machines. The acquisition of machines consists in concentrating directly in the zone of general assembly posts the units (mechanisms), assemblies and parts necessary for its implementation. Everything needed for assembly posts is transported by post kits.
Equipment and tools for assembly work
According to the purpose, the assembly devices are divided into the following groups:
- fixtures (stands) designed to fix the assembled units and large parts in the position required for assembly in order to facilitate it, for example, a stand for assembling a gearbox, a stand for welding;
- installation devices designed for the correct and accurate installation of the parts or assemblies to be connected relative to each other, which guarantees the accuracy of assembly dimensions;
- working devices designed to perform individual operations of the assembly process, for example, devices for pressing, installing and removing springs, etc .;
- control devices designed to control the accuracy of assembling parts and assemblies.
According to the nature of the application, assembly devices are divided into universal and special.
Universal devices and tools are used in assembly processes of small-scale and individual production, as well as in the repair of machines and equipment on site.
Special fixtures are designed and manufactured to perform specific steps in the assembly process. They are used in the assembly of specific nodes for which they are intended.
In assembly production, a variety of fixtures for assembling threaded, press and other joints, equipment for balancing parts and assemblies, portable and stationary fixtures and equipment for assembling by welding, benches for running in and testing assemblies, assemblies and machines in general, etc. are widely used. They are discussed below in relation to specific assembly operations.
Assembly quality control
In the technological processes of general and nodal assembly, an important place is occupied by technical quality control of the work. The quality of the final product is ensured by the incoming inspection of components, parts of our own production and semi-finished products, checking the accuracy of assembly equipment and tooling, as well as systematic checking of the progress of the assembly process to prevent and timely detect product defects. In the route technology, control operations and control elements included in assembly operations are indicated.
During nodal and general assembly, check:
- the correct position of the mating parts and assemblies;
- gaps in the joints;
- the accuracy of the relative position of parts and assemblies (parallelism, perpendicularity and coaxiality);
- accuracy of rotational movements (radial and axial runout) and translational movements (straightness) of moving parts, especially the executive bodies of machines and mechanisms;
- the tightness of the mating surfaces, the tightness of fixed and movable joints of parts;
- tightening of threaded joints, density and quality of setting rivets, density of rolling and other one-piece joints;
- the dimensions specified in the assembly drawings;
— fulfillment of special requirements (balance of rotating parts, adjustment of parts by weight, etc.);
- operational characteristics and parameters of assembled products and their components (productivity, developed pressure, accuracy of operation of traction and dividing devices, etc.);
— the appearance of the assembled products (the absence of deformations and damage to parts that may occur during the assembly process).
Most of these control operations are performed by assemblers and adjusters of equipment for assembling and assembled equipment. The function of control by the technological and control services includes checking the sequence established by the technological process and the correctness of the main and auxiliary assembly operations, compliance with the rules for using assembly fixtures and equipment.
Means of control are selected taking into account their metrological characteristics (limits and measurement accuracy) based on the required measurement accuracy. The permissible control error should usually not exceed 20% of the tolerance for the controlled value. The design features of controlled objects (configuration, overall dimensions, weight), economic factors, and the need to ensure safe working conditions are also taken into account.
For control operations, instruction cards are drawn up, which reflect in detail the sequence of control and the technical means used.
On fig. 6.7 shows the schemes of the main measurements during the assembly of mechanisms and machines.
In the process of measuring the gap, the shaft is shifted to the right or left, and the gap is determined by the deviation of the indicator arrow.
The parallelism of the two surfaces is checked with a ruler and a microstitch. The non-parallelism A is determined per 1 m of length according to the formula A -a / Ɩ mm / m, where a is the difference in the indicator readings at points 1 and 2, mm; Ɩ is the distance between points 1 and 2, m.
The perpendicularity of surfaces and axes is checked using a square or an indicator mounted on a tripod. The non-perpendicularity B is determined by the formula: B = b/Ɩ, mm/m, where b is the difference in the indicator readings when checking the perpendicularity at points 1 and 2; Ɩ is the distance between measurement points 1 and 2, m.
Rice. 6.7. Assembly control schemes: 1 - gap measurement; 2, 3, 8 — non-parallel control™; 4 - 6 - control of non-perpendicularity; 7 - definition of misalignment; 9-12 - beat control; 13 - height control; 14 - checking the parallelism of the axes of the crank and main journals
To improve the accuracy of the control of parallelism and perpendicularity, points 1 and 2 should be as far away from each other as possible.
The planes are checked for straightness and flatness using a ruler and a feeler gauge, as well as using a test plate “for paint”. In this case, the allowable number of paint spots per unit area is set.