Practical work No. 1
Development of a technological scheme for disassembling and assembling CE
Goal of the work
1. Study the concepts of the technology of disassembling and assembling assembly units.
2. Learn to develop a technological diagram for disassembling and assembling the CE and draw it up in the form of a technological diagram.
Initial data
The initial data for developing the assembly (disassembly) process flow diagram are:
Assembly drawing of the product with specification;
Technical conditions for assembly (disassembly) indicating the fit of mating parts, test modes of the product, technological instructions for the selection of parts, assembly, control and adjustment of matings or CE;
Repairable products program.
In addition to 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 technological scheme being developed.
1. Study the assembly drawing and the technical specifications for assembly attached to it.
2. Development of a structural and technological scheme for disassembling the SE.
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 dissect a given assembly into its component elements in such a way that disassembly can be carried out
the largest number of these elements independently of one another (in parallel).
This division makes it possible, when organizing repair work, to reasonably assign certain repair work to specific performers.
The disassembly diagram is constructed so that the corresponding assembly units are presented in it in the order in which these elements can be removed when disassembling the assembly. CE and parts are depicted on the diagram in the form of rectangles indicating the index, name and number of elements. For greater clarity, a rectangle depicting an assembly unit can be highlighted by marking its outline with a double line (Fig. 1).
In the diagram, rectangles characterizing assembly units are recommended to be placed on the left, and parts on the right along the line.
The beginning of 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 transmission input shaft assembly
1 - input shaft; 2 - nut; 3 - retaining ring; 4 - ball bearing
radial single row; 5 - retaining ring; 6 - 8x20 roller.
The report gives a brief description of the disassembly. Disassembly of the unit in question is carried out in the following sequence:
Unscrew the ball bearing nut 2, remove the retaining ring 3, remove the ball bearing 4, remove the retaining ring 5 and remove the rollers from the roller bearing 6.
A sample disassembly flow diagram is shown in Fig. 3.
The number of jobs is determined by the program of a particular repair enterprise and the complexity of performing the listed operations.
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Fig.3. Technological diagram for disassembling the primary shaft assembly
Disassembly must be carried out in a strict sequence prescribed by the technological regulations. The basic techniques and principles of disassembly are as follows:
Assembly units are disassembled directly at the general disassembly site, as well as at the sites of their repair and assembly in accordance with the technological diagram.
First, remove parts that can easily be damaged (discharge tubes, rods, levers, rods, etc.). Then individual assemblies are dismantled and disassembled at other workstations.
When removing large parts secured with a large number of bolts, to avoid the appearance of cracks, first loosen all the bolts and nuts half a turn and only then unscrew them.
Rusted connections are moistened with kerosene before unscrewing.
After disassembly, the fasteners are placed in mesh baskets for subsequent washing. It is not allowed to use a chisel or hammer to unscrew bolts, nuts, fittings, etc., as this may damage them. Shaped nuts and fittings are unscrewed with special keys.
Pressed parts are removed under a press or using pullers and devices. In some cases, fittings, bushings and axles can be pressed out with special drifts with copper tips and hammers with copper bikes.
When pressing a bearing out of the housing, force is applied to the outer ring, and from the shaft to the inner ring. Do not use percussion instruments.
It is advisable to place the removed parts on racks and devices for transportation to the sink, so as not to damage the working surfaces.
You cannot disassemble parts that are processed as an assembly during manufacturing (main bearing caps with blocks, etc.). In addition, it is prohibited to remove parts that are subject to joint balancing, as well as worn-in pairs of parts that are suitable for further work (bevel gears of the main drive, oil pump gears, etc.). Parts that are not subject to maintenance are marked, tied with wire, re-bolted and placed in a separate container or kept complete in other ways.
3. Construction of a technological diagram for the assembly of SE.
The assembly technological diagram, like the structural and technological diagram of disassembly, is an auxiliary technological document (not included in the mandatory technical documentation documents, which graphically shows:
The sequence of connecting parts and assembly units included in the product;
Composition of assembly units included in the product;
Performing operations not related to the connection of parts and assembly units (control, adjustment, filling of oil or working fluids, painting, packaging, etc.)
The assembly flow diagram is intended for:
Disclosure of the product structure and the possibility of using subassemblies;
Formalization and algorithmization of the development of the assembly technological process;
Product design assessments from a technological point of view.
For designing an assembly technological process, the most acceptable form of an assembly technological diagram is a diagram that provides ranking of assembly units by levels and orders. When drawing up such a technological assembly diagram, a number of formal descriptions and designations are also used.
1. Assembly units (AU) 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 supplied for assembly from outside (purchased or assembled in other departments).
2. The order of an assembly unit is always one greater than the maximum order of its constituent elements.
When determining the order of the assembly unit, the following must be taken into account:
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 connecting assembly units of a similar order (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 the assembly units in the ranked assembly process flow diagram, a rectangle is used, shown in Fig. 1.
3. The assembly flow diagram uses the following formal designations for actions associated with the assembly of product elements:
The connection of an assembly unit (Fig. 5a) is indicated by an arrow at a given assembly level with a transition number;
Attaching an assembly unit with additional actions (Fig. 56);
Actions not related to connecting the assembly unit and involving adjustment, measurement, testing, filling with working media, balancing, painting, packaging and others (Fig. 5c);
Intermediate disassembly when using adjustment using a fixed compensator (Fig. 5d).
General assembly line 7 8 9
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Rice. 6. Technological diagram of the assembly of the primary gearbox shaft
4. Drawing up a list of transitions of the nodal and general assembly.
The list of transitions must begin with a list of transitions of the general assembly.
The list of transitions of a subassembly is expressed in the listing 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. The structural diagram of constructing a route technological process for assembling a product is presented in Fig. 7.
Rice. 7. Block diagram of compiling a list of transitions of a nodal and general assembly
General assembly
1. _____________________________
2. _____________________________
CE2 assembly
CE11 assembly.
1. __________________________________________
2.______________________________________
CE12 assembly.
1.__________________________________________
2.______________________________________
The description of the route assembly technology is considered using the example of the assembly technology of the primary gearbox shaft.
General assembly
1. Install the primary shaft.
2. Lubricate the hole along the rollers with grease.
3. Install the rollers.
4. Install retaining ring 5.
6. Install the retaining ring.
7. Screw on and tighten the nut.
8. Punch the retaining ring.
Technological diagram is a graphic representation of the assembly sequence of a product and its components, performed according to certain rules and reflecting the technological structure of the machine.
The technological structure determines the hierarchy of assembly units included in the product (Fig. 2.7). The machine as a product is disassembled into 1st order assembly units and a corresponding set of parts. Assembly units of the 1st order are disassembled into assembly units of the 2nd order and many parts. Assembly units of the highest (d-1) order are disassembled only into parts.
Assembly is performed in reverse order. Assembly units of orders 1,..., (P- 1), corresponding to the completed stages of manufacturing a product (machine), are usually called assemblies, and the corresponding assembly is called a subassembly. The assembly, the object and product of which is the product, is called a general assembly (see Fig. 2.7). There are general and sub-assembly schemes.
In a course project, the role of a product is most often an assembly unit (assembly), however, dividing the assembly into a general and a subassembly is appropriate here as well. General assembly is a process whose product is an assembly unit specified in the task. A node is considered to be an assembly of nodes of a higher order that are included in a given one. The hierarchy of assembly units is necessarily reflected in assembly process diagrams.
Any assembly unit or part on the assembly diagram is depicted as a rectangle (Fig. 2.8, A). For an assembly unit, in the “Part Number” field, indicate the base part on which this assembly unit is assembled. Before the number of the base part, indicate the letters “sb”, before which they write a number indicating the order of the assembly unit, for example: “1 sb25” - assembly unit (assembly) of the first order based on part 25.
First, they draw up a general assembly diagram (Fig. 2.8, b), then - diagrams of the unit assembly (Fig. 2.8, V). Assembly begins with the base element (see Fig. 2.8, b). It can be either a part or an assembly unit
Rice. 2.7.
(node). If the basic element is a node, then in the general assembly diagram it should be designated as a first-order node, like other nodes shown in the diagram, regardless of whether they are manufactured or purchased (see Fig. 2.8, b). The product must have a base element number with the letters “sb” in front of it. The name of the base element and the product may differ. So, for example, when depicting a technological diagram for assembling a turbine rotor, the base part may be called “shaft”, and the product “rotor”. A unit assembled on the basis of a “body” part may be called a “body assembly” or, if the “body” was, for example, a valve body, and the assembly is a common one, a “valve”. On assembly diagrams, short words are written above the vertical leader lines.
Rice. 2.8. Assembly flow diagrams: A- image of the part (assembly unit); b- general assembly; V - subassembly
some instructions about the main technological actions being performed with verbs in the imperative mood: “press in”, “heat up”, “tighten”, etc.
Since assembly diagrams are developed only on the basis of an assembly drawing of a product or assembly unit (assembly), the greatest number of errors are made when high-order assemblies are identified. To avoid them, we must remember that a characteristic feature of an assembly is the ability to assemble it independently of other elements of the product. The assembly after assembly must be a single whole that does not fall apart when changing position. The connection of a shaft with a bushing with a clearance fit is not a unit. When the position changes, for example during transportation, such an assembly may spontaneously disintegrate into its constituent parts.
Assembly diagrams (see Fig. 2.8, V) depicted according to similar rules with strict adherence to the hierarchy of assembly units.
The sequence of connecting machine parts and assemblies cannot be arbitrary. For simple assemblies, most often only one assembly sequence is possible. For complex units and machines, various assembly sequence options are possible.
When determining the assembly sequence, the dimensional chains of the product are also analyzed. If there are several dimensional chains in a product, then assembly begins with the most complex and critical chain. In each dimensional chain, the assembly is completed by installing the elements that form the closing link. If there are dimensional chains with common links, assembly begins with the chain elements that have the greatest impact on the accuracy of the product. If the chains are equivalent in terms of the accuracy of the results obtained, then assembly begins with a more complex chain.
The assembly diagram reflects the sequence (order) of joining parts. However, it is often difficult to accurately reflect the true installation location of a particular part on the diagram.
Example 2.7. Figure 2.9 shows a diagram of the general assembly of the rear axis support of the spindle assembly of a lathe (see Figure 2.1).
Assembly begins with installation into the housing 1 flange 2 with three springs placed in it 3 and the outer ring of the bearing 4. Such a set of mutually oriented, connected, but not fixed parts is called a set. The kit parts arrive together for assembly.
After passing the spindle 8 through the hole in the flange 2, fixed in the housing U, a number of parts (inner ring of the bearing 6, pin 7, bushing 12 etc.) are installed on the spindle, which begins to serve as a base part. In particular, pin 7 is pressed into the spindle 8 , having previously drilled and unrolled the mounting hole.
The general assembly includes first order units and a separator (1sb5) and a glass (1sb 13). The separator is a purchased unit included in the bearing kit. The glass is a pre-assembled unit (installation of the cuff).
Example 2.8. Figure 2.10 shows diagrams of the general and subassembly of the oil pump (Figure 2.11).
Rice. 2.9.
NKP, V KP - outer and inner ring of the bearing, respectively
Rice. 2.10.
Rice. 2.11.
/ - drive gear; 2 - key; 3 - frame; 4 - drive gear; 5- key; 6 - drive roller; 7- cover;
8 - washer; 9 - bolt; 10 - pad; 11 - union; 12 - driven gear; 13 - driven roller; 14- screw; 15- cotter pin
For general assembly, two sets are used. The first is based on the first order unit - the drive roller (1sb6), the second - on the basis of the part - the driven roller 13. In accordance with this, the image of the kits is placed below and above the picking line.
When ensuring assembly accuracy by fitting and adjustment methods, partial disassembly of assembled units and reassembly are not reflected on technological diagrams.
The assembly diagram is a graphic representation of the composition and sequence of connection of elements and parts of the product in the form of symbols (Fig. 3). The diagram facilitates the development of a route technical process, giving a clear, visible idea of the sequence of product assembly. The diagram shows all the parts, assembly units and basic materials included in the device. The assembly diagram is depicted in the form of steps corresponding to the stages of assembly according to the principle “from simple to complex.”
The selected rational assembly route is designed graphically in the form of a technological diagram with a base part. The diagram itself is presented in the graphic part of the course project.
The assembly flow diagram with a base part shows in what sequence and by what processes it is necessary to attach to each other and secure the elements included in the product during its assembly. Stator with cover pos. 2 was chosen as the base part
5. Technological process of assembling um.
Check by external inspection the parts and assemblies arriving for assembly at a magnification of 6-9 times for the absence of contamination, burrs, burrs, sharp edges and mechanical damage. Check the availability of accompanying documentation for parts and assemblies.
Interoperational storage of parts: stator, cover with stator, housing and rotor, as well as the assembled device, should be carried out in desiccators with an indicator desiccant.
Subject all parts that have undergone complete mechanical processing to ultrasonic cleaning, except the stator with the cover.
Re-preserve the bearing according to the instructions specified in the technical specifications for ball bearings.
Store ball bearing parts at work places according to the instructions specified in the specifications for ball bearings.
Select pairs of ball bearings in terms of rigidity so that in terms of the displacement of the outer ring relative to the inner ring in the axial direction under a load of 1 kg, they do not differ from each other by more than 0.0005 mm.
Ensure that the outer ring of the w/p is seated in the cover socket, position 2, with a force of 0.2 ... 1 kg. Before checking the seating force, the outer ring of the w/p must be installed in the lid socket so that the outer end of the ring coincides with the plane of the end of the lid.
Secure the housing with the cover with 6 screws and washers.
Install screw position 6 first.
Secure flange pos. 5 with 6 screws.
Along the rotor necks pos. 1, ensuring a fit with a force of 5 ... 10 kg, press on the inner rings of the w/p. Traces from the landing of ball bearings in the form of scratches with a cleanliness of at least 7 are allowed on the rotor seating surfaces.
Install nuts pos. 9 onto the rotor journals and press them onto the rotor along Ø 3.5 into the groove.
Carry out dynamic balancing of the rotor.
Preparatory.
Flushing room.
Locksmith's shop.
Test.
Assembly.
Assembly.
Assembly
Adjustment.
The centers of the drilled holes (diameter and depth up to 2 mm) should be located at a distance of 2÷3 mm from the end of the VNZh7-3 alloy ring (balanced plane).
Check dynamic balancing.
Wipe the rotor assembly with inner rings from grease, metal dust and other contaminants.
Control.
The permissible imbalance is 0.01 gcm 2 .
Ensure that the outer ring of the w/p is seated in the housing socket, position 3, with a force of 0.2 ... 1 kg. Before checking the seating force, the outer ring of the w/p must be installed in the housing socket so that the outer end of the ring coincides with the plane of the housing bushing.
Check the fit of the outer ring of the w/p all the way into the housing socket, pos. 3, by pushing it back under an axial load of 15 kg. The housing, item 3, is suitable for assembly if a force of 15 kg causes a relative movement of the microcator pointer during 3-fold measurement by no more than 0.0004 mm.
Assembly.
Test.
If there is greater movement, it is allowed to remove the ring, additionally grind the socket and re-measure. Check the delivery of sh/p into the housing before each assembly.
Assemble the stator ball bearing with the cover and housing according to the specifications for the ball bearing.
Lubricate the ball bearings with VNII NP-228B OST 38 01438-87 grease, 20±2 mg each.
To ensure non-parallelism of the body plate pos. 3 regarding the cover pos. 2, within the limits indicated in the drawing, finishing of the plate before technological tests is allowed while maintaining the cleanliness and geometric shape of the surface.
Install the clamp pos. 4
Set the axial tension w/p. The amount of axial tension of the ball bearings is set according to the amount of elastic deformation of the bottom (membrane) of the device body. To determine the magnitude of elastic deformation of the membrane of the device body, it is necessary to apply an axial load P to the membrane, the value of which is equal to the value of the axial tension of the ball bearings in accordance with the technical requirements for the device.
Tighten screw pos.6 completely.
Lock the screw pos.6 through the flange pos.5 with clamps pos. 4.
Test.
Check axial interference.
Place screws 7,8,11 on EP-275 enamel.
In two diametrically located slots of the screw pos. 6 and onto the cylindrical surface of the part, pos. 5 opposite the slots of the screw pos. 6 apply EP-275 enamel.
Dry the device at a temperature of +80°C – 1.5 ÷ 2 hours.
Carry out technological tests according to specifications.
Place the device in the container.
Hand over to the warehouse for finished products.
Assembly.
Assembly.
Adjustment.
Assembly.
Thermal.
Test.
Transmission.
The assembly process is a set of operations as a result of which parts are combined into assembly units, blocks, racks, systems and products. The simplest assembly and installation element is a part that, according to GOST 2101-68, is characterized by the absence of detachable and permanent connections.
An assembly unit is a more complex assembly and installation element, consisting of two or more parts connected by a detachable or permanent connection. A characteristic feature of an assembly unit is the ability to assemble it separately from other assembly units.
The technological diagram of the assembly of a product is one of the main documents drawn up when developing the assembly process. The breakdown of the product into assembly elements is carried out in accordance with the assembly composition diagram, the development of which is guided by the following principles:
– the diagram is drawn up regardless of the product production program based on assembly drawings, electrical and kinematic diagrams of the product;
– assembly units are formed subject to the independence of their assembly, transportation and control;
– the minimum number of parts required to form an assembly unit of the first stage of assembly must be equal to two;
– the minimum number of parts attached to an assembly unit of a given group to form an assembly element of the next stage must be equal to one;
– the assembly structure diagram is constructed subject to the formation of the largest number of assembly units;
– the circuit must have the property of continuity, i.e. each subsequent stage of assembly cannot be carried out without the previous stage.
An assembly diagram with a base part indicates the time sequence of the assembly process. With such an assembly, it is necessary to select the base element, i.e. a basic part or assembly unit, which is usually chosen as the one whose surfaces will be used when installed in the finished product. In most cases, the base part is a board, panel, chassis and other elements of the product’s supporting structures. The direction of movement of parts and assembly units in the diagram is shown by arrows, and the straight line connecting the base part and the product is called the main axis of the assembly.
When constructing an assembly flow diagram, each part or assembly unit is depicted in the form of a rectangle (Fig. 1, a), in which the position of the part according to the specification for the assembly drawing (1), its name (2) and designation (3) are indicated according to the design document, as well as the number of parts (4) supplied per assembly operation. The rectangle dimensions are recommended 50x15 mm. It is allowed to depict normalized or standard fasteners in the form of a circle with a diameter of 15 mm, in which the position according to the specification and the number of parts are indicated (Fig. 1, b).
Technological instructions for performing assembly operations or electrical installation are placed in a rectangle bounded by a dashed line, and the place of its implementation is indicated with an inclined arrow at the point corresponding to this operation. Thus, on technological assembly diagrams the nature of the permanent connections is specified, for example, welding, soldering, gluing, pressing, etc.; material used during assembly; the nature of the installation operations of the elements: wave solder, electric soldering iron, etc.; the nature of the product’s moisture protection, control and labeling operations (Fig. 7.1).
To determine the number of electrical electronics and ICs to be installed on boards during assembly operations, a preliminary calculation of the assembly rhythm is necessary:
where T i is the complexity of the i-th assembly operation.
1. Average completeness of the assembly composition (number of assembly units at each assembly stage):
where mi is the number of groups, subgroups, assembly units.
2. Indicator of dismemberment of a given assembly process M:
where k is an indicator of accuracy quality;
q is the number of assembly units of a given accuracy level.
A correctly selected assembly composition scheme allows you to establish a rational order for completing assembly units and products during assembly.
For the designed metal detector, a circuit board assembly with a base part was chosen. The base part is a printed circuit board, manufactured in accordance with the presented design documentation. Assembly is proposed to be carried out in the following order:
– parts secured with detachable and permanent mechanical connections;
– radioelements and ICs installed on automatic and semi-automatic devices;
– elements installed manually;
– group soldering of elements (for example, wave solder);
– installation and soldering of elements manually;
– assembly quality control, locking of threaded connections, marking.
The technological diagram for assembling the metal detector, as well as other necessary documentation, is given in Appendix E.
To determine the assembly sequence of the product and its components, assembly process diagrams are developed. Assembly units of a product, depending on their design, can consist of either individual parts or assemblies and subassemblies and parts. There are subassemblies of the first, second and higher stages. The first stage subassembly is included directly in the assembly; the subassembly of the second stage is included in the first, etc. The subassembly of the last stage consists only of individual parts.
Technological diagrams are drawn up separately for the overall assembly of the product and for the subassembly of each of its components (subassemblies). Let's consider the principle of drawing up technological assembly diagrams. Figure 20.1 shows the assembly unit - a shaft with a worm wheel, and Figure 20.2 - a technological diagram of its assembly.
Fig. 20.1 Assembly unit - shaft with worm wheel
Technological diagrams are the first stage in the development of the assembly process. The diagrams clearly reflect the assembly route of the product and its components. Assembly flow diagrams are drawn up on the basis of assembly drawings of the product.
On the technological diagrams, each element of the assembly is indicated by a rectangle divided into three parts. In the upper part of the rectangle the name of the part or assembly unit (assembly or subassembly) is indicated, in the lower left part - the number assigned to the part or assembly unit on the assembly drawings of the product, in the lower right part - the number of assembled elements. Assembly units are designated by the letters “Sb” (assembly). Basic are the parts or assembly units from which assembly begins. Each assembly unit is assigned a number of its base part. For example, “Sb.14” is an assembly unit with base part 14 (wheel hub).
On the left side of the diagram (Fig. 20.2) the basic part or basic assembly unit is indicated. On the right side of the diagram the assembled product is indicated. These two rectangles are connected by a horizontal line. Above this line, rectangles indicate all the parts included directly in the product, in the order corresponding to the assembly sequence. Below this line, rectangles indicate assembly units directly included in the product.
Schemes for assembling assembly units can be built either separately or directly on the general diagram, developing it at the bottom of the diagram.
The corresponding level of the node is indicated by a digital index before the letter designation “Sat.” For example, if in the designation the assembly has the index “1Sb.7”, which means the first stage assembly with base part No. 7.
Assembly technological diagrams are accompanied by signatures if they are not obvious from the diagram itself, for example, “Press in”, “Weld”, “Check for runout”, etc.
Technological schemes for assembling the same product are multivariate. The optimal option is selected from the condition of ensuring the specified build quality, efficiency and productivity of the process at a given scale of product production . The design of the product must allow for its assembly from pre-assembled components. The component composition of a product can be determined by analyzing the assembly drawing and mentally disassembling the product. Assemblies can be “removed” entirely during disassembly.
Drawing up technological diagrams is advisable when designing assembly processes for any type of production. Technological diagrams simplify the development of assembly processes and facilitate the assessment of a product for manufacturability.
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