Fixing wires and harnesses in the product case. Industrial methods for harvesting wire harnesses. The technical characteristic of the production facility for which this technological process is being developed is the manufacture of harnesses
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1. Technical characteristics of the production facility
Specification the object of production for which this technological process is being developed is the manufacture of harnesses.
General information about harnesses and their manufacturing technology
Harness installation represents the electrical installation of EVA units using volumetric insulated wires united in a bundle.
The harness designs are determined by the structural features of the frames and the requirements for the maintenance and repair of equipment. Harnesses are divided into interblock and intrablock, which, in turn, are divided into flat, volumetric, with movable branches.
They are also distinguished by the degree of complexity: the number of branches and closed branches. Harness installation is carried out using mounting wires and cables various types and appointments. Wire insulation can be fibrous from kapron threads (MShDL, MGSH, MGSHD) or fiberglass (MGSL, MGSLE); polyvinyl chloride (PMV, MGV) and fibrous polyvinylchloride (MShV, MGSHV, LPBL), plastic in the form of a shell of polyvinyl chloride (MKSH, MPKSH); rubber (LPRGS, PRP, APRF, PRG) and fluoroplastic (MGTF). The choice of insulation is determined by the electrical voltage and operating conditions of the equipment.
At normal temperature and humidity, wires with fibrous or PVC insulation are used, at elevated temperature and humidity - with fiberglass or fluoroplast insulation.
If it is necessary to protect against external electrostatic fields, the installation is carried out with shielded wires and cables with mandatory grounding of each screen.
Part of the installation wires, especially those with rubber insulation, are supplied with tinned conductors. This preserves electrical resistance and mechanical strength copper wire, located in rubber or vulcanized rubber, and speeds up the process of preparing wires for mounting and soldering.
When designing, the tolerances for the harness parameters can be determined analytically. When calculating the dimensional chain, they take a wire with a margin for soldering and compensation for bends at contact connections. The deviations of the master link must take into account the tolerances for the geometric dimensions of the frame, the fastening of the bundle, the length of the wires during layout, the installation of technological studs on the template.
The initial development of the harness design is carried out as follows. On the assembled frame lay the wires according to the installation or circuit diagram. The ends of the wires are marked on both sides with tags indicating the route number (^ -2; 1 -6; 3 -5 etc.), after which their length is measured and the data is entered in the table of field connections.
The sketch is used to develop a template and. in particular, to determine the placement of technological studs. An experimental harness is assembled on the template, and after it is installed on the frame, the template is adjusted.
2. Manufacturability analysis
Technological design is called, which, at the lowest cost, is the easiest to manufacture. Technological design should include:
1. The widest possible use of unified assemblies, standardized and normalized parts of the elements of parts;
2. Perhaps a smaller number of parts of the original and complex shape and various names, as well as a greater repeatability of parts of the same name;
3. Creation of parts of a rational form with easily accessible surfaces for processing and sufficient rigidity in order to reduce the labor intensity and cost of the entire product;
4. It should be rational to assign the accuracy of the size and class of surface roughness;
5. The presence of basing surfaces on the details;
6. Most rational way obtaining blanks for parts (castings, stampings with sizes and shapes that are as close as possible to finished parts, i.e. providing the highest material utilization rate and the lowest labor intensity);
7. Complete elimination or possibly less use of fitting and fitting work during assembly by manufacturing interchangeable parts and mechanization, automation of assembly work;
8. Simplification of assembly and the possibility of parallel assembly in time and space separate parts products;
9. The design should be easy to assemble and disassemble, as well as provide access to any mechanism for adjustment, lubrication, repair.
The design being developed is technologically advanced, since it provides for:
1. Perhaps a smaller number of parts of the original and complex shape and various names, as well as a greater repeatability of parts of the same name;
2. Creation of parts of a rational form with easily accessible surfaces for processing and sufficient rigidity in order to reduce the labor intensity and cost of the entire product;
3. Simplification of assembly and the possibility of parallel assembly in time and space of individual parts of the product;
4. Complete elimination or possibly less use of fitting and fitting work during assembly by manufacturing interchangeable parts and mechanization, automation of assembly work.
3. Technological route for the manufacture of the tow
The technological route for the manufacture of a bundle is the following sequence of operations:
1. Preparatory operation
2. Equipment
3. Preparation of installation wires
4. Wire layout on the template
5. Knitting a tourniquet
6. Control
4. Detailed description of the main operations
1. Preparatory operation
2. Equipment
3 . Ppreparation of installation wires
Preparation of installation wires consists of the following operations: dimensional cutting, removal of insulation and termination of wire ends, marking, maintenance and twisting of wires. If the technological process provides for a continuous layout of the wire on the template, then cutting, removing insulation and terminating the ends is carried out after the formation of the bundle.
Wire cutting by hand simple tools(scissors, wire cutters), determining the length of the wire according to the sample or using a ruler. In mass production, this operation is automated. Universal are machines for measuring cutting and simultaneous removal of insulation from the ends of the wire.
Depending on the type of insulation used various ways stripping: notch , electric firing or thermal softening With subsequent mechanical contraction of the insulation, and certain ways termination of wire ends.
Textile, plastic and film insulation is removed by incision or electric firing. The removal of multilayer insulation has a number of features. So, in the presence of fiberglass, the outer plastic insulation is removed by electric firing, and the inner (fiberglass) is untwisted, twisted and cut off at a distance of 1 mm from the end of the outer insulation. Outer textile braids require stepped cutting of the ends of the wires. For example, between a cotton braid and a residential wire, a section (3-10 mm) of the main PVC or rubber insulation is left. The end of the braid is fixed with glue, an insulating tube or a thread bandage coated with glue.
Stripping of heat-resistant fluoroplastic insulation is carried out by electric firing at an elevated temperature of the filament. This releases toxic gas - fluorine, which must be removed from working area with a suction system.
The stripping must preserve the quality of the non-removable insulation, exclude a cut or break in the current-carrying conductors and be sufficiently productive. In addition to machines for cutting wires and stripping insulation, special devices have been developed for thermomechanical stripping. Their main working elements are a filament and sponge-knives.
The thread burns through the insulation when the wire is rotated around its axis. Sponges are a support for the wire when burning the insulation, protect it from charring and the thread from mechanical damage, provide insulation together with the thread. The working edges of the jaws have a rounding radius of 0.08 mm and are polished, which will exclude a notch and a break in the current-carrying wires. Insulation strippers - can be equipped with a device for connecting to vacuum system for suction of toxic products of insulation firing. The thermomechanical method allows you to remove insulation in one step from wires with a cross section of 0.07-0.35 mm 2.
For installation, shielded wires and RF coaxial cables are used, having an outer PVC coating on top of the shielding braid. The separation of the coating by notch is laborious and does not provide High Quality end splits.
The thermomechanical method allows you to remove the plastic insulation within 2-3 seconds without damaging the braid.
sponge knives , equipped with heaters penetrate the insulation and cover the shielding braid in diameter. The section of insulation inside the jaws heats up and expands, making it easy to remove it by pulling it off the end of the wire.
Further cutting of the ends of the shielded wires is to remove the shielded braid in a certain area. One of the removal methods is a circular cutoff of the braid using a punch-die cutting pair.
The working part of the punch is made in the form of a cone, turning into a sphere, which allows it to move quite easily inside the braid and provides an even cut of the screen end on the sharp edges of the matrix . The method is implemented with the help of devices of various designs, which make it possible to cut off in 3–4 s.
There are other ways to remove the shielding braid: a helical cut with rotating cutters and knives, cutting off the annular thickening of the braid.
To extract the end of the insulated wire through the shielding braid, the core is pulled apart with a sharp tool: the braids and the wire are pulled through the hole formed. The most common tool is a grooved needle, which is inserted from the end of the shielded wire between the braid and the insulated wire. In a certain place, the tip of the needle pushes the braid apart and, using the eye of the needle, pulls out the end of the wire. This operation is performed in 3-4 seconds manually, guiding the needle using simple devices.
Termination of the ends of shielded wires consists in grounding the shields or fixing the end of the braid relative to the wire. Grounding is carried out by attaching the free end of the braid to the elements of the frame, soldering an additional wire, applying a bandage of bare tinned wire, and then soldering it. Soldering points are protected with insulating tubes.
A non-grounded braid is terminated between two insulating tubes, one placed under the screen and the other outside or between layers of insulating tape. The end of the braid is fixed with a thread bandage or a wire bandage, followed by soldering.
After removing the insulation, the bare ends of the wires are stripped, and the stranded wires are twisted at an angle of 15-300 to the wire axis. last operation performed manually (core cross section less than 0.11 mm 2), with pliers or using special devices. The prepared ends of the wires are subjected to hot tinning by immersion in a solder bath.
Wire marking is necessary to facilitate installation, control, troubleshooting and repair. Use wires with colored insulation and mark them with tags, adhesive tapes or by applying markings directly to the wire insulation. Colored insulated wires are usually used for internal installation EVA. The wiring diagrams indicate the color of the mounting wires with abbreviated symbols or digital codes. Wire marking sticky tapes consists in applying bandages from this tape to the ends of the wires. Marking with the help of marking tags made of polyvinyl chloride tubes has received the greatest application. The tag is attached to the end of the wire. In this case, the tag should overlap the edge of its insulating braid by 1-3 mm. The tags are put on the wires in such a way that their slipping during shaking and vibrations is excluded.
Symbols on the surface of the marking tags are specified in wiring diagrams and are carried out in accordance with industry standards. The production of tags (marking, drying, cutting) is carried out on special machines. Mounting wires are twisted to eliminate electrical interference and reduce the mutual influence of circuits. The stranding pitch is 10-40 mm and increases depending on the increase in the wire cross-section (0.05-0.75 mm 2). This operation is performed manually with a drill or on special machines.
4 . Wire layout on the template
harness mounting wire isolated
Structural and technological development of the harness makes it possible to manufacture it outside the EVA by laying out the mounting wires and cables on the template. Depending on the configuration of the bundles, flat or three-dimensional templates are used. A flat template is a base on which, in accordance with the routing (see Fig. 2) and the configuration of the bundle, metal studs are located. Installation wires are laid between the studs. To protect the wires from damage, insulating tubes are put on the studs. To fix the ends of the wires, the design of the template provides holes located next to the studs, or special clips. Volumetric template has additional elements that allow you to lay out wires and fix them in three planes.
There are universal flat templates that have holes located with a certain pitch and are designed for installing studs. The layout of the studs on the template can be changed depending on the routing and bundle configuration.
Designs of electrified templates have been developed that increase the productivity of harness manufacturing and eliminate installation errors. On such a template, the ends of the mounting wires are fixed with special clamps electrically connected to signal (green) and control (red) lamps. The lamps and clip-buttons are switched in such a way that when the template is connected to the network, two lamps of the first route light up. With the correct laying and fixing of the wire, the lights of the second route light up, etc. Electrified templates are more expensive than conventional ones, and it is advisable to use them in the mass production of EVA.
When laying out wires on templates, some general rules. Several bundles should be made from wires of different cross-sections, combining wires that are close in diameter. insulation (eg 1 to 3 and 3 to 6 mm). Shielded drives must be located inside the bundle, so they start the layout with them. The screens are pre-cut and soldered, in the presence of an external metal braid, it is wrapped with a keeper tape or insulated with a tube. Short wires of small cross sections are laid inside the bundle. Long wires are laid outside to form front side. Spare wires should be on top with access to their ends. These rules are easy enough to follow when laying out manually.
The sequence of wire layout on the template is manually set in the connection table, taking into account the listed rules. Often a drawing is placed on the template with the designation of the tracks. The end of the wire wound from the coil is marked with a tag and fixed on the template. The wire is cut in place after laying out between the studs and its end is marked. These transitions are repeated many times. The cutting of the ends with such a sequence of operations is carried out after knitting the bundle. Manual layout on the template is performed by the installer, and it is very laborious. In serial production, it can be mechanized using a program-controlled device.
5 . Knitting harnesses
Two (or more) insulated wires with a length of more than 50 mm running in parallel along the same route must be bundled. The only exception can be an unacceptable increase in mutual pickups in electrical circuits. For knitting, threads, cords, braid, insulating tapes, heat shrink tubes, etc. are used. The operation is usually carried out on a template. Knit step t depends on wire section, number of wires n and diameter D tourniquet. On curved sections, the pitch should be reduced depending on the diameter of the bundle bend. At the branching of the wires, the knitting should have 2-5 turns on all branches, the bandages should be made from 2-3 adjacent loops. The ends of the bundle must have bandages and end nodes.
Knitting is carried out in one, two or more threads with manual tension or with the help of devices. To reduce the complexity, the process of knitting harnesses is mechanized using pneumatic guns, and sometimes automated, by knitting harnesses on special semi-automatic machines.
To protect against mechanical damage, the tourniquet is wrapped with insulating tape along its entire length or in a certain area. If it consists of wires with cotton or silk insulation, then the bundle is impregnated with a water-repellent composition to protect against moisture. To protect against exposure high temperature or aggressive environment, the bundles are placed in tubular, tape, strip or wicker casings. They are put on manually or on the machine after removing the tourniquet from the template. Thus, knitting harnesses is no less time-consuming operation than laying out and marking wires.
In addition to the use of various devices for the mechanization of the operations of manufacturing a tow, it is advisable to use conveyor lines in conditions of mass production. In this case, the technological process is divided into a number of small operations. At each workplace, the layout of wires of the same section and brand is completely carried out. When determining the cycle of the conveyor, they are guided by the layout operation, based on the fact that the knitting operation is easier to subordinate to the selected rhythm. For example, knitting 16-24 loops takes 3-5 minutes. Most often, the cycle of work is 5 or 7.5 minutes.
The conveyor method of making harnesses has other features. The layout of the wires is carried out continuously, winding them off the coils. A set of tags is preliminarily put on the end of the wire to mark all routes performed at a given workplace.
Universal templates are used, equipped with studs both in places of kinks and branches, and in places of subsequent cutting of wires. The layout routes are marked with the help of special stencils placed on the templates. For knitting harnesses, threads are used that can withstand sufficiently large tension forces. After knitting, the wires are cut, the bundle is removed from the stencil and the ends are cut.
The conveyor for the production of bundles is located in a horizontal plane, closed and transports templates using trolleys. In addition to templates, it is equipped with guns for knitting harnesses, devices for stripping insulation, and a tinning unit. The conveyor method simplifies the operations performed at each workplace and reduces the overall complexity of the production of harnesses. Its disadvantages are the tension of the wires during layout and the deformation of the bundle after removal from the template, which worsens the quality of knitting.
6 . Co.control
After the harness is made, the quality of the termination of the ends of the wires and screens, the presence of markings, the absence of damage to the current-carrying conductors and insulation, and the quality of tinning are controlled. Integrity electrical circuits check with probes. In circuits with a large number of intermediate connections, the resistance is measured.
During the control, the ribbon cables are checked for the absence of conductor breaks, the insulation resistance between the conductors and the ground buses, the presence of electrical connections between the connector contacts and the ribbon wire.
For control, special automated stands have been developed, for example, with the number of points to be checked is 90 and the main technological time for checking the product is not more than 30 s. The control is carried out by checking the electrical circuits, comparing the states of the switches and then transferring the results to the light indication panel. Stands can work in automatic and manual modes.
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4.1. Complete electrical devices with mounted internal secondary circuits must be manufactured at factories or (as an exception) at the MEZ.
4.2. The basis for the development of technical documentation is the task issued by the customer for the manufacture of electrical equipment.
4.3. Based on the task, design documentation for the product is developed (electrical schematic diagrams, connections and connections, documentation for the manufacture of metal cases and other metal structures).
4.4. Based on the drawings, a list of consumption rates of materials and components for the device is compiled. Technological documentation is developed for serial production.
4.5. After picking, the task is transferred to the production unit for work to be performed.
4.6. When performing secondary circuits on the same type of devices, there is no need to lay wires in each case in place. It is more productive to conduct preliminary preparation of wire harnesses on special tables-stands using templates. To work on these tables, you must first draw up a sketch of the wiring harness.
4.7. The sketch is made on the basis of the connection diagram, the layout of the laying route, as well as the laying places on the switched device. The wiring harness can be sketched in single line (see figure 4.1, a) and isometric (see Fig. 4.1, b) images.
On sketches, wire harnesses with all branches and bends should be drawn with one line.
On each rectilinear section of the bundle (from corner to corner or branch), the dimensions determined when measuring the route for laying the wiring harness are applied (see Fig. 4.1, a). On the sketches, straight sections and bending angles of the wire harness to the edge are depicted as lines, and the bending angles of the bundle to the plane are shown as a cross or other mark. On all sections of the flow in circles indicate the number of wires.
It is necessary to take measurements in place and apply dimensions on the sketch with an accuracy that excludes marriage during installation and excessive consumption of wires during the preparation of bundles.
According to the sketches, the length of the wires is determined and marked on the connection diagram.
Rice. 4.1. Wire Harness Sketches
4.8. With multi-wire laying, it is necessary to take measurements along the middle wire, i.e. in the center of the harness. Measure the branches from the main bundle to the apparatus, adding the length of the wire required for bending and connecting it to the apparatus. According to the sketch, the length and number of wires for pre-working are calculated. The lengths of the wires calculated according to the sketch are affixed to wiring diagram.
4.9. The wiring harnesses according to the sketches are arranged as follows. According to the marks on the wiring diagram, they take the required number of wires of the appropriate length, which are laid on the table in a stream of the intended shape. Since the assembly of the bundle, as a rule, starts from a series of clamps, the ends of the wires have different lengths depending on the place of their connection. Fasten the tourniquets with temporary bandages. The first bandage is applied at a distance of 50-60 mm from the beginning of the first straight section of the tourniquet. The following bandages are applied at intervals necessary to maintain the shape of the bundle being assembled (every 500-600 mm).
If it is necessary to form a tourniquet with an angle to the edge, then a mark is made on it with chalk according to the size of the straight section on the sketch. Stepping back from this mark to a distance equal to half the width of the bundle, a second mark is made on the inner wire, along which this wire is bent. All the following wires bend along this wire. When branching, the parts of the bundle do the same, only in this case they retreat to a distance equal to half the width of the branch. After the bend is completed, the next straight section is measured according to the sketch, and so on until the end of the bundle.
After complete assembly the tourniquet is bent to a plane. Since the lower row of wires is stretched when the wire harness is bent onto a plane, when assembling the bundle, an allowance is given to the lower row to compensate for this stretch.
Bundling (see fig. 4.2) and bending of wire harnesses to the plane (see fig. 4.3) should be performed using special tools or plates.
Rice. 4.2. Bundling wire flow:
a- compress for packing; b- package of wires; 1 - screw with washer; 2 - pressure plates; 3 - lower clamp bar with screw thread; 4 - gaskets
Rice. 4.3. Bending the flow of wires to a plane
a- using a wooden plate; b- using an aluminum bracket; 1 - wooden plate; 2 - wire flow; 3 - wooden plate; 4 - bandage; 5 - bracket made of sheet aluminum
4.10. If it is necessary to manufacture several identical bundles or jumpers according to the same scheme, it is recommended to use templates made from electric cardboard, plywood or other sheet material and representing a layout of a part or the entire electrical structure to be mounted, universal templates - tables on which plates with rows of holes are installed, where studs are laid according to the markup, as well as three-dimensional templates.
4.11. When preparing and installing a wiring harness on electrical structures using templates made of sheet material, for example, from electrical cardboard, you should:
On a sheet of electrical cardboard 0.5 mm thick, mark the panel diagram with a pencil and a ruler, mark the attachment points with crosses;
Through the marked electrical cardboard attached to the panel, using a center punch, mark on the panel the attachment points for devices, apparatus and wire harnesses;
After marking the panel, remove the template and mark the following electrical structures of the same type in the same way;
Transfer the marked electrical structures for further processing, and according to the template on the table-stand, prepare and route the flows and terminate the wires. In order to prevent the bundle on the template from shifting when laying and terminating the wires, through holes should be made along it on the template in three or four places, with the help of which the wire flow is temporarily attached to the template;
Install devices, devices and relays or their layouts (templates) - cut out from steel sheet base projections. To install mock-ups on the electrical structure in places corresponding to the mounting holes of apparatuses and devices, press in bushings 10 mm high, on which to place the mock-ups of the equipment, fixed to the electrical structure with screws;
Lay the prepared wiring harnesses and fix them on the electrical structures;
Remove mock-ups from electrical structures and install devices and devices instead;
Attach wires to dial-in clamps, devices and devices.
4.12. When preparing wire harnesses using universal templates (see Fig. 4.4), you should:
Screw the studs 2 into the holes of the inclined wooden plate 1, installed on the table, in the direction of the wiring harness 4, and if there are no holes, hammer nails without hats; also install the studs at the locations of the contact springs and the leads of the coils of the devices;
Lay out the wires according to the wiring diagram. To do this, install the turntables with wires near the universal template table; unwinding wire 3 from the turntable, lay it behind the studs in the direction of the wire flow and fasten it with two or three turns on the stud-pin of the device furthest from the terminals; fasten the other end of the wire in the same way on the pin of another device or clamp to which the wire is to be connected, and cut it off. Similarly, lay out the remaining wires of the bundle;
Perform bandaging (knitting) of wires in bundles in straight sections with a step of 150-200 mm, depending on the thickness of the bundle, as well as in all places where the wires exit the bundle;
Remove the ends of the wires from the studs imitating the outputs of the apparatus, straighten and bite off according to the ruler-template to a length that makes it possible to attach the wire to the output of the apparatus. The template ruler should be applied with an edge to the plate, and the plane should be applied to the bitten off ends of the wires;
Remove the prepared bundles from the stove, terminate the wires and mark the flows.
On universal templates, by rearranging the studs, it is possible to prepare wire harnesses according to various schemes.
Rice. 4.4. Preparing a wire harness using a universal template.
4.13. When preparing and laying wire harnesses using a three-dimensional template (see Fig. 4.5), you should:
Lay the wires on the dashboard;
Install the instrument sheet with the wires laid on the template;
Install the mounting clamps on the mounting structures in accordance with the assembled scheme;
Run the laying of wire flows descending from the instrument sheet to devices, devices, typesetting clamps and secondary buses;
Terminate the wires and attach their ends to the clamps;
Disconnect the ends of the wires from the terminals of the devices and secondary buses;
Remove the instrument sheet with wires from the template, transfer it to the device to be mounted and fix it on the panel.
Rice. 4.5. Harvesting wires using a three-dimensional template.
1 - three-dimensional template; 2 - mounting structure; 3 - assembly of typesetting clamps; 4 - front part of the template with a bundle of terminated wires; 5 - bandage; 6 - wiring harness
4.14. A large number of jumpers or simple streams consisting of three or four wires should also be made using templates (see Fig. 4.6):
In place, make one jumper-sample (see Fig. 4.6, a). If the jumper turns out to be bent in different planes, unfold its corners (but not unbend) into one plane;
Lay the prepared jumper sample on the first template - a piece of plywood or a smooth board (see Fig. 4.6, b). In one of the rings and internal parties at the corners of the jumper, hammer in the studs 1, which should protrude above the plane of the plywood (board) by 10-12 mm. Thus, a template is formed according to which the required number of jumpers can be made;
Remove jumper 2 from the studs, straighten it along its entire length and lay it on the second template - a piece of plywood (board) 200-250 mm wide (see Fig. 4.6, in) and a length that is 100-120 mm longer than the length of the straightened jumper;
On one side, along the width of the template, fix stop 3 with a height of 5-8 mm. Press the end of the jumper against the stop and mark the stripping line 4 and the wire cutting line 5 on the template;
According to the template, cut off pieces of wires of the required length, remove the insulation and terminate;
Bend the prepared wire segments on the first template, for which put one of the segment rings on the first stud, and then manually insert the wire alternately behind the subsequent studs and bend in one plane. Remove the prepared jumpers from the template studs. Bending jumpers in other planes, if necessary, should be done by deploying along the sample segment in the required directions.
Rice. 4.6. Jumper making
For the manufacture of simple (short) bundles, the sections of wires of the required length and configuration prepared in this way should be laid in bundles and bandaged.
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1. Technical characteristics of the production facility
The technical characteristic of the production facility for which this technological process is being developed is the manufacture of bundles.
General information about harnesses and their manufacturing technology
Harness installation is an electrical installation of EVA units using volumetric insulated wires combined into a bundle.
The harness designs are determined by the structural features of the frames and the requirements for the maintenance and repair of equipment. Harnesses are divided into interblock and intrablock, which, in turn, are divided into flat, volumetric, with movable branches.
They are also distinguished by the degree of complexity: the number of branches and closed branches. Harness installation is carried out using mounting wires and cables of various types and purposes. Wire insulation can be fibrous from kapron threads (MShDL, MGSH, MGSHD) or fiberglass (MGSL, MGSLE); polyvinyl chloride (PMV, MGV) and fibrous polyvinylchloride (MShV, MGSHV, LPBL), plastic in the form of a shell of polyvinyl chloride (MKSH, MPKSH); rubber (LPRGS, PRP, APRF, PRG) and fluoroplastic (MGTF). The choice of insulation is determined by the electrical voltage and operating conditions of the equipment.
At normal temperature and humidity, wires with fibrous or PVC insulation are used, at elevated temperatures and humidity - with fiberglass or fluoroplast insulation.
If it is necessary to protect against external electrostatic fields, the installation is carried out with shielded wires and cables with mandatory grounding of each screen.
Part of the installation wires, especially those with rubber insulation, are supplied with tinned conductors. This preserves the electrical resistance and mechanical strength of the copper wire in rubber or vulcanized rubber, and speeds up the process of preparing wires for mounting and soldering.
When designing, the tolerances for the harness parameters can be determined analytically. When calculating the dimensional chain, they take a wire with a margin for soldering and compensating for bends at contact connections. The deviations of the master link must take into account the tolerances for the geometric dimensions of the frame, the fastening of the bundle, the length of the wires during layout, the installation of technological studs on the template.
The initial development of the harness design is carried out as follows. On the assembled frame, wires are laid according to the wiring or circuit diagram. The ends of the wires are marked on both sides with tags indicating the route number (^ —2; 1 —6; 3 —5 etc.), after which their length is measured and the data is entered in the table of field connections.
The sketch is used to develop a template and. in particular, to determine the placement of technological studs. An experimental harness is assembled on the template, and after it is installed on the frame, the template is adjusted.
2. Manufacturability analysis
Technological design is called, which, at the lowest cost, is the easiest to manufacture. Technological design should include:
1. The widest possible use of unified assemblies, standardized and normalized parts of the elements of parts;
2. Perhaps a smaller number of parts of the original and complex shape and various names, as well as a greater repeatability of parts of the same name;
3. Creation of parts of a rational form with easily accessible surfaces for processing and sufficient rigidity in order to reduce the labor intensity and cost of the entire product;
4. It should be rational to assign the accuracy of the size and class of surface roughness;
5. The presence of basing surfaces on the details;
6. The most rational way to obtain blanks for parts (castings, stampings with sizes and shapes that are as close as possible to finished parts, i.e. providing the highest material utilization and the lowest labor intensity);
7. Complete elimination or possibly less use of fitting and fitting work during assembly by manufacturing interchangeable parts and mechanization, automation of assembly work;
8. Simplification of assembly and the possibility of parallel assembly in time and space of individual parts of the product;
9. The design should be easy to assemble and disassemble, as well as provide access to any mechanism for adjustment, lubrication, repair.
The design being developed is technologically advanced, since it provides for:
1. Perhaps a smaller number of parts of the original and complex shape and various names, as well as a greater repeatability of parts of the same name;
2. Creation of parts of a rational form with easily accessible surfaces for processing and sufficient rigidity in order to reduce the labor intensity and cost of the entire product;
3. Simplification of assembly and the possibility of parallel assembly in time and space of individual parts of the product;
4. Complete elimination or possibly less use of fitting and fitting work during assembly by manufacturing interchangeable parts and mechanization, automation of assembly work.
3. Technological route for the manufacture of the tow
The technological route for the manufacture of a bundle is the following sequence of operations:
1. Preparatory operation
3. Preparation of installation wires
4. Wire layout on the template
4. Detailed description of the main operations
1. Preparatory operation
Preparation of installation wires consists of the following operations: dimensional cutting, removal of insulation and termination of wire ends, marking, maintenance and twisting of wires. If the technological process provides for a continuous layout of the wire on the template, then cutting, removing insulation and terminating the ends is carried out after the formation of the bundle.
Manual cutting of wires is performed with simple tools (scissors, wire cutters), determining the length of the wire according to a sample or using a ruler. In mass production, this operation is automated. Universal are machines for measuring cutting and simultaneous removal of insulation from the ends of the wire.
Depending on the type of insulation, various stripping methods are used: , electric firing or thermal softening With subsequent mechanical tightening of the insulation, and certain methods of terminating the ends of the wires.
Textile, plastic and film insulation is removed by incision or electric firing. The removal of multilayer insulation has a number of features. So, in the presence of fiberglass, the outer plastic insulation is removed by electric firing, and the inner (fiberglass) is untwisted, twisted and cut off at a distance of 1 mm from the end of the outer insulation. Outer textile braids require stepped cutting of the ends of the wires. For example, between a cotton braid and a residential wire, a section (3-10 mm) of the main PVC or rubber insulation is left. The end of the braid is fixed with glue, an insulating tube or a thread bandage coated with glue.
Stripping of heat-resistant fluoroplastic insulation is carried out by electric firing at an elevated temperature of the filament. This releases a toxic gas - fluorine, which must be removed from the working area using a suction system.
The stripping must preserve the quality of the non-removable insulation, exclude a cut or break in the current-carrying conductors and be sufficiently productive. In addition to machines for cutting wires and stripping insulation, special devices have been developed for thermomechanical stripping. Their main working elements are a filament and sponge-knives.
The thread burns through the insulation when the wire is rotated around its axis. Sponges are a support for the wire when burning the insulation, protect it from charring and the thread from mechanical damage, provide insulation together with the thread. The working edges of the jaws have a rounding radius of 0.08 mm and are polished, which will exclude a notch and a break in the current-carrying wires. Insulation stripping devices - can be equipped with a device for connecting to a vacuum system for suction of toxic products of insulation burning. The thermomechanical method allows you to remove insulation in one step from wires with a cross section of 0.07-0.35 mm 2.
For installation, shielded wires and RF coaxial cables are used, having an outer PVC coating on top of the shielding braid. The separation of the coating by a notch is laborious and does not provide a high quality of cutting the ends.
The thermomechanical method allows you to remove the plastic insulation within 2-3 seconds without damaging the braid.
sponge knives , equipped with heaters penetrate the insulation and cover the shielding braid in diameter. The section of insulation inside the jaws heats up and expands, making it easy to remove it by pulling it off the end of the wire.
Further cutting of the ends of the shielded wires is to remove the shielded braid in a certain area. One of the removal methods is a circular cutoff of the braid using a punch-die cutting pair.
The working part of the punch is made in the form of a cone, turning into a sphere, which allows it to move quite easily inside the braid and provides an even cut of the screen end on the sharp edges of the matrix . The method is implemented with the help of devices of various designs, which make it possible to cut off in 3–4 s.
There are other ways to remove the shielding braid: a helical cut with rotating cutters and knives, cutting off the annular thickening of the braid.
To extract the end of the insulated wire through the shielding braid, the core is pulled apart with a sharp tool: the braids and the wire are pulled through the hole formed. The most common tool is a grooved needle, which is inserted from the end of the shielded wire between the braid and the insulated wire. In a certain place, the tip of the needle pushes the braid apart and, using the eye of the needle, pulls out the end of the wire. This operation is performed in 3-4 seconds manually, guiding the needle using simple devices.
Termination of the ends of shielded wires consists in grounding the shields or fixing the end of the braid relative to the wire. Grounding is carried out by attaching the free end of the braid to the elements of the frame, soldering an additional wire, applying a bandage of bare tinned wire, and then soldering it. Soldering points are protected with insulating tubes.
A non-grounded braid is terminated between two insulating tubes, one placed under the screen and the other outside or between layers of insulating tape. The end of the braid is fixed with a thread bandage or a wire bandage, followed by soldering.
After removing the insulation, the bare ends of the wires are stripped, and the stranded wires are twisted at an angle of 15-300 to the wire axis. The last operation is performed manually (core cross section less than 0.11 mm 2), with pliers or with the help of special devices. The prepared ends of the wires are subjected to hot tinning by immersion in a solder bath.
Wire marking is necessary to facilitate installation, control, troubleshooting and repair. Use wires with colored insulation and mark them with tags, adhesive tapes or by applying markings directly to the wire insulation. Colored insulated wires are commonly used for indoor EVA installations. The wiring diagrams indicate the color of the mounting wires with abbreviated symbols or digital codes. Marking wires with adhesive tapes consists in applying bandages from this tape to the ends of the wires. Marking with the help of marking tags made of polyvinyl chloride tubes has received the greatest application. The tag is attached to the end of the wire. In this case, the tag should overlap the edge of its insulating braid by 1-3 mm. The tags are put on the wires in such a way that their slipping during shaking and vibrations is excluded.
Symbols on the surface of the marking tags are specified in wiring diagrams and are carried out in accordance with industry standards. The production of tags (marking, drying, cutting) is carried out on special machines. Mounting wires are twisted to eliminate electrical interference and reduce the mutual influence of circuits. The stranding pitch is 10-40 mm and increases depending on the increase in the wire cross-section (0.05-0.75 mm 2). This operation is performed manually with a drill or on special machines.
4 . Wire layout on the template
harness mounting wire isolated
Structural and technological development of the harness makes it possible to manufacture it outside the EVA by laying out the mounting wires and cables on the template. Depending on the configuration of the bundles, flat or three-dimensional templates are used. A flat template is a base on which, in accordance with the routing (see Fig. 2) and the configuration of the bundle, metal studs are located. Installation wires are laid between the studs. To protect the wires from damage, insulating tubes are put on the studs. To fix the ends of the wires, the design of the template provides holes located next to the studs, or special clips. The three-dimensional template has additional elements that allow you to lay out the wires and fix them in three planes.
There are universal flat templates that have holes located with a certain pitch and are designed for installing studs. The layout of the studs on the template can be changed depending on the routing and bundle configuration.
Designs of electrified templates have been developed that increase the productivity of harness manufacturing and eliminate installation errors. On such a template, the ends of the mounting wires are fixed with special clamps electrically connected to signal (green) and control (red) lamps. The lamps and clip-buttons are switched in such a way that when the template is connected to the network, two lamps of the first route light up. With the correct laying and fixing of the wire, the lights of the second route light up, etc. Electrified templates are more expensive than conventional ones, and it is advisable to use them in the mass production of EVA.
When laying wires on templates, some general rules are defined. Several bundles should be made from wires of different cross-sections, combining wires that are close in diameter. insulation (eg 1 to 3 and 3 to 6 mm). Shielded drives must be located inside the bundle, so they start the layout with them. The screens are pre-cut and soldered, in the presence of an external metal braid, it is wrapped with a keeper tape or insulated with a tube. Short wires of small cross sections are laid inside the bundle. Long wires are laid outside to form the front side. Spare wires should be on top with access to their ends. These rules are easy enough to follow when laying out manually.
The sequence of wire layout on the template is manually set in the connection table, taking into account the listed rules. Often a drawing is placed on the template with the designation of the tracks. The end of the wire wound from the coil is marked with a tag and fixed on the template. The wire is cut in place after laying out between the studs and its end is marked. These transitions are repeated many times. The cutting of the ends with such a sequence of operations is carried out after knitting the bundle. Manual layout on the template is performed by the installer, and it is very laborious. In serial production, it can be mechanized using a program-controlled device.
Two (or more) insulated wires with a length of more than 50 mm running in parallel along the same route must be bundled. The only exception can be an unacceptable increase in mutual pickups in electrical circuits. For knitting, threads, cords, braid, insulating tapes, heat shrink tubes, etc. are used. The operation is usually carried out on a template. Knit step t depends on wire section, number of wires n and diameter D tourniquet. On curved sections, the pitch should be reduced depending on the diameter of the bundle bend. At the branching of the wires, the knitting should have 2-5 turns on all branches, the bandages should be made from 2-3 adjacent loops. The ends of the bundle must have bandages and end nodes.
Knitting is carried out in one, two or more threads with manual tension or with the help of devices. To reduce the complexity, the process of knitting harnesses is mechanized using pneumatic guns, and sometimes automated, by knitting harnesses on special semi-automatic machines.
To protect against mechanical damage, the tourniquet is wrapped with insulating tape along its entire length or in a certain area. If it consists of wires with cotton or silk insulation, then the harness is impregnated with a water-repellent compound to protect it from moisture. To protect against exposure to high temperatures or aggressive environments, the bundles are placed in tubular, tape, strip or braided sheaths. They are put on manually or on the machine after removing the tourniquet from the template. Thus, knitting harnesses is no less time-consuming operation than laying out and marking wires.
In addition to the use of various devices for the mechanization of the operations of manufacturing a tow, it is advisable to use conveyor lines in conditions of mass production. In this case, the technological process is divided into a number of small operations. At each workplace, the layout of wires of the same section and brand is completely carried out. When determining the cycle of the conveyor, they are guided by the layout operation, based on the fact that the knitting operation is easier to subordinate to the selected rhythm. For example, knitting 16-24 loops takes 3-5 minutes. Most often, the cycle of work is 5 or 7.5 minutes.
The conveyor method of making harnesses has other features. The layout of the wires is carried out continuously, winding them off the coils. A set of tags is preliminarily put on the end of the wire to mark all routes performed at a given workplace.
Universal templates are used, equipped with studs both in places of kinks and branches, and in places of subsequent cutting of wires. The layout routes are marked with the help of special stencils placed on the templates. For knitting harnesses, threads are used that can withstand sufficiently large tension forces. After knitting, the wires are cut, the bundle is removed from the stencil and the ends are cut.
The conveyor for the production of bundles is located in a horizontal plane, closed and transports templates using trolleys. In addition to templates, it is equipped with guns for knitting harnesses, devices for stripping insulation, and a tinning unit. The conveyor method simplifies the operations performed at each workplace and reduces the overall complexity of the production of harnesses. Its disadvantages are the tension of the wires during layout and the deformation of the bundle after removal from the template, which worsens the quality of knitting.
After the harness is made, the quality of the termination of the ends of the wires and screens, the presence of markings, the absence of damage to the current-carrying conductors and insulation, and the quality of tinning are controlled. The integrity of electrical circuits is checked by continuity probes. In circuits with a large number of intermediate connections, the resistance is measured.
During the control, the ribbon cables are checked for the absence of conductor breaks, the insulation resistance between the conductors and the ground buses, the presence of electrical connections between the connector contacts and the ribbon wire.
For control, special automated stands have been developed, for example, with the number of points to be checked is 90 and the main technological time for checking the product is not more than 30 s. The control is carried out by checking the electrical circuits, comparing the states of the switches and then transferring the results to the light indication panel. Stands can work in automatic and manual modes.
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Knitting harnesses
The basis of every electrical product is conductors. In this age of miniaturization, many of them are integrated into printed circuit boards, walls and panels, can be made in the form of ultra-thin plumes, transparent coatings and much more. However, the lion's share of the circuits is still connected by separate isolated copper wires and cables, which are combined into bundles for ease of installation and repair, more stringent standardization of parameters and simplification of access to various units.
Knitting harnesses is one of the most common operations in the general cable processing process, the manufacture of cable assemblies. In principle, it is produced after cutting and stripping the cables. But often (especially when many wires of the same type are used in the bundle that do not require complex stripping), cutting can be done directly on the knitting template after laying the wire along the route. That is, depending on the materials used, production conditions and the characteristics of a particular product, operations can be mixed and interchanged. This requires their implementation in the course of a single technological process, in any case, at one enterprise. LLC "CEPIKS" is one of the leaders of the Russian market in this specialization.
Knitting is a general term. In fact (in accordance with the specifications for specific bundles), wires can be fastened not only with a thread, but also with all kinds of clamps, ties and tapes, leather cases, special polymer bandages and so on. The material and method of knitting is determined by the type of wires, the conditions of installation, storage and operation of the equipment, the location of the bundle route in the product in relation to sharp, moving, heating elements. In some cases, threading is even unacceptable: in flexible areas where the wires must move freely relative to each other, inside insulating tubes(sheathing, windings), on wires and cables with insulation made of polyethylene, fluoroplastic and other materials with cold fluidity.
When knitting bundles, special attention is paid to shielded wires, the braids of which must be isolated from each other and from the device case, if this is not allowed by the electrical circuit. They are also enclosed in solid smooth dielectric tubes in areas where the bundle can be bent during operation. Additional insulation is also applied to the bundles at the points of their transition through sharp edges and holes in the structural elements of panels and devices. A reinforced bandage made of thread (or an additional tie) fastens the places where the wires branch from the trunk of the bundle, the edges of the flexible sections and some other key points.
Harnesses are knitted, as a rule, on templates specially made according to technical documentation - shields with pegs for turns and wire branches, providing the necessary bending radii and matching the shape of the harness to its route according to the project. The methods of knitting and layout of wires in bundles, depending on their cross section, type and functional purpose, are standardized by GOST 23586-96, the design of wire cutting and core fastening - by GOST 23587-96, and the requirements for cutting and connecting screens - by GOST 23585-96. Immediately, stripping, dialing and marking of cables is usually performed (since the wire numbers are signed directly on the shields), and their tinning or installation of lugs after removal from the template.
final stage harness manufacturing is its testing on special equipment with a thorough check and recording of all electrical and mechanical parameters.
Manufacturing cable harness products
Cable harness products are used for switching nodes, boards, blocks and switching racks in many industries. They can differ both in the degree of complexity (from a single-core conductor between two contact pads, to a combined bundle with a complex switching table), and functional purpose(ground wire, coaxial cable, fiber optic cable, etc.)
Regardless of the complexity and purpose, the cable assembly must meet the following quality criteria: reliability of signal transmission from the start to the end point; minimum loss of signal characteristics; ease of switching the harness in electrical equipment; durability of terminal connectors, contacts and connectors during the operation of electrical equipment; maintainability during service.
The manufacturing process of cable harness products (cable assemblies) is divided into several production stages:
Measured wire cutting
wire stripping
Crimping cable lugs (cremping)
Installation (assembly) of connectors
Knitting (installation) of harnesses
Wire (cable) marking
Preparation and installation of a special cable
Quality control and compliance terms of reference
Even at the design stage, factors affecting the characteristics of the harness are determined. They form the basis of the technological process for the manufacture of cable assemblies. dimensions, type of wire (cable), section, external diameter, installed contacts and connectors, marking, bandage and strapping - all these stages are strictly verified in the production process chain.
The production of cable harness products is carried out on assembly stands (with the exception of jumper wires). They allow you to minimize errors when knitting and bandaging harnesses, as well as reduce production time. Also on the stands there is an opportunity to check the technical characteristics of the knitting of the harness.
Checking the quality and compliance of the cable assembly with the terms of reference is checked at all stages of the production of the wire harness and at the final control (output control of the enterprise). All discrepancies are recorded in the test reports, on the basis of which a statistical analysis is carried out. Necessary adjustments are made to the manufacturing process, materials, terms of delivery of components, design and technological documentation.
ELECTRICAL HARNESS PRODUCTION TECHNOLOGIES high requirements to build quality and reliability. Accordingly, each unit and part of the car must meet these requirements. Composite element car is electrical wiring (wiring harnesses). A wiring harness is a finished product consisting of individual wires fastened together in a bundle, the ends of which are reinforced with contacts that are assembled into blocks or protective elements (tubes, rubber caps, covers) are put on them. The wires are fastened into bundles: bandages made of PVC adhesive tape, cable ties (toothed clamps made of thermoplastic polymers); heat shrink tube.  A modern car has harnesses with a total number of wire segments of about three hundred (and more often more), reinforced with various contacts. The reliability of such complex product depends on several factors. First of all, these are increased requirements for the quality of components and materials. Which, in turn, is influenced by the choice of supplier and the conduct of incoming control. The next factor is the use of modern high-performance and precise production and control - measuring equipment that meets the requirements of international standards. And, finally, the most important factor of reliability is the specialists involved in the production process. The quality and reliability of the product depends on their professionalism. Autotractor harnesses can be divided into: low and high voltage(battery and starter wires are most often single, less often - consisting of two to three wires).  The technological process of manufacturing a wire harness is divided into several basic operations: cutting wires, stripping the ends of wires from insulation, reinforcing wires with lugs or contacts, fastening wires into bundles (binding), installing detachable connectors, quality control. In order for you to better understand what components the wiring harnesses consist of and in what sequence they are used in their manufacture, we tried to give detailed description basic operations for the manufacture of harnesses and types of equipment used. For more better understanding assembly sequence of any harness in this section we will introduce general concepts bundle structures, which will be found later in the text. The harness can be divided into parts and give them names.
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Making and laying harnesses
The bundle is a set of wires and cables, fastened together in some way and, if necessary, equipped with electrical installation elements (lugs, connectors, etc.).
According to their purpose, harnesses are divided into intrablock and interblock.
Intra-block harnesses are used for electrical connection of individual nodes, blocks and electrical parts inside the device, and inter-unit harnesses - for the electrical connection of various radio equipment and devices in single system. Depending on the location of the nodes in the body, the bundles can be flat or voluminous.
To protect against exposure environment, mechanical damage or for the purpose of shielding, the bundles are wrapped on the outside with a keeper, nylon, lavsan or polyvinyl chloride tape, varnished or enclosed in a shielding braid.
1) different colors of wire insulation;
2) coloring or numbering of PVC tubes used to fix the ends of the insulation (the tubes are numberedon the machine, in special stamps or inscribed by hand with marking ink);
3) plastic tags with a symbol for the connection point, put on the wires.
Harnesses in which failed wires cannot be replaced are provided with spare wires. Their number is taken at the rate of 8 ... 10% of the total number in the bundle, but not less than two wires. The length and section of the spare wires must be equal to the largest length and section of the wires present in the bundle. The length of the harness leads must be sufficient for connection to the nodes and elements of the device circuit without tension; in addition, there must be a margin of 10 ... 12 mm for re-stripping and attaching each end of the wire.
A typical technological process for manufacturing a tow includes the following operations:
cutting wires and insulating tubes;
laying wires on the template and knitting them into a bundle;
termination of the ends of the wires of the bundle with their simultaneous marking;
harness control (continuity); protection of the harness with insulating tape;
output control (visual inspection for compliance with the standard, well, and continuity).
The length of the prepared wires must correspond to the dimensions indicated in the technological map or the table of wire blanks. Cutting wires and shielding braids is carried out on automatic machines, as well as using mounting or guillotine shears and a nipper.
It is more expedient to make a blank of wires of the same length and knit them into a bundle without branches on a special device (Fig. 1.25), which consists of two racks mounted on a board (the distance between the racks depends on the length of the prepared wires).
On the outer sides, the racks have grooves. First, the wire is wrapped around the posts, while the number of turns of wire should be half the number of wires in the bundle. Then the coils of wire located between the uprights are tied into a bundle with thread or twine. After tying, the turns of wire are cut in places located opposite the grooves in the racks.
With the manual method of harvesting wires for bundles, their length is determined using samples or a ruler. In serial production, special machines are used for measuring wire cutting to a predetermined length.
The wires are laid on the template in a certain order (according to the scheme printed on the surface of the template), after which they are tied with a thread or twine into a bundle. Template markup forthe wiring harness is laid according to the wiring diagram, the layout of the node or device in which the harness will be installed, and the mounting table of connections. On the marked template, the wires are first laid out and then knitted into a bundle (Fig. 1.26). Depending on the design of the device, the bundles are flat or voluminous.
When laying out, the ends of the wires are cut along the transverse "marks, marked and fixed. The laying of wires on the template starts with spare and long working wires and ends with the shortest wires. Shielded wires included in the bundle are wrapped with keeper tape and placed inside harness or in an insulating tube.
The harness should be knitted in one direction with cotton thread No. 00 or linen No. 9.5/5. For hand knitting, the device shown in Fig. 1.27 a. A spool 3 with threads is inserted into the body 4 of the device. Covers 5 and 2 serve to center the coil. In the top cover 5 there is an eye for giving the thread a certain direction, and a hook 1 is attached to the bottom cover.
To facilitate the winding of the thread from the spool, a slot and an outlet for the outer end of the wound spool are made in the body. First, a wound coil is inserted into the body of the device, the upper end of which is inserted into the slot of the body. Next, the lid is closed and the end of the thread is threaded through the eyelet.
The harness is knitted in accordance with the loop formation scheme. It takes 0.5 ... 1 s to knit one knot. To perform the operation, it is necessary to take the thread (see Fig. 1.27, b), hook the loop with a hook, stretch it under the tourniquet and thread the device through two loops, tightening the thread. At the moment of tightening the knot, the thread passing through the body must be pressed with a finger to its surface. The device helps to improve the quality of knitting harnesses and reduce the complexity of their knitting by 15...20 times. Recommended knitting methods are shown in fig. 1.28.
Loops are recommended to be knitted with tension at regular intervals (no more than 50 mm), as well as in places where wires branch off.
The knitting step of the loops is set by the designer, depending on the diameter of the bundle.
After knitting the wires into a bundle, their ends are terminated. First, all ends of the wires are marked according to the wiring diagram, and then the correct layout of the wires is checked with a dial tone. In the case of using electrified templates for making harnesses, continuity can be omitted.
The control of complex harnesses is carried out on special semi-automatic stands according to a given program. The harness on the panel of the stand is fixed manually, and the correct layout of the wires and the resistance of their insulation are controlled automatically.
First, control is carried out for compliance with the electrical wiring diagrams, that is, checking the correct layout of the wires. For this purpose, the required voltage is sequentially applied to one of the ends of the tested wire. At correct layout wires, the voltage must be recorded in all wires of the bundle electrically connected to the wire under test. Next, you need to make sure that there is no voltage in the wires of the bundle, which are not electrically connected to the wire under test. All information about the control is issued automatically in the form of coded holes on a punched tape or as a record on a tape with digital and alphabetic designations.
When monitoring the insulation resistance of wires, a consistent supply of constant voltage is automatically carried out to electrically isolated wires (circuits), while fixing the insulation resistance.
If necessary, the harness is protected with insulating tapes or a shielding braid. Finished bundles are laid according to the wiring diagram and the drawing of the device. Simultaneously with laying, the ends of the wires of the bundle are bred to the corresponding places in the device circuit and soldered. At the same time, it is necessary to ensure that individual wires do not obscure the markings and inscriptions of the nominal values on the parts.
Attention! When laying the harnesses in the device, care must be taken to avoid breakage and breakage of the conductive cores of the wires and conclusions of the hinged radio components, as well as short circuiting of bare conductive places.
Inside the device, the harness is attached to the chassis or walls with metal brackets (Fig. 1.29), under which you must firstput insulating materials from polyvinyl chloride, varnished fabric or pressboard. The edges of the gaskets should protrude from under the bracket by at least 5 mm. The brackets are made double-sided (attached with two screws) and one-sided (attached with one screw). The design of mounting brackets, especially single-sided ones, must be sufficiently rigid to prevent them from bending or deforming when attached to the chassis together with the harness.
To ensure the transition of unshielded (and, if necessary, shielded) harnesses from one unit of the device to another through the wall of the chassis or screen, insulating bushings are provided in this place.