Car body consists of a base, roof and frame, including racks, spars, cross members, beams and reinforcements to which welded and hinged front parts are attached - plumage. Moreover, all welded body parts (mud flaps, arches, floors, panels, etc.) can be attributed directly to the load-bearing or reinforcing elements of the body frame.

As a result of an accident, the body may be damaged and marks may appear on its surface. deformations, scratches, scuffs and other damage.

Deformation - change in body shape and size(parts, structures) as a result of external influences without changing its mass. The simplest types are stretching, compression, bending, torsion. Deformation is divided into superficial (smooth) and deep. As a result superficial deformations are formed dents, bulges. As a result deep deformations are formed folds,

hoods, fractures of stiffeners, destruction of the integrity of the material or connection with the formation of cracks, ruptures, separation of fragments,

The types of deformations and repairs of passenger car bodies are defined in some detail in VAZ regulatory documents.

Scratch - This is a mark on the surface that does not disturb the shape of the surface.

Badasses- damage leading to disruption of the surface material.

The bodies of modern passenger cars are a complex spatial system designed for large dynamic and static loads. Being a load-bearing body, the body perceives loads through the elements of the load-bearing frame, as well as internal and external panels.

Under normal operating conditions, car bodies reliably serve for 10-12 years or more.

It must be borne in mind that in case of traffic accidents and when driving at high speeds on potholed roads, residual deformation occurs in the body.

The most destructive body damage occurs when frontal collisions, in case of collisions with the front part of the body at an angle of 40 - 45° or from the side. If such collisions occur between two vehicles moving towards each other, then their velocities upon impact are added up. In such collisions, to the greatest extent is destroyed front Part car body. Acting at the same time large dynamic loads in longitudinal, transverse and vertical directions transmitted to all adjacent frame parts body and especially its power elements and can cause their deformation even from the opposite side.

Let's consider several examples of emergency body deformation.

The blow has been struck in the front part of the body in the area of ​​the left front fender, side member and left headlight(Figure I). With this direction of impact, it is most likely that damage will affect the following body details:

radiator frame panels, front guard, fenders, hood, mud flaps, front side members, windshield frame and roof. In the figures this can be seen from the dotted lines.

The car was hit into the front of the body at an angle about 40 - 45° (Fig. 2.). With this direction of impact, it is most likely that will receive damage the following bodywork details:

front fenders, hood, radiator frame panel, front guard, mudguard, front side members.

It is possible to restore the base points of the front part of the body using editing methods. In this case, it is also necessary to restore the dimensions along the openings of the front doors and the coordinates of the front and central pillars, since the force loads were transmitted through the front doors to the front and central pillars of the body and acted with compressive forces on the threshold and the upper part of the sidewall of the body.

Fig.2. Damage to the body when impacted in the front at an angle of 40-45°.

The impact was made from the side into the front part of the car body in the area where the front panel meets the front part of the spar and the left wing (Fig. 3). With this direction of impact, it is most likely that damage will affect the following body details:

front fenders, radiator frame, front guard, mudguards, side members, hood. Tensile forces disrupted the opening of the left front door, compressive forces caused deformation in the opening of the right door and in the sidewall of the left front door. The front and center pillars also received significant force overloads and have deviations from their original location.

Fig.3. Damage to the body due to a side impact in the area where the front panel meets the side member.

Impact - from the side into the A-pillar of the car body on the left side(Fig. 4). With this direction of impact, it is most likely that will receive damage the following bodywork details: .

left A-pillar, windshield frame, roof, floor and front side members, radiator frame, front guard, hood, fenders, mud flaps and front side members. At the same time, the front of the car body “went” to the left; the threshold and the upper part of the right sidewall absorbed the tensile loads of the central and rear pillars. -compressive loads; The right mudguard was “torn off” from the A-pillar. .

Technical specifications 017207-255-00232934-2006 “LADA car bodies, technical requirements for acceptance for repair, repair and release from repair by enterprises of the service and sales network of OJSC AvtoVAZ”, Togliatti 2006, provide for the following types of repairs damaged (deformed) bodies (TU clause 2.6.1.):

elimination of distortions body;

repair individual parts (straightening, welding);

replacement individual body parts or their damaged parts;

coloring And anti-corrosion treatment."

Body distortion - This violation beyond permissible limits geometric parameters openings (windows, doors, hood, trunk lid), as well as locations of base attachment points

"Eliminating distortions body (TU clause 2.6.3) is the restoration of the geometric parameters of the openings of windows, doors, hood, trunk lid, side members, interior frame and base points on the base of the body for attaching the power unit, transmission and suspensions.”

The geometric parameters of the bodies are given in the technical specifications (Appendix B). The presence of distortions is established by measuring the corresponding openings or base locations attachment points power unit, suspensions (axles) and transmission units based on the supporting body frame.

3.3. Elimination of distortions openings and body must be carried out before straightening and repair front panels.

3.4. Allowed produce elimination of distortions bodies with both front panels (fenders, sidewalls, front and rear panels, roof) and with disconnected front panels.

3.6. Depending on the degree of deformation of the body, the following classification of distortions is established:

opening misalignment;

simple distortion of the body;

body distortion of medium complexity;

complex body distortion;

body distortion of particular complexity.

3.7. Depending on the degree of damage or corrosion destruction of the body part, the following are provided: types of repairs with removed components and parts that impede straightening, welding and painting work:

repair.0- elimination of damage to the front surfaces of the body without damaging the paint;

repair 1- repairing damage in easily accessible places (up to 20% of the part surface);

repair 2 - elimination of damage with welding or repair 1 on the surface of a part deformed up to 50%;

repair 3 - elimination of damage with opening and welding, partial restoration* of the part up to 30%;

repair 4 - elimination of damage with partial restoration* of the part on the surface over 30%;

Partial replacement - replacement of a damaged body part with a repair insert** (from the range of spare parts or made from the latter); .

Replacement- replacement of a damaged body part with a part from spare parts***.

Large block repair- replacement of the damaged part of the body with blocks of parts from rejected bodies with marking, cutting, fitting, drawing, straightening, welding of the latter.”

* Partial restoration of a part- this is the elimination of damage by drawing or straightening, with metal shrinkage; cutting out areas that cannot be repaired; production of repair inserts from rejected body parts or sheet metal and giving it the shape of the part being restored.”

** Partial replacement Most often it is carried out when narrow and long parts are damaged (cross members, side members, sidewalls), when it is more economically feasible to replace not the entire part, but only its damaged part.

*** Part replacement of the body to be carried out in case of its irreparability or economic inexpediency of its repair.

Body repairs often involve the need to perform reinforcement works By disassembly, assembly, removal, installation units, parts. The list of reinforcement works is given in the technology for maintenance and repair of the corresponding automatic telephone exchange.

Reinforcement works most often include:

disassembly, assembly:

Front, rear and rear doors;

Removal and installation;

The hood and its mechanisms;

Battery;

Trunk lids and its mechanisms;

Windshield, rear and side windows;

Rear lights;

Front and rear bumpers;

Antennas, speakers, radio, radio, player;

Heater;

Instrument panels;

Roof trim;

Seat belts;

Seats;

Headlight block.

The complexity of work on repairing (replacing) body parts and eliminating body distortions, as a rule, are not taken into account the complexity of work on removing and installing components and parts that impede repair work.

In the labor intensity of replacing body parts taken into account the following work: detaching and removing the old part, removing metal residues, loose and sheet rust (corrosion), straightening the mating edges, fitting and welding a new part, cleaning welding points and seams, leveling surfaces with fillers and grinding defective areas. (“Labor intensity of work on maintenance and repair of VAZ cars” General provisions of paragraph 9. Tolyatti 2005)

Drawing up an inspection report

As a result of examination by a specialist are determined and entered in the relevant sections of the inspection report, all information necessary for the assessment about the object being assessed, its damage, defects, repair technology, as well as his opinion about the cause of the damage detected.

1. IDENTIFICATION section is entered:

REAL, and not specified in the submitted documents, numbers motor vehicle and its components (registration number, VIN identification number, body number, frame number, engine number, etc.);

mileage on the odometer;

For telephone exchanges that are located under warranty service, or which repaired and serviced at an official dealer or at a company service station, it is necessary to make a special confirming entry;

equipment motor vehicle, the presence of additional, non-staff, tuning equipment;

2. To section “INSTALLED UPON INSPECTION” The following information is entered, the correction of which is unacceptable:

was it produced replacement components, assemblies and expensive components;

has been subjected to the vehicle has previously been body repaired and what is its scope, nature and quality;

Availability on a motor vehicle operational defects, primarily the presence of metal corrosion (surface, deep or through).

Availability accident damage on a motor vehicle (deformations, scratches, scuffs, etc.) their type, nature, degree of complexity, size and location.

Damage can be classified by time of occurrence:

Relevant to this emergency;

Obtained from previous accidents.

The specialist conducting the inspection must make probabilistic conclusions about the attribution of the detected damage to this incident and make a corresponding entry in the Inspection Report of the following nature:

“With a high degree of probability, it can be assumed that the damage to the car identified during inspection may be a consequence of an accident recorded in the attached State Traffic Safety Inspectorate Certificate. Damages for which it can be assumed that they are NOT a consequence of this accident are marked in the “CONCLUSIONS” section with two asterisks **"

Defects can be classified as follows:

Obtained as a result of proper operation and storage of vehicles;

Received as a result of improper operation and storage of vehicles;

The result of poorly carried out repair work.

Since the description of damages and defects does not always give a complete picture of them... it is advisable to accompany information about damages and defects with appropriate photographs, video footage, sketches, sketches, diagrams, etc.

To this section NOT DESIRED include conclusions and suggestions about the possibility, methods, methods of restoring the automatic telephone exchange (replacement or repair of parts, the amount of labor involved in repairs, its technology, etc.).

It is advisable to include damage with a high degree of probability related to the incident in question in the inspection report indicating their presence or absence in the traffic police certificate. It is also necessary to indicate damage with a high degree of probability not related to this incident.

The presence of severe metal corrosion or other defects in the operation of the vehicle, which significantly affect the technology and cost of repairs, must be noted in the inspection report.

After filling out the section in the “Inspection Report” "INSTALLED UPON INSPECTION" This section is signed by the specialist performing the inspection, and after familiarization, by the interested parties present during the inspection. All signatories must have the opportunity to express their special opinion and comments in the Inspection Report.

When preparing the Inspection Report and other documents, you must use terminology, adopted in regulatory, technical, technological documentation: in the repair technology manual, maintenance and repair manual, in spare parts catalogs and other technical literature.

Each damaged part should have a separate section line and, if possible, a photograph.

The inspection must be carried out systematically and consistently. One option for the inspection sequence may be a scheme based on the principle of moving from one inspected group of parts to another only after completing the description of all damaged parts included in the group of the same name. The sequence of alternating groups is selected by a specialist, and the order of subgroups is preferably in accordance with the increase in their serial number. The proposed inspection procedure allows you to avoid missing damaged parts during inspection and is very convenient when calculating repair estimates, especially if it is performed using a computer.

For example, first we inspect parts of group 28 (frame, protective elements of the body), then group 84 (tails), etc.

3. For recommendations on vehicle repairs, the Inspection Report contains a section "CONCLUSIONS". This section is filled out by a specialist without discussion and agreement with other participants in the inspection, after analyzing the technical feasibility and economic feasibility of carrying out the proposed work.

During the initial inspection of the vehicle, it is not always possible to identify all damage and defects. In such cases, all assumptions for hidden damage, defects should be recorded in the Inspection Report and the document issued to the interested organization (person), but they should not be reflected in the cost of repairs until they are finally determined during subsequent inspections

AMTS. The necessary control and diagnostic operations may be included in the calculation of the cost of repairs.

As agreed with the customer Inspection report may not be compiled. In this case, all the necessary data is entered into the report.

Table 4.3.1.

Related information.

Car damage in accidents

As a result of the analysis of domestic (Moscow and Leningrad) and foreign (Stockholm) statistical data, the percentage of body damage in accidents in the main directions of impact was established (Fig. 1.5). As can be seen from the figure, the largest number of impacts occurs on the front of the car, a significant number on the rear, and the smallest on the right and left.

Damage to bodies resulting from a collision can be divided into three categories: the first includes very severe damage, as a result of which replacement of the body is necessary; the second category includes medium-sized damage, in which most of the parts require replacement or complex repairs; The third category includes less significant damage (holes, tears in the front panels, dents, scratches caused by an impact while moving at low speed). Damage of the third category does not pose a danger to driving a car, although its appearance does not meet aesthetic requirements.

The most destructive damage to the body is observed during frontal collisions, i.e., during impacts caused to the car directly in the front part of the body or at an angle of no more than 40 45 ° in the area of ​​the A-pillars. Typically, such collisions occur between two oncoming vehicles whose speeds add up, creating high impact loads. The amount of energy that must be absorbed during such collisions is enormous: about 80-100 kJ for a car weighing 950-1000 kg. This energy is absorbed when the vehicle deforms in less than 0.1 s. In such collisions, the car body is destroyed, especially its front part, but the large loads in the longitudinal, transverse and vertical directions are transferred to all adjacent parts of the body frame and especially to its power elements. Let's look at what has been said with examples.

Example I. A frontal collision of the car occurred with the front part of the body in the area of ​​the left front fender, side member and left headlight (Fig. 1.6). The front panel, fenders, hood, mudguards, front side members, windshield frame and roof suffered devastating damage. This deformation is determined visually. Invisible deformation occurs in the A-pillars, B-pillars and C-pillars on both sides, in the left front and rear doors, in the left rear fender and even in the rear trunk panel.

Example 2. The collision occurred with the front part of the car body at an angle of 40-45° (Fig. 1.7). The front fenders, hood, front panel, mudguards, and front side members received devastating damage.

It is almost impossible to restore the basic points of the front part of the body without replacing deformed parts with new ones. In this case, it is necessary to restore the dimensions along the front door openings and the position of the front and central pillars, since force loads were transmitted through the front doors to the front and central pillars of the body, creating compressive forces on the threshold and the upper part of the side of the body.

Rice. 1.5. Diagram of the distribution of the number of body damages in the main directions of impact I -IV (in% per 100 cars involved in collisions): I frontal impacts (impact types 01.02.03); II right side impacts (impact types 04, 05, 06); III collisions in the rear of the car (collision types OT, 08, 09) IV - left side collisions (impact types 10, II. 12), Moscow and Moscow region; L Leningrad and Leningrad region; From Stockholm (Sweden)

Rice. 1.6. Frontal impact of the vehicle with the front left part of the body

Rice. 1.7. Impact with the front part of the car body at an angle of 40-45°

Rice. 1.8. Side impact to the front part of the body in the area where the front panel meets the side member and the left wing

Rice. 1.9. Side impact to the left A-pillar

Example 3. An impact was struck from the side to the front part of the car body in the area where the front panel meets the front parts of the spar and the left wing (Fig. 1.8). Both front wings, the front panel, mudguards, side members, and the hood received devastating damage.

By performing an external inspection of the damaged body (in cases similar to those given above and in the tables of Chapter 2), a specialist can determine the presence of distortions in the protrusion (recession) of the doors, trunk lid and hood relative to the stationary surfaces of the body parts. Violation of the uniformity of gaps (above the permissible dimensions specified in the regulatory and technical documentation) for the mating of mounted and fixed parts also indicates the presence of deformations in the parts of the body frame caused by the collision of the car. It should be remembered that by external inspection it is impossible to determine deviations in the linear dimensions of body openings and geometric parameters based on the base points of the body base. For these purposes, it is necessary to use measuring instruments, control devices and stands. Their description and control methods are given in paragraph 3.4.

Types of wear and damage to the body

The main causes of wear and damage to bodies

Wear and damage to bodies can be caused by various reasons. Depending on the cause of the occurrence, malfunctions are divided into operational, structural, technological and those arising due to improper storage and care of the body.

During operation, elements and components of the body experience dynamic loads from bending in the vertical plane and torsion, loads from their own weight, the weight of cargo and passengers. Wear of the body and its components is also facilitated by significant stresses that arise as a result of vibrations of the body not only when moving over uneven surfaces and possible jolts and impacts when hitting these irregularities, but also due to engine operation and errors in balancing the rotating components of the car chassis (especially cardan shafts), as well as as a result of a shift in the center of gravity in the longitudinal and transverse directions.

Loads can be absorbed by the body completely if the car does not have a chassis frame, or partially when the body is installed on the frame.

Research has shown that variable voltages act on body elements during vehicle operation. These stresses cause fatigue to accumulate and lead to fatigue failure. Fatigue failure begins in the area of ​​stress accumulation.

There are two main groups of damage and malfunctions in car bodies undergoing major repairs:

damage that appears as a result of increasing changes in the condition of the body. These include natural wear and tear that occurs during normal technical operation of the vehicle, due to constant or periodic exposure to factors such as corrosion, friction, rotting of wooden parts, elastic and plastic deformations, etc. on the body;

malfunctions, the appearance of which is associated with human action and are the result of design defects, factory defects, violation of body care standards and technical operation rules (including emergency ones), poor-quality body repairs.

In addition to normal physical wear and tear, when the vehicle is used in difficult conditions or as a result of violation of maintenance and prevention standards, accelerated wear and tear may occur, as well as destruction of individual parts of the body.

Typical types of wear and damage to the body during vehicle operation are metal corrosion that occurs on the surface of the body under the influence of chemical or electromechanical influences; violation of the density of rivet and welded joints, cracks and breaks; deformation (dents, distortions, deflections, warping, bulges).

Corrosion is the main type of wear on the metal body of the body. In metal parts of the body, the electrochemical type of corrosion most often occurs, in which the metal interacts with an electrolyte solution adsorbed from the air, and which appears as a result of both direct contact with moisture on unprotected metal surfaces of the body, and as a result of the formation of condensation in its interskin space ( between the inner and outer panels of doors, sides, roof, etc.). Corrosion develops especially strongly in places that are difficult to inspect and clean in small gaps, as well as in flanges and bends of edges, where moisture periodically entering them can persist for a long time.

Thus, dirt, salt and moisture can accumulate in the wheel arches, stimulating the process of corrosion; the underbody is not resistant enough to the influence of factors that stimulate corrosion. The rate of corrosion is greatly influenced by the composition of the atmosphere, its contamination with various impurities (emissions from industrial enterprises, such as sulfur dioxide resulting from fuel combustion; ammonium chloride entering the atmosphere due to the evaporation of seas and oceans; solid particles in the form of dust), and also ambient temperature, etc. Solid particles contained in the atmosphere or falling onto the surface of the body from the road surface also cause abrasive wear of the metal surface of the body. As the temperature increases, the corrosion rate increases (especially if there are aggressive impurities and moisture content in the atmosphere).

Winter coating of roads with salt to remove snow and ice, as well as vehicle operation on sea coasts lead to increased vehicle corrosion.

Corrosion damage in the body also occurs as a result of contact of steel parts with parts made of some other materials (duralumin, rubbers containing sulfur compounds, plastics based on phenolic resins and others, as well as as a result of contact of metal with parts made of very wet lumber containing a noticeable amount of organic acids (formic acid, etc.).

Thus, studies have shown that when steel comes into contact with poly-isobutylene, the metal corrosion rate per day is 20 mg/m2, and when the same steel comes into contact with silicone rubber - 321 mg/m2 per day. This type of corrosion is observed in places where various rubber seals are installed, in places where chrome decorative parts (headlight rims, etc.) adhere to the body.

The appearance of corrosion on the surface of body parts is also caused by contact friction, which occurs under the simultaneous influence of a corrosive environment and friction, with the oscillatory movement of two metal surfaces relative to each other in a corrosive environment. This type of corrosion affects doors around the perimeter, fenders where they are bolted to the body, and other metal parts of the body.

When painting cars, contamination of body surfaces carefully prepared for painting may occur with wet hands and polluted air. If the coating is of insufficient quality, this also leads to corrosion of the body.

The process of corrosion of bodies occurs either evenly over a large area (surface corrosion), or corrosion proceeds into the thickness of the metal, forming deep local destruction - cavities, spots at individual points on the metal surface (pitting corrosion).

Continuous corrosion is less dangerous than local corrosion, which leads to the destruction of metal parts of the body, their loss of strength, a sharp decrease in the corrosion fatigue limit and to corrosion brittleness characteristic of body lining.

Depending on the operating conditions that contribute to the occurrence of corrosion, body parts and assemblies can be divided into those with open surfaces facing the road surface (bottom of the floor, fenders, wheel arches, door sills, bottom of the radiator trim), into those with surfaces that are in within the volume of the body (frame, trunk, top of the floor), and on surfaces that form a closed isolated volume (hidden parts of the frame, bottom of the outer door trim, etc.).

Body cracks occur upon impact as a result of a violation of the body metal processing technology (multiple impact processing of steel in a cold state), poor assembly quality during the manufacture or repair of the body (significant mechanical forces when connecting parts), as a result of the use of low quality steel, the influence of metal fatigue and corrosion with subsequent mechanical load, defects in the assembly of units and parts, as well as insufficiently strong design of the unit. Cracks can form in any part or part of a metal case, but most often in places subject to vibration.

Rice. 26. Damage found in the body of the GAZ-24 Volga car:
1 - cracks on the mudguard; 2 - violation of the welded connection of the spacer or the splash of the end cap with the frame spar; 3 - cracks on the spacer; 4 - cracks on the front panel and mudguards of the front wheels; 5 cracks on the windshield pillars; 6 - deep dents on the wind window pillar panel; 7 - skew of the wind window opening; 8 - separation of the front seat bracket; 9 - cracks on the body base casing; 10 - violation of welded joints of body parts; 11 - curvature of the gutter; 12 - dents on the outer panels covered with parts on the inside, irregularities remaining after straightening or straightening; 13 - local corrosion in the lower part of the rear window; 14 - separation of the rear pillars at the attachment points or cracks on the pillars; 15 and 16 - local corrosion of the trunk lid groove; 17 - separation of the trunk lock bracket; 18 - local corrosion in the rear part of the body base; 19 - dents on the lower rear panel of the body in the places where the rear lights are attached; 20 - local corrosion in the lower part of the mudguard; 21 - corrosion deposits and other minor mechanical damage; 22 - local corrosion of the wheel arch; 23 - bent rear wing mudguard; 24 - violation of the weld in the connection of the mudguard with the arch; 25, 32 - cracks on the base in the places where the seats are attached; 26 - local corrosion on the rear door pillar and on the base of the body. gripping rear spar reinforcement; 27 - cracks on the base of the body in the places where the rear spring brackets are attached, and others; 28 - dents on the pillar panel and bending of the central pillar; 29 - separation of the holders of the retainer plates and the body door hinge; 30 - local corrosion in the lower part of the side wall middle pillar; 31 - local corrosion and cracks in the side members of the body base; 33 - distortions of body doorways; 34 - continuous corrosion of the base thresholds; 35 - dents on the side members of the body base (ruptures are possible); 36 - thread failure on the fastening plates of the retainer and door hinges; 37 - tearing off the door lock cover; 38 - dents (possibly with tears) on the body side panel; 39 - local corrosion in the lower part of the front pillar; 40 - violation of the anti-corrosion coating; 41 - detachment of guy-holders; 42 - bent cross member No. 1; 43 - cracks on the front panel at the places where the strut is attached; 44 - separation of the buffer front mounting bracket; 45 - cracks on the radiator shield; 46 - local corrosion on the amplifier brace; 47 - cracks in the places where the spar is attached; 48 - weakening of the rivet connection of the bracket; 49 - making holes for the spring shackle pin and the front rear spring mounting bracket; 50 - separation of the body base spar amplifier; 51 - wear of the shock absorber mounting hole; 52 - cracks in the places where the fuel tank brackets are attached; 53 - dents with sharp corners or tears on the bottom panel; 54 - continuous corrosion on the lower rear panel; 55 - cracks in the places where the shock absorbers are attached; 56 - cracks on the propeller shaft casing

Destruction of welded joints in assemblies whose parts are connected by spot welding, as well as in continuous welds of the body, can occur due to poor-quality welding or the effects of corrosion and external forces: vibration of the body under the influence of dynamic loads, uneven distribution of loads during loading and unloading of bodies.

Wear due to friction occurs in fittings, axles and hinge holes, upholstery, and in the holes of rivet and bolt connections.

Dents and bulges in the panels, as well as deflections and distortions in the body appear due to residual deformation upon impact or poorly performed work (assembly, repair, etc.).

The concentration of stress in the connections of individual body elements in openings for doors, windows, as well as at the junctions of elements of high and low rigidity can cause destruction of parts if they are not reinforced.

Body structures usually provide for the necessary rigid connections, strengthening of individual sections with additional parts, and extrusion of stiffeners. However, during the long-term operation of the body and in the process of its repair, individual weak links in the body shell may become apparent, which require strengthening or changing the design of the components in order to avoid the occurrence of secondary breakdowns.

So, when the roof rigidity of the JIA3-695 bus was increased and, as a result, the twist angle was decreased, frames began to break. The breakdowns stopped after returning to the previous roof structure. Thus, structural defects arise as a consequence of imperfections in the design of the body and tail. Such defects include: insufficiently rigid fastening of parts to each other and to the body frame; incorrectly selected material; insufficient tightness in joints into which moisture is not allowed to penetrate (door window frame, in joints between the headlight rim and fenders, etc.); the presence of “pockets” from the sides, allowing the accumulation of moisture and dirt; insufficiently rigid edges of parts (for example, wings).

Technological defects arise as a result of a violation of the accepted technology for manufacturing or repairing a body. The most common technological defects of bodies include poor-quality welding, poor quality of the starting material, poor performance of individual operations during the manufacture and repair of parts (correction of irregularities in body panels, assembly after repair, etc.).

Below, as an example, is a list of damage found in the body of the GAZ-24 Volga car (Fig. 26).

Depending on the nature of the damage and how often it occurs, a decision is made on the advisability of making a repair part (RM) and methods for its manufacture in advance.

General structure of the technological process of body repair

Bodies entering for major repairs must meet the requirements of the technical specifications for acceptance for major repairs, approved by a higher organization.

Repair of automobile bodies is based on a clear delineation of work on dismantling, repairing and assembling the body and its components in specialized departments, installation on the body, as well as monitoring and adjustment of components in operation.

The main document defining the relationship of production operations, their duration, readiness and delivery dates for components and parts, as well as the duration of the entire technological cycle of body repair, should be a network schedule. Based on it, routing technology for the movement of parts and assemblies is being developed. These important technical documents provide guidance when drawing up an in-plant operational plan. Using route technology, operational schedules for the repair of parts and assemblies are drawn up in specialized areas: tinsmithing, reinforcement, wallpaper, etc. It is possible to ensure a clear organization of work in the body repair and assembly areas only if the specialized areas complete tasks on time. In this regard, it is necessary to create conditions for high organization of labor in specialized areas.

The technological process of a body overhaul is determined by its design features. In Fig. 27 shows a general diagram of the main stages of the body overhaul process, covering individual completed operations. As follows from this diagram, repairs begin with an inspection of the body when accepting it for repairs in order to determine the feasibility of the repair, check the completeness and detect damage visible without disassembly. Based on the results of the external inspection, the plant representative and the customer draw up a bilateral certificate of acceptance of the body for repair, indicating its technical condition and completeness. The report also notes emergency damage and reflects the additional work required that is not provided for by the repair rules. After washing, the body is subjected to preliminary flaw detection, the purpose of which is to determine the condition and feasibility of repairing components and parts that must be removed from the body (glass, interior upholstery, etc.), so as not to clutter the production premises with obviously unusable parts.

Rice. 27. General diagram of the technological process of body repair

After preliminary troubleshooting, general disassembly of the body is performed. During general disassembly, all units, components and parts installed on the body body are disconnected and removed. Only the body shell remains undisassembled. When washing the body externally, before disassembling it, surfaces covered by internal panels, the floor of the body (in buses), assemblies and parts installed on the body are not washed. Therefore, after general disassembly and removal of the internal panels and floor of the bus body, the inner surface and base of the body are thoroughly washed.

The disassembled and cleaned body, as well as the tail, are sent to the area for removing old paint; units and components that are subject to repair in other workshops of the plant or at other enterprises are sent to a storage warehouse for units awaiting repair; fittings, upholstery and other components and parts of the body that require repair - to the appropriate specialized departments of the body shop. Unusable parts are sent to the scrap warehouse, and suitable parts are sent to the usable parts warehouse, and from there to assembly.

The assembly area also receives repaired and new parts that are installed on the body to replace those rejected during its disassembly.

After removing the old paint, the body is subjected to careful control, during which the nature of the damage received during its operation and parts that have exhausted their service life are identified, and a decision is made on the need and possibility of repairing or replacing a particular body part. The results of inspection of parts are entered into the defect list. Systematic processing of these statements allows us to obtain data on the coefficients of suitability, repair and replacement of parts during major body repairs at a given auto repair plant. Having these ratios makes it easier to create realistic restoration plans, details and logistics. The body then goes to the repair site. At the first post of this section, the bodies of some structures are subjected to further disassembly necessary to perform repair operations.

So, from van-type bodies with wooden frames, metal cladding and damaged wooden parts are removed; Damaged trusses connected with rivets or bolts, panels, cladding, etc. are removed from bus bodies of the supporting structure.

After repair, the body is subjected to preliminary assembly; At the same time, doors are hung on the body, panels, tails and other parts that are to be painted along with the body are installed. Then the body is painted and finally assembled.

Schemes of technological processes for repairing bodies of cars, buses and truck cabins differ from each other in the presence of various equipment and mechanisms on them, as well as damage characteristic of each body structure and methods for eliminating them.

Preparing the body for repair

Preparation of the body for repair is carried out in accordance with the accepted technological process diagram for its repair and, as a rule, includes, after external washing and cleaning of the body, disassembling and removing paint and varnish coatings, identifying damage and determining the scope of repair work.

As can be seen from the above diagram of the main stages of body repair, disassembly during its overhaul is carried out in two sequential steps: removing from the body all components and parts installed on its body from the inside and outside; disassembling the case for repairs after removing the paint and varnish coating and identifying all damage to the case.

The sequence and scope of disassembly depend on the types of bodies, since they have different numbers of components and parts, installed and reinforced differently.

General disassembly of supporting structure bodies is closely related to disassembly of the car (bus) as a whole. Some components and body parts must be removed before disconnecting the electrical equipment and chassis components of the car (bus), and some can be removed only after removing the components. All these features are taken into account when drawing up the technological process for dismantling a car (bus).

A vehicle being repaired is transported using a tractor and a traction chain from the repair site to the external washing area. At the first post of this section, the possibility of heating the car in winter is provided. Then the interior upholstery and fuel tanks are removed from the car body and the body is washed. This post is usually equipped with a lift, with the help of which the body is raised to wash its bottom and the units attached to it. After the external wash, the car is moved using a traction chain to the disassembly area, where it is installed on a load-carrying periodic conveyor. On this conveyor, doors, hood, trunk lid, radiator trim, electrical equipment, buffer, glazing, fittings and other components and parts are removed from the body. To remove the chassis units from the body, the car is installed on a tilter (with a small production program, the entire disassembly process is carried out on tilters).

On some ARZs, the exterior of the car is washed after removing the wheels, side doors, fuel tank, interior upholstery, electrical equipment and wiring, trunk lid and muffler from the car.

Seat cushions and backrests removed from the body, as well as seat frames, are delivered by trackless transport to the appropriate repair areas; The plumage and bodies suitable for repair are transferred using a periodic overhead conveyor to a unit for removing old paint, and the fittings (locks, window regulators, etc.) are placed in baskets and sent to the fitting and fitting department.

After external washing, LiAZ, LAZ and Ikarus buses are moved by a traction chain to dismantling posts. At the first post, the bus is lifted using double-piston hydraulic lifts, installed on L-shaped racks that provide the ability to work from below, and chassis units, pipelines and other components and parts located under the floor of the body are removed. Then the body is installed on technological trolleys and moved along the rail track using a traction chain to the next disassembly stations. Assemblies and parts removed from the body that are subject to repair at the enterprise (seat frames, seat cushions and backs, glass with frames, body floor, etc.) are subjected to preliminary control and then sent to the appropriate departments for their repair. After complete disassembly, the bodies are moved to a chamber to remove old paint and thoroughly wash the inner surface of the body, and then to their repair stations.

When organizing disassembly in specially designated positions, it becomes possible to: eliminate clutter and reduce contamination in body repair areas at repair positions; equip workplaces with special tools and mechanized devices for removing heavy units and components, and also equip them, if necessary, with ventilation devices; rationally organize the disassembly process by specialized teams; increase the use of suitable parts.

Disassembly is carried out mainly using various universal metalwork tools, as well as mechanized impact wrenches and pneumatic tools. If necessary, gas cutting is used. Therefore, the installation of a disassembled body should ensure maximum scope of work, the possibility of using power tools and equipment, and minimal time spent on auxiliary operations.

In places where dismantling operations are performed, lifting devices (jacks, beam cranes, hoists), mechanized mobile carts, as well as pipelines for supplying oxygen and gas during gas-cutting operations are provided.

The technological disassembly process is selected depending on the accepted repair organization and local conditions.

If there is a significant volume of bodies produced from repair, which are repaired on an assembly line, disassembly can also be carried out using the flow-conveyor method.

Parts of detachable body joints are removed using a universal or specialized tool. Parts of permanent connections (welded, riveted), in order not to damage them, should be disconnected carefully.

To repair its parts, the body body is disassembled to the extent necessary to ensure high-quality performance of all repair operations. The all-metal welded body shell cannot be disassembled. Unusable panels (or parts of panels) are cut out and replaced with new repair parts. Bus bodies of riveted construction can be disassembled into their component elements. To ensure high-quality disassembly of the body and eliminate the possibility of damage to its parts, the disassembly order is established by the technological process.

Technological processes for body repair are usually developed in accordance with technical specifications, which contain requirements for the condition of the main components and parts of the body, acceptable methods for their restoration and the necessary data for monitoring them after repair.

Since it is not known in advance which part in the body body assembly (panel, base truss beam, etc.) will require repair or replacement, standard flow charts are drawn up for the disassembly and repair of all parts of the body body, the possibility of damage to which is revealed by analysis of a large number of similar bodies received at major repairs, according to the lists of defects, which are compiled when troubleshooting the body.

Preliminary disassembly of the body is usually carried out at car (bus) disassembly stations, and body disassembly, associated with the removal and repair of damaged parts of its body, is carried out at the appropriate repair areas. In this case, the body is installed in a position convenient for repair and measures are taken to protect it from the load of its own weight, which can cause deformation and distortion of its geometric parameters. Violation of the hermetic dimensions of the body can also occur when removing some of its components and parts on which other body components rest (when replacing side panels and central pillars on the body of a passenger car, removing the outer cladding of the sides of the body of some buses), if appropriate precautions are not taken . Therefore, before removing the frame support units, fixing devices (special spacers, conductors) are installed in the body openings, which hold the units that have lost their support in their normal position.

An example of a method for fixing the upper part of the rear of the body is shown in Fig. 28.

Rice. 28. Method of fixing the upper panels of the rear body when removing the lower destroyed parts

The device rests on one side against the right sidewall and floor of the body, and with its opposite upper part it is attached with two technological bolts to the corner panel of the body, thus fixing the correct position of the upper rear panels in width. The height position of these panels is fixed by a stretching device. Upon completion of the repair, the holes for the technological bolts are welded, and welding beads are cleaned.

Methods for removing paint coatings and cleaning the body surface from corrosion products

Old paint can be removed mechanically using a sandblasting machine or mechanized hand tools, or chemically - by treating with special removers or alkaline solutions.

When mechanically removing the paintwork, rust and scale are simultaneously removed, which could remain on the body panels or tail of the car after welding during routine repairs. It is advisable to carry out mechanical cleaning after degreasing. Failure to comply with these recommendations leads to a decrease in the efficiency of the process and the quality of cleaning and to premature wear of the processing material.

When shot blasting, the surface acquires a roughness that ensures good adhesion of the paint film to the metal. The most common abrasive material for shot blasting metal surfaces is metal sand. In recent years, the search for new materials, cheaper and more technologically advanced, has begun abroad. Among those tested, natural mineral materials (crushed rocks, natural corundum, zirconium eluvial sand with rounded grains), as well as artificial materials (electrocorundum, silicon carbide, etc.) are considered promising.

The main trends in the field of mechanical cleaning are automation of the process and combination with chemical action. To finish large surfaces, abrasive belts and rotary brush-type devices began to be used, working according to a given program. Polyester materials containing small (-0.5 microns) particles of carborundum, aluminum, chromium oxide, etc. have been successfully tested as abrasives.

Research has shown the influence of technological factors of shot blasting (the initial state of the surface being treated, the size and shape of the grain, the hardness of the abrasive material, the duration of treatment) and the microgeometry of the treated surface on the properties and strength of its adhesion to protective coatings. Maximum roughness is necessary to ensure good adhesion of sprayed metal and non-metallic coatings with a large layer thickness, especially powder ones. However, to obtain coatings with high protective properties and reduce material consumption, the roughness value should not be more than 30-40 microns, and the thickness of the applied layer should exceed the maximum profile depth. Some authors suggest two-stage processing: coarse-grained sand for cleaning and fine-grained sand for leveling the profile.

A significant influence on the relief is exerted not only by the initial shape of the grains, but also by the shape of their fragments, as well as the ability of the latter to retain sharp edges.

When cleaning the body, it is recommended to use metal shot of the DChK type, produced by factories in our industry with a grain size of 0.2-0.3 mm, as an abrasive substance. You should avoid using pellets with areas with a spherical surface and loose edges, since the edges of such pellets break off when they hit the metal and remain on it, which worsens the appearance and quality of the coating applied to the body. To clean body and tail panels made of sheet steel up to 1 mm thick from old paint and obtain the necessary roughness, the optimal angle of inclination of the shot jet to the surface being treated should be 45°, and the air pressure should be 2-3 kgf/cm2.

As a result of studies carried out at the Volzhsky Automobile Plant with the participation of the Magnitogorsk Mining and Metallurgical Institute and NIIATM on the durability of steel sheet coatings with various roughness parameters, it was found that the properties of the coating are influenced by indicators such as anisotropy, roughness heterogeneity and the degree of filling of the rough layer with metal. At the same time, it has been established that the dense fine-crystalline structure of the phosphate layer, determined by the high rate of crystallization, is formed only on a loose rough layer (CR = 0.35-0.45) at any Ra and n0* values. In addition, it was found that the uniformity of roughness and the absence of anisotropy have a beneficial effect on the physicochemical properties of the complex paint and varnish coating. Shagreen-type defects were observed only at a high roughness of 2.2 µm. With a decrease in the heterogeneity of the distribution of parameters and anisotropy of roughness, the heterogeneity in thickness decreased, and the gloss and appearance of the complex coating improved. Thus, the structure of the rough layer of the metal surface significantly affects the physicochemical and mechanical properties of the complex paint and varnish coating. The surface roughness of body panels to be painted can be limited to 4-5 cleanliness classes 2=20h-40 microns.

Sand can be supplied using a sandblasting (shot blasting) machine, but it is best to use for this purpose a mobile dust-free apparatus of the AD-1 type (Fig. 29) and a manual shot blasting gun (Fig. 30) developed and produced by the domestic industry.

These devices provide for automatic regeneration of abrasive shot and its supply to the shot blasting machine. Therefore, the advantage of such devices is the possibility of repeated use of abrasives, the absence of dust and the construction of special ventilation devices is not required. Metal shot is thrown onto the surface to be cleaned by compressed air through a nozzle. After hitting the surface, the shot, along with the resulting cleaning products, is sucked into the vacuum channel surrounding the nozzle using an injection device, separated and used again.

Rice. 29. Dust-free shot blasting machine AD-1

Rice. 30. Manual shot blasting dustless gun

Rice. 31. Shot blasting chamber for cleaning the internal surfaces of a carriage-type body

Shot blasting can also be carried out in a special chamber, similar to the type used at the Novorossiysk Car Repair Plant. The chamber is a closed metal hangar (Fig. 31), inside of which shot blasting machines are installed on platforms along the longitudinal walls. The devices are equipped with hoses that are connected to the cleaned surfaces manually.

Spent shot is poured into bunkers, from where it is picked up by elevators, rises up and, after separation, ends up in the upper bunkers. From these hoppers, the shot is loaded into shot blasting machines for reuse. The removal of shot from the floor of the horizontal elements of the body frame is carried out through the hose of a mobile suction unit mounted inside the chamber.

Separation of shot, i.e. removal of its crushed particles and purification products, is carried out using a fan, which is connected to the elevators by a central exhaust channel and side pipes.

Polluted air is expelled from the chamber by two fans through pipelines through ventilation openings in the windows. All three exhaust air ducts are equipped with cyclones. The supply of heated fresh air is provided by a ventilation unit.

Various installations are used to remove corrosion products manually and mechanically. Of these installations, the point of interest is the needle mill, which is a micro-cutting mill with several thousand cutting edges. The needle mill is made from straight pieces of high-strength wire with a certain packing density. The space filling factor on the working surface is 40-85%. Each fiber, pinched at one end by a weld and pressed with a certain force between similar fibers, represents a kind of semi-rigid cutter. Such a tool can cut off a layer of rust, scale, metal 0.01 - 1 mm thick, rotating in any direction at different angles to the axis of rotation. One of the features of a needle mill is the ability to create a predetermined roughness on the metal surface. This improves adhesion to the protected surface. The advantages of cleaning with this tool also include the absence of dust and the silent process. The service life of a needle mill is 200-300 hours of continuous operation (and ordinary steel brushes are 10-12 hours).

Rice. 32. Electromechanical brush:
1 - electric motor; 2 - gearbox; 3 metal brush; 4 - flexible shaft; 5 - starter: 6-axis device; 7 - trolley

Among the hand-held mechanized tools for cleaning surfaces, grinding machines МШ-1, И-144 and devices with pneumatic drive, grinding machines LLIP-2, LUP-6, an angle pneumatic machine and an electromechanical brush are also used (Fig. 32). These devices are equipped with steel brushes or abrasive wheels, which are used for cleaning. The electric motor is attached to the trolley 7 by means of an axial device 6, allowing rotation of the electric motor around a vertical axis. The weight of the device is about 16 kg.

To mechanize surface cleaning and remove paint and varnish coatings, disc brushes are also widely used (for working heads for pneumatic drills) (Fig. 33).

If hand-held power tools or a shot blasting machine that does not suck dust are used, the area must be adequately ventilated to remove generated dust. The study found that mechanical surface preparation with manual metal brushes will not provide adequate surface cleanliness, is ineffective and uneconomical. With this cleaning method, numerous scratches and nicks appear on the surface being treated. Sandblasting (using metal sand) provides the highest quality and most economical surface preparation.

Rice. 33. Disc brush for working heads for pneumatic drills:
1 - roller; 2 - flange; 3 - ring for fastening the pile; 4 - pile made from strands of steel cable; 5 - tightening screw

Various removers are used to chemically remove coatings and synthetic enamels.

The Leningrad branch of the State Industrial Enterprise "Lakokraspokrytie" has developed thixotropic removers SPS-1 and SPS-2, the advantage of which over other removers produced by the domestic industry is their reduced toxicity. SPS-1 remover is non-flammable, and SPS-2 is flammable, however, it has less toxicity compared to SPS-1 remover due to the presence of low-toxic solvents in its composition. The flushing effect of SPS-1 and SPS-2 removers is better in comparison with the removers currently produced by the domestic industry, as well as with the non-flammable emulsion remover SEU-1, developed by the Research Institute of Paint and Varnish Coating Technology (NIITLP), intended for removing old paint by immersion method. Removers can be applied using spatulas or airless sprayers. Industrial production of these removers is expected to be organized at the Riga Paint and Varnish Plant.

PKB Soyuzbytkhima (Vilnius) has developed an automatic remover for old paint, the advantages of which over the removers produced by the domestic industry are higher efficiency, versatility and manufacturability. The wash is non-flammable and is produced according to TU 6-15-732-72 by the Alytus chemical plant p/o "Litbytkhim" and the Shostka chemical reagents plant.

ZIL has developed an alkaline composition for quickly removing paint and varnish coatings made from synthetic enamels from the metal surfaces of conveyor hangers. This composition does not contain toxic or volatile compounds and allows you to mechanize the process - use the method of immersing products in a bath. Sodium gluconate and ethylene glycol are used as etching accelerators (GOST 19710-74).

Experience has shown that a solution consisting of 20% sodium hydroxide and 0.5% sodium gluconate (the rest is water), at a temperature of 95-98°C, removes a paint coating with a thickness of 60-75 microns in 5 minutes, and at a thickness of 120-150 µm - in 15 minutes. If 8% ethylene glycol is added to this solution, coatings of the specified thickness are removed in 3 and 5 minutes, respectively. The softened paint is completely removed by washing the surface with a stream of hot (50-60 °C) water.

After removing the old paint with a remover, corrosion remains on the surface of the body and an abrasive tool or chemical treatment methods (etching) are used to remove it.

To remove light corrosion deposits, it is enough to treat the surface with Dioxidin (a mixture of an aqueous solution of phosphoric acid, isopryl alcohol with the addition of a surfactant) or composition No. 1120. However, it is not always possible to completely remove corrosion products from painted surfaces, especially in hard-to-reach places. In these cases, it is recommended to use corrosion converting primer EVA-0112, produced by the Zagorsk paint and varnish plant according to TU 6-10-1234-72. This primer is used to treat corroded surfaces with a layer thickness of up to 100 microns, which significantly reduces the labor intensity of the work and improves the quality of the coating.

Before applying the primer, a thick (loose) layer of rust (over 100 microns) is removed mechanically. The EVA-0112 primer is prepared immediately before use by mixing the base and hardener, which is 85% ortho-phosphoric acid in the ratio of 100 parts base to 3 parts orthophosphoric acid.

According to GOSNITI and NIItractoroselkhozmash, 3-6 parts by weight of orthophosphoric acid are added to 1 liter of soil of initial viscosity (depending on the amount of corrosion products on the surface of the parts). After production, the primer is diluted with water (condensate) to a working viscosity of 26-27 s according to VZ-4. The primer is applied by spraying with a layer thickness of 25-30 microns. The drying time of the coating at 18-23 °C is 24 hours, and at 50-60 °C - 20 minutes. Primer consumption is approximately 300 g/m2 (on a metal surface coated with primer EVA-0112, you can apply primer GF-020, GF-019 or FL-OZk, as well as pentaphthalic enamels).

To mechanize the process of removing old paint from the cabs and tail of GAZ-bZA and ZIL-130 trucks, the Giproavtotrans Institute has developed a unit that consists of four compartments located sequentially one after another: removing old paint, washing with hot water, passivation and a device for blowing hot air. Between the mentioned compartments there are sections of drains through which the working fluid flows back into the compartment baths. Each of the compartments is a welded structure, covered with sheets, the space between which is filled with heat-insulating material. At the top of the compartments there is an overhead conveyor path, on which the products are processed by jetting.

The working fluid is heated by coils through which steam passes. The unit provides the ability to pump water from the hot water washing compartment into the old paint compartment, as well as from the cold water washing compartment into the neutralization compartment for its reuse. To adjust the concentration of working fluids and maintain a certain level in the compartments, there are appropriate automatic means.

To prevent harmful vapors from entering the production premises, the unit has an automatic ventilation system, the exhaust diffusers of which are located before the washing shower of the old paint removal compartment and after the washing shower of the cold water washing compartment. Between the washing showers of the compartments there are double-sided drainage zones, eliminating the possibility of mixing working fluids.

At the end of the process of removing old paint, the products are dried with hot air supplied from both sides of the product. To fully automate this process of removing old paint from the cockpit and tail, the designs of units installed at some ARZs (Voronezh, Lvov) provide a double-chain conveyor of periodic action. The cabins and empennage are supplied to the installation on a trolley with a lifting table and suspended on suspensions to the supporting part of the double-chain conveyor. Then the conveyor moves the suspended load horizontally and vertically downwards over the bath, immersing it in the alkali solution. After the cabin is immersed, the conveyor is turned off, and at the end of the work cycle, the conveyor is turned on again. Cabins (tail, body) rise vertically from the bath and move to the next bath, etc. The entire process of removing old paint in this installation is automated and lasts 30 minutes.

Cleaning the bodies of dump trucks from rocks adhering to them is carried out by mechanical means (pneumatic chisels and other devices) or by a hydraulic method using a hydromonitor installation similar to a high-pressure installation for the external washing of heavy-duty vehicles, developed by PKB Glavenergo-Stroymekhanizatsiya. This installation is stationary, walk-through, semi-automatic. The washing device is a swinging monitor with remote control and a swing angle in the horizontal plane +45° and vertical plane +30° and with vertical movement from the floor level from 0.8 to 2.4 m. The diameter of the monitor hole is 20 mm. The washing liquid is supplied by a centrifugal pump with a capacity of 80-150 m3/h. Pump electric motor power 55 kW. The return of recycled water is carried out by a sand pump with a capacity of 54 m3/h. Water purification is carried out by pressure and open upper hydrocyclones, the volume of which is 40 m3. The cleaning agent is hot water (70-85°), the consumption of which is 4 m3/day. The cleaning agent is heated by steam, the temperature of which is 120-130 °C. Steam consumption 125 kg/h. The total power of the installation is 75 kW.

Flaw detection of bodies

Flaw detection of bodies is an important part of the repair process. After removing the old paint, the body is subjected to careful control in order to reject unusable parts, select suitable ones, and determine the type and scope of repair work. Flaw detection of the body and its components is carried out in accordance with the technical conditions for its repair, developed for each type of car. The quality of the repair largely depends on the adopted method of defect detection and the thoroughness of its implementation.

Flaw detection of the body and its parts is organized in areas of general disassembly of the body and in areas of its repair. To detect defects in the body shell, as well as to control newly manufactured parts: welds, non-destructive testing methods are used.

The technical condition of the body at car repair plants is usually checked by external inspection of the surface of parts with the naked eye or using simple magnifying glasses. Typically, four- or nine-fold binocular loupes are used for this purpose. This method allows you to detect surface cracks, corrosion, deformations, etc. Measurement with special measuring tools, fixtures and templates allows you to detect deviations in the geometric dimensions of parts from the original (distortions, deflections, etc.).

To identify cracks and determine the tightness of fit of articulated parts, the method of tapping parts is also used, which is based on determining the tonality of the sound when tapping parts with a hammer. By changing the tone of the sound, you can identify cracks and loose connections (rivets, bolts, spot welding, etc.). The effectiveness of this method depends on the experience of the performer.

However, by external inspection it is possible to establish only large damage visible to the eye, for example, dents, broken shapes, areas of surface corrosion, cracks, etc. In some places of the load-bearing elements of the body, as a result of the accumulation of fatigue and significant hardening of the metal due to cold hardening, which appeared in the process of repeated panel repairs , hairline cracks appear, which can be detected using special methods.

Methods based on the molecular properties of a liquid are called capillary methods (penetrating liquid methods), based on the capillary penetration of indicator liquids into the cavities of surface defects and recording the indicator pattern. The most widely used are the kerosene colored and luminescent methods. Kerosene, having good wettability and surface tension, easily penetrates into leaks.

The essence of this method is that the area being examined is moistened with kerosene and wiped dry or dried with a stream of air. Then this place is covered with an aqueous solution of chalk. At sub-zero temperatures, add a non-freezing solvent to the solution (0.5 liters of ethyl alcohol per 1 liter of water). Due to the absorption of kerosene by the chalk, a grease mark appears on the chalk surface, by which the size of the crack is judged.

During color control, the area to be examined is thoroughly cleaned and degreased with gasoline, and then coated with a solution of penetrating red paint. After holding for 5-10 minutes, the solution is removed from the surface with water or a solvent (depending on the flaw detection materials used).

After cleaning the surface of the part, a layer of white developing mixture is applied to it by spraying or using a soft brush. After 15-20 minutes, characteristic bright stripes or spots appear on a white background at the locations of the defects. Cracks are detected as thin lines, the degree of brightness of which depends on the depth of the cracks. Pores appear in the form of points of various sizes, and intercrystalline corrosion appears in the form of a fine mesh. Very small defects can be observed through a magnifying glass or binocular microscope. At the end of the test, the developing mixture is removed from the surface by wiping the part with a rag soaked in a solvent. The part is dried.

Flaw detection materials are used as a set. The kit includes: cleaning composition, indicator (penetrating) paint “D”-M, showing “D”-V. They can be in ordinary containers, as well as in aerosol bottles.

Penetrating compositions can be made from lighting kerosene - 70-80 g, B-70 gasoline - 20-30 g, aniline dye or Sudan IV - 1-3 g, and developing ones from (as a percentage by weight) white nitro enamel NTs-25 - 70 g, RDV thinner - 20 g, thickly ground zinc white - 10 g.

Using the paint method, cracks with a width of 0.005 mm and a depth of up to 0.4 mm can be detected. When the part is heated to 50-80° C, smaller cracks can be detected.

Since car bodies are usually made of thin sheet steel, in order to avoid choosing the wrong repair method (whether to leave the corroded area, having previously removed corrosion products from its surface and then applying an anti-corrosion coating, or to replace the damaged area with a new one), during flaw detection of the body, the depth of the corroded area should be determined destruction. For this purpose, it is best to use non-destructive flaw detection methods, for example using a gamma thickness gauge (Fig. 34). This device measures the thickness of sheet steel of the body cladding when access to the object being measured is available on only one side. There are no special requirements for surface cleanliness when measuring with the device.

Rice. 34. Gamma thickness gauge:
1 - measuring block; 2 - sensor gun; 3 - power supply

The operation of the device is based on measuring the intensity of gamma rays (the source of which is cobalt-60) scattered when passing in the opposite direction through the thickness of the metal. The detector in the device is a counter with a sodium iodide crystal. Pulses from the detector enter an amplifier and then to a single-channel amplitude pulse analyzer, to the output of which an integrating circuit is connected. The readings are measured on a device whose scale is graduated in millimeters.

The device allows you to measure sheets with a thickness from 0 to 16 mm. The time required to carry out one measurement does not exceed 30 s. The device receives power from an AC mains voltage of 220 V.

To determine the depth of corrosion destruction, you can also use some magnetic thickness gauges for non-magnetic coatings on ferromagnetic substrates (MIP-10, VIP-2 devices, etc.).

TO Category: - Automotive bodies

The following types of repairs are provided for removed components and parts that impede straightening, welding and painting work:

• repair 0 – elimination of damage to the front surfaces of the body without damaging the paint
• repair 1 – elimination of damage in easily accessible places (up to 20% of the surface of the part)
• repair 2 – elimination of damage with welding, or repair No. 1 on the surface of a part deformed up to 50%
• repair 3 – elimination of damage with opening and welding, partial restoration of the part up to 30%
• repair 4 – elimination of damage with partial restoration of the part on the surface over 30%
• partial replacement - replacement of a damaged part of a body part with a repair insert (from the range of spare parts or made from the latest ones)
• replacement – ​​replacement of a damaged body part with a part from spare parts
• large-block repair - replacement of damaged body parts with blocks of parts from rejected bodies with marking, cutting, fitting, drawing, straightening, welding of the latter

Damage to the body can be very different, so repair rules must be individual. In almost all cases, it is necessary to remove some parts to detect damage and straighten and align the body frame. If damage is severe, the interior padding is removed to facilitate measurement, control, and installation of hydraulic or screw jacks to correct distortions and deflections.

Deformed surfaces repaired by mechanical or thermal impact on the metal, as well as by filling dents with quick-hardening plastics or solder.

Correcting the body by mechanical action involves stretching, extruding and straightening deformed parts of the body to give them their original shapes and configurations.

Body parts are straightened in hot and cold conditions. To straighten and straighten the body, a set of tools and devices is used, which includes hand tools, hydraulic cylinders with a pump and devices for extracting damaged areas.

Rice. Set of tools and accessories for body repair:
a – hammers; b – mallets; c – special mandrels; g – support

Rice. Set of tools for straightening the body:
1 – mandrel for drawing out concave parts; 2, 3 – self-locking hydraulic clamps; 4 – mandrel with teeth for gripping; 5 – hydraulic clamp; 6 – double grip; 7 – device for straightening the body; 8 – hydraulic pump; 9 – tension cylinder with grips; 10 – tension cylinder with pulling device

Rice. Removing bulges in body panels without heating:
a – section of the panel with a bulge; b – diagram of the direction of the hammer blow;
1 – bulge; 2 – panel; 3 – sections of the panel to be stretched by straightening with a hammer; 4 – panel curvature after correcting the bulge

Removing bulges in a cold state is based on stretching the metal in concentric circles or radii from the bulge to the undamaged part of the metal. When straightening, a smooth transition is formed from the highest part of the bulge to the surrounding surface of the panel.

To do this, a series of successive blows in a circle are applied with a hammer in the direction from the metal surrounding the bulge to the curved part of the surface. As the hammer approaches the boundary of the bulge, the impact force is reduced. The greater the number of circles on the panel during straightening, the smoother the transition from the bulge to the undamaged part of the metal.

Straightening of deformed surfaces is carried out using a mallet and shaped plates or anvils of a special profile.

Rice. Restoring the shape of parts using a straightening tool

Heated straightening is carried out in two ways:

• heating followed by cooling
• heating with metal deposition by impact

Heating and rapid cooling of the convex is based on the use of metal expansion and contraction processes. Heating of the metal is carried out with a carbon electrode of a welding machine or the flame of a gas burner. When heated, a small circle of metal quickly heats up red-hot, and the plasticity of the metal increases. Since the expansion of the heated metal is prevented by the less heated surrounding metal, the increase in the volume of the heated metal occurs due to its thickening. When cooling, the metal contracts, its volume decreases, but is held by the cold metal located around it. Since the metal has a temperature that does not correspond to maximum plasticity, when it contracts, it absorbs a small part of the surrounding metal. Acceleration of the process of metal precipitation is achieved by reducing the speed of heat propagation by creating a ring of wet cloth around the heated part of the metal, tapping the boundaries of a point of metal heated red-hot, and then the heated point itself with a mallet or straightening hammer.

A sharp cooling of the heated area of ​​the body is carried out with an asbestos swab or rag moistened with water. Cooling of the metal leads to the desired settlement and the body surface adopts the required profile. When eliminating a bulge using this method, the surface is cooled in the sequence shown in the figure:

Rice. Sequence of cooling of a heated body surface with a convexity

The bulge (dent) is heated and the metal is deposited in the following order. The metal is heated red hot (the diameter of the circle during heating is no more than 10 mm with a metal thickness of 0.6...0.8 mm). A hand anvil is placed under the heated area. Using a mallet when removing a bulge or a smoothing hammer when removing a dent, tap the non-reddened metal around the heated point, and then the heated point.

The sequence of preheating and striking when removing large bulges (dents) depends on the shape of the bulge. If the bulge is round, then impact points 1...4 are arranged in a spiral in the direction from the periphery to the center; if the bulge is long and narrow, impact points 1...16 are located in narrow rows.

Rice. The sequence of heating and cooling the metal when eliminating bulges

Removal of dents in hard-to-reach places is carried out using levers, support plates and a special impact device. The figure shows editing diagrams and examples of correcting body elements using levers.

Rice. Removing dents in hard-to-reach places using levers:
a – correction of the deformed area using a clamping lever; b – fixing dents using a hammer and a clamping lever; c – insertion of the clamping lever with a hammer blow between the deformed part of the panel and the box; d – examples of repairing dents under the hood reinforcements, door frame and in the hidden cavity of the front wing

Dents located under the amplifiers are removed with flat levers. Stampings and stiffeners in open areas are restored using support plates and a special chisel. Creases and dents in door panels, as well as fenders, are straightened with levers, using the internal elements of the hood panels, doors, mudguard, etc. as support.

Irregularities on panels can be smoothed out using polyester putties, thermoplastics, cold-curing epoxy mastics, and solder. Polyester putties form reliable connections with panels that have been stripped down to bare metal. These are two-component materials containing an unsaturated polyester resin and a hardener, which is a catalyst for rapid curing of the mixture, regardless of the thickness of the putty layer. Drying time at a temperature of 20°C is 15-20 minutes. In this case, there is no need to apply several layers of putty, which reduces the duration of its application.

Thermoplastic is available in powder form. It acquires the elastic properties necessary for its application to the metal surface of the panel at a temperature of 150-160 ‘C. The surface to be filled is thoroughly cleaned of rust, scale, old paint and other contaminants. For better adhesion, it is recommended to create roughness on the metal surface using an abrasive tool. To apply thermoplastic, the area to be leveled is heated to a temperature of 170-180 ‘C and the first thin layer of powder is applied, which is rolled with a metal roller, then the second layer is applied, and so on until the unevenness is filled. Each layer is rolled until a monolithic plastic mass is obtained. After curing, the layer is cleaned and leveled with a sanding machine.

Can be repaired with cold-curing epoxy mastics, which have high adhesion, sufficient strength and are easy to apply to damaged areas.

Solders POSSu-18, POSSu-20 are used for leveling areas, building up the edges of parts and eliminating gaps. To prevent metal corrosion, it is better to use an acid-free method of applying solder.

To eliminate body distortion of medium, increased or special complexity, mobile power devices and universal stands are used.

Correction of bodies on stands or mobile devices should be carried out taking into account a number of recommendations.

Before stretching, the force device is attached, positioning it on the central axis perpendicular to the deformed area.

The chain is secured in the center of the deformed area using clamps; if the sheet of the panel being straightened is weakened, then a reinforcing plate is welded to it. The chain is attached perpendicularly to the vertical arm of the device, precisely observing the straightening axis and taking into account the fact that the greatest force develops on the head of the power cylinder.

Rice. Installing a body straightening device on a car

As the height of the chain fastening to the lever increases, the force on the hydraulic cylinder rod gradually decreases. The minimum tensile force is generated at the upper end of the vertical arm. Stretching begins at the minimum stroke of the hydraulic cylinder rod. The angle formed by the vertical lever with the horizontal beam of the device must be acute, which allows stretching without shortening the chain.

Elimination of body deformations is carried out in the following order:

• determine the places where force is applied to eliminate distortion and select the necessary grips and stops from the set of accessories
• Having determined the place of application and the direction of the force to eliminate the distortion, fix the device for straightening the body in this direction
• install and secure screw braces or a hydraulic cylinder with the necessary extensions, grips and stops in the opening
• install and secure the chain of the power body with one end to a fixed grip or clamp, and the other to the power lever; in this case, the chain must be pre-tensioned and have an angle of inclination determined by the required direction of the tensile force
• with the help of a power organ, the damaged part or assembly is pulled out (squeezed out); Squeezing out damaged parts is carried out from inside the body using power stretchers or hydraulic devices
• after removing the load of power devices, check the geometric parameters of the body

Rice. Editing the rear door opening