Forming repair and maintenance methods for body stamping parts
Car body stamping parts account for 50% to 60% of the car's weight, and their maintenance mainly refers to the replacement and repair of body stamping parts.
1. Forming and repair of body stamping parts
1.1 Tools used for forming and repairing body stamping parts
Tools should be used in the forming repair of body stamping parts: hammers are mainly used to reset metal plates, and different hammers should be selected according to the characteristics of the parts that need to be repaired. There are various types of hammers, and different hammers have different uses. For example, short hammers are used in places where space is limited, long hammers are used in deeper forming areas, conical hammers are used in the laminating area of panels, and serrated hammers are used to tighten metal sheets, etc. When using a hammer, the principle of "avoiding the heavy and focusing on the light" should be followed, that is, during the forming process, heavy tapping should be avoided as much as possible. When striking, the hammer should be pulled simultaneously to make the hammer head slide on the metal surface. When the depression on the body panel is lower than the surface of the metal plate and faces the seat, the seat should be positioned lower than the depression on the opposite side of the metal plate, and then the edge of the depression should be struck with a hammer; When the indentation is higher than the seating surface, the hammer should strike the center of the indentation. When pinching the hammer, the thumb should be placed along the handle instead of gripping it tightly, which is beneficial for controlling the force and location of the strike. There are also various types of seats, each with different shapes and sizes. When choosing, it should be determined according to the specific situation.
The car body scraper is used to repair uneven marks left by tools such as hammers, retainers, and leveling knives. The car body scraper can only come into contact with protruding metal materials and is suitable for operations where the surface is rough after processing and needs to be polished.
When the dents on the car body panel gradually disappear and the height can be felt by hand, further repair is needed; If you can no longer feel the height with your hands, you need to use a car body scraper for identification. At this time, the car body scraper can only be used gently, in order to find the unevenness and facilitate the use of a hammer and seat for repair.
1.2 Repair of body stamping parts
The repair of car body damage can generally be carried out by first using machinery for initial forming, and then using manual tools for forming until the damage to the car body disappears and the deformation is restored. The commonly used mechanical tools for body repair work include portable hydraulic jacks, mobile body repair machines, fixed body doubling machines, and desktop body repair machines. The mobile hydraulic jack is mainly used for trimming operations such as pulling, pressing, expanding, bending, lifting, impacting, and tightening on deformed body parts, and its usage. The base of the mobile body trimming machine is a beam type, with one end supported by a frame shaft and a movable column installed on top. A hydraulic head is installed between the seat beam and the column, and small casters are installed on the bottom beam for movement. When the hydraulic head is subjected to hydraulic pressure, the pillar tilts, causing the body panels connected by the chain to be stretched, thus carrying out the finishing operation.
The fixed body trimming machine can firmly fix the entire body on the bearing platform, use power to trim the body, and also trim the edges and smooth edges of the body.
Using adhesives and sealants during vehicle maintenance
During the process of repairing the car body, there are many parts that need to be bonded. In bonding, different types of adhesives should be selected according to the materials and parts to be bonded; During the process of repairing the car body, there are also many parts that need to be sealed, and the selection of sealant should also be based on different situations.
3. Maintenance methods for body stamping parts
3.1 Rice Gold Forming
The formation of rice gold requires the operator to possess experience and skills. The commonly used basic technologies for vehicle body forming include:
3.1.1 Convex surface trimming: Align the hammer with the higher center position of the convex surface, and then gently tap with the strength of the wrist. The shape of the seat surface should be adapted to the shape of the steel plate surface, and the hardness of the seat surface should be higher than that of the vehicle body panel. The steel plate after trimming will have some extension, so it is necessary to carry out reshaping operations after trimming.
3.1.2 Concave surface trimming: Align the hammer with the edge of the concave groove and gently tap with the strength of the wrist, that is, tap the relatively higher part of the concave groove edge. Some of the repaired steel plates have been extended, and subsequent reshaping work should be carried out.
3.1.3 Trimming of large concave surface: First, heat the middle part of the large concave surface with a spray gun, then use a seat to lift it up on the lower side of the middle part to form a large flat surface, and then trim the raised parts at both ends according to the convex surface trimming method until they are restored.
3.1.4 Trimming of large curvature convex surfaces: When trimming parts with large curvature such as mudguards, it is advisable to touch the lower part of the concave surface with your hand and gently tap it with a hammer from the opposite side. When the surface being repaired is difficult to fit into the seat and leveling knife, a stretching tool can be used.
3.2 Repair and sealing of corroded surfaces
3.2.1 Repair. For lightly corroded and unperforated rust, it can be directly coated with rust removal, anti rust paint, secondary paint, and topcoat. For car body panels that are severely corroded and have holes or dents, transitional methods can be used for repair. One commonly used method is to apply fiber sheets such as fiberglass cloth, which eliminates the need to remove various decorations due to welding repairs. This method is suitable for exterior surface areas of the vehicle, such as doors, that are not subjected to stress or have low stress. The operation method is to remove rust, paint, and debris from the steel plate base layer, then apply a layer of fiberglass cloth soaked in resin to the area to be repaired, and then apply a layer of epoxy metal coating on the outer layer of fiberglass cloth to form the contour. After drying, polish the surface of the epoxy metal coating and spray paint.
3.2.2 Flattening and Polishing. After repair, the damaged area has basically recovered, but there are traces of tools and impossible dents left, so further flattening and polishing are needed to make its surface smooth.
3.2.3 Flatten. The file cutter is flexible and can be used in conjunction with a gripper. When filing the surface of the panel, it should be filed in one direction first, and then in a roughly vertical direction. When the filing knife returns, it should be lifted away from the already filed surface to ensure a smooth surface.
3.2.4 Polishing. The selected polishing disc should be flexible, and the polishing surface can change with the undulating shape of the vehicle surface. Usually, after finishing, a power polishing machine is used to find the high or low points on the surface. The main function of a power polishing machine is to polish the surface after finishing, and the polishing machine can also be used to polish the coating or other polishing materials around the damaged area, which is called "grinding edge".
Common polishing machines include disc polishing machines, oscillating polishing machines, box polishing machines, cone polishing machines, etc. When using a disc grinder, the machine is at an angle of about 20 ° to the surface, and the pressure applied to the disc causes a bend of about 25mm on the disc surface to come into contact with the polished surface. During operation, it is not allowed to swing in an arc. When moving, it should always be perpendicular to the surface scratches, which can reduce the workload before applying primer. When using an oscillating polishing machine for grinding, it should be made roughly parallel to the grinding mark. Cone polishing machine is used for polishing areas with deep indentations, such as around the headlights and at the connection of the baffle. When manually polishing, it should also be roughly parallel to the grinding marks.
3.3 Coating
The quality of painting will directly affect the external appearance of the vehicle and the corrosion resistance of metal materials. The coating of automobiles is a systematic engineering, where we learn about the basic knowledge of coatings and the general procedures of coating operations.
Coatings are generally composed of three components: resin, pigment, and solvent. Resin can make the coating have good gloss and hardness, and the shape is full, which can make the color distribution uniform; Pigments not only add color to coatings, but also increase the thickness of the coating; The solvent gives the coating fluidity and solubility, making it easy to apply during painting. The drying methods for coatings include natural drying and dry drying, and dry drying methods include thermal radiation drying and hot air drying. Coatings that belong to natural drying type include hard gloss paint, acrylic paint, weather resistant urethane resin paint, enamel paint, etc; Drying type coatings include amino alcohol casein rigid mesh coatings, acrylic resin coatings, urethane resin coatings, etc.
