Non-destructive repair technology is a new technology to repair all kinds of depressions (no obvious creases, no damage to paint surface, no slight plastic deformation and elastic deformation) caused by external force on the exposed parts of automobile body panels. To do a good job of nondestructive repair, we must equip the "secret weapon" for the repair of Jinfan sag and master the correct use process, strength and technological steps. Judging the damage is the premise, and choosing the right tool is very important. At the same time, it requires patient and meticulous operation. Never use too much force or blindly, otherwise the paint surface will be damaged, the maintenance time will be prolonged and the cost will be increased.

1 nondestructive repair tool

(1) sag repair rod. A set of concave repair rods with different shapes can be divided into large and small according to their sizes. The length of the large concave repair rod is 70 mm~80 mm, and the length of the small concave repair rod is 30 mm~40 mm, which can be selected as required.

(2) Wooden hand hammers and rubber hammers with different hammers.

(3) Special projection lamp for sag repair. The special projection lamp for dent repair consists of a transparent glass plate with straight lines, a light box body, a lamp tube, a flexible projection lamp bracket and a magnetic base (Figure 1).

Two steps of nondestructive repair

With the special tools for nondestructive repair, it is necessary to correctly master the process steps of concave surface repair, so that the Mijin covering parts repaired with concave surface damage can meet the quality requirements of painting-free. The basic operation steps of sag repair are as follows.

(1) First clean the dented damaged area and its surrounding surface of the automobile, and polish the surface paint film if necessary (when polishing, apply a small amount of polishing agent to the dented damaged area and its surrounding surface, and select the rotating speed of the polishing machine. When operating, hold the polishing machine, keep the polishing disc and the polished paint surface at about 5 ~ 15, and grasp the strength to polish). The purpose of cleaning and polishing paint surface is to enhance the brightness of paint film surface around the damaged area and improve the reflectivity of paint surface. Using the refraction effect of light on the surface of automobile can improve the flatness of the damaged area and its surrounding surface observed by maintenance personnel during maintenance, which is the concrete application of optical principle in sag repair.

(2) Place a special projection lamp for dent repair near the damaged part of the car. Because the projector base is magnetic, it can be placed anywhere on the metal surface of the car. In order to prevent the magnetic base of projection lamp from damaging the automobile surface coating, the base of projection lamp should be wrapped with soft textiles before use. Turn on the projector lamp, and adjust the irradiation angle of the projector lamp, so that the straight line on the projector lamp panel can be projected to the damaged area and its surrounding surface. Reasonable use of repair projection lamp and projection mirror to observe the projection line of the damaged area and its surrounding surface can clearly see that the projection line presents a uniform straight line or curve in the undamaged area, but a vortex or irregular projection line in the sunken damaged area.

(4) Select appropriate non-destructive repair lever, adhesive drawing equipment, hammer and chisel to repair the area with spiral or irregular projection lines. When the concave repair rod needs to extend into the concave part far away from the working window or hole, choose a larger concave repair rod or a suitable sticking and pulling tool; On the other hand, choose a smaller concave repair rod, and choose concave repair rods with different top shapes and different axial curvatures according to the space size and position of the concave part, which must match the repair position, otherwise the paint surface will be easily damaged. Choose the hammer according to the depth and area of the depression. In the process of operation, tools should be changed in time and flexibly according to the progress of sag repair and the change of sag damage, so as to make the operation handy.

(5) During nondestructive repair, the concave repair rod works through the working window or hole. When prying and jacking with the concave repair rod, the concave repair rod should gradually move from the periphery of the concave area to the center of the concave area. When jacking, the force should be moderate. Through the refraction of light, the projection line projected by the projection lamp in the concave area should be observed at any time, so that the projection line in the concave area is flush with the surrounding projection line or gradually consistent with the curvature of the surrounding projection line. If there is neither a working window nor a suitable hole for the dent repair rod to extend into, a special bonding stretching device can be used and the stretching point corresponding to the damage can be selected. For the bulging phenomenon caused by the damaged surrounding or lever and excessive tension, you can use special tools to knock it properly to make the hammering point more accurate and not damage the paint surface. When knocking, pay attention to make the projection line of the knocking point flush with the surrounding projection line or consistent with the curvature of the surrounding projection line. When the damaged area of the depression is flush with the surrounding projection line or the curvature is consistent with the naked eye, it can be considered to be repaired in place.

(6) During the whole nondestructive repair process, carefully observe the change of the projection line in the depressed area. When the depression repair is basically completed, it is necessary to use a special nylon rod to release the stress, so as to avoid uneven surface strength caused by uneven stress.

Traditional minor damage repair technology is used to repair dents on the surface of automobile doors. Generally, the interior trim panel of the automobile door is removed, and then the inner side is propped up with a pad iron or crowbar, and the outer side is knocked with a hammer, or repaired with a hammer by a meson machine. After shaping to be basically flat, there may still be small depressions and unevenness. At this time, the paint surface and anti-corrosion layer are also damaged in the process of wire drawing and hammer repair of meson machine, and paint surface repair and anti-corrosion treatment are needed. When repairing the paint surface, it is necessary to scrape and polish the putty repeatedly and spray paint many times, which is not only labor-consuming and time-consuming, but also prone to quality defects such as poor paint color, sagging and orange lines, so that the repair quality can not be guaranteed. The paint-free and damage-free repair technology for automobiles can reach 100% without the traditional maintenance method and painting process, which can restore the vehicle to its original state, which is not only environmentally friendly, but also greatly shortens the maintenance time and greatly reduces the maintenance cost and time, so it is deeply welcomed by 4S shops, repair shops and customers.