Insufficient fastener engagement length
After the fasteners are tightened, it is required to expose 2 to 3 threads. Otherwise, there is a risk of slipping or not sticking. Such design changes are generally to replace the fasteners or increase the sinking of the opponent parts to reduce the wall thickness.
Fast flange contact area of fasteners
The size of the opening hole of the instrument body bolt bolt hole is large, the sheet metal hole has the risk of exposure, and the bolt of the large washer is used for shielding; the injection molded parts such as the bottom bottom guard plate absorb the body precision tolerance and the mounting hole size is larger. If the flange cover area of the fastener is small, the stress is concentrated when the fastener is tightened, and the plastic shield is whitish, crushed or cracked. It is necessary to consider the use of large flange faces or self-contained large washers. Generally, the flange surface has a single side cover size of ≥ 4 mm and a tightening torque of ≤ 5 N·m.
Fastener torque attenuation
In the endurance test, the side door retaining limit, the sliding door guide, the four-door lock and other parts are attenuated, and the anti-loose rubber treatment needs to be added. A common method of anti-looking in automotive fasteners is pre-coated engineering plastics, which are commonly referred to as "Gute-resistant screws." During the locking process, the internal and external threads of the fastener generate a strong reaction force due to the extrusion of the engineering plastic, so that the friction between the inner and outer threads is greatly increased, and the contact of the full tooth joint is generated, thereby achieving the anti-loose function.
Insufficient dynamic check of assembly process
In the assembly process, the dynamic check is insufficient. When the fastener is tightened, the hole is difficult. The end of the fastener needs to be increased. The seat ball slide, the sliding door slide and other hexagonal flower-shaped bolts are tightened during the tightening process. The risk of escape is generally required to have a flower shape depth of ≥ 3.2 mm.