Application of threaded fasteners in automobile as

Analysis on the application of threaded fasteners in automobile assembly

threaded fastener connection is one of the common connection methods of automobiles, including welding, riveting and adhesive connection. The purpose of threaded fastener connection is to make the connected parts closely fit and bear certain external forces. It has the advantages of high degree, convenient assembly and convenient assembly and disassembly of parts and components, which will make jingasia Pacific innovation park the largest R & D center of BASF in the Asia Pacific region

there are four kinds of external forces on threaded connections, including tensile stress, shear stress, tensile stress + bending stress, tensile stress + bending stress + shear stress, etc. To ensure that the connection of threaded fasteners can overcome various static or dynamic external forces on the connected parts, the threaded fasteners should produce an axial clamping force on the connected parts, which is provided by the applied torque. The bolt overcomes the friction and realizes elastic deformation according to the rigidity ratio between the bolt and the connected parts, so as to form a clamping force between the mating surfaces at both ends of the bolt. The correct tightening process should be clamped. Therefore, the postponement purchasing force of high priced raw materials should be controlled. Therefore, the essence of assembly tightening is to control the axial clamping force of bolts within an appropriate range

during the connection and assembly of threaded fasteners, the dispersion of clamping force is affected by the selected assembly method and other external conditions. Solvay ultra performance polymers exhibit extremely high PV values of up to 4million psi*ft/min (140mpa*m/s) in harsh environments. During assembly, the clamping force must be large enough to ensure that the sensor failure of the connected parts during operation is mainly due to the overload of the experimental force, which can be reliably fitted without relative movement; On the other hand, the applied clamping force must ensure that the bolts and connected parts will not be damaged or plastic deformed during assembly and service. Market research shows that most problems in bolt connection, such as bolt looseness, fracture, collapse of connected parts, damage, etc., are caused by inaccurate or incorrect clamping force. The research shows that the greater the axial clamping force of the bolt, the better its anti loosening and anti fatigue performance. Generally, the best effect is achieved when the bolt is tightened to yield

at present, in the automobile assembly site, considering the actual production pace and operation, the clamping force of each bolt connection pair cannot be measured correctly, so the torque can be used as an intermediate value to evaluate the assembly quality of the bolt connection pair. For torque control, the torque control accuracy of the tightening tool and the tightening process method are the two keys. Generally, the torque control accuracy of pneumatic tools is 10% - 40%; The accuracy of manual fixed torque wrench is about 10%; The torque control accuracy of the electric tightening machine can reach 3% - 5%. The accuracy of tightening tools and torque control directly determines the level of assembly

according to the domestic automotive industry standard qc/t tightening torque of threaded fasteners for automobiles, the tightening accuracy of fasteners is divided into three levels, I, II and III. The torque tolerance and torque ratio corresponding to different levels of tightening accuracy are shown in Table 1

Table 1 torque ratio corresponding to tightening accuracy at different levels

note: k1= minimum tightening torque/maximum tightening torque

take m20x1.5x100 hexagon bolt with friction coefficient of 0.12 at level 10.9 as an example. When level III assembly is adopted, the target tightening torque is small, while the torque fluctuation range is large, and the clamping force on the working thread is minimum. After improving the assembly level, the target tightening torque is increased, and the torque fluctuation range is reduced, and the clamping force is increased. The target torque of level I assembly is 0.087% higher than that of level III assembly, and the clamping force on the thread is 32.5% higher. According to the foreign threaded fastener assembly standards, when the threaded connection level is level III, if M16 bolts are used, the use requirements can be met; When grade I assembly is selected, the bolt specification can be reduced to M12. It is necessary to grade the assembly of automotive threaded fasteners. When receiving orders, fastener suppliers should first consider the requirements of the technical agreement. Compared with level III assembly, using level I assembly increases the target tightening torque of bolts, reduces the torque fluctuation range, and improves the clamping force on bolts; When the clamping force requirements of the connecting structure on the bolt remain unchanged, the use of class I assembly can reduce the bolt size, achieve weight reduction, lightweight and compact structure