The Importance And Working Principle Of Fasteners

Fasteners are widely used and occupy an extremely important position in the automobile industry! On average, a car uses about 500 kinds of fasteners per 50Kg/4000 pieces; There are more than 88Kg/7100 pieces, of which high-strength fasteners account for about 1/3. The cost of fasteners on a car accounts for about 2.5% of the cost of the vehicle, accounting for 40% of the total number of basic parts of the vehicle, and the workload of fastening connections on the assembly line accounts for about 70%!

1. The importance of fasteners

Apply too little force and the gasket may not fit properly; use too much force and the threads will be worn away. According to recently published data, 23% of repair problems in the automotive industry are caused by loose fasteners, and 12% of new cars have fasteners that are not properly tightened. Bolts are one of the most important factors that determine the quality of assembly, and the failure of threaded fasteners to reach the corresponding capacity is an important cause of assembly accidents!

2. Fastener bolt tightening principle

The bolt connection must be able to resist external force, so that the assembled parts will not move in the direction of separation, otherwise it will cause the bolt joint to loosen, be damaged or fall off.

Therefore, we design the minimum clamping force of the bolt, which must be able to prevent the clamping part from being separated due to external force, and to maintain frictional clamping or ensure sealing, etc.

The bolt is inserted into the connected part, and the nut or internal thread is tightened to make the bolt stretch and deform. This elastic deformation produces an axial tensile force, which squeezes the clamped parts together, which is called pre-tightening force.

Theoretically, as long as sufficient clamping force is generated, the clamped parts can be guaranteed to work safely in harsh environments such as vibration, high and low temperature, without using auxiliary methods such as gluing.

3. Clamping force of fasteners

The sole purpose of the tightening procedure is to maintain the clamping force within the appropriate tolerances!

During assembly, the clamping force must be large enough to ensure that the assembled parts will never move relative to each other. But at the same time, it must be ensured that the clamping force applied during tightening will not damage or plastically deform the bolt.

Clamping force control is the core purpose of bolt assembly, improper control of clamping force will cause |serious consequences.

4. Torque distribution

By oiling the surface of the fastener, the friction force can be reduced and the pre-tightening force can be increased under the same torque. In other words, to achieve the same tightening effect, the torque required for the oiled bolts should be smaller.

Torque detection method:

① Loosening method: After loosening, it needs to be tightened, which is troublesome to operate and rarely used;

② Fastening method: the most commonly used, the detection torque is larger than the actual tightening torque range;

③ Marking method: the most accurate, complex operation, rarely used.

5. Commonly used tightening methods for fasteners

Torque control method: It is the most widely used tightening method, suitable for most non-critical bolt connections.

Disadvantages: It is greatly affected by the friction coefficient, the clamping force is discrete, and the utilization rate of bolt materials is low.

Other tightening methods include torque-angle control method and yield point control method.

Commercial vehicle final assembly adopts torque control method