In automotive bolt assembly, torque-controlled tightening is a widely used technique. Its core principle is to achieve bolt fastening by controlling the applied torque. Thanks to its simplicity, ease of control, and high repeatability, over 60% of assembly processes adopt this method. However, determining the appropriate torque value is not straightforward—it requires comprehensive consideration of factors such as bolt material properties, assembly requirements, and safety margins.

1. Torque Selection Based on Yield Strength

The torque value must be based on the bolt’s yield strength. Yield strength is the critical point at which the material begins to undergo plastic deformation. Beyond this point, the bolt may deform, compromising its performance. Therefore, the upper limit of the process torque is generally recommended not to exceed 90% of the yield torque. This limit ensures that the bolt does not enter the plastic deformation zone during tightening, preserving its structural integrity and functionality.

2. Lower Torque Limit for Effective Utilization

On the other hand, to ensure effective use of the bolt, the lower torque limit should not be too low. Typically, it is recommended to set the lower limit at 50% of the yield torque. This ensures that the bolt can fully utilize its elastic properties during assembly and avoids insufficient preload due to under-tightening, which could affect joint reliability.

3. Intelligent Screwdrivers in Real Applications

Danikor’s intelligent electric screwdrivers offer a variety of tightening strategies. These strategies can control torque output based on different assembly requirements and bolt characteristics. For example, intelligent screwdrivers can monitor torque and angle in real time, ensuring each tightening operation meets preset standards. Additionally, they feature self-learning capabilities, allowing them to optimize tightening parameters based on historical data and real-time feedback, thereby improving consistency and reliability in assembly.

4. Other Influencing Factors

When determining specific torque values, factors such as bolt size, material, surface treatment, and assembly environment must also be considered. For instance, high-strength bolts, due to their higher yield strength, may require greater torque to achieve the same preload. Surface treatments like galvanization or lubricant coatings can affect the friction coefficient, thereby influencing torque transmission efficiency.

Moreover, ambient temperature and humidity can also impact torque selection. In high-temperature or high-humidity environments, the material properties of bolts and connected parts may change, requiring appropriate adjustments to torque values to ensure assembly stability and safety.

Conclusion

Torque-controlled tightening plays a vital role in automotive bolt assembly. The selection of torque must take multiple factors into account. By setting a reasonable torque range and combining it with the precise control of intelligent screwdrivers, assembly quality can be effectively improved, ensuring joint reliability and safety. In practice, adjustments and optimizations should be made according to specific conditions to achieve the desired assembly outcome.