New Challenges in Fastening Battery Packs for New Energy Vehicles: How Do Hexagon Head Flange Screw Bolts Resist Thermal Vibration?

With the rapid development of the new energy vehicle industry, the safety and reliability of battery packs as core components of the power system have attracted more and more attention. Among them, hexagonal flange bolts, a seemingly inconspicuous fastener, play a key role in connecting battery modules and fixing structures. However, under the complex working conditions of electric vehicles, thermal expansion and high-frequency vibration have become two major challenges that they must deal with.

Thermal expansion: the "invisible killer" under temperature difference
The temperature of new energy vehicle battery packs fluctuates violently during operation. When charging, the internal temperature of the battery can rise to above 60°C; while in a low temperature environment, the temperature of the battery pack may drop sharply to below -30°C. This extreme temperature difference causes the materials (such as aluminum alloy and steel) between the battery module and the fixed bracket to undergo different degrees of thermal expansion. If the Hexagon Head Flange Screw Bolts is not designed properly, the preload may be attenuated or even fail due to mismatch of material expansion coefficients.

Technical response plan:
Material optimization: Use high-strength alloys with low expansion coefficients (such as titanium alloys or special stainless steels) to reduce the expansion difference between bolts and battery module materials.
Composite coating: Applying a thermally stable coating on the surface of the bolt not only improves the corrosion resistance, but also enhances the connection stability through the synergistic effect of thermal expansion between the coating and the substrate.
Dynamic preload design: Through finite element analysis (FEA) to simulate the stress distribution at different temperatures, design variable pitch threads or elastic washers to achieve dynamic compensation of preload force.
Vibration shock: "protracted battle" of high-frequency fatigue
During the driving process of electric vehicles, the battery pack continues to withstand vibration from the road, the impact of acceleration/deceleration, and the high-frequency vibration of the motor operation. Long-term accumulated alternating stress may cause fatigue fracture of the flange bolts, which in turn causes the battery module to loosen and cause short circuit risks.
Technical breakthrough direction:
Anti-loosening technology upgrade: From traditional friction anti-loosening (such as double nuts, spring washers) to structural anti-loosening (such as thread locking glue, wedge locking device), and even use smart bolts (built-in sensors to monitor preload changes).
Vibration damping design: Add a high damping material layer to the contact surface between the bolt and the battery pack to absorb vibration energy and reduce stress amplitude.
Fatigue life prediction: Combined with actual working condition data, tools such as the rain flow counting method are used to evaluate the fatigue life of bolts, providing a scientific basis for regular maintenance.
Industry collaboration and standard evolution
Meeting the challenges of thermal expansion and vibration requires not only innovations in material science and mechanical design, but also collaboration between upstream and downstream of the industry chain. Battery manufacturers, fastener suppliers and vehicle manufacturers need to jointly develop more stringent testing standards, such as:

Thermal cycle test: simulates the repeated thermal expansion and contraction of battery packs in an environment of -40℃ to 85℃.
Vibration durability test: reproduce multi-axis random vibration of vehicles during driving on a vibration table.
Preload attenuation monitoring: develop embedded sensors to track changes in bolt preload in real time.