The quality of bolts used in vehicle assembly significantly impacts the safety and reliability of the entire process. Selecting the right bolts is a crucial decision that involves considering various principles to ensure optimal performance. This article outlines key principles for bolt selection, the significance of surface treatment, and methods to prevent loosening of bolt threaded connections.

Principles for Bolt Selection

Priority Principle

Bolt selection is categorized into four priority levels. Whenever possible, opt for standard parts currently in production and use as long as they meet design requirements.

Generalization Principle

Minimize the introduction of new type bolts during early design stages. Particularly in the chassis section, reduce bolt variety and specifications to enhance assembly efficiency, minimize operator error, and streamline processes.

Principle of Reliability

Prioritize bolts that exhibit stability and dependability under normal working conditions, especially in critical areas like braking, suspension, and steering systems.

a. Loosening: Selected bolts should not loosen during reverse torque or fail in torque decay tests.

b. Hydrogen Embrittlement: Prevent hydrogen embrittlement-induced cracks that result from stress concentration.

c. Fatigue: Bolts must resist fatigue-induced failure.

d. Excessive Torque: Avoid selecting bolts prone to overtightening.

Application and Conservation Principles

Optimize standard part performance by selecting appropriate sizes and specifications that fulfill design functions and uphold product quality.

Selection of Bolt Head Structure

For bolts M10 and above:

Hexagonal flange surface with flat washer

Hexagonal flange surface

Hexagonal head with flat washer

Avoid using spring washers.

For bolts M6-M8:

Hexagonal head with flat washer and spring washer

Hexagonal flange surface

Hexagonal head with flat washer

Surface Treatment Selection for Bolts

Oil Coating for Rust Prevention

Ideal for welding bolts, nuts, and screws, oiling prevents rusting.

Electroplating

Suitable for welding studs, screws, bolts with a performance grade ≤8.8, grade 8 nuts, cap nuts, and wheel nuts.

Dacromet Coating

Use for bolts ≥8.8 performance grade and grade 8 nuts. Zinc-aluminum-chromium coating for non-passenger vehicles, and zinc-aluminum coating for environmental protection and passenger vehicles.

Anti-Loosening Methods for Threaded Connections

Riveting and Anti-Loosening

Incorporate methods like riveting or welding.

Friction Anti-Loosening

Options include double nuts, spring washers, lock nuts, and toothed lock washers.

Mechanical Anti-Loosening

Utilize methods like cotter pins, slotted nuts, lock washers, and tandem wire.

Thread Adhesive Anti-Loosening

Apply epoxy resin or anaerobic adhesive to the thread surface to increase loosening torque.

Anti-Drop Screw

Typically used for door locks.

Conclusion

Bolt selection is a critical aspect of vehicle assembly. This article serves as a concise guide to aid in choosing appropriate bolts for vehicle assembly. As manufacturing technology advances, the future of bolt development will undoubtedly focus on high-strength variants to meet evolving industry requirements.