The product design of screws and nuts encompasses various aspects-including structural elements, performance standards, application specifications, and anti-loosening technologies-aimed at meeting requirements for fastening, sealing, anti-loosening, and lightweighting under diverse operating conditions. In high-end manufacturing sectors such as automotive, wind power, and aerospace, the precision of such designs is particularly critical.
Design of Structural Elements
The design of structural elements for automotive fastener connections must strictly adhere to international standards (ISO) and national standards (GB). These elements include thread end types (e.g., flat end, chamfered end, conical end), thread run-out, shoulder length, and undercut features, all designed to prevent the occurrence of "false torque." The thread engagement depth for bolts and screws must be verified based on the material being joined (e.g., steel, bronze, cast iron, aluminum), calculated as a multiple of the nominal diameter (typically 1d, 1.5d, or 2d).
Torque Standards
Automotive screw torque standards consist of both general benchmarks (e.g., torque values corresponding to various performance grades for metric coarse-pitch specifications such as M3, M5, M8, and M12) and specialized specifications tailored to critical components, such as engines. During assembly operations, a calibrated torque wrench must be used, with the allowable error controlled within a range of ±10%. Furthermore, it is essential to note that torque values must be adjusted accordingly to accommodate fasteners made of different materials (e.g., aluminum alloy versus cast iron).
Application Example: Automotive Seat Screws
Automotive seat screws come in a wide variety of models, with common specifications including M6, M8, and M10. These fasteners feature various types-such as flat-head, ribbed, trilobular, and self-tapping designs-with the specific model selected varying depending on the vehicle model.
Principles and Technologies of Modern Anti-Loosening Design
Modern anti-loosening technology has moved beyond traditional thread structures, giving rise to a diverse array of innovative designs. Examples include anti-loosening threads that utilize asymmetric profiles to induce controlled plastic deformation; bolts featuring surface treatments with high hardness and low friction coefficients; assembly techniques that ensure tightening quality through real-time torque-angle monitoring; and methods employing integrated die-casting or "module-free" designs to reduce the number of connection points. Additionally, patented innovations within the industry serve as a testament to the continuous evolution of anti-loosening technologies.
