Fasteners include bolts, studs, screws, nuts, washers, and pins. Locking or biting often occurs on fasteners made of stainless steel, aluminum alloy, and titanium alloy materials. These metal alloys themselves have anti-corrosion properties, and when the surface is damaged, a thin oxide layer will be formed on the metal surface to prevent further corrosion. When stainless steel fasteners are locked, the pressure and heat generated between the teeth will damage this oxide layer, causing blockage or shear between the metal threads, leading to adhesion. When this phenomenon continues to occur, the stainless steel fasteners will be completely locked and can no longer be removed or locked again. Usually, this series of actions of blocking, shearing, sticking, and locking occur in just a few seconds, so correctly understanding and using such fasteners can prevent this phenomenon.
The variety and quality of fasteners have a significant impact on the level of the host and the overall quality of the vehicle. This article analyzes the localization and supply quality management of high-strength threaded fasteners from the perspective of the production process of high-strength threaded fasteners. The production process of high-strength threaded fasteners includes raw material modification → cold heading forming → thread processing (rolling or rolling) → heat treatment → surface treatment → sorting and packaging. For grades 10.9 and above, the rolling process after heat treatment is generally used.
1. Standards for fastener product dimensions: specifying the basic dimensions of the product; Threaded products also include basic dimensions of threads, thread ending, shoulder distance, tool groove and chamfer, and end dimensions of externally threaded parts. 2. Standards for technical specifications of fastener products. This mainly includes the standards and corresponding specific regulations for product tolerances, mechanical properties, surface defects, surface treatment, and product testing. 3. The standards for acceptance inspection, labeling, and packaging of screw products: specifically stipulate the qualified quality level and sampling plan of spot checks during product factory acceptance, as well as the content of product labeling methods and packaging requirements. 4. Standard marking methods for standard parts, fasteners, screws, and screws: Specific regulations on the complete marking methods and simplified marking methods for products. 5. Standards for other aspects of fasteners, such as fastener terminology standards, fastener product weight standards, etc.
The commonly used steel grades for high-strength bolts in automotive fasteners are grade 8.8 bolts made of 35 steel, 45 steel, and ML35 steel; 35CrMo is used for 10.9 grade bolts; 40Cr; 35CrMo, 42CrMo, SCM435 are used for 12.9 grade bolts. The raw materials used for fasteners in China are basically in hot-rolled state, while the steel used for fasteners produced in countries such as Japan can basically be directly cold forged, and users do not need pre-treatment, which can reduce costs from the link. The common failure modes of fasteners include assembly elongation, fatigue fracture, and delayed fracture. The quality of cold heading forming and thread processing (rolling or twisting, tapping) threaded fasteners is not only determined by the material, but also by the forming equipment, thread processing equipment, and molds (production process and equipment), which are key factors in ensuring their quality.
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