Fasteners are a general term for a class of mechanical parts used when two or more parts (or components) are fastened together to form a whole. The characteristics of fasteners are that there are many varieties and specifications, different performances and uses, and there is a high degree of standardization, serialization, and generalization. Therefore, some people have named a class of fasteners that have national standards as standard fasteners, or simply For standard parts. Others are called non-standard parts. But their important role is the same. Today, I will introduce the processing process of fasteners and materials.
1. High-strength thread fastener product process
The production process of high-strength thread fasteners is the transformation of raw materials → cold heading → thread processing (thread rolling or wire rolling) → heat treatment → surface treatment → sorting packaging. Rolling process after heat treatment is generally used for grades 10.9 and above.
2. Automotive fastener materials
常用 The steel grades commonly used for high-strength bolts are 35 steel, 45 steel, and ML35 steel for 8.8 bolts; 35CrMo for 10.9 bolts; 40Cr; 35CrMo, 42CrMo, and SCM435 for 12.9 bolts.
The domestic raw materials for fasteners are basically hot rolled, while the steels for fasteners produced in countries such as Japan are basically cold-rolled directly. Users do not need pretreatment and can reduce costs from the link.
The common failure forms of fastener failure are assembly elongation, fatigue fracture and delayed fracture.
3. Cold heading and thread processing (thread rolling or thread rolling, tapping)
In addition to the quality of thread fasteners, in addition to materials, forming equipment and thread processing equipment and molds (production technology and equipment) are the key factors to ensure their quality. Especially under the condition of large quantities and multiple varieties of supply, automotive fasteners that require high processing accuracy, how to ensure product consistency and defect prevention is one of the problems facing fastener production.
4. Heat treatment
Heat treatment and quenching and tempering is to improve the comprehensive mechanical properties of fasteners and to meet the specified tensile strength value and yield ratio of the product. The quenching and tempering heat treatment process has strict requirements on raw materials, furnace temperature control, furnace atmosphere control, and quenching medium. The main control defects are carbon segregation at the core of the material, surface decarburization during material and annealing, cold heading cracks, quench cracking and deformation during quenching and tempering.
Heat treatment process: feeding → cleaning → heating → quenching → cleaning → tempering → coloring → off-line.
5. Surface treatment
The surface treatment of automobile fasteners mainly has the following methods. a. Non-electrolytic plating is hot dip plating, penetration plating, mechanical plating, Dacromet sintered film, etc. b. Electrolytic plating is galvanized, zinc-nickel alloy, zinc-iron alloy, etc. c. Phosphating treatment. d. Blackening treatment and so on.