Fastener and material processing process

Fastener is a general term for mechanical parts, used when two or more parts (or components) are tightly connected into a whole. Fasteners are characterized by a variety of specifications, different performance and uses, and a high degree of standardization, serialization and generalization. Therefore, some people also refer to a type of fasteners with existing national standards as standard fasteners, or simply standard parts. The others are called non-standard parts. But their important roles are the same. Today, we will introduce the processing technology of fasteners and materials.

1. Product process of high-strength threaded fasteners
The production process of high-strength threaded fasteners includes raw material reorganization, cold heading, thread processing (thread rolling or thread rolling), heat treatment, surface treatment, sorting and packaging. The thread rolling process after heat treatment is generally used above 10.9.

2. Automotive fastener materials
The commonly used steel types for high-strength bolts are 35 steel, 45 steel and ML35 steel for 8.8 grade bolts. 35CrMo is used for 10.9 grade bolts; 12.9 grade bolts use 35CrMo, 42CrMo and SCM435
The raw materials of Chinese fasteners are basically hot-rolled, while the fastener steel produced in Japan and other countries is basically in a state of direct cold heading. The user does not need pre-processing, which can reduce the cost of the link.
Common failure modes of fasteners include assembly elongation, fatigue fracture, and delayed fracture.

3. Cold heading and thread processing
In addition to materials, forming equipment, thread processing equipment and molds (production technology and equipment) are key factors to ensure the quality of threaded fasteners. Especially in the case of large-volume, multi-variety supply, how to ensure product consistency and prevent defects is one of the problems faced by the production of automotive fasteners that require high machining accuracy.

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4. heat treatment
Heat treatment and tempering is to improve the comprehensive mechanical properties of fasteners and 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 shortcomings are carbon segregation in the middle of the material, surface decarburization during the material and annealing process, cold upsetting cracks, quenching cracks and quenching and tempering deformation.
Heat treatment process: feeding, cleaning, heating, quenching, cleaning, tempering, coloring and offline.

5. surface treatment
The surface treatment methods of automobile fasteners mainly include the following.
(1) Non-electrolytic plating includes hot dip plating, penetration plating, mechanical plating, Dacromet sintered film plating, etc.
(2) The electrolytic coating is galvanized, zinc-nickel alloy, zinc-iron alloy, etc.
(3) Phosphating treatment.
(4) Blackening treatment, etc.