In this survey, 13 domestic automobile fastener companies were visited and investigated, and the companies under investigation have passed the TS16949 system certification. The average fastener of a car is about 1,500, and the total assembly time of each car bolt is about 2.5~3.2h. It can be seen that the variety and quality of fasteners have an important impact on the level of the main engine and the quality of the vehicle. This paper analyzes the localization of high-strength threaded fasteners and the management of supply quality from the process of high-strength threaded fastener production. 1. High-strength threaded fastener product flow The process of producing high-strength threaded fasteners is raw material reforming → cold heading forming → thread processing (rolling or twisting) → heat treatment → surface treatment → sorting and packaging, and the rolling process of heat treatment is generally adopted above 10.9. 2. Automotive fastener materials The steel grades commonly used for high-strength bolts are 35 steel, 45 steel and ML35 steel for bolts of 8.8 grades; 35CrMo; 40Cr for bolts of 10.9 grade; 35CrMo, 42CrMo and SCM435 for bolts of grade 12.9. The domestic materials for automobile standard parts are mainly made of materials produced by Baosteel Co., Ltd., and they have a high market share in the steel market for special high-strength fasteners such as domestic car tires and commercial vehicle engines. At present, Baosteel has become the designated manufacturer of special standard steel for FAW, Dongfeng, SAIC and other companies. 10.9 and 12.9 engine fasteners are mainly imported from Kobe, Japan, Nippon Steel, and South Korea's Pohang. The imported materials have good hardenability, high purity and stable assembly. The cost is about 15%-20% higher than domestic materials. At present, Shanghai Superpower Co., Ltd., which produces the best quality domestic high-strength bolts, produces raw materials (import), cold heading process, heat treatment and surface treatment in accordance with the procedures of the Japanese joint venture party. The quality is stable but the cost is high. The largest auto standard parts company in China? Dongfeng steam standard is mainly based on imported materials for passenger car fasteners, and commercial vehicles use Baosteel materials. The raw materials for domestic fasteners are basically hot-rolled, while the steels for fasteners produced in countries such as Japan are basically directly cold-pressed, and users do not need to pre-treat, which can reduce costs from the link. Common failure modes for fastener failure are assembly elongation, fatigue fracture, and delayed fracture. 3. Cold head forming and threading (rolling or twisting, tapping) The quality of threaded fasteners In addition to materials, forming equipment and threading equipment and molds (production processes and equipment) are key factors in ensuring their quality. Especially in the large-volume and multi-variety supply state, how to ensure the consistency of the products and the prevention of defects are one of the problems faced by fastener production. The cold-press equipment and thread processing equipment of the company under investigation, its domestic equipment accounts for about 40%, Taiwan equipment accounts for 50%, and imports (Europe, America, Japan) equipment accounts for about 10%; common defects are size and shape tolerance tolerance, head Fractures, threaded flow lines, tooth wrinkles and cracks. For the introduction of high-efficiency and high-precision special-purpose machine tools, domestic enterprises are also investigating and exploring. For example, Shanghai Yizhong Company spent 14 million yuan in 2004 to introduce a Swiss Herdbar five-station cold heading machine; Dongfeng Automobile Standard Parts Company introduced Italy SACMA's cold forming equipment; SAIC Standards introduced the US GI company's online vortex sorter. At present, domestic fastener factories are limited to funds or other reasons. Domestically produced equipment and Taiwan equipment are used to produce automotive fasteners. To ensure the dimensional tolerance and shape tolerance of large-scale production of high-end fastener products, it should be increased. Online monitoring means and mold making level. Eliminate the non-conforming products in production, thus ensuring the assembly quality of the OEM and the OEM. 4. Heat treatment Heat treatment and quenching and tempering is to improve the comprehensive mechanical properties of the fastener and to meet the tensile strength and yield ratio specified by 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 of the core of the material, surface decarburization during material and annealing, cold cracking, quenching cracking and deformation in quenching and tempering. Heat treatment process: feeding→cleaning→heating→quenching→cleaning→tempering→coloring→offline. About 80% of the fastener companies surveyed have heat treatment equipment, and most of them use Taiwan's heat treatment process line; the process line equipment is a continuous mesh belt furnace with atmosphere protection, and the atmosphere, temperature and process parameters are controlled by computer. The problems are that the quenching medium lacks the cooling performance measurement, the carbon potential control is unstable, and the furnace temperature test cycle is too long, which may cause heat treatment defects.
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Quality Management and Analysis of High-strength Automotive Fasteners