High-speed automotive fasteners latest survey report

In this survey, a total of 13 domestic automotive fastener companies were interviewed and investigated. The companies surveyed have all passed the TS16949 system certification. On average, there are about 1,500 fasteners for a sedan, and the total time for assembling each vehicle bolt is about 2.5-3.2 hours. It can be seen that the variety and quality of the fasteners have an important influence on the host level and the overall vehicle quality. This article analyzes the localization and supply quality management of high-strength threaded fasteners from the manufacturing process of high-strength threaded fasteners.

1. High-strength threaded fastener product flow

The production process of high-strength threaded fasteners is raw material reforming → cold roll forming → threading (rolling or reeling) → heat treatment → surface treatment → sorting packaging. Above 10.9 level, the thread rolling process after heat treatment is generally used. High-strength threaded fastener product process shown in Figure 1.

2. Automotive fastener materials

The steel grades used for high-strength bolts are 35 steel, 45 steel, and ML35 steel for 8.8 bolts; 35CrMo for 40.95 bolts, 40Cr for bolts, and 35CrMo, 42CrMo, and SCM435 for bolts of grade 12.9.

The domestic standard materials used for automotive parts are mainly based on materials produced by Baosteel, and its market share in domestic high-strength fasteners, such as passenger car tires and commercial vehicle engines, is relatively high. At present, Baosteel has become a designated manufacturer of special standard steels for FAW, Dongfeng and SAIC.

10.9 and 12.9 engine fasteners imported from Japan mainly used Kobe Japan, Japan's Nippon Steel, South Korea's Pohang and other companies. The imported material has good hardenability, high purity, and stable assembly. The cost is about 15%-20% higher than domestic materials.

At present, the Shanghai High-Strength Company with the highest quality of high-strength bolts in the country produces raw materials (imports), cold heading, heat treatment, and surface treatment all in accordance with the procedures of the Japanese joint venture. Its quality is stable, but its cost is high. The largest automotive standard parts company in China – Dongfeng Automobile Standard’s selection of fasteners for passenger vehicles is based on imported materials. Commercial vehicles use Baosteel’s materials.

The raw materials used for domestic fasteners are basically hot-rolled. The fastener steels produced in Japan and other countries can basically be directly cold-headed. Users do not need to pre-treat and can reduce costs from the links.

Common failure modes for fastener failure include assembly elongation, fatigue fracture, and delayed fracture.

3. Cold forming and threading (rolling or twisting, tapping)

Quality of threaded fasteners In addition to materials, forming equipment and threading equipment and dies (production processes and equipment) are key factors in ensuring their quality. In particular, under the condition of large quantities and varieties of supply, it is one of the problems faced by fastener manufacturers that how to ensure the consistency of products and the prevention of defects in automotive fasteners that require high processing precision.

The company's cold-heading equipment and thread processing equipment accounted for about 40% of its domestic equipment, 50% of Taiwan's equipment, and about 10% of imported equipment (Europe, Japan, and Japan); common defects include poor tolerances on dimensions and shape tolerances. Partial folding, thread breaking, thread wrinkles and cracks.

For the introduction of high-efficiency, high-precision special machine tools, domestic companies 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 Standard's introduction of GI's on-line eddy current sorter.

At present, domestic fastener factories are limited to funds or other reasons, and more domestic and Taiwanese equipment are used to produce automotive fasteners. To ensure large-scale production of high-end fastener products, the dimensional tolerances and form-position tolerances should be increased. Online monitoring tools and mold making levels. Eliminating non-conforming products in production to ensure the assembly quality of OEMs and OEMs.

4. Heat treatment

Heat treatment is to improve the overall mechanical properties of fasteners, to meet the product specified tensile strength and yield ratio. The quenched and tempered heat treatment process has strict requirements on raw materials, furnace temperature control, furnace atmosphere control, and quenching media. The main control defects are carbon segregation in the core of the material, surface decarburization in the material and annealing process, cold crucible cracking, quench cracking and deformation in the 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 lines; the process line equipment is a continuous mesh belt furnace with atmosphere protection, and the computer controls the atmosphere, temperature and process parameters.

The problems include the lack of cooling performance of the quenching medium, the instability of the carbon potential control, and the long period of the oven temperature test, which are likely to cause defects in the heat treatment.

5. Surface treatment

The surface treatment of automotive fasteners mainly has the following methods. a. Electroless plating is hot dip plating, dialysis plating, mechanical plating, Dacro sintered film, etc. b. The electrolytic plating is galvanized, zinc-nickel alloy, zinc-iron alloy, etc. c. Phosphate treatment. d. Black treatment and so on.

The main drawbacks are the hydrogen embrittlement that occurs during electroplating and phosphating processes. The knowledge of surface protection of the domestic enterprises surveyed is still at the level of evaluation based on only salt spray tests. For high-strength threaded fasteners, the control of the surface friction factor is a very critical link. All process assembly parameters are developed based on the specified range of friction factors. Table 2 shows the specifications of the major automotive companies for friction factors.

The surface treatment plants under investigation were all equipped with different passivation processes and lubricants according to different friction factors. The solvents were imported directly. However, the necessary measures and instruments are not available for the adjustment and detection of friction factors that meet the process requirements.

6. Sorting, Packaging and Product Traceability

The sorting methods adopted by the fastener factory under investigation after surface treatment mainly include manual selection, eddy current sorting, optical sensing size and contour sorting. The sorting process is mainly to pick out bad products with obvious defects, such as quenching cracks, surface decarburization (vortex sorting), dimensional deformation and so on.

In the production of important fastening parts, some manufacturers use imported sorting instruments. These manufacturers can basically perform 100% inspection on the production of important fasteners.

Packaging and transportation are mainly to prevent the fasteners from being damaged, scattered, and the erosion of the external environment.

Product traceability is mainly for all batches of products can be traced back to the production shift, material lot number, heat treatment conditions and all other processes. The fastener factory being investigated, the implementation and management of the product flow card is gradually pushed in accordance with the requirements of the host plant, from the material into the plant, reform to form, heat treatment and surface treatment and other basic. Established a control system, but also found that some manufacturers flow in the form of coping and inspection.

For domestic fastener manufacturers, the process inspection and on-line sorting capabilities of important parts, especially high-strength threaded fasteners, are strengthened to eliminate some human interference factors and have a great effect on ensuring the quality of supply.

7. Laboratory capacity

The main problems are the obsolescence of the test equipment, the improvement of the quality of personnel, the improvement of test standards and measurement management.

8. Summary and discussion

This is mainly a survey of automotive fastener manufacturers. Overall, China has initially had the conditions and capabilities to produce high-strength automotive fasteners. In terms of key equipment for manufacturing and testing, domestic companies are improving their capabilities through technology introduction and digestion.

The speed of new product development of the surveyed manufacturers has a certain gap with foreign countries. The foreign fasteners Guangjia has formed a production chain relationship with the main engine plant or the vehicle manufacturer and jointly develop products. For example, Shanghai Teqiang mainly supplies Honda and other OEMs with significant advantages in R&D of new products.

Some companies surveyed have low levels of technology, processes, and equipment, and it is difficult to ensure the high-strength fasteners' dimensional accuracy, consistency, performance reliability, and interchangeability requirements from the technological conditions. Some enterprises have strong technical innovation capabilities, lack of technical strength and talents, lack of funds, necessary equipment and independent research and development capabilities.

Automotive fasteners are high-end products in their production areas. The companies surveyed are aware of the opportunities that companies face and the competitive pressures from foreign manufacturers, strengthen the exchange of related scientific and technological information technologies, and introduce advanced technologies from abroad. The phase of imitation and transition to the establishment of its own independent research and development forces.