There are many types of automotive fasteners, including bolts, studs, screws, washers, retaining rings, pins, rivets, welding nails and assemblies and connecting pairs.
The demand for automotive fasteners accounts for about 23% of the total sales volume of the entire fastener industry, accounting for the highest proportion in the industry.
According to the latest data released by the China National Association, from January to February this year, China's automobile production and sales were completed 36260,000 and 36250,000 units, down 145% and 152%。
Car sales in February were 19760,000 units, and new energy vehicles accounted for 266%。Among them, the new energy vehicle market also resumed growth, with production and sales in February being 5520,000 and 5220,000 units, an increase of 48 y/y8% and 559%, with a market share of 266%。
01. Demand for fasteners for new energy vehicles
In recent years, the lithium battery industry is the basic industry of new energy, and vigorously developing the lithium battery industry is an important measure for the country to achieve energy transformation and complete the "double carbon" strategic goal.
Under the guidance of industrial policies such as the "New Energy Vehicle Industry Development Plan (2021-2035)", the market demand of China's lithium battery industry will continue to be strong, the industrial chain will continue to improve, and the international competitiveness is expected to be further improved, which will also make the trend of new energy vehicle development not weaken in the next 10 years.
With the popularization of new energy vehicles, not only the scope and quantity of their applications continue to expand, but also the amount of fasteners is increasing, and in the process of continuously improving the energy density and performance of power batteries, the safety of fastener threaded connections has also become a topic of much concern and controversy.
Due to the large number of non-metallic materials in new energy vehicles, their requirements for temperature and safety protection are extremely high. Therefore, the tightening and assembly of fasteners is the top priority in the assembly of new energy vehicles.
The production and sales of new energy vehicles in 2023 will hit a record high, through the cultivation of the entire industrial chain of new energy vehicles over the years, each link has gradually matured, rich and diversified new energy vehicle products continue to meet market demand, and the use environment is gradually optimized and improved.
Screw Junhui ** count: China's production of automotive fasteners of the scale of enterprises there are more than 130, the types of enterprises can be roughly divided into two types: one is a large and considerable scale of foreign-funded, joint venture and domestic fastener enterprises, set up a special department responsible for the production and manufacturing of automotive fasteners;The second is a professional automotive fastener enterprise focusing on automotive non-standard fastener products.
Compared with foreign companies, there is still a certain gap in production scale and quality, and the high-end fasteners for new energy vehicles are insufficient.
In the future, with the rapid development of the market, the market demand for high-end fasteners will continue to increase, and the development of high-end products will become the mainstream trend in the future.
02. Interpretation of fastener technology for new energy vehicles
1. Application of lightweight materials.
Lightweight materials such as magnesium-aluminum alloy are increasingly used in the design and manufacture of new energy vehicles, and the presence of serious potential difference between steel and magnesium-aluminum alloy will lead to serious electrolytic corrosion, and the large difference in thermal expansion coefficient between steel and magnesium-aluminum alloy will also lead to serious preload changes, resulting in obvious relaxation of joints, and the use of aluminum alloy fasteners with high tensile strength can overcome these problems.
Considering the factor of automobile lightweight, a large number of high-strength steel plates are used in automobiles, and aluminum alloy plates are also used in some designs to further reduce the weight of the whole vehicle.
Metal sheet connection occupies a large proportion in automobile production and assembly, such as the welding of automobile body-in-white, the connection of body parts and the installation of body interior parts, etc., the use of fasteners to connect metal sheet is the main connection mode in automobile production in addition to welding, the application of aluminum alloy plate is mainly considering its light weight, in the non-important bearing parts of the car instead of steel plate, the welding characteristics of aluminum alloy are very poor, so fasteners are mostly used.
For example, the connection between the door hinge and the metal sheet of the body is generally made of double screws with welded nuts to ensure that the door effectively protects the occupants when the vehicle collides or rolls, and the connecting parts are not easy to deform in the accident, and the occupants can escape smoothly.
When choosing a joining process, it is necessary to consider avoiding potential corrosion caused by the superimposed connection of different types of metal sheets.
1) Ordinary threaded connection.
If the metal sheet is connected with a large thickness without a nut or can only be made with a blind hole, it can be screwed in and tightened directly using bolts or screws.
The connection with the ordinary nut can also be welded bolts, or welded studs, the bolts or studs are welded on the metal sheet first, and then the connected parts are installed, and finally fixed with ordinary nuts.
2) When using ordinary threaded connection, it is necessary to take into account the thread anti-loosening, and generally two ways can be used: preload control and pre-coated locking glue.
Type: Self-tapping screw connection;
Riveting, riveting fasteners, PBSO (PTSO) self-riveting screw sleeves;PS (PSS) series self-embedded nut;PFH (PFHS) series self-riveting screws;ARB-HEX Series Self-Riveting Nuts;tox join;
buckles, etc. 2. Application of high-strength bolts and heat-resistant bolts.
In recent years, as the new energy vehicle industry has entered the "fast lane", the lightweight of the body has become the top priority of new energy vehicle design.
Ultra-high-strength fasteners can not only reduce their own weight, but more importantly, they can provide greater potential space and safety guarantee for the lightweight design of other key components.
At present, domestic new energy vehicles are usually produced with 10B33, SCR440 (40CR), SCM435 (35CRMO) and SCM440 (42CRMO) steelGrade 9 high-strength bolts, ultra-high-strength bolts, its highest strength level is 1400MPa grade (14.).Level 9).
Under the trend of lightweight automobiles, the powertrain system, on the one hand, is facing increasing requirements for power density, and on the other hand, it is facing increasingly stringent emission requirements.
High power density inevitably leads to higher pressures, higher temperatures, and higher loads, while stringent emission standards require reduced weight and reduced internal friction.
Since new energy vehicles have almost strict weight requirements, weight reduction is very important for battery range.
Therefore, the use of ultra-high strength bolts can not only reduce the weight of the bolt itself, but also can correspondingly use smaller bolt holes, so that the weight of the connected parts will be greatly reduced.
Ultra-high strength bolts, mainly used in new energy vehicle engines, have also begun to be used in gearboxes and axles, in key areas of the engine, aConnecting rod;b.Cylinder head connection;c.Main bearing connection;d.flywheels and other parts.
Ultra-high strength bolts can be used in the chassis of new energy vehicles, such as the application of steering knuckle bearing connecting bolts, the number of bolts can be reduced, from 4 to 3, and the specification can be reduced from M12 to M10.
In the battery pack and motor, especially in the battery pack, the bolt connection of the module can be reduced from M8 to M6, and the body connection of the battery pack M10 can be reduced to M8.
In the connection design of bolt studs for new energy vehicles, designers should not only fully consider the size, material, tolerance grade, mechanical properties of the bolt, etc., but also fully consider the application environment of the bolt, such as temperature field (high and low temperature), vibration, alternating between cold and heat, corrosiveness and other environmental factors.
Non-quenched and tempered steel has excellent performance, high efficiency and energy saving, low cost, is conducive to environmental protection and energy saving, and the non-quenched and tempered steel used in the manufacture of fasteners is basically cold work strengthened, and there are three categories of ferrite + pearlite, ferrite + bainite and ferrite + martensitic duplex structure according to the structure.
There are 3 grades of MFT8, MFT9 and MFT10 in the national standard. In recent years, the non-quenched and tempered steel for fasteners of V-NB and V-NB-B-TI alloy systems has been developed and is being popularized and tested in related fields.
SCN430 and SCN435 energy-saving non-quenched and tempered cold heading steels, which do not require heat treatment, have been used in 88 levels of strength on products.
8Grade 8 M6 840, M6 930 long studs, using non-quenched and tempered steel MLF20MNvnb quenched and tempered free, the length of the studs made of wire rod by drawing, cold heading and wire rolling is 830 920 mm, and the performance of the studs reaches 8Class 8 is required, and the fatigue limit of 5 million cycles -1 is 86 101 (average 8640) MPA, to meet the requirements of the main engine (80 MPa), the product finally passed the OEM certification.
It can meet the straightness less than 0The requirement of 5mm m solves the problem of heat treatment deformation of slender studs and has important promotion value.
However, in practice, it is found that at present, there are still mold wear problems in the application of non-quenched and tempered steel in high-strength fasteners.
Due to the particularity of the engine exhaust system and the sealing problem between the connectors, the engine exhaust system has always been a design difficulty in the research and development process of various automobile manufacturers.
For the localization of automotive heat-resistant steel fasteners, the Society of Automotive Engineers of China issued two group standards, T CSAE99-2019 "Technical Conditions for Heat-Resistant Steel for Automotive Fasteners" and T CSAE136-2020 "Technical Conditions for Automotive High-temperature Connection Fasteners", and the National Fastener Standardization Technical Committee issued GB-T309824-2020 "Mechanical properties of fasteners Bolts, screws, studs and nuts of stainless steel and nickel alloys for high temperatures" and GB T309825-2020 "Fastener Mechanical Properties - Selection Guide for Stainless Steel and Nickel Alloy Fasteners" two national standards.
The main contents of the group standard and the national standard include the relevant technical requirements for heat-resistant materials for fasteners, the technical requirements for wire rods and wires, the technical conditions for the production and manufacturing of high-temperature fasteners and the technical conditions for surface treatment, as well as the technical conditions for system assembly verification including mechanical properties and torque tests, as well as the identification marks, packaging and delivery requirements, etc., which are suitable for engine fasteners, including hexagon bolts, stud studs and nuts.
At present, the commonly used material grades of domestic heat-resistant steel or nickel alloy fasteners are: ML06CR15NI25TI2MOALVB (GH2132), ML04CR11NB, ML41CRMOV, ML21CRMOV, 14CR17NI2 (1CR17NI2), NICR20TIAL (GH4080A), INCONEL718 (GH4169), etc.
Heat-resistant fasteners, although there are a large number of heat-resistant materials containing nickel and chromium, must be treated correctly to better play the function of heat-resistant steel.
For this reason, the heat treatment process is an important guarantee to improve the quality and reliability of heat-resistant steel fasteners.
High-strength fasteners can provide higher clamping force, reduce the size of fasteners, reduce their own weight, so as to meet the needs of lightweight, at the same time, high-strength fasteners are also conducive to the compactness of other structures of new energy vehicles, thereby improving heat dissipation and internal friction
Heat-resistant fasteners are used to solve the problem of connection failure in high temperature environment, and the rise of engine exhaust environment temperature will lead to changes in the mechanical properties of the product, such as creep due to the reduction of tensile strength and hardness or changes in metallographic structure leading to connection failure.
03. Screw Jun's experience and summary
Automotive fasteners are widely used, with changeable conditions and various failure modes.
Hydrogen embrittlement and fatigue of fasteners for new energy vehicles are currently the most common and costly forms of failure.
Fasteners can be at risk of failure throughout the life cycle of a car.
With the update and iteration of technology and the management method of new energy vehicle materials, higher requirements are also put forward.
The development of fasteners for new energy vehicles in the future lies in the continuous integration and progress of technologies such as artificial intelligence, machine Xi, big data and the Internet of Things.
The use of these technologies will provide higher accuracy in the application of fastener materials for new energy vehicles, control the quality and improve the prevention of failure measures from the aspects of fastener design, forming, heat treatment, surface treatment, assembly, installation, etc., and reduce the risk and failure rate, which is of great significance for improving the manufacturing and application level of fasteners in China and even the reliability of automobiles.
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