Automotive fasteners include numerous varieties that are used in different parts and have greatly different levels of importance. Evaluating their importance and implementing differentiated control management is of great significance for improving the safety of the entire vehicle. This article proposes principles, methods, and ideas for control and management of evaluation.

Automotive fasteners include various standard and non-standard fastening elements that are used to fasten and connect various loose parts of the vehicle. Bolts, screws, etc. are the main components that are fastened and connected by threads. In terms of the number of parts, the proportion of fasteners to the total number of parts in the vehicle far exceeds that of any other type of part, reaching 40% to 55%; The final assembly process of the entire vehicle and assembly mainly involves the use of fasteners to connect various components; Cases of vehicle accidents and fatalities caused by the failure of certain fasteners have also been heard from time to time. Therefore, fasteners should be important for the manufacturing and use of automobiles, but in reality, automotive fasteners have not received widespread and sufficient attention in China, which is a problem worth discussing. Here, the author attempts to make a preliminary exploration of this, and their opinions are for reference only.

1. Proposal of the problem

1.1 Parts that have not received sufficient attention

Automotive fasteners are one of the automotive parts that have not received sufficient attention, both in the design and manufacturing stages of automobiles and in the use and maintenance stages. Of course, not all manufacturers and users are like this, but insufficient attention or importance can be considered a common tendency. Here are some manifestations of this.

——A car uses thousands of fasteners, of which "irrelevant" may account for the vast majority, but there are also many that are related to people and the survival of the car. It is understood that fasteners that should be considered "key parts" are generally not clearly distinguished in the design and relevant management documents, making it difficult to carry out differentiated control and management.

——Reliable fastening is one of the basic conditions for ensuring the functionality and safety of the entire vehicle, and conducting systematic research on fasteners, fastening mechanisms, fastening methods, and equipment with the goal of "fastening reliability" is an important foundation. However, in China, it is rare for host manufacturers, professional factories, and relevant universities to systematically conduct such research. Host factories with considerable scale often do not have specialized personnel in fastening technology. Existing research is mostly limited to sporadic practical topics targeting a specific problem.

Many key fasteners are still widely fastened using the unreliable "torque method", and some imported fastening equipment based on advanced fastening theories are difficult to apply due to their inability to penetrate thoroughly. All reflect insufficient attention to the reference, research, promotion and application of "fastening reliability".

Although "special fasteners" are listed among the 25 key components recently supported by the country, the vast majority of these key components have been included in the scope of the "automotive product certification" plan, while "special fasteners" have not been included. This means that "special fasteners" that include "key components" are still outside the necessary national supervision and control and have not been noticed—— In the automotive parts market worth over 70 billion yuan, "specialized fasteners" that mainly involve safety critical components may account for less than 2%

3、 Its absolute value is also very tempting, with enterprises of all sizes and levels rushing in, resulting in mixed quality. "Authentic" and "branded" accessories are surrounded and squeezed by the proliferation of cheap and inferior accessories, while one of the important conditions for the proliferation of fake and inferior accessories is the neglect of the importance of critical fasteners by society.

1.2 The necessity of evaluating the importance of automotive fasteners

An important difference between automotive fasteners and other automotive components is that they contain hundreds or thousands of different functional varieties, which are applied to almost all parts of the vehicle of different importance. The term 'automotive fasteners' refers to the sum of numerous types and specifications of automotive fasteners with varying degrees of importance. Therefore, it is clearly necessary to analyze, evaluate, and provide necessary basis for differentiated management of the importance of automotive fasteners (broadly speaking, similar to other automotive components).

In the mid-1980s, a senior leader in the Chinese automotive industry told the head of a key automotive fastener enterprise, 'You say automotive fasteners are important, but some people say that the screws on the mop (known as' mop' in the south) and the screws on the car are both screws. '? Without clarifying the differences, it will be difficult for others to acknowledge your importance. This incident indicates that the idea of "clarifying" the importance level has long existed among the leadership of the industry.

In reality, information about car accidents leading to disasters is often obtained, including several accidents directly caused by fasteners. Unfortunately, there is no comprehensive and systematic statistics, analysis, and classification available. Here are just some examples collected by the author: In the summer of 1997, during the Hubei Great Flood, a BJ212 vehicle from Jiayu County Procuratorate was repaired with inferior steering arm fixing bolts. The bolts broke during the repair process, causing the vehicle to lose control of its direction and crash into a motorcycle on the roadside, resulting in a major accident that killed and injured several people.

——In the autumn of 1998, a Dongfeng truck equipped with a Yuchai engine owned by a private transport operator in Wuhan was destroyed and scrapped after only a few hundred kilometers of driving due to the use of unknown brand connecting rod bolts during maintenance.

——In the summer of 1984, a long-distance bus traveling from Jiangxi to Hubei caught fire due to a leaking fuel pipe joint. As it was located in the outskirts and unable to seek help, the bus burned down in less than half an hour. Fortunately, passengers were evacuated in time and no casualties were caused.

——People have witnessed accidents in Shenyang and Chongqing where car wheels flew out while driving, due to the sudden breakage of all wheel bolts.

In 1977, General Motors (GM) of the United States received complaints about the sudden breakage of a certain type of rear suspension adjustment arm bolt due to improper strength and material selection of the bolt. Although it passed strict testing and identification, after several years of production, the company had to recall 6.4 million vehicles equipped with this type of bolt and replace them with new bolts in accordance with the relevant car recall regulations of the US government. The estimated cost for this was about 50-70 million US dollars, which was in accordance with the law and for the long-term interests of the company. The final investigation by GM company found that the cause of the bolt fracture was delayed fracture of the high-strength (12.9 grade) bolt made of low-carbon boron steel due to environmental corrosion. The conclusion is that the use of low-carbon boron steel high-strength bolts in this area was an improper design.

——In 1988, the US Department of Defense released statistics investigating incidents of imported bolts being overcharged, stating that fasteners accounted for 25% of all accidents involving US military equipment (including vehicles).

These sporadic examples are sufficient to prove the view that certain automotive fasteners are indeed crucial. At the same time, it also proves that ignoring fasteners with minimal value can lead to losses of thousands, hundreds, or even tens of thousands of times their value.

Therefore, it is natural to study and evaluate the importance of automotive fasteners in order to provide targeted and differentiated control and management.

2. Evaluation of the Importance of Automotive Fasteners

To evaluate the importance of automotive fasteners or all automotive components, it is obviously necessary to first establish a standard or criterion. The automotive industry seems to have an inertia thinking that the more complex the technology and the higher the manufacturing difficulty, the more important it becomes. For example, in the small industry of automotive fasteners, the term "high-strength fasteners" has been popular for many years and has been included in national policy documents. This is a typical example of classification based on high requirements and manufacturing difficulty. Indeed, high-strength fasteners are often important fasteners, but it should also be said that this is not entirely the case. Obviously, this is a criterion for dividing based on the 'maker's position'. Since the only consumers of cars are people, the general public, then evaluating from a "user perspective" should be the most reasonable and ultimate principle. The question is how to concretize this principle.

2.1 A referenceable criterion

The automotive industry has recently issued a standard for inspecting and evaluating the quality of whole vehicle products - the "Quality Inspection and Evaluation Method for Whole Vehicle Products" (QC/T900-1997). Through analysis of this standard, the author believes that it can serve as the main reference criterion for evaluating the importance of various parts, including automotive fasteners.

2.1.1 Classification of faults and importance of components

QC/T900-1997 stipulates that the new vehicle inspection and evaluation includes four items: safety and environmental protection, basic performance, vehicle assembly adjustment and appearance quality, and reliable driving. The latter three items are partially or completely based on the nature and quantity of faults that occur during driving as the basis for inspection and evaluation. The "Failure Modes and Classification of Automobiles" (QC/T4-92) provides a classification of faults and the principle that "in principle, vehicle faults should be described based on the failure modes of parts". And QC/T900-1997 also provided thousands of characteristics and classifications of possible faults in various parts of the vehicle (see Appendix G of this standard). This provides a detailed basis for evaluating the importance of components in automotive use.

According to QC/T4-92 and QC/T900-1997, faults are classified into four categories (although the two standards have slight differences in defining the four categories of faults, they should be considered essentially the same). There are four categories: fatal, severe, moderate, and minor.

It can be seen that the components that cause fatal failures in the entire vehicle are crucial or critical parts. The components that cause serious malfunctions are important components, regardless of their complexity and value. This is a criterion for evaluating from the user's perspective, which we can refer to as the "user stance" criterion. In the current development of market economy

Dai, this should be the highest criterion.

Obviously, evaluating the importance of components based on the severity (category) of the faults caused by the components during vehicle use is exactly the method we are seeking.

2.1.2 Statistics of Vehicle Malfunctions Caused by Fasteners

Appendix G of QC/T900-1997 lists the classification, occurrence location, fault manifestations, and names of the faulty components for nearly 5000 faults, which is sufficient for us to know what components, where they will occur, and in what form they will cause what kind of faults. There is reason to believe that the list in Appendix G is a summary of long-term and extensive vehicle inspection and evaluation practices, and the vast majority of possible vehicle failures have been included. It should be fully regarded as the main reference for evaluating the importance of fasteners and other components.

Of course, we have noticed that this standard applies to "finished cars that have been finalized and put into production, and have been accepted by enterprises", which means that it is used for the inspection and evaluation of new cars. The prescribed test mileage for testing performance is only 5000 kilometers or 15000 kilometers, which is approximately a few percent of the vehicle's total life mileage. Obviously, in the long-term use of automobiles in the future, faults beyond the scope of Appendix G may occur, or although the scope has not exceeded it, the fault category or severity may change. This is a reasonable speculation. Therefore, relying solely on QC/T900-1997 standards is not enough, it is also necessary to consider new factors in long-term use.

The following is a classification and statistical analysis of all faults listed in Appendix G, including those caused by fasteners.

The grouping used in Appendix G is the main assembly, such as 10- engine, 17- transmission, etc. Among all 38 groups of the vehicle, 22 groups may experience fatal faults, of which 10 groups, accounting for 45.5%, have fatal faults caused by fasteners. Among serious faults, this proportion reaches 67.7%. There are 4997 possible faults in the vehicle, including 144 fatal faults, of which 22.9% (33) are caused by fasteners, and 12.7% (126) are caused by serious faults. When using fatal and serious faults, especially fatal faults, as the basis for determining the importance of components to the vehicle, the importance of fasteners is already very obvious.

Statistical table of total number of faults and faults caused by fasteners in each group

Fault category

Statistical object

Fatal, serious, generally minor, total number of groups containing such faults (groups) 22 31 38 38 38, counted by group, including groups with fastener failures (groups) 10 21 36 37

Proportion of this type of fault group (%) 45.267.795 97

The number of various types of faults (items) is 144 995 2783 1076 4997. Statistics by item show that there are fastener failure groups (items) 33 126 734 463 1356, accounting for 22.912.726.4 43 23.1% of the total number of such fault groups

2.2 Fasteners that may experience new or aggravated malfunctions during long-term use of the entire vehicle

The nearly 5000 faults listed in Appendix G of QC/T900-1997 are possible faults that may occur in qualified new vehicles under limited mileage testing

Obstacles, the following factors may cause new (beyond the scope of Appendix G) faults to occur in the long-term operation of the vehicle in the future, or cause the originally minor faults to evolve into serious or even fatal faults. Therefore, when evaluating the importance of fasteners, it is not limited to the scope given in Annex G.

2.2.1 Delayed fracture

It mainly occurs on externally threaded fasteners such as bolts and bolts. This is a sudden fracture that occurs months or years later with the increase of usage time, under external forces not exceeding the static or dynamic loads allowed by the design. According to existing research, there are many reasons that can lead to delayed fracture, such as the vehicle usage environment, the materials and manufacturing processes used in the parts, and the sensitivity of part shape and strength to delayed failure.

The aforementioned issue with the adjustment arm bolts of General Motors is a typical example of delayed failure

Although it is now possible to take preventive measures in design and manufacturing, such as using materials with low sensitivity to delayed damage, avoiding sensitive strength zones, reducing or avoiding processes that may allow hydrogen to infiltrate parts (such as electroplating, excessive acid washing, etc.), or removing hydrogen through post-treatment, etc. However, given the complexity and diversity of the reasons, it seems difficult to completely eliminate them.

2.2.2 Fatigue fracture

Due to the unique notch sensitive structure of threaded components, fatigue fracture is the most common form of fracture for threaded fasteners under dynamic loading conditions. It seems that by designing the dynamic fatigue strength of the parts and leaving enough room, they can be unharmed. But the actual situation is not entirely like this. The reason is that the fatigue life of the parts often has a certain limit, and the factors that affect their dispersion are complex. If their fatigue life is lower than the overall vehicle life, they will obviously break at some point during the use of the vehicle. There have been suggestions in China that certain important bolts should be forcibly replaced after driving tens of thousands of kilometers, indicating that this problem does exist. The problem lies in determining the "useful life" of various important bolts used in different parts, which is a quite difficult issue (this falls within the scope of "reliability design", but at least in the field of important automotive fasteners, it has not yet been carried out domestically. In practice, it is also extremely rare to make provisions for the replacement of important fasteners within a specified period of time. Therefore, fatigue fracture will also be an unexpected factor that may occur in sudden failures during vehicle use.

2.2.3 Poor quality fasteners

The proliferation of inferior fasteners used for repairing parts will inevitably lead to malfunctions, even fatal ones, in parts that would otherwise have no problems if they met the design requirements. This is another hidden factor of unexpected malfunction.

2.2.4 Irregular fastening

The reliability of threaded fastening depends on the connection design, fasteners, and fastening. Fasteners are often replaced or disassembled during maintenance. The maintenance points scattered throughout the country with vastly different water levels are bound to have non-standard fastening operations. Poor quality fastening, like poor quality fasteners, is another factor that can cause unexpected failures.

2.3 Classification and Confirmation of the Importance of Automotive Fasteners

2.3.1 Establishing Importance Grading Standards

In order to evaluate the importance of fasteners, it is necessary to first provide a way to indicate the difference in importance. As mentioned earlier, in actual production activities, there are already terms such as "high-strength fasteners", "security fasteners", and "ordinary fasteners", but no formal and clear definition has been given yet. Even the interpretation of these statements can be described as' subjective ', with different opinions. Some refer to fasteners with a grade of 8.8 or higher as "high-strength fasteners", while others only consider fasteners with a grade of 10.9 or higher as "high-strength", and some consider fasteners used in important parts as "critical fasteners".

The author attempts to provide a classification suggestion based on the degree of impact of the fastener on the overall safety of the vehicle (the severity of the fault caused), regardless of its strength or structural complexity.

——Secure fasteners, abbreviated as "security fasteners" or "security components": refers to fasteners that can cause fatal vehicle malfunctions due to the failure of the fastener.

——Important fasteners, abbreviated as "important parts": refers to fasteners that can cause serious vehicle malfunctions due to the failure of the fastener.

——General fasteners, abbreviated as "general parts": fasteners that may only cause general or minor malfunctions in the vehicle due to their failure.

The four types of "faults" mentioned above are defined based on the "Methods for Quality Inspection and Evaluation of Whole Vehicle Products" (QC/T900-1997) and "Failure Modes and Classification of Automobiles" (QC/T34-92).

Fastener failure refers to the phenomenon where the specified function is completely lost during service. The main forms of fastener failure include fracture or rupture, looseness or looseness, and detachment.

The above classification method seems to be applicable to other automotive components as well.

2.3.2 Evaluation and Grading of Automotive Fasteners

Once the grading standards are established, various fasteners can be evaluated and graded. In fact, only "security items" and "important items" need to be filtered out, and the rest are "general items". To avoid omissions in the factory, evaluation screening should focus on all fasteners actually used in automobiles.

The specific implementation of evaluation grading may also need to consider the following issues:

Firstly, considering that the proposed evaluation criteria are based on the severity of faults that fasteners can cause, the specific object will be "a certain fastener used for a certain part". For specialized fasteners (or parts) used in various parts of the vehicle, their usage locations are already clear, such as connecting rod bolts, pistons, etc., which have only one usage location. However, due to the extremely high degree of standardization of fasteners, it is possible to use standard fasteners for certain important parts (such as the main bearing cover bolts of an imported car engine using standard bolts), or to use specialized fasteners for two or more parts with different degrees of importance at the same time. Standardization and generalization are the development trends of many automotive components, especially fasteners. This raises the question of how to distinguish.

Secondly, when referring to Appendix G of QC/T900-1997 as the main basis for determining which parts may experience which faults, for fasteners, new fault parts and modes that may occur during long-term use should also be considered as much as possible, such as delayed failure as listed earlier.

Thirdly, who will conduct the evaluation within what scope? Given that the importance evaluation of automotive fasteners (or automotive components) is essentially driven by public safety needs, and regardless of the type of vehicle, due to their similar structures, the common parts of component evaluation will dominate. Therefore, the ideal approach is to collaborate and unify the industry. Of course, if the conditions for industry collaboration are not yet mature, the host companies that feel necessary can take the lead in developing their own vehicle models (some companies may have already done or are currently doing similar work), which can also provide experience for the industry to carry out this work in the future.

Regarding Implementation

Propose to evaluate and grade the importance of automotive fasteners, with the aim of clearly distinguishing their importance, in order to highlight key points for management and control, and ultimately improve the safety of automobiles. Here are some ideas related to implementation, but the management and control sections are beyond the scope of this article and are only provided as an overview for reference only.

3.1 Develop standards or specifications for the classification of the importance of automotive fasteners (or automotive components)

This is the first step. If there is a broad consensus on the necessity of division, there should not be too much difficulty in making such a division. The scope can only refer to "automotive fasteners", but it would be more meaningful if it could cover all automotive components. The form is better to follow industry standards, and it seems to be "mandatory". Other forms may also be a compromise option, such as regulations, norms, etc.

3.2 Conduct importance evaluation and prepare corresponding detailed catalog

After or at the same time as the formulation of the classification standards, the catalog only needs to include "security items" and "important items", and even only "security items" can be listed first. As an industry-specific catalog, it should be widely released to the society like the grading standards, in order to provide guidance, warning, and restraint for design, manufacturing, sales, use, and maintenance.

3.3 Establish and implement necessary management and control measures

Management and control must be carried out throughout the entire process of designing and manufacturing automobiles and their components in order to be effective. Obviously, this can only be achieved through the joint coordination and multi-faceted efforts of industry management departments such as automobile manufacturing, transportation, maintenance, and parts sales, as well as quality supervision and business management departments. Prioritize the management of "security components", such as including them in product certification, production licenses, and other areas by the automotive industry, gradually achieving certified production, and gradually phasing out unlicensed and unqualified production of "security components" within a specified period of time; Implement quality supervision and inspection by the automotive industry and quality supervision departments; Control the circulation of unlicensed and unqualified "security items" by the industrial and commercial department; Controlled, restrained, and regulated by relevant management departments, the sales of accessories, and the use of unlicensed and unqualified "security devices" in the maintenance industry. Obviously, the key is to control the source of production products.

In short, ensuring the safety of important fasteners or other components in automobiles, like cracking down on the proliferation of various counterfeit and shoddy products, can only focus on key areas, comprehensively manage, screen out and label the truly critical components, which is the first problem that needs to be solved.

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