Automotive fasteners include many varieties that are used in different parts and have great differences in importance. Evaluating their importance and giving them differentiated control management is of great significance to improving the safety of the vehicle. This article puts forward the principles of evaluation , methods and concepts of control and management.
Fasteners for automobiles include various standard and non-standard fastening elements of the whole vehicle, which are fastened and connected by various loose parts. Bolts, screws, etc. are fastened and connected by threads. Calculated by the number of parts, the proportion of fasteners in the total number of parts of the whole vehicle is much higher than that of any other parts, reaching 40% to 55%; the assembly process of the whole vehicle and the assembly is mainly to use fasteners to connect various parts. The process of some fastener failures resulting in car crashes are also heard. Therefore, fasteners should be important to the manufacture and use of automobiles, but in fact, automobile fasteners have not received widespread and sufficient attention in China, which is a problem worthy of discussion. Here, the author tries to make a preliminary discussion on this, just for reference only.
1 The question is raised
1.1 Parts that have not received enough attention
Automobile fasteners are one of the auto parts that have not received enough attention, that is, in the stage of automobile design and manufacture, but also in the stage of use and maintenance. Of course, this is not the case for all manufacturers and users, but attention or lack of attention can be regarded as a relatively common tendency. Here are some performances in this regard.
——There are as many as thousands of fasteners used in a car. Of course, most of them are "unrelated to the general", but there are not too many people who are related to the survival of the car, and those that should be regarded as " It is understood that the fasteners of "key parts" are generally not clearly distinguished in the design and related management documents, and it is difficult to carry out differentiated control and management.
——Reliable fastening is one of the basic conditions for ensuring the function and safety of the whole vehicle, and the systematic research and development of fasteners, fastening mechanisms, fastening methods and equipment with the goal of "fastening reliability" its important foundation. However, in China, it is rare for OEMs, specialized factories, and related institutions to carry out such research systematically. The OEMs with considerable scale often do not have specialized personnel in fastening technology. Existing research is mostly limited to sporadic practical topics for a specific problem.
Fasteners in many key parts are still widely tightened by the "torque method" with insufficient reliability, and some introduced tightening equipment based on advanced tightening theory is difficult to apply well because of incomprehension. All reflect the lack of attention to the reference, research, promotion and application of "fastening reliability".
Although "special fasteners" are listed among the 25 key parts and components recently supported by the state, most of these key components have been listed in the scope of the "Automotive Product Certification" program, while "special fasteners" are not. Not listed, which means that "special fasteners" containing "critical parts" are still outside the necessary national supervision and control, and have not been noticed. ——In the auto parts market of more than 70 billion yuan, the "special fasteners" mainly involving safety-related key parts may be less than 2%,
Third, its absolute value is also very attractive. Enterprises of all sizes and levels are rushing to enter, and even good and bad are mixed. "Authentic" and "famous brand" accessories are surrounded and squeezed by the flood of inferior and cheap accessories, while fake and inferior accessories One of the important conditions for breeding and flooding is the social neglect of the importance of key fasteners.
1.2 The necessity of evaluating the importance of automotive fasteners
An important difference between automotive fasteners and other auto parts is that it contains hundreds of thousands of varieties with different functions, and is used in almost all parts of the whole vehicle of different importance. That is, "automotive fasteners" are the sum of many varieties and specifications of automotive fasteners with extremely different degrees of importance. Therefore, it is obviously necessary to analyze and evaluate the importance of automobile fasteners (in a broad sense, other automobile parts should also be the same), and provide the necessary basis for differentiated management.
In the mid-1980s, a veteran leader of China's auto industry told the person in charge of a backbone enterprise of auto fasteners, "You say auto fasteners are important, but some people say that the mop (called "mop" in the south) is a Aren't the screws on the car and the screws on the car both screws? If you don't tell the difference, it will be difficult for others to recognize your importance. This case shows that the idea of "clarifying" the importance is long in the leadership of the industry.
In reality, from time to time, there will be information about automobile accidents leading to disasters, including a number of accidents directly caused by fasteners. Unfortunately, there is no comprehensive and systematic statistics, analysis, and classification. Here are just some of the examples collected by the author: - In the summer of 1997, during the great flood in Hubei, a BJ212 vehicle of the Jiayu County Procuratorate was installed with inferior steering arm fixing bolts during maintenance. It crashed into a motorcycle running on the side of the road, 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 self-employed transporter in Wuhan used connecting rod bolts of unknown brand for maintenance. The engine was destroyed and scrapped due to the broken connecting rod bolts after only running for a few hundred kilometers.
——In the summer of 1984, a long-distance bus from Jiangxi to Hubei caught fire due to leakage of fuel pipe joints. Because it was located in the countryside, there was no way to call for help, so the bus burned down within half an hour. Fortunately, the passengers were evacuated in time and no casualties were caused. .
——In Shenyang and Chongqing, some people have witnessed the accident of the wheel of the moving car flying out, the reason is that all the wheel bolts suddenly broke.
11. In 1977, the American General Motors (GM) Motor Company passed the strict test and appraisal due to the improper strength and material selection of the rear suspension adjusting arm bolts of a certain model produced. In order to maintain the company's reputation, the company has to recall the 6.4 million vehicles equipped with this kind of bolts and replace them with new bolts in accordance with the relevant automobile recall regulations of the US government, which is estimated to cost about 5,000— $70 million, taken by law and in the long-term interests of the company, can only do so. GM's final investigation found that the reason for the bolt fracture was the delayed fracture of the low-carbon boron steel high-strength (grade 12.9) bolts caused by environmental corrosion.
——In 1988, the statistics released by the US Department of Defense when investigating the incident of imported bolts filling high with low, said that in various accidents of US military equipment (including vehicles), 25% were caused by fasteners.
These sporadic cases are enough to prove that some "automotive fasteners are indeed critical" perception. At the same time, it also proves that ignoring the small value of the fasteners may lead to the loss of thousands, hundreds or even tens of thousands of times its value.
Therefore, it is a matter of course to study and evaluate the importance of automobile fasteners in order to provide differentiated control and management in a targeted manner.
2 Evaluation of the importance of automotive fasteners
To evaluate the importance of automotive fasteners or all automotive parts, it is obvious that a standard or criterion needs to be established first. The auto industry seems to have a kind of inertial thinking, the more complex the technology and the more difficult it is to manufacture, the more important it is. For example, in the small industry of automotive fasteners, the term "high-strength fasteners" has been popular for many years and has been incorporated into national policy documents. typical example. It is true that 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 by "maker's position". Since the only consumers of automobiles are people and the general public, it is the most reasonable and ultimate principle to evaluate based on the "user standpoint". The question is how to concretize this principle.
2.1 A guideline for reference
The automobile industry has recently promulgated a standard for inspecting and evaluating the quality of complete vehicle products - "Quality Inspection and Evaluation Method of Automobile Complete Vehicle Products" (QC/T900-1997). Through the analysis of this standard, the author believes that this standard can be used as an evaluation method. The main reference criterion for the importance of various parts including automotive fasteners.
2.1.1 Fault classification and importance of parts
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. and quantity as the basis for inspection and evaluation. "Failure Mode and Classification of Automobiles" (QC/T4-92) classifies the faults and gives such a principle: "In principle, the fault mode of the parts should be used to describe the failure of the automobile." And QC/T900-1997 also gives the characteristics and classification of thousands of possible failures of various parts of the vehicle (see Appendix G of the standard). This provides a detailed basis for evaluating the importance of components in the use of automobiles.
According to QC/T4-92 and QC/T900-1997, the faults are divided into four categories (although the definitions of the four types of faults in the two standards are slightly different, they should be regarded as the same in essence). The four categories are fatal, serious, normal, and minor.
It can be seen that the parts that cause fatal failures of the whole vehicle are crucial or critical parts. A component that causes a serious failure is an important component...regardless of the complexity and value of the component itself. This is a criterion evaluated from the user's point of view, which we may call the "user position" criterion. In the current market economy
generation, this should be the highest criterion.
Obviously, evaluating the importance of components in terms of their severity (category) of failures in the use of the entire vehicle is exactly what we are looking for.
2.1.2 Statistics of vehicle failures caused by fasteners
Appendix G of QC/T900-1997 lists nearly 5,000 types of faults, their locations, fault manifestations, and the names of the faulty parts, etc., which is enough to let us know what parts, where and in what form. what kind of failure. There are reasons to believe that Appendix G is a summary of long-term and large-scale vehicle inspection and evaluation practices. Most of the possible failures of the vehicle have been included, and it should be fully used as a tool for evaluating the importance of fasteners and other components. main reference.
Of course, we have noticed that this standard is applicable to "finished cars that have been finalized and put into production and have been accepted by the enterprise", that is to say, it is used for the inspection and evaluation of new cars, and the specified test mileage for inspecting performance is no more than 5,000 kilometers or 15,000 kilometers. About a few percent of the vehicle's full life mileage. Obviously, in the long-term use of the car in the future, failures beyond the scope of Appendix G may also occur, or although the scope is not exceeded, the failure category, that is, the severity, changes, which is a reasonable guess. Therefore, it is not enough to only rely on the QC/T900-1997 standard, and it is necessary to consider new factors in long-term use.
The following is a breakdown of all failures listed in Appendix G and those caused by fasteners.
The groupings used in Appendix G, namely large assemblies, such as 10-engine, 17-transmission...etc. Among all 38 groups of the whole vehicle, 22 groups may have fatal failures, of which 10 groups have fatal failures caused by fasteners, accounting for 45.5%, and the proportion of serious failures reaches 67.7%. There were 4997 failures of various kinds, including 144 fatal failures, 22.9% (33 failures) caused by fasteners, and 12.7% (126 failures) in serious failures, which caused fatal and serious failures, especially When the fatal failure is used as the basis for judging the importance of parts to the whole vehicle, the importance of fasteners is very obvious.
A statistical table of the total number of failures and failures caused by fasteners in each group
Fatal Serious Normal Minor Total Number of groups (groups) containing this type of failure 22 31 38 38 38 Statistics by group The number of groups (groups) with fastener failures 10 21 36 37
Account for the number of such failure groups (%) 45.267.795 97
Number of failures of various types (items) 144 995 2783 1076 4997 Statistics by item Among them, the number of failure groups with fasteners (items) 33 126 734 463 1356 accounted for the number of failure groups of this type (%) 22.912.726.4 43 23.1
2.2 Fasteners that may add or aggravate failures in the long-term use of the vehicle
Nearly 5000 faults listed in Appendix G of QC/T900-1997 are the possible faults of qualified new cars under the limited mileage test.
The following factors may cause new failures (outside the scope of Appendix G) of the vehicle in the long-term operation in the future, or cause the originally minor failure to evolve into a serious or even fatal failure. Therefore, when it is required to evaluate the importance of fasteners, it is not limited to the range given in Annex G.
2.2.1 Delayed fracture
It mainly occurs on externally threaded fasteners such as bolts and studs. This is a sudden change that occurs after several months or years with the increase of use time under the condition that the external force does not exceed the static load or dynamic load allowed by the design. Sexual rupture. According to the existing research, there are many reasons for delayed fracture, such as the environment in which the vehicle is used, the materials and manufacturing processes used for the parts, and the sensitivity of the shape and strength of the parts to the delayed fracture.
The aforementioned GM adjusting arm bolt problem is a typical example of delayed failure. ’
Although it is now possible to prevent from design and manufacture, such as using materials that are less sensitive to delayed damage, avoiding the use of sensitive strength areas, reducing or avoiding the use of processes that may allow hydrogen to penetrate the part (eg electroplating, excessive pickling) etc.) or the hydrogen is driven off by post-processing, etc. But given the complexity and variety of causes, it seems difficult to completely eliminate them.
2.2.2 Fatigue fracture
Due to the peculiar notch-sensitive structure of threaded parts, fatigue fracture is the most common form of fracture of threaded fasteners under dynamic load conditions. But the actual situation is not completely the case. The reason is that the fatigue life of parts often has a certain limit, and the factors affecting the degree of dispersion are complex. If the fatigue life is lower than the life of the whole vehicle, it will obviously break at some time during the use of the whole vehicle. Someone in China once suggested that some important bolts should be forced to be replaced when driving for tens of thousands of kilometers, which shows that this problem does exist. The problem is that it is quite difficult to determine the "usable life" of various important bolts used in various parts (this belongs to the scope of "reliability design", but it has not been carried out in China at least in important automotive fasteners. In practice, the deadline is set The replacement of important fasteners is also very rare. Therefore, fatigue fracture will also be an unexpected factor in the sudden failure that may occur in the use of the vehicle.
2.2.3 Inferior fasteners
The proliferation of inferior fasteners used for repair parts will inevitably lead to failures or even fatal failures in parts that would have no problem if they met the design requirements. This is yet another factor that hides unexpected failures.
2.2.4 Irregular tightening
The reliability of threaded fastening depends on the connection design, fasteners and fastening aspects, and fasteners will often be replaced and disassembled during maintenance. There are maintenance points all over the country and the water is very different, and there must be irregular tightening operations, and inferior tightening is the same as inferior fasteners.
The same is another factor for unexpected failures.
2.3 Classification and confirmation of the importance of automotive fasteners
2.3.1 Establish importance classification standards
In order to evaluate the importance of fasteners, a way of expressing the difference in importance must first be given. As mentioned above, in actual production activities, there have been expressions such as "high-strength fasteners", "security fasteners" and "ordinary fasteners", but no formal and clear definitions have been given yet. Even the interpretation of these statements can be described as "different opinions", and there are different opinions. Some refer to fasteners of grade 8.8 and above as "high-strength fasteners", while others only regard grades 10.9 and above as "high-strength", and some regard some as important. Fasteners used in parts as "critical fasteners".
The author here tries to give a suggestion for classification. The basic criterion for the classification is the degree of influence of the fastener on the safety of the vehicle (the severity of the failure), regardless of its strength or structural complexity.
——Security fasteners, referred to as "security fasteners" or "security parts": refers to fasteners that can cause fatal failures of vehicles due to the failure of the fasteners.
——Important fasteners, referred to as "important parts": refers to the fasteners that can cause serious failure of the vehicle due to the failure of the fasteners.
——General fasteners, referred to as "general parts": fasteners that may only cause general or minor failures of the vehicle due to the failure of the fasteners.
The four types of "failures" referred to above are based on the definitions of failures in "Quality Inspection and Evaluation Method for Vehicles" (QC/T900-1997) and "Failure Modes and Classification of Vehicles" (QC/T34-92).
Fastener failure refers to the phenomenon of complete loss of specified function in service. The main forms of fastener failure are: fracture or rupture, loosening or loosening, falling off, etc.
The above classification method seems to be applicable to other auto parts as well.
2.3.2 Evaluation and classification of automotive fasteners
Once the grading standard is established, various fasteners can be evaluated and graded. In fact, just filter out "security items" and "important items", and the rest are "general items". In order to avoid omissions, the evaluation and screening should be based on the fasteners actually used in all automobiles.
The specific evaluation and classification may also need to consider the following issues:
First, since the proposed evaluation standard is based on the severity of the failure caused by fasteners, it will take "a fastener used in a certain part" as the specific object, and the special purpose Fasteners (or special parts), its use parts are clear at a glance, such as connecting rod bolts, pistons... only the only use parts. However, due to the high degree of standardization of fasteners, there may be cases where standard fasteners are used in certain important parts (for example, standard bolts are used for the main bearing cap bolts of an imported car engine), or there may be some special-purpose bolts. Fasteners are used in two or more places of varying 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 differentiate.
Second, what kind of failure may occur in which part, when the main basis is Appendix G of QC/T900-1997, for fasteners, new failure parts and modes that may occur in long-term use should also be considered as much as possible, such as The previously listed delay corruption...etc.
Thirdly, who should conduct the evaluation in what scope, since the evaluation of the importance of automobile fasteners (or auto parts) is essentially for the needs of public safety, and no matter what kind of car, because the structure is generally similar, the evaluation of parts and components is not necessary. Common parts will prevail. Therefore, the ideal approach is to be carried out by industry cooperation and unity. Of course, if the conditions for joint industry cooperation are not yet mature, the main engine companies who feel necessary will take the lead for their own models (maybe some companies have already done or are doing similar work), which can also provide experience for the industry to carry out this work in the future.
3 About implementation
The purpose of evaluating and grading the importance of automobile fasteners is to clearly distinguish their importance, so as to highlight the key points for management and control, and ultimately improve the safety of automobiles. Some ideas about implementation are put forward here. The management and control part is beyond the scope of this article, and it is only an overview and is for reference only.
3.1 Formulate standards or specifications for the classification of the importance of automotive fasteners (or auto parts)
This is the first step. If there is broad consensus on the need for such a division, there should not be too much difficulty in making such a division. The scope can only refer to "automotive fasteners", it would of course make more sense to cover all auto parts. The form is better in the form of industry standards, and it seems to be "mandatory", and other forms are also optional methods of compromise, such as regulations, norms, etc.
3.2 Evaluate the degree of importance and compile the corresponding catalogue
After the classification standard is formulated or carried out at the same time, the catalog only needs to include "security items" and "important items", or even only "security items" can be listed first. As an industry catalog, it should be the same as the grading standard. It is widely published in the society in order to play a guiding, warning and restraining role in design, manufacture, sale, use and maintenance.
3.3 Establish and implement necessary management and control
Management and control can only play a role in the whole process of design, manufacture of automobiles and parts, and obviously this can only rely on the centralized management department and even the quality of the automobile manufacturing industry, transportation industry, maintenance industry, parts sales industry, etc. Supervision, business administration and other departments are jointly coordinated and carried out in multiple directions. Take "security parts" as the key point and first manage them. If the automobile industry will include them in the scope of product certification and production licenses, gradually realize licensed production, and gradually ban the production of unlicensed and unqualified "security parts" within a time limit; The industry and quality supervision departments implement quality supervision and inspection; the industry and commerce department controls the circulation of unlicensed and unqualified "security parts"; the relevant management departments control and restrain the use of unlicensed and unqualified "security parts" in the parts sales and maintenance industries... Wait. Obviously, the point is to control the source of the produced product.
In short, to ensure the safety of important automotive fasteners or other parts of the car is the same as cracking down on the proliferation of all kinds of counterfeit and shoddy products. It can only focus on the key points, comprehensively manage, and screen out and mark the really key parts and components. problem to be solved.
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