1. Definition of inspection
An inspection is an activity in which one or more characteristics of a product or service are measured, inspected, tested, measured, and compared to specified requirements to determine compliance. American quality expert Zhu Lan made a more concise definition of the term "quality inspection": the so-called inspection is such a business activity, whether the product is suitable for the requirements in the next process, or in the factory inspection, decide whether to Provided by consumers.

2. Understanding of inspection
In the early days of industrial production, production and inspection were combined into one, and producers were also inspectors. Later, due to the development of production and the refinement of the division of labor, the inspection was separated from the production and processing, and became an independent work, but the inspection is still a supplement to the manufacturing. Production and inspection are an organic whole, and inspection is an indispensable part of production. Especially in the production line and automatic line production of modern enterprises, the inspection itself is a component process in the process chain. Without inspection, the production process cannot be carried out.
From the perspective of quality management development process, the earliest stage is the quality inspection stage. Quality inspection was once the main means to ensure product quality. Statistical quality management and total quality management were developed on the basis of quality inspection. It can be said that quality inspection is the "root" of total quality management, and "root" can only be leafy. If this "root" is not solid, the foundation of total quality management will not be consolidated. When China implements further quality management and implements the ISO9000 series of international standards, especially when carrying out enterprise institutional reforms, it must not weaken the quality inspection work and cancel the quality inspection institutions. On the contrary, this work must be further strengthened and improved, and the role of inspection work should be played more effectively.
Modern industrial production is an extremely complicated process. Due to the influence of subjective and objective factors, especially the objective random fluctuations, it is difficult to absolutely prevent the production of non-conforming products. Therefore, there is a necessity for quality inspection. It is difficult to imagine that there is a so-called ideal production system, which does not produce non-conforming products at all, and the quality inspection and its corresponding institutions can be completely revoked. In fact, this ideal production system does not exist.

In order to correctly understand the quality inspection of enterprises, it is also necessary to clarify three concepts that are easily confused:
2.1 It is considered that the quality of the product is determined by design and manufacturing, not by inspection, so that the inspection work is not taken seriously or even relaxed. This concept is obviously not comprehensive. It is true that product quality is very close to design and manufacture, but the final formation of quality is by no means limited to the two aspects of design and manufacturing. As the famous American quality expert JM Julan said, it is in line with the rising law of “quality spiral”. It is determined by all the departments of the enterprise, including the quality function of the quality inspection department, and the inspection itself is also in the scope of manufacturing;
2.2 Considering total quality management, emphasizing the shift from turning to prevention, requiring the elimination of non-conforming products before they occur, and testing is only an after-the-fact check, so some companies consider testing to be dispensable, or just a Auxiliary means. This kind of view is also wrong. It is easy to make people's thoughts confusing. In fact, this is how to understand the relationship between "prevention" and "checking". Prevention is mainly about the guiding ideology of quality management, and it is also relative to the simple after-the-fact check. Because it is only after the matter, only the non-conforming products can be found and eliminated. Even if the non-conforming products are found, their losses have already been caused. Therefore, the idea of prevention is completely correct. In fact, many companies at home and abroad regard "prevention first, one success" as an important principle of quality management. Prevention is the mainstay and inspection is not contradictory and contradictory. They are complementary and mutually integrated. Their goals and objects are also different. "Prevention" is for products that are being produced or not yet produced. The check is usually aimed at the products that have already been produced. The former should strive to prevent the products from being 100% qualified and avoid or reduce losses. The latter should pass the inspection and strictly control. Non-conforming products flow to the next process or the hands of users, so prevention and control are indispensable in production, but should be based on prevention.

3. The basic functions of quality inspection
To sum it up, the test includes the following four specific tasks:
 · Metrics: Includes measurements and tests, either with general gages or with mechanical and electronic measuring instruments.
 · Comparison: Compare the measurement results with the quality standards to determine if the quality meets the requirements.
 · Judgment: According to the comparison result, determine whether the product to be inspected is qualified, or whether a batch of products meets the specified quality standards.
 · Handling: Whether a single product can be transferred to the next process or whether the product is allowed to leave the factory; whether the bulk product is decided to accept or reject, or re-check and filter

3.1 The functions of the customs:
Checking is the most basic function of quality inspection, and it can also be called quality assurance function. This kind of function exists when the quality inspection appears. No matter the past and the present, even if the production automation is highly developed, the means and technology of inspection may develop and change, and the quality inspection is still indispensable. of. The production of an enterprise is a complicated process. The factors such as human, machine, material, law, and ring (4MIE) may change the state of production. Each process cannot be in an absolutely stable state, and the fluctuation of quality characteristics is objective. It is actually impossible to guarantee that 100% of the qualified products are produced in each process. With the improvement of production technology and management work, the workload of inspection can be reduced, but inspections still exist. Only through inspection, strict control is carried out, so that unqualified raw materials are not put into production, unqualified semi-finished products are not in order, unqualified parts are not assembled, and unqualified finished products are not pretending to be qualified products, so that the quality of products can be truly guaranteed. .

3.2 Prevention functions:
The important point that modern quality inspection is different from traditional inspection is that modern quality inspection is not simply a function of prevention, but also plays a preventive role.
Broadly speaking, the entry inspection of raw materials and purchased parts, the inspection of the pre-process, can play a preventive role in the subsequent production process and the production of the next process. In particular, the preventive effect of testing is also reflected in the following aspects:
 · Preventive action by measuring process capability and using control charts. As we all know, whether it is the measurement of process capability or the use of control charts, it is necessary to obtain a batch or a set of data through product inspection, and then perform statistical processing. The purpose of this test is not to determine whether a batch or group of products is qualified, but to calculate the size of the process capability and reflect the state of the production process. If it is found that the process capability is insufficient, or the control chart indicates that the production process has an abnormal state, it is necessary to take technical organizational measures in time to improve the process capability or remove the abnormal state of the production process to prevent the occurrence of non-conforming products. The preventive effect is very effective (remarks: the calculation and use of process capability, currently applied weakly in electronic assembly enterprises, mainly used in the mechanical processing manufacturing industry, so this article does not elaborate)
 · Preventive action through the first inspection and inspection at the time of production. When a batch of products or a shift begins to process a batch of products, the first piece of inspection should generally be carried out (the first piece of inspection does not necessarily only check one piece), and when the first piece of inspection is qualified and approved, it can be officially put into production in batches. In addition, when the equipment is repaired or re-adjusted, the first inspection should also be carried out, the purpose of which is to prevent the occurrence of a large number of non-conforming products. After the formal production in batches, in order to find out in time whether the production process has changed, whether there is the possibility of non-conforming products, it is necessary to go to the workplace regularly or irregularly to conduct a random inspection (ie inspection). Take timely measures to correct it to prevent the production of non-conforming products.

3.3 Reporting functions:
The function of the report is also the function of information feedback. This is to enable leaders and relevant quality management departments to keep abreast of the quality status in the production process, and to evaluate and analyze the effectiveness of the quality system. In order to make correct quality decisions and understand the changes in product quality and existing problems, the test results must be reported to the leading decision-making department and relevant management departments in the form of reports, especially calculated indicators, in order to make correct Judge and take effective decision-making measures. The main contents of the report are as follows:
 · The inspection and acceptance of raw materials, purchased parts and outsourcing parts and the qualification rate indicators.
 · The pass rate of the finished product inspection, the repair rate, the scrap rate and the corresponding amount loss.
 · According to the average pass rate, repair rate, scrap rate, corresponding amount loss and arrangement chart of the workshop and sub-group.
 · Analysis of the arrangement of the reasons for product scrapping.
 · Report on the handling of nonconforming products.
 · Investigation, analysis and processing of major quality issues.
 · Suggested report on improving product quality.
 · Other related reports.

3.4 Improved functions:
Quality inspection and participation in quality improvement work is the key to giving full play to quality inspection and quality control and prevention. It is also a concrete manifestation of the inspection department's participation in improving product quality. Quality inspectors are generally employed by engineering and technical personnel or skilled workers with certain production experience and professional skills. They often work at the production site, and they have the clearest understanding of the factors affecting people, machines, things, laws, and rings in production, and the quality information is also the most informed. They are more advanced and deeper than the design and craftsmen to understand the quality, so they can put forward more practical suggestions and measures in the quality improvement, which is the advantage of the quality inspectors. In particular, the implementation of design, process, inspection and operation personnel to jointly improve quality can accelerate the pace of quality improvement and achieve better results.

4. The "three natures" of quality inspection
The construction of "three sexes" refers to the impartiality, scientificity and authority of the inspection work. This is also a basic requirement for inspection work, and it is very important to play the role of inspection work.
4.1 Fairness of inspection work:
The impartiality of the inspection work is the most important requirement for quality inspection. Without impartiality, the inspection loses its meaning, and it is impossible to talk about the functions of the customs. The so-called fairness of the inspection work means that the inspection agencies and personnel must strictly perform their duties when conducting product quality inspections, independently exercise the powers of product quality inspection, and adhere to the principle, do not consult the private affairs, do things impartially, and earnestly Responsible, seek truth from facts. Principle is the basis of impartiality. Adherence to principles is to strictly enforce technical standards, strictly enforce inspection systems, strictly enforce order contracts, and strictly enforce quality responsibility systems. It is necessary to be clear, rewards and punishments must be clear, laws must be followed, and law enforcement must Strict, everything works according to principles. The key to doing things according to principles is to be able to deal with problems objectively and fairly when confronted with contradictions, without any unreasonable interference from any forces or personnel, and not to exalt any ones because of their pleading or personal relationships. For example, when there is a contradiction between production and quality, when there is a contradiction between the interests of the factory and the interests of the users, or when there is a contradiction between the quality and the delivery date, the quality standards should be adhered to and the rules and regulations should be adhered to. Quality disputes often occur. Between enterprises and users in commercial trade, between workshops and workshops, between processes and processes, between inspection workers and production workers, there will be different evaluations and opinions on the quality of the same product. These disputes involve the interests of both parties. When they are small, they are arguing, and when they are big, they resort to the law. Finally, relying on third parties to make arbitrations and judgments, whether such arbitrations and judgments are correct depends on providing sufficient and effective test results and test data through inspection. To this end, the inspectors are required to have a high degree of ideological quality, and there is a high degree of originality. Generally, the full inspection is applicable to the following occasions:
 · Products or parts and components with higher precision requirements;
 · Size parts that have a greater impact on the next or subsequent processes;
 · Manually operated processes with significant weight and insufficient quality;
 · Some products (including zeros, parts) and processes that are not bulky and have no reliable quality guarantee;
 · When adopting a sampling plan, 100% re-inspection and screening are required for unqualified inspection batches.

4.2 Sampling inspection:
Sampling inspection refers to a pre-planned sampling plan based on the principles of mathematical statistics. From the batch of products submitted for inspection, some samples are randomly selected for inspection. According to the test results of the samples, according to the prescribed judgment criteria, it is determined whether the whole batch of products is qualified, and whether the batch of products is received or rejected, or other treatment is taken. the way.

The main advantage of the sampling inspection is that it significantly saves the inspection workload and inspection costs, shortens the inspection cycle, and reduces inspection personnel and equipment. Especially for destructive inspections, only sampling inspections can be used. The main drawback of sampling inspection is that there is a risk of wrong judgment. For example, the qualification is incorrectly judged as unqualified, or the failure is judged as qualified. Although the use of mathematical statistics theory has reduced the risk to a certain extent and improved the reliability, as long as the sampling test method is used, this risk cannot be absolutely avoided.
Sampling inspection is applicable to the following occasions:
 · Production of products or processes with large batch sizes, high degree of automation, and relatively stable product quality;
 · products or processes with destructive testing;
 · Acceptance inspection of outsourced parts and purchased parts in batches;
 · Certain products or processes with high production efficiency and long inspection time;
 · Inspection of products or processes that are too costly;
 · Products that miss a small number of non-conforming products will not cause significant losses, such as some large-volume standard parts such as pins, washers, and screw nuts.

4.3 Divided by quality characteristic values
 · Count check count check:
Including piece inspection and checkpoint inspection, only the number of failures (pieces or points) is recorded, and the specific measurement values after the inspection are not recorded. In particular, some quality characteristics are difficult to express by themselves. For example, whether the shape of the product is beautiful, whether the taste of the food is delicious, etc., they can only be judged by the sense of quality. There is also a type of quality characteristics, such as the size of the part, although it can be expressed by numerical values, but it can also be measured. However, in mass production, in order to improve efficiency, save manpower and cost, often only use "over-the-end" and "but not only". The caliper check is within the allowable range of the upper and lower tolerances, that is, it is only divided into qualified products and non-conforming products, and the actual size is not measured.
 · Measurement test:
The measurement test is to measure and record the value of the quality characteristic, and judge whether it is qualified according to the comparison with the standard. This type of inspection is extensive and widespread in industrial production.
4.4. According to the nature of inspection
 · Physical and chemical testing:
Physical and chemical testing is the use of physical or chemical methods, using some kind of measuring tools or equipment, such as micrometers, dial gauges, inspections, microscopes, etc. The characteristics of physical and chemical testing are usually able to measure specific values, and the artificial error is small. Therefore, when conditions are met, physical and chemical testing should be used as much as possible.
 · Functional testing:
Functional testing relies on the human sensory organs to evaluate and judge the quality of the product. Such as the shape, color, and gas of the product