Basic Introduction Chinese Name: Qualified Quality Level mbth: Acceptance Quality Limit Abbreviation: AQL Interpretation: Sampling inspection, description, concept, example 1, example 2, AQL sampling inspection, judgment, application, sampling scheme, sampling method, introduction, meaning of quality level, determination of AQL principle, determination of AQL method, distribution of AQL, Clothing quality inspection adopts sampling scheme. The AQL of clothing batch is 2.5, the inspection level is general inspection level, and the inspection strictness is normal inspection. See the table for the sampling scheme: normal inspection one-time sampling scheme (AQL-2.5). AQL is the abbreviation of-acceptance quality limit, which is an international standard. 1)AC = acceptable number = use the first numerical value below the arrow = use the first numerical value above the arrow to conduct general inspection level II inspection. 2) AQL 0.0 10-0. 10 is used for inspection of electronic products and medical devices. AQL 1.0-6.5 is used to inspect clothing, textiles, etc. Refers to a sampling parameter, which is generally used for mass production. The inspector's sample sampling and the qualified parameter table explain this concept. When the number of orders is less than or equal to the number of samples, Re——Reject. For example, if the order number of a batch of clothes is 3000 pieces, randomly select 125 pieces according to AQL2.5 standard, the number of defective products is less than or equal to 7 pieces, and the number of defective products is greater than or equal to 8 pieces. For example, the order number of the second order is 7 pieces, and 3 pieces are randomly selected according to AQL2.5 standard. If there are no defective products, pass, and one defective product fails; . According to AQL4.0 standard, only 5 pieces will be randomly selected. Order quantity, number of pieces, sampling quantity of AQL2.5 AQL4.0 sampling batch, ACREAC RE 2-8 2019-1003 sampling inspection procedure (main table) through AQL2.5/4.0 sampling table. 438+0 0 1 26-50 8 0 1 12 5 1-90 13 12 12 9 150 20 12 23 15 15 / Kloc-0/2 23 15 1AQL (acceptable quality level) is the basis of the adjustable sampling system, and it is the upper limit of the process average value of the continuously submitted inspection lots agreed by both the supplier and the supplier. The process average is the average quality of a series of continuously submitted inspection lots, which is expressed by "batch failure rate" or "defective rate per 100 unit". AQL and sample size (the so-called sample size can be understood as "sample size" or sample size? ) lies in the conversion between one inspection level (three general inspection levels I, II and III, and four special inspection levels S- 1, S-2, S-3 and S-4) and the severity. For example, if the batch number of a product is N=4000, the agreed AQL= 1.5%, and the inspection level is selected as II, then the steps to determine the adjusted primary sampling scheme are as follows: 1) According to table GB2828-8 1, the sample content code is L; 2) Determine the "normal sampling scheme": the number of qualified judgments corresponding to L and AQL= 1.5% is 7, the number of unqualified judgments is 8, and the sample content is n=200. Its meaning is: 200 samples are taken from 4000 products for inspection, and if the number of unqualified products in these 200 is less than or equal to 7, the whole batch of products is qualified; Greater than or equal to 8, the whole batch is unqualified; 3) By the same token, determine the sampling schemes of "tightening", "relaxing" and "ultra-wide"; 4) Four sampling schemes are merged into one place, and dynamic conversion rules (in SAP system, the term is dynamic modification rules) are used to form an "adjusted one-time sampling scheme"; 5) The above examples follow the GB2828 standard and correspond to ISO2859 (counting); There is an ISO version of the sample scheme. 6) in version 4.5b of SAP system, please refer to the dynamic modification of ru AQL sampling inspection judgment in SAP standard system 4.5b. Sampling inspection is to use the extracted samples to inspect and judge the products or processes. Applicable sampling inspection applicable: 1) inspection is destructive to the product; 2) The measured object is process material; 3) I hope to save the cost and time of unit inspection. The sampling scheme specifies the number of unit products (sample size or series sample size) to be inspected in each batch, as well as the specific scheme of relevant batch acceptance standards (including the number of products received, the number of products rejected, and the judgment rules, etc.). ). Sampling method 1, simple random sampling method; Everyone has the same chance, similar to the familiar lottery. Systematic random sampling method; (equidistant or mechanical) 3. Stratified sampling method; (Simple random sampling according to product characteristics, such as: safety, serious and extremely serious sampling in three times) 4. Group sampling method. (Grouping) Introduction When using national standards to formulate statistical sampling inspection scheme, quality level (AQL, PRQ, LQ, RQL, AOQ, AOQL), inspection level (IL) and batch number N are usually important parameters for retrieval sampling scheme. The rules or principles for selecting inspection level (IL) and batch number (N) are generally clear and easy to master. The choice of quality level is the focus of attention of both producers and users, which involves quality control, production management and marketing strategy. It is related to the theory and practice of statistical inspection, and there are many clues that are difficult to grasp. This paper only focuses on the significance that quality level is mainly acceptable quality level AQL, and introduces the principle, method and distribution of AQL in the process of designing continuous batch sampling scheme for your reference. The Significance of Quality Level Firstly, several concepts related to quality level in statistical sampling inspection standards are briefly introduced. They are: acceptable quality level AQL, producer risk quality PRQ, limit quality level LQ, unqualified quality level RQL, average detected (ex-factory) quality AOQ and average detected (ex-factory) quality upper limit AOQL. The definition of 1. 1 acceptable quality level AQL 1. 1 AQL continuous batch sequence is considered to meet the minimum quality level required by sampling inspection. The significance of 1. 1.2 AQL When the batch for inspection is a series of continuous batches, the sampling scheme of GB/T2828 is adopted. The main purpose is to receive the batch with high probability when the batch quality is in AQL, that is, when the batch quality is in the qualified quality level, the risk of controlling the producer is relatively small. On the one hand, it protects producers; On the one hand, tell the producer that as long as the average quality of his products is better than AQL. Then, most batches can be accepted by users, which can urge producers to maintain and improve product quality. On the other hand, by adjusting the strictness of inspection, producers can also be urged to improve product quality. The function of 1 1.3 AQL is mainly used to retrieve the continuous batch sampling scheme. See GB/T2828, ISO2859 and GB/T6378. 1.2 Definition of manufacturer's risk quality PRQ 1.2. 1 PRQ The quality p0 of the * * * batch proposed by the manufacturer according to the contract meets the requirements, but according to the statistical sampling inspection scheme, the batch may still be rejected. This p0 is PRQ. The meaning of 1.2.2 PRQ In general, when the product quality is equal to PRQ. The statistical sampling scheme should be received with a probability higher than (1-α). It is essentially what we often call qualified quality level, which can also be called qualified quality level, also called AQL. The possibility of rejection α is the risk borne by the producer-statistically called the probability of rejecting the truth. The significance of 1.2.2 PRQ PRQ is an important parameter for making statistical sampling scheme. In order to protect producers, PRQ should adopt statistical sampling scheme and two-point statistical sampling scheme. 1.3 Definition of limit quality LQ and applicable risk quality CRQ 1.3. 1 LQ and CRQ1.3.2 Significance of LQ and CRQ If the inspection lots are isolated or few, so that the inspection strictness cannot be adjusted, it is particularly important to strictly control the chance that an inferior batch is judged as qualified. There are also cases where, for the producer, what he produces is indeed a series of continuous batches; However, users only buy a batch of them, and such users are particularly concerned about the LQ value. The effects of 1.3.3 LQ and CRQ are among GB/T805 1, GB/T 13546 and GB/T 15239. LQ is used as the batch quality index. 1.4 the average detected quality AOQ and the upper limit of the average detected quality AOQL1.4.1the meaning of aoq and AOQL1.4.2 the role of aoq and aoql determines that AQL principle AQL is the dividing line between acceptable and unacceptable process average, and it is a quality parameter related to sampling scheme and also based on GB/. However, so far, there is no one method that can be applied to all different situations. The following are some principles that should be followed when determining the AQL: (1) The AQL value is a satisfactory process average quality, and it is expected that the average batch quality of suppliers will not exceed this value. ⑵ Consider the purpose of the product and the consequences caused by product failure. For example, the AQL value of electronic components with the same specifications used in general civilian equipment can be larger than that used in military equipment; The AQL value of ordinary instruments can be larger than that of precision instruments. (3) Although AQL is not a requirement for the quality of individual batches, if it is really known that the number of unqualified products per 100 unit (or the number of unqualified products per 100 unit) of a batch of products does not exceed the specified AQL value, the batch shall be accepted; Otherwise, this batch of products will be rejected. (4) From the user's point of view, the AQL value should not be too small, otherwise it will increase the inspection fee and product cost, or often reject the product batch, so that the supplier refuses to sign the contract. 5. If it is difficult to improve the quality of the product urgently needed by users, in order to obtain the product, the AQL value has to be appropriately larger, and the AQL value will be adjusted after the quality of the producer is improved. [6] When there are many spare parts, and unqualified parts are easy to be found and replaced by qualified parts during overall assembly, you can choose larger AQL; If a part fails and cannot be removed from the whole part for replacement, resulting in the failure of the whole part, the AQL should be smaller. At one time, considering the assembly sequence, if the unqualified products in the previous process would cause the waste of time and material resources in the following process, the AQL value of the previous process should be less than that of the following process. ⑻ You can specify the AQL value for a single inspection item or jointly specify the AQL value for a group of inspection items. ⑼ Considering the severity of the impact of unqualified products on product performance, in the same acceptance sampling problem, the AQL value of Class A unqualified products is generally required to be less than that of Class B unqualified products; The AQL value of Class B nonconforming product is less than that of Class C nonconforming product. For example, the AQL values of unqualified products of Class A, Class B and Class C are 0. 15, 0.40 and 0.65 respectively. ⑽ AQL can't tell users how much quality protection a single batch of products can get. In order to clearly protect the quality of users, it is necessary to look at the OC curve of the one-time sampling scheme of design values given in GB 2828 1 ~ Figure1and its corresponding numerical table. ⑾ The determination of ⑾AQL value depends on the compromise between the quality that the producer may provide and the quality that the user thinks is ideal, that is, the compromise between the quality that the user wants and the quality that he can afford at cost. The stricter the quality requirements, the more difficult it is for manufacturers to meet, and the higher the inspection fee, which will eventually be counted on the products. ⑿ AQL value is not stipulated again for each batch, but stipulated by the responsible department (or person in charge) in the contract. Once specified, it cannot be changed at will. Determination of AQL The following are some methods for determining the AQL value for your reference. 3. 1 engineering law engineering law regards the quality that must be guaranteed technically as AQL based on the quality requirements of products such as performance, service life, interchangeability, assembly and safety. 3.2 There is no historical data on the quality of new products with similar methods. In order to determine the AQL value, we can refer to the AQL value of similar products (raw materials, structure, technology, etc.). ) .3.3 The empirical AQL is determined by the responsible department personnel, engineering technicians and quality management personnel according to the experience of process capability. 3.4 Experimental method The experimental method is to temporarily specify an AQL value without any bright information for reference, and then adjust the AQL according to the relevant quality information obtained during use. 3.5 Calculation method For multi-component complex systems, the relationship between parts, components and the whole machine can be considered to calculate AQL. If a system or component consists of several identical parts or different parts with the same AQL. Then the AQL value of this part (marked as AQLx) should be appropriately smaller than the AQL value of the whole part (marked as AQLX). Suppose the whole machine is composed of n identical parts in series, that is, the failure of one part will lead to the failure of the whole machine. At this time, AQLx and AQLX have the following relationship: (AQLX/100) =1-(AQLX/100)) N3.6 Estimation method In factories or enterprises, 3.7 Reverse derivation is not directly specified. Instead, a normal test sampling scheme is found, so that the OC curve passes through an important point with low receiving probability, such as the indifference point (the control point of the OC curve) and the risk point of the user, and the required AQL value is reversely deduced. 3.8 The cost model is established by the model method, and the AQL value is selected to minimize the total cost of the corresponding sampling scheme. The distribution of AQL is 4. 1. Generally, there are many ways to assign AQL values to different types of nonconformities. The simplest method is to divide all nonconformities into two categories, A and B, and assign an AQL value to each category. For example, after specifying the sampling scheme type, two different sampling schemes can be taken from the sampling scheme under inspection, and only when both schemes are qualified can the batch of products be judged to be qualified in the inspection; As long as one sampling scheme is judged unqualified, it cannot be judged that the batch is qualified in normal inspection. 4.2 There are more than two kinds of unqualified products. For more than two types of cases, such as unqualified A, B and C AQL 0.40% unqualified products 1.0% unqualified products, the inspection lot is judged to be qualified, and only three sampling schemes corresponding to A, B and C can make a qualified judgment. 4.3 In combination with synthesis, assign an independent AQL to each performance of the product, and assign an AQL to all performances. For example, a certain type of disqualification includes three types as shown in the following table: disqualification category performance 1 performance 2 performance 3 AQL 1.0% disqualification 1.0% disqualification 1.0% disqualification comprehensive AQL 1.5% disqualification. This method has certain reference value for complex products that need to test multiple independent performances. 4.3 Define an AQL for Class A nonconformity separately and in combination, and define an AQL for Class A nonconformity and Class B nonconformity at the same time, for example, unqualified Class A+Class B AQL 1.0% nonconformity and 4.0% nonconformity. Let's consider a concrete example. [Example] The batch number of a product is N= 1000. Each sample unit to be inspected must be inspected in five dimensions. After considering the influence of various nonconformities, the nonconformities of dimension 1 and dimension 2 are classified as Class A nonconformities, and the nonconformities of the other three dimensions are classified as Class B nonconformities. Their AQL regulations are as follows: unqualified inspection items AQL A size 1 size 2 0.65% unqualified product B size 3 size 4 size 5 2.50% unqualified product Assuming that inspection level II is specified for both unqualified products A and B, the sample size code can be found in Table 2 of GB/T2828 as J. According to Table 3 of GB/T2828, The sampling scheme of normal inspection can be found as follows: unqualified sample size, qualified judgment number, Ac (qualified product), unqualified judgment number, Re (unqualified product) and A 80. In the inspection process, because the size measurement is non-destructive, only 80 sample units are needed to measure the five dimensions involved in Class A and Class B nonconformities. If 80 sample units are taken from this batch of products, the measurement results are as follows. There are unqualified products with sizes 2 and 3; There are two unqualified products, only No.3 is unqualified; There is a nonconforming product, No.4 and No.5 are unqualified. Because, according to the definition of GB/T2828, "a unit product with one or more Class A nonconformities and possibly Class B and/or Class C nonconformities is called Class A nonconformities" (see 2. 1. 13 of GB/T2828), "one or more Class B nonconformities and possibly Class C nonconformities. Therefore, although No.2 and No.3 are unqualified, a nonconforming product can only be regarded as a class A nonconforming product; Unqualified products with sizes 4 and 5 can only be counted as Class B nonconforming products.