Acceptance Sampling
Acceptance sampling is a quality control technique used to inspect a sample of products to determine if the entire batch meets quality standards. It involves randomly selecting a sample from a larger batch and making a decision about whether to accept or reject the entire batch based on the quality of the sample. This method is commonly used in manufacturing and production processes to ensure product quality.
7 Key excerpts on "Acceptance Sampling"
eBook - ePub- Lawrence S. Aft(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
...10 Acceptance Sampling Introduction Even before the 1920’s, industry was learning how to do things more scientifically, using such techniques as the Gantt chart, under principles developed by Taylor, Gilbreth, and others in a movement called “scientific management” And in 1922, G.S. Radford published his book, The Control of Quality in Manufacturing. But the Bell System group was organized with what proved to be a new approach to the problem of quality, having as its broad objective the quality of performance of a rapidly growing nationwide communications system. New techniques and procedures were sought for getting the highly needed, highly uniform quality of the many elements of the complete telephone system. At that time, when it was common practice for products and services to strike a balance between schedules and costs, it was proposed to add a third factor — quality …A number of techniques, such as …Acceptance Sampling inspections plans, were essentially statistical in nature. (Dodge, 1969, p. 78) Thus, Acceptance Sampling has been used in some form since the 1920s. When a manufacturing concern purchases parts, when a restaurant purchases food, or when any other organization purchases raw material for further processing, it hopes to purchase only material meeting specifications. But since no supplier ever provides completely acceptable material all of the time — random variation enters every process — most concerns inspect the product that has been ordered to determine if the material conforms to the agreed upon quality standards. Inspection is the process of comparing actual measurable characteristics with predetermined standard characteristics. There are three basic ways to perform inspections. First, every single part that is received may be inspected. This is referred to as 100 percent inspection. It has several drawbacks. Often the cost is prohibitive, as is the time required to inspect every piece of material received...
eBook - ePub- Nick Lee, Mike Peters(Authors)
- 2015(Publication Date)
- SAGE Publications Ltd(Publisher)
...This can happen because machinery may wear out, or the environment (e.g. temperature, etc.) may change. There may also be a problem building with operator fatigue, or laxity. Or, if the pattern of data points is such that almost all the points are on one side of the mean, some shift may have occurred in the process, which might indicate a potential problem. Maybe the materials have changed? Or maybe some specific issue in the machinery is at the root of this? As such, it is not only their ability to provide statistical evidence that makes control charts useful. Acceptance Sampling Acceptance Sampling is a way of deciding whether or not to accept a lot of some raw material or other sort of input into a production process. Just to clarify, a ‘lot’ is defined here as some group of items (the number of items in the lot is not really important). As such, while control charts deal with the end result of a production process, Acceptance Sampling deals with the inputs into that process. This is a common situation in most manufacturing operations. Say I run a company that makes high-end leather jackets. Of course, it is highly unlikely that I breed my own cows and run a leather tanning operation myself. Most likely, I buy in my leather from a specialist leather producer. In all such operations, it is highly important to make sure the quality of my raw materials is up to scratch. I can use Acceptance Sampling methods to decide whether to accept or reject a batch of raw materials, on the basis of some specified quality criterion...
eBook - ePub- Edward G. Schilling, Dean V. Neubauer(Authors)
- 2017(Publication Date)
- Chapman and Hall/CRC(Publisher)
...19 Administration of Acceptance Sampling Effective Acceptance Sampling involves more than the selection and application of specific rules for lot inspection. As an integral part of the quality system, the Acceptance Sampling plan, applied on a lot-by-lot basis, becomes an element in the overall approach to maximizing quality at minimum cost. Acceptance Sampling plans are, after all, action rules and as such must be adapted in a rational way to the current results and the nature and history of the inspection performed. This is what we have called acceptance control, involving a continuing strategy of selection, application, and modification of Acceptance Sampling procedures to a changing inspection environment. While Acceptance Sampling is sometimes regarded as a passive procedure for adjudication of quality, the active role of inspection was recognized early by Dodge. In accepting the Shewhart Medal from the American Society for Quality Control, Dodge (1950, p. 6) pointed out that Using the inspection results as a basis for action on the product at hand for deciding whether to accept or reject individual articles or lots of the product as they come along is, of course, an immediate chore that we always have with us. However, the inspection results also provide a basis for action on the production process for the benefit of the future product, for deciding whether the process should be left alone or action taken to find and eliminate disturbing causes. As such, inspection should involve Good data Quick information Incentives for the producer to provide quality at satisfactory levels Quantity of inspection in keeping with quality history Indeed, according to Dodge (1950, p. 8) A product with a history of consistently good quality requires less inspection than the one with no history or a history of erratic quality...
eBook - ePub- Irving W. Burr(Author)
- 2018(Publication Date)
- Routledge(Publisher)
...The use of sampling acceptance tends to concentrate only on the second, taking action, such as adjusting the level up or down. For decision-making on a particular lot from a producer, or a series of lots, control charts can still be of much use, but the primary job is to take action on this one lot. Then Acceptance Sampling is a natural decision-making tool. If we cannot tell what kind of distribution of measurements we have in the lot, then we are much safer to use a random sample of parts or pieces and measure each, comparing each x with specification limits L and U, and taking action on the basis of some attribute plan. This will call for a substantial sample size in general. The measurements can well be recorded too, and thus build up knowledge on the producer’s frequency distribution. If this proves to be normal or nearly so we may begin to try the normal curve methods described in this chapter. These would be unknown-σ x plans, Section 11.6. In a series of lots, plotting of R or s charts can quickly lead to a good estimate of σ x, if there is control. Then we can use this in known- σ x plans, Sections 11.4, 11.5, and thereby further decrease the required sample size. Military Standard 414 is an effective system of integrated plans, providing normal, tightened and reduced sampling, for protection against one or two specification limits. It is concerned with fraction or per cent defective. The plans assume normality, but one hedge, if this is not an available assumption, is to use variables – attributes inspection, permitting quick acceptance via measurements, but only rejecting via attributes. Checks on process level and process capability were also given, for use when normality of x’s can be assumed. PROBLEMS 11.1. Verify the risks given in the two-way check of level in Section 11.9, for Pa vs. μ. 11.2. Verify the risks given in the one-way check of level in Section 11.9, for Pa vs. μ. Also verify the three corresponding fractions defective for Pa vs. p′. 11.3...
eBook - ePub- Robin Kent(Author)
- 2016(Publication Date)
- William Andrew(Publisher)
...Chapter 6 Acceptance Sampling The AQL approach to quality is needed for quality control and inspection of products where it is impossible to perform standard SPC process control. This is primarily where purchased products or materials are being inspected at Inwards Goods and where AQL is used as an acceptance testing protocol because it is impossible to control the process. AQL is based on sampling a ‘lot’ or ‘batch’ of product and inspecting the samples to see if they meet the specification (or not). The number of nonconforming samples is used to decide if the complete batch will be accepted or not. AQL is not inspection to weed out any bad products - if the number of nonconforming samples exceeds the limits then the complete batch is rejected back to the supplier. Obviously a sample is simply a snapshot of the complete population (see Section 5.1) and removing any nonconforming products from the samples does not improve the quality of the batch. Removing nonconforming products is not the aim of AQL. It is to form a view on the overall quality level of the batch and to act on this view with some statistical basis. A possibly apocryphal story is told about a customer who used AQL as an Inwards Goods inspection method. They notified their (very reputable) Japanese supplier that under their AQL rules they would accept 10 nonconformities/10,000 products. On the first delivery of 10,000 products they opened the boxes and found 10 products in a small bag with a note which read ‘We are not sure why you want 10 nonconforming product but they are in this bag’. The supplier had good control and was sure that all their product met the specification but had produced 10 nonconforming products specifically for the customer. AQL can be used as method of setting inspection levels for in-process inspection or as the final inspection of a product immediately prior to despatch to the customer...
eBook - ePubSystem Verification
Proving the Design Solution Satisfies the Requirements
- Jeffrey O. Grady(Author)
- 2016(Publication Date)
- Academic Press(Publisher)
...Concurrent development will then leap out of its current physical bindings. Hopefully, by then, we will have learned how to get the best out of the human component in this environment. 9.2 Nontest Item Acceptance Methods Coordination 9.2.1 Organizational Responsibilities The whole acceptance process could be accomplished by a test and evaluation organization, manufacturing organization, or a quality engineering organization. In many organizations, this work is partitioned up so that two or even three of these organizations are involved. Design engineering could even be involved with some analyses of test results. Mass properties may require access to manufactured products to weigh them. Software acceptance may be accomplished by a software quality assurance (SQA) function independent of the QA organization. These dispersed responsibilities make it difficult to manage the overall acceptance process, assure accountability of all participants, and acquire and retain good records of the results so that they are easily accessible by all. In a common arrangement, the acceptance test procedures are prepared by engineering; manufacturing is responsible for performing acceptance tests and producing test results. The tests are witnessed and data sheets stamped by QA. Demonstrations may be accomplished by manufacturing or engineering personnel and witnessed by quality. Some tests may require engineering support for analysis of the results. Quality assurance may be called upon to perform independent examinations in addition to their witnessing of the actions of others, which qualify as examinations in themselves. An organizational arrangement discussed earlier pools QA, test and evaluation, and system engineering into one organization focused on system requirements, risk, validation, verification, integration, and optimization...
- Peter Jones(Author)
- 2017(Publication Date)
- Routledge(Publisher)
...9 Other sampling approaches In many respects this chapter is worth a book in its own right, but our aim is to provide a relatively short, practical text specifically for auditors, and a brief and selective overview will suffice. Acceptance Sampling This is a particularly useful technique if auditors, at the strategic planning stage, or for whatever reason, are faced with a range of populations and wish to concentrate most of their efforts on systems with risk of unacceptable control deviation rates. Usually a standard sample size is chosen simply in the light of time available, and the auditor rejects or accepts the sample depending on the UEL given by however many errors are found. For example, it may be decided that the following range of results lead to the following actions. A standard sample size of 50 control events (authorizations, separations, and so on) is chosen, and in the first sample compliance tested one error is found. The auditor wants to be 90 per cent confident. Table 9.1 Acceptance Sampling UEL Action 5% or less maximum reliance >5% to 10% moderate reliance >10% no reliance (e.g. no compliance testing, maximum substantive testing) Rearranging the attribute-sampling formula – sample size = reliability factor / UEL – for attribute sampling for compliance testing (see Chapter 5) we get: UEL = reliability factor / sample size The reliability factor for one error at 90 per cent confidence is 3.89 (from Table 4.1) UEL = 3.89 / 50 = 7.8%, i.e. moderate reliance In the next sample compliance tested no errors are found: UEL = 2.31 / 50 = 4.6%, maximum reliance The next compliance test two errors are found: UEL = 5.33 / 50 = 10.7%, just unacceptable! And so on. By now it is clear that for these samples no errors means maximum reliance, one error moderate reliance, two or more errors no reliance. The audit approach that will be taken in each case will, naturally, depend on all the other circumstances...
