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ASQ Z1. WI-PG C. It provides tightened, normal, and reduced plans to be applied for attributes inspection for percent nonconforming or nonconformities per units. An American National Standard is intended as a guide to aid the manufacturer, the consumer, and the general public.
The existence of an American National Standard does not in any respect preclude anyone, whether he has approved the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not conforming to the standard. American National Standards are subject to periodic review and users are cautioned to obtain the latest editions.
The procedures of the American National Standards Institute require that action be taken to reaf? Purchasers of American National Standards may receive current information on all standards by calling or writing the American National Standards Institute.
SCOPE 1. This publication establishes sampling plans and procedures for inspection by attributes. When speci? Sampling plans designated in this publication are applicable, but not limited, to inspection of the following: a. End items. Components and raw materials. Materials in process. Supplies in storage. Maintenance operations. Data or records. Administrative procedures. These plans are intended primarily to be used for a continuing series of lots or batches.
The plans may also be used for the inspection of isolated lots or batches, but, in this latter case, the user is cautioned to consult the operating characteristic curves to? Inspection is the process of measuring, examining, testing, or otherwise comparing the unit of product see 1. Inspection by attributes is inspection whereby either the unit of product is classi? The unit of product is the unit inspected in order to determine its classi?
It may be a single article, a pair, a set, a length, an area, an operation, a volume, a component of an end product, or the end product itself. The unit of product may or may not be the same as the unit of purchase, supply, production, or shipment. The following two de?
DEFECT: A departure of a quality characteristic from its intended level or state that occurs with a severity sufficient to cause an associated product or service not to satisfy intended normal, or foreseeable, usage requirements.
These acceptance sampling plans for attributes are given in terms of the percent or proportion of product in a lot or batch that depart from some requirement.
The general terminology used within the document will be given in terms of percent of nonconforming units or number of nonconformities, since these terms are likely to constitute the most widely used criteria for acceptance sampling. In the use of this standard it is helpful to distinguish between: a. This standard is a sampling system indexed by lot-size ranges, inspection levels, and AQLs.
The extent of nonconformance of product shall be expressed either in terms of percent nonconforming or in terms of nonconformities per hundred units. The percent nonconforming of any given quantity of units of product is one hundred times the number of nonconforming units divided by the total number of units of product, i.
The number of nonconformities per hundred units of any given quantity of units of product is one hundred times the number of nonconformities contained therein one or more nonconformities being possible in any unit of product divided by the total number of units of product, i. The AQL is the quality level that is the worst tolerable process average when a continuing series of lots is submitted for acceptance sampling. The concept of AQL only applies when an acceptance sampling scheme with rules for switching between normal, tightened and reduced inspection and discontinuance of sampling inspection is used.
These rules are designed to encourage suppliers to have process averages consistently better than the AQL. If suppliers fail to do so, there is a high probability of being switched from normal inspection to tightened inspection where lot acceptance becomes more difficult.
Once on tightened inspection, unless corrective action is taken to improve product quality, it is very likely that the rule requiring discontinuance of sampling inspection will be invoked. Although individual lots with quality as bad as the AQL can be accepted with fairly high probability, the designation of an AQL does not suggest that this is necessarily a desirable quality level.
The AQL is a parameter of the sampling scheme and should not be confused with a process average which describes the operating level of a manufacturing process. It is expected that the product quality level will be less than the AQL to avoid excessive non-accepted lots. The sampling plans in this standard are so arranged that the probability of lot acceptance at the designated AQL depends upon sample size, being generally higher for large samples than for small samples for a given AQL.
To determine the speci? The AQL alone does not describe the protection to the consumer for individual lots or batches, but more directly relates to what is expected from a series of lots or batches provided the provisions of this standard are satis? The designation of an AQL shall not imply that the supplier has the right to knowingly supply any nonconforming unit of product.
The AQL to be used will be designated in the contract or by the responsible authority. Different AQLs may be designated for groups of nonconformities considered collectively, or for individual nonconformities. For example, Group A may include nonconformities of a type felt to be of the highest concern for the product or service and therefore be assigned a small AQL value; Group B may include nonconformities of the next higher degree of concern and therefore be assigned a larger AQL value than for Group A and smaller than that of Group C, etc.
The classi? An AQL for a group of nonconformities may be designated in addition to AQLs for individual nonconformities, or subgroups, within that group. AQL values of The product shall be assembled into identi? Each lot or batch shall, as far as is practicable, consist of units of product of a single type, grade, class, size, and composition, manufactured under essentially the same conditions, and at essentially the same time.
The lot or batch size is the number of units of product in a lot or batch. The formation of the lots or batches, lot or batch size, and the manner in which each lot or batch is to be presented and identi?
As necessary, the supplier shall provide adequate and suitable storage space for each lot or batch, equipment needed for proper identi? Acceptability of a lot or batch will be determined by the use of a sampling plan or plans associated with the designated AQL or AQLs. The acceptance of a lot is not intended to provide information about lot quality. If a stream of lots from a given process is inspected under an acceptance sampling scheme such as provided in this standard, some lots will be accepted and others will not.
If all incoming lots are assumed to be at the same process average and if the nonconforming items that are discovered and replaced by conforming items during sample inspection are ignored, it will be found that both the set of accepted lots and the set of non-accepted lots will have the same long run average quality as the original set of lots submitted for inspection.
Inspection of incoming lots whose quality levels vary around a? Replacement of the nonconforming items that are discovered during sample inspection does not alter this? The purpose of this standard is, through the economic and psychological pressure of lot non-acceptance, to induce a supplier to maintain a process average at least as good as the speci? The standard is not intended as a procedure for estimating lot quality or for segregating lots.
Rejection in an acceptance sampling sense means to decide that a batch, lot or quantity of product, material, or service has not been shown to satisfy the acceptance criteria based on the information obtained from the sample s. The right is reserved to reject any unit of product found nonconforming during inspection whether that unit of product forms a part of a sample or not, and whether the lot or batch as a whole is accepted or rejected.
Rejected units may be repaired or corrected and resubmitted for inspection with the approval of, and in the manner speci? In general, the function of such classi? The supplier may be required at the discretion of the responsible authority to inspect every unit of the lot or batch for designated classes of nonconformities.
The right is reserved to inspect every unit submitted by the supplier for speci? The right is reserved also to sample, for speci? Lots or batches found unacceptable shall be resubmitted for reinspection only after all units are re-examined or re-tested and all nonconforming units are removed or nonconformities corrected.
The responsible authority shall determine whether normal or tightened inspection shall be used on reinspection and whether reinspection shall include all types or classes of nonconformities or only the particular types or classes of nonconformities which caused initial rejection. A sample consists of one or more units of product drawn from a lot or batch, the units of the sample being selected at random without regard to their quality.
The number of units of product in the sample is the sample size. When appropriate, the number of units in the sample shall be selected in proportion to the size of sublots or subbatches, or parts of the lot or batch, identi? In so doing, the units from each part of the lot or batch shall be selected at random, as de? Samples may be drawn after all the units comprising the lot or batch have been produced, or samples may be drawn during production of the lot or batch.
Where double or multiple sampling is to be used, each sample shall be selected over the entire lot or batch. Normal inspection will be used at the start of inspection unless otherwise directed by the responsible authority.
Normal, tightened or reduced inspection shall continue unchanged on successive lots or batches except where the switching procedures given below require change. When normal inspection is in effect, tightened inspection shall be instituted when 2 out of 5 or fewer consecutive lots or batches have been non-acceptable on original inspection i.
When tightened inspection is in effect, normal inspection shall be instituted when 5 consecutive lots or batches have been considered acceptable on original inspection. When normal inspection is in effect, reduced inspection shall be instituted providing that all of the following conditions are satis?
Production is at a steady rate; and d. Reduced inspection is considered desirable by the responsible authority. When reduced inspection is in effect, normal inspection shall be instituted if any of the following occur on original inspection: a. A lot or batch is rejected; or b. A lot or batch is considered acceptable under the procedures for reduced inspection given in Production becomes irregular or delayed; or d.
Other conditions warrant that normal inspection shall be instituted. If the cumulative number of lots not accepted in a sequence of consecutive lots on tightened inspection reaches 5, the acceptance procedures of this standard shall be discontinued.
Inspection under the provisions of this standard shall not be resumed until corrective action has been taken. Tightened inspection shall then be used as if 8. When agreed upon by responsible authority for both parties to the inspection, that is, the supplier and the end item customer, the requirements of 8.
This action will have little effect on the operating properties of the scheme. A schematic diagram describing the sequence of application of the switching rules is shown in Figure 1.
ASQ/ANSI Quality Standards Z1.4 & Z1.9
October RSS Feed. Ansi Asq Z1. It provides tightened, normal, and reduced plans to be applied for attributes inspection for percent nonconforming or nonconformities per units. Ansi Z1.
Z1.4 2008: AQL, Nonconformities, and Defects Explained
Q: My question is regarding the noncomformities per hundred units and percent nonconforming. Specifically, I am having problems understanding the following unit numbers just above the Acceptance and Rejection numbers example, 0. As you may see, I am very confused by these numbers, and I was hoping to have some light shed on this subject. Thank you for your answers in advance. A: The numbers on the top of the table are just as the questioner stated:. That is the acceptable quality limit AQL number. Scratch and dent sales are a common result of these higher numbers.