1、Designation: B697 88 (Reapproved 2016)Standard Guide forSelection of Sampling Plans for Inspection ofElectrodeposited Metallic and Inorganic Coatings1This standard is issued under the fixed designation B697; the number immediately following the designation indicates the year oforiginal adoption or,
2、in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide gives guidance in the selection of samplingplans to be used in the ins
3、pection of electrodeposited andrelated coatings on products for the purpose of decidingwhether submitted lots of coated products comply with thespecifications applicable to the coatings. This supplements TestMethod B602 by giving more information on sampling inspec-tion and by providing additional s
4、ampling plans for the userwho finds the limited choice of plans in Test Method B602 tobe inadequate.1.2 When using a sampling plan, a relatively small part ofthe articles in an inspection lot is selected and inspected. Basedon the results, a decision is made that the inspection lot eitherdoes or doe
5、s not satisfactorily conform to the specification.1.3 This guide also contains several sampling plans. Theplans are attribute plans, that is, in the application of the planseach inspected article is classified as either conforming ornonconforming to each of the coating requirements. Thenumber of non
6、conforming articles is compared to a maximumallowable number. The plans are simple and relatively few.Additional plans and more complex plans that cover moresituations are given in the Refs (1-7) at the end of this guideand in MIL-STD-105.1.4 Acceptance sampling plans are used:1.4.1 When the cost of
7、 inspection is high and the conse-quences of accepting a nonconforming article are not serious.1.4.2 When 100 % inspection is fatiguing and boring and,therefore, likely to result in errors. In these cases a samplingplan may provide greater protection than 100 % inspection.1.4.3 When inspection requi
8、res a destructive test. Here,sampling inspection must be used.1.5 Another general type of acceptance sampling plan that isnot covered in these guidelines is the variables plan in whichmeasured values of characteristics are analyzed by statisticalprocedures. Such plans, when applicable, can reduce in
9、spec-tion cost and increase quality protection. Information onvariables plans is given in Test Method B762, MIL-STD-414,ANSI/ASQC Z1.9-1979, and Refs (1-2).2. Referenced Documents2.1 ASTM Standards:2B602 Test Method for Attribute Sampling of Metallic andInorganic CoatingsB762 Test Method of Variable
10、s Sampling of Metallic andInorganic Coatings2.2 ANSI Standard:3ANSI/ASQC Z1.9-1979 Sampling Procedures and Tablesfor Inspection by Variables for Percent Nonconformance2.3 Military Standards:4MIL-STD-105 Sampling Procedures and Tables for Inspec-tion by AttributesMIL-STD-414 Sampling Procedures and T
11、ables for Inspec-tion by Variables for Percent Defective3. General3.1 ProcedureThe use of acceptance sampling consists ofa series of decisions and actions. These are listed in orderbelow and are discussed in this standard.3.1.1 Select characteristics to be inspected,3.1.2 Select type of sampling pla
12、n,3.1.3 Select quality level,3.1.4 Define inspection lot,3.1.5 Select sample,3.1.6 Inspect sample,3.1.7 Classify inspection lot, and3.1.8 Dispose of inspection lot.3.2 The need for acceptance sampling arises when a deci-sion must be made about what to do with a quantity of articles.1This guide is un
13、der the jurisdiction of ASTM Committee B08 on Metallic andInorganic Coatings and is the direct responsibility of Subcommittee B08.10 on TestMethods.Current edition approved Nov. 1, 2016. Published November 2016. Originallyapproved in 1981. Last previous edition approved in 2010 as B697 88 (2010).DOI
14、: 10.1520/B0697-88R16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Stand
15、ards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,
16、PA 19428-2959. United States1This quantity (called the inspection lot in this guide) may be ashipment from a supplier, may be articles that are ready for asubsequent manufacturing operation, or may be articles readyfor shipment to a customer.3.3 When acceptance sampling is done, several of thearticl
17、es in the inspection lot are selected at random (see Section7). These articles constitute the sample. Each article in thesample is inspected for conformance to the requirementsplaced on it. If an article meets a requirement, it is classified asconforming. If not, it is classified as nonconforming. I
18、f thenumber of nonconforming articles in the sample is no morethan a predetermined number (called the acceptance number),the inspection lot is accepted. If it exceeds the acceptancenumber, the inspection lot is rejected.3.4 The disposition of rejected inspection lots is beyond thescope of this guide
19、 because, depending on the circumstances,lots may be returned to the supplier, kept and used, put to adifferent use, scrapped, reworked, or dealt with in some otherway. An exception is rectifying inspection (3.11) in whichrejected lots are screened and used.3.5 Because the decision about the disposi
20、tion of an inspec-tion lot is based on the inspection of a sample, and becausethere is a chance that a sample will not be representative of aninspection lot, some inspection lots that have the desiredquality level (Note 1) will be rejected and some inspection lotsthat do not have the desired quality
21、 level will be accepted.There are only two situations in which the results of acceptancesampling are totally predictable (Note 2). One is when there areno nonconforming articles in the inspection lot. There, ofcourse, will be no nonconforming articles in the sample and thedecision to accept the lot
22、will always be made. The othersituation is when no article in the inspection lot conforms. Allof the articles in the sample will be nonconforming and thedecision to reject the lot will always be made (Note 3).NOTE 1In this guide the term “quality level” means the percentage ofnonconforming articles
23、in an inspection lot or it means the averagepercentage of nonconforming articles in a series of inspection lotsreceived from a single source. Terms such as high quality, increasedquality, and better quality mean a relatively smaller percentage ofnonconforming articles, while terms such as low qualit
24、y, decreasedquality, and poorer quality mean a relatively larger percentage ofnonconforming articles.NOTE 2In this discussion and elsewhere in this guide, it is assumedthat no errors are made.NOTE 3To be strictly correct, lots that contain no more nonconform-ing articles than the acceptance number w
25、ill always be accepted, and lotsthat contain fewer conforming articles than the sample size minus theacceptance number will always be rejected.3.6 The discussion in 3.5 leads to two important points: (1)acceptance sampling plans will permit the acceptance ofinspection lots that contain nonconforming
26、 articles, and (2)ina series of inspection lots, each containing the same percentageof nonconforming articles, some will be accepted and somewill be rejected, and the percentage of nonconforming articlesin the accepted inspection lots will be the same as in therejected lots. In other words, acceptan
27、ce sampling does not, byitself, result in higher quality. Rectifying inspection (3.11) willresult in higher average quality in the product leaving inspec-tion.3.7 Because acceptance sampling plans permit the accep-tance of inspection lots that contain nonconforming articles,basic to the selection of
28、 a sampling plan is a decision about thepercentage of nonconforming articles that is acceptable. If thefunction of the article is so important that no nonconformerscan be tolerated, acceptance sampling cannot be used. In thesecases, every article must be inspected, and, to guard againsterror, may ha
29、ve to be inspected twice.3.8 The protection that an attributes sampling plan providesagainst accepting an undesirable number of nonconformingarticles is determined by the size of the sample and by theacceptance number. The protection provided by a plan isusually expressed in the form of an operating
30、 characteristic(OC) curve. Fig. 1 is the OC curve for the plan that calls for asample of 55 articles and an acceptance number of two. Plottedalong the horizontal axis is the quality level of an inspection lotexpressed as the percentage of the articles in the lot that arenonconforming (Note 1). The v
31、ertical axis is the probability, asa percentage, that an inspection lot will be accepted by the plan(Note 4). Inspection lots with zero percent nonconformingarticles will be accepted 100 % of the time (Note 2). As thepercentage of nonconforming articles in the inspection lotincreases, the probabilit
32、y of acceptance decreases. Forexample, as shown in Fig. 1, an inspection lot containing 1.5 %nonconforming articles has a 95 % chance of being accepted,while one containing 9.6 % nonconforming articles has only a10 % chance of being accepted.NOTE 4The vertical axis of the OC curve can have two meani
33、ngs. Oneis the probability that a particular inspection lot will be accepted. Theother meaning is the percentage of a series of lots of a given quality levelthat will be accepted. The latter meaning is the one that is strictly correctmathematically. The former meaning is also correct, as long as the
34、inspection lot is at least ten times bigger than the sample.3.9 The characteristics of a sampling plan are often ex-pressed in terms of the Acceptable Quality Level (AQL) andthe Limiting Quality Level (LQL). TheAQLis the quality levelthat will result in the acceptance of a high percentage ofincoming
35、 inspection lots; usually it is the quality level that willresult in the acceptance of 95 % of the incoming inspectionlots. In Fig. 1, the AQL is 1.5 %. The LQL is the quality levelFIG. 1 Operating Characteristic Curve for Single Sample, Attri-butes Sampling Plan, Sample Size = 55, Acceptance Number
36、 = 2B697 88 (2016)2that will result in the rejection of a high percentage of incominginspection lots; usually it is the quality level that will result inthe rejection of 90 % of the incoming inspection lots. In Fig. 1the LQL is 9.6 %. In this standard, AQL and LQL are definedas the quality levels th
37、at will be accepted 95 and rejected 90 %of the time, respectively.3.10 Another characteristic of sampling plans that is used inthis standard is the 50/50 point. This is the quality level thatwill result in the acceptance of half of the incoming inspectionlots. In Fig. 1 the 50/50 point is 4.8 %.3.11
38、 Rectifying Inspection:3.11.1 As stated in 3.4, one of the options when an inspec-tion lot is rejected is screening of the lot. In this procedure,called rectifying inspection, all of the articles in a rejected lotare inspected and the nonconforming ones are removed andreplaced with conforming articl
39、es. The now 100 %-conforminginspection lot is accepted and is passed along with theinspection lots that were accepted on the basis of acceptancesampling. The addition of these 100 %-conforming inspectionlots improves the average quality level of all the inspection lotstaken together. The amount the
40、quality level is improved can becalculated if the average quality level of incoming inspectionlots is known. The calculations reveal that if the incomingquality level is high, few inspection lots will be rejected andscreened and so the average quality of the outgoing lots will beonly slightly improv
41、ed over the incoming. If the quality levelof the incoming inspection lots is low, many of the inspectionlots will be rejected and screened. The addition of this largenumber of 100 %-conforming lots will result in a high outgo-ing quality level. At intermediate incoming quality levels, theoutgoing qu
42、ality will be poorer than these two extremes, andthere will be a particular incoming quality level for which theoutgoing level will be the poorest.3.11.2 When rectifying inspection is used the average qual-ity level of a series of outgoing lots is called the AverageOutgoing Quality (AOQ) and the wor
43、st possible AOQ for agiven plan is called the Average Outgoing Quality Limit(AOQL). Fig. 2 is a plot of the AOQ for the sampling plan ofFig. 1 (Note 5). This shows that the worst AOQ, the AOQL, is2.5 % and occurs only if the average incoming quality level is4.2 %. Fig. 2 also shows that when the qua
44、lity level ofincoming lots is high, the improvement caused by inspection issmall. For example, if the incoming lots are of AQL quality,1.5 %, the AOQ is 1.4 %. At lower incoming quality levels therelative improvement is greater; for example, at an incomingquality level of 3 %, the AOQ is 2.3 %.NOTE
45、5The AOQs and AOQLs in this guide are calculated on thebasis that when rejected lots are screened the nonconforming articlesfound are replaced with conforming articles. If the discarded nonconform-ing articles are not replaced, a practice that is frequently done, the AOQsand AOQLs will be somewhat d
46、ifferent from those in this guide. Chapter16 of Ref (4) discusses this point.3.11.3 Use of rectifying inspection will assure that with acontinuous series of inspection lots the average quality level ofall the accepted articles, considered as a whole, will not beworse than the AOQL of the sampling pl
47、an used. However,rectifying inspection can significantly increase inspection costssince every rejected inspection lot is 100 % inspected. Thelower the quality of incoming lots, the more of them that willbe rejected and then 100 % inspected. Fig. 3 shows how, for thesampling plan of Fig. 1 and lots o
48、f 550, the average number ofarticles inspected per inspection lot increases as the qualitylevels of incoming lots decrease. In lots containing up to about1.5 % nonconforming articles the increase in inspection ismoderate. Beyond that point the average amount of inspectionincreases rapidly. At an inc
49、oming quality level of 2.1 % theamount of inspection is doubled. And with incoming qualitylevels of 15 % virtually every inspection lot is 100 % in-spected.3.11.4 Because the cost of inspection using rectifying in-spection plans is so greatly influenced by the quality level ofincoming inspection lots, past information of that level isnecessary before choosing an AOQL. The AOQL plans inTable 1 give the range of incoming quality level for which eachplan is recommended. The cost of the inspection is alsodetermined by the size of the inspection lot and by the size ofthe sample. I
