1、Designation: B 697 88 (Reapproved 2005)Standard Guide forSelection of Sampling Plans for Inspection ofElectrodeposited Metallic and Inorganic Coatings1This standard is issued under the fixed designation B 697; 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 (e) 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
3、inspection 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 B 602 by giving more information on sampling in-spection and by providing addition
4、al sampling plans for theuser who finds the limited choice of plans in Test MethodB 602 to be 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 o
5、r does 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 o
6、f nonconforming 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 co
7、st of 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
8、requires 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 redu
9、ce inspec-tion cost and increase quality protection. Information onvariables plans is given in Test Method B 762, MIL-STD-414,ANSI/ASQC Z1.9-1979, and Refs (1-2).2. Referenced Documents2.1 ASTM Standards:2B 602 Test Method of Attribute Sampling of Metallic andInorganic CoatingsB 762 Test Method of V
10、ariables Sampling of Metallic andInorganic Coatings2.2 ANSI Standard:3ANSI/ASQC Z1.91979 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
11、 and Tables 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 sampli
12、ng plan,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.This quanti
13、ty (called the inspection lot in this guide) may be ashipment from a supplier, may be articles that are ready for a1This guide is under the jurisdiction of ASTM Committee B08 on Metallic andInorganic Coatings and is the direct responsibility of Subcommittee B08.10 on TestMethods.Current edition appr
14、oved May 15, 2005. Published June 2005. Originallyapproved in 1981. Last previous edition approved in 1999 as B 697 88 (1999).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,
15、 refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.4Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-50981C
16、opyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.subsequent manufacturing operation, or may be articles readyfor shipment to a customer.3.3 When acceptance sampling is done, several of thearticles in the inspection lot are selected at r
17、andom (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. If thenumber of nonconforming articles in t
18、he 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 because, depending on the circumstances,l
19、ots 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 disposition of an inspec-tion lot is based on the
20、 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 level will be accepted.There are only two
21、 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 will always be made. The othersituation is
22、 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 in an inspection lot or it means the avera
23、gepercentage 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 quality, decreasedquality, and poorer quality me
24、an 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 will always be accepted, and lotsthat conta
25、in 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 articles, and (2)ina series of inspection
26、 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, acceptance sampling does not, byitself, result in
27、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 a sampling plan is a decision about thepe
28、rcentage 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 have to be inspected twice.3.8 The protectio
29、n 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 characteristic(OC) curve. Fig. 1 is the O
30、C 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 vertical axis is the probability, asa perce
31、ntage, 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 probability of acceptance decreases. For ex-ample, a
32、s 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 meanings.One is the probability that a partic
33、ular 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 theinspection lot is at least ten times big
34、ger 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 inspection lots; usually it is the qual
35、ity 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 levelthat will result in the rejection of a high percentage of incomingFIG. 1 Operating Characteristic Curve for Single Sample,Attributes Sampling Plan, Sample Size
36、 = 55, AcceptanceNumber = 2B 697 88 (2005)2inspection 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 that will be accepted 95 and rejected 90 %of
37、 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 Rectifying Inspection:3.11.1 As stated in
38、 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 articles. The now 100 %-conforminginspection lot
39、 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 quality level is improved can becalculated
40、 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 improved over the incoming. If the quality level
41、of 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 quality will be poorer than these two extrem
42、es, 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 worst possible AOQ for agiven plan is called
43、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 quality level ofincoming lots is high, the im
44、provement 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 5The AOQs and AOQLs in this guide are calc
45、ulated 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 different from those in this guide. Chapter
46、16 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 plan used. However,rectifying inspection can
47、 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 of 550, the average number ofarticles inspe
48、cted 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 incoming quality level of 2.1 % theamount of
49、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. If rectifying inspection is to be used on a
