SANS 21747-2008 Statistical methods - Process performance and capability statistics for measured quality characteristics《统计方法 评估质量特征的过程性能和性能统计学》.pdf

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1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA

2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any

3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. ISBN 978-0-626-21178-3 SANS 21747:2008 Edition 1 ISO 21747:2006 Edition 1SOUTH AFRICAN NATIONAL STANDARD Statistical methods Process performance and capa

4、bility statistics for measured quality characteristics This national standard is the identical implementation of ISO 21747:2006 and is adopted with the permission of the International Organization for Standardization. Published by Standards South Africa 1 dr lategan road groenkloof private bag x191

5、pretoria 0001 tel: 012 428 7911 fax: 012 344 1568 international code + 27 12 www.stansa.co.za Standards South Africa This standard may only be used and printed by approved subscription and freemailing clients of the SABS.SANS 21747:2008 Edition 1 ISO 21747:2006 Edition 1 Table of changes Change No.

6、Date Scope National foreword This South African standard was approved by National Committee StanSA TC 169, Applications of statistical methods, in accordance with procedures of Standards South Africa, in compliance with annex 3 of the WTO/TBT agreement. This SANS document was published in April 2008

7、. This standard may only be used and printed by approved subscription and freemailing clients of the SABS. Reference number ISO 21747:2006(E) ISO 2006INTERNATIONAL STANDARD ISO 21747 First edition 2006-07-01 Statistical methods Process performance and capability statistics for measured quality chara

8、cteristics Mthodes statistiques Performances de processus et statistiques daptitude pour les caractristiques de qualit mesures SANS 21747:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 21747:2006(E) PDF disclaimer This PDF file may con

9、tain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsib

10、ility of not infringing Adobes licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation pa

11、rameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. ISO 2006 All rights reserved. Unless other

12、wise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright

13、 office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2006 All rights reservedSANS 21747:2008This standard may only be used and printed by approved subscription and freemailing clients of the SAB

14、S.ISO 21747:2006(E) ISO 2006 All rights reserved iii Contents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references . 1 3 Terms and definitions. 1 3.1.1 Variation-related concepts. 1 3.1.2 Fundamental process performance and process capability related terms 3 3.1.3 Process performance m

15、easured data 6 3.1.4 Process capability measured data . 8 3.2 Specifications, values and test results. 10 3.2.1 Specification-related concepts 10 4 Symbols and abbreviated terms . 12 5 Process analysis. 13 6 Time-dependent distribution models 13 7 Process capability and performance indices 22 7.1 Me

16、thods for the determination of performance and capability indices Overview 22 7.2 General geometric method (M1 l,d ) 23 7.3 Explicit inclusion of additional variation (M2 l,d,a ). 26 7.4 Alternative method of explicit inclusion of additional variation (M3 l,d,a ). 27 7.5 Calculation of fractions non

17、conforming (M4) 28 7.6 One-sided specification limits. 29 8 Reporting process performance/capability indices 31 Bibliography . 32 SANS 21747:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 21747:2006(E) iv ISO 2006 All rights reservedFo

18、reword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a tec

19、hnical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters o

20、f electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated

21、to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible fo

22、r identifying any or all such patent rights. ISO 21747 was prepared by Technical Committee ISO/TC 69, Application of Statistical Methods, Subcommittee SC 4, Application of Statistical Methods and Process Management. SANS 21747:2008This standard may only be used and printed by approved subscription a

23、nd freemailing clients of the SABS.ISO 21747:2006(E) ISO 2006 All rights reserved v Introduction Many standards have been created concerning the quality capability/performance of processes by international, regional and national standardization bodies and also by industry. However, all of them assum

24、e that the process is in a state of statistical control, with stationary, normal processes behaviour. However, a comprehensive analysis of production processes shows that it is very rare for processes to remain in a normally distributed, stationary state. In recognition of this fact, this Internatio

25、nal Standard provides a framework for estimating the quality capability/performance of industrial processes for an array of standard processes. These standard processes are categorized by the stability of the first and second distributional moments, as to whether they are constant, change systematic

26、ally, or randomly. As such, the quality capability/performance can be assessed for very differently shaped distributions with respect to time. SANS 21747:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.SANS 21747:2008This standard may only

27、be used and printed by approved subscription and freemailing clients of the SABS.INTERNATIONAL STANDARD ISO 21747:2006(E) ISO 2006 All rights reserved 1 Statistical methods Process performance and capability statistics for measured quality characteristics 1 Scope This International Standard describe

28、s a procedure for the determination of statistics in order to estimate the quality capability of product and process characteristics. The process results of these quality characteristics are tabularized into eight possible distribution types. Calculation formulae for the statistical values are place

29、d with every distribution. These statistics relate to continuous quality characteristics exclusively. This International Standard is applicable to processes in any industrial or economical sector. NOTE This method is usually applied in case of a great number of serial process results, but it can als

30、o be used for small series (a small number of process results). 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced documen

31、t (including any amendments) applies. ISO 9000:2005, Quality management systems Fundamentals and vocabulary 3 Terms and definitions For the purpose of this document, the terms and definitions given in ISO 9000 and the following apply. 3.1 quality characteristic inherent characteristic of a product,

32、process or system related to a requirement NOTE 1 Inherent means existing in something, especially as a permanent characteristic. NOTE 2 A characteristic assigned to a product, process or system (e.g. the price of a product, the owner of a product) is not a quality characteristic of that product, pr

33、ocess or system. ISO 9000:2005, 3.5.2 3.1.1 Variation-related concepts 3.1.1.1 variation difference between values of a characteristic NOTE Variation is often expressed as a variance or standard deviation. ISO 3534-2: 1) , 2.2.1 1) To be published. (Revision of ISO 3534-2:1993) SANS 21747:2008This s

34、tandard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 21747:2006(E) 2 ISO 2006 All rights reserved3.1.1.2 inherent process variation variation (3.1.1.1) in a process when the process is operating in a state of statistical control NOTE 1 When it is expr

35、essed in terms of standard deviation, the subscript “w” is applied, (e.g. w , S w , or s w ), indicating inherent. See also 3.1.4.1, NOTE 2. NOTE 2 This variation corresponds to “within subgroup variation”. ISO 3534-2:, 2.2.2 3.1.1.3 total process variation variation (3.1.1.1) in a process due to bo

36、th special causes (3.1.1.4) and random causes (3.1.1.5) NOTE 1 When it is expressed in terms of standard deviation, the subscript “t” is applied (e.g. t , S tor s t ), indicating total. See also 3.1.3.1, Note 3. NOTE 2 This variation corresponds with the combination of the “within-subgroup variation

37、” and the “between-subgroup variation”. ISO 3534-2:, 2.2.3 3.1.1.4 special cause process variation source of process variation other than inherent process variation (3.1.1.2) NOTE 1 Sometimes “special cause” is taken to be synonymous with “assignable cause”. However, a distinction is recognized. A s

38、pecial cause is assignable only when it is specifically identified. NOTE 2 A special cause arises because of specific circumstances that are not always present. As such, in a process subject to special causes, the magnitude of the variation from time to time is unpredictable. ISO 3534-2:, 2.2.4 3.1.

39、1.5 random cause common cause chance cause process variation source of process variation that is inherent in a process over time NOTE 1 In a process subject only to random cause variation, the variation is predictable within statistically established limits. NOTE 2 The reduction of these causes give

40、s rise to process improvement. However, the extent of their identification, reduction and removal is the subject of cost/benefit analysis in terms of technical tractability and economics. ISO 3534-2:, 2.2.5 3.1.1.6 stable process process in a state of statistical control constant mean process subjec

41、t to only random causes (3.1.1.5) NOTE 1 A stable process will generally behave as though the samples from the process at any time are simple random samples from the same population. NOTE 2 This state does not imply that the random variation is large or small, within or outside of specification, but

42、 rather that the variation (3.1.1.1) is predictable using statistical techniques. SANS 21747:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 21747:2006(E) ISO 2006 All rights reserved 3 NOTE 3 The process capability (3.1.4.1) of a stabl

43、e process is usually improved by fundamental changes that reduce or remove some of the random causes present and/or adjusting the mean towards the preferred value. NOTE 4 In some processes, the mean of a characteristic can have a drift or the standard deviation can increase due, for example, to wear

44、 out of tools or depletion of concentration in a solution. A progressive change in the mean or standard deviation of such a process is considered due to systematic and not random causes. The results, then, are not simple random samples from the same population. ISO 3534-2:, 2.2.7 3.1.1.7 out-of-cont

45、rol criteria set of decision rules for identifying the presence of special causes (3.1.1.4) NOTE Decision rules may include those relating to points outside of control limits, runs, trends, cycles, periodicity, concentration of points near the centre line or control limits, unusual spread of points

46、within control limits (large or small dispersion) and relationships among values within subgroups. ISO 3534-2:, 2.2.8 3.1.2 Fundamental process performance and process capability related terms 3.1.2.1 distribution of a characteristic information on the probabilistic behaviour of a characteristic NOT

47、E 1 The distribution of a characteristic can be represented, for example, by ranking of the values of the characteristic and showing the resulting pattern of measures or scores in the form of a tally chart or histogram. Such a pattern provides all of the numerical value information on the characteri

48、stic except for the serial order in which the data arises. NOTE 2 The distribution of a characteristic is dependent on prevailing conditions. Thus, if meaningful information about the distribution of a characteristic is desired, the conditions under which the data is collected should be specified. N

49、OTE 3 It is important to know the class of distribution, for instance, normal or log-normal, before predicting or estimating process capability and performance measures and indices or fraction nonconforming. ISO 3534-2:, 2.5.1 3.1.2.2 class of distributions particular family of distributions (3.1.2.1) each member of which has the same common attributes by which the family is fully specified EXAMPLE 1 The two-parameter, symmetrical bell-shaped, normal distribution with parameters mean and standa