1、BRITISH STANDARD BS ISO 12303:1995 Implementation of ISO 12303:1995 Plain bearings Quality characteristics Calculation of machine and process capabilitiesBSISO12303:1995 This British Standard, having been prepared under the directionof the Engineering SectorBoard, was published underthe authority of
2、 the Standards Board and comesintoeffect on 15August1995 BSI 01-2000 The following BSI references relate to the work on this standard: Committee reference MCE/12 Draft for comment 92/78676 DC ISBN 0 580 24690 6 Committees responsible for this British Standard The preparation of this British Standard
3、 was entrusted to Technical Committee MCE/12, Plain bearings, upon which the following bodies were represented: Association of Bronze and Brass Founders British Plastics Federation Copper Development Association Institution of Diesel and Gas Turbine Engineers Institution of Mechanical Engineers Soci
4、ety of Motor Manufacturers and Traders Ltd. Amendments issued since publication Amd. No. Date CommentsBSISO12303:1995 BSI 01-2000 i Contents Page Committees responsible Inside front cover National foreword ii Foreword iii Text of ISO 12303 1BSISO12303:1995 ii BSI 01-2000 National foreword This Briti
5、sh Standard reproduces verbatim ISO12303:1995 and implements it as the UK national standard. This British Standard is published under the direction of the Engineering Sector Board whose Technical Committee MCE/12 has the responsibility to: aid enquirers to understand the text; present to the respons
6、ible international committee any enquiries on interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK. NOTEInternational and European Standards, as well as overseas standards, are available from Cu
7、stomer Services, BSI, 389 Chiswick High Road, London W44AL. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from
8、legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, theISO title page, pagesii toiv, pages1 to5 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the am
9、endment table on the inside front cover.ISO12303:1995(E) ii BSI 01-2000 Contents Page Foreword iii 1 Scope 1 2 Normative reference 1 3 Definitions 1 4 Symbols and abbreviations 1 5 Machine and process capabilities as part of an SPC implementation programme 1 Annex A (informative) Example of graphica
10、l test using probability paper 4 Figure A.1 Example of a graphical test for crush height 5 Table 1 Constant for calculation of estimated standard deviation 3ISO12303:1995(E) BSI 01-2000 iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standa
11、rds 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 technical committee has been established has the right to be represented on that committee. International organ
12、izations, 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 of electrotechnical standardization. Draft International Standards adopted by the technical committees are ci
13、rculated to the member bodies for voting. Publication as an International Standard requires approval by at least75% of the member bodies casting a vote. International Standard ISO12303 was prepared by Technical Committee ISO/TC123, Plain bearings, Subcommittee SC5, Quality analysis and assurance. An
14、nex A of this International Standard is for information only.iv blankISO12303:1995(E) BSI 01-2000 1 1 Scope This International Standard specifies for plain bearings details of the calculation of machine and process capabilities for quantitative (variable) quality characteristics in accordance with I
15、SO12302. 2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based o
16、n this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 12302:1993, Plain bearings Quality characteristics Statistical pr
17、ocess control (SPC). 3 Definitions For the purposes of this International Standard, the following definitions apply. 3.1 machine capability a measure relating the actual performance of a machine to specified requirements. It is normally expressed as an index, viz. C m , C mk 3.2 process capability a
18、 measure relating the actual performance of a process to specified requirements. It is normally expressed as an index, viz. C p , C pk 3.3 statistical process control (SPC) control of quality characteristics of plain bearings during the production process by means of statistical techniques in order
19、to comply with quality requirements 3.4 quality characteristic characteristic by means of which the quality of a plain bearing is assessed 4 Symbols and abbreviations 5 Machine and process capabilities as part of an SPC implementation programme 5.1 Machine capability Machine capability studies are f
20、or evaluating the performance of a machine. They give only a short-term indication. They do not identify special cause effects in the process. A machine capability study is normally carried out on an uninterrupted run of parts of a predetermined sample number and would normally be undertaken prior t
21、o assessing process capability. Machine capability can only be determined when a normal distribution exists. 5.1.1 Machine capability index (spread only), C m The C mindex is a value used to determine the spread ratio of the machine. For the general case: For a normal distribution: 5.1.1.1 Prelimina
22、ry precautions a) A minimum of50 pieces should preferably be tested. b) Set the machine at the midpoint of the tolerance of the characteristic to be checked. c) For the study, use parts which have been manufactured consecutively. C m Machine capability index (spread only) C mk Machine capability ind
23、ex (spread and setting) C p Process capability index (spread only) C pk Process capability index (spread and setting) d 2 Factor G Judgement of normality LL Lower specified limit UL Upper specified limit k Number of subgroups n Subgroup size R Subgroup range Arithmetic mean of subgroup ranges x i Ob
24、servations (readings) Arithmetic mean of observations (readings) Arithmetic mean of subgroup means Standard deviation Estimated standard deviation R x = x ISO12303:1995(E) 2 BSI 01-2000 5.1.1.2 Test for normality 5.1.1.2.1 Graphical test using probability paper (for an example, seeFigure A.1) a) Fil
25、l in the measured values in the frequency tabulation of the probability paper. b) Check the histogram for normal distribution. c) Determine the arithmetic mean, and standard deviation, . d) Determine the cumulative frequency values and plot points on the probability paper. e) Draw a straight line on
26、 the graph which best fits the experimental data. If a straight line can be fitted through the experimental points, the normality can be accepted. Otherwise, it shall be rejected and the formulae for C mand C mkdo not apply. 5.1.1.2.2 Statistical test a) Arithmetic mean of observations (readings), ,
27、 is given by b) Standard deviation, , is given by 5.1.1.2.3 Normal distribution test a) Judgement of normality, G, is given by Limiting values 0,5 b) Machine capability index, C m , is given by 5.1.2 Machine capability index (spread and setting), C mk The C mkindex is a value used to determine the s
28、pread of the machine and the setting of the mean value of the frequency distribution within the limits of the specification. The value of C mkis given by whichever is the smaller value. The value of C mkshould beW 1,33 (1,67). 5.2 Process capability Process capability indices are more representative
29、 of the quality level achieved, since the effects of equipment, materials, methods, environment and time are taken into account. Process capability can only be determined when a normal distribution exists. 5.2.1 Process capability index (spread only), C p The C pindex is a value used to determine th
30、e spread of the manufacturing process. a) A minimum of100 observations (readings) is needed. Gather observations from k subgroups of n consecutive parts, taken at regular intervals over a significant period of time. b) Arithmetic mean of observations (readings), , is given by c) Subgroup range, R, i
31、s given by R = x i, max x i, min d) Arithmetic mean of subgroup means, , is given by e) Arithmetic mean of subgroup ranges, is given by f) Estimated standard deviation, , is given by where the factor d 2is given inTable 1. g) Process capability index, C p , is given by 5.2.2 Process capability index
32、 (spread and setting), C pk The C pkindex is a value used to determine the spread of a manufacturing process and the setting of the mean value of the frequency distribution within the limits of the specifications. The value of C pkis given by whichever is the smaller value. The value of C pkshould b
33、eW 1 (1,33). x x x = x R ISO12303:1995(E) BSI 01-2000 3 Table 1 Constant for calculation of estimated standard deviation Subgroup size Factor a n d 2 2 1,128 3 1,693 4 2,059 5 2,326 6 2,534 7 2,704 8 2,847 9 2,970 10 3,078 a Confidence level of99,73%.ISO12303:1995(E) 4 BSI 01-2000 Annex A (informati
34、ve) Example of graphical test using probability paper Figure A.1 gives an example of a graphical test for crush height.ISO12303:1995(E) BSI 01-2000 5 Figure A.1 Example of a graphical test for crush heightBS ISO 12303:1995 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI i
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