ASTM_D_5406_-_93_2011.pdf

Designation:D540693(Reapproved 2011)Standard Practice forRubberCalculation of Producers Process PerformanceIndexes1This standard is issued under the fixed designation D5406;the number immediately following the designation indicates the year oforiginal adoption or,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 practice provides a calculation procedure and aformat for reporting the process performance of a manufactur-ing operation for a rubber or rubber product.1.2 This practice is specifically designed to be used fortechnically significant properties of the final product.2.Referenced Documents2.1 Quality Assurance for the Chemical and Process Indus-tries,American Society for Quality Control,Chemical andProcess Industries Division,Chemical Interest Committee,1987.23.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 common cause variationthat residual variation in-herent in any process that(1)is operating in a state of statisticalcontrol,and(2)is operating at some recognized or ascertainedlevel of technological competence.3.1.2 lower specification limit(LSL)the producers mini-mum permissible value of any relevant measured productproperty.3.1.3 Pp8 producers process performance indexthe ratioof the difference(USL LSL)to the total process variation;the index does not consider where the process is centered.(See7.4.)3.1.4 Ppk8 producers process performance indextheminimum of two ratios:(1)the ratio of the difference(USL process mean)to one-half of the total process varia-tion,or(2)the ratio of the difference(process mean LSL)toone-half of the total process variation;the magnitude of theminimum index value,used with the Pp8 index,indicates howwell the process mean is centered.(See 7.5.)3.1.5 special cause variationthat variation attributable tocertain specific or assignable sources that have been(or maybe)discovered through an investigation of the process.3.1.6 target valuethe aiming point of the process;this isoften(USL+LSL)/2.3.1.7 total process variationa range,along the measuredproperty scale,defined as six times the standard deviation(determined under specified process conditions);the variationmay contain either common or combined common and specialcause sources.3.1.8 upper specification limit(USL)the producers maxi-mum permissible value of any relevant measured productproperty.4.Summary of Practice4.1 During the production of any product,certain physicalor chemical properties,or both,are normally measured tocontrol the properties of the final product.When enough datahave been accumulated to form a sufficient database,it ispossible to determine the centering(mean)and variation(rangeor standard deviation)of the process property distribution.These results may be informally compared to the desired targetand specification limits to determine if the process is producingan acceptable product.4.2 On a more formal basis,the two process performanceparameters,the“process mean”and the“standard deviation,”are used to calculate two Producers Process PerformanceIndexes designated as Pp8 and Ppk8.These indexes allow astandardized comparison of an actual process performance tothe general specifications,the comparison of different pro-cesses for producing the same product,or comparison of thesame process at different times.5.Significance and Use5.1 This practice is used to evaluate the conformance of aproduction process to specifications when(1)special causes ofvariation may be present,and(2)the process may not be in astate of statistical control.This evaluation may also be used tocompare different manufacturing operations for conformanceto specifications.1This practice is under the jurisdiction ofASTM Committee D11 on Rubber andis the direct responsibility of Subcommittee D11.16 on Application of StatisticalMethods.Current edition approved May 1,2011.Published July 2011.Originally approvedin 1993.Last previous edition approved in 2006 as D5406 93(2006).DOI:10.1520/D5406-93R11.2Available from American Society for Quality(ASQ),600 N.Plankinton Ave.,Milwaukee,WI 53203,http:/www.asq.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.Background and Precautions6.1 A process is said to be in a state of statistical controlwhen there are only common causes of variation present(noassignable causes).Astate of statistical control is a requirementto perform a process capability calculation which can be usedfor prediction.A state of statistical control is not required toperform the process performance calculations covered by thispractice.6.2 Although the defining calculation equations for theproducers process performance indexes(Pp8 and Ppk8)givenin 7.4 and 7.5 bear a resemblance to the defining equations forthe process capability indexes(Cp and Cpk),a legitimatecalculation of Cp and Cpk ca