Using process capability indices to express process capability has made the setting and communication of quality goals much simpler, and their use is expected to continue to increase. There is quit some confusion about the use of these indices. Read process capability indices in theory and practice ebook. The comparison is made by forming the ratio of the spread between the process specifications the specification width to the spread of the process values, as measured by 6 process standard deviation units the process. Process capability analysis with focus on indices for one. Samples from the batch may need to be quite large to be representative of the variation in the batch. Request pdf on may 1, 2000, lora zimmer and others published process capability indices in theory and practice find, read and cite all the research you need on researchgate. Pdf download process capability indices in theory and practice pdf online. The distribution of the process considered is normal. Based on the yield analysis among capability indices c pk, c pm, and c pmk, the result illustrates that the three indices provide the same lower bounds on process yield for normally distributed processes, that is, yield. Pdf process capability indices in theory and practice.
Standard practice for process and measurement capability indices. Pearnb, samuel kotzc a department of industrial engineering and systems management, feng chia university, 100, wenhwa road, seatwen, taichung 40724, taiwan. Fixing values for minimum acceptable process capability targets is a matter of personal opinion. Process capability indices in theory and practice book, 1998. Pearnb, samuel kotzc a department of industrial engineering and systems management, feng chia university, 100, wenhwa road, seatwen, taichung 40724, taiwan b department of industrial engineering and management, national chiao tung university, taiwan. More and more efforts have been devoted to studies and applications of process capability indices. Based on the process capability analysis one can determine how the process performs relative to its product requirements or specifications. It is important to determine if when the quality characteristics of a product are assembled the final. Read process capability indices in theory and practice. It differs from process capability in that process performance only applies to a specific batch of material. Process capability analysis and process analytical technology. Process capability cp, cpk and process performance pp, ppk. There are several capability indices cp, cpk, ppk, cpm, ncpk. Process capability indices pcis, cp, ca, cpk, cpm, and cpmk have been developed in certain manufacturing industry as capability measures based on various criteria, including process consistency, process departure from a target, process yield, and process loss.
Applications of process capability and process performance. But the statistical measurements of cp, cpk, pp, and ppk may provide more insight into the process. The index is usually used to relate the natural tolerance 3. Process capability indices for skewed populations chang. Process capability indices compare the variability of a process quality measure against product specifications or tolerances and assume the process is in a state of statistical control. Adekeye redeemers university department of mathematical sciences redemption camp mowe, nigeria. Expected relative loss fraction nonconforming process capability indices process consistency process relative departure quality assurance. Process capability calculations with nonnormal data in the. An important part within process capability analysis is the use of process capability indices. An overview of theory and practice on process capability. The relationship between the actual process performance and the specification limits or tolerance may be quantified using suitable process capability indices. Statistical methods in process management capability and performance part 4. It is important to determine if when the quality characteristics of a product are assembled the final product.
Different from c p, c pk describes how well the process fits within the specification limits, taking. Process capability uses the process sigma value determined from either the moving range, range or sigma control charts pp and ppk are used for process performance. This book describes all of the various indices and shows how to use them in a format that is easy to useand understand. An overview of theory and practice on process capability indices for quality assurance. The goal is to ensure process output that is capable of consistently meeting the specifications. Journal of quality technology 341, 119 survey but from a different perspective. An assessment of the most widely used process capability indices is also presented.
Process capability indicesan overview of theory and practice leslie j. Cp, cpl, cpu, and cpk are the four most common and timed tested measures of process capability. Process capability indicesan overview of theory and. Process capability index example a manufacturing process produces a certain part with a mean diameter of 2 inches and a standard deviation of 0. In this article we will discuss the most common used indices cp, cpk, pp and ppk. Values near or below zero indicate processes operating off target \displaystyle \hat \mu far from t or with high variation. Pearn and samuel kotz, an overview of theory and practice on process capability indices for quality assurance, international journal of production economics, 117, 2, 338, 2009. The process capability indices have been used widely in the manufacturing industry to provide a numerical measure on whether a manufacturing process is capable of producing items meeting the capability requirement preset by the product designer. The primary motivation for this dissertation was to examine the use of pcis in the measurement of key quantifiable test results. The process capability index c pk is used to provide an indication of the variability associated with a process and how a process has conformed to its specifications. A practical implementation of the process capability indices. If these assumptions are not met, the resulting statistics may be highly unreliable. Process capability indices datalyzerspectrum denmark. Process capability indices in theory and practice samuel.
Specification limits and process capability indices 4. An overview of theory and practice on process capability indices for quality assurance chienwei wua, w. Porter the european centre for total quality management, university of bradford management centre, emm lane, bradford, w. Astm e2281 15 standard practice for process capability and. Process capability compares the output of an in control process to the specification limits by using capability indices. This book therefore covers material essential for quality engineers and applied statisticians who are interested in maximizing process capability. Jul 01, 2016 read book online now process capability indices in theory and practice ebook free.
Usl lsl cp process is not a capable process since cp mar 12, 2012 2000. An important part of any spc implementation is the use of process capability indices. Process capability indices based on median absolute deviation. Unfortunately, there are few studies about the product capability. To compare a process with customer requirements or specifications, it is common practice to think of capability in terms of the proportion of the process output that is within product specifications or tolerances. Process capability analysis is an important part of an overall quality. So, the main aim of this thesis is to present an alternative to determine the product capability. Process capability indices based on median absolute deviation kayode s. Usl lsl cp process is not a capable process since cp process capability indices are constructed to express more desirable capability with increasingly higher values. Process capability compares the output of an incontrol process to the specification limits by using capability indices. Abstract process capability is the performance of a process under normal and in control conditions. The comparison is made by forming the ratio of the spread between the process specifications the specification width to the spread of the process values, as measured by 6 process standard deviation units the process width. Specification limits and process capability indices. Process capability cp, cpk and process performance pp.
Process capability indices pcis, in particular c p, c a, c pk, c pm and c pmk, which provide numerical measures of whether or not a manufacturing process is capable to meet a. Using process capability indices to express process capability has simplified the process of setting and communicating quality goals, and their use is expected to continue to increase. It is noted in certain recent quality assurance and capability analysis works that the three indices, cpk, cpm, and cpmk provide the. Process capability indices in theory and practice request pdf. It is noted in certain recent quality assurance and capability analysis works that the three indices, cpk, cpm. Six sigma process performance is reported in terms of sigma. Pdf process capability and capability index cp and cpk. In both cases we want to try to verify if the process can meet to meet customer ctqs requirements. Generally you use this when a process is too new to determine if it is under statistical control.
Process capability indices pcis, c p, c a, c pk, c pm, and c pmk have been developed in certain manufacturing industry as capability measures based on various criteria, including process consistency, process departure from a target, process yield, and process loss. Process capability indices measure the degree to which your process produces. Pdf process capability for a complete electronic product. An example of this is for a short preproduction run. Connection between the process capability and six sigma 3.
Learn the definitions, interpretations and calculations for cp, cpk, pp and ppk. In a later modules we will discuss capability analysis for nonnormal data. Process capability indices for shape parameter of weibull distribution. Sep 01, 2016 pdf download process capability indices in theory and practice pdf online. Introduction process capability analysis deals with how to assess the capability of a manufacturing process, where information about the process is used to improve the capability. Understanding process capability indices stefan steiner, bovas abraham and jock mackay institute for improvement of quality and productivity department of statistics and actuarial science university of waterloo waterloo, ontario n2l 3g1 1. This thesis focuses on process capability indices in the situation when the specification limits are onesided. It also discusses the more recent developments during the years 20022006. Process capability indices pcis, cp, ca, cpk, cpm, and cpmk have been developed in certain manufacturing industry as capability measures based on various criteria, including process consistency. Standard practice for process and measurement capability.
Process capability indicesan overview of theory and practice. Abstract process capability is the performance of a process under normal and in. Process capability indices, as a process performance measure, have become very popular in assessing the capability of manufacturing processes in practice during the past decade. The lower and upper engineering specification limits are 1. Generally you use this when a process is under statistical control. Read book online now process capability indices in theory and practice ebook free. Process capability indices in theory and practice book. Astm e2281 15 standard practice for process capability. There are many studies about the process capability indices which are used to study if a process can meet specification. Measures of process capability process capability indices.