Process capability is the longterm performance level of the process after it has been brought under statistical control. In both cases we want to try to verify if the process can meet to meet customer ctqs requirements. The process capability metrics are provided to support quality improvement methodologies such as six sigma, design for six sigma dfss, and lean principles. The capability maturity model cmm is a development model created in 1986 after a study of data collected from organizations that contracted with the u. Process capability index an overview sciencedirect topics. Strategic process performance metrics serve to show if the organization is achieving the objectives set by senior management, socalled strategic goals. Process capability and process performance metrics introduction traditionally, process capabilityperformance index studies are conducted to assess a process relative to specification criteria. Process capability is a measure of the inherent process performance. A systematic and solid corporate performance management process is of paramount importance for organizations to survive in this information. The importance of a capability can be tied to specific outcomes and metrics. In the example above, the process used to collect the samples allows consideration of each daily collection as a particular rational subgroup. Process capability metrics formulas the process capability metrics are provided to support quality improvement methodologies such as six sigma, design for six sigma dfss, and lean principles. Many of todays quality management philosophies, such as six sigma, focus on reducing variations and scrap. Measure of how well the data fits between the lsl and usl.
It differs from process capability in that process performance only applies to a specific batch of material. Process capability determines if a process will deliver a product or service that meets the customers requirements. To predict the extent to which the process will be able to hold tolerance or customer. Process performance is only used when process control cannot be evaluated. Process capability is defined as the minimum spread of a specific measurement variation which will include 99. The cpk associated with a process or a group of items is either the value for cpu or cpl, whichever calculation results in the smallest number. Process capability metrics you dont have to be a statistician to understand process capability metrics. Walter shewart working in the bell telephone laboratories in the 1920s conducting research on methods to improve quality and lower. Accurate, actionable and timely consistent metrics avoid confusing requirements and expectations internal and external balanced score card vertical and hori zontal alignment catchball process to deploy metrics to all levels. Descriptions and formulas for these metrics are described below.
Process performance generally uses sample sigma in its calculation. An example of this is for a short preproduction run. Metrics and performance measurement system for the lean enterprise. The proposed metric consists of two economic capability measures. In a later modules we will discuss capability analysis for nonnormal data. Process capability is defined as a statistical measure of the inherent process variability of a given characteristic. Procedures when dealing with nonnormal data will be considered in the following edition of extraordinary sense. Attributes capability measures are taken directly from attributes control charts. Customer requirements are defined using an upper specification limit usl and a. Capability metrics evaluation and recommendations asq 1106 section meeting april 21, 2011. Chapter 11 process capability and process performance. Various regulatory authorities such as validation guidance for. Process capability by sanjaya kumar saxena the capability of a process is a statistical indicator of how well it is functioning, or, in other words, how successful it is at running within its specified limits. Process capability uses the process sigma value determined from either the moving range, range or sigma control charts.
Process capability is simply a measure of how good a metric is performing against and established standards. Walter shewart working in the bell telephone laboratories in the 1920s conducting research on methods to improve quality and lower costs. Samples from the batch may need to be quite large to be representative of the variation in the. There is seldom much argument anymore about the necessity of having metrics at the process level to enable process owners and. The capability maturity model integration cmmi project was formed to sort out the problem of using multiple models for software development processes, thus the cmmi model has superseded the cmm model, though the cmm model continues to be a general theoretical process capability model used in the public domain. Process capability cp, cpk and process performance pp. Measurement process capability trends and approaches eva kurekova abstract a measurement control system ensures that measuring equipment and measurement processes are fit for their intended use and its important in achieving product quality objectives.
Introduction a process capability index is a numerical summary that compares the behavior of a product. Generally you use this when a process is too new to determine if it is under statistical control. Process capability indices can help identify opportunities to improve manufacturing process robustness, which ultimately improves product quality and product supply reliability. In 2007 a generic or public version of this assessment instrument was published on the cert web page as the incident management capability metrics. In this case, besides the variation in quantity, the process mean also affects the indicators. In the absence of any special or assignable causes of variation, a process will still have some inherent variability. A capability baseline is essentially a snapshot of the process capability at a time. He developed the concept of control with regard to variation, and came up with statistical process control charts which provide a simple way to. Research efforts in the area of process capability have largely been devoted to finding a better process capability index pci and to a lesser extent on the stochastic behavior of the estimated pcis 1, 2.
The process capability analysis a tool for process performance measures and metrics a case study october 2014 international journal for quality research 80620. Fred spiring is a senior member of the american society of quality, adjunct professor in the department of statistics, the university of manitoba, and a retired director of pollard banknote ltd. You can use a process capability study to assess the ability of a process to meet specifications. There is, of course, much more that can be said about the case of nonnormal data. They appear in forecast charts when a forecast definition includes a lower specification limit lsl, upper specification limit usl, or both. 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. Process capability compares the output of an incontrol process to the specification limits by using capability indices. Good capability models are relevant to the business and defined in business terms.
The comparison is made by forming the ratio of the spread between the process. A widely used tool to assist in determining these goals is the balanced scorecard. Level 3 metrics, measurement processes, and goal setting are generally inadequate. Process capability studies are done on the machines to find out the capability of individual mcs. 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. Chapter 11 process capability and process performance metrics. 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. If these assumptions are not met, the resulting statistics may be highly unreliable. Cp capability index cpk capability centering index. The capability of a process specifies what is the range of expected outcomes if the process is followed. Alternatively, you could use a process capability index that applies to nonnormal distributions. Process capability measurements allow us to summarize process capability in terms of meaningful percentages and metrics. Performance measurement is the process of measuring efficiency, effectiveness and capability, of an action or a process or a system, against given norm or target. Capabilities models provide a fairly stable view of the business because the fundamental capabilities rarely change.
Adequate resource commitment manpower, money, facilities and training evaluate relevancy over time. Capabilities are described in a capability model which is a hierarchical description of what the business does. Pdf the process capability analysis a tool for process. Interpret the key results for normal capability analysis. Six sigma process performance is reported in terms of sigma. Methods for defining andanalyzing keyea performance metrics.
A new economic approach to process capability assessment is presented, which differs from the commonly used engineering metrics. The observed performance as well as the performance relative to the normal distribution are output. Process capability ratios such as c p and c pk are produced. The distribution of the process considered is normal. Enhanced process capability analysis report smarter solutions. Measuring process performance one of the most important but frequently most challenging and vexing aspects of installing business process management in an organization is metrics. A process has to be stable before it can be determined to be capable. Various regulatory authorities such as validation guidance for industry 2011, international conference on harmonisation ich q10 2009, the health canada guidelines 2009, health science authority, singapore. Process capability is also the ability of the combination of people, machine, methods, material, and measurements to produce a product that will consistently meet the design requirements or customer expectation.
Enhanced process capability analysis report smarter. Process capability cp, cpk and process performance pp, ppk. Capability is a measure of ability required to do both the job. The capability ratio indicates what proportion of tolerance is occupied by the data. You can use a processcapability study to assess the ability of a process to meet. Six is the number of sigma measured in a process, when the variation around the target is such that less than four outputs out of one million are defects under.
Chapter 255 capability analysis introduction this procedure summarizes the performance of a process based on userspecified specification limits. Lean government metrics guide page 1 lean government metrics guide this lean government metrics guide is a resource to help government agencies understand and select metrics to support their implementation of lean and six sigmatwo powerful and proven methods to improve organizational performance. The sigma scale of measure is correlated to other metrics of six sigma such as defects per million opportunities dpmo, throughput yield, process capability indices cp and cpk, etc. But the statistical measurements of cp, cpk, pp, and ppk may provide more insight into the process. The cpm is an uncommonly used capability index that can be used when you have a target value. During a quality improvement initiative, such as six sigma, a capability estimate is typically obtained at the start and end of. The c pk capability rate is calculated by the formula. Process capability an overview sciencedirect topics.
Measure of how well the data is centered between the lsl and usl. The following paper introduces theoretical foundations for determination of the mea. Introduction to statistical process control techniques. The capability ratio indicates what proportion of tolerance is. The proposed metric consists of two economic capability. Metrics and performance measurement system for the lean. The following table lists and defines the statistics shown in capability metrics view and indicates whether each statistic is displayed for longterm or shortterm data. The observed performance as well as the performance. Statistical process control is the application of statistical methods to the measurement and analysis of variation process.
Competitive companies understand that satisfying customers needs and running a successful operation requires a system that is dependable, predictable and consistent. The integrated enterprise excellence iee business management system for 30,000footlevel predictive performance reporting is the approach that is described in the article. Process capability analysis tells us how well a process meets a set of specification limits, based on a sample of data taken from a process. Metrics should foster process understanding and motivate. Learn the definitions, interpretations and calculations for cp, cpk, pp and ppk. Process capability indices are intended to provide single number assessment of the ability of a process to meet specification limits on quality characteristics of interest. A free online reference for statistical process control, process capability analysis, measurement systems analysis, and control chart interpretation, and other quality metrics. However, if a boxcox transformation can be successfully performed, one is encouraged to use it. Capability building has remained a high strategic priority since we first surveyed executives on organizational capabilities in 2010.
When a process is in statistical control, ppk and cpk are approximately equal. The difference between ppk and cpk represents the improvement in process capability that you could. The process capability analysis report linkedto pdf highlights issues with traditional process capability indices reporting and what can be done to resolve the problem. Accurate, actionable and timely consistent metrics avoid confusing requirements and expectations internal and external balanced score card vertical and hori zontal alignment catchball. One statistic is called cnpk for nonparametric cpk.
Four years later, many companies are using the same approaches to learning and skill developmentnamely, onthejob teachingthat were most common in the earlier survey. The foundation for statistical process control was laid by dr. The equations for process capability performance indices are quite simple but are very sensitive to the input value for standard deviation. The basic three capability indices commonly used in manufacturing industries are cp, cpk,cpm and cpmk. 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.
Lean government metrics guide page 1 lean government metrics guide this lean government metrics guide is a resource to help government agencies understand and select metrics to support their. Competitive companies understand that satisfying customers needs and running a successful operation requires a system that is dependable. Customer requirements are defined using an upper specification limit usl and a lower specification limit lsl. Capability maturity model, cmm and cmmi are registered in the u. Measurement process capability trends and approaches. Capability analysis for attributes data collection tools. A popular transformation is the boxcox transformation. It can be used to establish baseline for the process and measure the future state performance of the process for comparison.
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