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<title>Process capability</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Process capability</span></span>

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</style><div role="note" class="hatnote navigation-not-searchable">This article is about the quantifiable measure of a process. For software process capability, see <a href="Capability_Maturity_Model" title="Capability Maturity Model">Capability Maturity Model</a> and <a href="ISO/IEC_15504" title="ISO/IEC 15504">ISO/IEC 15504</a>.</div>

<p>The <b>process capability</b> is a measurable property of a <a href="Process_(engineering)" title="Process (engineering)">process</a> to the specification, expressed as a <a href="Process_capability_index" title="Process capability index">process capability index</a> (e.g., C<sub>pk</sub> or C<sub>pm</sub>) or as a <a href="Process_performance_index" title="Process performance index">process performance index</a> (e.g., P<sub>pk</sub> or P<sub>pm</sub>). The output of this measurement is often illustrated by a <a href="Histogram" title="Histogram">histogram</a> and calculations that predict how many parts will be produced out of specification (OOS).

</p><p>Two parts of process capability are:

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<ol><li>Measure the variability of the output of a process, and</li>

<li>Compare that variability with a proposed specification or product tolerance</li></ol>

<div class="mw-heading mw-heading2"><h2 id="Capabilities">Capabilities</h2></div>

<p>The input of a process usually has at least one or more measurable characteristics that are used to specify outputs. These can be analyzed statistically; where the output data shows a <a href="Normal_distribution" title="Normal distribution">normal distribution</a> the process can be described by the process <a href="Mean" title="Mean">mean</a> (average) and the <a href="Standard_deviation" title="Standard deviation">standard deviation</a>.

</p><p>A process needs to be established with appropriate <a href="Process_control" class="mw-redirect" title="Process control">process controls</a> in place. A <a href="Control_chart" title="Control chart">control chart</a> analysis is used to determine whether the process is "in statistical control" If the process is not in statistical control then capability has no meaning. Therefore, the process capability involves only <a href="Common_cause_variation" class="mw-redirect" title="Common cause variation">common cause variation</a> and not <a href="Special_cause_variation" class="mw-redirect" title="Special cause variation">special cause variation</a>.

</p><p>A batch of data needs to be obtained from the measured output of the process. The more data that is included the more precise the result, however an estimate can be achieved with as few as 17 data points. This should include the normal variety of production conditions, materials, and people in the process. With a manufactured product, it is common to include at least three different production runs, including start-ups.

</p><p>The process mean (average) and standard deviation are calculated. With a normal distribution, the "tails" can extend well beyond plus and minus three standard deviations, but this interval should contain about 99.73% of production output. Therefore, for a normal distribution of data the process capability is often described as the relationship between six standard deviations and the required specification.

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<div class="mw-heading mw-heading2"><h2 id="Capability_study">Capability study</h2></div>

<p>The output of a process is expected to meet customer requirements, <a href="Specification" class="mw-redirect" title="Specification">specifications</a>, or <a href="Engineering_tolerance" title="Engineering tolerance">engineering tolerances</a>. Engineers can conduct a process capability study to determine the extent to which the process can meet these expectations.

</p><p>The ability of a process to meet specifications can be expressed as a single number using a <a href="Process_capability_index" title="Process capability index">process capability index</a> or it can be assessed using <a href="Control_chart" title="Control chart">control charts</a>. Either case requires running the process to obtain enough measurable output so that engineering is confident that the process is stable and so that the process mean and variability can be reliably estimated. <a href="Statistical_process_control" title="Statistical process control">Statistical process control</a> defines techniques to properly differentiate between stable processes, processes that are drifting (experiencing a long-term change in the mean of the output), and processes that are growing more variable. <a href="Process_capability_index" title="Process capability index">Process capability indices</a> are only meaningful for processes that are stable (in a state of <a href="Statistical_control" class="mw-redirect" title="Statistical control">statistical control</a>).

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<ul><li><a href="Process_(engineering)" title="Process (engineering)">Process (engineering)</a></li>

<li><a href="Control_chart" title="Control chart">Control chart</a></li>

<li><a href="Corrective_and_preventative_action" class="mw-redirect" title="Corrective and preventative action">Corrective and preventative action</a> (CAPA)</li>

<li><a href="Kurtosis" title="Kurtosis">Kurtosis</a></li>

<li><a href="Normal_distribution" title="Normal distribution">Normal distribution</a></li>

<li><a href="Six_Sigma" title="Six Sigma">Six Sigma</a></li>

<li><a href="Statistical_interference" title="Statistical interference">Statistical interference</a></li>

<li><a href="Statistical_process_control" title="Statistical process control">Statistical process control</a></li>

<li><a href="Tolerance_(engineering)" class="mw-redirect" title="Tolerance (engineering)">Tolerance (engineering)</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

<ul><li><a href="Thomas_Pyzdek" title="Thomas Pyzdek">Pyzdek, T</a>, "Quality Engineering Handbook", 2003, <style data-mw-deduplicate="TemplateStyles:r1238218222">

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</style><a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-8247-4614-7</bdi></li>

<li>Bothe, D. R., "Measuring Process Capability", 2001, <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-07-006652-3</bdi></li>

<li>Godfrey, A. B., "Juran's Quality Handbook", 1999, <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>007034003X</bdi></li>

<li>ASTM E2281 Standard Practice for Process and Measurement Capability Indices</li></ul>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://www.itl.nist.gov/div898/handbook/pmc/section1/pmc16.htm">What is Process Capability?</a> at <a href="NIST" class="mw-redirect" title="NIST">NIST</a>/<a href="SEMATECH" title="SEMATECH">SEMATECH</a> <a rel="nofollow" class="external text" href="https://www.itl.nist.gov/div898/handbook/index.htm">Engineering Statistics Handbook</a></li>

<li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20070711230708/http://www.spcpress.com/pdf/The_Final_6_Sigma_Zone.pdf">The Six Sigma Zone</a> by <a href="Donald_J._Wheeler" title="Donald J. Wheeler">Donald J. Wheeler</a></li></ul>

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</style><div id="Six_Sigma_tools92" style="font-size:114%;margin:0 4em"><a href="Six_Sigma" title="Six Sigma">Six Sigma</a> tools</div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Define phase</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Project_charter" title="Project charter">Project charter</a></li>

<li><a href="Voice_of_the_customer" title="Voice of the customer">Voice of the customer</a></li>

<li><a href="Value-stream_mapping" title="Value-stream mapping">Value-stream mapping</a></li>

<li><a href="SIPOC" title="SIPOC">SIPOC</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Measure phase</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Business_process_mapping" title="Business process mapping">Business process mapping</a></li>

<li><a href="Pareto_chart" title="Pareto chart">Pareto chart</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Analyse phase</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Root_cause_analysis" title="Root cause analysis">Root cause analysis</a></li>

<li><a href="Failure_mode_and_effects_analysis" title="Failure mode and effects analysis">Failure mode and effects analysis</a></li>

<li><a href="Multi-vari_chart" title="Multi-vari chart">Multi-vari chart</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Improve phase</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Design_of_experiments" title="Design of experiments">Design of experiments</a></li>

<li><a href="Kaizen" title="Kaizen">Kaizen</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Control phase</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li>Control plan</li>

<li><a href="Statistical_process_control" title="Statistical process control">Statistical process control</a></li>

</div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div><a href="DMAIC" title="DMAIC">DMAIC</a></div></td></tr></tbody></table></div>

<div class="navbox-styles"></div><div role="navigation" class="navbox authority-control" aria-label="Navbox391" style="padding:3px"><table class="nowraplinks hlist navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="row" class="navbox-group" style="width:1%">Authority control databases: National </th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"><ul><li><span class="uid"><a rel="nofollow" class="external text" href="https://d-nb.info/gnd/4553619-3">Germany</a></span></li></ul></div></td></tr></tbody></table></div></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2024-06-06" href="https://en.wikipedia.org/wiki/?title=Process_capability&oldid=1227640151">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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