Mar 19, 2009 as mentioned by sj, the cpk is a short term capability and ppk is the long erm capability. Calculations and comparisons to other capability indexes. This video explains the concept of process capability in detail and change in the values of cp and cpk when the process shifts within or beyond the limits of the specifications. Six sigma conversion table lean six sigma training and software. Cpk is a short term process index that numerically describes the within subgroup or potential capability ppk is long term indicator of a process assuming it was analyzed and stays in control. Process performance index ppk, cpk, pp what is six sigma. Six sigma spc oem products six sigma and spc statistical process control software applications six sigma spc 2070 w. A target value from historical performance or the customer can be used to estimate the cpm. Yes, we have been producing these monthly publications for a long time. From the cpk value, one can derive that machine 1 is better than 2. Jan 1, 2019 using the most common short term capability index. Learn the definitions, interpretations and calculations for cp, cpk, pp and ppk. The process capability cpk, ppk and the machine capability cmk describe the ability to achieve a desired result.
Cpk the ratio of the process spread to the tolerance using the within subgroup standard deviation. Process capability cp, cpk and process performance pp. Six sigma conversion table lean six sigma training and. Oct 05, 2005 besides the fact that cpk and ppk are worse than useless and an abomination on the face of the earth imho, the original definitions and the ones most reputable statistical software use are this.
Sep 11, 2009 i received a note asking how to do a capability analysis in jmp 8. There is a time and a place to use each of these numbers depending on the individual situation. Generally you use this when a process is under statistical control. Those acronyms are sometimes written with some of the letters in superscript to better explain the process. This system is also now used in other fields, including software.
Byjus online cpk calculator tool makes the calculation faster, and it calculates the performance of the process in a fraction of seconds. Lori, a software customer, phoned to ask if cpk is the best statistic to use in a process that slits metal to exacting widths. Use spc software to minimize production costs, optimize product quality, and. Should the first project a black belt works on the one that the black belt does for training be one of. Actually nothing much have changed in how to do it.
But the statistical measurements of cp, cpk, pp, and ppk may provide more insight into the process. Free desktop six sigma, dpmoppm, yield, cpk calculator and converter. Ppk ppl ppu pp cpm cpk cpl cpu cp std ev overall std ev w ithin sample n mean lsl target usl 0. That will help you look like a data analysis, charting and statistics wizard. Learn the difference between cp cpk process capability and pp ppk process. Once statistical control is established, then the histogram and process capability may be analyzed properly. But the statistical measurements of cp, cpk, pp, and ppk may provide more insight. We have developed an interactive excel workbook that lets you visually see how changing the average and standard deviation of your process impacts your process capability. Lori, one of our customers, phoned to ask if cpk is the best statistic to use in a process that slits metal to exacting widths. Cpk statistical process control, lean six sigma, cpk. There are additional features which are really helpful but the basic steps on computing cp, cpk, pp, and ppk are basically shared by versions jmp 5, jmp 6, jmp 7, and jmp 8. In the six sigma quality methodology, process performance is reported to the.
Frequently cited capability metrics include cpk, ppk, defects per million opportunities dpmo, and sigma level. So, even with a large shift in the average, the 6 sigma level process still is. Process capability study i process capability cp and cpk i cp cpk and pp ppk duration. Then, go to statquality toolscapability analysisnormal to run the analysis. Software today makes it easy to plug the data in and generate the results. This often happens with a mature process that has been around for a while. Typically, it is considered that cpk and ppk should be greater than 1. As a technical support analyst, i too wondered what index would be best suited for her application. The equations for cpk and ppk are shown in table 1. It measures the performance of the process related to both dispersion and centeredness.
In simple words, ppk is an index of process performance, which tells how well. The capability study is one of the main tools of six sigma. The two metrics starting with c measure short term capability. Six sigma process performance is reported in terms of sigma.
That spread being centered around the midpoint is part of the cpk and ppk calculations. Qi macros is an affordable, intuitive, timesaving addin for excel. Well have it back up and running as soon as possible. Successful six sigma practitioners must have strong communication and quantitative skills. The x with double bar over it is the overall average.
The capability indices of ppk and cpk use the mean and standard deviation to estimate probability. In six sigma we want to describe processes quality in terms of sigma. Spc software for excel six sigma software qi macros. The solution is an integrated dmiacchange management roadmap. The main difference between pp and cp on one side and ppk and cpk on the other side is whether we use complete set of data for calculation pp and ppk where we calculate real performance of the system, or we use sample preproduction, batch, logical subgroups where we calculate capability of the process.
Fixing values for minimum acceptable process capability targets is a matter of personal opinion, and what consensus exists varies by industry, facility, and the process under consideration. Like the cp index, the cpk shows the relationship of the 6sigma spread to the. In this article you will learn how to calculate machine and process capability using excel. You will also find out whether your values meet the requirements for calculating machine. Since cpk uses specification limits and parts variation sigma, we can also arrive at. Process capability cp, cpk and process performance pp, ppk.
When it comes to data collection software and statistical analysis, you may feel like you are. See the 30minute pizza delivery example in delight your customers the six sigma way. Using minitab software, arrange above as data structure as shown on minitab worksheet below. This is a script i developed to help me in explaining the concepts of cppp and cpkppk whenever i am conducting six sigma trainings. Six sigma can bring significant benefits to any business, but reaping those benefits requires the collection and analysis of data so you can understand opportunities for improvement and make significant and sustainable. Minitab is the leading provider of software and services for quality improvement and statistics education. Both cpk and ppk are the minimum of two process indices. Ppk is used as a snapshot of the process variation at any given point in time. Cpk informs the user about the future capability of a process. If the process is in control and the distribution is well within the specification limits then the difference between the upper. There is some confusion about the difference between cp and pk along with cpk and ppk. Jan 26, 2018 this video explains the concept of process capability in detail and change in the values of cp and cpk when the process shifts within or beyond the limits of the specifications. Cpk takes into account the center of the data relative to the specifications, as well as the variation in the process.
You know, things like cpk, ppk, sigma level, ppm out of spec and so on. The dmaic toolkit is excellent for solving technical complexity problems. Since a process capability is null and void unless the process is stable and in control, always look at the control charts, x bar and r bar, first. It is a data driven program that is focused on financial return. Because cp and cpk use estimated sigma, and pp and ppk use actual sigma, they have different uses. Ppk is the 6 sigma range of a processs total variation where sigma is estimated by the samples standard deviation. It allows me to customize demostrations for my trainees that visually aid them in. I received a note asking how to do a capability analysis in jmp 8. By convention established at motorola, where the six sigma program originated, the sigma level is adjusted by 1.
Cp, cpk distribution cpk is centering of the process cpkinterpretation. There are 4 main metrics used to define capability. Fro simplicity you could create a small table where in cpk0. Besides the fact that cpk and ppk are worse than useless and an abomination on the face of the earth imho, the original definitions and the ones most reputable statistical software use are this. Calculate cpk data collection tools quality advisor. Also shown is a direct conversion to a cpk level based on the area under a normal curve. Capability analysis cp, cpk, pp, ppk part 4 how to. Two tables below provide both shortterm and longterm conversions of sigma level zscore, cpk or ppk, and defect rate respectively. If the result of this transformation is a normally distributed dataset the pp, ppk and % out of tolerance can be used. Cp and cpk can be used to measure a systems potential capabilities, while pp and ppk measure the systems actual performance. According to six sigma philosophy, cp or pp and cpk or ppk should be greater than 1. This goal can be expressed in terms of process sigma level or in terms of cpkppk. The cpk and ppk measures will be very close when the process remains in a state of consistent statistical control, as both the actual sigma and estimated sigma will be similar.
Total variability is used in the denominator instead of the short term. They must have excellent process knowledge and need to apply to appropriate tools. Ppk is useful to determine if a process will be capable cpk if process conditions maintain stability. Cpk vs ppk cp cpk versus pp ppk compare to sigma qi macros. Process capability uses the process sigma value determined from either the moving range, range or sigma control charts. Its an option along with zscore and ppm when describing process baseline measurement in the measure phase or in the control phase. Cpk is a standard index to state the capability of one process, the higher the cpk value the better the process is. Spc, ppk, pp, cpk, and cp are some of the major abbreviations to know. The addition of k quantifies the amount of which a distribution. Process capability analysis of varying cp and cpk value. Cpk calculator is a free online tool that displays the process performance for the specified range. Software testing the tao of friday mit school of business undergraduate ctq linkage, critical to quality linkage.
Ppk informs the user of how the process has performed in the past. The difference is in how you calculate the actual sigma, or standard deviation, either using an estimate, or the actual calculations. In these cases, cp is ignored and only cpk can be used. As a pq systems technical support analyst, i too wondered what index would be best suited for her application, a highly specialized one. Spc software statistical process control infinityqs. For more information on these and on pp and ppk, please see our. Examples of process capability and process performance analysis qtrendcontrol demo application. Process performance index, is a statistical tool to verify if the sample that have generated from the process is capable to meet the customer requirement.
Perform ppk analysis for each parameter weight, hardness, thickness and shoot for a number of 1. As mentioned by sj, the cpk is a short term capability and ppk is the long erm capability. A target value from historical performance or the customer. It measures how well the data might fit between the spec limits usl, lsl. In addition, the workbook shows how cp, cpk, the sigma level, and the ppm out of. March 2014 this months publication takes a look at process capability a topic we first covered almost 10 years ago. Notice the difference between shortterm and longterm is an industry. Statistical software minitab quality companion process improved soft tools. Ppk ppk is an process capability index that assesses how close the process mean is from the specification limit. Process capability and sigma level applicability in it. This goal can be expressed in terms of process sigma level or in terms of cpk ppk. Cpk will never exceed the cp similar to ppk, the cpk capability index is only a function of the standard deviation and mean of the data, not a nominal target value that may be historical or provided by the customer. From a technical standpoint, six sigma deems a process being acceptable only after achieving a maximum defect rate of 3. There are some acronyms used to indicate both process capability and process performance.
More than 90% of fortune 100 companies use minitab statistical software, our flagship product, and more students worldwide have. Process capability analysis and process analytical technology. It doesnt care if the process is centered within the limits only if it would fit if it was centered. The most commonly used measures of capability are cp, cpk, pp, and ppk. An interactive look at process capability spc for excel software. It helps us understand what our process capability is and tells us the probability that the process will produce defects.