Tag: Cpk

One must necessarily understand that the short-term standard deviation reports on the “instantaneous reproducibility” of a process whereas the long-term standard deviation reflects the “sustainable reproducibility.”  To this end, the short-term standard deviation is comprised of the “within group” sums of squares (SSW).  The long-term standard deviation incorporates the “total” sums-of-squares (SST).  Of […]

Cpk is one of the metrics calculated for determining whether a process is capable of meeting customer specifications or requirements. 

In the Six Sigma quality methodology, process performance is reported to the organization as a sigma level. The higher the sigma level, the better the process is performing. Another way to report process capability and process performance is through the statistical measurements of Cp, Cpk, Pp, and Ppk. This article will present definitions, […]

Cp is one of the metrics calculated for determining whether your process is capable of meeting customer specifications or requirements. It is useful in comparing different functions and their ability to meet their unique specifications.

Use this table to go between and convert Sigma to DPMO to Yield to Cpk.

Capability Indices How do you calculate capability indices? Capability analysis is an essential tool for statistical process control (SPC) and process improvement, applicable to a variety of environments from hospitals and labs to assembly and manufacturing. How to Calculate Capability Indices The formula for calculating a Cpk index is easily found: USL, upper […]

How do you convert DPMO to Sigma Level? There are several metrics you can use to measure how well your process is performing. Let’s look at three of them and discuss how to calculate them and how they relate. The three are DPMO, Sigma Level, and Cpk. Convert DPMO/Sigma to Cpk  Before discussing […]

So what is the real difference when looking at Cpk and Sigma Level? If you’re new to Six Sigma, there is no shortage of acronyms and calculations to keep in mind as you work on your knowledge base. Both Cpk and Sigma Level are valuable tools when looking at your processes and production. […]

In Part 2 we look at failure rates and material conditions for a surface finish example.

In Part 1, we explore the concept of process capability, including how to calculate it and what to do with non-normal data.

The capability of a process, statistically speaking, is the ability of that process – based on historical performance – to achieve measurable results that satisfy established specifications and statistical limits. In a nutshell, process capability indicates how well a process is able to perform its specified purpose. Why is process capability important? When the capability […]

Have you tried to explain the concept of process capability to someone who then looks at you like you have two heads? Try using the following analogy to explain the subject more easily. Driving in a Construction Area Imagine you are driving on a highway that is undergoing construction. The width of your vehicle – […]

The process capability indices Pp and Cp describe how closely a process can operate within its specification limits. Many articles describe the difference between Pp and Cp simply: one is short term, one is long term. Moving beyond such a description, this article focuses on the untapped power of capability analysis and shows you how […]

In my process engineering experience I have found a good number of people confused about the important process measure indices of capability and performance. The capability index is useful for measuring: Continual improvement using trends over time, or For prioritizing the order in which process will be improved, and For determining whether or not a […]

In manufacturing, key quality indices – performance capability index (Cpk), defects per million opportunities (DPMO) and first pass yield (FPY) – are prevalent criteria for gauging the performance of products and processes. These indices however, often are interpreted wrongly and used without taking into account the conditions of application. Moreover, alternative indices such as rolled […]

For many years industries have used Cp, Cpk, Pp, and Ppk as statistical measures of process quality capability. Some segments in manufacturing have specified minimal requirements for these parameters, even for some of their key documents, such as advanced product quality planning and ISO/TS-16949. Six Sigma, however, suggests a different evaluation of process […]