The formula to calculate the Process Performance Index (Ppk) is:
\[ Ppk = \min \left( \frac{USL - X}{3 \times STD}, \frac{X - LSL}{3 \times STD} \right) \]
Where:
Ppk, also known as the Process Performance Index, is a metric used to evaluate the capability of a process to meet specified requirements. It provides a quantitative measure of how well the process is performing in terms of quality and consistency. The Ppk is calculated using data collected from the process, such as measurements or observations, and compares it to the desired target or specification limits. It considers the process mean (average) and the process variation to determine how closely the process is centered on the target and how much variation is present. A Ppk value greater than 1 indicates that the process can meet the specified requirements, while a value less than 1 signifies that the process is not meeting the desired standards. The higher the Ppk value, the better the process performance.
Let's assume the following values:
Using the formula to calculate the Ppk:
\[ Ppk = \min \left( \frac{USL - X}{3 \times STD}, \frac{X - LSL}{3 \times STD} \right) = \min \left( \frac{10 - 6}{3 \times 1}, \frac{6 - 2}{3 \times 1} \right) = \min \left( \frac{4}{3}, \frac{4}{3} \right) = 1.33 \]
The Process Performance Index (Ppk) is 1.33.
