How do you determine the process capability and performance indices for your product features?

1 What is statistical process control?

Statistical process control (SPC) is a method of using statistical techniques to control and reduce the variation in a process. SPC involves collecting and plotting data from a process, and applying rules to detect any signals of instability or abnormality. SPC can help you identify the sources of variation, such as common causes (inherent to the process) or special causes (due to external factors), and take corrective actions to eliminate or minimize them.

2 What is process capability?

Process capability is a measure of how well a process can meet the specifications or requirements of a product feature. Process capability compares the natural variation of a process with the tolerance limits or customer expectations. A process is capable if it can produce outputs that are within the specifications most of the time, and not capable if it produces too many defects or errors.

3 How to calculate process capability indices?

Process capability indices are numerical values that indicate how capable a process is. Cp and Cpk are two types of indices; Cp measures the potential capability of a process, while Cpk measures the actual capability of a process. To calculate Cp and Cpk, you need to know the upper and lower specification limits of the product feature, as well as the mean and standard deviation of the process data. The formula for Cp is (USL - LSL) / (6 * s), and the formula for Cpk is min [(USL - X-bar) / (3 * s), (X-bar - LSL) / (3 * s)].

4 How to interpret process capability indices?

Process capability indices can help you evaluate how well your process meets the specifications and how much improvement is needed. Generally, the higher the indices, the better the capability. However, if Cp and Cpk are equal, the process is centered and capable. If Cp and Cpk are not equal, the process is not centered and may need adjustment. If Cp and Cpk are both greater than 1, the process is capable and has room for improvement. On the other hand, if Cp and Cpk are both equal to 1, the process is capable and meets the specifications. Lastly, if Cp and Cpk are both less than 1, the process is not capable and needs improvement.

5 What is process performance?

Process performance is a measure of how well a process performs in relation to the customer or market requirements. Process performance compares the actual variation of a process with the target or expected variation. A process performs well if it can meet or exceed the customer or market expectations, and not well if it falls short of them.