Process Capability Cp

Process capability, for a stable manufacturing process, is the ability to produce a product that conforms to design specifications. Because day-to-day variations can occur during manufacturing, process capability is a statement about product uniformity. Process capability, as measured by the quality characteristics of the product of the process, is expressed as the mean value plus or minus three standard deviations. Mathematically:

It is desirable for CP to be greater than one. This implies that the process of three-sigma limit is well within the customer's specification limits, as shown in Figure 20-31.

The following are generally accepted rules for CP:

• CP > 1.33: The process is well within the customer's specifications requirements.

• 1.33 > CP > 1.0: The process is marginally acceptable. The process may not completely satisfy the customer's requirements. Improvements in process control are needed.

• CP < 1.0: The process is unacceptable as is. Improvements are mandatory.

To illustrate the use of the formula, assume that your customer's requirements are to produce metal rods that are 10 inches ± .05 inches. Your manufacturing process has a sigma of 0.008.

Project Management Made Easy

Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

Get My Free Ebook


Post a comment