Question

Quality of a steel garage doors. Specification is set at [74kg, 86kg] following customer's voice.

The door weight of the current process follows normal distribution with mean of 82.5kg and a standard deviation of 4kg.

What are the process capability ratio and process capability index?
How can you improve the process?

Answer 1

The process capability ratio measures the proportion of products that fall within the specification limits, while the process capability index measures how well the process is centered between the specification limits. To improve the process, the standard deviation needs to be reduced.

Step-by-step explanation:

The process capability ratio measures the proportion of products that fall within the specification limits. It is calculated by dividing the specification width (upper specification limit minus lower specification limit) by six times the standard deviation.

The process capability index, also known as Cpk, measures how well the process is centered between the specification limits. It is calculated by taking the minimum of two ratios: (upper specification limit minus mean) divided by three times the standard deviation, and (mean minus lower specification limit) divided by three times the standard deviation.

To improve the process, the standard deviation needs to be reduced. This can be achieved by identifying and addressing the sources of variation in the process, such as adjusting the machinery or refining the production methods.