How can you use moving range charts to monitor process variability in Six Sigma?

1 What are moving range charts?

Moving range charts are a type of control chart that plot the absolute differences between consecutive observations of a process output. They are also known as MR charts or individuals and moving range charts. They are often used in conjunction with X-bar charts, which plot the mean values of the process output. Together, they form a pair of control charts that monitor both the central tendency and the variability of a process.

3 How to interpret moving range charts?

Interpreting a moving range chart requires looking for points or patterns that fall outside the control limits or indicate a change in the process variation. Common signals of special cause variation include a point above the UCL or below the LCL, two out of three consecutive points above 2.115 times the average moving range, four out of five consecutive points above 1.128 times the average moving range, and nine consecutive points below 1.128 times the average moving range. If any of these signals are found on the chart, it is necessary to investigate the cause and take corrective actions to eliminate or reduce the special cause variation.

4 How to use moving range charts for process improvement?

Moving range charts are a simple and effective way to monitor process variability in Six Sigma. They can provide feedback on the stability and capability of your process, such as estimating the process standard deviation and comparing it with customer specifications. Additionally, moving range charts can identify opportunities for improvement if your process is unstable or incapable, and they can be used to analyze the impact of any changes or improvements that you implement. Moreover, they can enhance communication and teamwork by allowing you to share and discuss the process data with your team members, stakeholders, and customers. Ultimately, moving range charts can help you ensure that your process is stable, capable, and continuously improving.