When the control phase of the DMAIC project has been reached, the goal becomes ensuring that the improved process can genuinely meet and sustain its ability to deliver on key performance variables. Control charts show a process's performance on one axis and the period measured on the other. Different control charts are best applied to various types of data. Deciding what control chart will work best is relatively easy once the data type is determined and the size or number of data points is known.
Control charts to continue monitoring and contingency plans are typically one of the last steps in a Lean Six Sigma project to be developed by the process team before it is returned to the process owners. The control plan is simply a hard copy document for the process owner to record the significant data for a given process, which states the control limits of process performance. The control plan, therefore, sets targets for key process output and input variables. Ongoing quality assurance of the process owners will be to check and verify that control plans are operating to ensure that improvements are sustained and that the process continues to produce the quality, quantity, and other factors considered critical. In constructing an effective control plan, it is best if it is kept as concise as possible, but it should include the information listed below:
- Identify who the process owners are
- Name the specific process to which the plan applies
- State the process characteristics or specifications
- State and describe the measurement system
- State what will be done if the process moves outside the control limits
