When the control phase of the DMAIC project has been reached, the goal becomes ensuring that the improved process is truly able to meet and sustain its ability to deliver on key performance variables. Control charts are two-dimensional graphs that show the performance of a process on one axis, and the time period being measured on the other axis. Different control charts are best applied to different types of data. Once the type of data is determined and the size or number of data points are known, it is fairly easily to determine what particular control chart will work best.
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 handed off back 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. On going 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