About this lesson
The control plan provides guidance on how to maintain control of the new process and the measurements that will show if the process is deviating from the new approach.
When to use
The control plan should be prepared as part of the implementation for any new process or changed process. If an existing control plan for the process is already in use, it should be updated. If there is no control plan, it should be created and released with the process.
It is hard to make a permanent change to a process. People and systems have a tendency to drift back to the old way of doing things. The control plan is the set of activities that are used by process managers and operators to ensure the process continues to perform as designed.
There are four process states and each requires the support of a control plan:
- The ideal state is that a process is in statistical control and delivering conforming results. The control plan should keep the process operating in this fashion.
- The threshold state is that the process is in statistical control but the process capability is poor, so some nonconforming results are produced. The process is always at the threshold of very poor performance. The control plan is essential to both keep the process centered and to provide guidance for how to disposition the non-conformances.
- The poor performance state is a process that is not in statistical control and is creating non-conforming results. When this is the case, the Lean Six Sigma project is not complete and the team needs to find solutions before considering a control plan.
- The false-sense-of-security state is when a process is not in statistical control, but is creating conforming results. The process manager and operators may think that all is OK, but due to the presence of special cause variation, the process is not predictable and may suddenly start to create non-conforming results. Keep in mind that special cause variation can create a special condition where everything looks good, but the process cannot sustain that. The control plan is needed to recognize this situation and provide guidance to the managers and operators concerning what they should monitor and they should respond to this.
The control plan normally contains three sections:
- Documentation of the process step or related information for each step of the process.
- The Monitoring plan for all critical metrics in the process. This means a description of the metric, how it is measured, who measures it and how it is recorded.
- The Response plan for a measurements which directs the managers and operators what to do if the measurement is beyond the allowable limits.
Hints & tips
- The control plan should address all process outputs that are critical to the customer.
- The control plan should address all inputs that are critical to process performance.
- The monitoring plan should provide clear limits on acceptable performance.
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