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Quick reference
Control Plan
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.
Instructions
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.
- 00:05 Hi I'm Ray Sheen and it's no surprise that during the control phase for
- 00:09 project we will need to create a control plan.
- 00:12 Let's take a look at the elements of a control plan.
- 00:16 I'll start by considering the control strategies based upon your process
- 00:20 performance.
- 00:21 There're four different strategies that you could pursue.
- 00:24 These strategies are based upon the typical performance of your process.
- 00:27 It could be in statistical control,
- 00:29 meaning there are no special cause variation, only common cause.
- 00:33 Or it could be out of statistical control,
- 00:35 meaning there is the presence of special cause variation.
- 00:38 Second, your process may have been producing conforming parts and
- 00:42 items or it could be creating errors.
- 00:45 Now it should be no surprise that our goal is to have a process that is in
- 00:49 statistical control and always producing conforming items. That is the ideal state.
- 00:53 We should strive to do design a solution that gets us there and
- 00:57 then put in place a control plan to stay there.
- 01:00 Sometimes the process is in control, but there are some nonconfirming results.
- 01:05 This is a process capability issue.
- 01:08 The specification limits are tighter,
- 01:10 than what the process is able to consistently achieve.
- 01:13 We called this threshold performance,
- 01:15 because we're on a threshold to being able to get to ideal state or
- 01:18 we're also on a threshold of having a large amount of a defects.
- 01:21 From a control strategy standpoint, we want to maintain control, and
- 01:25 be constantly monitoring for the instance where the result is nonconforming so
- 01:30 that it can be reworked.
- 01:32 This is also a candidate for a further Lean Six Sigma project.
- 01:35 The third strategy is for the case where the process is out of control and
- 01:39 routinely producing nonconforming results.
- 01:42 In this case, the process is broken and typically,
- 01:45 everyone knows this. There are ongoing problems and chaos is evident at times.
- 01:49 You should not be in this state at the end of a Lane Six Sigma project.
- 01:54 Although, this is often the case at the beginning of the project.
- 01:57 If your team is still in this condition, your project is not yet over.
- 02:01 The fourth condition is actually the most dangerous.
- 02:04 The process is not in control, but it is producing conforming results.
- 02:08 That means that some special cause is overriding normal process performance to
- 02:12 ensure that the result is conforming,
- 02:14 this condition can lead to a false sense of security.
- 02:17 It's also difficult to create a control plan for this condition because
- 02:20 the process does not have the inherent ability to control what is happening.
- 02:25 It is the special cause that is overriding everything, and
- 02:28 as soon as the special cause changes, the results will likely be disastrous.
- 02:33 So let's look at the control plan.
- 02:35 The control plan is a set of activities performed by the process operators,
- 02:39 equipment, or supervisors that will maintain the process performance at
- 02:43 acceptable levels of customer satisfaction.
- 02:46 Without a control plan, the process improvement often fades away, and
- 02:49 the process reverts back to what had been happening originally.
- 02:53 On top of that, the Control Plan should be generating and monitoring
- 02:57 the process performance data which can provide insight into further improvements.
- 03:00 It should immediately note the introduction of special cause variation,
- 03:04 so that they can be controlled and prevented.
- 03:07 When I build a Control Plan, I build it with three components.
- 03:11 The documentation, it must be there for others to reference, the monitoring plan,
- 03:15 what we are watching for and what we should expect, and
- 03:18 then finally, the response plan.
- 03:21 When something different than expected happens, what should be done?
- 03:25 Here's an example of a very simple template that I've used.
- 03:29 The first two columns are the documentation.
- 03:31 This is the process step, and what are the procedures, work instructions or
- 03:36 checklists that instructors and operators use to accomplish that step.
- 03:40 If we don't document it, we can't expect it to stay under control.
- 03:44 The next three columns are for monitoring.
- 03:46 This is what is being measured, how it is being measured, and how it is recorded.
- 03:50 Now you don't have to have a measurement for every step, but
- 03:54 every critical process output should be measured at some point.
- 03:58 And some steps such as an inspection or
- 04:00 a test step in the process are strictly measurement steps.
- 04:04 The last few columns are the Response Plan, and I'm showing one, for
- 04:07 what to do if a measurement is out of the allowed range, another call for
- 04:11 highlighting preventive actions that can be done with this step.
- 04:14 The response plan strategies are so important,
- 04:17 that we'll spend an entire module on them here in a few minutes, but
- 04:21 let's wrap this up with a few more comments about monitoring.
- 04:25 As part of the measurement aspect to the monitoring plan, each process output
- 04:29 should be identified at the appropriate step, and the target performance,
- 04:33 along with the allowable tolerances and specifications, should be included.
- 04:38 And where it's appropriate, the monitoring plan should also include
- 04:41 a targeted tolerances for the process inputs.
- 04:44 In many cases it's the control of the inputs
- 04:47 that will screen out special cause variation effects.
- 04:50 Finally, they could clear the Monitoring Plan how the measurement is taken,
- 04:54 who takes the measurement and where this recorded.
- 04:57 Is it going on a run chart or control chart.
- 05:00 It is going in a database that automatically tracks and flags problems.
- 05:04 The point here is that monitoring implies someone or
- 05:06 something is actually checking the data to be sure it's acceptable.
- 05:10 We don't just record in order to have an activity to do.
- 05:14 We record it to be able to conduct realtime tracking of the process.
- 05:20 We aren't trying to be control freaks, but experience tells us that if we don't
- 05:25 change the way we control the process, any improvement will soon slip away.
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