Using a Control Plan in Six Sigma

For Lean and Six Sigma professionals, you probably know that a control plan is a key component of process improvement. As part of the control phase in the DMAIC approach, it allows you to sustain gains made during your Six Sigma project.

In this post, we’ll explain everything that you need to know about the Six Sigma control plan. You’ll learn the purpose and elements that make up an effective plan, as well as how to develop your own control plan.

Whether you’re new to Six Sigma or deep into a project, this guide will equip you to create a control plan that drives lasting process improvements. With a strong control plan, you can standardize processes to reduce variation and optimize workflow.

What is a Six Sigma Control Plan?

A Six Sigma control plan is a detailed document that outlines the steps required to sustain improvements and standardize processes after a Six Sigma project. It helps you control and monitor a process to keep it operating at peak performance.

The control plan identifies key process inputs and outputs, along with metrics that need to be measured, and specifies the appropriate sampling rates and data collection methods.

Additionally, it documents the acceptable ranges for each metric and outlines corrective actions when measurements fall outside tolerance.

An effective Six Sigma control plan provides a framework for maintaining the gains made during the Define, Measure, Analyze, Improve, and Control (DMAIC) phases. It includes the procedures, responsibilities, and controls needed to minimize process variation and defects on an ongoing basis.

With proper adherence to the control plan, you can sustain dramatic improvements made by Six Sigma projects over the long term.

What is the Control Process in Six Sigma?

The control process is the last phase in the Six Sigma DMAIC methodology. After you’ve completed the previous phases of Define, Measure, Analyze, and Improve, the control process helps sustain the gains.

This phase establishes the procedures and systems needed to monitor performance of the improved process. The goal is to prevent backsliding and ensure that improvements from Six Sigma projects become permanent.

To achieve this, you will develop control mechanisms such as statistical process control charts, audits, defect tracking, and standard operating procedures (SOPs). These provide the quantitative and qualitative data you need to control ongoing process variation.

By diligently executing the control process, you can identify anomalies and correct them before they result in significant defects. This allows you to lock in the benefits of reduced costs and increased speed, quality, and customer satisfaction delivered by your Six Sigma initiative. Sustaining the gains is just as crucial as achieving them in the first place.

Purpose of Control Plan in Six Sigma

The Six Sigma control plan is developed for the following purposes:

Standardize Processes

A control plan establishes standardized processes, procedures, and responsibilities. This reduces ambiguity and variations that could undermine improvements and maintains process discipline.

Prevent Backsliding

By monitoring critical metrics, a control plan identifies adverse trends before they become problems thereby allowing you to take prompt corrective action and avoid backsliding.

Control Variation

Ongoing inspection, sampling, and measurement provide data to keep variation in check as control limits and responses are triggered automatically when data falls outside tolerance zones.

Simplify Training

With clear documentation on how to operate the improved process, training new employees is simplified. A control plan also aids in cross-training existing staff.

Support Audits

The documentation provided by the control plan supports process audits to verify continued compliance with updated procedures.

Six Sigma Control Plan Elements

A Six Sigma control plan contains various elements to fully define the activities required to sustain process improvements. While formats can vary, some typical components include:

  • Process Steps: This lists the actual workflow steps of the process in sequence and provides an overview of the process flow.
  • Metrics: The key process metrics that will be monitored are defined here. These are typically critical to quality characteristics or CTQs.
  • Measurement Technique: The methods for data collection for each metric are specified here. This includes inspection, sampling, testing protocols, and measurement tools.
  • Performance Limits: The upper and lower control limits or acceptable tolerance range is provided for each metric to define the thresholds for variation.
  • Sample Size and Frequency: The sample size and how often measurements will be taken are indicated for each metric to support consistent data collection.
  • Response Plan: Corrective actions are predefined for when measurements fall outside of limits to enable quick response to out-of-control conditions.
  • Roles and Responsibilities: Accountability is established by naming the owners who will perform each step and take measurements.
  • Reporting and Verification: The plan sets the format, frequency, and recipients for reporting on control data. Process audits are scheduled to verify conformance.
  • Standard Operating Procedures: Detailed work instructions are provided for executing process steps to minimize variation. These are linked to training.
  • Documentation: Forms are created to record measurements, corrections taken, audits, revisions made, and any key event history.
  • Control Plan Review: A regular review schedule is set to evaluate the control plan’s effectiveness and alignment with current conditions. This keeps the plan current.

What to Know Before Developing the Control Plan

Creating an effective Six Sigma control plan requires thoughtful preparation. Here are some key things to consider:

Understand Process Inputs/Outputs

Determine the inputs that affect process performance along with the resultant outputs. Control the vital few inputs that drive the desired outputs.

Identify Critical Metrics

Pinpoint the quantitative metrics that indicate process health and quality, then prioritize controlling the vital few over the trivial many.

Set Control Limits

Define the upper and lower control limits for each critical metric based on process capability. This helps quickly flag out-of-control conditions.

Determine Sampling Plan

Specify the sample size and frequency of measurement for optimal control without overburdening resources while striking the right balance.

Develop Response Protocols

Predefine corrective actions to take when metrics approach or breach control limits. This enables swift reaction to anomalies.

Document Procedures

Record step-by-step instructions for process operation to minimize variation and errors. Make them readily accessible for training.

Assign Responsibilities

Clarity in roles is key. Therefore, name specific personnel to take measurements, implement corrections, audit adherence, and update the plan.

Plan Ongoing Reviews

Schedule regular reviews to evaluate control plan effectiveness and make enhancements. Keep it current and aligned to conditions.

How to Make a Control Plan in Six Sigma

Here are key steps to take to make a Six Sigma control plan:

Define Metrics

List the vital few metrics that indicate process performance and output quality. These should tie to critical customer requirements.

Set Control Limits

Determine upper and lower control limits for each metric that define the allowable range of variation. Aim for 3-sigma limits if possible.

Develop a Data Collection Plan

Specify the sampling size, measurement frequency, and data collection techniques needed to monitor metrics.

Document Procedures

Record detailed standard operating procedures for executing the improved process to minimize errors and variation.

Assign Responsibilities

Name the specific staff who will measure, analyze data, identify exceptions, and implement corrections.

Establish Response Protocol

Define corrective actions to take when metrics approach or breach control limits. This enables swift reaction.

Develop Reporting Plan

Outline the frequency, distribution, and format of reports to communicate control data trends and actions taken.

Conduct Trial Runs

Test the control plan under varying conditions to identify enhancements before full deployment, and refine as needed.

Provide Training

Educate all stakeholders on their role and the importance of rigorously following the control plan.

Schedule Audits

Plan regular audits to verify adherence, gauge effectiveness, and identify control plan improvements for maximum sustainment.

Control Plan Six Sigma Example

Now let’s walk through an example control plan for a Six Sigma project aimed at reducing defects in a furniture manufacturing process.

The critical metric chosen to monitor is the defect rate per batch. The upper control limit is set at 2% defective and the lower limit at 0.5% defective based on the improved process capability.

A sample size of 50 units will be randomly tested from each batch. The production supervisor will conduct the inspections daily using a statistical sampling technique and input the results into the defect tracking database.

If the defect rate exceeds the 2% upper limit, the supervisor will alert the production manager to do a root cause analysis and implement corrective actions like retraining personnel or adjusting equipment.

The production manager will file an incident report for any defect rate above 1.5% detailing the actions taken and the results. A weekly summary report will be automatically generated from the database and sent to the operations leadership team.

Monthly audits of the entire control plan administration will be performed by the quality team. The plan will be reviewed quarterly and revised as needed based on audit findings and process changes.

With this example, you can see how a control plan provides the rigor to sustain gains from Six Sigma projects.

Final Thoughts on the Six Sigma Control Plan

A Six Sigma control plan is vital for sustaining improvements made during process optimization projects. By establishing clear procedures to control and monitor critical metrics, it helps maintain enhanced performance over the long term.

Whether you’re looking to standardize processes, prevent backsliding, or simplify training, a well-designed control plan provides the blueprint. Now that you understand the purpose, elements, and best practices for developing a Six Sigma control plan, you can confidently implement one.


Which Six Sigma Role Is Accountable For the Control Plan?

The Six Sigma Black Belt is the key role accountable for developing and executing the control plan during the Control phase of the DMAIC methodology. The Black Belt ensures the control plan is comprehensive and aligns with the improvements made in the project. They also provide training on the control plan and conduct periodic audits to verify adherence.

When Does a Six Sigma Control Plan End?

A Six Sigma control plan does not have a set end date. It should be followed continually to sustain process improvements implemented by a Six Sigma project. The control plan is regularly reviewed and updated to keep it current, but remains active as long as the process is running to ensure ongoing control and stabilization.

Is a Lean Six Sigma Control Plan a Living Document?

Yes, a Lean Six Sigma control plan is considered a living document. It is continually updated as processes change to remain relevant. Control plans have no end date, as they provide ongoing guidance for sustaining process improvements. Reviews and audits also identify enhancements to the control plan over time for maximum effectiveness.

David Usifo (PSM, MBCS, PMP®)
David Usifo (PSM, MBCS, PMP®)

David Usifo is a certified Project Management professional, professional Scrum Master, and a BCS certified Business Analyst with a background in product development and database management.

He enjoys using his knowledge and skills to share with aspiring and experienced Project Managers and Business Analysts the core concept of value-creation through adaptive solutions.

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