The Control Phase represents the final and arguably most critical stage of the DMAIC (Define, Measure, Analyze, Improve, Control) methodology in Six Sigma. While many organizations celebrate after implementing improvements, the real challenge lies in maintaining these gains over time. This comprehensive guide explores how the Control Phase ensures that your process improvements become permanent fixtures rather than temporary successes.
Understanding the Control Phase
The Control Phase serves as the guardian of all improvements achieved during the previous DMAIC phases. After investing considerable time and resources in defining problems, measuring performance, analyzing root causes, and implementing solutions, organizations must establish systems that prevent processes from reverting to their previous inefficient states. This phase transforms temporary fixes into standardized practices that deliver consistent results month after month, year after year. You might also enjoy reading about Big Data and AI: Modern Approaches to the Recognize Phase in Lean Six Sigma.
Without proper controls, even the most brilliant improvements gradually deteriorate. Employees revert to old habits, new team members lack proper training, and management attention shifts to other priorities. The Control Phase addresses these challenges by creating sustainable systems that maintain improved performance regardless of personnel changes or organizational distractions. You might also enjoy reading about How to Validate Your Measurement System Before Collecting Data: A Complete Guide.
Key Objectives of the Control Phase
The Control Phase pursues several interconnected objectives that work together to sustain improvements:
- Standardization: Document new processes and establish them as the official way of working
- Monitoring: Create ongoing measurement systems to track process performance
- Correction: Develop response plans for when processes deviate from targets
- Documentation: Record all changes, lessons learned, and best practices
- Transfer: Hand over the improved process to process owners and operators
Essential Tools and Techniques
Statistical Process Control Charts
Statistical Process Control (SPC) charts form the backbone of process monitoring in the Control Phase. These powerful visual tools help teams distinguish between normal process variation and true problems requiring intervention.
Consider a customer service call center that improved its average call handling time from 8.5 minutes to 6.2 minutes during the Improve Phase. To maintain this improvement, the team implements an X-bar and R chart with the following sample data collected over ten days:
Sample Data Set:
Day 1: 6.1, 6.3, 6.0, 6.4, 6.2 minutes (Average: 6.2, Range: 0.4)
Day 2: 6.0, 6.3, 6.1, 6.2, 6.4 minutes (Average: 6.2, Range: 0.4)
Day 3: 6.3, 6.1, 6.2, 6.5, 6.1 minutes (Average: 6.24, Range: 0.4)
Day 4: 6.4, 6.0, 6.3, 6.1, 6.2 minutes (Average: 6.2, Range: 0.4)
Day 5: 6.2, 6.3, 6.1, 6.4, 6.3 minutes (Average: 6.26, Range: 0.3)
Day 6: 6.1, 6.2, 6.0, 6.3, 6.2 minutes (Average: 6.16, Range: 0.3)
Day 7: 6.3, 6.4, 6.2, 6.1, 6.0 minutes (Average: 6.2, Range: 0.4)
Day 8: 6.2, 6.1, 6.3, 6.4, 6.2 minutes (Average: 6.24, Range: 0.3)
Day 9: 6.0, 6.2, 6.1, 6.3, 6.1 minutes (Average: 6.14, Range: 0.3)
Day 10: 6.3, 6.2, 6.4, 6.1, 6.2 minutes (Average: 6.24, Range: 0.3)
The control chart would display the daily averages plotted against calculated control limits. If any point falls outside these limits or shows non-random patterns, the team investigates immediately. This real-time monitoring prevents small problems from becoming major failures.
Control Plans
A control plan documents exactly how the improved process should operate and be monitored. This living document includes process steps, key input and output variables, measurement methods, specifications, sampling plans, and response protocols.
For our call center example, the control plan might specify that team leaders randomly sample five calls per day per representative, measure handling time using the phone system’s automated timer, maintain times between 5.5 and 6.5 minutes, and conduct immediate coaching if any representative exceeds limits on two consecutive days.
Standard Operating Procedures
Standard Operating Procedures (SOPs) translate improvements into step-by-step instructions that anyone can follow. Effective SOPs use clear language, include visual aids, and anticipate common questions or problems.
The call center might create an SOP that details the improved call script, explains the new knowledge base system implemented during the Improve Phase, and provides troubleshooting steps for common customer issues. These documents ensure consistency regardless of which employee handles a customer’s call.
Real-World Control Phase Example
A manufacturing company producing automotive components faced chronic defect rates of 4.2 percent in their welding process. After completing the Improve Phase, they reduced defects to 0.8 percent by optimizing welding parameters and implementing better operator training. The Control Phase implementation involved several strategic steps.
First, they established control charts tracking daily defect rates using samples of 50 parts per shift. Their baseline data for the first month post-improvement showed:
Weekly Defect Rates:
Week 1: 0.7%, 0.9%, 0.8%, 0.6%, 0.8% (Average: 0.76%)
Week 2: 0.9%, 0.7%, 0.8%, 0.9%, 0.7% (Average: 0.80%)
Week 3: 0.6%, 0.8%, 0.9%, 0.7%, 0.8% (Average: 0.76%)
Week 4: 0.8%, 0.7%, 0.8%, 0.9%, 0.8% (Average: 0.80%)
Second, they created detailed SOPs covering welding machine setup, parameter verification, and quality checks. Third, they implemented a training certification program ensuring every operator demonstrated competency with the new procedures. Fourth, they established monthly process reviews where the team examined control charts, discussed concerns, and identified opportunities for further refinement.
Six months later, the improved defect rate remained stable at 0.75 percent, representing sustained savings of over $180,000 annually. Without the Control Phase, previous improvement attempts had consistently failed within three months.
Common Control Phase Challenges
Organizations frequently encounter several obstacles when implementing the Control Phase. Recognizing these challenges helps teams prepare appropriate responses.
Resistance to Documentation
Team members often view documentation as bureaucratic busywork rather than valuable protection for their hard work. Leadership must emphasize that documentation preserves improvements and enables replication across other areas.
Inadequate Monitoring Resources
Effective monitoring requires time and attention. Organizations must allocate sufficient resources for ongoing measurement and analysis rather than expecting process owners to add these responsibilities without adjusting other workloads.
Lack of Response Protocols
Detecting problems means nothing without clear action plans. Teams must establish escalation procedures, decision authorities, and corrective action processes before problems occur.
Sustaining Improvements Through Culture
The most successful Control Phase implementations extend beyond tools and documents to embed continuous improvement into organizational culture. This requires visible leadership support, regular communication about sustained results, recognition for maintaining standards, and consequences for reverting to old practices.
Organizations should celebrate Control Phase milestones just as enthusiastically as initial improvements. When a process maintains improved performance for six months, one year, or longer, acknowledge this achievement publicly. These celebrations reinforce the importance of sustaining gains and motivate teams working on other improvement projects.
Measuring Control Phase Success
Several metrics indicate whether the Control Phase is functioning effectively. Process performance should remain within control limits at least 95 percent of the time. Response time to out-of-control situations should decrease as teams become more proficient. The frequency of process audits finding non-compliance should trend downward. Finally, the cost of maintaining controls should represent a small fraction of the financial benefits generated by improvements.
Conclusion
The Control Phase transforms temporary improvements into permanent competitive advantages. By implementing statistical process control, creating comprehensive documentation, training personnel thoroughly, and establishing monitoring systems, organizations protect their improvement investments and create foundations for ongoing success. While this phase requires discipline and attention to detail, the alternative of watching improvements evaporate wastes all previous DMAIC efforts.
The journey from identifying problems to sustaining solutions demands expertise, methodology, and commitment. Organizations that master the Control Phase discover that each successful project builds capability for the next, creating a virtuous cycle of continuous improvement that competitors cannot easily replicate.
Enrol in Lean Six Sigma Training Today
Understanding the Control Phase intellectually differs significantly from implementing it successfully in real-world situations. Comprehensive Lean Six Sigma training provides the knowledge, tools, and practical experience necessary to sustain process improvements effectively. Whether you are beginning your continuous improvement journey or seeking to enhance existing skills, professional certification programs offer structured learning paths from Yellow Belt through Black Belt levels. These programs combine theoretical knowledge with hands-on projects, ensuring you can apply Control Phase techniques immediately in your organization. Do not let your improvement efforts fade away due to inadequate sustainment systems. Invest in proper training and join thousands of professionals who have transformed their careers and organizations through Lean Six Sigma expertise. Enrol today and become the champion of lasting change your organization needs.
