Control and Sustain Improvements

Learning Objectives

By the end of this lesson, the learner will be able to:

Explain why sustaining improvement is an essential part of Six Sigma.
Describe the transition from project improvement to routine process management.
Explain the role of the Control Plan in sustaining project gains.
Identify the key elements required for effective process control.
Establish appropriate performance measures and monitoring methods.
Use SPC and other monitoring methods to detect deterioration.
Develop effective reaction plans for abnormal process conditions.
Explain the importance of standard work and process documentation.
Establish clear Process Owner responsibility after project completion.
Apply audits and management reviews to sustain improvements.
Recognize process drift and conditions that can cause improvement to deteriorate.
Use visual management and escalation mechanisms appropriately.
Verify financial, customer, quality, and operational benefits after implementation.
Conduct an effective project handover and closure.
Develop a practical sustainment plan for a completed Six Sigma project.

1. Introduction

The objective of Six Sigma is not simply to produce a temporary improvement.

A successful project must produce a result that remains effective after the project team moves on to other priorities.

This is the central purpose of sustaining improvement.

Consider a process that has improved from:

8% defects → 2% defects

The project team celebrates the improvement and closes the project.

Six months later, the defect rate has returned to 6%.

The project achieved an improvement, but the improvement was not sustained.

This situation can occur when:

Standard work is not maintained.
Process ownership is unclear.
Employees are not trained.
Control charts are not reviewed.
Corrective actions are not followed.
Process changes are introduced without assessment.
Performance measures are discontinued.
Management attention decreases.
The original cause returns.
New sources of variation emerge.

Therefore:

Sustaining improvement is part of the improvement itself.

The final responsibility of the Green Belt is not merely to demonstrate that the process improved.

The Green Belt must help establish a system that allows the organization to continue performing at the improved level.

2. Concept / Theory

2.1 What Is Sustaining Improvement?

Sustaining improvement means maintaining the gains achieved by a Six Sigma project over time while ensuring that the improved process remains effective as conditions change.

Sustainment requires:

Standardization
Ownership
Measurement
Monitoring
Reaction
Training
Auditing
Review
Continuous improvement

The improved process must become part of normal operations.

2.2 Improvement vs Sustained Improvement

There is an important difference.

Improvement

The process demonstrates better performance after an intervention.

Sustained Improvement

The improved performance continues over an appropriate period under normal operating conditions.

For example:

Before project:

Defect rate = 7%

After improvement:

Defect rate = 2%

If the process remains near the improved level for an appropriate monitoring period, the evidence for sustainment becomes stronger.

The exact monitoring period should depend on:

Process frequency
Business cycle
Risk
Customer requirements
Process variability
Historical behavior

There is no universal number of days that guarantees sustainment.

2.3 Process Drift

Process drift occurs when process performance gradually moves away from the intended operating condition.

Examples:

Machine settings gradually change.
Operators develop workarounds.
Materials change.
Work instructions become outdated.
Equipment deteriorates.
Customer demand changes.
Process volume changes.
Software is modified.
Employees are not adequately trained.

Process drift may be gradual and therefore difficult to detect without monitoring.

This is one reason SPC and performance measurement are important.

2.4 Control Strategy

A control strategy defines how the improved process will be maintained.

It should address:

What is important?
What is measured?
What is the acceptable condition?
How often is it measured?
Who reviews it?
What indicates abnormal behavior?
What action is required?
Who owns the response?
How is the response documented?

This is the operational foundation of sustainment.

2.5 Control Plan

A Control Plan documents the controls necessary to maintain important process characteristics.

It may include:

Process step
Critical characteristic
CTQ
Specification
Target
Measurement method
Measurement system
Sample size
Frequency
Control method
Responsible person
Reaction plan
Records

A Control Plan should be practical.

A document that nobody uses is not an effective control mechanism.

2.6 Standard Work

Standard work defines the agreed method for performing an important process activity.

It helps reduce variation caused by differences in how people perform the work.

Standard work should describe, as appropriate:

Sequence
Method
Required conditions
Key parameters
Safety requirements
Quality requirements
Response to abnormalities

When an improvement changes the process, standard work should be updated.

3. Key Topics

3.1 Process Owner Responsibility

After project completion, responsibility should transition to the Process Owner.

The Process Owner should understand:

What changed.
Why it changed.
What performance is expected.
What must be monitored.
What constitutes abnormal behavior.
What action is required.
When escalation is required.

The Green Belt should not remain the permanent owner of routine process control unless that is explicitly part of the organization’s role structure.

3.2 Performance Measures

Sustainment requires appropriate measures.

Possible measures include:

Quality

Defect rate
First-pass yield
Rework
Scrap
Customer complaints

Delivery

Cycle time
Lead time
On-time delivery

Productivity

Throughput
Productivity
Resource utilization

Financial

Cost per transaction
Scrap cost
Labor cost
Verified project savings

Customer

Customer satisfaction
Response time
Service-level performance

Measures should remain connected to the original project objective.

3.3 Leading and Lagging Measures

Lagging Measures

Show the result after performance has occurred.

Examples:

Monthly defect rate
Customer complaints
Cost of poor quality

Leading Measures

Provide earlier indications of process conditions that may influence future performance.

Examples:

Preventive-maintenance completion
Training completion
Process audit compliance
Adherence to critical process settings

A strong sustainment system may use both.

3.4 Control Charts in Sustainment

Control charts can provide ongoing statistical monitoring when appropriate.

The Green Belt should monitor for:

Points outside control limits
Runs
Trends
Shifts
Cycles
Other predefined signals

The purpose is early detection of changes in process behavior.

A control chart should not become a chart that is generated but never reviewed.

There must be a defined response.

3.5 Reaction Plan

A reaction plan defines what happens when the process deviates from the expected condition.

For example:

Signal → Notify → Contain if Necessary → Investigate → Correct → Verify → Document → Resume

The exact response depends on:

Risk
Process
Customer impact
Regulatory requirements
Organizational procedures

3.6 Process Audits

Audits can verify whether the improved process is being followed.

An audit may examine:

Standard-work compliance
Control-plan compliance
Measurement records
Training status
Equipment condition
Data accuracy
Reaction-plan compliance

An audit should identify opportunities for correction and improvement rather than become merely a paperwork exercise.

3.7 Layered Process Audits

In some organizations, different levels of management periodically verify critical process conditions.

For example:

Operator checks daily.
Supervisor reviews weekly.
Process Owner reviews monthly.
Management reviews key performance periodically.

This creates multiple levels of visibility.

The exact frequency should be appropriate to process risk and organizational requirements.

3.8 Visual Management

Visual management makes important information easy to understand.

Examples:

Control charts
KPI boards
Process-status displays
Performance dashboards
Standard-work visuals
Escalation indicators

Effective visual management should help people recognize:

Normal → Abnormal → Required Response

3.9 Training and Competence

A process cannot remain stable if employees do not know how to perform it correctly.

When personnel change:

New employees should be trained.
Existing employees may require refresher training.
Competence should be verified where appropriate.
Training records should be maintained.

Training should reflect the current standard.

An outdated training document can undermine an otherwise effective Control Plan.

3.10 Change Control

A sustained process can become unstable when changes are introduced without adequate assessment.

Examples:

New equipment
New material
New supplier
New software
New process sequence
New staffing arrangement
New product
New customer requirement

Change control should consider:

Risk
Impact
Required testing
Documentation
Training
Measurement
Control Plan updates

3.11 Financial Benefit Verification

Six Sigma projects frequently include financial objectives.

The Green Belt should distinguish between:

Estimated Benefit

The projected financial impact used when evaluating the project.

Realized Benefit

The actual benefit achieved after implementation.

Verified Benefit

The benefit confirmed according to the organization’s financial or governance process.

Finance involvement may be required to validate savings.

Not every operational improvement automatically becomes a financial saving.

For example, reducing processing time may increase capacity without reducing actual expenditure.

Therefore, financial benefits should be defined and validated carefully.

3.12 Project Closure

Project closure should confirm that:

The objective was addressed.
Results were validated.
Controls are in place.
Ownership has transferred.
Documentation is complete.
Training is complete.
Benefits are verified where applicable.
Remaining risks are understood.
Lessons learned are captured.

A project should not be considered fully closed merely because the team has completed its analysis.

4. Tools / Methodology

4.1 Sustainment Planning Methodology

Step 1 — Define the Improved Standard

Clearly document the validated future-state process.

Step 2 — Identify Critical Characteristics

Determine which process inputs and outputs require control.

Step 3 — Define Performance Measures

Specify:

Measure
Target
Specification
Data source
Calculation method

Step 4 — Define Monitoring

Specify:

What?
Who?
When?
How often?
How?

Step 5 — Select Control Method

Possible methods:

SPC
KPI monitoring
Automated alarms
Audits
Checklists
Error-proofing
Standard work

Step 6 — Define Reaction Plan

Specify what happens when performance becomes abnormal.

Step 7 — Assign Ownership

Identify the Process Owner and supporting roles.

Step 8 — Update Documentation

Update:

SOPs
Standard work
Control Plan
FMEA
Training material
Forms
System instructions

Step 9 — Verify Implementation

Confirm that the controls are actually being used.

Step 10 — Monitor Sustainment

Review results over an appropriate period.

Step 11 — Conduct Handover

Transfer responsibility to the Process Owner.

Step 12 — Close the Project

Document:

Results
Lessons learned
Benefits
Risks
Ownership
Monitoring requirements

4.2 Sustainment Plan Template

A practical sustainment plan can include:

Element	Definition
Process	Process being controlled
CTQ/KPI	Critical performance measure
Target	Desired performance
Specification	Required limit
Measurement	Measurement method
Frequency	Monitoring frequency
Control Method	SPC, audit, KPI, etc.
Owner	Responsible person
Reaction	Required response
Escalation	Escalation condition
Record	Where evidence is stored
Review	Management/process review frequency

4.3 Control Plan Review

A Control Plan should be reviewed when:

Process changes occur.
New failure modes emerge.
Customer requirements change.
Performance deteriorates.
New equipment is introduced.
New materials are introduced.
Audit findings identify gaps.
Corrective actions alter the process.

The Control Plan should remain a living operational document.

5. Worked Example / Case Study

Case Study: Reducing Customer Complaint Response Time

A service organization completed a Six Sigma project.

Before Improvement

Average response time:

20 hours

Project Goal

Reduce average response time to:

≤ 10 hours

Improvement Actions

The team:

Standardized work allocation.
Introduced priority categories.
Established escalation rules.
Added automated reminders.
Defined response-time ownership.

After Improvement

Average response time:

8 hours

The team now needs to sustain the result.

5.1 Define the Control Measure

The primary CTQ is:

Customer response time

Operational definition:

Time from receipt of a valid customer request to the first qualified response.

This definition prevents inconsistent measurement.

5.2 Define Monitoring

The Process Owner monitors:

Daily response-time performance.
Percentage exceeding 10 hours.
Weekly trend.
Significant process signals.

5.3 Establish Reaction Criteria

If performance deteriorates:

Review the affected transactions.
Determine whether the issue is isolated or systemic.
Check workload.
Check staffing.
Review priority classification.
Verify adherence to standard work.
Check system availability.
Investigate the cause.
Correct the verified cause.
Confirm recovery.

5.4 Update Documentation

The team updates:

Standard operating procedure.
Control Plan.
Training material.
Escalation procedure.
Performance dashboard.

5.5 Transfer Ownership

The Process Owner accepts responsibility for:

Monitoring
Review
Escalation
Training
Corrective action
Control-plan maintenance

The Green Belt remains available according to the organization’s project-governance model but does not become the permanent process owner.

5.6 Verify Sustainment

Suppose performance remains:

Month 1: 8.2 hours
Month 2: 8.5 hours
Month 3: 8.1 hours
Month 4: 8.7 hours

The results indicate continued performance around the improved level.

However, the team should also examine:

Variation
Customer complaints
Exceptions
Process adherence
Control-chart behavior where appropriate

Sustainment is evaluated using evidence, not one favorable data point.

6. Practical Application

Exercise 1 — Develop a Sustainment Plan

Select a completed or hypothetical Six Sigma project.

Define:

Process
CTQ/KPI
Target
Specification
Measurement method
Sampling
Frequency
Control method
Process Owner
Reaction plan
Escalation criteria
Review frequency

Exercise 2 — Project Handover

Prepare a project-handover checklist.

Include:

Improved process documented.
Standard work updated.
Control Plan completed.
FMEA updated.
Training completed.
Measurement method defined.
Monitoring established.
Reaction plan defined.
Process Owner identified.
Performance dashboard available.
Benefits documented.
Risks documented.
Open actions transferred.
Handover accepted.

Exercise 3 — Detecting Process Drift

Suppose a process has performed at approximately 2% defects for several months.

The defect rate then begins increasing:

2.0% → 2.1% → 2.3% → 2.6% → 2.9%

Ask the Green Belt:

Is this evidence of a possible deterioration?
What additional data should be examined?
Is there a control-chart signal?
What process changes occurred?
Did materials change?
Did equipment change?
Did staffing change?
Did standard-work compliance change?
Has the measurement system changed?
What action should be taken?

The objective is to investigate the process rather than wait until a major failure occurs.

Exercise 4 — Benefit Verification

For a project claiming financial savings, distinguish:

Estimated benefit
Actual operational improvement
Realized financial impact
Verified financial benefit

Identify which functions should participate in verification.

Exercise 5 — Sustainment Audit

Conduct a simulated audit three months after project closure.

Check:

Are employees following the new process?
Are measurements being collected?
Are control charts/KPIs reviewed?
Are reaction plans followed?
Is training current?
Is the Control Plan current?
Has the FMEA changed?
Has process performance remained improved?
Are benefits being realized?
Are new risks emerging?

Document findings and corrective actions.

6.1 Final Sustainment Checklist

Before closing a Six Sigma project, verify:

Project objective has been addressed.
Improvement has been validated.
Measurement definitions are clear.
Measurement system is appropriate.
Process is stable where applicable.
Capability has been assessed where appropriate.
Standard work is updated.
Control Plan is completed.
FMEA is updated where necessary.
SPC/KPI monitoring is established.
Reaction plan is defined.
Process Owner accepts responsibility.
Training is completed.
Documentation is updated.
Change-control requirements are defined.
Benefits are documented.
Financial benefits are verified where applicable.
Open risks are documented.
Project handover is completed.
Sustainment monitoring is scheduled.
Lessons learned are captured.
Project closure is formally approved.

7. Lesson Summary

Sustaining improvement is an essential component of Six Sigma.

The major principles are:

Improvement must continue after project completion.
Sustained performance requires standardization and ownership.
Control Plans document important process controls.
Standard work establishes the required method.
Process Owners are responsible for routine process performance.
Performance measures provide visibility.
Leading and lagging measures can complement each other.
SPC can detect changes in process behavior where appropriate.
Reaction plans define the response to abnormal conditions.
Audits can verify adherence to the improved process.
Training and competence must be maintained.
Change control helps protect process stability when conditions change.
Financial benefits should be distinguished from operational improvements and verified according to organizational requirements.
Project closure should include a proper handover.
Sustainment should be monitored using evidence over an appropriate period.
Control documents should be updated when the process changes.

The sustainment cycle is:

Standardize → Measure → Monitor → React → Verify → Review → Improve

8. Lesson Learnt / Conclusion

The final measure of a Six Sigma project is not simply the result achieved during the project.

The deeper question is:

Can the organization maintain the improved performance after the project team has moved on?

A strong Six Sigma project leaves behind more than a collection of analysis files.

It leaves behind:

A better process.
Clear standards.
Reliable measurements.
Defined controls.
Trained people.
A capable Process Owner.
A practical Control Plan.
A reaction mechanism.
Performance monitoring.
Documented benefits.
A method for responding to future change.

The Green Belt should understand that Control is not the end of improvement; it is the mechanism that protects improvement and creates the foundation for the next cycle of improvement.

When deterioration is detected, the organization should not simply restore the old condition and move on. The event should be treated as an opportunity to understand why the control system did not prevent or detect the deterioration earlier.

The long-term objective is therefore:

Improve → Standardize → Control → Sustain → Learn → Improve Again

Key takeaway:

A Six Sigma improvement becomes a true organizational gain only when the improved performance is built into the process and sustained over time.