Six Sigma- Improvement Methodology

Six Sigma is a set of techniques and tools for process improvement
Six Sigma seeks to improve the quality of process outputs by

• Identifying and removing the causes of defects (errors)
• Minimizing variability in manufacturing and business processes.

It uses a set of quality management methods, including statistical methods, and creates a special infrastructure of people within the organization ("Champions", "Black Belts", "Green Belts", "Yellow Belts", etc.) who are experts in the methods.

Each Six Sigma project carried out within an organization follows a defined sequence of steps and has quantified value targets,
for example:

• Reduce process cycle time,
• Reduce pollution,
• Reduce costs,
• Increase customer satisfaction
• Increase profits

The term "six sigma process" comes from the notion that if one has six standard deviations between the process mean and the nearest specification limit, practically no items will fail to meet specifications.
This is based on the calculation method employed in process capability studies.

Capability studies measure the number of standard deviations between the process mean and the nearest specification limit in sigma units, represented by the Greek letter σ (sigma). As process standard deviation goes up, or the mean of the process moves away from the center of the tolerance, fewer standard deviations will fit between the mean and the nearest specification limit, decreasing the sigma number and increasing the likelihood of items outside specification.

In Six Sigma, mainly two methodologies followed:
1. DMAIC- Define, Measure, Analyze, Improve & Control
2. DMADV-Define, Measure, Analyze, Design & Validate.

Six sigma methodology can be applied in most of the fields i.e. production /manufacturing, service, IT, Administration, Quality, HR, Purchase, etc.

What is Six Sigma : 6σ

Sigma(σ)

·         Degree of variation;

·         Level of performance in terms of defects;

·         Statistical measurement of process capability;

·         Benchmark for comparison;

·         Process improvement methodology;

Business Definition

A break through strategy to significantly improve customer satisfaction and shareholder value by reducing variability in every aspect of business.

Technical Definition

A statistical term signifying 3.4 defects per million opportunities

Sigma Level	DPM Opportunity
1σ	6,90,000
2σ	3,08,000
3σ	66,800
4σ	6,210
5σ	230
6σ	3.4

DPM= Defect per Million.

DMAIC-   Define-   Measure-  Analyze-  Improve- Control

Define

• Identify, evaluate and select projects for improvement
• Set goals
• Form teams. 

The purpose of this step is to clearly articulate the business problem, goal, potential resources, project scope and high-level project timeline.

This information is typically captured within project charter document.

Write down what you currently know.

Seek to clarify facts, set objectives and form the project team

Define the following:

• A Problem
• The Customer
• Critical To Quality
• Project Target
• Project Boundry/scope
• A Project charter for Agreement between sponser and leader.

Measure

• Collect data on size of the selected problem,
• identify key customer requirements,
• Determine key product and process characteristic 

The purpose of this step is to objectively establish current baselines as the basis for improvement.

This is a data collection step, the purpose of which is to establish process performance baselines.

The performance metric baseline(s) from the Measure phase will be compared to the performance metric at the conclusion of the project to determine objectively whether significant improvement has been made.

The team decides on what should be measured and how to measure it.

It is usual for teams to invest a lot of effort into assessing the suitability of the proposed measurement systems.

Good data is at the heart of the DMAIC process

Analyze

• Analyze data, establish and confirm the “ vital few “ determinants of the performance.
• Validate hypothesis 

The purpose of this step is to identify, validate and select root cause for elimination.

A large number of potential root causes (process inputs, X) of the project problem are identified via root cause analysis (for example a fishbone diagram).

The top 3-4 potential root causes are selected using multi-voting or other consensus tool for further validation.

A data collection plan is created and data are collected to establish the relative contribution of each root causes to the project metric, Y. This process is repeated until "valid" root causes can be identified. Within Six Sigma, often complex analysis tools are used.

However, it is acceptable to use basic tools if these are appropriate. Of the "validated" root causes, all or some can be

• List and prioritize potential causes of the problem
• Prioritize the root causes (key process inputs) to pursue in the Improve step
• Identify how the process inputs (Xs) affect the process outputs (Ys)
• Data is analyzed to understand the magnitude of contribution of each root cause, X, to the project metric, Y.
• Statistical tests using p-values accompanied by Histograms, Pareto charts, and line plots are often used to do this.
• Process maps can be created to help pin-point where in the process the root causes reside, what might be contributing to the occurrence.

Improve

• Improvement strategy
• Develop ideas to remove root causes
• Design and carry out experiments,
• Optimize the process.
• Final solutions 

The purpose of this step is to identify, test and implement a solution to the problem; in part or in whole.

Identify creative solutions to eliminate the key root causes in order to fix and prevent process problems.

Use brainstorming or techniques like Six Thinking Hats and Random Word.

Some projects can utilize complex analysis tools like DOE (Design of Experiments), but try to focus on obvious solutions if these are apparent.

Control

• Establish standards to maintain process;
• Establish the controls, implement and monitor. 
• Evaluate impact of the project

The purpose of this step is to sustain the gains. Monitor the improvements to ensure continued and sustainable success. Create a control plan. Update documents, business process and training records as required.

A Control chart can be useful during the control stage to assess the stability of the improvements over time

Related Topics

Quality     QA/QC     Quality-Problem  Quality Improvement   RCA  CAPA  SQC  Kaizen   Six Sigma   Scatter Plot   FMEA  Bench-marking   5'S   LEAN  Kanban