The Concepts of Six Sigma

Since the 1920's the word 'sigma' has been used by mathematicians and engineers as a symbol for a

unit of measurement in product quality variation

Six sigma was originally developed by Motorola Inc. In the 1980’s

What is Six Sigma ?

The UK Department for Trade and Industry says Six Sigma is:

"A data-driven method for achieving near perfect quality. Six Sigma analysis can focus on any element of production or service, and has a strong emphasis on statistical analysis in design, manufacturing and customer-oriented activities." June 2005.

Six Sigma is a highly disciplined process that helps us focus on developing and delivering near-perfect

products and services. Why "Sigma"? The word is a statistical term that measures how far a given

process deviates from perfection. The central idea behind Six Sigma is that if you can measure how

many "defects" you have in a process, you can systematically figure out how to eliminate them and get

as close to "zero defects" as possible.

Six Sigma's aim is to eliminate waste and inefficiency, thereby increasing customer satisfaction by delivering what the customer is expecting.

Six Sigma is a highly disciplined process that helps us focus on developing and delivering near-perfect products and services.

Six Sigma is a data driven methodology, and requires accurate data collection for the processes being analyzed.

Six Sigma is a business-driven, multi-dimensional structured approach to:

Improving Processes Lowering Defects Reducing process variability Reducing costs Increasing customer satisfaction Increased profits

At the core that’s what it is, it is the application of statistical methods to ensure quality with

consistency.

Key Concepts of Six Sigma

At its core, Six Sigma revolves around a few key concepts.

Critical to Quality: Attributes most important to the customer.

The term critical to quality, CTQ, identifies the elements of a process that significantly affect the output of the process that are important to the end customers of that process. Not delivering these CTQ factors directly affects customers' satisfaction with a service or product.

Defect: Failing to deliver what the customer wants.A defect is a measurable characteristic of a process or its output that does not meet the customers' specifications. When defects occur time is spent correcting the problems. Six sigma identifies and eliminates the defects so that the process always delivers the customers' CTQs.

Process Capability: What your process can deliver.

Variation: What the customer sees and feels.Variation is a change in a process that affects the expected outcome. It is the gap between the standard output and the actual output of the process. There will always be some variation in a process and the key issue is whether that variation affects the final outcome and the customers' CTQ requirements.

Stable Operations: Ensuring consistent, predictable processes to improve what the customer sees and feels.Process control, sometimes called process standardization or stable operations, ensures that the improvements made in the process are sustained over time. It focuses on problem prevention rather than detection.

Design for Six Sigma (DFSS): Designing to meet customer needs and process capability.It is used to develop new processes rather than improve existing processes. It may also be used to radically re-design a service process or product. Like other six sigma concepts, it is driven by the customers' critical to quality requirements.

Statistical Basis of Six Sigma

Six Sigma began by stressing a common measure for quality.

Defects per unit= number of defects discovered/number of units produced

However, this type of output measure tends to focus on the final product, not the process that produces the product. The six sigma concept redefines quality performance as defects per million opportunities (dpmo)”

Dpmo= (number of defects discovered/opportunities for error) x 1,000,000

Six sigma represents a quality level of at most 3.4 defects per million opportunities. That is, 0.00034% of 1M or 3.4 parts per million.

One to six sigma conversion table

'Long Term Yield' (basically the percentage of successful outputs or operations)%

Defects Per Million Opportunities (DPMO)

'Processs Sigma'

99.99966 3.4 6

99.98 233 5

99.4 6,210 4

93.3 66,807 3

69.1 308,538 2

30.9 691,462 1

One sigma (one standard deviation) will contain 68.2% of the population. Two standard deviation will contain an additional 27.2 % for a total of 95.4% of the population. Six standard deviations (six sigma) will contain 99.9997% of the population. Another way to say this is that only 3.4 of the one million products a company makes are defective. That would be a six sigma product.

Project Selection For Six Sigma

According to Kepner and Tregoe, a problem is a deviation between what should be happening and what actually is happening. Every instance of quality problem solving falls into one of the five categories:

1. Conformance problems: Defined by unsatisfactory performance by a well-specified system. Users are not happy with system outputs, such as quality or customer service levels. The system has worked before, but for some reason it is not performing acceptably. The causes of deviations must be identified, and the system must be restored to its intended mode of functioning.

2. Unstructured performance problems: Result from unsatisfactory performance by a poorly specified system. That is, the task is nonstandardized and not fully specified by procedures and requirements. An example would be poor sales. No one right way of selling a product means the problem cannot be cured by enforcing standards that do not exist.

3. Efficiency problems: Result from unsatisfactory performance from the standpoint of stakeholders other than customers. Typical examples are cost and productivity issues. Even though the quality of the outputs may be acceptable, the system’s performance does not achieve internal organizational goals.

4. Product design problems: Involve designing new products that better satisfy user needs-the expectations of customers that matter most of them. In six sigma, those vital characteristics are called “critical to quality”

5. Process design problems: Involve designing new processes or substantially revising existing processes. The challenge here is determining process requirements, generating new process alternatives, and linking these processes to customer needs.

Six Sigma Problem Solving

Problem solving is the activity associated with changing the state of what is actually happening to what should be happening.

Juran defined breakthrough as the accomplishment of any improvement that takes an organization to unprecedented levels of performance. The objectives of six sigma projects often focus on breakthrough improvements that add value to the organization and its customers through systematic approaches to problem solving.

A six sigma project leader is called a Black Belt. Black Belt is a specific Six Sigma term to describe a team leader and one who has achieved accredited 'Black Belt' qualification via an appropriate training course. Other project members are called Green Belts. Green Belt is a Six Sigma team member who has received Green Belt training and who works part-time on Six Sigma projects under the guidance of a Black belt team leader.

Principal Problem-solving methodology used by Six Sigma:

DMAIC (Define, Measure, Analyze, Improve, Control)

Define: After six sigma project is selected, the first step is to clearly define the problem. This activity is significantly different from project selection.

Define who customers are, what their requirements are for products and services, and what their expectations are

Define project boundaries the stop and start of the process Define the process to be improved by mapping the process flow

Measure: This phase of the DMAIC process focuses on how to measure the internal processes that affect CTQs (critical to quality). It requires an understanding of the causal relationships between process performance and customer value.

Six Sigma uses the notion of a function in mathematics to portray the relationship between process performance and customer value:

Y=f(x)

The simple looking equation mentioned above can be described as the core of the Six sigma philosophy. The component parts of the equation are as follows:

Y = Outputs also known as Dependant Variables X = Inputs also known as independent Variables F = Function of

What the equation is actually saying is that the outputs we receive are the function of the inputs that we give to our process. Hence if we were able to control the inputs with precision, the outputs would also be controlled in a precise manner

Analyze: focuses on why defects, errors, or excessive variation occur, which often result from one or more of the following:

A lack of knowledge about how a process works A lack of knowledge about how a process should work A lack of control of materials and equipment used in a process Waste and complexity Lack of training

After potential variables are identified, experiments are conducted to verify them. These experiments generally consist of formulating some hypothesis to investigate, collecting data, analyzing the data, and reaching a reasonable and statistically supportable conclusion.

Improve: Once the root cause of a problem is understood, the analyst or team needs to generate ideas for removing or resolving the problem and improve the performance measures and CTQs.

Control: The control phase focuses on how to maintain the improvements, which includes putting tools in place to ensure that the key variables remain within the maximum acceptable ranges under the modified process.