Technical Article

What is Six Sigma and How is it Used in Manufacturing?

December 28, 2020 by Anish Devasia

Six Sigma can be used to effectively manufacture highly standardized products. This article covers Six Sigma's philosophy, implementation, and certifications while looking at why it works for control systems engineers.

Six Sigma (6σ) is a set of tools and techniques developed by Motorola engineer Bill Smith for process improvements. The philosophy behind Six Sigma is to identify, remove/improve the processes that cause defects in manufacturing or business processes. It aims to remove the variability in production and processes to bring about a highly standardized product. 


When production happens at a fast pace for huge quantities, standardized, defect-free end products are essential.

Figure 1. When production happens at a fast pace for huge quantities, standardized, defect-free end products are essential.


Successful implementation of Six Sigma techniques should yield defect-free products in 99.9997% of the total production. This number comes from defects per million opportunity (DPMO) calculations shown in Table 1. 


Table 1. Defect per Million Opportunity (DPMO)

Sigma % Good  % Defective DPMO
1 30.9% 69.1% 691,462
2 69.1% 30.9% 308,538
3 93.3% 6.7% 66,807
4 99.38% 0.62% 6,210
5 99.977% 0.023% 233
6 99.9997% 0.00034 3.4


This article looks at Six Sigma’s philosophies, implementation, and uses and explores why control engineers can benefit from employing it.


Six Sigma Philosophy

When a process has less than 3.4 defects per million opportunities (DPMO), it is compliant with Six Sigma. In statistics, Sigma refers to the standard deviation. The results of processes are plotted on a bell-curve with the desired specification as mean. 

One Sigma refers to one standard deviation away from the mean. A defect happens when the event is three standard deviations above the mean or three standard deviations below the mean. That is when the event is out of range of six standard deviations, or six Sigma (where the name Six Sigma is derived). This level of deviation translates to 3.4 defects per million events.

The three pillars of Six Sigma are:

  1. Continuous efforts are of vital importance to achieve stable and predictable process results.
  2. Characteristics of manufacturing and business processes can be defined, measured, analyzed, improved, and controlled.
  3. Commitment from the entire organization to achieve sustained quality improvement, especially from top-level management.


Implementation of Six Sigma

There are many methodologies to implement Six Sigma. One methodology is DMAIC, which stands for Define-Measure-Analyze-Improve-Control. 


One popular methodology of Six-Sigma implementation is DMAIC.

Figure 2. One popular methodology of Six-Sigma implementation is DMAIC.


Let’s look at what each of these parts means to the larger methodology.

Define: The first step is to define the scope and objectives of process improvements. The process improvements should be aligned with business strategy and consumer needs.

Measure: Without having a real quantitative understanding of current processes, they cannot be improved. All the aspects of current processes should be measured, and all the relevant data should be collected.

Analyze: The data accumulated needs to be verified and analyzed. With the analysis, the cause and effect relationships of the processes have to be identified. How different parts of the process interact with each other has to be explored making sure all factors have been considered. This exercise is to identify the root cause of the defect and not just the immediate relationship.

Improve: Once the root cause for defects is identified, it reveals insights on improving the process. The improvements must be tested with pilot runs and experiments to determine process stability before final implementation.

Control: The mistakes identified should not creep into the improved process. The improved process should be controlled so the deviations from the target are caught in time, keeping the defects from occurring. Statistical process control, production boards, and visual workplaces can be used to continuously monitor processes.

Another methodology is DMADV or DFSS. DMADV is an acronym for Define-Measure-Analyze-Desig-Verify. DFSS stands for Design For Six Sigma. There is also the Lean Six Sigma approach which blends the lean manufacturing philosophy with Six Sigma.


Six Sigma and Control Engineering

Six Sigma doctrines and techniques are not restricted to one industry or discipline. At its core, Six Sigma is a set of statistical tools to analyze processes and identify the root causes of defects. For any process, especially in manufacturing and industrial processes automation drastically reduces defects and deviations from the desired output. Control systems and automation are pivotal in achieving Six sigma compliant processes.

Control systems can help eliminate bottlenecks in processes, brings stability to industrial processes. A control engineer with Six Sigma knowledge can improve processes in ways that improve the mechanical process while aligning with the business objectives of the firm. 

Control systems and automation are powerful tools to achieve a Six Sigma level of process improvement. Control system engineers with Six Sigma expertise can be at the vanguard of process improvement and champions of Six Sigma philosophy in companies.


Six Sigma Practitioners and Certifications

The Six Sigma process improvements are always a team effort. Professionals from multiple disciplines and varying levels of professional experience come together to take Six Sigma projects forward. Top management provides high-level guidance and promotes Six Sigma within the business.

Demonstrable expertise in Six Sigma implementation is certified by various certification programs. The levels of expertise are rewarded in a belt system similar to martial arts. The novice practitioners are white belts. According to the expertise demonstrated, practitioners are awarded yellow, green, black, and master belts. Six Sigma certification programs help demonstrate a person’s level of expertise and are widely recognized in every industry.

The Six Sigma philosophy initiated by Motorola was popularized by the legendary CEO of General Electric, Jack Welch. By the start of this century, three-quarters of Fortune 500 companies had Six Sigma initiatives. Today the scope of Six Sigma goes further. The Council for Six Sigma Certification sets the standards for Six Sigma implementations and certifications. Their website has a comprehensive list of Six Sigma certification providers. They also keep tabs on certification providers and provide alerts on providers with a lousy reputation.