What is six sigma?

Six sigma is a set of methods and tools that help businesses improve product quality and production efficiency. This is done by finding defects in processes, determining their cause, and making improvements.

For maintenance teams, six sigma can be used to find and address weaknesses in maintenance workflows that can result in improved asset uptime, faster job turnaround, and reduced costs.

Six sigma vs. lean manufacturing and maintenance

Although both six sigma and lean manufacturing and maintenance are methodologies meant to improve the way a business operates, there are a couple of key differences that set them apart from each other.

Lean manufacturing’s primary focus is on reducing waste. That includes trying to minimize wasted materials, wasted product, and wasted time.

Six sigma, on the other hand, prioritizes the quality of the final product above all things. Every iteration of the process is designed and completed with an eye to reducing product and process defects.

How to start using six sigma

In order to apply six sigma to a maintenance environment, managers should familiarize themselves with the DMAIC method of implementing process improvements. DMAIC stands for:


This involves defining the problem you’re trying to fix, the impact the problem has on the rest of the process, and the standard of success.


Before you begin making changes, take measurements of current performance, costs, productivity, and other significant metrics required so you have a baseline.


Collected data should be closely analyzed in order to get to the root of the problem.


Solutions are developed, tested, and implemented in this phase. Results from each applied solution are recorded and adjusted as necessary in order to achieve the desired result.


After the improvements have been made, the maintenance department should continue to monitor the process and make incremental improvements over time.

Examples of six sigma in maintenance

Here’s a sample scenario of six sigma in action:

Let’s say the maintenance manager has noticed the costs for spare parts are getting out of hand. They then call for an investigation into possible causes for this cost creep, with the goal of eventually reducing expenses and getting the budget back under control (Define).

Inventory costs for the quarter are pulled in: Everything from invoices to purchase orders and usage records (Measure). According to analysis, a handful of parts make up a significant portion of the elevated budget as the price for each is higher than expected. Upon investigation, it’s determined that the supplier of these components has raised its prices, which inflated the total costs (Analysis).

After this discovery, purchasing agreements for some suppliers are renegotiated, while other suppliers are dropped in favor of cheaper alternatives (Improve). The team then implements an annual price review process in order to prevent future cost creep (Control).

The levels of six sigma

There are six main levels in the six sigma certification process. The levels help teams focus on continuous improvement in their manufacturing facilities. Those who obtain the six sigma certification are well versed in the lean six sigma (LSS) methodology.

White belt

The first level is a white belt or sigma white belt. At this level, professionals most likely have not completed any formal certification programs. White belts can participate in projects, problem solving, quality management, and waste reduction. They generally utilize lean thinking and sigma principles for process improvement.

Yellow belt

The second level is yellow belt or sigma yellow belt. At this level, professionals have a stronger understanding of the six sigma methodology. Yellow belt professionals have most likely attended training sessions and can actively contribute to sigma projects, but will need guidance from higher level managers who are at the black belt level.

Green belt

The third level is green belt or sigma green belt. At this level, professionals earn what's called a lean six sigma green belt certification. The certification requires a certain level of courses to be completed, and these professionals use the six sigma methods to improve services and processes. They also apply the DMAIC frameworks to understand complex business challenges and implement solutions. Professionals at this level undergo green belt training and are adept at project management, since they have a good basis in understanding data.

Black belt

The fourth level is black belt or sigma black belt. At this level, most professionals have a very strong understanding of the six sigma methodology. Some may even continue their education by obtaining what's called a six sigma black belt certification. At this level professionals work on lean six sigma projects (LSS), observe results, and manage a team.

Master black belt

The fifth level is a master black belt or sigma master black belt. At this level, professionals have a strong understanding in the sigma methodology. Most master black belts use the lean six sigma (LSS) methodology and their problem solving skills to overcome business challenges. They are also team champions and most likely embed sigma principles into their team processes and practices.


The last level of the sigma certification is a champion. At this level, professionals obtain their graduate certificate and are well versed in the lean six sigma methodology. They have officially completed their sigma training, and can teach their team the principles. These individuals work closely with executive teams to ensure principles of lean management are followed and ensure their teams are in a state of continual improvement.

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Six sigma and beyond

The sigma methodology and principles can help teams run more efficiently and improve quality management across the business. As a business leader, it may be worth considering having your team members obtain sigma certification. Learn more about lean maintenance and how it can help run your processes, business, and team even more efficiently.

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