How Six Sigma Uses Failure Modes and Effects Analysis

Six Sigma’s purpose is to help prevent errors, failures and defects that impact the customer. Failure Modes and Effects Analysis (FMEA) gives project teams a framework to identify potential process failures and to estimate how the failure will affect the customer.

Project teams use FMEA in the Analyze stage of DMAIC. It helps them spot tasks or product features that might experience high rates of failure. FMEA can also be used in the Design stage to identify processes that can be improved. FMEA helps project teams implement a current process in a new way, revamp an existing process, or create a new process at any point in the life of the product or service.

How to Use FMEA

To use FMEA properly, the project team must have an intimate knowledge of every step of the production process. Teams that operate within a clearly defined project scope usually get the best results from FMEA. The team applies FMEA in a series of stages:

• Identify what failures could occur at every step of the process.
• Determine the results of every failure. Ask, “What happens when this failure occurs?”
• Calculate a severity ranking for each opportunity for failure on a scale from 1 to 10. 1 has no impact on the customer; 10 is a disaster.
• Establish the likelihood of failure on a 10 point scale. 10 is an absolute certainty; 1 is no chance.
• Estimate the probability of detecting the error before the customer notices it. Failures that are the easiest to notice are assigned a 1; those that go unnoticed are assigned a 10.

Once probabilities are ranked, the next step is to calculate the Risk Priority Number (RPN). Multiplying the rankings of the severity, occurrence and detection levels gives each step in the process an RPN.

Each potential cause of failure will then have a risk priority number between 0 and 1,000. Potential causes of failure with the high RPNs indicate the greatest areas of vulnerability to the process. These are the first steps to be targeted for improvement.

Of the three components in the risk priority number (severity, detection and occurrence), the most cost-effective area to address is occurrence. Reducing the number of errors has a direct impact on reducing the process’s RPN and encourages a long-term solution.

When project teams use the Failure Modes and Effects Analysis framework to evaluate every step of a production process, they can discover where the greatest possibility for failure lies. They will also be able to estimate the effect that failure might have on customers.

Six Sigma emphasizes the importance of addressing the root causes of defects and failure. FMEA enables project teams to take this philosophy one step further by assigning each potential cause a risk priority number so that the most likely causes of failure that have the greatest impact on the customer can be identified easily and addressed first.

FMEA is the quintessential Six Sigma tool. It helps decrease defects while increasing customer satisfaction.