Design for Six Sigma by Elizabeth A. Cudney & Tina Kanti Agustiady

Author:Elizabeth A. Cudney & Tina Kanti Agustiady
Language: eng
Format: epub
Publisher: CRC Press

Failure Modes and Effects Analysis

FMEA is a structured approach to assess the magnitude of potential failures and identify the sources of each potential failure. Corrective actions are then identified and implemented to reduce or prevent the potential of a failure occurrence.

FMEA is a prevention-based strategy. It is used to anticipate potential failures, identify potential causes for these failures, prioritize the failures, and subsequently take action to reduce, mitigate, or eliminate these failures. This reduces costs by spending time upfront focusing on preventive action rather than reactive action after the product reaches the customer. Product changes can be implemented more easily and less expensively during the early stages of product development. FMEAs enable the DFSS team to determine what can go wrong, how likely it is to go wrong, and what can be done to prevent it. It is important that a multidisciplinary team conducts the FMEA to ensure a balanced view of the potential failures and their associated causes and impacts.

There are two key types of FMEAs: process and design. Process FMEAs (PFMEAs) are used in Six Sigma to improve processes. Design FMEAs (DFMEAs) are used to improve the design of a product, process, or service by defining and ranking the failure modes for a system. DFMEAs should be conducted for new concepts as a preventive effort to improve the robustness of the concept to failure modes. DFMEAs can also be conducted on each concept generated prior to the Pugh Concept Selection Matrix. A DFMEA should be performed on the concept that emerges as the superior concept from the Pugh Concept Selection Matrix.

In addition, FMEAs can be used to prioritize selected action items from the cause and effect diagram for improvement efforts. The FMEA will identify the causes, assess risks, and determine further steps. A template based on the Automotive Industry Action Group (AIAG) format is provided in Figure 17.1.

The steps to performing an FMEA are the following:

1. Define process steps.

2. Define functions.

3. Define potential failure modes.

4. Define the potential effects of failure.

5. Define the severity of a failure.

6. Define the potential mechanisms of failure.

7. Define current process controls.

8. Define the occurrence of failure.

9. Define current process control detection mechanisms.

10. Define the ease of detecting a failure.

11. Multiply severity, occurrence, and detection to calculate a risk priority number (RPN).

12. Define recommended actions.

13. Assign actions with key target dates to responsible personnel.

14. Revisit the process after actions have been taken to improve it.

15. Recalculate RPNs with the improvements.

The design function requirements represent the form, fit, and functions of the product being designed. These should reflect the requirements that are being fulfilled by the product.

Potential failure modes are the ways in which a product, process, service, subsystem, or component could fail to meet the design intent. Potential failure modes should be listed in technical terms for each function. Examples could include torque fatigue, cracking, or deformation. In addition, since DFMEAs are performed for a system, it is important to recognize that a failure mode in one component can also serve as a failure mode in another component.

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