13-02-2013, 02:13 PM
FAILURE MODE & EFFECT ANALYSIS
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ABSTRACT
Failure Mode and Effects Analysis (FMEA) has become a common tool on risk assessment which applying in manufacturing or service industries. The priorities of improvement are based on RPN numbers, which starts with known potential failure modes within a system by severity or determination of the effect of failures. Failure modes are any errors or defects in a design, process, or operation, especially those that affect the customer, and could be potential or in practice. Failures are prioritized based on how serious on consequences; how frequently on occurrences; and how easily on detections. Many scholars queried the formula from traditional algorithm, and presented the revised methodologies respectively to prioritize applications. Several new techniques were proposed in recent years.
FMEA/FMECA History:
The FMEA technique was first reported in the 1920s but its use has only been significantly documented since the early 1960s.
FMEA (FMECA) discipline was developed in the United States Military. Military procedure MIL-P 1629 titled procedures for performing a Failure Mode Effects and critically analysis is dated 9th November 1949.
• The term “personnel/equipment”, taken directly taken directly from an abstract of Military Standard MIL-STD 1629, is notable. The modern manufacturing context of producing consumer goods. Department of Defense developed and revised the guidelines during the 1970s.
• In the late 1970’s, the automotive industry was driven by liability costs to use FMEA .Later, the automotive industry saw the advantages of using this tool to reduce risks related to poor quality
• In 1988, The International Organization for standardization issued the 9000 series of business management standards.
• QS 9000 is the automotive analogy to ISO 9000.A task force representing Chrysler Corporation, Ford Motor Company, and General Motors Corporation developed QS 9000in an effort Standardize supplier quality systems. The automotive Industry Action Group (AIAG) and the American Society of Quality Control (ASQC) copyrighted industry-wide FMEA standards in February 1993.
Definition of FMEA:
FMEA is a systematic analysis of potential failure modes aimed at preventing failures. This is intended to be a preventative action process carried out before implementing new or changes in products or processes. An effective FMEA identifies corrective actions required to prevent failures from reaching the customer and to assure the highest possible yield, quality and reliability. A successful FMEA activity helps a team to identify potential failure modes based on past experience with similar products or processes or based on common failure mechanism logic, enabling the team to design those failures out of the system with the minimum of effort and resource expenditure, thereby reducing development time and costs. FMEA is focused on preventing problems, enhancing safety, and increasing customer satisfaction. A tool used to evaluate potential failure modes and their causes. By its self FMEA is not a problem solver. It is used in combination with other problem solving tools. ` The FMEA presents opportunity but does not solve the problem.
Objectives Of FMEA
To identify potential design and process failures before they occur and to minimize the risk of failure by either proposing design changes or, if these cannot be formulated, proposing operational procedures. Essentially the FMEA is to:
• Identify the equipment or subsystem, mode of operation and the equipment;
• Identify potential failure modes and their causes;
• Evaluate the effects on the system of each failure mode;
• Identify measures for eliminating or reducing the risks associated with each failure mode.
• Identify trials and testing necessary to prove the conclusions; and
• Provide information to the operators and maintainers so that they understand the capabilities and limitations of the system to achieve best performance.
• ISO requirement-Quality Planning
– “Ensuring the compatibility of the design, the production process, installation, servicing, inspection and test procedures, and the applicable documentation”.
Standards used for FMEA
There are a number of standards to which an FMEA can be carried out. The use of standards is important so that the FMEA will be accepted by all parties interested in it.
Using a common standard for an FMEA has other benefits such as the customer gets a report to a consistent standard and the companies bidding to carry out
FMEA will also benefit because they will have a level playing field standards include:
♦ US Department of Defense MIL-STD-1629A,
♦ CEI/IEC812 – Analysis techniques for system reliability - Procedure for failure modes and effects analysis (FMEA)
♦ BSI (BS 5760-5:1991 (Reliability of systems, equipment and components. Guide to failure modes, effects and criticality analysis).
IMO MSC Resolution 36(63) Annex 4 – Procedures for Failure Mode and Effects Analysis (Whilst this is primarily for high speed craft, it gives good guidance on FMEA procedures).
Implementation:
In FMEA, failures are prioritized according to how serious their consequences are, how frequently they occur and how easily they can be detected. An FMEA also documents current knowledge and actions about the risks of failures for use in continuous improvement. Ideally, FMEA begins during the earliest conceptual stages of design and continues throughout the life of the product or service. The outcomes of an FMEA development are actions to prevent or reduce the severity or likelihood of failures, starting with the highest-priority ones. It may be used to evaluate risk management priorities for mitigating known threat vulnerabilities. FMEA helps select remedial actions that reduce cumulative impacts of life-cycle consequences (risks) from a systems failure (fault).
Occurrence:
In this step it is necessary to look at the cause of a failure mode and the number of times it occurs. This can be done by looking at similar products or processes and the failure modes that have been documented for them in the past. A failure cause is looked upon as a design weakness. All the potential causes for a failure mode should be identified and documented. Again this should be in technical terms. Examples of causes are: erroneous algorithms, excessive voltage or improper operating conditions. A failure mode is given an occurrence ranking (O), again 1–10. Actions need to be determined if the occurrence is high (meaning > 4 for non-safety failure modes and > 1 when the severity-number from step 2 is 9 or 10). This step is called the detailed development section of the FMEA process. Occurrence also can be defined as %. If a non-safety issue happened less than 1%, it can be given a 1. It is based on product and customer specification.
Limitations:
Since FMEA is effectively dependent on the members of the committee which examines product failures, it is limited by their experience of previous failures. If a failure mode cannot be identified, then external help is needed from consultants who are aware of the many different types of product failure. FMEA is thus part of a larger system of quality control, where documentation is vital to implementation. General texts and detailed publications are available in forensic engineering and failure analysis. It is a general requirement of many specific national and international standards that FMEA is used in evaluating product integrity. If used as a top-down tool, FMEA may only identify major failure modes in a system. Fault tree analysis (FTA) is better suited for "top-down" analysis. When used as a "bottom-up" tool FMEA can augment or complement FTA and identify many more causes and failure modes resulting in top-level symptoms. It is not able to discover complex failure modes involving multiple failures within a subsystem, or to report expected failure intervals of particular failure modes up to the upper level subsystem or system.