FMEA

Failure Mode – A particular way in which an item fails, independent of the reason for failure.

 Failure Mode and Effects Analysis (FMEA) – A procedure by which each credible failure mode of each item from a low indenture level to the highest is analyzed to determine the effects on the system and to classify each potential failure mode in accordance with the severity of its effect.

Indenture Levels – The hierarchy of hardware levels from the part to the component to the subsystem to the system, etc.

Redundancy – More than one independent means of performing a function.  There are different kinds of redundancy, including:
(1) Operational – Redundant items, all of which are energized during the operating cycle; includes load-sharing, wherein redundant items are connected in a manner such that upon failure of one item, the other will continue to perform the function.  It is not necessary to switch out the failed item or switch in the redundant one.

            (2) Standby – Items that are inoperative (have no power applied) until they are switched in upon failure of the primary item.

            (3) Like Redundancy – Identical items performing the same function.

            (4) Unlike Redundancy – Non identical items performing the same function

THE FMEA PROCESS

• Define the system to be analyzed.  A complete system definition includes identification of internal and interface functions, expected performance at all indenture levels, system restraints, and failure definitions.  Also state systems and mission phases not analyzed giving rationale for the omissions.

• Indicate the depth of the analysis by identifying the indenture level at which the analysis is begun.

• Identify specific design requirements that are to be verified by the FMEA.

• Define ground rules and assumptions on which the analysis is based.  Identify mission phases to be analyzed and the status of equipment during each mission phase.

• Obtain or construct functional and reliability block diagrams indicating interrelationships of functional groups, system operation, independent data channels, and backup or workaround features of the system.

• Identify failure modes, effects, failure detection and workaround features and other pertinent information on the worksheet.

• Evaluate the severity of each failure effect in accordance with the prescribed severity categories.

FMEA Flow Diagram:

History:

The FMECA was originally developed by the National Aeronautics and Space Administration (NASA) to improve and verify the reliability of space program hardware.

FMECA Flow Diagram: ( Failure Mode, Effects and Criticality Analysis )

Criticality Analysis Flow:

Who is the Team ?

 

Areas to be represented are:

• Quality

• Logistics

• Engineering

• Purchasing

• Manufacturing

• Sales

• Tooling

• Marketing

• Customer

• Supplier

INTERVIEW QUESTIONS:GERNAL:

• Explain the Second Law of Thermodynamics.
  The entropy of the universe increases over time and moves towards a maximum value.

 

• How do you measure temperature in a Wet Bulb Thermometer?
  Wet bulb temperature is measured in a wet bulb thermometer by covering the bulb with a wick and wetting it with water. It corresponds to the dew point temperature and relative humidity.

 

• What is Bending moment?
  When a moment is applied to bend an element, a bending moment exists in the element

 

• What are the points in the Stress Strain curve for Steel?
  Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.

 

• Define Reynolds number.
  Reynolds number is the ratio of inertial force and viscous force. It is a dimensionless number. It determines the type of fluid flow.

 

• What is a Newtonian fluid?
  A Newtonian fluid possesses a linear stress strain relationship curve and it passes through the origin. The fluid properties of a Newtonian fluid do not change when any force acts upon it.

 

• How many Joules is 1 BTU?
  1 BTU is equal to 1055.056 joules.

 

• What is PS?
  PS is Pferdestarke, the German unit for Horsepower.

 

• Explain Otto cycle.
  Otto cycle can be explained by a pressure volume relationship diagram. It shows the functioning cycle of a four stroke engine. The cycle starts with an intake stroke, closing the intake and moving to the compression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. It was designed by Nicolas Otto, a German engineer.

 

• Explain the nomenclature of a 6203-ZZ bearing.
  6 is the type code, which shows it is a single-row ball bearing, 2 is the series, means light, 03 is the bore, which is 17 mm and ZZ is the suffix meaning double shielded bearing.

 

• What is Gear ratio?
  It is the ratio of the number of revolutions of the pinion gear to one revolution of the idler gear.

 

• What is Annealing?
  It is a process of heating a material above the re-crystallization temperature and cooling after a specific time interval. This increases the hardness and strength if the material.

 

• Define Torque.
  Torque is defined as a force applied to an object that results in rotational motion.

 

• What is Ductile-Brittle Transition Temperature?
  It is the temperature below which the tendency of a material to fracture increases rather than forming. Below this temperature the material loses its ductility. It is also called Nil Ductility Temperature.