Failure Mode and Effect Analysis | ETM 5291, Study notes of Engineering

Download Failure Mode and Effect Analysis | ETM 5291 and more Study notes Engineering in PDF only on Docsity! 1 Failure Mode and Effect Analysis Lecture 2-3 Design FMEA 2 FMEA • The definition of "customer" for a Design FMEA can be the . . . . REPAIR CENTER MANUFACTURING NEXT ENGINEERING GROUP END USER Customer Defined 2 3 FMEA • The Design FMEA is a living document and should be initiated at or by the design concept finalization, be continually updated as changes occur throughout the phases of product development, and be fundamentally completed along with the final drawings. Drawings Living Document 4 FMEA A Design FMEA is an analytical technique utilized by product or process designers as a means to ensure that, to the extent possible, potential failure modes and their associated causes have been considered and addressed. What is DFMEA? 5 9 FMEA HARDWARE BOTTOM-UP TOP-DOWN FUNCTIONAL BLOCK RELIABILITY BLOCK Technique - Listed Items 10 FMEASystem Breakdown Concept System A composite of subsystems whose functions are integrated to achieve a mission or specific output Subsystem composite of assemblies whose functions are integrated to achieve a specific activity necessary for achieving a mission Assembly a composite of subsystems Component a composite of piece parts Piece Part least fabricated item, not further reducible Interface the interactions point(s) necessary to produce the necessary effects between system elements (interfaces transfer energy/information, maintain mechanical integrity, etc. 6 11 FMEAFunctional vs. Geographic • Functional – Cooling system – Propulsion system – Braking system – Steering system • Geographic – Engine compartment – Passenger compartment – Dashboard / Control Panel – Rear end – etc. Interface components If an engine-driven belt powers both a water pump and a power steering system, be sure to include it as part of one, or as a separate interface element. 12 FMEASystem Breakdown Example ETC . . . .TRANSMISSION ETC . . . .ENGINE BATTERY GENERATOR PLUGS COIL DISTRIBUTOR SPARK / IGNITION CARBURATORAIR STORAGE DELIVERY FUELPROPULSION RADIATOR WATER PUMP COOLANT HOSES, CLAMPS THERMOSTAT COOLINGAUTOMOBILE SUBASSEMBLYASSEMBLYSUBSYSTEMSYSTEM 7 13 FMEAFunctional FMEAs Focus on the functions that a product, process, or service is to perform rather than on the characteristics of the specific implementation. When developing a functional FMEA, a functional block diagram is used to identify the top-level failure modes for each functional block on the diagram. 14 FMEA MOUNTING DECK, COVER BASE DECK STAMPED COVER COVER SEAL TAPE SEAL FUNCTIONAL BLOCK Much of a complex product can be analyzed by looking at functional blocks rather than individual items Functional Block 10 19 FMEADFMEA Form 20 FMEAWorksheet FMEA WORKSHEET PRODUCT: ENGR PG TYPE: DESIGN PROCESS OTHER____________ ITEM: FUNCTION POTENTIAL EFFECTS OF POTENTIAL VERIFICATION OR FAILURE MODE FAILURE S CAUSES O CURRENT CONTROL E RPN 11 21 FMEA PRODUCT: FMEA NO. PROCESS/OPERATION: PAGE OF DESIGN (OR PROCESS) FMEA PLANNING REFERENCE: DATE: BY: Oklahoma City POTENTIAL POTENTIAL S POTENTIAL O CURRENT D RPN ACTION CORRECTIVE RESPONSIBILITY ACTION RESULTING FUNCTION FAILURE MODE EFFECTS OF CAUSE(S) OF CONTROLS PRIORITY ACTION & DATE DUE TAKEN FAILURE FAILURE S O D RPN DETECTIONOCCURRENCESEVERITY RPN = S x O x D ENGINEER WITH PROGRAM TEAM3.DESIGN ENGINEER (MANUF ENGINEER)1. DESIGN ENGINEER, MANUFACTURING ENGINEER, QUALITY ENGINEER, RELIABILITY ENGINEER 2. DFMEA Steps - Teams 22 FMEAGround Rules 1. Do not consider all conceivable failure modes 2. Initially write the failure mode as loss of function 3. Decide on the approach - function or hardware 4. Develop each column of the FMEA independently. 12 23 FMEAFunction Common problems • Not all functions are identified • The description is not exact or concise • The description is not in direct language FMEA WORKSHEET PRODUCT: ENGR PG TYPE: DESIGN PROCESS OTHER___________________ ITEM: FUNCTION POTENTIAL EFFECTS OF POTENTIAL VERIFICATION OR FAILURE MODE FAILURE S CAUSES O CURRENT CONTROL E RPN 24 FMEAPotential Failure Mode • The manner in which the item (product, component, system) could potentially fail to meet the design intent. • Assume that the failure mode could occur but may not necessarily occur. • Potential failure modes should be described in “physical” or technical terms, not as a symptom noticeable by the customer FMEA WORKSHEET PRODUCT: ENGR PG TYPE: DESIGN PROCESS OTHER___________________ ITEM: FUNCTION POTENTIAL EFFECTS OF POTENTIAL VERIFICATION OR FAILURE MODE FAILURE S CAUSES O CURRENT CONTROL E RPN 15 29 FMEAPotential Causes • For each potential failure mode, list all possible causes • Goal is to get to root cause, or to a reasonable place to break the cause-effect chain. • Rotate columns is necessary. If the team starts finding causes of causes, “promote” the original cause to potential failure mode. FMEA WORKSHEET PRODUCT: ENGR PG TYPE: DESIGN PROCESS OTHER___________________ ITEM: FUNCTION POTENTIAL EFFECTS OF POTENTIAL VERIFICATION OR FAILURE MODE FAILURE S CAUSES O CURRENT CONTROL E RPN 30 FMEATesting the Relationships • Use the following to see if you got the relationships in the proper sequence: IF cause THEN failure mode HOW DO I KNOW? effect 16 31 FMEA FAILURE MODE LIKELY CAUSES LIKELY EFFECTS ACTIONS TRIGGER PREVENTIVE CONTINGENT - ADAPTIVE - CORRECTIVE Cause-Effect Model 32 FMEAOccurrence • The likelihood that a specific cause will occur and result in the failure mode. • Rank on a scale of 1 - 10 FMEA WORKSHEET PRODUCT: ENGR PG TYPE: DESIGN PROCESS OTHER___________________ ITEM: FUNCTION POTENTIAL EFFECTS OF POTENTIAL VERIFICATION OR FAILURE MODE FAILURE S CAUSES O CURRENT CONTROL E RPN 17 33 FMEAOccurrence of Cause Design OCCURRENCE EVALUATION CRITERIA Probability the CAUSE will occur Possible Failure Rate (DPPM) Ranking Remote Failure is unlikely. No known failures associated with almost identical designs <1 in 106 1 (<1) Very Low Only isolated failures associated with similar designs < 1 in 20,000 2 (<50) Low Occassional failures associated with similar designs <1 in 4,000 3 (<250) Moderate Previous designs have experienced problemsor occassiona lfactory out-of control conditions 1 in 1,000 4 1 in 400 5 1 in 80 6 High Similar designs have experience problems which have led to stop-ship conditions 1 in 40 7 1 in 20 8 Extreme Failure almost inevitable 1 in 8 9 1 in 2 10 34 FMEAOccurrence – Another Example 20 39 FMEA Occurrence x Severity x Effectiveness RPN = O x S x E Risk Priority Number FMEA WORKSHEET PRODUCT: ENGR PG TYPE: DESIGN PROCESS OTHER___________________ ITEM: FUNCTION POTENTIAL EFFECTS OF POTENTIAL VERIFICATION OR FAILURE MODE FAILURE S CAUSES O CURRENT CONTROL E RPN 40 FMEA Priority RPN range A OVER 200 B 100-199 C 26-99 D 1-25 Final ranking (or risk assessment) in order of importance Action Priority 21 41 FMEA A 8 4 3 96 B 4 8 3 96 SAME RESULT Handbook pg. 29 Fa ilu re Mo de Se ve rit y Oc cu rre nc e Ef fec tiv en ess RP N Shortcomings of RPN Method 42 FMEA A 8 4 3 96 B 4 8 3 96 Fa ilu re Mo de Se ve rit y Oc cu ren ce Ef fec tiv en ess RP N FOCUS ON SEVERITY Shortcomings of RPN Method 22 43 FMEAAnother Scoring Approach FMEA “Area Chart”* HIGH PRIORITY MEDIUM PRIORITY LOW PRIORITY 1 2 3 4 5 6 7 8 9 10 10 9 8 7 6 5 4 3 2 1 OCCURRENCE SE VE R IT Y * Failure Modes and Effects Analysis, Paul Paladay, PT Publications, 1995 44 FMEA The design must be improved based on the results of the FMEA study. A well-developed Design FMEA will be of limited value without positive and effective corrective actions. Actions