Phase B: Parameter Level Design 1
FMEA A chart describing the ways in which the product may fail, the impact, and what has been done to alleviate any problems. Measure of the inability to achieve overall program objectives within defined costs, schedule, and technical constraints It has two components Probability of failing to achieve a particular outcome Consequences/impacts of failing to achieve that outcome (NASA Systems Engineering Handbook, SP 2007) 2
(Tyson R. Browning) Cost risk Risk associated with the ability of the program / project to achieve its life-cycle cost objective and secure appropriate funding Two risk areas bearing on cost are: (1) risk that the cost estimates and objectives are not accurate or reasonable (2) risk that program execution will not meet the cost objectives as a result of failure to handle cost, schedule and performance risks (NASA Systems Engineering Handbook, SP 2007) 3
Technical risk Risk associated with the evolution of design and the production of the system of interest affecting the level of performance necessary to meet the stakeholder expectations and technical requirements The design, test and production processes affect the(process risk) influence the technical risk and the nature of the product (NASA Systems Engineering Handbook, SP 2007) Programmatic risk Risk associated with action or inaction from outside the project, over which project manager has no control, but which may have significant impact on the project Impacts may manifest themselves in the terms of technical, cost and/or schedule (NASA Systems Engineering Handbook, SP 2007) 4
Hazard is distinguished from risk A hazard represents a potential for harm whereas risk includes not only the potential for harm, but also scenarios leading to adverse outcomes and the likelihood of these outcomes (NASA Systems Engineering Handbook, SP 2007) We want to design in quality Anticipate failures and their impact therefore we can redesign by priority All failure modes should relate to performance, function, compliance, or safety FMEA is a continuous analysis throughout design 5
Aid to engineers in directing timely design actions to prevent defects and failures and achieve reliable, safe and customer-pleasing products Aid for planning appropriate test programs Document of rationale for the manufacturing and assembly process being developed A valuable database for tracking future actions and improvements Failure is any change or any design or manufacturing error that renders a component, assembly, or system incapable of performing its intended function 6
Mature, yet not effectively used Several Standards: MIL-STD-1629A, SAE J-1739 Often treated as after-the-fact check-lists Success dependent on user s experience The big challenge: Identifying failure modes Existing FMEA: mostly component-based Often leaves out many failure modes Hard to apply in early design stage Requires detailed design (components) Hard to link with customer perceived failures Asks these questions What can go wrong? What is the likely cause? How likely is it to occur? What are the consequences? How easy is it to diagnose? How can the problem be eliminated or alleviated? 7
(Ishii) Identify failure modes: focus on phenomena (-VOC, -function) Loss of function or intent / Annoying Effects Associate cause(s) Components / Inter-component / External factors Assess local and end effects Evaluate the following (1-10 rating) Likelihood of occurrence (O) Detection difficulty (D) Severity of effect (S) Calculate Risk Priority #: RPN=(O)x(D)x(S) Generate Actions to Reduce RPN Design, Manufacturing, and Service Resolutions 8
(Ishii) Function/Requirement intent of system Failure Mode failure to satisfy intent Potential Causes reason for failure mode Occurrence Rating How likely is the Mode to occur? (1-10) 9
Failure scenario Departure from intended function or requirement Sub-function occurring improperly or not at all Negation of the customer requirement The specific behavior or attribute intended by design Use function analysis to list major sub -functions Use value graph or QFD to list main customer requirements If it doesn t perform function or requirement, it is a failure 10
What if it fails to perform at the right time? What if it fails to perform in the proper sequence? What if it fails to perform at all? What if it fails to stop operating at the prescribed time? What if operation is intermittent? What if it wears out? Both are -VOC 11
QFD-based Function-Structure-based (Ishii) Use QFD Start with -VOC Relate to Engineering Metrics Link to Functions Use FS Map Relate to Causes 12
(Ishii) (Ishii) 13
Why the desired function or requirement fails (may require some in-depth analysis) consider needed conditions for each function or customer requirement what has to happen for the function or requirement to occur properly List possible causes of failure due to components, usage conditions, human interaction, operating environment, interfacing, etc. Design deficiencies Deficiencies in selection of materials Imperfection in material due to manufacturing Overload and other abuses in service Inadequate maintenance and repair Environmental factors 14
4 Manifestations of failure Plastic deformation, plastic deformation, rupture or fracture, material change 4 Failure inducers Force (steady, transient, cyclic, random), time (short to long), temperature (level and f(t)), environmental reaction 2 Locations Body and surface Force and/or temperature-induced elastic deformation Yielding Brinnelling Ductile rupture Brittle fracture Fatigue High-cycle fatigue Low-cycle fatigue Thermal fatigue Surface fatigue Impact fatigue Corrosion fatigue Fretting fatigue Corrosion Direct chemical attack Galvanic corrosion Crevice corrosion Pitting corrosion Intergranular corrosion Selective leaching Erosion corrosion Cavitation corrosion Hydrogen damage Biological corrosion Stress Corrosion Wear Abrasive wear Adhesive wear Corrosive wear Surface fatigue wear Deformation wear Impact wear Fretting wear Fretting Fretting fatigue Fretting wear Fretting corrosion Creep Thermal relaxation Stress rupture Thermal shock Galling an seizure Spalling Radiation damage Buckling Creep buckling Stress corrosion Corrosion wear Corrosion fatigue Combined creep and fatigue 15
Bent Blistered Brittle Bound Broken Cracked Corroded Damaged Deformed Discolored Distorted Grounded Hot Leaking Loose Melted Misaligned Misassembled Omitted Porous Rough Shorted Tight Wrinkled Likelihood that a specific cause results in failure mode and effect Since some causes could have many different effects, likelihood refers to failure scenario 16
(Lumsdaine et al., 2006.) Local Effects effect of failure on the system End Effects effect on customer, performance, safety Severity how severe is the end effect? (1-10) performance penalty, annoyances (1-3) limits functionality (4-7) total lack of function, safety problem (7-10) 17
Immediate effects of the failure mode within the product or system being analyzed Local effects then impact other sub -functions E.g., local effect for heat air may be reduced current to the heater coil Noticeable effects on performance, safety, and perceived quality Trying to prevent these 18
How serious the failure mode affects the function or safety of the system Endangering humans should get a 9 or 10 (Lumsdaine et al., 2006.) 19
Detection Method / Current Controls what is now in place to catch failure modes Detection Rating during design and development (1-3) during manufacturing (4-6) during installation (7-8) during use (9-10) How difficult the cause is to detect The earlier the detection of the failure mode, the lower the score If can do during design better than after delivery 20
(Lumsdaine et al., 2006.) Each failure scenario (mode, cause, and effect) has its own RPN RPN = Occurrence x Severity x Detection Larger RPN indicate the need for corrective action If severity is high it needs work regardless of RPN 21
List of corrective actions and failure resolutions that require implementation Priorities Design solutions to eliminate the failure mode or reduce likelihood functional redundancies and error proofing of assembly, installation, and usage Actions to reduce severity Reduce occurrence Developing means of detecting causes of failure modes during mfg. Inspection, testing, error proofing Tests to provide more information to assess likelihood and severity Providing diagnostics to easily identify the failure mode or cause during mfg. or use Establish periodic maintenance or check-ups to enhance availability and safety 22
Prioritized list of failure modes and actions recommended to mitigate these risks 23
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Applying it too late can t get at design changes do FMEA even if you lack details Anticipating critical failure modes interfaces with other systems assembly and service errors manufacturing variation unexpected operating conditions unanticipated customer use 25
Process FMEA List failure modes of mfg. and assy. steps and proceed from there FMEA in design concept selection Analysis of risk of not meeting customer needs Plot sorted list of RPN v. Failure modes for design concepts 26