FMEA ProcedureList all Function & Re- evaluate requirements (New RPN ) List all conceivable Define Responsibility failure modes & Time- frame Consider effects, if above Recommend failure mode happens improvements Look possible causes & mechanism for Calculate the Risk failures mode Priority Number (RPN) Assess the frequency of Assess the possibility of occurrence of Failure being failure modes (O) detected ( D ) Assess the Severity of effect (s)
Occurrence tableOccurrence (o)Suggested Evaluation Criteria: Probability of Failure Possible Failure Rates Ranking Very High : Persistent > 100 per thousand vehicles/ items 10 failures 50per thousand vehicles/ items 9High : Frequent failures 20 per thousand vehicles/ items 8 10 per thousand vehicles/ items 7 Moderate : Occasional 5 per thousand vehicles/ items 6 failures 2 per thousand vehicles/ items 5 1 per thousand vehicles/ items 4 Low : Relatively few 0.5 per thousand vehicles/ items 3 failures 0.1 per thousand vehicles/ items 2 Remote : Failure is < 0.010 per thousand vehicles/ items 1 unlikely
Severity table Effect Criteria : severity of Effect RankingHazardous Very high severity ranking when a potential failure mode affects safe 10without vehicle operation and/or involves noncompliance with governmentwarning regulation without warning.Hazardous Very high severity ranking when a potential failure mode affects 9with warning safe vehicle operation and/or involves noncompliance with government regulation with warning.Very High Vehicle/ item inoperable (loss of primary function). 8High Vehicle/ item operable but at reduced level of performance. 7 Customer very dissatisfied.Moderate Vehicle/ item operable, but Comfort/ Convenience item(s) 6 inoperable. Customer dissatisfied.Low Vehicle/ item operable, but Comfort/ convenience item(s) operable 5 at a reduced level of performance. Customer somewhat dissatisfied.Very Low Fit & Finish/ Squeak & Rattle item does not conform. Defect noticed 4 by most customers (greater than 75%).Minor Fit & Finish/ Squeak & Rattle item does not conform. Defect noticed 3 by 50% of customers.Very Minor Fit & Finish/ Squeak & rattle item does not conform. Defect noticed 2 by discriminating customer (less than 25%).None No discernible effect. 1
Detection Table Detection Criteria : Likelihood of Detection by Design Control Ranking Absolute Design control will not and/or can not detect a potential cause/ 10 Uncertainty mechanism an subsequent failure mode; or there is no Design controlVery Remote Very remote chance the Design control will detect a potential 9 cause/ mechanism and subsequent failure mode. Remote Remote chance the Design control will detect a potential cause/ 8 mechanism and subsequent failure mode. Very Low Very low chance the Design control will detect a potential cause/ 7 mechanism and subsequent failure mode. Low Low chance the Design control will detect a potential cause/ 6 mechanism and subsequent failure mode. Moderate Moderate chance the Design control will detect a potential cause/ 5 mechanism and subsequent failure mode.Moderate High Moderate high chance the Design control will detect a potential 4 cause/ mechanism and subsequent failure mode. High High chance the Design control will detect a potential cause/ 3 mechanism and subsequent failure mode. Very High Very high chance the Design control will detect a potential cause/ 2 mechanism and subsequent failure mode.Almost Certain Design control will almost certainly detect a potential cause/ 1 mechanism an subsequent failure mode.
Requirements & TrendsLets discuss the functional requirements of an engine...
Customer Requirements• Not just power and speed range• Not just rated torque but torque profile• Weight/space• Fuel economy/emissions/noise• Duty cycle/durability/reliability• Service intervals and serviceability• Cost sensitivity• Iterations on materials/cost/temperature pressure capability and target performance• Upgrade capability• End of life considerations. Many methodical techniques such as QFD available for use
Drivers & ChallengesDRIVERS : CHALLENGES:• High Specific Power • Emission• High torque back-up • Noise• Low fuel consumption • Cost• Low fuel cost • DurabilityEVOLUTION OF SPECIFIC POWER FOR DIESEL VEHICLES 25 FUEL CONSUMPTION OF INDIAN DIESEL VEHICLES 20 FC (kmpl) 15 10 5 0 0 500 1000 1500 2000 2500 3000 3500 Cubic Capacity
State of Art – Trends in Engine SpecificationsOther cutting edge design considerations – peak cylinder pressure, fuel injectionpressure, piston speed, valve seating velocity, exhaust temperature limit etc.
• Analyze the engine/components/systems and summarizevarious functions and failure modes.• 50 components and 10 systems to be listed and their functionsand failure modes to be studied.• 5 out 60 components/systems are picked. DFMEA to beconducted for these 5 components/systems.•These components & systems all had failure modes and acorresponding Risk Priority Number (RPN) to be calculatedusing severity, occurrence & detection rankings.•The idea is to reduce this RPN value so that thecomponents/systems are designed more towards reliability andsafety. These reductions are to be done through design changes.
• FAILURE MODES & EFFECTS ANALYSIS (FMEA) isa paper-and-pencil analysis method used in engineering todocument and explore ways that a product design mightfail in real-world use.• Failure Mode & Effects Analysis is an advanced qualityimprovement tool.• FMEA is a technique used to identify, prioritize andeliminate potential failures from the system, design orprocess before they reach the customer.• It provides a discipline for documenting this analysis forfuture use and continuous process improvement.
• Historically, FMEA was one of the first systematic techniques for failureanalysis developed by the U.S. Military on 9th November, 1949. FMEAwas implemented in the 1960‟s and refined in the 70‟s. It was used byreliability engineers working in the aerospace industry.• Then the Automotive Industry Action Group formed by Chrsyler, Ford &GM restructured the FMEA techniques which found a lot of importance inthe automotive industry.• Since then FMEA has been instrumental in producing quality goods inthe automotive sector.
• SYSTEM FMEA - Chassis system - Engine system - Transmission• COMPONENT FMEA - Piston - Crankshaft•PROCESS FMEA - Involves machine, manufacturing process, materials
DFMEA: Starts early in process. It is complete by the timepreliminary drawings are done but before any tooling is initiated.PFMEA: Starts as soon as the basic manufacturing methods havebeen discussed. It is completed prior to finalizing productionplans and releasing for production.
MIL-STD 1629, “Procedures for Performing a Failure Mode and EffectAnalysis”IEC 60812, “Procedures for Failure Mode and Effect Analysis (FMEA)”BS 5760-5, “Guide to failure modes, effects and criticality analysis (FMEAand FMECA)”SAE ARP 5580, “Recommended Failure Modes and Effects Analysis(FMEA) Practices for Non-Automobile Applications”SAE J1739, “Potential Failure Mode and Effects Analysis in Design (DesignFMEA)”SEMATECH (1992,) “Failure Modes and Effects Analysis (FMEA): A Guidefor Continuous Improvement for the Semiconductor Equipment Industry”
• They can only be used to identify single failures and notcombinations of failures• Failures which result from multiple simultaneous faults are notidentified by this• Unless adequately controlled and focused, the studies can be timeconsuming• They can be difficult and tedious for complex multi-layered systems• They are not suitable for quantification of system reliability
RESPONSIBILITY AND SCOPE OF THE DFMEA• The DFMEA is a team function – All team members must participate – Multi-disciplinary expertise and input is beneficial • Input from all engineering fields is desirable • Representatives from all areas (not just technical disciplines) are generally included as team members• The DFMEA is not a one meeting activity – The DFMEA will be refined and evolve with the product – Numerous revisions are required to obtain the full benefit of the DFMEA• The DFMEA must include all systems, sub-systems, and components in the product design
• Form the cross functional team.• Call FMEA Meeting with advance intimation.• Complete the top of the form – Project, year, team members, date, and DFMEA iteration – There will be many iterations• List items and functions – Start with the system, then subsystems and finally components• Document potential failure modes – How could the design potentially fail to meet the design intent? – Consider all types of failure• Document the potential effects of failure – How would design potentially fail to meet the design intent?
• Rate the severity of the failure effect – See ranking guidelines – Severity ranking is linked to the effect of the failure• Document potential causes and mechanisms of failure – Failure causes and mechanisms are an indication of design weaknesses – Potential failure modes are the consequences of the failure causes – A single failure mode may have multiple failure mechanisms – Use group brainstorming sessions to identify possible failure mechanisms – Don‟t be afraid to identify as many potential causes as you can – This section of the DFMEA will help guide you in necessary design changes – The output of the DFMEA will indicate on which item to focus design efforts
• Rate the occurrence – See attached page for ranking guidelines – Things that may help you rate the occurrence • Are any elements of the design related to a previous device or design? • How significant are the changes from a previous design? • Is the design entirely new?• List the design controls – Design controls are intended to: • Prevent the cause of the failure mode (1st choice solution) • Detect the cause of the failure mode (2nd choice solution) • Detect the failure mode directly (3rd choice solution) – Applicable design controls include • Predictive code analysis, simulation, and modeling • Tolerance “stack-up” studies • Prototype test results (acceptance tests, DOE‟s, limit tests) • Proven designs, parts, and materials
• List any critical or special characteristics – Critical characteristics: Severity > 8 and Occurrence >1 – Special characteristics: Severity > 6 and Occurrence >2• Detection rate – See attached page for ranking guidelines• Calculate the RPN of each potential failure effect – RPN = (Severity) x (Occurrence) x (Detection) – What are the highest RPN items?• Define recommended actions – What tests and/or analysis can be used to better understand the problem to guide necessary design changes ?
• Assign action items – Assemble team – Partition work among different team members – Assign completion dates for action items – Agree on next team meeting date• Complete “Action Results” Section of DFMEA – Note any work not accomplished (and the justification for incomplete work) in the “actions taken” section of the DFMEA. • Why was nothing done? – Change ratings if action results justify adjustment, but the rules are: • Severity: May only be reduced through elimination of the failure effect • Occurrence: May only be reduced through a design change • Detection: May only be reduced through improvement and additions in design control (i.e. a new detection method, better test methodology, better codes, etc.) – Include test and analysis results with DFMEA to validate changes.
Example of Significant/ Critical Threshold Special Characteristics Matrix 10 POTENTIAL CRITICAL 9 CHARACTERISTICS Safety/Regulatory S E 8 POTENTIAL V 7 SIGNIFICANT E 6 CHARACTERISTICS Customer Dissatisfaction R 5 I 4 ANOYANCE T 3 ZONE ALL OTHER CHARACTERISTICS Y 2 Appropriate actions / 1 controls already in place 1 2 3 4 5 6 7 8 9 10 OCCURRENCE
RPN / Risk Priority Number Top 20% of Failure Modes by RPN R P N Failure Modes
• Repeat: undertake the next revision of the DFMEA The DFMEA is an evolving document! Revise the DFMEA frequently! Diligence will eliminate design risk! Include documentation of your results!
Potential __ System Failure Mode and Effects Analysis __ Subsystem (Design FMEA) __ Component FMEA Number: Page 1 or 1 Model Year/Vehicle(s): Design Responsibility Prepared by: FMEA Date (Orig.): Core Team: Key Date:Item C Potential O Current Current D Responsibility Action Results Potential Potential S L C E R. Recommended Cause(s)/ Design Design & Target Failure Effect(s) of E A Mechanism(s) C T P. S O D R. Controls Controls Action(s) Completion Actions Mode Failure V S U E N. Date E C E P. Function S Of Failure R Prevention Detection C Taken V C T N. 30
Cylinder Head Compression Brake Additional Clearances Arm Group Assembly Shaft Assembly •Injector & Spring •Intake rocker assembly •Shaft Intake Rocker Assembly •Exhaust rocker assembly •Cup Valve Cover •Injector & Spring Base Exhaust Rocker Assembly •Stand(s) W & W/o oil supply •Pin •Body •Injector & retainer •Shaft Assembly •Insert •Injector & Bridge •Mounting Bolt •Roller •Spring/Spacer •Injector & injector clamp •Pin •Clip Valve Bridge Lube Oil Pushrod •Injector oil •Rod •Cup Spring Group •Ball •Inner & Outer Springs Cylinder Head •Spring Base •Retainer/Rotator •Valve Keeper Lifter Assembly •BodyValve Stem Seal Valve Group •Insert •Intake Valve •Roller •Exhaust Valve •Pin •Intake Seat •Clip Lube Oil •wire Oscillating Lifter •Exhaust Seat •Valve Guide •Pressure Lube CAM Shaft Cylinder Head •Valve Guide Seal OR Bore in Block Valve Seat CAM Bearings •Pressure Lube Seat Insert Thrust Plate Cylinder Head Cylinder Block
Tensioner Cylinder Head Main Hydraulic Lash Rockers Gallery Adjuster Vacuum Pump Orifice Camshaft Cam Journal Cylinder Block Main GalleryB/Pass Main Bearing Drive & Oil Filter Turbocharge Valve No. 1, 2, 3 Tensioner r Oil Cooler Oil Jet Con rod Oil Pump R/Valve BRG. No.1, 2, 3 1, 2, 3 Oil Strainer 2 Part Oil PAN with Filter in between
• CYLINDER BLOCK• CYLINDER HEAD• CYLINDER HEAD GASKET• VALVES• PISTON• CONNECTING ROD•CRANKSHAFT• AIR INTAKE SYSTEM• EXHAUST SYSTEM• TURBOCHARGER
The crankshaft, sometimes casually abbreviated to crank, is thepart of an engine which translates reciprocating linear pistonmotion into rotation. To convert the reciprocating motion intorotation, the crankshaft has "crank throws" or "crankpins",additional bearing surfaces whose axis is offset from that of thecrank, to which the "big ends" of the connecting rods from eachcylinder attach.
• Crankshaft literature Survey• Crankshaft functions/requirement• Crankshaft benchmarking• Visit to vendors place for understanding production process• Crankshaft concept development• Crankshaft failure modes• Design FMEA at vendor’s place• Crankshaft model• Classical strength analysis• Excite strength analysis• Factor of Safety analysis• Crankshaft draft drawing• Sending draft drawing & filled questionnaire to vendor• Preliminary Design Review with vendor• Finite Element Analysis by vendor & web optimization• Material & Heat Treatment discussions• Closing Design FMEA• Quotation & Purchase Order• Process FMEA at vendor’s place• Die making & production
• Convert reciprocating motion of piston to rotary motion• Transfer energy from engine• Requires Balancing (In case of 3 cylinder, primary &secondary couples can be balanced by Balancer shaft,Rotary couples needs to be balanced by counterweightoptimization)• Defines piston Travel• Requires resistance to fatigue (Weak points at the filletradius)• Requires resistance to alternating torsion (Oil holes areweak points)
• Should withstand forces - gas pressure, rotating andreciprocating inertia• Should withstand vibratory forces• Should damp torsional vibrations• Requires infinite life under high cycle bending• Requires friction & wear reduction at the bearings• Requires smooth grain flow through critical regions• Requires high strength to weight ratio(Stress increases by 4 times for every doubling of speed)
• High cycle bending at webs, nose & flywheel flange• Galling fillets (Similar to Adhesive wear)• Radii fracture (at pin & journal)• Scored bearing journals• Bends, warpage and cracks• Abrasive wear• Chipping•Torsional failure• Bearing failure
• Major Input Data (at Max BMEP operating point) :- Sr. No. Parameter Value 1 Main Brg Centre Distance [mm] 100.oo 2 Section modulus of left crank web [mm3] 2008.63 3 Section modulus of Right crank web [mm3] 2008.63 4 Thickness of left and right webs [mm] 20.5 5 Eq length of left crank web [mm] 116.00 6 Eq length of right crank web [mm] 116.00 7 Crank pin / main journal fillet radius [mm] 3.5 8 Material of Crankshaft (Present ) 30CrNiMo8 9 UTS crankshaft material [N/mm2] 1250 10 Fatigue Strength of CS material [N/mm2) 510 11 Engine Speed [rpm] 2000
No. Position Amplitude Mean stress Stress (N/mm2) (N/mm2)1 Left Crank pin 239.34 217.052 Right Crank pin 239.34 217.053 Left Main journal 330.20 299.444 Right Main journal 330.20 299.44
SAFETY FACTORS------------------------------------------------------- CRANK PIN MAIN JOURNAL FILLET FILLET LEFT RIGHT LEFT RIGHT------------------------------------------------------- 1.90 1.90 1.65 1.65------------------------------------------------------- 2 1.8 1.6 1.4 PERMISSIBLE FOS 1.2 CRANKPIN FILLET LEFT 1 CRANKPIN FILLET RIGHT 0.8 JOURNAL PIN FILLET LEFT 0.6 JOURNAL PIN FILLET RIGHT 0.4 0.2 0 1
MAIN BEARING OFT UPPER SHELL (in mm) No. MAIN BEARING 1 MAIN BEARING 2 MAIN BEARING 3 MAIN BEARING 4 2000 0.0075 0.02 0.0045 0.0075 4200 0.004 0.004 0.0037 0.004MAIN BEARING OFT LOWER SHELL (grooved) No. MAIN BEARING 1 MAIN BEARING 2 MAIN BEARING 3 MAIN BEARING 4 2000 0.00225 0.002 0.00175 0.0022 4200 0.0024 0.00185 0.0015 0.0024BIG END BEARING OFT UPPER SHELL (grooved) No. BIG END BEARING 1 BIG END BEARING 2 BIG END BEARING 3 2000 0.001 0.001 0.001 4200 0.0014 0.0014 0.0014 BIG END BEARING OFT LOWER SHELL No. BIG END BEARING 1 BIG END BEARING 2 BIG END BEARING 3 2000 0.007 0.007 0.007 4200 0.002 0.002 0.002 Desirable OFT ≥ 0.001 mm ( 1 micron ) for conventional bearings ≥ 0.0003 mm ( 0.3 micron ) with sputter bearings
3-layer-bearing Steel backing bronze layer intermediate layer (Ni if nessesary) running layer (sputtered, electroplated, sprayed)The sputtering process produces a material that combines the high wear-resistanceproperties of an aluminum-tin sliding layer with the extremely high-loadwithstanding capacity of a cast copper-lead-bearing metal layer.
2000 rpm 4200 rpmORDER PULLEY PULLEY 0.5 0.063 0.049 1 0.094 0.084 1.5 2 0.3 Torsional resonance is visible between 4.5 and 6th 2 0.057 0.02 order i.e corresponding speed range of 3345 to 2.5 0.0635 0.064 4460 rpm. Since this falls within operating speed 3 0.2 0.01 3.5 0.05 0.074 range, a TV damper is MUST. 4 0.042 0.08 PULLEY END TV AMPLITUDES 4.5 0.03 0.32 5 0.002 0.65 2.5 5.5 0.03 0.08 MAGNITUDE 2 6 0.02 0.09 1.5 6.5 0.0235 0.02 1 7 0.0215 0.013 0.5 0 7.5 0.03 0.025 1 2 3 4 5 6 7 8 9 10 11 12 0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 8 0.02 0.007 8.5 0.02 0.006 ORDER 9 0.04 0.01 PULLEY END AMPLITUDES @ 2000 rpm PULLEY END AMPLITUDES @ 4200 rpm 9.5 0.025 0.005 10 0.06 0.001 10.5 0.19 0.06 11 0.019 0.002 11.5 0.01 0.001 12 0.014 0.002
The three main potential failure modes are:• Crankshaft fracture• High noise & vibration• Bearing wear & failureAs we know, the crankshaft is a component which takes a lot ofstresses and vibrations. The entire gas force is transferred to thecrankshaft. So when failure modes such as fracture occur, theengine stalls and this is a potential effect of failure. Otherobservations made are those caused due to vibrations. There canbe loosening of fasteners, extreme vibrations throughout thevehicle and lower the life of engine mounts.
• Micro alloyed steel is the material that will be used to develop the crankshaft. Stress risers generate from the sharp edges and therefore fillets are crucial in a crankshaft design. The fillet radius is an important parameter and here the CAE analysis is carried out with different fillet radii and the final radius is calculated.• Noise and vibration is optimized by modal testing where the component is checked for resonance between the operating engine RPM.• Surface treatment is vital too.• Induction hardening is done on the crankshaft to improve the ultimate tensile strength and fatigue bending strength.
For design of high performance engines, quality tools like DFMEA playsan important role to achieve desirable performance and durabilityrequirements. If this is done right from concept stage, the risk of failuressubstantially reduces and lot of time, energy and cost is saved.The DFMEA sheets are customized and prepared for this project. However,as a special case, DFMEA of Crankshaft shows those columns also with anaim to show how these actions are closed and how the RPN reduces. Forexample, the RPN after the actions are closed, have reduced from the rangeof 20 - 175 to 20 – 70.The DFMEA sheets become the input to the designers to model componentswith reduced failure potential. It is this final design that is sent to thevendors for development.
• “Potential Failure Mode & Effects Analysis (FMEA)” – ReferenceManual, Chrysler, Ford & G.M, Issued, First Edition February 1993• D.H. Stamatis, “Failure Modes and Effects Analysis”, Productive Press,1997• SAE Standard „SAEJ1739‟ – Failure Modes & Effects Analysis• www.wikipedia.com (http://en.wikipedia.org/wiki/DFMEA)• Kevin Hoag, “Vehicular Engine Design”, Springer Wien New York,2006• Richard Basshuysen, Internal Combustion Engine – Handbook, SAEInternational• Hiroshi Yamagata, The Science and Technology of materials inautomotive engines, Woodhead Publishing Limited