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INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERINGing and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 09AND TECHNOLOGY (IJMET)me 4, Issue 3, May - June (2013) © IAEME ISSN 0976 – 6340 (Print) IJMET ISSN 0976 – 6359 (Online) Volume 4, Issue 3, May - June (2013), pp. 232-243 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) © I A E M E www.jifactor.com ROOT CAUSE ANALYSIS OF FIELD FAILURE CONCERN FOR IMPROVEMENT IN DURABILITY OF VEHICLE SYSTEM 1 2 A. D. Lagad , Dr. K. H. Inamdar 1 Department of Mechanical Engineering, Walchand College of Engineering, Sangli, Maharashtra, India, 2 Department of Mechanical Engineering, Walchand College of Engineering, Sangli, Maharashtra, India ABSTRACT Durability and reliability of an automobile are equally important from industry as well as customer point of view. Automotive industries are still riddled with significant warranty costs that incur due to premature failure of their products in the customer hands. The key to reduce the design and development expenses and warranty expenses is to subject the product for reliability and/or durability tests for failure modes investigation. Design of the vehicle components must be adapted as accurately as possible to the operating conditions. In order to achieve these goals, durability tests are performed through a combination of physical testing, on road at a proving ground test track, and using a servo-hydraulic road test simulator in laboratory. In this study, root cause analysis is carried out for bonnet cable failure in vehicle model of an automotive industry. Various possible causes are identified using fishbone diagram, why-why analysis is carried to find root cause and solution is proposed. Modified design of hood latch reduced operating efforts for hood latch and avoided bonnet cable failure. Keywords: Durability, Reliability, Root cause analysis, Fishbone diagram. 1. INTRODUCTION In automotive industry, vehicle safety and product quality are prime factors on which automotive manufacturers give significant attention. During vehicle manufacturing, defects 232 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME arise during manufacturing, assembly and other processes. For continuous quality improvement and customer satisfaction, plant quality functions are planned, integrated and executed to detect these defects and make action plans, preventive measures to resolve them. Currently, automotive industries are dedicating a lot of attention to improve product quality, durability and reliability already in a virtual simulation environment. A major issue that designers and manufacturers in this field have to face is to improve vehicle lifetime [1,2]. Durability and reliability of a vehicle are equally important from a customer point of view. Automotive industries are still riddled with significant warranty costs that incur due to premature failure of their products in the customer hands . Vehicle manufacturers discover issues through their own vehicle tests, inspection procedures, or information gathering . In order to achieve improved durability and reduced warranty costs, durability tests are performed through a combination of physical testing, on road at a proving ground test track, and using a servo-hydraulic road test simulator in laboratory . Modern vehicles exhibit a variety of performance, safety and comfort features in which they fundamentally differ from previous models. Durability and reliability in vehicle components are prime considerations for successful functioning of vehicles in all aspects mentioned above [5, 6]. In this study, root cause analysis is carried out for bonnet cable failure in vehicle model of an automotive industry and solution is implemented accordingly. Various finished vehicle audits performed in automotive industry considered are ANOVA-C (Advanced New Overall Vehicle Audit), GD (Global Demerit) test and Durability ANOVA-C. The purpose of Durability ANOVA-C is to check and capture data on internal/known customer vehicles periodically to get early feedback on field failure and make action planning [7,8]. 2. CONCERN RESOLUTION- BONNET CABLE FAILURE Concern identified and considered for resolution is ‘High Operational Effort for Hood Latch Release Lever’ which results in bonnet cable failure. This concern is identified during durability ANOVA-C and GD audit. Effort readings taken on internal customers’ vehicle are shown in table 1. Specifications are 40-80 N. Table 2 shows hood latch release lever effort readings for 60 Ready for Inspection (RFI) vehicles. Higher operational efforts are observed for some vehicles. Table 1: Hood latch release lever efforts for internal customers Customer Lower Limit Upper Limit Phase 1 Phase 2 Phase 3 (N) (N) (N) (N) (N) 1 40 80 55 110 122 2 40 80 55 110 85 3 40 80 69 72 75 4 40 80 76 98 100 5 40 80 99 108 105 233 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME Table 2: Hood latch release lever effort readings for 60 vehicles Sr. No Effort Sr. No Effort Sr. No Effort Sr. No Effort (N) (N) (N) (N) 1 73 16 64.9 31 71.3 46 70 2 67.8 17 69.7 32 69.3 47 74.3 3 56.8 18 54.6 33 58.4 48 71.9 4 59.3 19 64.4 34 66.7 49 76.5 5 78.1 20 86.1 35 77.8 50 62.8 6 76.1 21 61.4 36 74.3 51 64.1 7 78 22 78 37 55.4 52 64.4 8 66.9 23 64 38 67.3 53 71.3 9 63.3 24 80.6 39 67.8 54 69.1 10 70.8 25 71.2 40 66.1 55 64.6 11 69.4 26 65.2 41 77.5 56 66.1 12 77.3 27 59.3 42 70.6 57 72.7 13 74.2 28 63.2 43 62 58 71.4 14 66.1 29 73.1 44 72.2 59 100 15 77.4 30 76.1 45 77.5 60 69.2 Bonnet cable failure is third in the list of significant field failure concerns as shown in pareto diagram in fig. 1. Analysis is already carried out for first two concerns. 2.1 Process Flow for Bonnet Cable and Lock assembly Bonnet cable and bonnet lock are fitted and assembled on assembly line in TCF. Steps involved in this process are mentioned below, 1.Bonnet cable fitment is done on body with grommet and plugs (Trim Line). 2.Bonnet cable bracket is fitted on cockpit (Trim Line). 3.Hook of bonnet cable is assembled with bottom side hood latch (Underbody Line) 4.Bottom side hood latch is fitted on front grill upper body panel with 3 bolts by giving full torque (Underbody line) 5.Loose mounting of top side hood latch on bonnet bottom side with 2 bolts by pre torque. (Final line) 6.Alignment of bonnet as well as both hood latch parts. Tightening of top side hood latch by giving full torque to bolts (Final line) 234 InternationallJourrnal of Meechanical Enngineering and TTechnoology (IJMEETT),ISSSN 09976 – 6340(Print), ISSN 0976 – 63559(Online) Volumee 4,Issue 3,Maayy -June (2013) © IAEEMEE Fig. 1 Pareto dagramm forsignificantfieldfailureconncerns Alignmeent process s done in ollowiing sepss,, 1.Alignmeenttofhoood by reightening hingees(both locks arein oooseconndiion).. 2.Gaap & Flushneesscorrected by giving erk to he hoodd.. 3.Bonnet is locked first time. 4.Oppening of bonneetby giving slghhtstroke to hood with maalettfrst time ift isnottopeened due to stuck..Toop side lock assembbly is again algnned wiih respecttto bottom sside lock assembly. 5.Fulltightening ofthe both hooddlock assembblies(bodyyside & boonnet sde)) 6.Aggainboonnet s locked & oppened 2 o 3 tmees.. Fig. 2 showsshoood atch assembbly on vehicle s weel as op and bottom hoood lach.. (a) (b) (C) Fig. 2 (a)Hoood latchassemmbly on vehicle (b) Top side hood latch (cBootomm side hood latch 235 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 3. ROOT CAUSE ANALYSIS After brainstorming, various possible causes contributing to bonnet cable failure are enlisted. Cause and effect diagram (Fishbone diagram) by using relevant possible causes identified in brainstorming is shown in fig. 3. Probable causes for bonnet cable failure are highlighted in figure. Fig. 3 Cause and effect diagram for bonnet cable failure 3.1 Verification of probable causes 1. Damage to cable while fitment: i. Fitment process is observed on assembly line. ii. No damage is observed to cable while fitment iii. Remark: Invalid 2. Improper cable assembly: i. Standard operation procedure is followed during cable assembly. ii. No abnormalities found during cable fitment on body as well as cable assembly with cockpit and hood latch. iii. Remark: Invalid 3. Improper cable routine: i. Bonnet cable routine is observed from release lever end to cable hook end during fitment, also on finished vehicles ii. Cable routine was found ok in vehicles. All clips were found on position. 236 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME iii. Cable routine found ok in vehicles for which higher efforts reported to operate hood latch release lever iv. Remark: Invalid 4. Improper alignment of bonnet as well as latch-striker: i. Alignment is done as per standard operation procedure. ii. Gaps are measured for bonnet on finished vehicles and alignment found ok. iii. However, during first locking-unlocking operation in alignment process, cable failure incidences were observed on final line iv. As alignment is done in 2-3 attempts by operator judgment- chances that striker gets stuck in latch in first cycle. v. Remark: Valid 5. Nut runner not applying required torque/ bolt looseness: i. Nut runner calibration done as per scheduled frequency ii. Bolts used for tightening of both latch and striker were checked on finished vehicles for looseness- Found ok iii. Torque is measured on finished vehicles, also on vehicles for which higher efforts reported- torque found as per specification. iv. Remark: Invalid 6. Deviation of cable length from required length: i. Bonnet cable length is measured for cables in storage area at side of assembly line ii. No variation in cable length, length found as per specifications iii. Remark: Invalid 7. Cracks on cable flap or bracket: i. Bonnet cables were examined visually for any cracks or damages to cable flap or bracket ii. No cracks or damage observed iii. Remark: Invalid 8. Less thickness for cable flap or bracket: i. Previous actions: Bracket wall thickness increased by 1.2 mm, Reinforcement added to flap ii. Cable flap and bracket thickness measured- Found okas per modified dimensions iii. Remark: Invalid 9. Bottom hood latch spring has more stiffness: i. Parameters such as free length, number of turns, coil diameter contributing spring stiffness were checked for bottom hood latch spring. ii. No variation in stiffness- Found ok iii. Remark: Invalid 10. Cable routine disturbed: i. Cable routine observed in RFI area, also on customer vehicles during dealer visit. ii. Cable clips were ensured for position (not fallen) 237 InternationallJouurnal of MeechanncaalEnngineering annd Teechnology (IJME ET)),ISSN 009766 – 6340(Print), ISSN 0976 – 63359(Onnlnee)Vooummee4,,Isuee3,,Maay -Junne 20113)© IIAEMMEE iii. No abnormalities found iv. Remark: Invalid 11. Bonnet as well as latch-tiker algnmmeentgetting diturbed ovverusaggeoffvehicle: i. BBonnnetalignmeenttobservedd,gapp meaasuremeentsdoone and bonnnet eforts were taken onn cusommeervehicles during dealervisit ii. Gap vaaiation s observeed on rghttand leftside (misalignmeent)also higher effors weere noted iii. n somme vehhices (atdeeaerrand production shop)) bonnnetgootoppened aftergiving slight erk from side (because stiker getstuck in atch ) iv. Remark: Valid 3.2 Valid causes Bonnet cable failure occurs because striker gets stuck into bottom latch. i. Bonnet as well as latch-sriker aignmmenntgettnggdisturbed oveerusage of vehicle. ii. During first lockingunlockkngg operatoon n aaignmeenttprocess,,chanceesthat sriker get stuck in latch. Stackk up anaaysis of top hoood lacch and bootom hhoood lachh showss haatonnly 2 mmm clearance given betweeen the op andd botomm hoood atch for algnmmenntas shownn infig. 4. It is not geting maaintained due o conntibution of hngges and in process. Onn aa vehicle whhich hhad runn 70000 kilomeeters,fronttgrill s remmovved; bonnnet is slammmeed eww tmees and obbserved thatboonnet isnottopennngg by operating hooddlatch release lever. Refer fig. forexpplanatonn.. (a) (b) Fig. 4 Stack up analysisofftop hood latch and Fig. 5(a) Bonnnetts notoppened because bottom hoood lach strkeergottstuck nto latch(b) Stuck up marks on bottom l atch 238 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME During dealer visit, customer vehicles were observed for bonnet alignment. Hood latch release lever efforts were taken and bonnet gaps were measured. Table 3 shows effort and gap measurement readings. Higher operational efforts were seen in customer vehicles. Table 3: Effort and gap measurement readings on customer vehicles Sr. Hood latch Gaps (mm) No. lever effort RH Side LH Side (N) 1 2 3 4 5 6 1 2 3 4 5 6 1 83.9 5 4.9 4.6 5.5 5.2 5.2 4.1 4 4.8 3 3.1 4.1 2 77.1 5.1 2.5 2.1 4.2 4.6 6 6.3 6.3 6.5 4.1 4.7 4.8 3 95.6 5 2.1 1 2.9 3.7 4.4 5.6 5.9 5 3.8 4 5.8 4 114.5 5.8 5 4.7 7.5 4.8 4.9 5.2 3.8 6 2.3 2.8 6 5 103 5 4.8 4.1 5 4.5 4.7 6.1 3.6 4.5 2.8 3.5 4.6 6 80.3 3.8 2.9 1.3 4.1 3.9 6 5.9 5.4 5.2 2.6 3.4 5 7 78.1 6.3 4.9 3.8 5.7 5.7 6.1 6.1 4.8 6.2 2.5 3.9 4 8 82.7 6 4.8 4.2 6.2 5.8 6 6 4.7 5.1 2.8 3 4.6 9 87.5 5.2 4.4 3.8 5.3 5.1 5.1 6 5.1 6.1 3.2 3.2 4.1 10 91.4 5.5 3.2 2.2 4.6 2.8 5.3 5.6 4.9 5.9 4 4.1 5.1 3.3 Why-Why analysis Cause for bonnet cable failure is explained below, i. Why: Higher operational efforts for hood latch release lever ii. Why: Striker get stuck into bottom latch iii. Why: Striker and bottom latch not remain inline iv. Why: Latch-striker alignment getting disturbed over usage of vehicle or during first cycle of alignment v. Why: This factor is not considered during design 4. PROPOSED SOLUTION As there is problem that striker of top hood latch assembly getting stuck into bottom latch due to misalignment, there is a need of keeping striker and bottom latch in one line i.e. to avoid misalignment (oblique travel of striker in latch). After observation and study of structural design of hood latch parts of vehicle, proposal is given to implement a groove in the striker of top hood latch and guide on bottom hood to avoid misalignment and stuck up issue because of which bonnet cable failure occurs. For this, structural benchmarking was done with hood latch of another vehicle as shown in fig. 6 and 7. 239 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME (a) (b) Fig. 9 Change in top hood latch (a) Existing (b) Proposed 5. IMPLEMENTATION AND RESULTS Sample hood latches were received from supplier with said design modifications in given proposal. 5.1 Concept trial Concept trial was conducted on three vehicles with new hood latch samples. Table 4 shows comparison of hood latch release lever operational efforts for three vehicles with existing and modified hood latch parts. Table 4: Hood latch release lever operational efforts during concept trial Vehicle Specification Readings with existing Readings with modified No. (N) hood latch (N) hood latch (N) 1 2 3 1 2 3 1 40-80 78.4 76.1 76.3 53.7 53.2 53.2 2 40-80 79.1 78.4 78 56 56.2 55.5 3 40-80 76.8 76.5 75.9 50.2 49.8 49.1 i. During concept trial, fitment was observed for any difficulties in fitment process as well as alignment. ii. No issue regarding fitment or alignment was noticed. iii.After operating hood latch release lever and primary lock getting released, secondary lock (to be released by operating lever of top side hood latch) was found ok in all three vehicles. iv. Bonnet opening-closing cycle was performed for 500 times on three vehicles with modified hood latch parts to check whether there is bonnet cable failure. Bonnet cable failure incidence was not observed and cable found ok. 5.2 Fitment trial After receiving modified hood latch samples, fitment trial was conducted and completed for five numbers of vehicles. 241 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME Table 5: Hood latch release lever operational efforts during fitment trial Vehicle Specification Readings with modified hood No. (N) latch (N) 1 2 3 1 40-80 56.5 56.2 55.9 2 40-80 59.3 58.4 58.6 3 40-80 50.2 50.2 50.1 4 40-80 53.8 53.5 53.1 5 40-80 60.4 60.9 60.7 No fitment related issue was observed during trial. Bonnet opening-closing cycle was repeated for five vehicles and no abnormality was observed (No higher efforts, secondary locking ok). Hood latch release lever operating efforts were measured on five vehicles and found within specifications. Readings are shown in table 5. 5.3 Validation and part trial Validation process is conducted for modified hood latch samples. In validation, bonnet cable withstands and passed target of 5000 cycles of bonnet opening and closing for all samples. Part trial is conducted on 200 vehicles and readings were taken. All vehicles have shown effort readings within specification. No bonnet cable failure incidence was occurred. Range of effort readings was found between 45 to 62 N (Specification is 40-80 N). This shows significant operational effort reduction for hood latch release lever. 6. CONCLUSION 1. Root cause analysis is carried out for the concern “Higher operational efforts for hood latch release lever which results in bonnet cable failure.” i. Bonnet cable failure occurs due to disturbance in alignment of striker-latch which results in stuck up condition of striker in latch. ii. To avoid stuck up condition, design modifications are suggested in hood latch with provision of locking bracket (guide cup). 2. Trials with modified hood latch samples showed reduction in hood latch release lever operational effort than that in case of customer vehicles as well as new vehicles with existing design. 3. In validation, bonnet cable withstand for 5000 cycles of bonnet opening and closing. During trials as well as implementation for 200 vehicles, no bonnet cable failure incidence occurred with modified hood latch. 7. REFERENCES  R.d'Ippolito, M. Hack, S. Donders, L. Hermans, N. Tzannetakis, D. Vandepitte, Improving the fatigue life of a vehicle knuckle with a reliability-based design optimization approach, Journal of Statistical Planning and Inference, 139, 2009, pp. 1619-1632 242 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME  Alan S. Abrahamas, Jian Jiao, G. Alan Wang, Weiguo Fan, Vehicle defect discovery from social media, Decision Support Systems, 2012, pp. 1-11.  Senthilnathan Subbiah, O. P. Singh, Srikanth K. Mohan, Arockia P. Jeyaraj, Effect of muffler mounting bracket designs on durability, Engineering Failure Analysis, 18, 2011, pp. 1094–1107.  V. Veloso , H.S. Magalhaes , G.I. Bicalho , E.S. Palma , Failure investigation and stress analysis of a longitudinal stringer of an automobile chassis, Engineering Failure Analysis, 16, 2009, pp. 1696–1702.  Roland Meuller-Fiedler, Volker Knoblauch, Reliability aspects of microsensors and micromechatronic actuators for automotive applications, Microelectronics Reliability, 43, 2003, pp. 1085–1097.  D. G. Yang, F. F. Wan, Z. Y. Shou, W. D. van Driel, H. Scholten, L. Goumans, R. Faria, Effect of high temperature aging on reliability of automotive electronics, Microelectronics Reliability, 51, 2011, pp. 1938–1942.  ANOVA-C Guidelines in automotive industry.  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