Through Pass Rate Improvement in a Assembly Line by BPS Methodology: A Case Study of a Manufacturing Company

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1 Internatinal Jurnal f Manufacturing and Mechanical Engineering Vlume 1, Number 1 (2015), pp Internatinal Research Publicatin Huse Thrugh Pass Rate Imprvement in a Assembly Line by BPS Methdlgy: A Case Study f a Manufacturing Cmpany Arun.M 1, Siva Kumar.P 2, Rshan.R.H.V. 3 1 Assciate Prfessr, 2,3 UG Student Department f Mechanical Engineering St.Jseph s Cllege f Engineering, Chennai Camrun4a.5a@gmail.cm Abstract The fast changing ecnmic cnditins such as glbal cmpetitins, declining prfit margin, custmer demand fr high quality prduct, prduct variety and reduced lead time etc. had a majr impact n manufacturing industries.this wrk discusses abut the successful implementatin f Basic Prblem Slving (BPS) methdlgy t imprve the thrugh pass rate f a Gear Bx assembly line in a large scale manufacturing cmpany. Each and every Gearbx is tested t ensure that there are n defects. Gear Bx nce rejected are again rewrked and tested t ensure their perfrmance, this increases the cst f prductin f gear bxes.the bjective f this wrk is t imprve the thrugh pass rate f Gearbx assembly line. Rejectin data frm the each test beds are cllected and analysis were made t find the rt causes fr the rejectin f gear bx. Slutins were identified and validated fr the rt causes. After pilt implementatin f slutins, rejectin data was again cllected and checked fr imprvement. It was fund ut that the thrugh pass rate has increased. Keywrds Manufacturing, Thrugh Pass Rate, Paret Analysis, Cause and Effect Diagram, Six Sigma Intrductin In an Autmbile Sectr, success f an rganisatin resides in its ability t respnd quickly t its need f the custmers[4]. The custmer needs must be attended with minimum manufacturing csts and minimum lead time[4]. This can be identified by the manufacturing metrics.thrugh pass Rate (TPR) is ne f the manufacturing

2 2 Arun.M et al metric and is defined as the number f units cming ut f a prcess divided by the number f units ging int that prcess ver a specified perid f time. Only gd units with n rewrk r scrap are cunted as cming ut f an individual prcess. The gal f every manufacturer is t eliminate rewrk in favur f imprving TPR t achieve the lwest prduct csts pssible[3]. But t d this requires a methdlgy fr accurately measuring and tracking TPR thrughut the manufacturing prcess, since it is impssible t cnsistently imprve r maintain smething that isn t quantified. This invlves recrding results at each step in such a way that TPR can be calculated while prperly accunting fr the rewrk and re-testing f failed parts.[1] This wrk is carried ut by Basic Prblem Slving (BPS) methdlgy. The BPS methdlgy has seven steps namely Define, Observatin, Analysis, Actin, Check, Standardize and cnclude. Each step has its wn quality tls such as Paret chart, Check sheet, Cntrl chart, Hypthesis testing, Cause and effect diagram, Design f experiments, etc. The prject requires supprt frm Manufacturing, Quality, Unit planning and Lgistics. During testing, a Gearbx is checked fr defects such as nise, il leak, gear engagement issues, reverse switch malfunctining, tightness f flange, vibratin, etc. Rejectins data were cllected and a paret analysis was made t find ut the mst frequently ccurring reasns fr rejectins. Since Oil Leakage accunts fr almst 30% f the ttal Gearbx rejectin, this wrk fcuses nly n Oil leakage reductin t imprve the thr pass rate. Imprving the thr pass rate leads t reductin in peratr effrt, imprvement in quality and increased cst savings[2]. All the plts were pltted using Minitab Sftware. Fig 1: Paret Chart shwing the amunt f rejectins fr varius reasns Literature Review and Survey Literature survey fcuses n implementatin f Six Sigma in manufacturing Industries, Methdlgy fllwed fr this wrk is BPS, but still Six Sigma and BPS have a clse crrelatin. Five Steps f Six Sigma is made mre wide as seven steps in

3 Thrugh Pass Rate Imprvement in a Assembly Line by BPS Methdlgy 3 Basic Prblem Slving Methdlgy. The fllwing are the areas where Six Sigma is applicable in a autmbile Industry,[4] Imprving safety and reliability f finished vehicles. Reducing manufacturing defects at each stage. Reducing time t manufacture. Reducing variatin in all the critical parameters that impact the finished prduct. Imprving the verall incming material quality r parts quality. Reducing supplier lead time. Basic Prblem Slving methdlgy was fllwed t imprve the TPR f GearBx assembly line. It is als a breakthrugh business strategy used fr quality and prcess imprvement by using a set f structured tls and statistical measures t evaluate prcesses.[1] CASE STUDY Phase 1: PROBLEM The frequency f the prblem was analysed by the Quality management team. In this case there were rejectins in the assembled gearbx when it was tested. The gearbxes are rejected due t varius reasns. This affects the thrugh pass rate f the gearbx assembly line which eventually affects the chassis assembly and it brings dwn the verall prductin rate f the factry. It als gives rise t the inventry f the ther parts which is needed in the chassis assembly. Nw, t increase the thrugh pass rate the majr cause fr the rejectin is t be fund and the varius ways f attacking the cause has t be decided which can ultimately increase the prductin rate. Phase 2 : OBSERVATION In rder t find the majr reasns cntributing t the prblem, real time data were cllected frm all the test beds. Details f the tested gearbxes were cllected, which includes shift, mdel, reasn fr rejectin, tested quantity and rejected quantity. The reasns fr rejectin included Nise, Flange nt rtating, Twer mvement, Oil leak, Gear nt engaging, Flange wbbling, Brken nzzle, Pwer Take Off nt wrking, etc. With the cllected data a Paret Analysis was made t narrw dwn n the majr cause. It shwed that NisePrblem was at the peak and il leak at the secnd place. Oil leak issue was taken as it fell under the scpe f BPS methdlgy. Checking fr Binmial Distributin Being attribute data, rejectin data fllws Binmial distributin. T find this, several steps has t be fllwed. They are, Step 1: Histgram was pltted with the rejected data. Step 2: Prbability Plt (with fit) P-value > was pltted. Step 3: Cntrl Chart (P-Chart) was pltted. Step 3: Prcess capability Plt was pltted.

4 4 Arun.M et al Step 1 Fig 2: Histgram f Gear Bx Rejected In this plt it shwed the rejectin f Gear Bxes fr varius reasns such as Abnrmal nise, Oil Leak, Twer mvement, Gear nt engaging etc. Step 2: Fig 3: Prbability plt f Gearbx Rejected The purpse f a prbability plt is t check the P-value with the cllected data. Since the P- value is greater than 0.05.It was cncluded that data was fllwing binmial distributin.

5 Thrugh Pass Rate Imprvement in a Assembly Line by BPS Methdlgy 5 Step 3: Calculatin f UCL and LCL p(1 p) σ = n z=3 UCL = p + zσ = p + z p(1 p) n = UCL = LCL = p + zσ = p z p(1 p) n ( ) ( ) Fig 4 : Chsing a Cntrl Chart = LCL = = 0 (Since negative value is nt pssible, 0 is cnsidered) Fig 5: Cntrl Chart

6 6 Arun.M et al Frm the abve plt it was clear that the rejectin data fllws binmial distributin and the rejectins are stable. Step 4: Fig 6: Chsing capability plt Fig 7: Prcess Capability plt If the prcess is nt in statistical cntrl then capability has n meaning. Therefre the prcess capability des nt deal with special cause variatin but nly cmmn cause variatin. Phase 3: ANALYSIS Analysis dne t arrive at the Rt causes f the prblem. This was dne using Paret analysis and Cause and Effect diagram with the cllected data. The data cllected frm the test beds were srted int 4 different frms, Test Bedwise Rejectins Reasnwise Rejectins Shiftwise Rejectins Mdelwise Rejectins

7 Thrugh Pass Rate Imprvement in a Assembly Line by BPS Methdlgy 7 Test Bedwise Rejectins The data were taken frm fur test beds and the number f gear bxes rejected in each test bed each day per shift was summed and a paret analysis was dne. Frm the analysis it was fund ut that the rejectins are similar inall the test beds. Therefre it was cncluded that there was n prblem with the test beds. Table 1: Rejectin details f gearbxes frm each test bed Test Bed GB Tested GB Rejected GB Rejected % Fig 8: Paret Chart fr Test Bed rejectins Mdel wise Rejectins There are abut 10 series f Gear Bx being assembled and tested. Few series have mre demand while sme have less demand. Based upn the number f gear bxes assembled in a particular series and gt rejected,aparet analysis was made t check whether there is any rejectins ccurring frequently in any particular series. Frm this chart it was evident all the mdels have similar rate f rejectins. S we cnclude that the there is n prblem with any particular mdel.

8 8 Arun.M et al Table 2: Rejectin details f Gear Bxes mdelwise Series GB Tested GB Rejected GB Rejected % Fig 9: Paret Chart fr Mdelwise rejectins Reasn wise Rejectins Gear Bx rejected fr varius reasns was summed up and a paret analysis were made t arrive at the mst frequent ccurring cause fr il leakage. Frm this analysis we ranked the first five spts frm where il leakage ccurs frequently. Frm this analysis we culd target at that particular pint in the assembly stage as these are the majr reasns fr il leakage. Reasns fr rejectins are ranked as fllws: 1. IPS Cver Oil Leak 2. Idler Cver Oil Leak 3. Flange Side Oil Leak 4. Dummy Plug Oil Leak 5. Bell Husing Oil Leak

9 Thrugh Pass Rate Imprvement in a Assembly Line by BPS Methdlgy 9 Table 3: Rejectin details f Gear Bxes Reasnwise Reasns fr Rejectin GB Tested GB Rejected Bell Husing Oil Leak 60 4 Casing Oil Leak 6 1 Dummy Plug Oil Leak Elbw Oil Leak 59 3 Flange Side Oil Leak End Cver Oil Leak Idler Cver Oil Leak IPS Cver Oil Leak PTO Oil Leak 54 4 Twer Oil Leak 81 6 Wrm Gear Oil Leak 8 1 Fig 10: Paret Chart fr Reasnwise rejectins. Shift wise Rejectin Ttally there are 3 shifts viz, First Shift, Day Shift, Night Shift. Gear Bxes tested and rejected in each shift were summed up and an analysis were made t find ut in which shift mst f the rejectins are ccurring. Frm the analysis fund ut that mst f the rejectins ccur in the day shift and night shift. Table 4 : Rejectin details f Gear Bxes Shiftwise Shift GB Tested GB Rejected GB Rejected % D/S N/S F/S

10 10 Arun.M et al Fig 11: Paret Chart fr Shiftwise rejectins. As a result f analysis phase, ur next step is t target the five reasns ranked, in the day shift and night shift, as these have the mst frequency fr il leakage. FishBne Diagram Fishbne diagram fr the varius reasns f rejectins ranked frm paret has been made. These are the ptential causes which may lead t il leakage in gear bxes. Frm these ptential causes, rt causes fr the prblem was arrived by mnitring the assembly prcess in the day shift and night shift. Fig 12: Cause and Effects fr IPS cver il leak Fig 13: Cause and Effects fr Idler cver il leak.

11 Thrugh Pass Rate Imprvement in a Assembly Line by BPS Methdlgy 11 Fig 14: Cause and Effects fr Flange il leak Fig 15: Cause and Effects fr Dummy Plug il leak Fig 16: Cause and Effects fr Bell Husing il leak ROOT CAUSES When analysed with the Paret and fish bne diagramthe rt causes fr the prblems was determined. The causes fr each f the prblem is listed separately as shwn belw, IPS COVER OIL LEAK N Oil seal

12 12 Arun.M et al Oil seal damage Lay shaft shim ffset Input shaft shim ffset IDLER COVER OIL LEAK Blt tightening Gasket damage FLANGE OIL LEAK Oil seal damage Oil seal missing DUMMY PLUG OIL LEAK Nt fully tightened Dummy plug missing BELL HOUSING OIL LEAK Gasket shift Phase 4 : Actin With the determinatin f the rt causes fr the prblem the varius pssible slutin t get rid f each cause is brainstrmed by the implementatin f which there can be an imprvement in the thrugh pass rate f the gearbx assembly line. They are shwn in the list belw, Table 5: Causes and Slutins fr Oil Leakage Causes Suggestins N Oil Seal Machine Mdificatin Oil Seal Damage Guide Bush Mdificatin Lay Shaft Shim Offset Instructin Sheet Input Shaft Shim Offset Instructin Sheet Blt tightening Creating Operatr awareness Gasket Damage Prper Gasket Strage Gasket Shift Guide Pin Mdificatin Dummy Plug Nt Tightened Instructin Sheet Dummy Plug missing Instructin Sheet Phase 5: Check The slutins given in the actin phase was pilt implemented and 15 days gear bx rejectins data were cllected, t check whether there is any change in the Thrugh Pass Rate. By Hypthesis testing it was fund that the TPR has imprved. Therefre the next stage is t standardize the given slutins in the assembly prcess.

13 Thrugh Pass Rate Imprvement in a Assembly Line by BPS Methdlgy 13 Phase 6: Standardize The slutins given in the actin phase were included in the assembly prcess and the slutins were standardized. Phase 7: Cnclude Thus the Basic Prblem Slving Methdlgy(BPS) has been adpted t increase the Thrugh Pass Rate f the gear bx assembly line. By increasing the thrugh pass rate cst spent n rewrking fr a gear bx has been reduced and the labur s time has been saved. After pilt implementatin f the suggestins, data was cllected t verify imprvement in thrugh pass rate. A cntrl Chart was pltted and it was fund that every pints were within the limits. This shws that the rejectins has reduced. Fig 17: Cntrl Chart after implementing the suggestins References: [1] E.V.GijJhnyScaria, Prcess Imprvement thrugh Six Sigma with Beta Crrectin : a case study f a manufacturing cmpany Internatinal Jurnal f Advanced f Manufacturing Technlgy(2014). [2] Tushar and Desai and Dr.R.L. Srivashtava, Six Sigma- A New Directin t Quaity and Prductivity Management.- Prceedings f the Wrld Cngress n Engineering and Cmputer Science [3] G.V.S.S. Sharma and SrinivasaRa, A DMAIC apprach fr prcess capability imprvement an engine crankshaft manufacturing prcess - Internatinal Jurnal f Industrial Engineering. [4] Vind G. Surange, Implementatin f Six Sigma t reduce Cst f Quality: A Case Study f Autmbile Sectr Jurnal f Failure Analysis and Preventin. [5] S.V.Deshmukh and R.R.Lakhe. Six Sigma An Innvative Apprach fr Waste Reductin : A Case Study f an Indian SME [6] M.Mahesh. A Six Sigma Apprach fr benchmarking f RP&M Prcess - Internatinal Jurnal f Advanced Manufacturing Technlgy.

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