IMPROVING PROCESS PERFORMANCEIMPROVING PROCESS PERFORMANCEBY REDUCING INPROCESS BY REDUCING INPROCESS

REJECTION USING SIX REJECTION USING SIX SIGMA METHODOLOGYSIGMA METHODOLOGY

CONTENTSCONTENTS

INTRODUCTIONINTRODUCTION

METHODOLOGYMETHODOLOGY

CASE STUDYCASE STUDY

ANALYSIS AND RESULTSANALYSIS AND RESULTS

CONCLUSION AND RE COMMENDATIONS.CONCLUSION AND RE COMMENDATIONS.

INTRODUCTIONINTRODUCTION

As international competition is growing, every industry is As international competition is growing, every industry is trying to improve quality of the product and in turn reduce trying to improve quality of the product and in turn reduce rejection.rejection.

In-house rejection should be controlled as it affects COQIn-house rejection should be controlled as it affects COQ Six sigma methodology discussed in this paper is the business Six sigma methodology discussed in this paper is the business

philosophy that enables world-class quality and continuous philosophy that enables world-class quality and continuous improvement.improvement.

This paper discusses the success story carried out by the This paper discusses the success story carried out by the authorsauthors

SIX SIX σσ METHODOLOGY METHODOLOGY

DMAIC Methodology is central to six sigma DMAIC Methodology is central to six sigma improvement process.improvement process.

Specific tools are used to turn a practical problem Specific tools are used to turn a practical problem into statistical problem,genrate a statistical into statistical problem,genrate a statistical solution and then convert back into practical solution and then convert back into practical solutionsolution

DMAIC FLOW CHARTDMAIC FLOW CHART

DEFINE

MEASURE

ANALYSE

PROCESSOPPORTUNITY

LIKELY BENIFITS

CURRENT PERFORMANCESOURCES OF

VARIABILITY

KEY VARIABLESRELATIONSHIPS

IMPLEMENTED SOLUTION

PREDECTED RESULTS IMPROVE

CONTROLCONTROL VARIABLES

PLAN FOR STABILITY

CASE STUDYCASE STUDY

A manufacturing unit producing wheel cylinder A manufacturing unit producing wheel cylinder was facing a problem of rejection. The jobs were was facing a problem of rejection. The jobs were rejected due to several reasons.rejected due to several reasons.

After studying the statistics of rejection data ,it After studying the statistics of rejection data ,it was decided to Solve the problem by DMAIC was decided to Solve the problem by DMAIC approach.approach.

DEFINE PHASEDEFINE PHASE In this phase all the parameters related with the

process flow were studied. The process flow chart is as follows,

Receiving casting from foundry department

Loading the casting at station 1 by pneumatic feeder

continue

Mounting hole drilling operation

Drilling operation by Φ 3 drill

Tapping operation by M6 tap

Main bore drilling by Φ 15 solid carbide toolFollowed by reaming by Φ 15.87 reamer

Boot grooving operation by form tool

Unloading the job and placing it to storage bin

MEASURE PHASEMEASURE PHASE

MonthMonth Total Total productionproduction

Rejected jobsRejected jobs PPMPPM

SeptemberSeptember 5926559265 344344 58045804

OctoberOctober 7031970319 290290 41244124

NovemberNovember 5716157161 205205 35863586

DEFECTDEFECT NO. OF JOBS REJECTEDNO. OF JOBS REJECTED

Main bore shiftMain bore shift 107107 8585 9090

M 10 damagedM 10 damaged 7676 7070 5050

Face damagedFace damaged 0909 2525 1515

Bore or tool markBore or tool mark 1616 2525 88

Groove stepsGroove steps 1515 88 77

Groove undersizeGroove undersize 2525 1010 00

Acidic etchingAcidic etching 1919 1515 00

M 6 damagedM 6 damaged 8585 1414 3535

Poor finishPoor finish 1212 2828 00

DEFECTWISE REJECTION

ANALYSIS PHASEANALYSIS PHASE

Pareto for month of November.Pareto for month of November.Co

unt

Perc

ent

C1

Count24.4 17.1 7.3 3.9 3.4

Cum % 43.9 68.3 85.4 92.7

90

96.6 100.0

50 35 15 8 7Percent 43.9

Other

bore toolm

ark

face dam

aged

M 6 d

amag

ed

Thread dam

aged

Main

bore s hift

200

150

100

50

0

100

80

60

40

20

0

Fig.2 Pareto Chart of defects

Main causes of rejectionMain causes of rejection

From pareto diagram it can be seen that the From pareto diagram it can be seen that the prime elements causing rejection of the jobs are,prime elements causing rejection of the jobs are,

1) Main bore shift.1) Main bore shift.

2) M10 damaged.2) M10 damaged.

Hence it was decided to find out the root causes Hence it was decided to find out the root causes for this defects by plotting fishbone diagram.for this defects by plotting fishbone diagram.

Analysis of main bore shiftAnalysis of main bore shift

Cause and effect diagram for main bore shiftCause and effect diagram for main bore shift

BORESHIFT

Methods

Material

Machines

Personnel

lack of skill

new operator

belt tension

spindle feed

slide feed rate

hyd.oil leakage

casting defect

slide feed rate

predrilling

coolant flow

tooling

Fig.3 cause and effect diagram for bore shift

Analysis of M10 shiftAnalysis of M10 shift

Cause and effect diagram for M10 shiftCause and effect diagram for M10 shift..

m/oshift

Methods

Material

Machines

Personnel

no fixedoperator

lack of skill

runout of slide

air pressure

belt tension

casting defect

tool material

clamping pressure

Fig.4 cause and effect diagram for M10 shift

IMPROVEMENT PHASEIMPROVEMENT PHASE

Implementation planImplementation planConcerned Concerned parameterparameter

Current statusCurrent status Corrective actionCorrective action Present statusPresent status

M 10 shiftM 10 shift Air pressure drop Air pressure drop below 0.8 Mpabelow 0.8 Mpa

Reservoir added Reservoir added to reduce to reduce pressure droppressure drop

ImplementedImplemented

M 10 shiftM 10 shift Excess material Excess material jobjob

Proper fettling of Proper fettling of liquid metal liquid metal during casting during casting processprocess

ImplementedImplemented

Bore shiftBore shift V block damagedV block damaged V block rework for V block rework for perfect clampingperfect clamping

ImplementedImplemented

Bore shiftBore shift Hydraulic leakage Hydraulic leakage causing pressure causing pressure dropdrop

Hydraulic leakage Hydraulic leakage correctedcorrected

ImplementedImplemented

ResultResult

Improvement in sigma ratingImprovement in sigma ratingMonthMonth No. Of No. Of

rejectionsrejectionsNo. Of No. Of Units Units ProducedProduced

Rejections Rejections per unitper unit

ppmppm Sigma Sigma ratingrating

SeptemberSeptember 344344 5926559265 0.005840.00584 58045804 2.752.75

OctoberOctober 299299 7028870288 0.002970.00297 41244124 2.962.96

NovemberNovember 205205 5716157161 0.003580.00358 35863586 2.922.92

DecemberDecember 9090 5899058990 0.001520.00152 15251525 3.623.62

Saving in materialSaving in material

Approximate annual rejection before study=3840 unitsApproximate annual rejection before study=3840 units

Approximate proposed annual rejection after Approximate proposed annual rejection after implementation=1080 unitsimplementation=1080 units

Proposed reduction in annual rejection raty=2760 unitsProposed reduction in annual rejection raty=2760 units

Proposed saving=2760 x 15.5 =Rs.42780/annumProposed saving=2760 x 15.5 =Rs.42780/annum

CONCLUSIONCONCLUSION

The purpose of this study is to give more insight The purpose of this study is to give more insight to six sigma methodology.to six sigma methodology.

Comprehensive quality management system is Comprehensive quality management system is required to achieve six sigma levelrequired to achieve six sigma level

Case study shows that sigma level for a Case study shows that sigma level for a manufacturing unit increased to 3.62,hence more manufacturing unit increased to 3.62,hence more emphasis is required to improve the quality.emphasis is required to improve the quality.