REDUCTION OF WELDING DEFECTS USING SIX SIGMA TECHNIQUES
Int. J. Mech. Eng. & Rob. Res. 2013Shashank Soni et al., 2013ISSN 2278 – 0149 www.ijmerr.comVol. 2, No. 3, July 2013 2013 IJMERR. All Rights ReservedResearch PaperREDUCTION OF WELDING DEFECTS USING SIXSIGMA TECHNIQUESShashank Soni1*, Ravindra Mohan1, Lokesh Bajpai1 and S K Katare1*Corresponding Author: Shashank Soni, shashank.soni@ymail.comIn this paper discusses the quality and productivity improvement in a manufacturing enterprisethrough a case study. The paper deals with an application of Six Sigma DMAIC (Define-MeasureAnalyze-Improve-Control) methodology in an industry which provides a framework to identify,quantify and eliminate sources of variation in an operational process in question, to optimize theoperation variables, improve and quality performance, viz., process yield with well executedcontrol plans. Six Sigma improves the process performance (process yield) of the criticaloperational process, leading to better utilization of resources, decreases variations and maintainsconsistent quality of the process output. In this Paper identifies the root causes of failure for awelding process at a manufacturing plant and proposes to use Operational Six Sigma techniqueto eliminate the problem. In contrast to other method which measure and identify thenonconformance through destructive testing, a technique is proposed to use a mathematicalmodel, which is later charted using SPC technique. The control chart for the mathematicalmodel identifies the failure of the process in real time and will reduce/eliminate the testing process.Keywords: Quality Management, Six Sigma, DMAIC Process, Statistical Process ControlINTRODUCTIONstrategy which is built on foundation ofcontinuous improvement and organizationwide involvement, with core focus on quality.TQM is a process of embedding qualityawareness at every step of production orservice while targeting the end customer. It isa management strategy to embed awarenessTotal Quality Management (TQM): It hasevolved as a strategic approach in most of themanufacturing and service organizations torespond to the challenges posed by thecompetitive business world. Today TQM hasbecome a comprehensive management1Department of Mechanical Engineering, Samrat Ashok Technological Institute, Vidisha (M.P), India. 464001.404
Int. J. Mech. Eng. & Rob. Res. 2013Shashank Soni et al., 2013of quality in all organizational processes. Bypursuing the process of continuousimprovement and never-ending improvementthe companies can out distance theircompetitors by enticing the customers withhigh quality products at low price. TQM hasculminated Six Sigma, which targets99.99927% defect free manufacturing (TusharN Dasia and Shrivastava, 2008).elements of TQM. Six Sigma has become amuch broader umbrella compared to TQM(Tushar N Dasia and Shrivastava, 2008).THE DMAIC SIX SIGMAMETHODOLOGYThe DMAIC is a basic component of SixSigma methodology—a better way to improvework process by eliminating the defects ratein the final product. The DMAIC methodologyhas five phases define, measure, analysis,improvement and control.SIX SIGMASix Sigma is considered as a methodology ofimplementing TQM. Six Sigma is an innovativeapproach to continuous process improvementand a TQM methodology. Since qualityimprovement is the prime ingredient of TQM,adding a Six Sigma program to the company’scurrent business system covers almost all theDefine PhaseGoal: In this phase, define the purpose ofproject, scope and process background forboth internal and external customers. There area different tools which is used in define phaselike SIPOC, Voice of Customer and QualityFunction deployment.Figure 1: DMAIC Methodology for Running Six Sigma ProjectDEFINE MEASURE Economic considerations of quality.Basic tools.Flow charting the process.Capability studies.Cause/effect diagram.Measurement system analysis.ANALYZE IMPROVEProblem solving teams.Defect per unit.Brainstorming.Failure mode and effectanalysisDesign of experiment. Design of experiment. Advance statistical tools. Employee involvementCONTROL Control plans. Revise standard operatingprocedures.405
Int. J. Mech. Eng. & Rob. Res. 2013Shashank Soni et al., 2013OutputFigure 2: Pareto Chart Showing SAWWelding Process1. A clear understanding of processimprovement and how is it measured by the2. Implementation of different tools.3. High level of process is achieved.4. A lot of successful factors list show that whatcustomer requirement is?SAW machine process is lowest in thegiven period; a Pareto chart illustrates inFigure 2. It was decided to increase thisproject. Table 1 presents the team charter forthis project.Describes the transformation process ofinputs form suppliers to output for customersand gives a high level understanding of theprocess, the process steps (sub processes)and their correlation to each other.Table 1: Project Team CharterDeptt. NameTQM Facilitation & IndustrialEngineering Deptt.Project LocationA large scale manufacturing unit,Surat, Gujarat, India.Project Start Date11-January to 11-April.Business CaseIm provement in SAW weldingprocess will reduced COPQ, nonproduction idle hours, delay indelivery of jobs; which will satisfythe customer, which will lead toimprovement in quality, productionand good products.Figure 3: SIPOC ricalsupply,WeldingbyTank, ion &Dish ers,Project TitleReduced the welding defectsusing Six Sigma techniques.Team MemberMr. Shashank Soni, (M-Tech,student) and employees of theQA/QC Deptt.Process DeliverablesStake HolderEmployees of TQM facilitation &Industrial Engineering Deptt.2. Reduction of COPQ.Subject MatterExpertSr. manager, HOD, IndustrialEngineering Deptt.Phase of projectsDefine phasePrincipal CustomersMeasure PhaseInternal customers are:SuppliersInputProcessLogisticsOutputCustomer1. Reduction of non-production idle hours.3. Increase in SAW welding machine processyield.Analyze phaseImprove Phase1. Project management group.Control Phase2. Manufacturing shops.406
Int. J. Mech. Eng. & Rob. Res. 2013Shashank Soni et al., 2013process and then mapping various subactivities in it. This mapping helped to visualizeand separate value-added.3. Inspection departments.External customers are:1. Clients / Third party Inspectors.Figure 5: Process Mapping Diagramof SAW Welding Process2. Customer Representatives.Defining Process Boundaries andCustomer CTQ RequirementsINPUTProcess Boundaries - Process Start Point: Unwelded Rolled shell from PFS shop, SWP &WPS of the job.PRODUCTION/MEProcess Stop Point: Welded Shell which isready for inspection clearance.ESTIMATING DEPTT.CUSTOMERCustomer CTQ RequirementsThe customer data (VOC) revealed thatinternal customers are mainly affected by lowSAW machine welding process yield. CTQcharacteristics are established and a CTQtree (Figure 4) is prepared on the basis of theVOC and project objective.QUALITY DEPTT.ENGINEERING DEPTT.OUTPUTMeasure PhaseOperational DefinitionThis phase presents the detailed processmapping, operational definition, datacollection chart, evaluation of the existingsystem, assessment of the current level ofprocess performance, etc.SAW welding machine process is defined asthe ratio of net operating hours to grossavailable hoursType of DataThe type of data is continuous (variable).Figure 4: Critical to Quality Tree(CTQ tree)NeedImprovingweldingdeposition rateAssessing current level of processperformance (process sigma level).CTQSAW Welding Process SAW weldingutilizationNet Operating hrs.Gross Available hrs.Analyze PhaseThe analyze phase is the third step in theDMAIC improvement cycle. This sectiondescribes the work and result of the cause andeffect diagram, Pareto analysis of the causes,Why-Why analysis, is which identify to identifyProcess MappingThe process map of the SAW welding process(Figure 5) is prepared by visually studying the407
Int. J. Mech. Eng. & Rob. Res. 2013Shashank Soni et al., 2013the few factors in order to identify the rootcauses of the defects/problems and helped toexamine the processes that affect the CTQ.solution, recognize the risks and implementselected solution. Practically, the improvementmust investigate necessary knowledge basedon brainstorming to create the best solution.Figure 6: Pareto Analysis DiagramBrain Storming“This figure shows results after the solution ofdefect in controlled condition, hence the actionis validated on the basic of data collection.”Main project implementations by expectedbenefit are:Tangible Benefits Production efficiency increase by section/day.Why-Why Analysis Reduction in COPQ by 50%.Figure 8 Shows a why-why diagram whichhelped in identifying root cause of the problem. Saving of INR 8,43,000.Improve PhaseThe goals of this phase are to select problemIntangible Benefits TPT reduced by 2 days, Customer satisfaction.Figure 7: The Causes and Effect Diagram408
Int. J. Mech. Eng. & Rob. Res. 2013Shashank Soni et al., 2013Table 2: Final Action forValidation MethodFigure 8: Why-Why AnalysisZurking during RotationCausesFinal ActionsValidationY/NMethodMachine due to LS bead heightWelding start point near to T-jointImproperGrinding photo toremoval ofbe displayed intab platesSOPImproperGauge developmentDOEYDOEYYGap near T-jointW eldOvality in shells.W eldingTo specify to startDatastart pointwelding from 90collectionnear todegree to T-JointT jointin SOPOvality inMonitoring sheet toshellsbe made to checkgrooveImproper removal of tab platesPicking/flatness near T-jointDataYcollectionwaiting time Restingplatform to be madeEvolution ofsolutionInput PFMEAfor shell storageBrainOutputStormingZurkingTo Specify the wayDataof tractorof grinding how tocollectionmachinegrinding with photoYfor visualization Availability improvement (OTIF),LS Bead Possibility of failure reduced.heightCost1.5 mm Cost of tooling.Figure 8: The Machine Process of StructureGauge developmentDOEYmore than Cost of training, gauges development.Benefits Reduction in 0.02 defects/ MW. Reduction in welding rework. Improved availability of section for blastingand painting for commissioning.Impact on Business Goals Throughput time reduction by 2 days againstexisting. COPQ to be reduced by 50%.409
Int. J. Mech. Eng. & Rob. Res. 2013Shashank Soni et al., 2013The Business Quality Council executedstrategic controls by an ongoing process ofreviewing the goals and progress of thetargets. The council met periodically andreviewed the progress of improvementmeasures and their impacts on the overallbusiness goals.Figure 9: Implementation ProcessProject implementation (Realized benefits):AfterBeforeTangible Benefits Saving (Approx INR 8.431). Rework of defect trend is in decreasing andnow 4.8 defects/section. After implementation ROI is 0.2.(a)Intangible Benefits Improved customer satisfaction. Reduced possibility of failure. Improved availability. Closure of potential failure mode.In this, final phase of DMAIC methodology,a control plan was developed to ensure thatprocesses and products consistently meetsour and customer requirements, and to checkhow external/internal welding process onquality production levelAfterBefore(b)Control PhaseRESULTS AND DISCUSSIONThe last phase of DMAIC is control, which isthe phase in which we ensure that theprocesses continue to work well, producedesired output results, and maintain qualitylevels. This is about holding the gains whichhave been achieved by the project team.Six Sigma is an effective way to find out wherethe greatest process needs are and which thesoftest points of the process are. Also, SixSigma provide measurable indicators andadequate data for analytical analysis.Systematic application of Six Sigma DMAICtools and methodology within an automotiveparts production results with severalachievements.Implementing all improvement measuresduring the improve phase, periodic reviews ofvarious solutions and strict adherence on theprocess yield is carried out.The achieved results are:410
Int. J. Mech. Eng. & Rob. Res. 2013Shashank Soni et al., 2013 Reduced possibility of failure.viz., DMAIC project shows that theperformance of the company is increased toa better level as regards to: enhancement incustomers’ (both internal and external)satisfaction, adherence of delivery schedules,development of specific methods to redesignand reorganize a process with a view to reduceor eliminate errors, defects; development ofmore efficient, capable, reliable and consistentmanufacturing process and more better overallprocess performance, creation of continuousimprovement and “do it right the first time”mindset. Reduced costs of poor quality (CORQ). Reduced labors expenses. Improved customer satisfaction. Closure of potential failure mode.Also, the significant results are achieved bytwo indexes that are not dependent on thevolume of production: Production time reduction. Index cost/volume reduction.Generally, improvements through reducedProduction time, Control time, Material andInternal scrap.Definitely, Six Sigma is powerfulmethodologies that can, properly implemented,result with significance savings andimprovements.Six Sigma provides business leaders andexecutives with the strategy, methods, toolsand techniques to change their organizations.Six Sigma as a powerful business strategy hasbeen well recognized as an imperative forachieving and sustaining operational (process)effectiveness, producing significant savings tothe bottom line and thereby achievingorganizational excellence. If implementedproperly with total commitment and focus, SixSigma can put industries at the forefront of theglobal competition.CONCLUSIONREFERENCESConducted improvement project based onSix Sigma methodology provides closeacquaintance with all phases of process whileSix Sigma tools enables right decisions andthe most significant improvements.1. Tushar N Dasia and Shrivastava R L(2008), “Six Sigma- A new direction toquality and productivity management”,Proceeding of the World Congress AnEngineering and Computer Science, SanFrancisco, USA.Operational Six Sigma methodology wasselected to solve the variation problem in awelding process. The study proposal a realtime monitoring system by which the shearstrength of the weld can be eliminated, withoutdestructive resting. Due to 100% inspection,error made by the selective sampling can beeliminated, reducing the scrap page cost. Theimplementation of the new system will pay foritself in a long run.2. Anup A Junankar and Shende P N (2011),“Minimization Of Rework In Belt IndustryUsing Dmaic”, International Journal ofApplied Research in MechanicalEngineering, Vol. 1, No. 1.This Six Sigma improvement methodology,411
Int. J. Mech. Eng. & Rob. Res. 2013Shashank Soni et al., 2013& Engineering, Vol. 46, No. 9, pp. 841848.doi:10.1080/03602550701278103.3. Sokovic M, Pavletic D and Krulcc E(2006),“SixSigmaprocessimprovements in automotive partsproduction”, Journal of Achievements inMaterialsandManufacturingEngineering, Vol. 19, No. 1.8. Van Waveren C (2009), “Evaluation ofQuality Concepts Influencing aManufacturing Environment in SouthAfrica”, South African Journal ofIndustrial Engineering, Vol. 20, No. 2, pp.93-105. Retrieved from AcademicSearch Complete database.4. All About Plastic Moulding (2011),Retrieved December 15, 2011, from http://www.plasticmoulding.com.5. E Banovac and D Kozak (2008), “AnAnalytic Review of the Characteristics ofthe Lot Acceptance Sampling Plans Usedfor Acceptance of Large Lots”,International Review of ElectricalEngineering, Vol. 3, No. 6, pp. 10701076. Retrieved from Academic SearchComplete database.9. Wu J, Liu G and Xi C (2008), “The Studyon Agile Supply Chain-based SupplierSelection and Evaluation”, inProceedings of 2008 InternationalSymposium on Information Science andEngineering, pp. 281-282.10. Sogunro O A (2001), “Selecting aQuantitative or Qualitative ResearchMethodology: An Experience”,Educational Research Quarterly, Vol. 26No. 1, pp. 3-6.6. Breyfoggle III and Forrest W (2003),“Implementing Six Sigma – SmarterSolutions Using Statistical Methods”,Hoboken, J N: John Wiley & Sons, Inc(US).11.7. Chung-Feng Jeffrey K, Te-Li S and YungChang L (2007), “Construction andAnalysis in Combining the TaguchiMethod and the Back Propagation NeuralNetwork in the PEEK Injection MoldingProcess”, Polymer-Plastics TechnologyTang C L (2007), “Fortification of SixSigma: Expanding the DMAIC Tools”,Wiley Inter Science, OH.12. The UK Office of Government Commerce(2006), “Category Management Toolkit:Causes and Effect Analysis”, available at:http://www.ogc.gov.uk/documents/Cause and Effect Analysis(1).pdf(accessed 16 April 2010).412
THE DMAIC SIX SIGMA METHODOLOGY The DMAIC is a basic component of Six Sigma methodology—a better way to improve work process by eliminating the defects rate in the final product. The DMAIC methodology has five phases define, measure, analysis, improvement and control. Define Phase Goal: In this phase, define the purpose of
There are numerous welding processes including arc welding, electron beam welding, friction welding, laser welding, and resistance welding. This article will concentrate on arc welding, which is the most common technique used to join most steels. Factors affecting weld quality will be discussed and how to avoid common weld defects will be .
6.3 Mechanised/automatic welding 114 6.4 TIG spot and plug welding 115 7 MIG welding 116 7.1 Introduction 116 7.2 Process principles 116 7.3 Welding consumables 130 7.4 Welding procedures and techniques 135 7.5 Mechanised and robotic welding 141 7.6 Mechanised electro-gas welding 143 7.7 MIG spot welding 144 8 Other welding processes 147 8.1 .
seam butt welding resistance butt welding flash butt welding resistance butt welding shielded unshielded other process plasma laser resistance butt welding inert gas welding submerged arc welding atomic hydrogen shielded metal arc welding (coated electrode) esepl w w w . e u r e k a e l e c t r o d e s .
the welding processes most often used in today's industry including plasma arc cutting, oxyfuel gas cutting and welding, Gas Metal Arc Welding (GMAW), Flux-Cored Arc Welding (FCAW), Shielded Metal Arc Welding (SMAW), and Gas Tungsten Arc Welding (GTAW). Flat welding positions and basic joints will be practiced. Pipe and tube welding
3. Classification of Underwater Welding Underwater welding may be divided into two main types: a) Wet welding b) Dry welding Fig. 3.1 Classification of underwater welding 3.1 Wet welding 3.1.1. Wet welding with coated electrode Wet welding is performed at ambient pressure with the welder-diver in the water and no physical barrier
10.6 Braze-welding 460 Exercises 466 11 Joining processes (welding) 467 11.1 Fusion welding 468 11.2 Oxy-acetylene welding 468 11.3 Manual metal-arc welding 490 11.4 Workshop testing of welds 504 11.5 Miscellaneous fusion welding processes 506 11.6 Workholding devices for fusion welding 509 11.7 Resistance welding 515
Welding residual stresses and stress relieve Formation of the weld metal Solidification of the weld metal Phase transformations during welding Basics of welding methods used in welding of zirconium alloys TIC Laser Welding Electron Beam Welding Upset shape welding Resistance Appendix C -R
affected zone. Welding processes that are commonly used with the corrosion-resistant alloys are shown in Table 1. In addition to these common arc welding processes, other welding processes such as plasma arc welding, resistance spot welding, laser beam welding, electron beam welding, and submerged arc welding can be used. Because of
