What is Quality?

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Quality at Source Manufacturing Systems Analysis Professor: Nour El Kadri e-mail: nelkadri @ site.uottawa.ca. What is Quality?. Quality : The ability of a product or service to consistently meet or exceed customer expectations. - PowerPoint PPT Presentation


  • Quality at Source

    Manufacturing Systems Analysis

    Professor: Nour El Kadrie-mail: nelkadri@ site.uottawa.ca

  • What is Quality?Quality: The ability of a product or service to consistently meet or exceed customer expectations.Not something tacked on, but an integral part of the product/service.Comes from the fundamental process, not from material or from inspection

  • What does a customer perceive as qualityPerformanceAestheticsFeaturesConformanceReliabilityDurabilityPerceived quality (eg: reputation)Serviceability

  • ExpectationsCustomers perceptions and expectations shift and evolve:With product life cycle:Features & functionality are critical in a leading-edge hi-tech productReliability, durability, serviceability are critical in a mature productWith an evolving industry, market or technology (cf: Quality & the Ford Model T)

  • Why is Quality Important?

  • Quality is:A critical basis of competition (ie: A critical differentiator)Critical to SC effectiveness (Partners demand objective evidence of quality measures, programs)A measure of efficiency & cost saving (Quality does not cost anything)NB: Quality as one key identifier of a High-Performance company

  • Cost of QualityPrevention Costs: All training, planning, customer assessment, process control, and quality improvement costs required to prevent defects from occurringAppraisal Costs: Costs of activities designed to ensure quality or uncover defectsFailure Costs: Costs incurred by defective parts/products or faulty services.Internal Failure Costs: Costs incurred to fix problems that are detected before the product/service is delivered to the customer.External Failure Costs: Costs incurred to fix problems that are detected after the product/service is delivered to the customer.

  • Consequences of Poor QualityLiabilityLoss of productivityLoss of business:Dissatisfied customers will switchYou usually wont know why (
  • The Evolution of Quality ManagementCraft production: Strict craftsman concern for qualityIndustrial revolution: Specialization, division of labour. Little control of or identification with overall product quality

  • SPC (Statistical Process Control)

  • Quality Control ChartsDefinitionsVariablesMeasurements on a continuous scale, such as length or weightAttributesInteger counts of quality characteristics, such as # of good or badDefectA single non-conforming quality characteristic, such as a blemishDefectiveA physical unit that contains one or more defects

  • Types of Control Charts

    Data monitored Chart name Sample size

    Mean, range of sample variables MR-CHART 2 to 5 unitsIndividual variables I-CHART 1 unit% of defective units in a sample P-CHART at least 100 unitsNumber of defects per unit C/U-CHART 1 or more units

  • Control Factorsn A A2 D3 D4 d2 d32 2.121 1.880 0 3.267 1.128 0.8533 1.732 1.023 0 2.574 1.693 0.8884 1.500 0.729 0 2.282 2.059 0.8805 1.342 0.577 0 2.114 2.316 0.864

    Control factors are used to convert the mean of sample ranges ( R ) to:(1) standard deviation estimates for individual observations, and(2) standard error estimates for means and ranges of samples

    For example, an estimate of the population standard deviation of individual observations (x) is:x = R / d2

  • Control Factors (cont.)Note that control factors depend on the sample size n.

    Relationships amongst control factors:A2 = 3 / (d2 x n1/2)D4 = 1 + 3 x d3/d2D3 = 1 3 x d3/d2, unless the result is negative, then D3 = 0

    A = 3 / n1/2D2 = d2 + 3d3D1 = d2 3d3, unless the result is negative, then D1 = 0

  • Mean-Range control chartMR-CHART1. Compute the mean of sample means ( X ).

    2. Compute the mean of sample ranges ( R ).

    3. Set 3-std.-dev. control limits for the sample means:UCL = X + A2RLCL = X A2R

    4. Set 3-std.-dev. control limits for the sample ranges:UCL = D4RLCL = D3R

  • Control chart for percentage defective in a sample P-CHART1. Compute the mean percentage defective ( P ) for all samples:P = Total nbr. of units defective / Total nbr. of units sampled

    2. Compute an individual standard error (SP ) for each sample:SP = [( P (1-P ))/n]1/2

    Note: n is the sample size, not the total units sampled.If n is constant, each sample has the same standard error.

    3. Set 3-std.-dev. control limits:UCL = P + 3SPLCL = P 3SP

  • Control chart for individual observations I-CHART1. Compute the mean observation value ( X )X = Sum of observation values / Nwhere N is the number of observations

    2. Compute moving range absolute values, starting at obs. nbr. 2:Moving range for obs. 2 = obs. 2 obs. 1Moving range for obs. 3 = obs. 3 obs. 2Moving range for obs. N = obs. N obs. N 1

    3. Compute the mean of the moving ranges ( R ):R = Sum of the moving ranges / N 1

  • Control chart for individual observations I-CHART (cont.)4. Estimate the population standard deviation (X):X = R / d2Note: Sample size is always 2, so d2 = 1.128.

    5. Set 3-std.-dev. control limits:UCL = X + 3XLCL = X 3X

  • Control chart for number of defects per unit C/U-CHART1. Compute the mean nbr. of defects per unit ( C ) for all samples:C = Total nbr. of defects observed / Total nbr. of units sampled

    2. Compute an individual standard error for each sample:SC = ( C / n)1/2

    Note: n is the sample size, not the total units sampled.If n is constant, each sample has the same standard error.

    3. Set 3-std.-dev. control limits:UCL = C + 3SCLCL = C 3SC

    Notes: If the sample size is constant, the chart is a C-CHART. If the sample size varies, the chart is a U-CHART. Computations are the same in either case.

  • SPC & Cost of QualityDeming (Promoted SPC in Japan):The cause of poor quality is the system, not the employeeMgmt is responsible to correct poor qualityJuran (Cost of Quality: Emphasized need for accurate and complete identification of the costs of quality) :Quality means fitness for useQuality begins in knowing what customers want, planning processes which are capable of producing the required level of quality

  • From Quality to Quality AssuranceChanging emphasis from Quality to Quality Assurance(Prevent defects rather than finding them after they occur)New techniques for Quality Improvement (eg: TQM, Six Sigma):New quality programs (Provide objective measures of quality for use of customers, SC partners, etc.)Baldridge AwardISO 9000/14000 CertificationIndustry-specific programs (eg: TL9000(Telecom))

  • Energy needed to close doorDoor seal resistanceCheck force on level groundEnergy needed to open doorAcoustic trans., windowWater resistanceMaintain current levelReduce energy level to 7.5 ft/lbReduce force to 9 lb.Reduce energy to 7.5 ft/lbMaintain current levelMaintain current levelEngineering characteristicsCustomer requirementsImportance to customer54321Easy to closeStays open on a hillEasy to openDoesnt leak in rainNo road noiseImportance weighting7533210669

    Source: Based on John R. Hauser and Don Clausing, The House of Quality, Harvard Business Review, May-June 1988.

    23xxxxxx*Competitive evaluationxAB(5 is best)1 2 3 4 5= Us= Comp. A= Comp. BTarget valuesTechnical evaluation (5 is best)Correlation:Strong positivePositiveNegativeStrong negativexxxxxxxxxxxABABABBABAAAAAAABBBBBBRelationships:Strong = 9Medium = 3Small = 1

  • Taguchi analysisLoss functionL(x) = k(x-T)2wherex = any individual value of the quality characteristicT = target quality valuek = constant = L(x) / (x-T)2

    Average or expected loss, variance knownE[L(x)] = k(2 + D2)where 2 = Variance of quality characteristic D2 = ( x T)2

    Note: x is the mean quality characteristic. D2 is zero if the mean equals the target.

  • Taguchi analysis (cont.)Average or expected loss, variance unkownE[L(x)] = k[ ( x T)2 / n]

    When smaller is better (e.g., percent of impurities)L(x) = kx2

    When larger is better (e.g., product life)L(x) = k (1/x2)

  • TQM Total Quality Management: A philosophy that involves everyone in an organization in a continual effort to improve quality and achieve customer satisfaction.The TQM Approach:Find out what the customer wantsDesign a product or service that meets or exceeds customer wantsDesign processes that facilitates doing the job right the first timeKeep track of resultsExtend quality initiatives to include suppliers & distributors.

  • Elements of TQMContinual improvementCompetitive benchmarkingEmployee empowerment (eg: Quality circles, etc.)Team approachDecisions based on factsKnowledge of toolsSupplier qualityIdentify and use quality championDevelop quality at the sourceInclude suppliers

  • Criticism of TQMCriticisms of TQM include:Blind pursuit of TQM programsPrograms may not be linked to strategiesQuality-related decisions may not be tied to market performanceFailure to carefully plan the program

  • Obstacles to Implementing TQMPoor inter-organizational communicationView of quality as a quick fixEmphasis on short-term financial resultsInternal political and turf warsLack of: Company-wide definition of qualityStrategic plan for changeCustomer focusReal employee empowermentStrong motivationTime to devote to quality initiativesLeadership

  • Six SigmaSix Sigma (eg: Jack Welch @ GE):Statistically: Having no more than 3.4 defects per millionConceptually: A program designed to reduce defects

  • Six Sigma progra