quality engineering - cecscourses.cecs.anu.edu.au/courses/engn8101/quality... · 2011-02-02 · the...

31/07/200731/07/2007 ENGN8101 Modelling and OptimizationENGN8101 Modelling and Optimization 11

QUALITY ENGINEERINGQuality engineering – robust design

In the West….- separate from development, design and manufacturing- responsibility of staff engineers

who are not on product development team- tasks include statistical analysis of data

+ maintaining servers

In Japan….- responsibility of all engineers and management


Chapter ObjectivesChapter Objectives

Basically understand what Basically understand what ““QualityQuality”” meansmeansGain a sense of the importance of quality in business and Gain a sense of the importance of quality in business and manufacturingmanufacturingUnderstand that quality can be measured, controlled, and Understand that quality can be measured, controlled, and improvedimproved


The Meaning of Quality

A quality product or service is one

that meets or exceeds customer

expectations.


Distribution of Color Density of Sony Television Sets

Distribution of Color Density of Distribution of Color Density of Sony Television SetsSony Television Sets

Sony of Tokyo TVs

Sony of San Diego

TVs

Lower Specification

Limit

Upper Specification

Limit

Target Value


Measuring the Costs of QualityMeasuring the Costs of QualityMeasuring the Costs of Quality

Prevention costs

Appraisal costs

Internal failure costs

External failure costs


Quality Cost MeasurementQuality Cost MeasurementQuality Cost Measurement

Prevention Costs Appraisal (Detection) CostsQuality engineering Inspection of materialsQuality training Packaging inspectionRecruiting Product acceptanceQuality audits Process acceptanceDesign reviews Field testingQuality circles Continuing supplier

verificationMarketing research Prototype inspectionVendor certification


Internal Failure Costs External Failure CostsScrap Lost sales (performance-

related)Rework Returns/allowancesDowntime (defect-related) WarrantiesReinspection Discounts and defectsRetesting Product liabilityDesign changes Complaint adjustmentRepairs Recalls

Quality Cost MeasurementQuality Cost MeasurementQuality Cost Measurement


Estimating Hidden Quality CostsEstimating Hidden Quality CostsEstimating Hidden Quality Costs

The Multiplier MethodThe Multiplier MethodThe Market Research The Market Research MethodMethodThe Taguchi Quality Loss The Taguchi Quality Loss FunctionFunction

Hidden Quality Costs are opportunity costs resulting from poor quality.


The Multiplier MethodThe Multiplier MethodThe multiplier method assumes that the total failure cost is simply some multiple of measured failure costs:

Total external failure cost = k(Measured external failure costs)

where k is the multiplier effect

If k = 4, and the measured external failure costs are $3 million, then the actual external failure costs are estimated to be $12 million.


The The market research methodmarket research method uses formal market uses formal market research methods to assess the effect of poor research methods to assess the effect of poor quality on sales and market share.quality on sales and market share.

Customer surveys and interviews with members of a Customer surveys and interviews with members of a companycompany’’s sales force can provide significant insights s sales force can provide significant insights into the magnitude of a companyinto the magnitude of a company’’s hidden costs.s hidden costs.

The Market Research MethodThe Market Research Method

Market research results can be used to project future profit losses attributable to poor quality.


The Taguchi Quality Loss FunctionThe Taguchi Quality Loss Function

The Taguchi loss function assumes any variation from the target value of a quality characteristic causes hidden quality costs.

Furthermore, the hidden quality costs increase quadratically as the actual value deviates from the target value.


Dimensions of QualityDimensions of Quality

PerformancePerformanceReliabilityReliabilityDurabilityDurabilityServiceabilityServiceability

FeaturesFeaturesPerceived QualityPerceived QualityConformance to Conformance to standardsstandards

Definitions of QualityDefinitions of Quality

QualityQuality means fitness for usemeans fitness for use-- quality of designquality of design-- quality of conformancequality of conformance

QualityQuality is inversely proportional to variability.is inversely proportional to variability.


Dimensions of QualityDimensions of Quality

Quality ImprovementQuality ImprovementQuality improvementQuality improvement is the reduction of is the reduction of variability in processes and products.variability in processes and products.

Alternatively, Alternatively, quality improvementquality improvement is also seen as is also seen as ““waste reductionwaste reduction””..


Quality Engineering TerminologyQuality Engineering Terminology

Quality CharacteristicsQuality Characteristics

PhysicalPhysical -- length, weight, voltage, viscositylength, weight, voltage, viscositySensorySensory -- taste, appearance, colortaste, appearance, colorTime Orientation Time Orientation -- reliability, durability, reliability, durability, serviceabilityserviceability

Quality engineeringQuality engineering is the set of operational, managerial, is the set of operational, managerial, and engineering activities that a company uses to ensure and engineering activities that a company uses to ensure that the that the quality characteristics quality characteristics of a product are at the of a product are at the nominal or required levels.nominal or required levels.


SpecificationsSpecificationsQuality characteristics being measured are often Quality characteristics being measured are often compared to standards or compared to standards or specificationsspecifications..Nominal or target valueNominal or target valueUpper Specification Limit (USL)Upper Specification Limit (USL)Lower Specification Limit (LSL)Lower Specification Limit (LSL)


SpecificationsSpecifications

Remember their originRemember their originSpecifications are not targets!!Specifications are not targets!!When we make them targets:When we make them targets:

LS US

Uniform Distribution

Zero Defects!


How does this happen?How does this happen?

During manufacture and assembly outliers are During manufacture and assembly outliers are adjusted to fall within the specs.adjusted to fall within the specs.Targets are forgotten!Targets are forgotten!Before final assembly all units have been either Before final assembly all units have been either scraped or reworked to provide complete adherence scraped or reworked to provide complete adherence to specifications.to specifications.Zero defectsZero defects

uniform dissatisfaction!uniform dissatisfaction!


How does this happen?How does this happen?

Normal distribution slowly, but surely is transformed into Normal distribution slowly, but surely is transformed into uniform distribution. Performance is in specsuniform distribution. Performance is in specs--no defects, no defects, but at what cost?but at what cost?

LS

US

LS

US

US

LS

LS

US


Uniform DistributionUniform Distribution

LS USUniform Distribution

Target(customer preference)

AB A BC C

Do we really want as much “C” grade performance as “A” grade performance? Customers want grade “A”performance. Why do we insist on providing products that just pass with a grade of “C”?


AdjustAdjust to Targetto Target

Target and small normally distributed Target and small normally distributed variation about the target produce customer variation about the target produce customer satisfaction.satisfaction.

Normal Distribution

Target


Use Specifications, butUse Specifications, but……..

Think small variationThink small variationmake performance consistentmake performance consistentreduce sensitivity to all forms of variationreduce sensitivity to all forms of variation

Think targetThink targetbring average performance to customer bring average performance to customer preferencepreference


Traditional Quality MetricTraditional Quality Metric

All products within specifications equality good.All products within specifications equality good.All products outside specifications equally bad.All products outside specifications equally bad.

US

All products equally good

Equallyunacceptable

LS


Continuous ImprovementContinuous Improvement

Move specifications closerMove specifications closerIncrease costIncrease costQuality and cost tradeQuality and cost trade--off!off!

LS US

tightertolerances


Traditional Quality MetricTraditional Quality Metric

TradeTrade--off quality and costoff quality and cost

Cost

Qua

li ty

How much quality can we afford?


The Quadratic Loss FunctionThe Quadratic Loss Function

Rewards onRewards on--target performancetarget performanceFacilitate continuous improvementFacilitate continuous improvementContinuous functionContinuous functionEasy to useEasy to use


The Quadratic Loss FunctionThe Quadratic Loss Function

A0=cost of corrective actionΔ0=point of intolerancem=target valuey=quality characteristicL=loss ($) Δ0m

A0

L

y

k =

L=k(y-m)2

A0

Δ02


“main man” = Dr. Dr. GenichiGenichi TaguchiTaguchi

An engineer who has developed an approach An engineer who has developed an approach (Taguchi Methods) involving statistical planned (Taguchi Methods) involving statistical planned experiments to reduce variationexperiments to reduce variation19501950’’s: applied his approach in Japans: applied his approach in Japan19801980’’s: introduced his ideas to US s: introduced his ideas to US


Dr. Genichi TaguchiDr. Genichi TaguchiBorn in Japan, 1924; Electrical EngineerBorn in Japan, 1924; Electrical Engineer

Widely acknowledged leader in the U.S. industrial quality movemeWidely acknowledged leader in the U.S. industrial quality movement.nt.

Worked during 1950Worked during 1950’’s to improve Japans to improve Japan’’s posts post--WWII telephone WWII telephone communication systemcommunication system. .

Credited for starting the Credited for starting the ““Robust DesignRobust Design”” movement in Japan in 1950movement in Japan in 1950’’s.s.

1980 introduced Taguchi method to AT&T.1980 introduced Taguchi method to AT&T.


DonDon’’t run away!t run away!

Not a mathematician? Not a mathematician?

You can still successfully apply Taguchi You can still successfully apply Taguchi Method concepts to your service business.Method concepts to your service business.

Basic concepts are simple.Basic concepts are simple.

Just keep reading.Just keep reading.


Taguchi TechniquesTaguchi TechniquesExperimental design methods to Experimental design methods to improve product & process designimprove product & process design

Identify key component & process Identify key component & process variables affecting product variationvariables affecting product variation

TaguchiTaguchi ConceptsConceptsQuality robustnessQuality robustnessQuality loss functionQuality loss functionTarget specificationsTarget specifications


Ability to produce Ability to produce products uniformly products uniformly regardless of regardless of manufacturing manufacturing conditionsconditionsPut robustness in Put robustness in House of Quality House of Quality matrices besides matrices besides functionalityfunctionality

© 1984-1994 T/Maker Co.

© 1995 Corel Corp.

Quality RobustnessQuality Robustness


Robust DesignRobust Design

““An Engineering methodology for improving An Engineering methodology for improving productivity during research and development productivity during research and development so that highso that high--quality products can be produced quality products can be produced quickly and at low costquickly and at low cost”” (1).(1).Products and services designed defect free Products and services designed defect free and of high qualityand of high qualityA design with minimum sensitivity to A design with minimum sensitivity to variations in uncontrollable factors.variations in uncontrollable factors.


DefinedDefined--economical and societal penalties incurred as a result economical and societal penalties incurred as a result of purchasing a nonconforming product.of purchasing a nonconforming product.Shows social cost ($) of deviation from target valueShows social cost ($) of deviation from target valueAssumptionsAssumptions

Most measurable quality characteristics (e.g., Most measurable quality characteristics (e.g., length, weight) have a target valuelength, weight) have a target valueDeviations from target value are undesirableDeviations from target value are undesirable

Equation: L = DEquation: L = D22CCL = Loss ($); D = Deviation; C = CostL = Loss ($); D = Deviation; C = Cost

Quality Loss FunctionQuality Loss Function


DeterminingDeterminingQuality Loss FunctionQuality Loss Function

Specifications are setSpecifications are setSpecify a target with minimal Specify a target with minimal variationvariationIncrease in variation cause loss to Increase in variation cause loss to societysociety


Set SpecificationsSet Specifications

Loss to societyLoss to society--Product rejectionProduct rejection--Product reworkProduct rework--PollutionPollution


Specify a target withSpecify a target with minimal minimal variationvariation


Quality Loss FunctionQuality Loss FunctionFr

eque

ncy

Target UpperLower

Target-oriented quality yields more product in the "best" category

Distribution of Specifications for Products Produced

Conformance-oriented quality keeps products within 3 standard deviations

Los

s

High Loss

Low Loss

Unacceptable

Poor

Fair

Good

Best


A study found U.S. consumers preferred Sony TV’s made in Japan to those made in the U.S. Both factories used the same designs & specifications. The difference in quality goals made the difference in consumer preferences.

Freq.

XTarget USLLSL

Japanese factory (Target-oriented)

U.S. factory (Conformance-oriented)

Target Specification ExampleTarget Specification Example


The specifications for The specifications for the diameter of a gear the diameter of a gear areare 25.00 25.00 ±± 0.25 mm0.25 mm..If the diameter is out If the diameter is out of specification, the of specification, the gear must be scrapped gear must be scrapped at a cost ofat a cost of $4.00$4.00. . What is theWhat is the loss loss functionfunction??

© 1984-1994 T/Maker Co.

Quality Loss Function Quality Loss Function ExampleExample


Involves examining items to see if Involves examining items to see if an item is good or defectivean item is good or defectiveDetect a defective productDetect a defective product

Does not correct deficiencies in Does not correct deficiencies in process or productprocess or product

IssuesIssuesWhen to inspectWhen to inspectWhere in process to inspectWhere in process to inspect

InspectionInspection


When and Where to InspectWhen and Where to Inspect

At the supplierAt the supplier’’s plant while the supplier is producings plant while the supplier is producingAt your facility upon receipt of goods from the supplierAt your facility upon receipt of goods from the supplierBefore costly or irreversible processesBefore costly or irreversible processesDuring the stepDuring the step--byby--step production processesstep production processesWhen production or service is completeWhen production or service is completeBefore delivery from your facilityBefore delivery from your facilityAt the point of customer contactAt the point of customer contact


Service quality is more difficult to measure than Service quality is more difficult to measure than for goodsfor goodsService quality perceptions depend on Service quality perceptions depend on

Expectations versus realityExpectations versus realityProcess and outcomeProcess and outcome

Types of service qualityTypes of service qualityNormal: Routine service deliveryNormal: Routine service deliveryExceptional: How problems are handledExceptional: How problems are handled

TQM In ServicesTQM In Services


Under-standing

Tangibles

Reliability

CommunicationCredibility

Security

Responsiveness

Competence

Courtesy

Access

© 1995 Corel Corp.

Service Quality AttributesService Quality Attributes


Determinants of Service QualityDeterminants of Service Quality

Reliability Reliability –– consistency and dependabilityconsistency and dependabilityResponsiveness Responsiveness –– willingness/readiness of employees to willingness/readiness of employees to provide service; timelinessprovide service; timelinessCompetence Competence –– possession of skills and knowledge possession of skills and knowledge required to perform servicerequired to perform serviceAccess Access –– approachability and ease of contactapproachability and ease of contactCourtesy Courtesy –– politeness, respect, consideration, friendliness politeness, respect, consideration, friendliness of contact personnelof contact personnel


Determinants of Service Quality Determinants of Service Quality --ContinuedContinued

Communication Communication –– keeping customers informed in keeping customers informed in languages they understandlanguages they understandCredibility Credibility –– trustworthiness, believability, honestytrustworthiness, believability, honestySecurity Security –– freedom from danger, risk or doubtfreedom from danger, risk or doubtUnderstanding/knowing the customer Understanding/knowing the customer –– making the making the effort to understands the customereffort to understands the customer’’s needss needsTangibles Tangibles –– the physical evidence of the servicethe physical evidence of the service


The Design Process is DividedThe Design Process is Divided

System DesignSystem DesignChoose the subChoose the sub--systems, mechanisms, form of the systems, mechanisms, form of the prototype.prototype.

Parameter DesignParameter DesignOptimize the design, set up the design so that it Optimize the design, set up the design so that it improves quality and reduces costimproves quality and reduces cost

Tolerance DesignTolerance DesignStudy the tradeoffs that must be made and determine Study the tradeoffs that must be made and determine what tolerances and grades of materials are necessarywhat tolerances and grades of materials are necessary


Parameter Design (Robust Design)Parameter Design (Robust Design)

Optimize the settings of the design to minimize Optimize the settings of the design to minimize its sensitivity to noise its sensitivity to noise –– ROBUSTNESS.ROBUSTNESS.Taguchi really opened a whole area that Taguchi really opened a whole area that previously had been talked about only by a few previously had been talked about only by a few very applied people.very applied people.His methodology is heavily dependent on design His methodology is heavily dependent on design of experiments, but he wanted to look at not just of experiments, but he wanted to look at not just the mean but also the variance.the mean but also the variance.


Classification of FactorsClassification of FactorsControl FactorsControl Factors––Design factorsDesign factors that are to be set at optimal that are to be set at optimal levels to improve quality and reduce sensitivity to noiselevels to improve quality and reduce sensitivity to noise

Dimensions of parts, type of material, etcDimensions of parts, type of material, etcNoise FactorsNoise Factors––Factors that represent the noise that is Factors that represent the noise that is expected in production or in useexpected in production or in use

Dimensional variationDimensional variationOperating Temperature Operating Temperature

Adjustment Factor Adjustment Factor –– Affects the mean but not the variance Affects the mean but not the variance of a responseof a response

Deposition time in silicon wafer fabricationDeposition time in silicon wafer fabricationSignal Factors Signal Factors –– Set by the user to communicate desires of Set by the user to communicate desires of the userthe user

Position of the gas pedalPosition of the gas pedal


AnalysisAnalysis

Taguchi uses signal to noise ratios as response variables.Taguchi uses signal to noise ratios as response variables.e.g.,e.g.,

It is often more informative to analyze mean and It is often more informative to analyze mean and standard deviation separately (standard deviation separately (sdsd), rather than combine ), rather than combine into a signal to noise ratiointo a signal to noise ratio

analyze analyze sdsd in the same manner that we have in the same manner that we have previously analyzed the mean.previously analyzed the mean.

Taguchi analysis techniques are often inefficientTaguchi analysis techniques are often inefficient……

SNt = −10logy 2

s2⎛ ⎝ ⎜ ⎞

⎠ ⎟


We should support TaguchiWe should support Taguchi’’ss philosophy of quality philosophy of quality engineering. However, we must rely on simpler, more engineering. However, we must rely on simpler, more efficient methods that are easier to learn and apply to efficient methods that are easier to learn and apply to

carry this philosophy into practicecarry this philosophy into practice……

You can use the techniques presented thus far in class You can use the techniques presented thus far in class to analyze to analyze

Taguchi Designs.Taguchi Designs.


Taguchi’s method

Created quality engineering as a disciplined engineering process to find best expression of product design

What is ‘best’?

Best = lowest-cost solution based on customer needs:- to the product design specification- include manufacturing, life-cycle costs and losses to society- Reduce the variation but more importantly make the system

insensitive to variation

Holistic approach to minimizing cost and maximizing quality

High quality products minimize costs by performing consistently


High-quality system = insensitive to variationwhilst maintaining target values

Signal-to-noise again!

Costing of a design – equally important as actual design

To define system quality in terms of control of insensitivityto variability…

…Focal point must be signal-to-noise ratios


Quality – defined using performance measures

i.e. random variables

Random variables – have a target value and scattersignal noise

Primary aim – to reduce noise whilst increasing the signal- defined as ‘robustness’

i.e. make the signal as immune as possible to unforseen aspects of system changes


NOISENOISENoise factor = anything that causes a characteristic to

deviate from the target value

Examples:high power transmission lines on AM radio signalwater in petrolwear on a punch press dieimpurity on a hard disk driveetc…

3 types: External noisesources of variability outside the productUnit-to-unit noisevariability within a productDeteoration noiseageing of a product when with customer


Nature of noiseNature of noise

External factorsExternal factorsElectromagnetic interferenceElectromagnetic interferenceTemperature and humidityTemperature and humidityInput voltage variationsInput voltage variations

UnitUnit--toto--Unit noise factorsUnit noise factorsResistance of electrical resistorsResistance of electrical resistorsAmount of lubricant used Amount of lubricant used Dimensional variation due to machiningDimensional variation due to machining

Deterioration noise factorsDeterioration noise factorsTotal current passed through a car batteryTotal current passed through a car batteryWear of brake padsWear of brake padsWeathering of paint on a houseWeathering of paint on a house


Noise → reliability problem → failure of product

Early life failure – normal design life failure – end of life failure

Exponential?

Failure duringNormal designLife should berare


RobustnessRobustness

- Sensitivity of the design to noise

- minimize variability = maximize robustness

“A product or process is said to be robust when it is insensitiveto the effects of sources of variability, even though the sources

themselves have not been eliminated”


Cost-based design

Unit manufacturing cost = costs directly associated with production

e.g. material, labour etc.very backward and retrogressive

Life-cycle cost = costs due to operation of producte.g. consumables and repair

Quality loss cost = e.g. less tangible costslost profit due to malfunction (customer loss)return, recall, lawsuits (server loss)pollution, injury, transportation (society loss)


Different loss costsDifferent loss costs

Losses to customerLosses to customerTime and effort to work around minor repairsTime and effort to work around minor repairsRental costs to replace a machine being repairedRental costs to replace a machine being repairedNonwarranty service costs & service contract costsNonwarranty service costs & service contract costs

Losses to manufacturerLosses to manufacturerInspection, scrap, and reworkInspection, scrap, and reworkWarranty costsWarranty costsLost sales and customersLost sales and customersLawsuitsLawsuits

Losses to societyLosses to societyPollution and wastePollution and wasteInjury, loss of lifeInjury, loss of lifeDisruption of communications and transportationDisruption of communications and transportation


Robust design in product commercialization

Quality engineering – offline or online


OfflineOffline

= quality engineering during development and design


OnlineOnline= quality engineering taking place during actual production

Statistical process control- identify random variation v. assignable variation

Static S/N optimization- e.g. reduce noise whilst maintaining signal

define an optimal S/N ratio

Loss-function-based process control- Taguchi approach equating variation to cost

Most effective method – EXPERIMENTAL DESIGN!EXPERIMENTAL DESIGN!

quality engineering - cecscourses.cecs.anu.edu.au/courses/engn8101/quality... · 2011-02-02 · the...

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