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1 Chapter 12 Chapter 12 Design for Design for Six Sigma Six Sigma
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Page 1: The Scope and Language of Operations Management

11

Chapter 12Chapter 12Chapter 12Chapter 12

Design forDesign for

Six SigmaSix Sigma

Page 2: The Scope and Language of Operations Management

DFSS ActivitiesDFSS Activities

Concept development, determining product functionality based upon customer requirements, technological capabilities, and economic realities

Design development, focusing on product and process performance issues necessary to fulfill the product and service requirements in manufacturing or delivery

Design optimization, seeking to minimize the impact of variation in production and use, creating a “robust” design

Design verification, ensuring that the capability of the production system meets the appropriate sigma level

Page 3: The Scope and Language of Operations Management

Key IdeaKey Idea

Like Six Sigma itself, most tools for DFSS have been around for some time; its uniqueness lies in the manner in which they are integrated into a formal methodology, driven by the Six Sigma philosophy, with clear business objectives in mind.

Page 4: The Scope and Language of Operations Management

Tools for Concept Tools for Concept DevelopmentDevelopment

Concept development – the process of applying scientific, engineering, and business knowledge to produce a basic functional design that meets both customer needs and manufacturing or service delivery requirements. – Quality function deployment (QFD)– Concept engineering

Page 5: The Scope and Language of Operations Management

Key IdeaKey Idea

Developing a basic functional design involves translating customer requirements into measurable technical requirements and, subsequently, into detailed design specifications.

Page 6: The Scope and Language of Operations Management

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Quality Function Quality Function DeploymentDeployment

technicalrequirements

componentcharacteristics

processoperations quality plan

Page 7: The Scope and Language of Operations Management

Key IdeaKey Idea

QFD benefits companies through improved communication and teamwork between all constituencies in the value chain, such as between marketing and design, between design and manufacturing, and between purchasing and suppliers.

Page 8: The Scope and Language of Operations Management

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House of QualityHouse of Quality

Technical requirements

Voice of the customer

Relationship matrix

Technical requirement priorities

Customerrequirement priorities

Competitive evaluation

Interrelationships

Page 9: The Scope and Language of Operations Management

Building the House of Building the House of QualityQuality

1. Identify customer requirements.2. Identify technical requirements.3. Relate the customer requirements to the

technical requirements.4. Conduct an evaluation of competing

products or services.5. Evaluate technical requirements and

develop targets.6. Determine which technical requirements

to deploy in the remainder of the production/delivery process.

Page 10: The Scope and Language of Operations Management

Concept EngineeringConcept Engineering

Understanding the customer’s environment.

Converting understanding into requirements.

Operationalizing what has been learned.

Concept generation. Concept selection.

Page 11: The Scope and Language of Operations Management

Tools for Design Tools for Design DevelopmentDevelopment

Tolerance designTolerance design Design failure mode and effects Design failure mode and effects

analysisanalysis Reliability predictionReliability prediction

Page 12: The Scope and Language of Operations Management

Key IdeaKey Idea

Manufacturing specifications consist of nominal dimensions and tolerances. Nominal refers to the ideal dimension or the target value that manufacturing seeks to meet; tolerance is the permissible variation, recognizing the difficulty of meeting a target consistently.

Page 13: The Scope and Language of Operations Management

Tolerance DesignTolerance Design

Determining permissible variation Determining permissible variation in a dimensionin a dimension

Understand tradeoffs between Understand tradeoffs between costs and performancecosts and performance

Page 14: The Scope and Language of Operations Management

Key IdeaKey Idea

Tolerances are necessary because not all parts can be produced exactly to nominal specifications because of natural variations (common causes) in production processes due to the “5 Ms”: men and women, materials, machines, methods, and measurement.

Page 15: The Scope and Language of Operations Management

DFMEADFMEA

Design failure mode and effects analysis (DFMEA) – identification of all the ways in which a failure can occur, to estimate the effect and seriousness of the failure, and to recommend corrective design actions.

Page 16: The Scope and Language of Operations Management
Page 17: The Scope and Language of Operations Management

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Reliability PredictionReliability PredictionReliability PredictionReliability Prediction

ReliabilityReliability – Generally defined as the ability of a Generally defined as the ability of a

product to perform as expected product to perform as expected over timeover time

– Formally defined as the Formally defined as the probabilityprobability that a product, piece of equipment, that a product, piece of equipment, or system or system performsperforms its intended its intended function for a stated period of function for a stated period of timetime under specified under specified operating conditionsoperating conditions

Page 18: The Scope and Language of Operations Management

Types of FailuresTypes of Failures

Functional failureFunctional failure – failure – failure that occurs at the start of that occurs at the start of product life due to product life due to manufacturing or material manufacturing or material detectsdetects

Reliability failureReliability failure – failure – failure after some period of useafter some period of use

Page 19: The Scope and Language of Operations Management

Types of ReliabilityTypes of Reliability

Inherent reliabilityInherent reliability – predicted – predicted by product designby product design

Achieved reliabilityAchieved reliability – observed – observed during useduring use

Page 20: The Scope and Language of Operations Management

Reliability Measurement Reliability Measurement

Failure rate (Failure rate ()) – number of – number of failures per unit timefailures per unit time

Alternative measuresAlternative measures– Mean time to failureMean time to failure– Mean time between failuresMean time between failures

Page 21: The Scope and Language of Operations Management

Cumulative Failure Rate Cumulative Failure Rate CurveCurve

Page 22: The Scope and Language of Operations Management

Key IdeaKey Idea

Many electronic components commonly exhibit a high, but decreasing, failure rate early in their lives (as evidenced by the steep slope of the curve), followed by a period of a relatively constant failure rate, and ending with an increasing failure rate.

Page 23: The Scope and Language of Operations Management

Failure Rate CurveFailure Rate Curve

“Infant mortality period”

Page 24: The Scope and Language of Operations Management

Average Failure RateAverage Failure Rate

Page 25: The Scope and Language of Operations Management

Reliability FunctionReliability Function

Probability density function of Probability density function of failures failures

f(t) = f(t) = ee--tt for t > 0 for t > 0 Probability of failure from (0, T) Probability of failure from (0, T)

F(t) = 1 – eF(t) = 1 – e--TT Reliability functionReliability function R(T) = 1 – F(T) = eR(T) = 1 – F(T) = e--TT

Page 26: The Scope and Language of Operations Management

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Series SystemsSeries Systems

RS = R1 R2 ... Rn

1 2 n

Page 27: The Scope and Language of Operations Management

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Parallel SystemsParallel Systems

RS = 1 - (1 - R1) (1 - R2)... (1 - Rn)

1

2

n

Page 28: The Scope and Language of Operations Management

Series-Parallel SystemsSeries-Parallel Systems

Convert to equivalent series Convert to equivalent series system system

AA BB

CC

CCDD

RRAA RRBB RRCCRRDD

RRCC

AA BB C’C’ DD

RRAA RRBB RRDD

RRC’C’ = 1 – (1-R = 1 – (1-RCC)(1-R)(1-RCC))

Page 29: The Scope and Language of Operations Management

Tools for Design Tools for Design OptimizationOptimization

Taguchi loss function Optimizing reliability

Page 30: The Scope and Language of Operations Management

Key IdeaKey Idea

Design optimization includes setting proper tolerances to ensure maximum product performance and making designs robust, that is, insensitive to variations in manufacturing or the use environment.

Page 31: The Scope and Language of Operations Management

3131

Loss FunctionsLoss Functions

loss lossno loss

nominaltolerance

loss loss

Traditional View

Taguchi’s View

Page 32: The Scope and Language of Operations Management

Taguchi Loss Function Taguchi Loss Function CalculationsCalculations

Loss function: L(x) = k(x - T)2

Example: Specification = .500 .020. Failure outside of the tolerance range costs $50 to repair. Thus, 50 = k(.020)2. Solving for k yields k = 125,000. The loss function is:

L(x) = 125,000(x - .500)2

Expected loss = k(2 + D2)

where D is the deviation from the target.

Page 33: The Scope and Language of Operations Management

Optimizing ReliabilityOptimizing Reliability

StandardizationStandardization RedundancyRedundancy Physics of failurePhysics of failure

Page 34: The Scope and Language of Operations Management

Tools for Design Tools for Design VerificationVerification

Reliability testingReliability testing Measurement systems evaluationMeasurement systems evaluation Process capability evaluationProcess capability evaluation

Page 35: The Scope and Language of Operations Management

Key IdeaKey Idea

Design verification is necessary to ensure that designs will meet customer requirements and can be produced to specifications.

Page 36: The Scope and Language of Operations Management

Reliability testingReliability testing

Life testingLife testing Accelerated life testingAccelerated life testing Environmental testingEnvironmental testing Vibration and shock testingVibration and shock testing Burn-in (component stress Burn-in (component stress

testing)testing)

Page 37: The Scope and Language of Operations Management

Measurement System Measurement System EvaluationEvaluation

Whenever variation is observed in measurements, some portion is due to measurement system error. Some errors are systematic (called bias); others are random. The size of the errors relative to the measurement value can significantly affect the quality of the data and resulting decisions.

Page 38: The Scope and Language of Operations Management

Metrology - Science of Metrology - Science of MeasurementMeasurement

Accuracy - closeness of agreement between an observed value and a standard

Precision - closeness of agreement between randomly selected individual measurements

Page 39: The Scope and Language of Operations Management

Repeatability and Repeatability and ReproducibilityReproducibility

Repeatability (equipment Repeatability (equipment variation)variation) – variation in multiple – variation in multiple measurements by an individual measurements by an individual using the same instrument. using the same instrument.

Reproducibility (operator Reproducibility (operator variation)variation) - variation in the same - variation in the same measuring instrument used by measuring instrument used by different individualsdifferent individuals

Page 40: The Scope and Language of Operations Management

Repeatability & Repeatability & Reproducibility StudiesReproducibility Studies

Quantify and evaluate the Quantify and evaluate the capability of a measurement capability of a measurement systemsystem– Select m operators and n partsSelect m operators and n parts– Calibrate the measuring instrumentCalibrate the measuring instrument– Randomly measure each part by each Randomly measure each part by each

operator for r trialsoperator for r trials– Compute key statistics to quantify Compute key statistics to quantify

repeatability and reproducibilityrepeatability and reproducibility

Page 41: The Scope and Language of Operations Management

Spreadsheet TemplateSpreadsheet Template

Page 42: The Scope and Language of Operations Management

R&R EvaluationR&R Evaluation

Under 10% error - OKUnder 10% error - OK 10-30% error - 10-30% error - maymay be OK be OK over 30% error - unacceptableover 30% error - unacceptable

Page 43: The Scope and Language of Operations Management

Key IdeaKey Idea

One of the most important functions of metrology is calibration—the comparison of a measurement device or system having a known relation-ship to national standards against another device or system whose relationship to national standards is unknown.

Page 44: The Scope and Language of Operations Management

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Process CapabilityProcess Capability

The range over which the natural The range over which the natural variation of a process occurs as variation of a process occurs as determined by the system of determined by the system of common causescommon causes

Measured by the proportion of Measured by the proportion of output that can be produced output that can be produced within design specificationswithin design specifications

Page 45: The Scope and Language of Operations Management

Types of Capability Types of Capability StudiesStudies

Peak performance studyPeak performance study - how a - how a process performs under ideal conditionsprocess performs under ideal conditions

Process characterization studyProcess characterization study - how a - how a process performs under actual process performs under actual operating conditionsoperating conditions

Component variability studyComponent variability study - relative - relative contribution of different sources of contribution of different sources of variation (e.g., process factors, variation (e.g., process factors, measurement system)measurement system)

Page 46: The Scope and Language of Operations Management

Process Capability StudyProcess Capability Study

1.1. Choose a representative machine or processChoose a representative machine or process

2.2. Define the process conditionsDefine the process conditions

3.3. Select a representative operatorSelect a representative operator

4.4. Provide the right materialsProvide the right materials

5.5. Specify the gauging or measurement methodSpecify the gauging or measurement method

6.6. Record the measurementsRecord the measurements

7.7. Construct a histogram and compute descriptive statistics: mean and standard deviationConstruct a histogram and compute descriptive statistics: mean and standard deviation

8.8. Compare results with specified tolerancesCompare results with specified tolerances

Page 47: The Scope and Language of Operations Management

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Process CapabilityProcess Capability

specification specification

specification specification

natural variation natural variation

(a) (b)

natural variation natural variation

(c) (d)

Page 48: The Scope and Language of Operations Management

Key IdeaKey Idea

The process capability index, Cp (sometimes called the process potential index), is defined as the ratio of the specification width to the natural tolerance of the process. Cp relates the natural variation of the process with the design specifications in a single, quantitative measure.

Page 49: The Scope and Language of Operations Management

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Process Capability IndexProcess Capability Index

Cp = UTL - LTL 6

Cpl, Cpu }

UTL - 3

Cpl = - LTL 3

Cpk = min{

Cpu =

Page 50: The Scope and Language of Operations Management

Spreadsheet TemplateSpreadsheet Template