Statistical Process Statistical Process ControlControl

Module 2Module 2 Dr. Salih Duffuaa & Dr. Mohamed Ben Dr. Salih Duffuaa & Dr. Mohamed Ben

Daya Daya

Systems Engineering DepartmentSystems Engineering Department

King Fahd University of Petroleum & King Fahd University of Petroleum & MineralsMinerals

Training ObjectivesTraining Objectives

• The overall objective of this program is The overall objective of this program is to to build a strong learning base build a strong learning base in the in the area of Statistical Process Control (SPC) area of Statistical Process Control (SPC) in order to sustain the implementation of in order to sustain the implementation of SPC and contribute to the growth of the SPC and contribute to the growth of the man-power inman-power in Quality Assurance Quality Assurance LaboratoriesLaboratories and production.and production.

• This require knowledge in basic This require knowledge in basic statistics and SPC tools and their statistics and SPC tools and their interpretation.interpretation.

Objectives (cont’d)Objectives (cont’d)

• Create a culture of continuous Create a culture of continuous improvement.improvement.

• Improve the skills of the man-power Improve the skills of the man-power in data analysis and the in data analysis and the interpretation of SPC results.interpretation of SPC results.

Training Program Training Program Outcomes of Module 1Outcomes of Module 1

• Summarize and present data in meaningful Summarize and present data in meaningful format.format.

• Analyze data.Analyze data.

• Assess variability in data.Assess variability in data.

• Construct confidence interval using excel.Construct confidence interval using excel.

• Develop regression models and understand Develop regression models and understand their use in calibration of instruments. their use in calibration of instruments.

Training Program Training Program Outcomes of Module 2Outcomes of Module 2

• Understand the relation between variability and quality.Understand the relation between variability and quality.

• Construct control charts for plant key processes.Construct control charts for plant key processes.

• Assess whether a process is in control or out of control.Assess whether a process is in control or out of control.

• Utilize SPC tools to identify major causes of poor quality.Utilize SPC tools to identify major causes of poor quality.

• Initiate process improvement based on information from Initiate process improvement based on information from SPC analysisSPC analysis

• Assess process capability.Assess process capability.

• Suggest action plans to improve plant's process Suggest action plans to improve plant's process capabilitycapability

Training ModulesTraining Modules Module 1Module 1

• Data collection and Data collection and presentationpresentation

• Descriptive statistics.Descriptive statistics.• ProbabilityProbability• Probability distribution. Probability distribution. • RegressionRegression• EstimationEstimation• Concept of variationConcept of variation• SPC toolsSPC tools• All with real data and All with real data and

realistic examples.realistic examples.

Duration: Duration: 4 months: 4 months: March – June, 2005March – June, 2005

Module 2Module 2

• Improvement using SPC toolsImprovement using SPC tools• Fundamentals of control Fundamentals of control

chartscharts• Control charts for variablesControl charts for variables• Control charts for attributesControl charts for attributes• Process capabilityProcess capability• Process improvements.Process improvements.• SPC implementation and SPC implementation and

case studiescase studies

Duration: 1Duration: 1 months: months: November, 2005November, 2005

Typical ScheduleTypical Schedule

• 8:30– 9:30 : 8:30– 9:30 : First PresentationFirst Presentation

• 9:30 – 9:45 : 9:30 – 9:45 : BreakBreak

• 9:45– 10:30 : 9:45– 10:30 : ExercisesExercises

• 10:30 – 10:45 : 10:30 – 10:45 : BreakBreak

• 10:45 – 11:45 : 10:45 – 11:45 : Second PresentationSecond Presentation

• 11:45 – 1:00 : 11:45 – 1:00 : Lunch BreakLunch Break

• 1:00 – 3:00 : 1:00 – 3:00 : Exercises and casesExercises and cases

• 8:30– 9:30 : 8:30– 9:30 : First PresentationFirst Presentation

• 9:30 – 9:45 : 9:30 – 9:45 : BreakBreak

• 9:45– 10:30 : 9:45– 10:30 : ExercisesExercises

• 10:30 – 10:45 : 10:30 – 10:45 : BreakBreak

• 10:45 – 11:45 : 10:45 – 11:45 : Second PresentationSecond Presentation

• 11:45 – 1:00 : 11:45 – 1:00 : Lunch BreakLunch Break

• 1:00 – 3:00 : 1:00 – 3:00 : Exercises and casesExercises and cases

AssessmentAssessment

• Final ExamFinal Exam• Small projectSmall project• Two homeworks.Two homeworks.

Team Formation and Team Formation and ProjectProject

• Teams of 2 to apply SPC on a processTeams of 2 to apply SPC on a process• Identify a process (latter)Identify a process (latter)• Project requirementsProject requirements

– Define processDefine process– Choose appropriate measuresChoose appropriate measures– Develop control chartsDevelop control charts– Assess process capabilityAssess process capability– Suggest action plan to improve Suggest action plan to improve

capability. capability.

Week 1 ScheduleWeek 1 Schedule• 8:30 – 9:30 : 8:30 – 9:30 : Module 2 IntroductionModule 2 Introduction

Process improvement Process improvement using SPC toolsusing SPC tools

• 9:15 – 9:30 : 9:15 – 9:30 : BreakBreak

• 9:30 – 10:30 : 9:30 – 10:30 : Basics of Control Basics of Control chartscharts

• 10:30 – 10:45 : 10:30 – 10:45 : BreakBreak

• 10:45 – 11:45 : 10:45 – 11:45 : Basics of Control chartsBasics of Control charts• 11:45 – 1:00 : 11:45 – 1:00 : Lunch BreakLunch Break• 1:00 – 3:00 : 1:00 – 3:00 : Cases and ExamplesCases and Examples

Next week’s assignmentNext week’s assignment

• 8:30 – 9:30 : 8:30 – 9:30 : Module 2 IntroductionModule 2 IntroductionProcess improvement Process improvement using SPC toolsusing SPC tools

• 9:15 – 9:30 : 9:15 – 9:30 : BreakBreak

• 9:30 – 10:30 : 9:30 – 10:30 : Basics of Control Basics of Control chartscharts

• 10:30 – 10:45 : 10:30 – 10:45 : BreakBreak

• 10:45 – 11:45 : 10:45 – 11:45 : Basics of Control chartsBasics of Control charts• 11:45 – 1:00 : 11:45 – 1:00 : Lunch BreakLunch Break• 1:00 – 3:00 : 1:00 – 3:00 : Cases and ExamplesCases and Examples

Next week’s assignmentNext week’s assignment

Learning OutcomesLearning Outcomes• Define Statistical Process Control.

• Define quality and quality improvement.

• Describe the role of variability and statistical methods in controlling and improving quality.

• Explain the link between quality and productivity and

• Define quality costs.

Learning OutcomesLearning Outcomes

• Distinguish between random and assignable causes

• Use SPC tools other than control charts.Use SPC tools other than control charts.• Define a control chart.Define a control chart.• Explain the statistical basis for control Explain the statistical basis for control

charts.charts.• Explain essential factors in control chart Explain essential factors in control chart

designdesign• State the steps to implement SPCState the steps to implement SPC

Definition of SPCDefinition of SPC• S: for statistical: means based on the S: for statistical: means based on the

science of data collection and analysis.science of data collection and analysis.

• P: for process: A process is P: for process: A process is A process is no more than the steps and decisions involved in the way work is accomplished. Everything we do in our lives involves processes and lots of them. Here are some examples:

writing a work order, shooting a weapon, getting out of bed repairing a valve , ordering a part, performing a test, conducting an UNREP, preparing a message, loading a missile allocating a budget , mooring a ship , conducting a drill.

• A sequence of activities (steps) that takes an input A sequence of activities (steps) that takes an input and produces an output.and produces an output.

• C: for control : stability and C: for control : stability and predictability. predictability.

Definitions and Definitions and MeaningMeaning of of QualityQuality

The Eight Dimensions of QualityThe Eight Dimensions of Quality

1.1. PerformancePerformance2.2. ReliabilityReliability3.3. DurabilityDurability4.4. ServiceabilityServiceability5.5. AestheticsAesthetics6.6. FeaturesFeatures7.7. Perceived QualityPerceived Quality8.8. Conformance to StandardsConformance to Standards

•This is a traditional definition

•Quality of design

•Quality of conformance

This is a modern definition of quality

How do we measure variability ?

The Transmission The Transmission ExampleExample

• The transmission example illustrates the utility of this definition

• An equivalent definition is that quality improvement is the elimination of waste. This is useful in service or transactional businesses.

TerminologyTerminology

Terminology cont’dTerminology cont’d• SpecificationsSpecifications

– Lower specification limitLower specification limit– Upper specification limitUpper specification limit– Target or nominal valuesTarget or nominal values

• Defective or nonconforming productDefective or nonconforming product• Defect or nonconformityDefect or nonconformity• Not all products containing a defect Not all products containing a defect

are necessarily defectiveare necessarily defective

1-2. History of Quality 1-2. History of Quality ImprovementImprovement

Statistical Methods for Quality Improvement

Statistical MethodsStatistical Methods

• Statistical process control (SPC)Statistical process control (SPC)– Control charts, plus other problem-solving toolsControl charts, plus other problem-solving tools– Useful in monitoring processes, reducing Useful in monitoring processes, reducing

variability through elimination of assignable variability through elimination of assignable causescauses

– On-line techniqueOn-line technique

• Designed experiments (DOX)Designed experiments (DOX)– Discovering the key factors that influence process Discovering the key factors that influence process

performanceperformance– Process optimizationProcess optimization– Off-line techniqueOff-line technique

• Acceptance SamplingAcceptance Sampling

Walter A. Shewart (1891-1967)

• Trained in engineering and physics

• Long career at Bell Labs

• Developed the first control chart about 1924

A factorial experiment with three factors

Quality Philosophies and Quality Philosophies and Management StrategiesManagement Strategies

W. Edwards DemingW. Edwards Deming

• Taught engineering, physics Taught engineering, physics in the 1920s, finished PhD in the 1920s, finished PhD in 1928in 1928

• Met Walter Shewhart at Met Walter Shewhart at Western ElectricWestern Electric

• Long career in government Long career in government statistics, USDA, Bureau of statistics, USDA, Bureau of the Censusthe Census

• During WWII, he worked During WWII, he worked with US defense with US defense contractors, deploying contractors, deploying statistical methodsstatistical methods

• Sent to Japan after WWII to Sent to Japan after WWII to work on the censuswork on the census

DemingDeming• Deming was asked by JUSE to lecture Deming was asked by JUSE to lecture

on statistical quality control to on statistical quality control to managementmanagement

• Japanese adopted many aspects of Japanese adopted many aspects of Deming’s management philosophyDeming’s management philosophy

• Deming stressed “continual never-Deming stressed “continual never-ending improvement”ending improvement”

• Deming lectured widely in North Deming lectured widely in North America during the 1980s; he died 24 America during the 1980s; he died 24 December 1993December 1993

Deming’s 14 PointsDeming’s 14 Points1. Create constancy of purpose toward improvement 1. Create constancy of purpose toward improvement 2. Adopt a new philosophy, recognize that we are in a 2. Adopt a new philosophy, recognize that we are in a

time of change, a new economic agetime of change, a new economic age3. Cease reliance on mass inspection to improve quality3. Cease reliance on mass inspection to improve quality4. End the practice of awarding business on the basis 4. End the practice of awarding business on the basis

of price aloneof price alone5. Improve constantly and forever the system of 5. Improve constantly and forever the system of

production and serviceproduction and service6. Institute training6. Institute training7. Improve leadership, recognize that the aim of 7. Improve leadership, recognize that the aim of

supervision is help people and equipment to do a supervision is help people and equipment to do a better jobbetter job

8. Drive out fear8. Drive out fear9. Break down barriers between departments9. Break down barriers between departments

14 Points cont’d14 Points cont’d

10. Eliminate slogans and targets for the workforce 10. Eliminate slogans and targets for the workforce such as zero defectssuch as zero defects

11. Eliminate work standards11. Eliminate work standards12. Remove barriers that rob workers of the right 12. Remove barriers that rob workers of the right

to pride in the quality of their workto pride in the quality of their work13. Institute a vigorous program of education and 13. Institute a vigorous program of education and

self-improvementself-improvement14. Put everyone to work to accomplish the 14. Put everyone to work to accomplish the

transformationtransformation

Note that the 14 points are about change

Deming’s Deadly Deming’s Deadly DiseasesDiseases

1.1. Lack of constancy of purposeLack of constancy of purpose

2.2. Emphasis on short-term profitsEmphasis on short-term profits

3.3. Performance evaluation, merit rating, Performance evaluation, merit rating, annual reviewsannual reviews

4.4. Mobility of managementMobility of management

5.5. Running a company on visible figures Running a company on visible figures alonealone

6.6. Excessive medical costs for employee Excessive medical costs for employee health carehealth care

7.7. Excessive costs of warranteesExcessive costs of warrantees

Joseph M. JuranJoseph M. Juran• Born in Romania (1904), Born in Romania (1904),

immigrated to the USimmigrated to the US• Worked at Western Worked at Western

Electric, influenced by Electric, influenced by Walter ShewhartWalter Shewhart

• Emphasizes a more Emphasizes a more strategic and planning strategic and planning oriented approach to oriented approach to quality than does quality than does DemingDeming

• Juran Institute is still an Juran Institute is still an active organization active organization promoting the Juran promoting the Juran philosophy and quality philosophy and quality improvement practicesimprovement practices

The Juran TrilogyThe Juran Trilogy

1.1. PlanningPlanning

2.2. ControlControl

3.3. ImprovementImprovement

• These three processes are These three processes are interrelatedinterrelated

• Control versus breakthroughControl versus breakthrough• Project-by-project improvementProject-by-project improvement

Some of the Other Some of the Other “Gurus”“Gurus”

• Kaoru IshikawaKaoru Ishikawa– Son of the founder of JUSE, promoted Son of the founder of JUSE, promoted

widespread use of basic toolswidespread use of basic tools

• Armand FeigenbaumArmand Feigenbaum– Author of Total Quality Control, promoted Author of Total Quality Control, promoted

overall organizational involvement in quality,overall organizational involvement in quality,– Three-step approach emphasized quality Three-step approach emphasized quality

leadership, quality technology, and leadership, quality technology, and organizational commitment organizational commitment

• Lesser gods, false prophets Lesser gods, false prophets

Quality Systems and Quality Systems and StandardsStandards

• The ISO certification process focuses heavily on quality assurance, without sufficient weight given to quality planning and quality control and improvement

Quality CostsQuality Costs

Legal Aspects of QualityLegal Aspects of Quality

• Product liability exposureProduct liability exposure

• Concept of Concept of strict liabilitystrict liability1.1. Responsibility of both manufacturer Responsibility of both manufacturer

and seller/distributorand seller/distributor

2.2. Advertising must be supported by Advertising must be supported by valid datavalid data

Quality and ProductivityQuality and Productivity

• Example: Suppose a worker Example: Suppose a worker produces 100 units and 20% are produces 100 units and 20% are defective. Which is better option to defective. Which is better option to improve quality by 20% or improve quality by 20% or productivity by 20%.productivity by 20%.

Does improving quality improves Does improving quality improves productivity?productivity?

Seven Quality ToolsSeven Quality Tools

Seven Quality Control Seven Quality Control ToolsTools

• Pareto ChartPareto Chart– Histogram Histogram

• Process flow diagramProcess flow diagram• Check sheetCheck sheet• Scatter diagramScatter diagram• Control chartControl chart• Run ChartRun Chart• Cause and Effect DiagramCause and Effect Diagram

Pareto PrinciplePareto Principle

• Vilfredo Pareto (1848-1923) Italian Vilfredo Pareto (1848-1923) Italian economisteconomist– 20% of the population has 80% of the 20% of the population has 80% of the

wealthwealth

• Juran used the term “vital few, Juran used the term “vital few, trivial many”. He noted that 20% of trivial many”. He noted that 20% of the quality problems caused 80% of the quality problems caused 80% of the dollar loss.the dollar loss.

7 Quality Tools7 Quality Tools

Pareto chartPareto chart

7 Quality Tools7 Quality Tools

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7 Quality Tools7 Quality Tools

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FlowchartsFlowcharts

• FlowchartsFlowcharts– Graphical description of how work is Graphical description of how work is

done.done.– Used to describe processes that are to Used to describe processes that are to

be improved.be improved.

7 Quality Tools7 Quality Tools

Flow DiagramsFlow Diagrams

" Draw a flowchart for whatever you " Draw a flowchart for whatever you do. Until you do, you do not know do. Until you do, you do not know what you are doing,what you are doing,you just have a job.”you just have a job.”

-- Dr. W. Edwards Deming.-- Dr. W. Edwards Deming.

FlowchartFlowchart

Activity

DecisionYesYes

NoNo

7 Quality Tools7 Quality Tools

FlowchartFlowchart

Flow DiagramsFlow Diagrams

Process Chart SymbolsProcess Chart Symbols

Operations

Inspection

Transportation

Delay

Storage

Check SheetCheck SheetCheck SheetCheck Sheet

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7 Quality Tools7 Quality Tools

Cause-and-Effect Cause-and-Effect DiagramsDiagrams

Cause-and-Effect Cause-and-Effect DiagramsDiagrams

• Show the relationships between a Show the relationships between a problem and its possible causes.problem and its possible causes.

• Developed by Kaoru Ishikawa (1953)Developed by Kaoru Ishikawa (1953)• Also known as …Also known as …

– Fishbone diagramsFishbone diagrams– Ishikawa diagramsIshikawa diagrams

7 Quality Tools7 Quality Tools

Cause and Effect Cause and Effect “Skeleton”“Skeleton”

Cause and Effect Cause and Effect “Skeleton”“Skeleton”

QualityProblem

Materials

EquipmentPeople

Procedures

7 Quality Tools7 Quality Tools

Fishbone Diagram Fishbone Diagram

QualityProblem

MachinesMeasurement Human

ProcessEnvironment Materials

Faulty testing equipment

Incorrect specifications

Improper methods

Poor supervision

Lack of concentration

Inadequate training

Out of adjustment

Tooling problems

Old / worn

Defective from vendor

Not to specifications

Material-handling problems

Deficienciesin product design

Ineffective qualitymanagement

Poor process design

Inaccuratetemperature control

Dust and Dirt

Cause and effect Cause and effect diagramsdiagrams

• AdvantagesAdvantages– making the diagram is educational in making the diagram is educational in

itselfitself– diagram demonstrates knowledge of diagram demonstrates knowledge of

problem solving teamproblem solving team– diagram results in active searches for diagram results in active searches for

causescauses– diagram is a guide for data collectiondiagram is a guide for data collection

Cause and effect Cause and effect diagramsdiagrams

To construct the skeleton, remember:To construct the skeleton, remember:• For manufacturing - the 4 M’sFor manufacturing - the 4 M’s

man, method, machine, materialman, method, machine, material

• For service applicationsFor service applicationsequipment, policies, procedures, peopleequipment, policies, procedures, people

Scatter DiagramScatter Diagram

.

Run ChartsRun Charts

• Run Charts (time series plot)Run Charts (time series plot)– Examine the behavior of a variable over Examine the behavior of a variable over

time.time.– Basis for Basis for Control ChartsControl Charts

Control ChartControl Chart

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Control ChartsControl Charts Control ChartsControl Charts

7 Quality Tools7 Quality Tools

• A process is operating with only chance causes of variation present is said to be in statistical control.• A process that is operating in the presence of assignable causes is said to be out of control.

• A control chart containsA control chart contains– A A center linecenter line– An An upper control limitupper control limit– A A lower control limitlower control limit

• A point that plots within the A point that plots within the control limits indicates the control limits indicates the process is in controlprocess is in control– No action is necessaryNo action is necessary

• A point that plots outside the A point that plots outside the control limits is evidence control limits is evidence that the process is out of that the process is out of controlcontrol– Investigation and corrective Investigation and corrective

action are required to find action are required to find and eliminate assignable and eliminate assignable cause(s)cause(s)

• There is a close connection There is a close connection between control charts and between control charts and hypothesis testinghypothesis testing

Photolithography Photolithography ExampleExample

• Important quality Important quality characteristic in hard characteristic in hard bake is resist flow widthbake is resist flow width

• Process is monitored by Process is monitored by average flow widthaverage flow width– Sample of 5 wafersSample of 5 wafers– Process mean is 1.5 Process mean is 1.5

micronsmicrons– Process standard deviation Process standard deviation

is 0.15 micronsis 0.15 microns

• Note that all plotted Note that all plotted points fall inside the points fall inside the control limitscontrol limits– Process is considered to be Process is considered to be

in in statistical controlstatistical control

Shewhart Control Chart Shewhart Control Chart ModelModel

More Basic PrinciplesMore Basic Principles

• Charts may be used to estimate process Charts may be used to estimate process parameters, which are used to determine parameters, which are used to determine capabilitycapability

• Two general types of control chartsTwo general types of control charts– Variables Continuous scale of measurementVariables Continuous scale of measurement

• Quality characteristic described by central tendency and a Quality characteristic described by central tendency and a measure of variabilitymeasure of variability

– Attributes Attributes – Conforming/nonconformingConforming/nonconforming

• CountsCounts

• Control chart designControl chart design encompasses selection encompasses selection of of sample sizesample size, , control limitscontrol limits, and , and sampling sampling frequencyfrequency

Types of Process Types of Process VariabilityVariability

• Stationary Stationary andand uncorrelated uncorrelated data vary around a fixed data vary around a fixed mean in a stable or predictable mannermean in a stable or predictable manner

• StationaryStationary and and autocorrelated autocorrelated successive observations successive observations are dependent with tendency to move in long runs on are dependent with tendency to move in long runs on either side of meaneither side of mean

• NonstationaryNonstationary process drifts without any sense of a process drifts without any sense of a stable or fixed meanstable or fixed mean

Reasons for PopularityReasons for Popularityof Control Chartsof Control Charts

1.1. Control charts are a proven technique Control charts are a proven technique for improving productivity.for improving productivity.

2.2. Control charts are effective in defect Control charts are effective in defect prevention.prevention.

3.3. Control charts prevent unnecessary Control charts prevent unnecessary process adjustment.process adjustment.

4.4. Control charts provide diagnostic Control charts provide diagnostic information.information.

5.5. Control charts provide information about Control charts provide information about process capability.process capability.

• 3-Sigma Control Limits3-Sigma Control Limits– Probability of type I error is 0.0027Probability of type I error is 0.0027

• Probability LimitsProbability Limits– Type I error probability is chosen directlyType I error probability is chosen directly– For example, 0.001 gives 3.09-sigma control limitsFor example, 0.001 gives 3.09-sigma control limits

• Warning LimitsWarning Limits– Typically selected as 2-sigma limitsTypically selected as 2-sigma limits

• Pattern is very nonrandom in appearance• 19 of 25 points plot below the center line, while only 6 plot above• Following 4th point, 5 points in a row increase in magnitude, a run up• There is also an unusually long run down beginning with 18th point

• Phase I is a Phase I is a retrospective analysisretrospective analysis of of process data to construct process data to construct trial control limitstrial control limits– Charts are effective at detecting large, sustained Charts are effective at detecting large, sustained

shifts in process parameters, outliers, shifts in process parameters, outliers, measurement errors, data entry errors, etc.measurement errors, data entry errors, etc.

– Facilitates identification and removal of assignable Facilitates identification and removal of assignable causescauses

• In phase II, the control chart is used to In phase II, the control chart is used to monitormonitor the process the process– Process is assumed to be reasonably stableProcess is assumed to be reasonably stable– Emphasis is on Emphasis is on process monitoringprocess monitoring, not on , not on

bringing an unruly process into controlbringing an unruly process into control

SPC Implementation SPC Implementation IssuesIssues

• Define processDefine process• Chose Quality characteristic and Chose Quality characteristic and

measurement systemmeasurement system• Focus on trends and shiftsFocus on trends and shifts• Calculate control charts limits.Calculate control charts limits.• Investigate and actInvestigate and act• SPC training SPC training

• Nonmanufacturing applications do not differ Nonmanufacturing applications do not differ substantially from industrial applications, substantially from industrial applications, but sometimes require ingenuitybut sometimes require ingenuity

1.1. Most nonmanufacturing operations do not have a Most nonmanufacturing operations do not have a natural measurement systemnatural measurement system

2.2. The observability of the process may be fairly lowThe observability of the process may be fairly low• Flow chartsFlow charts and and operation process operation process

chartscharts are particularly useful in developing are particularly useful in developing process definition and process process definition and process understanding. This is sometimes called understanding. This is sometimes called process mappingprocess mapping..

– Used to identify Used to identify value-addedvalue-added versus versus nonvalue-nonvalue-addedadded activity activity