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Copyright 2006 John Wiley & Sons, Inc.Beni Asllani University of Tennessee at ChattanoogaStatistical Process ControlOperations Management - 5th EditionChapter 4Roberta Russell & Bernard W. Taylor, III
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Lecture OutlineBasics of Statistical Process ControlControl ChartsControl Charts for AttributesControl Charts for VariablesControl Chart PatternsSPC with ExcelProcess Capability
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Basics of Statistical Process ControlStatistical Process Control (SPC)monitoring production process to detect and prevent poor qualitySamplesubset of items produced to use for inspectionControl Chartsprocess is within statistical control limits
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*VariabilityRandomcommon causesinherent in a processcan be eliminated only through improvements in the systemNon-Randomspecial causesdue to identifiable factorscan be modified through operator or management action
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*SPC in TQMSPCtool for identifying problems and make improvementscontributes to the TQM goal of continuous improvements
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Quality MeasuresAttributea product characteristic that can be evaluated with a discrete responsegood bad; yes - noVariablea product characteristic that is continuous and can be measuredweight - length
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Nature of defect is different in servicesService defect is a failure to meet customer requirementsMonitor times, customer satisfactionApplying SPC to Service
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Copyright 2006 John Wiley & Sons, Inc.4-*Applying SPC to Service (cont.)Hospitalstimeliness and quickness of care, staff responses to requests, accuracy of lab tests, cleanliness, courtesy, accuracy of paperwork, speed of admittance and checkoutsGrocery Storeswaiting time to check out, frequency of out-of-stock items, quality of food items, cleanliness, customer complaints, checkout register errorsAirlinesflight delays, lost luggage and luggage handling, waiting time at ticket counters and check-in, agent and flight attendant courtesy, accurate flight information, passenger cabin cleanliness and maintenance
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Applying SPC to Service (cont.)Fast-Food Restaurantswaiting time for service, customer complaints, cleanliness, food quality, order accuracy, employee courtesyCatalogue-Order Companiesorder accuracy, operator knowledge and courtesy, packaging, delivery time, phone order waiting timeInsurance Companiesbilling accuracy, timeliness of claims processing, agent availability and response time
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Where to Use Control ChartsProcess has a tendency to go out of controlProcess is particularly harmful and costly if it goes out of controlExamplesat the beginning of a process because it is a waste of time and money to begin production process with bad suppliesbefore a costly or irreversible point, after which product is difficult to rework or correctbefore and after assembly or painting operations that might cover defectsbefore the outgoing final product or service is delivered
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Control ChartsA graph that establishes control limits of a processControl limitsupper and lower bands of a control chartTypes of chartsAttributesp-chartc-chartVariablesrange (R-chart)mean (x bar chart)
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Process Control Chart
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Normal Distribution
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*A Process Is in Control If no sample points outside limits most points near process average about equal number of points above and below centerline points appear randomly distributed
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Control Charts for Attributesp-chartsuses portion defective in a samplec-chartsuses number of defects in an item
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*p-Chart
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*p-Chart Example
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Copyright 2006 John Wiley & Sons, Inc.4-*p-Chart Example (cont.)
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*p-Chart Example (cont.)
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*c-Chart
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*c-Chart (cont.)
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*c-Chart (cont.)
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Control Charts for VariablesMean chart ( x -Chart )uses average of a sampleRange chart ( R-Chart )uses amount of dispersion in a sample
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*x-bar Chart
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*x-bar Chart ExampleExample 15.4
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*x- bar Chart Example (cont.)Retrieve Factor Value A2
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*x- bar Chart Example (cont.)
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*R- Chart
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*R-Chart ExampleExample 15.3
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*R-Chart Example (cont.)Example 15.3Retrieve Factor Values D3 and D4
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*R-Chart Example (cont.)
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Using x- bar and R-Charts TogetherProcess average and process variability must be in control.It is possible for samples to have very narrow ranges, but their averages is beyond control limits.It is possible for sample averages to be in control, but ranges might be very large.
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Control Chart Patterns
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Control Chart Patterns (cont.)
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Zones for Pattern Tests
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Control Chart Patterns8 consecutive points on one side of the center line8 consecutive points up or down across zones14 points alternating up or down2 out of 3 consecutive points in zone A but still inside the control limits4 out of 5 consecutive points in zone A or B
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Performing a Pattern Test
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Sample SizeAttribute charts require larger sample sizes50 to 100 parts in a sampleVariable charts require smaller samples2 to 10 parts in a sample
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*SPC with Excel
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*SPC with Excel: Formulas
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Process CapabilityTolerancesdesign specifications reflecting product requirementsProcess capabilityrange of natural variability in a process what we measure with control charts
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Copyright 2006 John Wiley & Sons, Inc.4-*Process Capability
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Process Capability (cont.)
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Copyright 2006 John Wiley & Sons, Inc.4-*Process Capability Measures
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Computing Cp
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Process Capability Measures
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*Computing CpkNet weight specification = 9.0 oz 0.5 ozProcess mean = 8.80 ozProcess standard deviation = 0.12 oz
Copyright 2006 John Wiley & Sons, Inc.
Copyright 2006 John Wiley & Sons, Inc.4-*FactorsAppendix: Determining Control Limits for x-bar and R-ChartsReturn
Copyright 2006 John Wiley & Sons, Inc.
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