Bài giảng Operations Management - Chapter 10 Quality Control

Quality ControlChapter 10Copyright © 2015 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.You should be able to:LO 10.1 Explain the need for quality controlLO 10.2 Discuss the basic issues of inspectionLO 10.3 List and briefly explain the elements of the control processLO 10.4 Explain how control charts are used to monitor a process, and the concepts that underlie their useLO 10.5 Use and interpret control chartsLO 10.6 Perform run tests to check for nonrandomness in process outputLO 10.7 Assess process capabilityChapter 10: Learning ObjectivesWhat is Quality Control?Quality ControlA process that evaluates output relative to a standard and takes corrective action when output doesn’t meet standardsIf results are acceptable no further action is requiredUnacceptable results call for correction actionInspection alone is not is generally not sufficient to achieve a reasonable level of qualityMost organization rely upon some inspection and a great deal of process control to achieve an acceptable level of quality.LO 10.1InspectionAn appraisal activity that compares goods or services to a standardInspection issues:How much to inspect and how oftenAt what points in the process to inspectWhether to inspect in a centralized or on-site locationWhether to inspect attributes or variablesInspectionLO 10.2Sampling and corrective action are only a part of the control processSteps required for effective control:Define: What is to be controlled?Measure: How will measurement be accomplished?Compare: There must be a standard of comparisonEvaluate: Establish a definition of out of controlCorrect: Uncover the cause of nonrandom variability and fix itMonitor: Verify that the problem has been eliminatedControl ProcessLO 10.3Control ChartA time ordered plot of representative sample statistics obtained from an ongoing process (e.g. sample means), used to distinguish between random and nonrandom variabilityControl limitsThe dividing lines between random and nonrandom deviations from the mean of the distributionUpper and lower control limits define the range of acceptable variationControl Charts: The Voice of the ProcessLO 10.4Control Charts for VariablesVariables generate data that are measuredMean control chartsUsed to monitor the central tendency of a process.“x-bar” chartsRange control chartsUsed to monitor the process dispersionR chartsLO 10.5Establishing Control LimitsLO 10.5Used to monitor the central tendency of a processX-Bar Chart: Control LimitsLO 10.5Used to monitor process dispersionRange Chart: Control LimitsLO 10.5Attributes generate data that are counted.p-Chart Control chart used to monitor the proportion of defectives in a processc-Chart Control chart used to monitor the number of defects per unitControl Charts for AttributesLO 10.5Run TestsEven if a process appears to be in control, the data may still not reflect a random processAnalysts often supplement control charts with a run testRun testA test for patterns in a sequenceRunSequence of observations with a certain characteristicLO 10.6Nonrandom PatternsLO 10.6Once a process has been determined to be stable, it is necessary to determine if the process is capable of producing output that is within an acceptable rangeTolerances or specificationsRange of acceptable values established by engineering design or customer requirementsProcess variabilityNatural or inherent variability in a processProcess capabilityThe inherent variability of process output (process width) relative to the variation allowed by the design specification (specification width)Process CapabilityLO 10.7CpLO 10.7