student slides chapter 10

8/2/2019 Student Slides Chapter 10

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McGraw-Hill/Irwin Copyright 2009 by The McGraw-Hill Companies, Inc. All Rights Reserved.

Chapter 10

Quality Control


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Chapter 10: Learning Objectives

You should be able to:

List and briefly explain the elements in the control proces

Explain how control charts are used to monitor a process

Explain the concepts underlying the use of control charts

Use and interpret control charts

Understand the use of run tests

Assess process capability


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Statistical Process Control (SPC)

Quality control seeks

Quality of Conformance

A product or service conforms to specifications

A tool used to help in this process:

SPC

Statistical evaluation of the output of a process

Helps us to decide if a process is in control or ifcorrective action is needed


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Process Variability

All processes generate output that exhibitssome degree of variability

The fundamental question:

Is the variation within acceptable boundaries?


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Control Chart

UCL

LCL

Mean

Out ofcontrol

Normalvariationdue tochance

Abnormal variation

Abnormal variationdue to assignable causes

Each point on the control chart represents a sample of nobservations


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Control Charts for Variables

Variables generate data that are measured

Mean control charts

Used to monitor the central tendency of a process.

X bar charts

Range control charts

Used to monitor the process dispersion

R charts


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Establishing Control Limits

samplesofnumber

sampleofmean

meanssampleofAverage

where

1

k

ix

x

k

x

x

i

k

i

i

iR

k

R

i

k

i

i

sampleofRange

rangessampleofAverageR

where

R 1


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X-Bar Chart: Control Limits

Used to monitor the central tendency of aprocess

nA

RAxLCL

RAxUCL

x

x

size,sampleonbasedfactorchartcontrolawhere

LimitsControlchartx

2

2

2


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Range Chart: Control Limits

Used to monitor process dispersion

nD

nD

RDLCL

RDUCL

R

R

size,sampleonbasedfactorchartcontrola

size,sampleonbasedfactorchartcontrola

where

LimitsControlChartR

4

3

3

4


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Control Charts for Attributes

Attributes generate data that are counted.

p-Chart

Control chart used to monitor the proportion of

defectives in a process

c-Chart

Control chart used to monitor the number of defects perunit


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Process Capability

Once a process has been determined to be stable, it isnecessary to determine if the process is capable ofproducing output that is within an acceptable range

Tolerances or specifications

Range of acceptable values established by engineeringdesign or customer requirements

Process variability

Natural or inherent variability in a process

Process capability

Process variability relative to specification


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Cp: Process Capability Ratio

limitification)rance(speclower toleLTL

limittion)(specificaranceupper toleUTL

where

6

LTL-UTL

pC


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Cpk: Process Capability Index

Used when a process is not centered at itstarget, or nominal, value

3

LTL,

3

UTLmin

,minxx

CCC plpupk


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Taguchi Loss Function


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Operations Strategy

Quality is a primary consideration for nearly allcustomers

Achieving and maintaining quality standards is ofstrategic importance to all business organizations

Product and service design

Increase capability in order to move from extensive useof control charts and inspection to achieve desiredquality outcomes

student slides chapter 10

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