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Operations ManagementQuality Part 2
Knowledge of TQM Tools
source: (Heizer & Render 2008) and (Gardiner 2008)
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Tools of TQM – Identifying the real problem
• Tools for Generating IdeasTools for Generating Ideas•Check sheetsCheck sheets•Scatter diagramsScatter diagrams•Cause-and-effect diagramsCause-and-effect diagrams
• Tools to Organize the DataTools to Organize the Data•Pareto chartsPareto charts
• FlowchartsFlowcharts• Tools for Identifying ProblemsTools for Identifying Problems
•HistogramHistogram•Statistical process control chartStatistical process control chart
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Check Sheets
//
/ / /// /// ///// ////
//////
HourDefect 1 2 3 4 5 6 7 8
ABC
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(a)(a) Check Sheet: An organized method of Check Sheet: An organized method of recording datarecording data
Figure 6.6Figure 6.6
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Scatter Diagrams(b)(b) Scatter Diagram: A graph of Scatter Diagram: A graph of
the value of one variable the value of one variable vs. another variablevs. another variable
AbsenteeismAbsenteeism
Prod
uctiv
ityPr
oduc
tivity
Figure 6.6Figure 6.6
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Cause and Effect Ishikawa Diagram/ Fishbone Diagram
(c)(c) Cause-and-Effect Diagram: A tool that Cause-and-Effect Diagram: A tool that identifies process elements (causes) that identifies process elements (causes) that might effect an outcomemight effect an outcome
CauseCauseMaterialsMaterials MethodsMethods
ManpowerManpower MachineryMachinery
EffectEffect
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Pareto 80/20 rule
(d)(d) Pareto Chart: A graph to identify and plot Pareto Chart: A graph to identify and plot problems or defects in descending order of problems or defects in descending order of frequencyfrequencyFr
eque
ncy
Freq
uenc
y
Perc
ent
Perc
ent
AA BB CC DD EE
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Flow Charts
(e)(e) Flowchart (Process Diagram): A chart that Flowchart (Process Diagram): A chart that describes the steps in a processdescribes the steps in a process
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Histogram(f)(f) Histogram: A distribution showing the Histogram: A distribution showing the
frequency of occurrences of a variablefrequency of occurrences of a variable
DistributionDistribution
Repair time (minutes)Repair time (minutes)
Freq
uenc
yFr
eque
ncy
Figure 6.6Figure 6.6
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Statistical Process Control(g)(g) Statistical Process Control Chart: A chart with Statistical Process Control Chart: A chart with
time on the horizontal axis to plot values of a time on the horizontal axis to plot values of a statisticstatistic
Figure 6.6Figure 6.6
Upper control limitUpper control limit
Target valueTarget value
Lower control limitLower control limit
TimeTime
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SPC• Uses statistics and control charts to tell when Uses statistics and control charts to tell when
to take corrective actionto take corrective action
• Random Samples from processRandom Samples from process
• Pre-calculated rangePre-calculated range
• If outside the range , investigate the causesIf outside the range , investigate the causes
• Adjust to bring back in to controlAdjust to bring back in to control
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Natural and Assignable Variation
• Natural– Affect virtually all production processesAffect virtually all production processes– Expected amount of variationExpected amount of variation– Output measures follow a probability distributionOutput measures follow a probability distribution– Distribution of outputs falls within acceptable limits, the process Distribution of outputs falls within acceptable limits, the process
is said to be “in control”is said to be “in control”
• Assignable– Generally this is some change in the processGenerally this is some change in the process– Variations that can be traced to a specific reasonVariations that can be traced to a specific reason– The objective is to discover when assignable causes are presentThe objective is to discover when assignable causes are present– Eliminate the bad causes, incorporate the good causesEliminate the bad causes, incorporate the good causes
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Establishing Control ChartsFr
eque
ncy
Freq
uenc
y
WeightWeight
##
#### ##
####
####
##
## ## #### ## ####
## ## #### ## #### ## ####
Samples, say five boxes of cereal taken off theSamples, say five boxes of cereal taken off thefilling machine line, vary from each other in filling machine line, vary from each other in weight. weight. Stable process > distributionStable process > distribution
Freq
uenc
yFr
eque
ncy
WeightWeight
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Establishing Control Charts
WeightWeightTimeTimeFr
eque
ncy
Freq
uenc
y
PredictionPrediction
Figure S6.1Figure S6.1
If only natural causes of variation are present, theIf only natural causes of variation are present, theoutput of a process forms a distribution that is output of a process forms a distribution that is stable over time and is predictablestable over time and is predictable
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Establishing Control Charts
WeightWeightTimeTimeFr
eque
ncy
Freq
uenc
y
Figure S6.1Figure S6.1
If assignable causes are present, the processIf assignable causes are present, the processoutput is not stable over time and is not output is not stable over time and is not predicablepredicable
PredictionPrediction
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Constructed from historical data, the Constructed from historical data, the purpose of control charts is to help purpose of control charts is to help distinguish between natural variations distinguish between natural variations and variations due to assignable causesand variations due to assignable causes
Control Charts
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Figure S6.2Figure S6.2
FrequencyFrequency
(weight, length, speed, etc.)(weight, length, speed, etc.)SizeSize
Lower control limitLower control limit Upper control limitUpper control limit
(a) In statistical (a) In statistical control and capable control and capable of producing within of producing within control limitscontrol limits
(b) In statistical control (b) In statistical control but not capable of but not capable of producing within producing within control limitscontrol limits
(c) Out of control(c) Out of control
Process Control
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Establishing Control Charts
17 = UCL17 = UCL
15 = LCL15 = LCL
16 = Mean16 = Mean
Control Chart Control Chart for sample of for sample of 9 boxes9 boxes
Sample numberSample number
|| || || || || || || || || || || ||11 22 33 44 55 66 77 88 99 1010 1111 1212
Variation due Variation due to assignable to assignable
causescauses
Variation due Variation due to assignable to assignable
causescauses
Variation due to Variation due to natural causesnatural causes
Out of Out of controlcontrol
Out of Out of controlcontrol
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Mean and Range Charts(a)(a)These These sampling sampling distributions distributions result in the result in the charts belowcharts below
(Sampling mean is (Sampling mean is shifting upward but shifting upward but range is consistent)range is consistent)
R-chartR-chart(R-chart does not (R-chart does not detect change in detect change in mean)mean)
UCLUCL
LCLLCL
x-chartx-chart(x-chart detects (x-chart detects shift in central shift in central tendency)tendency)
UCLUCL
LCLLCL
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Mean and Range Charts
R-chartR-chart(R-chart detects (R-chart detects increase in increase in dispersion)dispersion)
UCLUCL
LCLLCLFigure S6.5Figure S6.5
These These sampling sampling distributions distributions result in the result in the charts belowcharts below
(Sampling mean (Sampling mean is constant but is constant but dispersion is dispersion is increasing)increasing)
x-chartx-chart(x-chart does not (x-chart does not detect the increase detect the increase in dispersion)in dispersion)
UCLUCL
LCLLCL
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Calculating UCL and LCL for Mean and Range
•Work through examples in text book.
•Calculate UCL and LCL for mean and range
•Review Figure S 6.7
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Process Capability Ratio
Calculation of Cp to +- 3 sigma
Cp= Upper Specification – Lower Specification6 sigma
Where sigma is the standard deviation of the process
Cp of at least 1 = capable (2.7 parts per 1000 out of spec)
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References• Heizer, J., & Render, B. (2008). Operations management (9th
ed.). Saddle River, New Jersey: Pearson Prentice Hall.
• Gardiner, D.,(2008). Operations Management for Business Excellence (2nd ed.). Rosedale, North Shore: Pearson Education New Zealand.
