MAS 9 Chapter 1 9 Introduction to Statistical Quality Control, 6th Edition by Douglas C. Montgomery.
Copyright (c) 2009 John Wiley & Sons, Inc.

Slide 10:

MAS 10 Shewart Control Charts:
The distribution of Statistic (T) is assumed to be
Normally Distributed.

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MAS 11

Slide 12:

MAS 12 99.73% of observations lie in μ ±3σ.
LCL = (Mean of T) – 3(S.D. of T)
CL = (Mean of T)
UCL = (Mean of T) + 3(S.D. of T)

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MAS 13 CL UCL LCL Control Charts: * * * * * * * * * * * *

STATISTICAL BASIS OF CONTROL CHART :

KHS 14 STATISTICAL BASIS OF CONTROL CHART

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MAS 15

Slide 16:

KHS 16 Types of Control Charts :
_
Charts for Variables : X , R
Charts for Attributes : p, np, c

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KHS 17 Charts for Variable :
X bar chart monitors the between sample variability
R chart monitors the within sample variability.

Slide 18:

KHS 18 Here,
n = Number of units in the sample = 5 m = Number of samples = 25

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KHS 19 R =

Slide 20:

KHS 20

Slide 21:

KHS 21

Control Limits for Chart :

KHS 22 Control Limits for Chart depends on value of n.

Control limits for R Chart :

KHS 23 Control limits for R Chart D3 and D4 are depend on value of n.

Slide 24:

JBS 24 EXAMPLE 1

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JBS 25

Slide 26:

JBS 26 UCL
CL
LCL R 25.17
22.5
19.83 9.71
4.6
0 X-bar and R Control Chart Limits

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JBS 27

Slide 28:

JBS 28 X-bar & R Chart Interpretation X-bar chart indicates that no point is above UCL OR below LCL.
R-bar chart indicates that no point is above UCL OR below LCL.
So, Process is considered as under control.

MAS 31 UCL
CL
LCL R 60.38
49.63
38.89 39.40
18.63
0 X-bar and R Control Chart Limits

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MAS 32

Slide 33:

MAS 33

Slide 34:

MAS 34 X-bar & R Chart Interpretation X-bar chart indicates that one point is above the UCL (at sample 2).
R chart indicates that one point is above the UCL (at sample 29).
So, Measures would be investigated to reduce process variation at that point.

Control Limits, Specification Limits, and Revised Limits :

MAS 35 Control Limits, Specification Limits, and Revised Limits Control limits are functions of the natural variability of the process
Specification limits are determined by developers/designers

Control Limits, Specification Limits, and Revised Limits :

MAS 36 Control Limits, Specification Limits, and Revised Limits Revised limits are the limits for the future production
There is no mathematical relationship between control limits and specification limits.

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