STATISTICAL QUALITYCONTROL(SQC) : KHS 1 STATISTICAL QUALITYCONTROL(SQC)
Slide 2: KHS 2 What is Quality…???
Quality is a relative term.
Slide 3: KHS 3 The 5 Main Dimensions of Quality
Pre-determined Standards
Reliability
Durability
Serviceability
Performance
Slide 4: KHS 4 What is Quality Control ?
Maintaining pre decided standards of the products.
Slide 5: KHS 5 What is STATISTICAL Quality Control?
Statistical techniques used for
Controlling or Maintaining
“ Pre-determined Quality”.
Slide 6: JBS 6 Any two Products never be same in all aspects.
This difference is called “VARIATION”.
Slide 7: JBS 7 Causes of Variation:
Due to Man, Machine,
Material, Time and so on…
Slide 8: JBS 8 Types of Variations:
Assignable Causes :
Chance Causes :
Slide 9: 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.
Slide 11: 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)
Slide 13: MAS 13 CL UCL LCL Control Charts: * * * * * * * * * * * *
STATISTICAL BASIS OF CONTROL CHART : KHS 14 STATISTICAL BASIS OF CONTROL CHART
Slide 15: MAS 15
Slide 16: KHS 16 Types of Control Charts :
_
Charts for Variables : X , R
Charts for Attributes : p, np, c
Slide 17: 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
Slide 19: 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
Slide 25: 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
Slide 27: 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.
Slide 29: MAS 29 Example 2 Sample X-bar R Sample X-bar R Sample X-bar R
1 55.6 22 11 51.2 15 21 50.0 11
2 61.0 23 12 49.4 14 22 47.0 14
3 45.2 20 13 44.0 32 23 50.6 15
4 46.2 11 14 51.6 14 24 48.8 16
5 46.8 18 15 53.2 12 25 44.6 22
6 49.8 23 16 52.4 23 26 46.8 16
7 46.8 18 17 50.6 8 27 49.2 8
8 44.2 20 18 56.0 18 28 45.6 19
9 50.8 32 19 50.2 19 29 57.6 40
10 48.4 16 20 44.0 23 30 51.4 17
Slide 30: MAS 30 Summary Information
Slide 31: MAS 31 UCL
CL
LCL R 60.38
49.63
38.89 39.40
18.63
0 X-bar and R Control Chart Limits
Slide 32: 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.