# ch 4 - Chapter 4 Methods and Philosophy of Statistical...

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Introduction to Statistical Quality Control, Chapter 4 Methods and Philosophy of Statistical Process Control

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Introduction to Statistical Quality Control, 4-1. Introduction Statistical process control is a collection of tools that when used together can result in process stability and variability reduction
Introduction to Statistical Quality Control, 4-1. Introduction The seven major tools are 1) Histogram or Stem and Leaf plot 2) Check Sheet 3) Pareto Chart 4) Cause and Effect Diagram 5) Defect Concentration Diagram 6) Scatter Diagram 7) Control Chart

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Introduction to Statistical Quality Control, 4-2. Chance and Assignable Causes of Quality Variation A process that is operating with only chance causes of variation present is said to be in statistical control. A process that is operating in the presence of assignable causes is said to be out of control. The eventual goal of SPC is reduction or elimination of variability in the process by identification of assignable causes.
Introduction to Statistical Quality Control, 4-2. Chance and Assignable Causes of Quality Variation

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Introduction to Statistical Quality Control, 4-3. Statistical Basis of the Control Chart Basic Principles A typical control chart has control limits set at values such that if the process is in control, nearly all points will lie between the upper control limit (UCL) and the lower control limit (LCL).
Introduction to Statistical Quality Control, 4-3. Statistical Basis of the Control Chart Basic Principles

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Introduction to Statistical Quality Control, 4-3. Statistical Basis of the Control Chart Out-of-Control Situations If at least one point plots beyond the control limits, the process is out of control If the points behave in a systematic or nonrandom manner, then the process could be out of control.
Introduction to Statistical Quality Control, 4-3. Statistical Basis of the Control Chart Relationship between hypothesis testing and control charts We have a process that we assume the true process mean is μ = 74 and the process standard deviation is σ = 0.01. Samples of size 5 are taken giving a standard deviation of the sample average, , as x 0045 . 0 5 01 . 0 n x = = σ = σ

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Introduction to Statistical Quality Control, 4-3. Statistical Basis of the Control Chart Relationship between hypothesis testing and control charts Control limits can be set at 3 standard deviations from the mean. This results in “3-Sigma Control Limits” UCL = 74 + 3(0.0045) = 74.0135 CL= 74 LCL = 74 - 3(0.0045) = 73.9865
Introduction to Statistical Quality Control, 4-3. Statistical Basis of the Control Chart Relationship between hypothesis testing and control charts Choosing the control limits is equivalent to setting up the critical region for testing hypothesis H 0 : μ = 75 H 1 : μ 75

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Introduction to Statistical Quality Control, 4-3. Statistical Basis of the Control Chart Relationship between the process and the control chart
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ch 4 - Chapter 4 Methods and Philosophy of Statistical...

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