Quality Control and Statistical Quality Control - Kickoffall Info Hub

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Monday, October 21, 2019

Quality Control and Statistical Quality Control

Quality control refers to the means of fulfilling quality requirements. Quality control aims to prevent the defects before the detection of defects.   Quality control process includes the activities such as:
  • To establish quality standards
  • To appraise the quality conformance
  • To take corrective actions to reduce deviations
  • To plan for quality improvement.

Statistical quality control (SQC)
Statistical process control is a method of quality control which applies statistical methods to control a process to ensure that the process operates efficiently conforming high productivity and less waste. SQC is manifested through control charts
Control chart
Control chart is used for graphical presentation of process changes over time-based on statistical findings checking the consistency of process variation and unpredictability. The control chart includes a central line for the average, an upper line for the upper control limit, and a lower line for the lower control limit.
Types of control charts
1. Control charts for variables. (Variables are quality characteristics that can be measured on a continuous scale. 
Mean chart
Range chart
2. Control charts for attributes. (Attributes: attributes are quality features which can’t be measured, but can be categorized into good or bad. An example is a painted surface.)
 ‘np’ chart: number of defectives charts for a constant sample.
 ‘p’ chart: fraction defective chart for varying sample size.
 ‘c’ chart: number of defects chart for constant sample size.
‘u’ chart: the number of defects per unit chart for varying sample size.

(The difference between defective and defect: The term Defective refers to something that has a fault in it and doesn’t work like it’s supposed to; the term Defect refers to a quality characteristic of the defective product. A defective product might have multiple defects.)


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