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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