Tools of quality control

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Tools of quality control

• A-Team

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Basic tools of quality control

• control chart
• histogram
• Pareto chart
• check sheet
• cause-and-effect diagram
• flowchart
• scatter diagram

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control chart / Shewhart chart /
process-behaviour chart

• used to determine whether a manufacturing or
  business process is in a state of statistical
  control or not
• if the chart indicates that the process is
  currently under control then it can be used with
  confidence to predict the future performance of
  the process
• if the chart indicates that the process being
  monitored is not in control, the pattern it
  reveals can help determine the source of
  variation to be eliminated to bring the process
  back into control

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A control chart consists of the following

• points representing measurements of a quality
  characteristic in samples taken from the process
  at different times
• a centre line, drawn at the process
  characteristic mean which is calculated from the
  data
• upper and lower control limits that indicate the
  threshold at which the process output is
  considered statistically 'unlikely'

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The chart may contain other optional features

• upper and lower warning limits, drawn as separate
  lines, typically two standard deviations above
  and below the centre line
• division into zones, with the addition of rules
  governing frequencies of observations in each
  zone
• annotation with events of interest, as determined
  by the Quality Engineer in charge of the
  process's quality

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Ishikawa diagram / fishbone diagram /
cause-and-effect diagram

• brainchild of Kaoru Ishikawa, who pioneered
  quality management processes in the Kawasaki
• diagram that shows the causes of a certain event
• first used in the 1960s
• known as a fishbone diagram because of its shape,
  similar to the side view of a fish skeleton
• can reveal key relationships among various
  variables, and the possible causes provide
  additional insight into process behaviour

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Categories of causes

• 6 M's
• Machine / Method / Materials / Measurement / Man
  / Mother Nature (Environment)
• 8 P's
• Price / Promotion / People / Processes / Place /
  Plant / Policies / Procedures / Product (or
  Service)
• 4 Ss
• Surroundings / Suppliers / Systems / Skills

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