SPC (Statistical Process Control)

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SPC (Statistical Process Control)
What it is

• SPC is a statistical technique which compares
  current process output against a historical
  template.
• The template is usually based around a centre
  value with 3 standard measures of variation
  (of the characteristic being measured).
• The objective is to keep the current process
  stable, within these 3 control limits and to
  limit variation within them.
• Industry-standard rules are adopted If data
  from the current process approaches these
  control limits or forms non-random patterns
  within the limits, then appropriate action to
  control the process is taken.
• No reference to specifications are made in SPC
• SPC was developed by Walter Shewhart and
  others, and many traditionalists refer to SPC
  charts as Shewhart charts

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SPC (Statistical Process Control)
What it is

• The UCL/LCL is set by default at 3 standard
  measures of variation (of the characteristic
  being measured).
• Additional control limits can be added, but
  usually industry-standard rules apply.

How to use it

• Detailed information regarding how to
  construct an SPC chart manually, how to run one
  in Minitab, how to select the correct SPC chart,
  and the main industry-standard rules are found
  in the aTQ training material referred to in the
  References.

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SPC (Statistical Process Control)
Example
Actions to follow if Rules are breached
Chart rules follow industry standards or adapt to
suit
Standard Shewhart Control Factors, used to
manually calculate centre lines and limits.
Table for data collection
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SPC (Statistical Process Control)
How it helps
SPC charts must be seen alongside Process
Capability graphs and indexes.
References

• ASG aTQ training modules
• 8.4, 8.5, 8.6, 8.7 SPC (and non-SPC
  control)

• ASG seniors aTQ training module 1.5
  Capability