| Ideally all parts of a
running production are checked (100% check). However, this takes a lot of
time, man power and thus money. This is why the approach has been changed,
and only random sample tests are carried out. In this test, for example
every 100th part is checked. The checked values are entered into a so-called
quality control chart (see figure).
As long as the entered values are between the
upper and lower warning limits (UWL and LWL),
everything is okay. When the warning limits are exceeded, a new random
sample is taken as soon as possible, to check whether the values are again
within the warning limits.
When the upper or lower control limit are exceeded (UCL and LCL), it is necessary to intervene
in the manufacturing process, which - depending on the particular case -
must be stopped or readjusted.
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