From analyses of the defect cycle, the manufacturing
system variables, and the adequacy of the control
procedures within the management of a manufacturing
plant, the probabilities for the occurrence and frequency of
variables causing defects can be estimated. Subsequently, a
density and probable time for a defect and its source can be
determined. The fault tree, as shown in Fig. 2, can be
structured in order to determine the overall probability for
the production of a defective product; the fault tree can
also attribute the cause of the defect to a specific area.
P ðdefective partÞ ¼ ðB1 B2Þ [ ðB3 B4Þ
[ ðB5 B6Þ [ ðB7 B8Þ.
The fault tree as shown in Fig. 2 assumes that a single fault,
or a combination of all faults, may lead to a defective
product. Therefore, the quality improvement process
requires efforts to restrict the possibility of the occurrence
of further faults.