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Background
to the Evolution of TPM
Traditionally
in many manufacturing companies, high buffer stocks were allowed to
develop between major pieces of machinery within our plants to ensure
that if there was a problem with one piece of machinery or equipment
then it would not affect production in the rest of the plant. Hence
the role of maintenance was to cost effectively ensure major pieces of
machinery & equipment were available for an agreed period of
scheduled time, for example 90%.
 Because
of the practice of retaining high buffer stocks, most machines or
equipment could be considered independent. If the machinery in a
process was maintained such that it achieved 90% availability, the
availability of the process was 90% (see Figure 1). If the machinery
started to cause quality problems, these would probably be noticed in
final quality inspection and the cause traced back
to the offending piece of machinery or equipment and corrected by
maintenance.
At
Nippon Denso in 1970 with the introduction of the Toyota Production
System, the buffer stocks were substantially reduced in their quest
for shorter leadtimes, lower costs and improved quality. Statistical
Process Control (SPC) supported by "Prevention at Source"
was introduced to ensure quality right first time. This approach
ensures maximum customer value by providing the highest quality at the
lowest cost supported by quick responsiveness and superior customer
service. Hence buffer stocks were reduced to both reduce leadtimes and
force the identification of any ‘cost consuming’ problems.
Unfortunately, this also resulted in any individual machinery or
equipment problems affecting the whole process.
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