Although process engineers are generally familiar with the notion of dependent and independent process steps, many do not fully appreciate what these concepts imply for manufacturing operations. The reason for this neglect is simple: consultants that...
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Although process engineers are generally familiar with the notion of dependent and independent process steps, many do not fully appreciate what these concepts imply for manufacturing operations. The reason for this neglect is simple: consultants that championed Six Sigma mostly came from the semiconductor industry, which, unlike the motor industry, has an abundance of dependent processes. Indeed, the author once heard an engineer describe a semiconductor process as a cascade of miracles – a miracle anything survived!
By way of contrast, the consultants (sensei) at Toyota’s mechanical assembly plants initially struggled until: “Kiichiro realized that his initial focus had not been narrowed down to basic system verification, or one-by-one confirmation. He recognized the costly lesson of not confirming the quality at each step of the process.”(Ref. 1)
When we say two steps are dependent, we usually imply the two steps are correlated, which does not necessarily imply a causal relati
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