Getting Lean

John BornemanData distribution, explained.

In my December column I listed three items to watch out for when evaluating capability study results: Cp versus Pp, the distribution of data, and sample size. I hopefully cast some light on the differences between the two measures of capability, Cp and Pp.

In this column I will dive deep into the distribution of data. The thing to remember is the standard capability study assumes the data are normally distributed. This assumption of normality, while not so critical in other statistical tools, is very important in capability studies.

Cp and Pp give us predictions based on a sample of how our population will behave in the far tails of the normal curve. These measures use mean and standard deviation to create a normal distribution, and, from this, predict how many of our parts, over the entire population of parts, will fall outside the tolerance limits.

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APQP techniques for identifying and eliminating bottlenecks.

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Fernando Ruiz

APQP techniques for identifying and eliminating bottlenecks.

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John BornemanWhen you ask for Cp (or Cpk), are you really getting Pp (or Ppk)?

OK, I admit it: I was trying to be funny in the title. But the issue is how capable is a capability study? Or, to state it another way: When should we be careful in how much we trust our capability study results?

Here are three items we should be aware of when designing, running and calculating a capability study:

 

 

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Part supplies are getting tighter. Here are new rules for dealing with the constraints.

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Eliminating waste in medical box-build production.

Contract manufacturers typically have to find middle ground in the use of Lean manufacturing principles. Unless a customer is completely committed to a holistic Lean environment, there will also be some level of waste (muda) in the process attributable to customer-related constraints. That said, use of Lean principles to minimize the seven wastes can help mitigate defects and lower costs that would otherwise occur as a result of inefficiency.

These seven wastes are defined as:

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