Frequently Asked Questions

We shall be pleased to answer your questions and share them with other visitors of our web pages.
Also, we appreciate your comments to our answers and we guarantee to public them if it is useful for readers of this column.

List of topics and questions:

Measuring System Analysis (R&R and other)

%R&R of our measuring system for layer thickness measurement results to  35%. Is there ever a chance to improve it (%R&R<10%)? 
Probably yes. First at all compare the two components of %R&R - repeatability and reproducibility.   more...

How to execute the R&R study for a destructive measurement (tensile strength), where the repeated measurement is impossible?
We recommend to consider 9 samples (if we plan study with 3 operators and 3 tests ) as a "one sample". This assumes, the 9 samples have fairly similar values of the measured characteristic.  more...

Process Capability, Cp/Cpk (Pp/Ppk) Indices

We are going to evaluate the process capability by capability indices Cp/Cpk. Why should we investigate the normality of distribution?
Because the capability indices Cp/Cpk are defined for normal distribution only.   more...

What is the difference between capability indices Cp and Pp or Cpk and Ppk respectively?
They differ by the means, how estimate the process variability and by the conditions, which guarantee to estimate trustworthy the quality level.  more...

How to calculate Cp/Cpk for process of shafts production, when shaft diameter according drawing tolerance is  ø17k6 (17,00 +0,012/+0,001 mm)?
Use usual procedure assuming (UTL - LTL) = (17,012 - 17,001).   more...

How to evaluate machine capability?
From the  Cp/Cpk or Pp/Ppk indices calculation point of view, there is no change comparing to process capability.   more...

Problem Solving

Which problem solving methodology is more effective: 8D or DMAIC?
Clear answer is impossible, because there is no radical difference between them. But we can recommend:    more... 

FMEA

Our customer reclaimed, that in our Process FMEA, no actions have been taken for failure modes with RPN more than 100. Why just that RPN value?
In our opinion, there is no reason to identify just this RPN value as a threshold.  more ...

If we deal with probability of occurence and probability of detection, should we refer to failure or to failure cause?
Concluding from our practice with various FMEA development in various segments of design or processes, we can offer following pragmatical and sufficiently clear definitions:   more...