Cp – Process Capability Index

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    When you look into the process capability, Cp, and using USL and LSL what happens wher there are no upper and lower speicification limits.


    Ken Feldman

    By definition, Cp and all capability indices are designed to compare the voice of the process with the voice of the customer, that is specs. If you don’t have specs, what is your intention of looking at process capability?????



    There are many instances where customer specs may not exist, for example early in a process where the results are not easily translated into a customer impact.  For example, in electronic circuit production there are dozens are early steps used to set the base silicon properties which are very difficult to relate to final customer related outputs.
    In these situations the primary focus should be on stability of the process by establishing control limits, and the removal of any assignable causes of variation.   What needs to be considered is how much resource to allocate to processes which may have such indirect association to final customer specs.   
    It is also a possibility to create internal specs as there are some limits to what can be considered good product.  These can be used to develop Cpk indices for internal consideration and prioritization of work.

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