I am a BB in a reman plant for a major diesel engine manufacturer and I understand what you are asking. At a remanufacturing location, you are inspecting cores that have been returned to your facility and as long as the feature being measured falls within an acceptable specification range the part is deemed good. For example, we resurface cylinder heads at our facility. When we receive the head cores, the thickness is generally at the nominal specification. After resurfacing, the thickness of most of the cores is less than nominal but still within specification. In addition, some cores will fall out as scrap because too much material must be taken off to remove surface damage. If a CpK study was done on this particular feature, the results would be much less than 1.33; however, the process is not a “broken” process. We do perform CpK studies on features such as surface finish, valve guide bore diameters, valve seat insert diameters, etc. As a general rule of thumb, if you are targeting a particular specification value, a CpK study is probably applicable. If you are performing a machining process and merely hoping that the finished product falls somewhere in between specifications when the damage is removed, CpK is probably not applicable. Cpk is also useful for monitoring process parameters such as wash solution temperature, chemical concentration, coolant concentration, etc. I’ve found that in a reman. plant the most important aspects of any process are the gage R&R (if gages are being used) and the attribute R&R (if visual inspection is employed). It is gaging capability that determines if you’re making alpha or beta inspection errors and possibly passing on defects to your customers.
.
