Does the type of out control point indicate root cause?
I thought that the “limits” on a control chart were calculated directly from the data and indicated how the process should perform under normal circumstances subject only to its inherent randomness and that the limits said nothing about whether or not the product was “acceptable” to the customer. In answer to your question. We do have specifications and any drum produced outside those specifications is scraped. The cpk using these specifications (Ppk as Minitab reports it is on the order of 0.75, Cpk as Minitab reports is ~1.8) is acceptable (?), and the control charts tend to indicate the process is out of control, many points outside the 3 sigma limit and I have not even tried to look at the other tests for control. The problem is that while we currently produce material to SPEC the material is used in another process in house. This secondary process produces the finished product and is having significant quality issues. They indicate that the issue is the “variability” of the materi
