My company use's the process in from the injection molding machines to control the quality of the parts being made. During the new mold samples the process parameters are saved using the machine SPC. The SPC data is then used to come up with control plan limits. My problem with this is that we are using Ppk calulations during this process to justifiy that our limits are right. I say this is wrong becuase there are no USL/LSL for the process to calualte the Ppk against. I'm I right?