Re: Tolerance for Cpk purposes
Bob, Thanks for your help and insight.
Our runs are 10k - 50k parts, so we don't run into a lot of tool wear issues. We will run into galling which requires a polish of the punch from time to time. We set the die using different punches (or slightly modifing the punch we have) in an attempt to account for the material variability. We look for that fine line where the punch and material react to get us as close to the nominal dimension as possible, and then we run. Even so, a tiny fluctuation in the material will cause a potential problem. For example, the material thickness changes .0005, well that is .001 on the part and you're using half your tolerance on that alone.
If you are doing drawn stamping, do you start with (for example) ID tooling large to allow the stamping die to wear to the small side, or is your material influence variation so large that it masks tool wear?
Our runs are 10k - 50k parts, so we don't run into a lot of tool wear issues. We will run into galling which requires a polish of the punch from time to time. We set the die using different punches (or slightly modifing the punch we have) in an attempt to account for the material variability. We look for that fine line where the punch and material react to get us as close to the nominal dimension as possible, and then we run. Even so, a tiny fluctuation in the material will cause a potential problem. For example, the material thickness changes .0005, well that is .001 on the part and you're using half your tolerance on that alone.