Statistical Process Control
DAVCO indicates some characteristics on engineering drawings with a diamond shaped symbol (◊) indicating that the specified feature is critical to the form, fit or function of our product. These characteristics require special treatment as you develop your process controls. As a minimum, characteristics so marked must be treated as follows:
- Statistical data consisting of no less than 30 samples from a production run of no less than 300 pieces must be included with your PPAP submission.
- The control chart must show that the feature is in statistical control
- A minimum PPK of 1.33 must be achieved
- On-going SPC is strongly recommended. If SPC is not used, a suitable alternative should be indicated in the control plan. Typically, alternative methods would include increased sampling frequency using a statistically derived sample size.
NOTE: There may be limited cases where the above is not feasible. Please contact DAVCO’s Quality Department if you believe this may be the case.
If a critical characteristic cannot achieve statistical control and/or a PPK of 1.33 you must include 100% inspection of this characteristic in your process controls. Acceptability may be determined by DAVCO.
Measurement System Analysis
Any gauge used to determine conformance to DAVCO’s specifications must:
- Be calibrated (with the calibration standard traceable to NIST or another appropriate standards body)
- Have the measurement uncertainty determined at a sensible frequency.