Manufacturing & Quality>Initial process studies / process capability plan
Initial process studies / process capability plan
Significant & Critical Features are part characteristics that significantly affect performance, fit, function or workability on the completed units, and therefore require application of statistical measures for capability assessment and control. The purpose of such studies is to gain confidence in the production process withpotential to produce products that will meet the customer requirements and result in customer satisfaction.

Short Term CPK Long Term PPK
Sample Size 100 (30 minimum) ≥50 or as required to determinevariability source
Expectation Variable Data ≥1.67, Stable ≥1.33, Stable
If expectation is not met 1.P rocess control method is required (ie: increased audit, SPC,100% inspection, etc.)
2. Inspect 100% since the last in-control point and implement corrective action. Notify if parts escaped and begin containment activity.

The Ppk study should be based on 100 (minimum 30) consecutively. For all Significant and Critical characteristics, the concerned processes should be stable and under statistical control with preliminary process capability index (PPK) above 1.67 in production trial run & on-going process capability index (CPk) above 1.33 in regular production.

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