Sample Sufficiency Criteria

Evaluation Scope and Metrological Standards

Statistical process control in small-batch additive manufacturing requires reliable sample sufficiency criteria. Testing every single component from a multi-part print run quickly inflates inspection labor, while examining only one or two specimens leaves significant blind spots regarding spatial variances across the build plate. A calculated sample size provides actionable statistical confidence without overburdening inspection cycles.

When evaluating batch production runs across multi-head or high-speed polymer printers, random variations in ambient chamber heat and localized airflow create non-uniform shrink rates. Establishing clear sample size threshold criteria ensures metrologists capture both within-build and run-to-run drift before serial components advance to functional assembly.

Process Variation Breakdown

Variations between center-nest and perimeter-nest parts often demand stratified sampling rather than pure random selection. The following criteria benchmark minimum inspection envelopes for serial runs:

• Establish minimum sample threshold of N ≥ 5 per build plate quadrant to catch localized cooling gradient variations.
• Verify normality and dispersion using standard deviation (s) thresholds against ISO 2768-m linear tolerances.
• Target a minimum process capability index (Cpk) of 1.33 across sampled lots to prevent downstream assembly clearance failures.