Tolerance Grades a Toolroom Signs under DIN 16742
DIN 16742 defines nine tolerance grades based on resin shrinkage variance, requiring toolmakers to split tool-bound and parting-line tolerances during sign-off.
First Article Inspection FAI
Meaning
Production quality validation protocols establish formal physical and dimensional verification of the initial parts produced from a new or modified injection mold. Performing a first article inspection fai verifies that tool geometry and raw material specifications consistently produce compliant parts before mass manufacturing begins. Quality engineers measure all drawing dimensions, evaluate surface finish, and verify resin density against approved datasheets.
Failing this check halts tool release and requires mold modifications or process adjustments.
Dimensional Verification
Full inspection layouts verify every dimension indicated on part engineering prints using coordinate measuring machinery or optical gauges. Executing a first article inspection fai identifies out-of-tolerance features caused by unpredicted resin shrinkage or steel machining errors. Toolmakers use these dimensional reports to modify core pins, cavity walls, or gate locations through steel-safe grinding or EDM operations.
Process conditions must remain frozen during sample production to ensure representative measurements.
Material Qualification
Resin verification requires laboratory testing of molded samples to confirm material composition and mechanical performance. Performing a first article inspection fai includes melt flow rate testing, tensile testing, and differential scanning calorimetry to verify resin integrity post-processing. Thermal degradation during plastication reduces molecular weight and compromises impact strength.
Comparison between virgin resin datasheets and molded sample properties confirms processing suitability.
Production Approval
Customer sign-off depends on full approval of physical samples alongside complete inspection documentation. Successfully completing a first article inspection fai unlocks commercial production and establishes the baseline process capability metrics for future quality audits. Tool modifications or resin supplier changes require repeat inspection protocols.
Mold approval remains bound to the validated process window.