Meaning
Dimensional tolerancing of molded plastic parts requires a standardized framework that accounts for the inherent shrinkage of polymer materials. The application of DIN 16742 precision defines the allowable dimensional variations for injection-molded components across different resin groups and manufacturing conditions. It specifies the achievable tolerances based on the mold construction and the specific polymer used, ensuring that both designers and molders work to realistic dimensional limits.
Tolerance Class
Material selection dictates the shrinkage behavior and the difficulty of holding tight tolerances. High-precision parts molded from amorphous resins utilize the DIN 16742 precision classes to establish boundaries that are technically feasible during continuous production runs. This framework avoids the specification of unachievable tolerances that drive up production costs through high rejection rates.
Manufacturing Constraint
Moulders face challenges when attempting to meet tight specifications with semi-crystalline polymers like polyamide or polypropylene. The DIN 16742 precision standard categorizes these resins into groups with high shrinkage rates, making it clear that different manufacturing parameters must be controlled to achieve the desired fit. This prevents costly mold modifications after the first trial.
Economic Value
Over-specifying tolerances leads to excessive rework and increased inspection times. Aligning part drawings with this standard ensures that the molding process remains economical while meeting assembly requirements. This establishes a clear agreement between the purchaser and the molder.
