ISO 20457

Meaning

International standard guidelines define the dimensional tolerances and acceptable variances for plastic parts produced by injection moulding. Applying ISO 20457 allows designers and toolmakers to agree on realistic dimensional boundaries based on polymer shrinkage behavior. This framework ensures that parts remain functional without imposing unnecessary tooling costs.

Tolerance Class

Material groups are categorised by their typical moulding shrinkage rates into different precision levels. Specifications using ISO 20457 adjust tolerances according to the size of the part and the inherent stability of the resin. Amorphous resins allow tighter tolerances than semi-crystalline types.

Moulding Accuracy

Actual dimensions of moulded parts are affected by processing variables like pack pressure and cavity temperature. Although ISO 20457 establishes the baseline for acceptable production deviation, the moulder must maintain tight control over the process to meet these limits. Drift in melt temperature causes dimensions to change.

Quality Inspection

Verification of dimensions must be performed under standard laboratory conditions of temperature and relative humidity to ensure consistency. Molded polymers continue to shrink for up to forty-eight hours after ejection, meaning that measurement timing is critical for compliance. Standardizing the testing protocol prevents disputes between the moulder and the customer regarding whether the parts conform to the drawings.

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