Meaning
Industrial guidelines for plastic mouldings establish the permissible dimensional variations based on the material properties and manufacturing conditions. Utilizing standard din 16742 allows designers and moulders to agree on realistic tolerances for injection moulded parts. This standard replaces older, generic tolerance systems that did not account for polymer-specific shrinkage.
Tolerance Application
Dimensioning plastic parts requires separating the tolerance into tooling-related and process-related components. Under standard din 16742, tolerances are assigned based on whether a dimension is formed by a single tool part or across moving tool splits. This division ensures that toolmaker tolerances and moulding process variations are calculated separately, which prevents the process window from being compressed to an impossible degree.
Material Classification
Thermoplastic and thermoset materials are grouped into different evaluation categories depending on their inherent shrinkage behavior. Applying standard din 16742 involves identifying whether a resin is low-shrinkage, such as polycarbonate, or high-shrinkage, such as polyethylene. This classification determines the achievable tolerance class for a given part dimension.
Moulding Variation
Real-world production conditions often lead to minor shifts in part dimensions due to polymer batch changes and thermal drift. The guidelines in standard din 16742 provide a structured framework to determine if a dimension remains within acceptable limits. This framework protects the moulder from unreasonable quality disputes.
