Stable and capable processes (CPk > 1.33) are essential for achieving TG5. Measurement conditions are critical: dimensions must be measured after conditioning (e.g., 24-48 hours at 23°C) to allow for post-mold shrinkage stabilization. The environment must be controlled (50% ±10% RH) as hygroscopic materials like Nylon change size with humidity.
The table below highlights the key distinctions between the old and new standards:
Variations in thickness cause uneven cooling, leading to internal stresses and warpage that break TG5 limits. Use coring or ribs to reduce thick sections. Draft Angles and Ejection Incorporate generous draft angles (typically 1∘1 raised to the composed with power 2∘2 raised to the composed with power Iso 20457 Tg5
The reference ISO 20457 TG5 relates to specific dimensional tolerances for plastic injection molded parts
The full text of (Plastics moulded parts — Tolerances and acceptance conditions) is a copyright-protected document and is not available for free legally online. However, it can be purchased from authorized standards organizations or viewed through specific preview tools. Where to Access the Full Paper Stable and capable processes (CPk > 1
Design plays a crucial role. Mold-fixed dimensions (features from the same mold half) generally have tighter tolerances than non-mold-fixed dimensions (determined by moving mold elements). Features like wall thickness, snap-fit clearances, and sealing surfaces all have different capability ranges. For multi-cavity molds, cavity-to-cavity variation can consume up to 30-50% of the tolerance band, requiring careful mold balancing.
Under the ISO 20457 framework, the permissible deviations scale proportionally with the nominal size of the part. For geometric features like flatness and straightness, TG5 enforces standard operational bands: Part / Feature Length (Nominal Size) TG5 Flatness & Straightness Tolerance Typical Applications ± 0.30 mm to ± 0.45 mm Snap-fit battery covers, small gear housings Medium (50 mm to 150 mm) ± 0.50 mm to ± 0.75 mm Consumer electronic enclosures, toy chassis Long (150 mm to 400 mm+) ± 0.80 mm to ± 1.50 mm Storage bins, appliance panels, shipping crates 2. Tool-Specific vs. Non-Tool-Specific Dimensions The table below highlights the key distinctions between
D1 & D2 & D3 --> G[Accept final tolerance group<br>based on material & shrinkage] F --> G
ISO 20457 specifies possible manufacturing tolerances for plastic molded parts produced through processes like injection molding, extrusion, or thermoforming. It provides a framework for defining general tolerances for integral features and surface profiles within a specified datum system. The standard replaced the older German standard DIN 16742 and is now the international benchmark for plastic part tolerancing.