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The standard classifies manufacturing accuracy into . Each group represents a specific balance between the complexity of the production process and the inherent properties of the plastic material. Tolerance Group Accuracy Classification Typical Application Examples TG1 to TG3 Extreme Precision Micro-optics, medical devices, ultra-tight aerospace gears. TG4 High Precision
Unlike metal parts machined to standard linear profiles, plastics exhibit unpredictable shrinkage, moisture absorption, and thermal expansion. Officially titled "Plastics moulded parts — Tolerances and acceptance conditions," harmonizes these nuances. It handles dimensions across multiple molding processes, including injection molding, compression molding, transfer molding, and rotational molding. Core Engineering Principles Covered:
China’s GB/T 14486 aligns closely with ISO 20457. The Chinese standard uses a similar approach with material shrinkage categories (MT1 through MT7) and tolerance grades A (precision), B (standard), and C (coarse). This alignment facilitates international trade and ensures that parts designed to ISO 20457 can be manufactured in China using the GB/T 14486 framework. iso 20457 tolerance table pdf
To use the ISO 20457 system effectively, engineers typically follow these steps:
Ranges (e.g., 0-30 mm, 30-100 mm) determine the base allowance.
The standard helps engineers move away from arbitrary "general tolerances" (like ±0.1mm across the board) and instead use scientifically backed limits based on material properties and manufacturing capabilities. Key Factors Determining Plastic Tolerances This public link is valid for 7 days
For flatness, ISO 20457 provides standard tolerances based on overall part dimensions:
| Nominal Wall Thickness ($e_n$) (mm) | Tolerance (mm) | | :--- | :--- | | $3.0 < e_n \le 4.0$ | $\pm 0.5$ | | $4.0 < e_n \le 5.0$ | $\pm 0.6$ | | $5.0 < e_n \le 6.0$ | $\pm 0.7$ | | $6.0 < e_n \le 7.0$ | $\pm 0.8$ |
Clear reference points to ensure repeatable results. Why ISO 20457 vs. ISO 2768? Can’t copy the link right now
: Used for non-critical, general-purpose applications where loose tolerances are acceptable. How to Use the Tolerance Tables
Clearly separate Series NW and Series W dimensions on your prints so quality control teams inspect the parts using the correct reference values.