The ISO 20457 standard, which replaces the older DIN 16742, is the primary international guideline for determining tolerances of plastic molded parts. Unlike metal components, plastic parts undergo significant shrinkage and environmental changes, making standard rigid-body tolerance chains (like ISO 286) often unsuitable. Core Tolerance System (Tolerance Groups)
ISO 20457 uses Tolerance Groups (TG) to define the achievable accuracy based on the manufacturing process and material properties.
TG6 (Standard Baseline): The most common tolerance group for standard industrial injection molding.
TG4 (High Precision): Used for Critical-to-Quality (CTQ) dimensions, such as snap-fits or bearing housings, though it requires more expensive tooling and process control.
General Tolerances: If no individual tolerance is specified on a drawing, the standard applies "general tolerances" based on the selected TG to ensure all features are controlled. Factors Affecting Tolerance Selection
To develop a piece or select the correct table value, you must consider:
ISO 20457:2018 is the primary international standard for determining manufacturing tolerances and acceptance conditions for non-porous plastic molded parts. It replaces the older DIN 16742 standard and provides a systematic way to calculate achievable tolerances based on material properties and manufacturing processes. Unlike metal machining standards, ISO 20457 accounts for the unique behavior of plastics, such as mold shrinkage and environmental sensitivity. Key Components of ISO 20457
The standard uses a tiered system to assign tolerance groups (TG) based on the material's complexity and the required precision:
(and its German equivalent DIN ISO 20457 ) is the primary international standard for specifying manufacturing tolerances of plastic molded parts
. It replaces the withdrawn DIN 16901 and DIN 16742 standards, providing a modern framework based on Tolerance Groups (TG) rather than generic fixed values. Key Tolerance Classifications organizes tolerances into Tolerance Groups (TG)
ranging from TG1 to TG10. These groups are further divided into based on production effort: Series 1 (Standard Production):
General tolerances used when dimensional requirements are not the primary quality focus. Series 2 (Accurate Production):
Oriented toward higher dimensional accuracy, requiring more rigorous manufacturing and quality assurance. Series 3 (Precision Production):
For parts requiring extremely tight tolerances, often involving higher production costs and surcharges. Achievable General Tolerances
While exact values depend on material groups (shrinkage rates) and nominal dimensions, typical baseline performance for injection molding includes: Super-Ingenuity Standard Features: plus or minus 0.05 plus or minus 0.15 mm for small to medium parts. Critical Features: plus or minus 0.025
mm, but only for specifically designated critical-to-quality (CTQ) features. Large Parts: iso 20457 tolerance table pdf
Wider tolerance bands are required due to potential warpage and shrinkage variations. Comparison with ISO 286 The standard correlates its Tolerance Groups (TG) International Tolerance (IT) grades defined in
Lower TG numbers (e.g., TG1–TG4) represent high-precision requirements.
Higher TG numbers (e.g., TG6–TG9) represent lower precision, standard industrial production. OKW Gehäusesysteme Necessary Callout Information
To properly use an ISO 20457 tolerance table, design documentation must specify:
The Tolcap Rough Guide to Tolerancing Plastic Mouldings - Tol
Here’s a clear, professional write-up on ISO 20457 and its tolerance tables, suitable for inclusion in a technical document, training material, or engineering summary.
Let’s walk through a real-world example to solidify your understanding of the ISO 20457 tolerance table PDF.
Scenario: A company is designing a mounting bracket for an electric motor. The bracket is a sheet metal part (2mm thick, 200mm long). The motor has a shaft that aligns to a hole.
Result: The machinist reads the PDF, applies the correct deviations, and the bracket is cheap to produce (not over-toleranced) but still fits the motor.
A search for "iso 20457 tolerance table pdf" will lead you to sketchy third-party websites offering free downloads. Proceed with caution. Here is why:
On your 2D drawing (PDF or CAD), add a general note: “All dimensions subject to ISO 20457:2020, tolerance grade PT3, Category A unless otherwise stated. Parting line dimensions subject to Category B multiplier.”
For critical features, apply an individual tolerance using the table’s specific value.
ISO 20457 is a critical reference for the pump industry, bridging the gap between design theory and physical reality. The tolerance tables contained within the standard are essential tools for ensuring the reliability, efficiency, and safety of pumping systems. While accessing the official PDF requires adherence to copyright protocols, the value it provides in reducing downtime and ensuring part compatibility is an investment that pays for itself in operational efficiency.
ISO 20457 (and its German equivalent DIN 16742) is the definitive global standard for manufacturing tolerances and acceptance conditions of plastic molded parts
. It replaced older standards like ISO 8062 to better account for the unique properties of plastics—such as shrinkage and thermal expansion—which differ significantly from metals. www.makrolar.eu Core Function of ISO 20457 The ISO 20457 standard, which replaces the older
The standard provides a systematic way to determine achievable tolerances based on the combination of material properties, molding processes, and part geometry. It primarily covers: Dimensional Tolerances : General tolerances for linear and angular dimensions. Geometrical Tolerances : Surface profile and position deviations. Acceptance Conditions : Specific environment requirements, such as measuring at 23 raised to the composed with power cap C 50% relative humidity , to ensure consistency across different facilities. ISO - International Organization for Standardization Tolerance Groups (TG) Breakdown The ISO 20457 tolerance table is organized into Tolerance Groups (TG) , typically ranging from TG1 to TG9 . These groups correlate to the ISO 286 IT grades used in metal machining. ResearchGate ISO 20457:2018(en), Plastics moulded parts
The ISO 20457 standard (which succeeded DIN 16742) provides a standardized framework for tolerances and acceptance conditions for plastic molded parts. It defines tolerance groups (TG) ranging from TG1 to TG9, where lower numbers indicate higher precision. For many standard industrial thermoplastics, TG6 is the commonly used baseline for general tolerances. Key Tolerance Tables and Documents
Because ISO 20457 is a copyrighted standard, full official tables are typically accessed through authorized distributors or summarized by manufacturers. You can find detailed overviews and downloadable PDF guides at the following sources:
PolTolerances Guide (Makrolar): A comprehensive 28-page PDF that includes detailed tolerance tables, explanations of dimensional deviations, and the relationship between ISO 20457 and DIN 16742.
OKW Gehäusesysteme Tolerance Overview: Provides a concise technical data sheet focusing on TG6 tolerances for various nominal dimensions.
ISO Official Store: The definitive source to purchase and download the official ISO 20457:2018 PDF for full compliance.
Super Ingenuity Template Library: Offers downloadable quality and tolerance templates, including Excel-based CTQ (Critical to Quality) feature tables and 2D note blocks for ISO 20457-TG6. Understanding the Tolerance Groups (TG)
The tolerance applied to a part depends on both the chosen Tolerance Group and the Nominal Dimension (the size of the feature). Nominal Dimension (mm) TG4 (High Precision) TG6 (Standard/Technical) TG8 (General Purpose) > 10 to 18 > 18 to 30
Note: These values are typical approximations for linear dimensions; refer to the official standard for the full matrix covering all dimensions and specific material groups. Selection Process
ISO 20457 (and its German equivalent DIN 16742) is the international standard for dimensional and geometrical tolerances of plastic molded parts. It replaces older standards like DIN 16901 to provide a more consistent framework for injection molding and related processes. Key Tolerance Tables & TG Groups
The standard classifies tolerances into Tolerance Groups (TG), typically ranging from TG1 to TG9. TG6 is the most common baseline for commercial plastic parts. Nominal Dimension (mm) TG4 (Precision) TG6 (General) TG8 (Coarse)
Values are approximate based on standard industry applications of ISO 20457/DIN 16742. How to Choose a Tolerance Group
Choosing the right TG depends on the material's shrinkage behavior and the part's functional requirements.
Material Family: Amorphous resins (e.g., ABS, PC) have lower shrinkage and can often achieve TG4 or TG5. Semi-crystalline resins (e.g., PA66, POM) have higher shrinkage and usually require TG6 or higher.
Production Difficulty: Tighter groups (TG1–TG3) are rarely used as they significantly increase mold costs and scrap rates. Hole for shaft bearing: Requires tight fit
Baseline Standard: Most engineering components default to TG6 unless specified otherwise for critical fitments like snap-fits. PDF Resources & Technical Guides
You can access detailed guides and full tolerance tables through these technical document repositories:
PolTolerances Guide: A detailed 4-page overview of ISO 20457 and DIN 16742 including classification tables.
Standard Preview: An official abstract and sample pages of the ISO 20457:2018 Standard.
Engineering Guidelines: Practical application guides from manufacturers like OKW Gehäusesysteme showing how they apply TG6 to their thermoplastic products. PolTolerances en ISO-20457 (DIN 16742) - Scribd
The ISO 20457 standard (formerly DIN 16742) defines the manufacturing tolerances and acceptance conditions for plastic molded parts. It is primarily used to align expectations between designers and manufacturers regarding dimensional accuracy in injection molding and other plastic processes. Key Tolerance Group: TG6
For general thermoplastics, the standard typically defaults to Tolerance Group 6 (TG6) unless otherwise specified.
Application: General tolerances (Series 1) apply to explicitly drawn dimensions that lack individual tolerance indications.
Typical Note: Engineering drawings often include the note: General tolerances ISO 20457 – TG6. ISO 20457 Tolerance Table Overview
The standard uses two main tables to determine the applicable tolerance: INTERNATIONAL STANDARD ISO 20457
Scenario: You have a PE100 pipe with a nominal OD of 110mm. Look up in ISO 20457:
Result:
*This paper is a technical summary for educational purposes. For manufacturing, quality control, or legal compliance, you must purchase and reference the official, current version of the ISO 20457 standard document directly from
Do not default to PT1. Interview your injection moulder first. Ask:
Most moulders can reliably hold PT2 for well-designed tools and stable materials. PT1 is only achievable with automated cells, hot runners, and 100% inspection.