To consistently achieve TG5 tolerances, injection molders must use high-quality tooling and exercise steady control over the injection molding process. The Tolerance Hierarchy (TG1 – TG7)
: Selecting TG5 is often a strategic choice to balance quality and cost. Striving for tighter grades (like TG4 or TG3) significantly increases the cost of tools and quality assurance. Comparison of Tolerance Groups Accuracy Level Typical Examples TG3 Medical devices, aerospace components TG4 Automotive interiors, electronics TG5 General/Standard Toys, household housings, packaging TG6 Large shipping containers, basic structural parts
Applications and Performance Considerations TG5 is intended for components subjected to cyclic loading, abrasive contact, or elevated service stress—examples include gears, shafts, bearings, forging dies, and wear-critical tooling. Designers choose TG5 where resistance to surface wear must be paired with sufficient core toughness to resist crack initiation and propagation. In applications where corrosion resistance is a factor, TG5 may require surface treatments, coatings, or selection of an alternate stainless grade.
ISO 20457:2018 (which replaced DIN 16742) provides a standardized framework for specifying geometrical and dimensional tolerances based on the specific behavior of polymers, such as and post-production changes. Within this framework, TG5 represents the following: Precision Level: Standard precision applications.
The standard achieves its predictability through a logical, step-by-step methodology. Instead of relying solely on material lists or basic dimension ranges, ISO 20457 introduces a five-factor scoring system (P1 to P5) to determine the correct tolerance grade. These factors include the molding process, material stiffness, shrinkage rate, shrinkage anisotropy, and the intended production effort. This systematic approach avoids the ambiguity of older standards, making tolerance negotiation and part definition more quantifiable and reliable. Iso 20457 Tg5
: Coarse to very coarse (e.g., packaging or parts with high, unpredictable shrinkage). Key Components of an ISO 20457 Callout
| Feature | DIN 16742 (Old) | DIN ISO 20457 (New) | | :--- | :--- | :--- | | | Primarily a national German standard | An international ISO standard adopted in Germany and elsewhere | | Material Focus | Standard and reinforced thermoplastics | Broadened to include thermoplastics, elastomers, and thermosets| | Processes | Primarily injection molding | Expands to compression molding, transfer molding, and rotational molding| | Tolerance Group (TG) for Injection Molding | TG 1 to TG 11 | Now TG 3 to TG 9, aligning with the new, broader material and process scope |
This taxonomy enables three critical market functions:
For years, the plastics industry suffered from a "Tower of Babel" problem. A recycler in Germany and a compounder in Japan might use the same test method for a glass-fiber reinforced polypropylene, but with slight variations in temperature, sample preparation, or conditioning. The result was inconsistent data, leading to product failures and supply chain mistrust. ISO 20457:2018 (which replaced DIN 16742) provides a
ISO 20457:2018 ("Plastics — Tolerances for moulded components") is the international standard that superseded the old German DIN 16901 standard. It was designed to provide a more modern, globally applicable framework for defining acceptable dimensional deviations for plastic molded parts.
Toolmakers must use high-grade steel, incorporate precise cooling channels, and often leave "steel-safe" margins for iterative adjustments after first-article inspections.
Represents custom or fine manufacturing tolerances . It is the bridge between standard industrial molding and highly critical precision engineering.
Housings for medical instruments and syringes. Without TG5 compliance
: TG5 typically represents a "standard" or "simple" production level for certain materials like ABS .
By staying up-to-date with the latest developments in standards and test methods, manufacturers, researchers, and regulatory bodies can ensure that plastic materials meet the demands of a rapidly changing world.
Without TG5 compliance, a recycled plastic is technically "un-verifiable" for high-performance use.