Din 16742 - Tg5 New! File

The feature regarding DIN 16742 TG5 refers specifically to the tolerance grade for thermoplastics injection molded parts.

Here is the precise technical feature of TG5 within the standard:

1. Material Selection

While TG1 or TG2 might be used for stable engineering plastics like ABS or Polycarbonate (PC), TG5 is frequently applied to:

• Semi-crystalline Thermoplastics: Materials like Polyethylene (PE), Polypropylene (PP), or Polyamide (PA/Nylon) often exhibit variable shrinkage, making tighter groups difficult to maintain without high costs.
• Elastomers (Rubber): Flexible materials often fall into higher tolerance groups due to the difficulty of measuring rigid dimensions on a soft substrate.
• Large Parts: As part size increases, the absolute shrinkage increases. For large polymeric components, TG5 is often the standard "precision" benchmark because maintaining TG2 across a large surface area is physically impractical.

What is TG5?

TG5 stands for Tolerance Group 5. The tolerance groups in DIN 16742 are generally arranged by precision level: din 16742 - tg5

• TG1: Highest precision (tightest tolerances). Typically used for precision technical parts or specific amorphous thermoplastics.
• TG2: Standard precision.
• TG3 & TG4: Moderate precision.
• TG5: Reduced precision / Large tolerances.

Is TG5 Right for Your Project? A Decision Matrix

| If your part requires... | TG5 Recommended? | | :--- | :--- | | Sliding fit with metal shaft | Yes | | Ultrasonic welding alignment | Yes | | Living hinge geometry | No (Use TG3 – residual stress affects hinge) | | Overmolding with silicone | Yes (for shut-off surfaces) | | Large part > 300 mm | No (Use TG3/TG4 – warp dominates) | | High-volume consumer goods (>1M parts) | Yes (tool amortization justifies precision) |

9. When NOT to Use TG5

Avoid TG5 if:

• Press-fit or snap-fit with tight functional clearance (< 0.1 mm total).
• Bearing journals or guide rails requiring consistent clearance.
• Parts mate with metal components without adjustment.
• Temperature changes > 30°C affect critical fits (then tighter or selective assembly needed).

In those cases, specify TG3 or TG4, or add individual tolerances on drawings. The feature regarding DIN 16742 TG5 refers specifically

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Summary Table: TG5 vs TG4 (Fine)

| Feature | TG4 (Fine) | TG5 (Very Fine / Precision) | | :--- | :--- | :--- | | Relative stringency | Standard precision | High precision | | Mold cost | Moderate | High (requires hardened steel, 3+ slides) | | Typical application | Snap-fits, enclosures | Gears, bearings, optical housings | | Process window | Wide | Very narrow (requires dry resin, controlled environment) |

1. What is DIN 16742?

DIN 16742 is the German standard for Tolerances for injection-molded plastic parts. It replaced older standards like DIN 16901. It provides a systematic way to define allowable deviations in dimensions, geometry, and surface for thermoplastics, thermosets, and elastomers.

The standard defines several tolerance groups (TG) – from TG1 (very fine/precision) to TG7 (very coarse). What is TG5

TG5 sits in the middle, representing normal industrial precision for injection molding without special tooling or process controls. It is the most commonly specified tolerance grade for functional plastic parts.

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7. Comparison of TG Levels

| TG level | Typical use | Relative cost | Mold precision needed | |----------|-------------|---------------|------------------------| | TG1–TG2 | Medical, optical, micro parts | Very high | Precision tooling, hard steel | | TG3–TG4 | Precision fits, moving parts | High | Good toolmaking | | TG5 | General mechanical parts | Standard | Standard CNC mold | | TG6–TG7 | Non-critical covers, spacers | Low | Less precise mold |

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