DIN 16742 is the central German standard for determining plastic part tolerances, and TG5 (Tolerance Group 5) is frequently cited as the baseline for "Standard Injection Molding". Understanding TG5 (Tolerance Group 5)

| Material group | Typical shrink range (%) | TG5 achievable? | |----------------------|--------------------------|------------------| | Amorphous (PS, PC) | 0.3 – 0.7 | Yes, easily | | Semi-crystalline (PA, POM) | 0.8 – 2.2 | Yes, if mold designed for nominal | | Filled (GF30, mineral) | 0.1 – 0.5 | Yes, better precision even at TG5 |

Shrinkage Allowance

The molder must design the steel mold to compensate for shrinkage. Under TG5, the allowed deviation from nominal shrinkage is tightly managed. For example, if the material datasheet says 0.5% shrinkage, the molder cannot let real shrinkage drift between 0.4% and 0.6%—TG5 forces a narrower band (e.g., 0.47%–0.53%).

5. Draft Angle Recommendations for TG5

While draft angles are not strictly a tolerance, they are critical for achieving TG5 reliably.

Pekago and other major manufacturers often list TG5 as their standard for high-quality injection molding. It provides a balance between functional accuracy and production cost. Key characteristics of TG5 include:

1. Optical comparators for contour (not calipers alone).
2. Surface profilometers for Rz values.
3. First article inspection (FAI) with 30+ consecutive parts from 4 cavities to measure capability.
4. Defect catalog: Air traps < 0.1 mm depth, no visible weld lines on functional surfaces.