Fehlruns

Fehlruns, or misruns, are a defect in casting and molding processes in which molten material fails to completely fill the mold cavity, producing an underfilled or incomplete part. The term is used in plastics injection molding, metal casting, and related processes; the resulting piece may be called a short shot.

Common causes include high material viscosity, insufficient processing temperatures, low injection or packing pressures, and short fill times that prevent complete filling. Poor gate or runner design, which restricts flow, also contributes. Mold design and geometry matter as well: thick sections, internal features with limited flow, poor venting, air traps, and inadequate mold temperature can hinder full fill.

Detection and assessment rely on visual inspection and dimensional checks; non-destructive testing such as X-ray or CT imaging, along with end-of-fill indicators, helps identify underfilled areas.

Prevention involves process optimization: increasing melt temperature or reducing viscosity, adjusting injection speed and pressure, extending hold or packing time, and improving venting and gate design. Material preparation and selection are also important; drying plastics, choosing lower-viscosity grades, or using additives can improve flow.

Design changes to part geometry can reduce Fehlruns, including reducing extreme thickness variations, relocating or adding gates, and optimizing runners. In manufacturing quality control, Fehlruns lead to rejects or require secondary operations, increasing lead time and cost. Overall, managing material behavior, tooling, and part design is essential to minimize these defects.