This article explains why the theoretical production quantity in sand casting never matches the actual output and how this gap distorts defect rates, cost accounting, and production control. It introduces a practical method to determine true production quantity by measuring casting weight after shot blasting and linking it with batch IDs, enabling accurate, real‑time data for factory operations.

Many factories visualize defect data, yet the numbers often don’t make sense. In several plants I supported, the same production batch showed different defect rates depending on the inspector—2% by an expert versus 8% by others. The issue wasn’t product quality but human behavior shaped by inadequate KPIs. When inspectors are evaluated by “how many items they check,” speed is prioritized, judgment becomes inconsistent, and defect data becomes unreliable. This leads not only t