Automotive Case Studies

I was sitting in a conference room in Toledo staring at a containment spreadsheet growing by the hour. We were a Tier 1 automotive powertrain supplier and our customer had flagged a porosity defect in a transmission housing casting. Initial PPM was 450. After sorting three warehouses and two distribution centers we had over 12,000 defective parts in the supply chain. Under 20x magnification the defect showed interconnected voids roughly 0.3 mm deep near a sealing face. The leak test caught 70 percent but 30 percent passed QC and failed only after assembly. That triggered an IATF 16949 audit — detection system failure plus process stability failure. Our D1 war room included process engineering, metallurgy, the casting supplier, and the customer SQE. D2 traced every suspect part to mold cavities, shot numbers, and melt batches. Is/Is-Not analysis was crucial: porosity appeared only in cavities 3 and 7, on the evening shift, when the melt furnace held for more than four hours. D4 found the immediate cause was dissolved hydrogen during extended holding, but the deeper cause was that cavities 3 and 7 were at the end of the ladle pour path where temperature dropped below the degassing threshold of 720...