Thresholds used: steel window — tensile strength below 800 N/mm² and elongation at fracture above 14% (peer-reviewed review of clinching for sheet materials, He 2017). Geometry — individual sheets 0.1 to 3 mm, two-to-four-layer stacks 0.2 to 13 mm, best behavior at 1 to 4 mm total, matched punch and die diameters 1.5 to 12 mm (ASSEMBLY Magazine, 2016). Brittle sheet is excluded because clinching is a cold-forming process.