r-value & n-value: Sheet Metal Science
r 值与 n 值：深冲材料科学速成
标签：r值, n值, 加工硬化, 塑性应变比, 拉伸试验
深冲性能两个量化指标：r 值（塑性应变比，ASTM E517 拉伸试验测宽向/厚向应变比）越大越抗变薄，紫铜 r ≥0.9、无氧铜可达 1.1，极限拉深比可提到 2.0；n 值（加工硬化指数，按 Hollomon σ=Kεⁿ 拟合）越大应变越易均匀分散，铜合金 n 为 0.3–0.5，半硬态 H65 的 n 偏低拉深必裂。采购时向铜带厂索取 0°/45°/90° 三方向实测单，Δr=(r0+r90−2r45)/2 用于评估制耳。退火制度（450–550 °C 保温 1–2 h）直接重塑这两项指标，是拉深工艺窗口的根。
Two numbers govern drawability: r (plastic strain ratio per ASTM E517, width/thickness strain in tension) — higher resists thinning; copper sits at r ≥0.9 and oxygen-free grades reach 1.1, lifting the limiting draw ratio toward 2.0. n (work-hardening exponent from Hollomon σ=Kεⁿ) spreads strain evenly; copper alloys run n = 0.3–0.5, and half-hard H65 with low n tears. Ask the mill for 0°/45°/90° test data and compute Δr=(r0+r90−2r45)/2 for earing risk. Annealing (450–550 °C, 1–2 h) resets both — it is the root of your process window.