Progressive Stamping Dies, Sheet-Metal Blanking/Piercing & Turret Punching
Sheet-Metal Blanking Shear Force & Die Clearance Formula
Calculate Single-Side Punch-to-Die Radial Clearance c (mm), Flat-Punch Peak Shear Force F_shear (kN), Stripper-Plate Unloading Force F_strip (kN), and Total Stamping Press Force (kN).
Why punch-to-die clearance is specified PER SIDE—and forgetting stripper-plate spring tonnage stalls progressive dies!
Punching holes (piercing, where the slug is scrap and the punch sets hole diameter) or stamping outer contours (blanking, where the die cavity sets part size and clearance is subtracted from the punch!) shears metal along cut perimeter P (mm) through thickness T (mm) against Material Ultimate Shear Strength tau_u (~0.70–0.80 * UTS, MPa)! Two shop-floor mistakes ruin dies: (1) confusing Single-Side Radial Clearance c = T * (c_% / 100) mm (typically 5%–8% of T per side for mild steel, meaning Total Diametral Difference D_die - D_punch = 2 * c!) with diametral clearance, causing double-sheared burrs or galling; and (2) sizing the press solely for Peak Flat-Punch Shear Force F_shear = (P * T * tau_u) / 1,000 kN while ignoring Stripper-Plate Spring/Urethane Force F_strip = k_strip * F_shear (~5%–10% of shear force needed to strip elastic-springback stock off the retracting punch)!
Verify on a 320 mm Perimeter Progressive Stamping Station—Cut_Perimeter P = 320.0 mm (B2), Sheet_Thickness T = 2.50 mm (B3), Material_Shear_Strength tau_u = 340.0 MPa (B4), Per_Side_Clearance_Pct = 6.0% (B5), and Stripper_Force_Fraction = 0.08 (B6): Single-Side Radial Clearance equals 2.50 * 0.06 = 0.150 mm per side (0.300 mm total diametral allowance, E2), Peak Flat Shear Force hits (320 * 2.50 * 340) / 1,000 = 272.00 kN (E3), Stripper Unloading Force adds 21.76 kN (E4), and Total Press Station Force reaches 293.76 kN (~29.96 metric tons, E5)!
| Stamping Blanking KPI (Perim=320 mm, T=2.5 mm, Shear=340 MPa, 6%/side, 8% Strip) | Formula | Verified Output |
|---|---|---|
| Per-Side Radial Clearance c (mm) | Sheet_Thickness_T * (Clearance_Pct / 100) | 0.150 mm (0.240 mm @ T = 4.0 mm) |
| Peak Flat Shear Force Fshear (kN) | (Perimeter_mm * T_mm * Shear_MPa) / 1000 | 272.00 kN (435.20 kN @ T = 4.0 mm) |
| Stripper Spring Force Fstrip (kN) | F_shear_kN * Stripper_Fraction | 21.76 kN (34.82 kN @ T = 4.0 mm) |
| Total Station Press Force (kN) | F_shear_kN + F_strip_kN | 293.76 kN (470.02 kN @ T = 4.0 mm) |
Stamping Die Per-Side Clearance, Shear Force & Stripper Tonnage Formula
Validate Perimeter > 0, Thickness T > 0, Shear_Strength in [40, 1200] MPa, Per_Side_Clearance in [2%, 20%], and Stripper_Fraction in [0.02, 0.25]!
=LET(pm_m, B2, th_m, B3, ts_h, B4, cl_p, B5, st_f, B6, IF(OR(pm_m <= 0, th_m <= 0, ts_h < 40, ts_h > 1200, cl_p < 2, cl_p > 20, st_f < 0.02, st_f > 0.25), "Invalid Stamping Input", LET(fs_k, (pm_m * th_m * ts_h) / 1000, ROUND(fs_k * (1 + st_f), 2))))Heavy-Gauge 4.0 mm Bracket Gauge-Up Check (Set Thickness T = 4.00 mm)
Step stock gauge B3 up from 2.50 mm to 4.00 mm: Per-Side Die Clearance E2 widens to 0.240 mm (requiring a wider die button to prevent slug pulling and punch chipping!), Flat Shear Force E3 climbs to 435.20 kN, Stripper Force E4 hits 34.82 kN, and Total Press Demand E5 reaches 470.02 kN!
=IF(ISTEXT(E5), E5, ROUND((B2 * B3 * B4) / 1000, 2))Try the example
Use the original values or change them to test your understanding.