Plastics Manufacturing, Injection Molding Tooling & Press Sizing
Injection Molding Clamping Tonnage & Shot Weight Formula
Calculate Total Part+Runner Projected Area (cm²), Required Mold Clamping Force (kN), Press Clamping Rating (Metric Tons-Force at g = 9.81), and Polymer Shot Weight (g).
Under-sizing clamping force by even 10% lets pack/hold cavity pressure crack the parting line and flash the mold!
During thermoplastic injection molding pack-and-hold, peak hydraulic melt pressure inside the cavities P_cav (MPa, typically 30–60 MPa depending on flow-length-to-wall-thickness ratio L/t and polymer viscosity) pushes outward against the mold parting plane across Total Projected Area A_proj = N_cavities * A_part + A_runner (cm²)! Because 1 cm² * 1 MPa = 10^-4 m² * 10^6 N/m² = 100 N = 0.10 kN, multiplying by a Parting-Line Safety Factor SF (1.10–1.20) yields Required Clamping Force F_kN = 0.10 * A_proj_cm2 * P_cav_MPa * SF (and dividing by 9.81 m/s² converts kN directly into standard European/Asian press Metric Tons-Force)! Meanwhile, Barrel Shot Weight equals Shot_Volume_cm3 * Solid_or_Melt_Density_g_cm3!
Verify on a 4-Cavity Polypropylene Automotive Housing Tool—Part_Projected_Area = 45.0 cm² (B2), Cavity_Count N_cav = 4 (B3), Cold_Runner_Projected_Area = 20.0 cm² (B4 -> Total Projected Area = 4 * 45 + 20 = 200.00 cm² in E2), Peak_Cavity_Pressure P_cav = 40.0 MPa (400 bar, B5), Clamp_Safety_Factor = 1.15 (B6), Total_Shot_Volume = 160.0 cm³ (B7), and Polymer_Melt_Density = 0.92 g/cm³ (B8): Required Clamping Force hits 0.10 * 200 * 40 * 1.15 = 920.00 kN (E3), Press Tonnage Rating equals 920 / 9.81 = 93.78 metric tons (select a 100–120 ton press!, E4), and Shot Weight equals 160 * 0.92 = 147.20 g (E5)!
| Injection Press Sizing KPI (4 Cav x 45 cm² + 20 cm² Runner, 40 MPa, SF=1.15) | Formula | Verified Output |
|---|---|---|
| Total Projected Area (cm²) | N_Cavities * Part_Area + Runner_Area | 200.00 cm² (380.00 @ 8 cavities) |
| Required Clamping Force (kN) | 0.10 * Total_Area_cm2 * P_MPa * SF | 920.00 kN (1,748.00 @ 8 cavities) |
| Press Clamping Tonnage (t-f) | Clamping_Force_kN / 9.81 | 93.78 t (178.19 t @ 8 cavities) |
| Total Barrel Shot Weight (g) | Total_Shot_Volume_cm3 * Density_g_cm3 | 147.20 g |
Parting-Line Mold Clamping Force & Metric Tonnage Formula
Validate Part_Area > 0, integer Cavities >= 1, Runner_Area >= 0 (0 for hot-runner valve gates!), Cavity_Pressure in [10, 150] MPa, Safety_Factor >= 1.0, Shot_Volume > 0, and Density in [0.70, 2.50] g/cm³!
=LET(ap_c, B2, nc_v, B3, ar_c, B4, pc_m, B5, sf_c, B6, vs_c, B7, rh_g, B8, IF(OR(ap_c <= 0, nc_v < 1, INT(nc_v) <> nc_v, ar_c < 0, pc_m < 10, pc_m > 150, sf_c < 1, vs_c <= 0, rh_g < 0.7, rh_g > 2.5), "Invalid Molding Input", LET(at_c, nc_v * ap_c + ar_c, ROUND(0.1 * at_c * pc_m * sf_c, 2))))8-Cavity High-Volume Production Tool Press Upgrade Check (Set Cavities = 8)
Scale tooling from 4 cavities to 8 cavities (B3 = 8): Total Projected Area E2 rises to 380.00 cm², boosting Required Clamping Force E3 to 1,748.00 kN = 178.19 metric tons (E4, requiring a 200-ton class molding machine)!
=IF(ISTEXT(E3), E3, ROUND(E3 / 9.81, 2))Try the example
Use the original values or change them to test your understanding.