Injection Molding Clamp Force & Shot Size Calculator
Calculate injection molding clamp force, required machine tonnage, shot volume, and material weight using projected area, cavity pressure, cavity count, runner dimensions, and resin density. Check preliminary machine capacity before tooling.
Injection Molding Tonnage Calculator: Projected Area Inputs
Estimate injection molding clamp force using projected part and runner area at the mold parting plane, number of cavities, mean cavity opening pressure and a user-selected safety factor. Use actual mold-layout values for machine selection.
Use the mean mold-cavity opening pressure, not the injection unit’s maximum nozzle pressure. The 40 MPa value is an editable illustration, not a verified pressure for a particular resin or mold.
Injection Molding Shot Size Calculator: Volume Inputs
Hot runner: set runner volume and projected runner area to zero only when the layout truly eliminates them. Shot weight uses entered solid density for a nominal material estimate; the machine-capacity check compares volumes, not resin-independent PS-rated grams. Screw cushion, purge and startup scrap are not part of the injected cavity/runner volume.
Injection Molding Machine Tonnage Calculator: Results
Screening results do not verify injection flow rate, achievable injection pressure, screw residence time, plasticizing capacity, tie-bar spacing, mold dimensions or cycle-time capability.
Clamp Force Calculator Injection Molding: Calculation Method
Total projected area = (part projected area per cavity × cavity count) + runner projected area. The mold opening force is area (cm²) × mean cavity pressure (MPa) × 0.1 = kN. Multiply by (1 + selected safety margin/100) for the preliminary recommended clamp rating. Divide kN by 9.80665 for metric ton-force (tf), or by 8.89644 for US short ton-force.
The pressure must correspond to the mean cavity pressure acting to open the mold. It is not the nominal hydraulic pressure or the highest machine injection-pressure specification. This calculator estimates static clamp demand, so a toolmaker must still consider pressure peaks, projected geometry and mold/machine rigidity.
| Assumed cavity pressure | Opening force | Clamp including margin | Metric ton-force |
|---|---|---|---|
| Adjust inputs to compare pressure assumptions. | |||
Injection Molding Shot Size Calculator: Material and Machine Fit
Injected volume per shot = (net part volume per cavity × cavities) + total runner volume. Estimated solid-equivalent shot mass = total shot volume × entered material solid density. For machine screening, compare the injected volume with the available screw stroke volume in the same units, rather than assuming a PS-rated maximum shot weight applies directly to every material.
A 20–80% screw stroke-volume utilization window is a commonly used preliminary selection reference. Values outside it trigger a review, not an automatic process rejection. A final press decision needs the machine maker’s molding data, material melt properties, screw cushion, injection pressure/flow and plasticizing throughput.
These formulas are a preliminary machine-sizing screen, not verified mold-opening pressure or press certification. For project-specific tooling, resin and machine requirements, see rapid injection molding services.
Injection Molding Clamp Force and Shot Size: Common Questions
How to calculate injection molding tonnage?
Calculate the total projected area of every cavity and pressurized runner on the parting plane. Multiply that area by representative cavity opening pressure, convert the force to kN or ton-force, and add a justified clamp safety margin. Verify pressure and projected area with the mold designer.
How to calculate shot size?
Multiply the volume of one molded part by cavity count and add the total runner volume actually injected in that cycle. Multiply the volume by the specified material density for a nominal shot mass; compare volume with the machine’s actual screw stroke-volume capacity.
Can injection pressure replace cavity pressure in the clamp equation?
No. The machine’s injection or nozzle pressure includes pressure losses and is not equivalent to the mean pressure acting across the mold cavity. Use a validated cavity-opening pressure or a documented preliminary estimate.
Does the shot size include screw cushion or purging?
No. The injected part-and-runner volume is separated from screw cushion, which remains ahead of the screw, and from startup purge or process scrap. Actual screw dosing settings and process yield must be checked during molding trials.
Does a green clamp and shot rating guarantee the injection machine is suitable?
No. Mold dimensions, tie bars, platen support, attainable injection pressure and speed, screw residence time, plasticizing capacity and process validation still matter. This is a preliminary equipment-screening tool.
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