Injection Molding Machine
Clamping force is the force that holds the mold halves closed against the pressure of the melt trying to open the mold during injection; it is expressed in tons or kN, and this value is the machine's "tonnage". It is calculated as the product of the part's projected area on the mold parting plane and the cavity pressure. Too little clamping force means flash; too much means unnecessary machine cost and load on the mold.
The most fundamental selection criterion for an injection molding machine is its clamping force. The melt enters the cavity at hundreds of bar; this pressure acts on every square centimeter of the mold and forces it open. To keep the mold closed, the machine must apply a clamping force greater than this total force.
The logic of the calculation is simple: the projected area of the part (and the runner) on the parting plane is multiplied by a cavity pressure factor that depends on the material and part geometry. Thin-walled parts with long flow paths require a higher cavity pressure; filled materials also push this value up. A safety margin of 10–20% is usually added to the result.
Tonnage ranges overlap between series. The same 400 ton requirement goes to different machine series for thin-walled packaging, a medical part and general-purpose production; what decides is not the tonnage but the application.
Projected area (cm²) × cavity pressure factor (ton/cm², roughly 0.3–0.7 depending on the material) + safety margin. The calculator on the site does this by material and part type and lists the suitable DKM models.
Yes. A clamping force larger than necessary closes the mold vents, leading to trapped gas and burn marks; it creates a risk of permanent sinking in the mold plates. It should be set to suit the mold.