Meaning
Maximum clamping force that an injection moulding machine can apply to hold the mould halves closed against the internal pressure of the molten resin prevents polymer from leaking out of the cavity. This platen tonnage determines the maximum projected area of the part that a specific press can successfully mould.
Clamping Force
Selecting the correct machine size depends on both the material viscosity and the geometry of the part. While high-viscosity resins require higher injection pressures and consequently more force to hold the mould shut, low-viscosity materials can be processed on machines with lower platen tonnage. If the machine cannot provide sufficient force, the molten polymer will force the mould halves apart during the injection phase.
Calculation Method
Estimating the required force involves multiplying the projected area of the part by the average cavity pressure, with factors added for thin walls or complex flow paths. A datasheet value for resin flow can guide this calculation, but the actual press run requires margins to account for viscosity fluctuations during production. Molders usually apply a safety factor of ten to twenty percent to ensure the machine runs well within its mechanical limits.
Operating Defect
Running a job with insufficient clamping force causes flash, which is the thin web of excess plastic that squeezes into the parting line of the tool. Conversely, setting the platen tonnage too high can compress the mould face, damage the parting line, and crush the venting channels, which leads to burn marks on the parts due to trapped air. Proper calibration of this force extends the life of the tooling and ensures consistent part dimensions.
