Determining Optimal Injection Molding Cavitation Counts and Processing Parameters
Optimal cavitation balances machine hourly rates, clamp tonnage, and shot capacity against thermal cooling limits and cross-cavity dimensional distribution.
Clamping Tonnage
Meaning
Injection moulding presses require a specific mechanical force to keep the mould halves closed against the internal pressure of the injected polymer. This force is measured as clamping tonnage, which represents the maximum rating of the machine’s hydraulic or mechanical clamp. It prevents the mould from opening during the high-pressure injection phase.
Force Calculation
Calculating the required closing force involves multiplying the projected area of the part by the average cavity pressure. High-viscosity polymers and thin-walled parts demand higher injection pressures, raising the required clamping tonnage to prevent defects. If the clamp force is too low, the pressure of the melt will force the tool apart.
This yields flashing, dimensional inaccuracy and weight fluctuations across the production run.
Machine Selection
Selecting an inappropriately large press increases energy consumption and accelerates tool wear because of excessive compressive stress on the parting line. Operators must balance the clamp force with the size of the mould plates to avoid deforming the tool. Over-clamping can also compress the venting channels, trapping air and causing burn marks on the moulded parts.
This forces moulders to use machines that match the part requirement.
Operational Risk
Moulders often run machines at ninety percent of their maximum rating to ensure a safety margin during continuous operation. Fluctuations in resin viscosity, which are common when transitioning from virgin to regrind material, can cause sudden spikes in cavity pressure that exceed the clamping tonnage. Regular calibration of the hydraulic valves and toggle mechanisms ensures the clamping system provides consistent pressure.
Preventive maintenance on the platen parallelism further protects the tool from uneven force distribution.