Meaning
Mathematical formulas determine the amount of clamping force required to keep a mould closed during the injection phase. Performing an accurate mold tonnage calculation prevents the machine from opening and creating flash on the part. The process involves multiplying the projected area of the cavities and runners by the expected internal plastic pressure.
It ensures that the selected machine has enough power to hold the tool shut against the force of the molten resin.
Projected Area
Measuring the total surface of the part as seen from the direction of the clamp is the first step. This area represents the surface upon which the plastic pressure will act to push the mould halves apart.
Pressure Factor
Viscosity of the resin and the thickness of the part wall influence the internal pressure required to fill the cavity. Thinner walls or high-viscosity materials like polycarbonate demand more pressure and therefore higher tonnage. The mold tonnage calculation uses these variables to predict the peak force reached at the end of the fill.
Safety Margin
Adding a percentage to the calculated value accounts for fluctuations in the process or material. A mold tonnage calculation that is too tight leaves no room for changes in melt temperature or injection speed. Running at the absolute limit of the machine also increases the wear on the platens and the tool.
Proper estimation protects the machine toggle system from premature fatigue. Each unique part geometry requires a fresh assessment of these force requirements.
