Mold Cavity Pressure
Estimate the pressure that actually reaches the mold cavity by multiplying the injection pressure (at the screw tip) by the pressure transmission factor, which accounts for pressure losses along the runners, nozzle and gates to the cavity. Typically only 40–60% of the machine pressure reaches the part. It is the cavity pressure that defines the clamping force and fill quality. Enter the injection pressure and the transmission factor.
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Mold cavity pressure
The pressure shown on the injection molding machine gauge is not the pressure that reaches the part. Injection pressure is measured at the screw tip; from there to the cavity, the molten plastic travels through the nozzle, the sprue, the runners and the gate, losing pressure to friction at every restriction. Typically only 40% to 60% of the machine pressure actually arrives at the cavity — this is the pressure transmission factor. It is the pressure in the cavity, and not the machine pressure, that sets the required clamping force and the quality of filling and packing. Cavity pressure sensors are therefore the gold standard of quality control in injection molding: they measure what really matters. Poorly designed runners (long, thin, with sharp corners) drag the transmission factor down and demand more powerful machines. Enter the injection pressure and the transmission factor.
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Plastic Mold Shrinkage
Compute the final dimension of a plastic part after molding shrinkage, part_dim = mold_dim · (1 − shrinkage%/100). Every thermoplastic shrinks as it cools and solidifies in the mold — from ~0.5% (amorphous like ABS) to 2–3% (semicrystalline like PP and PA). That is why the mold cavity is machined larger than the final part, compensating exactly for this shrinkage. Getting it wrong ruins an expensive mold. Enter the mold dimension and the material's shrinkage rate.
Plastic Injection Flow Rate
Compute the injection flow rate by dividing the injected volume by the fill time, in cm³/s. It is the speed at which the molten plastic enters the mold — a parameter that controls the shear rate, molecular orientation, surface finish and defects such as jetting or flow marks. High flow fills fast but may degrade; low flow may solidify before filling. Enter the injected volume and the fill time.
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Compute head loss hf = f·(L/D)·v²/(2g) using Darcy-Weisbach.
Injection Cycle Time
Compute the total cycle time of a plastic injection by adding the injection time (fill + pack), the cooling time and the mold open/eject time. Cooling is usually the largest share (50–80% of the cycle). The cycle time directly determines productivity: parts/hour = 3600/cycle × cavities. Reducing it is the constant focus of optimization. Enter the injection, cooling and opening times.
Injection Shot Volume
Compute the shot volume of a plastic part by dividing the injected mass by the molten material density. The shot is the total volume of plastic injected per cycle (parts + runners), a parameter that must fit the injection barrel capacity. Together with the machine capacity, it defines how many cavities can be filled per cycle. Enter the injected mass (g) and the material density (g/cm³).
Shear Rate (Injection)
Compute the shear rate of the molten plastic in a rectangular channel, γ = 6Q/(W·H²), from the flow rate (Q), the channel width (W) and height (H). It is a critical parameter of polymer processing: thermoplastic viscosity drops with shear rate (pseudoplastic behavior), and excessive rates degrade the material. It guides the design of runners and gates. Enter the flow rate, the width and the height of the channel.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.