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.
Resultado
—
Contração de plástico no molde
Eis um dos segredos da moldagem de plásticos: a peça que sai do molde é menor que a cavidade que a moldou. Ao esfriar de ~200 °C para a temperatura ambiente e solidificar, todo termoplástico encolhe — dim_peça = dim_molde · (1 − contração%/100). A contração varia muito com o material: plásticos amorfos (ABS, PS, PC) encolhem pouco (~0,4–0,7%), pois suas moléculas já estão desordenadas; os semicristalinos (PP, PE, PA, POM) encolhem bem mais (1,5–3%), porque suas cadeias se reorganizam em cristais compactos ao solidificar. Por isso o fabricante do molde usina a cavidade maior que a peça desejada, na proporção exata da contração esperada. Errar esse cálculo num molde de aço que custa dezenas de milhares de reais é um pesadelo — a peça sai fora de medida e o molde precisa ser retrabalhado ou refeito. Informe a dimensão do molde e a contração do material.
Related Tools
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.
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.
Mold Clamping Force
Compute the clamping force needed on a plastic injection machine, F = projected area · cavity pressure, to keep the mold closed against the molten plastic pressure. If the force is insufficient, the mold opens during injection and plastic leaks out at the parting lines (flash). It is the parameter that defines the machine tonnage required for a part. Enter the part's projected area (mm²) and the cavity pressure (MPa).
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.