The first step is predicting the shrinkage is to estimate the pressure and temperature of the polymer melt from the mold geometry and expected machine set-points.Since the exact pressure and temperature are not known beforehand,the mold designer may assume that the melt temperature is equal to the mid-range temperature recommended from the material supplier.The melt pressure is more difficult to predict since the molder will adjust the filling and packing pressures to address a variety of needs(including shrinkage).However, a common molding practice is that the packing pressure is initially set to 80% of the pressure required to filled the mold.

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