MODELING OF POLYMER PRODUCTS SHRINKAGE IN INJECTION MOLDING

Abstract

Injection molding is one of the main ways of plastics processing, which allows to produce parts of simple and complex shapes. There are used thermoplastics without fillers or particulate fillers for the producing tools. The main prerequisites for the systematic identification, analysis of causes and elimination of tools’ defects is the optimal design of the mold, the correct setting of the machine and the establishment of rational technological parameters of molding. The deformation is characterized by the distinction of the part from the desired shape. Causes of deformation can be due to settings or design. Ways to eliminate the deformation is to decrease the dwell pressure; increase the temperature of the mold and to increase the injection speed; increase the temperature of the cylinder; cooling the mold uniformly and to withstand the temperature regime; change the geometric shape of the product taking into account the nature of the polymer.A specific configuration and dimensions of the product takes form and further cooling causes a change in volume of the polymer and the reduction of linear dimensions, that is, the appearance of shrinkage. Shrinkage describes the reduction of linear dimensions relative to the size of the form. The aim of the research is to conduct numerical studies of the process of injection molding by the action of such factors as the temperature of the melt and shape, stay in shape in order to minimize deformation and shrinkage details. The thin-walled casting product of the "cover" type from low density polyethylene has been considered. It is shown, the simulation results helped to identify the dependence of the deformation, the average shrinkage of time staying in shape and time of temperature completion of the form. The simulation results also allowed to set the minimum required time of mold filling and pressure drop. From the simulation results it is seen that with increasing temperature decreases the deformation of the product, the necessary pressure drop and time of form filling, however, increases the time of stay in shape. That is, the increase in temperature has a positive effect on most parameters of the injection molding and the quality of the product, but reduces performance.