Study On Mechanism Of Precision Plastication In Injection Molding Machine

Injection molding is one of the most important methods for polymer processing. In recent years, with the increasing demands for injection molding products, the precision of injection molding technology are paid more attention by people. There are many factors what can affect the quality and weight repeatability of injection molding products, such as plasticizing system, mold, hydraulic system, control system, process conditions, and so on. In this paper, taking the precision of injection molding as the center, the plasticizing system what is the most important factor in the injection molding was studied, especially on the structure, parameters and properties of injection screws. Through analysis of the requirements of precision plasticizing system, the evaluaton of performance of injection screws were proposed, and some methods of performance determination of plasticizing melt and injection screws were developed. Otherwise, I studied a set of optimization methods of injection screws. These works were contributed to the precision injection molding technology. The main contents of this paper are as following:(1) The performance monitoring and experimenting platform of Precision plasticiznig systems of injection molding machine was set up, which included the dynamic parameters acquisition system of injection molding machine, the melt temperature measuring devices, screw speed and torque tester, mold, and pressure and temperature sensors, etc.. The experimenting platform can on-line acquaint processing parameters, such as screw speed, torque, melt temperature and pressure, and injection power.(2) Based on the requirements of precision plasticizing system, what the melt quality must be met in precision plasticizing process and the relationship between molding products and plasticizing performance of injection screws were analyzed. The evaluation system of precision plasticizing system (mainly injection screw) was set up.(3) The detection methods of polymer melt uniformity in the injection molding process were systematically studied, which including melt temperature uniformity, melt viscosity uniformity, melt density uniformity, melt dispersion and mixing, the accurate meter of injection molding machine, injection stability and residence time distribution. In these methods, ultrasonic on-line determine the injection molding process were especially studied.(4) To eliminate and decrease the influences of molding conditions to the determination results, DOE (design of experiment) were used. Chossing four important process conditions (barrel temperature, screw speed, back pressure and material plasticizing length), experimental programs were designed with DOE. In accordance with the combination of process conditions, nine different types of injection screws were tested and evaluated. The results verified the feasibilities of these determination methods, and performance evaluations of precision injection screw were established as the basis of the experimental results.(5) Based on polymer pVT testing theory, the melt ultrasonic melt measurement system was developed. Using it, we studied on the relationship between ultrasonic signal (velocity and attenuation) and the content of inorganic particles filled polymer, and the ultrasonic velocity of uniform polymer melt at different temperatures and pressure.(6) Through theoretical analysis and derivation, a method that measuring ultrasonic velocity to reflect the density of polymer melt was proposed. The polypropylene (PP) melt were tested by using self-designed ultrasonic measuring device, and the single value between ultrasonic velocity and the density of polymer melt was verified by experiments. The method was feasible by verification of both theory and experiments. This method could be used for on-line measurement of polymer melt density uniformity in the polymer processing, and it was useful for optimization of process conditions and weight control in the injection molding process.(7) The optimization method of precision injection screw was studied. At first, the key structural parameters of screw were designed and combined with DOE, and different screws were simulated by using Injection Molding Plastification analysis software; then analysis the impact of parameters to the results, and made targeted optimization for the structural parameters of screw. The optimized results of three sections screw and separated screw got the better results.