Simulation And Optimization Of Conventional Injection Molding Screws

Injection molding screw is the key element of injection molding machine in the plasticizing system. In order to produce homogeneous melt, it is quite important to design the structure and form of screws. Formerly, designers determine the configuration parameters according to the experiences and extrusion theory. In fact, injection molding screw is different from the extrusion screw, because injection molding screw works with the axial and intermittent movement. With the continuous increase in the types of material and people's requirements on the injection products, systematically and deeply studying the injection molding screws becomes more and more important.In the first, we have established the simulation and optimization platform for optimizing the injection screws. The platform is based on Injection Molding Plastification (IMP) software, combing with the DOE (Design of Experiment) method, and we take the screw design or optimization as an experiment process which is based on experiences. Experiment parameters (key configuration parameters of screw) and optimizing objects (output, temperature and so on) are determined according to the practical experiences, and the experiment process is to simulate different screws by IMP, the simulation results are the experiment process. Then, we analyze and optimize the results, and we can obtain the optimized configuration parameters of screws according to the optimizing goals and constraints. In this paper, we focus on the design of metering section for the conventional injection screws, and we respectively use the simulative optimization method and experimental optimization method to optimize the metering depth and metering pitch. On this basis, we have designed the modular structure of the injection screws, so that we can study several screws that are different in metering depth and metering pitch. Before simulation, the reliability of IMP is verified through the comparison between the simulative and experimental results of the pressure along the screw or the screw torque. The results show that the software is basically able to reflect the actual process more accurately.In order to reduce the effects of processing conditions as possible as we can, in this paper, we use DOE method to optimize several main plasticizing process parameters (screw speed, temperature, back pressure and screw stroke), and we obtain the optimal processing conditions. Under those conditions, we do simulative and experimental research on conventional screws. The results show that the optimal results between simulation and experiment are nearly the same. In addition, we have studied the relations between metering depths and screw performances, or relations between metering pitches and screw performances. Thus, we can further evaluate the screw performances, such as weight repeating precision of products, injection energy repeating precision, viscosity homogeneousness of plasticizing melt, mechanical properties of products and plasticizing capacity of screws. As a result, it is better to choose big depth and small pitch of metering section for the crystalline materials (PP), small depth and big pitch of metering section for the amorphous materials (PS).