Study On Quality Control Method Based On Melt PVT Relationships

With the development of science and technology in our country, the accuracy and performance requirements have become more and more strict. Polymers precision injection molding technology has become one of the most important questions in plastic production and processing. There are two methods to improve precision of injection molding, which contain improvement of equipment precision and optimization of process parameters. Process control techniques of precision injection molding, whose core is polymer PVT relationships, were researched in this thesis.The control principle of the starting point, the process and the ending point of holding stage were researched. Existing injection molding control techniques during holding process were summarized. On the bases of polymers PVT control methods and theories, an innovative process control techniques named PT control method based on injection molding equipment were presented.Based on the fundamental of polymers injection molding, a series of typical PVT control methods, which take cavity pressure and temperature as control variables, were presented. The relationships between holding process and PVT diagram were described in detail. The PVT diagrams of best Injection molding holding curve of one part and different holding control methods was drawn. It explains the reasons why different methods have different control precision, and why the PT control method has the best weight repeatability precision in theoretical analysis.In order to verify the effect of the new PVT control methods, relevant control experiments were done on HaiTian injection molding machine, including switchover control by cavity pressure and temperature, holding ending point control by cavity pressure and temperature, holding process control by cavity temperature,(PT control technique) and multi parameters group control technique. The results show that the quality and weight repeatability of parts with these new control methods can be improved to a great degree. The best method is switchover point control by cavity pressure+ process control by P-T technique. The weight repeatability precision (0.0629% for PP and 0.0367% for ABS) shows that this method satisfies the weight repeatability requirements of precision injection molding. The normal injection molding machines with the new control method can product precision parts.