Study On Key Technology Of Hollow Products Extrusion Molding And Its Application

Extrusion die is the parison formation mold for extrusion molding of hollow products which forms plastic melts in its runner to certain cross-section shape parison. In the process of extrusion, extrusion die’s structure directly affects the flow field distribution of plastic melts. Unreasonable extrusion die structure parameters will cause error in geometrical dimension and product defects, such as uneven wall thickness, wrinkles, plastic melt fracture and warping of plastic products. Structure and dimension parameters of extrusion die have great impact on the shape and performance of plastic products. Therefore, it is necessary to make an optimization of extrusion die structure so as to improve plastic products performance and reduce material consumption.The first chapter mainly introduces the research background and significance of the thesis from two aspects:extrusion process analysis and design of extrusion die. The present research on extrusion die design and extrusion fluid flow analysis was discussed. One design optimization method of extrusion die which takes extrusion fluid flow and parison formation into consideration was proposed according the deficiencies in present research. Moreover, the research content and framework of this thesis were presented in the last section of chapter one.In the second chapter, we first analyzed the properties of extrusion die and described the influence factors in the extrusion flow process based on the functions of extrusion die in the extrusion blow molding equipment. Extrusion property evaluation model of extrusion die was built based on fluid flow property of the plastic melts in the extrusion die, including extrusion capacity evaluation model and parison formation dimension constraints model which provide theoretical foundations to the following extrusion flow simulation and design optimization of extrusion die.The third chapter mainly studies the fluid flow property of the plastic melts in the extrusion die. Influence curves of extrusion die structure parameters on fluid flow property were obtained through fluid flow simulations of plastic melts in the extrusion die with CFD (POLYFLOW) software. According to the simulation results, we built associations between fluid flow property of the plastic melts and structure parameters of the extrusion die with the grey relation entropy method and obtained key design parameters of the extrusion die.In the forth chapter, the parison extrusion formation process and dimension prediction of parison was studied considering the influence of parison swelling phenomenon on the design of extrusion die. Shape and dimension of extrusion parison with different extrusion die parameters was obtained with finite element method. Response relationship between extrusion die parameters and parison dimensions was built with Kriging model which were used to predict the parison dimension.In the fifth chapter, extrusion die was designed according to the dimension mapping relation between hollow plastic products and extrusion parison taking extrusion fluid flow of plastic melts in the extrusion die and parison formation into consideration. Taking extrusion fluid flow property as objective function and key structure parameters of extrusion die as design variables, extrusion die was designed and optimized with NSGA-II multi-objective optimization algorithm. Then optimum structure parameters of extrusion die can be obtained through this method.In the sixth chapter, the main content of this thesis was summarized and an outlook of the future work was presented.