Study On Numerical Analysis Of Plastic Extrusion Flow And Design Optimization Of Extrusion Die

The design of extrusion die is very important in the extrusion molding technology and it has important influence on product quality, production efficiency, and other factors. Therefore, it is very important to study the extrusion die design. The structure parameters of extrusion die and the relationships between extrusion process conditions and extrusion results were gained by numerical analysis and computer simulation of the flow condition of plastics melt in extrusion die, which can be used to carry on the optimal design of extrusion die. By the numerical analysis of the plastic extrusion process, the extrusion flow laws can be found. The optimal design of extrusion die based on the feedback information of the numerical analysis results has important theoretic and practical meaning to the extrusion die design.In this paper, the disadvantages of three-dimensional parameterized modeling of extrusion die and some problems in practical application were analyzed firstly. Based on the analysis results, a parameterized modeling method of streamlined extrusion die, which is oriented multi-objective optimization and based on function partition, was presented. The ray tracing method and proportional spacing method were combined in the proposed method to find the position of distributed data points on the entrance circle. The fast parameterized modeling oriented CAE was realized based on the function partition that affects extrusion flow, where the cubic polynomial was viewed as the curve of mould.Secondly, the laws that the extrusion flow is affected by extrusion die structure parameters, such as diversion angle, compression angle, compression ratio, length of flat section, etc, were analyzed deeply by adopting finite element numerical analysis, where the influence of the distributing of profile section shape and dimension on die structure and uniformity of extrusion flow was taken into account. Some die structures that were used to adjust the balance of flow in practice, such as structure of block reinforce, individual feed structure of dividing panel, etc, were quantitatively analyzed and simulated in numerical. Point to the difficulty of finite element modeling of some function modules, such as dividing panel, the method that the geometrical characters of these function modules were set in virtual by constraint substitute or load substitute was presented based on the geometrical characters of these structures and the boundary conditions of extrusion flow finite element analysis. The dividing panel was taken as an example to analyze the implement process of proposed method in detail. Compared with the analysis results that the real dividing panel was used, the uniformity indices are the same basically.Finally, on the base of systemic analysis of the influence laws of die structure parameters on extrusion flow, an optimal design method was presented to design the runner of product main frame based on the theory of polymer rheology, where the penalty finite element method was used as numerical analysis tool and the optimization design theory was introduced. The optimization mathematics model was established based on the function partition of theextrusion die runner structure. In the model, the premise was the three-dimensional parameterized model of the runner. The design variables (including physical parameters of material and extrusion process parameters) were the main structure parameters of each function domain of the die. The constraint variables (state variables) were the maximal flow of runner (the maximal production efficiency) or the maximal pressure drop. The objective function was the mean square-deviation of the average flow velocity of each sub-field of product section at extrusion die exit. Based on different engineering requirements, the geometrical domain of research objective can be changed. The purpose that is to study the flow laws of plastics melt in extrusion die and to optimize the structure parameters of extrusion die runner to make the flow balance was achieved by adopting different o...