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Research of Die Runners Optimal Design and Simulated for WPC Profiles Based on CAE

Author: ZhaoFeng
Tutor: XuePing
School: Beijing University of Chemical Technology
Course: Mechanical Design and Theory
Keywords: extrusion die numerical simulation wood-plastic composite profile runner orthogonal test optimization design
CLC: TQ320.5
Type: Master's thesis
Year: 2011
Downloads: 83
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Abstract

Wood-plastic composites profiles indicate both the dual characteristics of wood and plastics, which has been successfully applied in many fields. Extrusion die is the key for shaping WPC profiles, of which the runner structure directly affects the stability and efficiency of the forming process. In the face of the specificity of rheological properties of materials and the diversity of products, conducting research on die runners optimal design and simulation for WPC profiles is particularly important.In this paper, a PE/wood pillar (90mm X 90mm) and a PVC/wood construction wallboard profiles(600mm X 120mm) with large width and thickness were researched and the optimal design and simulation of profile extrusion die runners by using the Polyflow software was carried out. A design method of die runners for WPC profiles based on numerical simulation and orthogonal test was putted forward, which had better adaptability and feasibility by dividing the optimization into two parts, including the initial optimization and orthogonal test optimization. The procedure of this method was as follows:the rheological properties of WPC materials used in practical processing and the parameters of forming device were defined as simulation conditions; the geometrical model of extrusion die were preliminary established, the flow fields in runners of extrusion dies were simulated by using the Polyflow software, and the distribution of pressure, velocity and shear-rate of flow field in the dies were obtained. Under the guidance of the simulation results, he initial optimization model has been established through the gradual improvement; Length of stereotype, contraction angle, expansion angle, compression ratio and length of damping element were defined as the key parameters of test factors, test schemes were arranged by orthogonal experimental design method, and test models were quickly created by 3d of parameterized modeling technology of Inventor software; by adopting the uniformity of melt flow rate of the die head, the ability to build pressure, the distribution of pressure drop and the maximum shear rate as the evaluation indexes, the simulation results were optimized by orthogonal test. Through data processing, excellent runner structure parameters were obtained.In view of stable production of PE/wood pillars and PVC/wood construction wallboard, structural parameters of runners of the die were optimized by using the Polyflow software. The extrusion die designed according to parameters optimization in this study shows good extrusion stability, die pressure stability and flow velocity uniformity, which indicates that the die optimization design according to this method is successful and feasible. Some useful conclusions on the design of WPC profiles were concluded as follows:(1) Due to the poor fluidity of WPC, for the die whose runner is wider, the pressure loss along the flow direction is great, which often leads to the uneven flow velocity. To ensure enough molding pressure, it is necessary to design a die with a higher compression ratio.(2) Due to the swelling effect of WPC, the shape of the die obtained by Polyflow inverse extrusion method has a certain distortion and the fillet size is relatively small. But the method can provide the correcting direction of the die, which offers guidance in practical design of cross-section shape and size of the die.(3) For WPC profile products with small and medium-sized specifications, the structure and size of the distributary core plays a critical important role in the melt distribution. Through reasonable design of distributary core structure, favorable melt distribution can be achieved without installing resistance components. For WPC hollow profile products with broad width, in addition to the reasonable design of distributary core structure, it is necessary to install resistance components in position so as to achieve uniform melt distribution by means of disturbing the velocity and direction of the melt.(4) For WPC profile products with inconsistent wall thickness dimensions, the homogeneity of melt velocity at the outlet of the die can be effectively improved by employing setting section with different length.

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