For optimization design of polymer extrusion dies, dimensional accuracy is critical to product quality of the extrudate. The extrusion dies used to be a regular geometrical profile, which is mostly composed by a straight line. Traditional optimization methods for extrusion die design used to have poor controllability when dealing with a curved profile. In this paper, the response surface optimization method is used to find out an optimal solution of the design of the extrusion die. Firstly, the Latin Hypercube Sampling method is used to generate the experiment samples for the design of experiments. Secondly, ANSYS Polyflow software is adopted to execute the computational fluid dynamics analysis. Thirdly, the Kriging method is used to generate the response surface. Finally, nonlinear programming by using Quadratic-Lagrangian algorithm is applied to find out the optimal solution. It is worth noting that Non-uniform Rational B-Splines (NURBS) modeling is used to optimize flow channel of an extrusion die in order to obtain a qualified extrudate. Thus, design variables for the optimization involve control points of the NURBS curve of the inlet cross-section. Meanwhile, two new objective functions, including minimization of point displacement and minimization of dimensional tolerance are proposed in the optimization process. Compared with existing objective functions of flow balancing and homogeneous die swell, the new objective functions of minimization of point displacement and minimization of dimensional tolerance have significant advantages of strong adaptability, more precise shape of the extrudate and fast convergence, which significantly improve efficiency of the optimization design and thus lower manufacturing costs of the extrusion die.
Traditional tubular structures with multilayer annular structures (MAS) are limited in the number of layers; as a result of fewer layers, the layers are typically thick, rigid, and unsuitable for many tubular applications. An advanced technique to produce MAS with layer numbers up to 2048 and individual layer thickness remaining low to a few micrometers is successfully designed here. Planar multilayers with high layer numbers were first produced via a flat-die layer multiplication coextrusion, followed by being shaped into an annular structure by using a custom-made annular die that is designed with the aid of numerical simulation. Experimental verifications show that the microlayer pipes with layer numbers up to 2048 and uniform thickness on the circumference can be readily produced by using this advanced technique. Therefore, this work may provide a valuable solution to develop the processes and equipment for tubes with microlayer structures.
Extrusion process has excellent capability in continuous manufactures with high production volume, low cost, and steady quality for very complex cross-sectional products. However, manufacturing a proper extrusion die is challenging, but essential for good quality products, which needs to consider many influence factors in the die design. This paper shows an improved inverse design method for thin-wall hollow profiled polymer extrusion die by using computational fluid dynamics simulation. Also, design criteria of the inverse design method for extrusion die are proposed and discussed. The simulation results show that the thickness of the die lip gap can be enlarged with the decreasing of the inlet flow rate. Additionally, it shows that the geometry profile of the die lip gap can be widened with the increasing of the length of the free jet. The analytical results have been verified by experiments and show a good agreement. It is concluded that the improved inverse design method with FEM-CFD simulations can provide better accuracy and significantly reduce the manufacturing difficulty of micro and thin-walled extrusion die.
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