Effect of Process Parameters on Short Fiber Orientation along the Melt Flow Direction in Water-Assisted Injection Molded Part

Hindawi Advances in Materials Science and Engineering Volume 2019, Article ID 7201215, 10 pages https://doi.org/10.1155/2019/7201215 Research Article Effect of Process Parameters on Short Fiber Orientation along the Melt Flow Direction in Water-Assisted Injection Molded Part Haiying Zhou ,1,2 Hesheng Liu ,1,2 Qingsong Jiang,2 Tangqing Kuang,3 Zhixin Chen,2 and Weiping Li2 1 School of Mechanical and Electrical Engineering, Nanchang University, Nanchang 330031, China Jiangxi Province Key Laboratory of Polymer Micro/Nano Manufacturing and Devices, East China University of Technology, Nanchang 330013, China 3 School of Mechanical and Electrical Engineering, East China Jiaotong University, Nanchang 330013, China 2 Correspondence should be addressed to Hesheng Liu; Received 21 February 2019; Revised 8 July 2019; Accepted 22 July 2019; Published 19 August 2019 Academic Editor: Francisco Chinesta Copyright © 2019 Haiying Zhou et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The short fiber orientation (SFO) distribution in the water-assisted injection molding (WAIM) is more complicated than that in traditional injection molding due to the new process parameters. In this work, an improved fiber orientation tensor method was used to simulate the SFO in WAIM. The result was compared with the scanning electron micrograph, which was consistent with the experiments. The effect of six process parameters, including filling time, melt temperature, mold temperature, delay time, water pressure, and water temperature, on the SFO along the melt flow direction were studied through orthogonal experimental design, range analysis, and variance analysis. An artificial neural network was used to establish the nonlinear agent model between the process parameters and A11 representing the fiber orientation in melt flow direction. Results show that water pressure, melt temperature, and water temperature have significant effects on SFO. The three-dimensional (3D) response surfaces and contour plots show that the values of A11 decrease with the increase in water pressure and melt temperature and increase as the water temperature rises. 1. Introduction With the development of advanced, economical, and environmentally friendly society, higher requirements are placed on the performance of plastic products. The short-fiber-reinforced polymer composite (SFRPC) is a material with a polymer as a matrix and short fibers as a dispersed phase. Its characteristics are lightweight, high specific strength and specific modulus, stable chemical properties, heat resistance, and good wear resistance [1]. In recent years, SFRPCs have gradually replaced metal materials in some fields, making them widely used in aviation, automotive, shipping, and medicine [2, 3]. Fluid-assisted injection molding is an emerging process that includes gas-assisted injection molding (GAIM) and water-assisted injection molding (WAIM) [4, 5]. The fluids used in GAIM and WAIM are nitrogen and water, respectively. Due to incompressibility, high heat capacity, and good thermal conductivity of water, the advantages of WAIM over GAIM are high product efficiency, more uniform and thinner residual wall thickness (RWT) [6]. Based on whether or not the cavity is completely filled with melt, WAIM can be categorized into two types: short-shot WAIM and overflow WAIM. In short-shot WAIM, the mold cavity is partially filled with melt, followed by the injection of water into the core of melt. In overflow WAIM, the mold cavity is completely filled with melt, followed by the injection of water that pushes the melt into the overflow cavity to form a part with a hollow cross section. Compared with the standard injection molding, WAIM offers significant advantages in the preparation of shaped hollow plastic parts with uniform RWT. However, due to the difficulty in controlling the water injection pressure and the turbulence characteristics of the injection water, the quality of the products is not stable [7, 8]. Present researches on WAIM focus on the 2 distribution of RWT [9], the length of water column penetration [10, 11], and the defects of molded parts [12, 13]. The RWT of water-assisted injection molded parts is thin, and the mechanical properties of the parts can be greatly improved by using SFRPC as a raw material. Many studies reported that the distribution of short fiber orientation (SFO) determined the mechanical and physical properties of the plastic parts, while fiber orientation was affected by mold structure, molding process parameters, flow field distribution, initial state of fibers, fiber properties, and matrix properties [14–16]. The molding process parameters influence temperature, velocity distribution, melt viscosity gradient, and flow field, which ultimately determine the fiber orientation. Liu et al. [7, 12] found that the short fibers mostly aligned along the melt flow direction in WAIM. Huang et al. [17] suggested that high-pressure water penetration significantly affected fiber orientation in WAIM, and increasing melt temperature decreased fiber orientation. Systematic studies on the influence of process parameters on the SFO help understand the fiber orientation mechanism, optimize the SFO distribution, and improve the overall performance of the parts in WAIM. WAIM, including the melt and high-pressure water filling stages, is more complicated than the standard injection molding process. Due to the difficultly in accurately controlling all the process parameters simultaneously, the research of SFO in laboratory is performed for qualitative analysis. With the development of computer technology, the three-dimensional numerical simulation technology developed rapidly, enabling simulating complex injection molding. The process parameters can be accurately controlled in simulation, but the reliability of SFO simulation depends on the accuracy of the mathematical model. The fiber orientation distribution in injection molding is very complicated microscopically. In the past three decades, theoretical studies on fibers suspension rheology have achieved a great success. Based on the classic fiber orientation models, including Jeffery hydrodynamics model, Folgar–Tucker model [18], and ARD-RSC model [19], Tseng et al. recently proposed an improved iARD-RPR model [20, 21], which can provide good simulation results of SFO in standard injection molding. In this work, based on the iARD-RPR model, the SFO in WAIM was simulated, and the results were compared with the scanning electron micrographs (SEMs) to verify the applicability of this model for WAIM. The influences of process parameters on the fiber orientation along the melt flow direction were studied through the methods of orthogonal experimental design, range analysis, and variance analysis. The nonlinear proxy model between process parameters and fiber orientation along t (...truncated)