The nature of high viscosity and pressure in the injection molding process poses a great challenge for numerical simulation in terms of numerical stability, especially when using particle-based meshless methods. In the present work, 3D filling stage of injection molding is simulated using smoothed particle hydrodynamics (SPH) method. To counter the instability caused by high viscosity and pressure, various methods including a new non-penetration boundary treatment, modified low-dissipation Riemann solver, kernel gradient correction and particle shift technique are applied. GPU parallel computing is achieved by using Taichi language to boost computing efficiency. 3D non-isothermal injection molding process is performed for rectangular cavity, tensile test specimen and a customized transparent injection mold which we intend to perform visual injection experiment to verify our simulation in future work. The properties of flow field such as pressure and velocity are shown and compared with Moldflow simulation. The results of our simulation show good agreement with Moldflow.

In this article, a multiscale simulation method of polymer melt injection molding filling flow is established by combining an improved smoothed particle hydrodynamics method and clustered fixed slip-link model. The proposed method is first applied to the simulation of HDPE melt in a classic Poiseuille flow case, and then two high-speed and high-viscosity injection molding flow cases in two simple long 2D rectangular cavities with and without a circular obstacle, respectively, are analyzed. For each case, the macro velocity results, and the micro average number of entanglements Zave and orientation degree S results are demonstrated and discussed, and the changing trends of Zave and S are analyzed. The results of the two injection molding cases are compared, and the influence of the obstacle on the injection flow at both the macro and micro levels is analyzed. Furthermore, based on the multiscale results, reason of some structural features and defects in injection molded products are analyzed.

Simulations are performed for the polymer melt injection molding filling flow using an improved SPH (smoothed particle hydrodynamics) method. For improving the numerical stability of the high-pressure and high-viscosity injection molding filling simulation, a modified low-dissipation Riemann solver is proposed, and the Tait equation of state and several improvements are adopted in the improved SPH method. Simulations with three cavities are performed for verification of the SPH method, including a simple long rectangular cavity and two relatively complex cavities for study of injection flow balancing. For each cavity, the pressure and velocity results of the injection molding filling simulation are demonstrated, discussed, and compared with the results of the corresponding Moldflow simulation. Furthermore, results of particle motion tracking are also analyzed for an insight into the fountain flow effect. The SPH simulation results indicate that the improved SPH method can well weaken the non-physical pressure oscillation with reasonable pressure results and controlled melt compressibility, and the SPH results are in good agreement with the Moldflow results.

This paper proposes an integrated two-step strategy for an optimal design of liquid-cooled channel layout based on the moving morphable component (MMC)-density approach. The proposed strategy intends to take the advantage of both the MMC approach for its high flexibility in searching a physically reasonable layout and the density approach for its better capacity of topology description. On the basis of the above-mentioned strategy, an intermediate layout is obtained through MMC approach and further optimized as initial solution of density approach step. Through density approach step, the final layout shows smoother boundary while retaining reasonable feature size. The original contributions of this paper are as follows: (i) An assembled quadratic Bézier curves component is proposed to describe the largely curved channel with limited numbers of optimization variables and computation order. (ii) Benefited from explicit geometric description, adaptive mesh refinement (AMR) is applied in MMC approach step for the first time. The application of AMR, from the numerical point of view, has two key ingredients to be highlighted: (i) the accuracy of solution in fluid–solid boundary region can be ensured with relatively limited computational cost. (ii) The contradiction that the difference step of MMC updating needs to be both as small as possible and integer multiple of the mesh size can be avoided. The performance of our methodology is demonstrated by numerical examples aiming for maximal heat exchange with power dissipation constraint. The main finding reveals that the proposed strategy can offer reasonable channel layout with better thermal performance, compared with conventional density approach. The whole numerical implementation relies on OpenFOAM and PETSc open-source software packages.

In the present study, a topology optimization method of thermal-fluid-structural problems is researched to design the three-dimensional heat sink with load-carrying capability. The optimization is formulated as a mean temperature minimization problem controlled by Navier-Stokes (N-S) equations as well as energy balance and linear elasticity equations. In order to prevent an unrealistic and low load-carrying design, the power dissipation of the fluid device and the normal displacement on the load-carrying surface are taken as constraints. A parallel solver of multi-physics topology optimization problems is built-in Open Field Operation And Manipulation (OpenFOAM) software. The continuous adjoint method is adopted for the sensitivity analysis to make the best use of built-in solvers. With the developed tool, the three-dimensional (3D) thermal-fluid topology optimization is studied. It is found that the Darcy number, which is suitable for fluid design, may cause severe problems in thermal-fluid optimization. The structural features of 3D thermal-fluid-structural problems are also investigated. The “2D extruded designs” are helpful to improve the structural stiffness, and channels with a larger aspect ratio in high-temperature areas improve the cooling performance.

Over the past two decades, numerical simulation of injection molding has made great progress, not only with its increasingly widespread use, but also with problems and challenges such as unreliable simulated performance, difficulty integrating commercial software with new methods, and inadequate consideration of microscopic mechanisms. This paper thoroughly explores the historical development of injection molding theoretical models and the key results of each point, and briefly introduces multiscale simulation methods. The characteristics and spectrum of application of the substance constitutive models are studied, and the effects of crystallization on the state and constitutive equations are demonstrated. Therefore, the characteristics of numerical methods for solving problems with injection molding are analyzed, and the variations between viscous and viscoelastic methods are studied. Analysis of the advantages and disadvantages of methods of flow front monitoring was performed. Also, simulations were implemented with the meshless approach for filling flow for certain special physical phenomena such as the fountain flow. The paper also forecasts the growth patterns and urgent problems of simulating injection molding based on examining and testing existing theories, algorithms, and the real demands of the plastics processing industry.

充填阶段是注塑成型中最复杂也是最重要的阶段.考虑到Moldflow软件在注塑成型模拟中的局限性,越来越多的学者使用Fluent等通用计算流体动力学(CFD)软件进行注塑成型模拟.然而,大多数基于通用CFD软件的注塑充填模拟中都忽略了气体相.基于Fluent软件实现了三维注塑充填模拟,并将没有考虑空气相,以及考虑空气相时使用两种不同界面追踪方法的模拟结果分别与Moldflow进行了对比.结果表明,在基于Fluent的注塑充填模拟中应该考虑空气,且使用流体体积函数(VOF)和水平集(Level Set)的耦合方法(CLSVOF)比单纯的VOF方法界面追踪效果更好.