Zhigao Huang

Efficient numerical simulation of injection mold filling with the lattice Boltzmann method

Purpose n n n n nLattice Boltzmann method (LBM) has made great success in computational fluid dynamics, and this paper aims to establish an efficient simulation model for the polymer injection molding process using the LBM. The study aims to validate the capacity of the model for accurately predicting the injection molding process, to demonstrate the superior numerical efficiency in comparison with the current model based on the finite volume method (FVM). n n n n nDesign/methodology/approach n n n n nThe study adopts the stable multi-relaxation-time scheme of LBM to model the non-Newtonian polymer flow during the filling process. The volume of fluid method is naturally integrated to track the movement of the melt front. Additionally, a novel fractional-step thermal LBM is used to solve the convection-diffusion equation of the temperature field evolution, which is of high Peclet number. Through various simulation cases, the accuracy and stability of the present model are validated, and the higher numerical efficiency verified in comparison with the current FVM-based model. n n n n nFindings n n n n nThe paper provides an efficient alternative to the current models in the simulation of polymer injection molding. Through the test cases, the model presented in this paper accurately predicts the filling process and successfully reproduces several characteristic phenomena of injection molding. Moreover, compared with the popular FVM-based models, the present model shows superior numerical efficiency, more fit for the future trend of parallel computing. n n n n nResearch limitations/implications n n n n nLimited by the authors’ hardware resources, the programs of the present model and the FVM-based model are run on parallel up to 12 threads, which is adequate for most simulations of polymer injection molding. Through the tests, the present model has demonstrated the better numerical efficiency, and it is recommended for the researcher to investigate the parallel performance on even larger-scale parallel computing, with more threads. n n n n nOriginality/value n n n n nTo the authors’ knowledge, it is for the first time that the lattice Boltzmann method is applied in the simulation of injection molding, and the proposed model does obviously better in numerical efficiency than the current popular FVM-based models.

Highly flexible and stretchable MWCNT/HEPCP nanocomposites with integrated near-IR, temperature and stress sensitivity for electronic skin

There is an urgent demand for flexible multifunctional sensitive electronic devices in several potential applications, including personalized health monitoring, human motion detection, human–machine interfaces, soft robotics, and so on. Although exciting progress has been witnessed in recent decades, the excessive dependence on inorganic sensors and flexible substrates makes it difficult to attain multi-function sensing and excellent flexibility simultaneously, as well as their complicated fabrication, technical barriers and high cost. Herein, we report on a family of flexible multi-functional sensitive nanocomposites consisting of multi-walled carbon nanotubes (MWCNTs) uniformly distributed in a high elastic form-stable phase change polymer (HEPCP) that exhibit dramatic response to infrared light (IR), temperature and tensile stress in air, together with outstanding flexibility and stretchability. Optimum sensitivity to on/off IR, temperature and tensile stress is demonstrated with electrical conductivity ratios of 103.7, 11.8 and 1084.0 times at room temperature, respectively. The excellent performance of the MWCNT/HEPCP nanocomposites was largely attributed to the cyclic and reversible changes of their MWCNTs conductive network owing to the reversible form-stable phase transitions and high elasticity of the HEPCP substrate, which subsequently affected the thickness of the interfacial HEPCP between adjacent conductive MWCNTs, and thereby the electron tunneling efficiency between the MWCNTs. The novel MWCNT/HEPCP nanocomposites open a new window for multi-function sensing of electronic skin.

Data driven injection molding process monitoring using sparse auto encoder technique

Injection molding process monitoring is quite essential for the stabilization of product quality. One of the most important things is to identify the character of injection batch process. In this study, sparse auto encoder technique is applied to extract features from the raw trajectories of system pressure and screw position. Subsequently, the process condition is identified by performing a classification on the features, in comparison with the raw trajectories data, and the principal components. The mean reconstruction error and the classification accuracy are selected to evaluate the representation capability of the extracted features. The experimental results show that the sparse auto encoder is an effective method of extracting features from the injection processing batch data, indicating that it is useful in injection molding process monitoring.

The inter-element coupling effect of triangular flat shells

Purpose – The purpose of this paper is to study the inter-element coupling effect of membrane and plate components between two adjacent shells occurring on the common boundary. Design/methodology/approach – In this paper, three triangular flat shells developed by combining an excellent membrane element (OPT) with three outstanding plate bending elements (DKT, RDKTM and DST-BK), respectively, are used to study this phenomenon. Benchmark tests are implemented to evaluate the performance of three selected plate elements and the formulated flat shells. Findings – The inter-element coupling effect of membrane and plate components belonging, respectively, to two adjacent shells deteriorate the performance of shells. Therefore, a shell’s performance cannot be guaranteed certainly by the superimposed membrane and plate behaviors. Practical implications – The “order matching” criterion is proposed to explain this phenomenon and it is concluded that the flat shell that follows this criterion explicitly may alleviat...

A surface model using the eccentric shell and multi-point constraint for warpage prediction of plastics

Purpose – The purpose of this paper is to propose a new surface model combining the eccentric shell with multi-point constraint (MPC) for warpage prediction of injection molded plastics. Design/methodology/approach – In this paper, three benchmark tests and a practical example are implemented to evaluate the performance of the new surface model and existing models. Findings – The results demonstrate that the proposed model could give satisfactory solutions and has advantages over the existing models. Practical implications – More precisely predicted warpage field for injection molded plastics can be achieved with the purposed model, such as that in the practical case. Originality/value – The surface models are efficient and still popular for practical injection molding analysis. However, the existing models for warpage prediction cannot properly represent the true strain energy and obey material continuity assumption, and also they have not been assessed rigorously by benchmark tests. To overcome above-me...

Constitutive modelling of polycarbonate at low, moderate, and high strain rates

The objective of this paper is to experimentally investigate and predict the mechanical behavior of polycarbonate at strain rates ranging from 10−4 to 5000 s−1. Compression tests at low, moderate, and high strain rates were conducted with a Shimadzu universal testing machine, a Gleeble 3500 thermo-mechanical simulator, and a split Hopkinson pressure bar, respectively. Considering the effects of the glass (α) transition and the second (β) transition on the mechanical behavior of polycarbonate, a new constitutive model is proposed, which is decomposed into the α and β components. The α component dominates the low and moderate rate deformations, and the β component is related to the high rate deformation. In comparison with the experimental results, the model can accurately predict the mechanical behavior of polycarbonate at low, moderate, and high strain rates.

A robust finite volume method for three-dimensional filling simulation of plastic injection molding

Purpose n n n n nThe purpose of this paper is to develop a finite volume approach for the simulation of three-dimensional two-phase (polymer melt and air) flow in plastic injection molding which is capable of robustly handling the mesh non-orthogonality and the discontinuities in fluid properties. n n n n nDesign/methodology/approach n n n n nThe presented numerical method is based on a cell-centered unstructured finite volume discretization with a volume-of-fluid technique for interface capturing. The over-relaxed approach is adopted to handle the non-orthogonality involved in the discretization of the face normal derivatives to enhance the robustness of the solutions on non-orthogonal meshes. A novel interpolation method for the face pressure is derived to address the numerical stability issues resulting from the density and viscosity discontinuities at the melt–air interface. Various test cases are conducted to evaluate the proposed method. n n n n nFindings n n n n nThe presented method was shown to be satisfactorily accurate by comparing simulations with analytical and experimental results. Besides, the effectiveness of the proposed face pressure interpolation method was verified by numerical examples of a two-phase flow problem with various density and viscosity ratios. The proposed method was also successfully applied to the simulation of a practical filling case. n n n n nOriginality/value n n n n nThe proposed finite volume approach is more tolerant of non-orthogonal meshes and the discontinuities in fluid properties for two-phase flow simulation; therefore, it is valuable for engineers in engineering computations.

The multi-point constraint ensuring convergence of surface models for warpage analysis of injection-molded plastics

The surface models have been widely used to predict warpage of plastics for several years, but very less attention has been paid to the convergence of this kind of models. In this article, the multi-point constraint ensuring convergence of surface models is deduced based on the theoretical basis of domain decomposition method. And a new corresponding surface model is developed to verify its effectiveness in practice. Three numerical tests are used to evaluate the performances of the new surface model. In the former two cases, the proposed surface model can rapidly converge to the exact solutions, as same as the mid-plane model. And in the last case, the results from the proposed models are much closer to the experiment data than the existing models. It proves that the proposed multi-point constraint is sufficient to ensuring convergence of surface models.

Dimensional precision simulation of the formed picture tube panel

In the forming process of picture tube panel, the accumulated residual stresses cause the formed part to shrink, and the thermal and mechanical loads cause the mold blocks to deform. These two factors result in large deviations on the dimensions of the formed panel, which are both modeled and simulated in this paper. For residual stresses analysis, a thermo-rheologically simple viscoelastic material model is introduced to consider the stresses relaxation effect and to describe the mechanical behavior according to the temperature change. The shrinkage of formed parts induced by the residual stresses is calculated based on the theory of shells, represented as an assembly of flat elements formed by combining the constant strain and the discrete Kirchhoff triangular elements. A thermoelastic model is presented to predict the deformation of the mold blocks during pressing, which is based on the steady mold temperature field and thermoelastic boundary element method. The integrated simulation results suggest the amounts that the mold cavity should be machined by, and have been verified by comparing the dimensional precision of the panels produced by the mold considering a uniform part shrinkage and mold expansion or the mold considering the predicted ununiform part shrinkage and mold deformation.