Optimization of filling process in RTM using a genetic algorithm and experimental design method

In the resin transfer molding (RTM) process, preplaced fiber mat is set up in a mold and thermoset resin is injected into the mold. An important issue in RTM processing is minimizing the cycle time without sacrificing part quality or increasing the cost. In this study, a numerical simulation and optimization process for the filling stage was conducted in order to determine the optimum gate locations. The control volume finite element method (CVFEM), modeled as a 2‐dimensional flow, was used in this numerical analysis along with the coordinate transformation method to analyze a complex 3‐dimensional structure. Experiments were performed to monitor the flow front to validate the simulation results. The results of the numerical simulation corresponded with that of the experimental quite well for every single, simultaneous, and sequential injection procedure. The optimization analysis of the sequential injection procedure was performed to minimize fill time. The complex geometry of an automobile bumper core was chosen. A genetic algorithm was used to determine the optimum gate locations in the 3‐step sequential injection case. Taguchi's experimental design method was also used for determining the pressure contribution of each gate. These results could provide the information on the optimum gate locations and injection pressure in each injection step and predict the filling time and flow front.     

Three-dimensional nonisothermal mold filling simulations in resin transfer molding

The manufacture of polymer composites through the process of resin transfer molding (RTM) involves the impregnation of the reactive polymer resing into a mold with preplaced fibrous reinforcements. Determination of RTM processing conditions requires the understanding of various parameters, such as material properties, mold geometry, and mold filling conditions. Modeling of the entire RTM process provides a tool for analyzing the relationship of the important parameters. This study developed a nonisothermal 3-D computer simulation model for the mold filling process of RTM based on the control volume finite element method. The model will be able to simulate mold filing in molds with complicated 3-D geometry. Results of some numerical studies in RTM show the applications of the proposed model.     

A fast computational model to the simulation of non‐isothermal mold filling process in resin transfer molding

The numerical simulation of mass and heat transfer model for the curing stage of the resin transfer molding (RTM) process is known as a useful method to analyze the process before the mold is actually built. Despite the intense interest in the modeling and simulation of this process, the relevant work is currently limited to development of flow models during filling stage. Optimization of non‐isothermal mold filling simulation time without losing the efficiency remains an important challenge in RTM process. These were some reasons that motivate our work; namely the interested on the amelioration of the performance of RTM simulation code in term of execution time and memory space occupation. Our approach is accomplished in two steps; first by the modification of the control volume/ finite element method (CV/FEM) and second by the implementation in the modified code of an adapted conjugate gradient algorithm to the compressed sparse row storage scheme. The validity of our approach is evaluated with analytical results and excellent agreement was found. The results show that our optimization strategy leads to maximum reduction in time and space memory. This allows one to deal with problems with great and complex dimensions mostly encountered in RTM application field, without interesting in the constraint of space or time. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Modeling and simulation approaches in the resin transfer molding process: A review

A review of current approaches in modeling and simulation of the resin transfer molding (RTM) process is presented. The processing technology of RTM is discussed and some available experimental techniques to monitor the process cycle are presented. A master model is proposed for the entire process cycle consisting of mold filling and curing stages. This master model contains the fundamental and constitutive sub‐models for both stages. The key elements of the master model discussed in this study are: flow, heat and mass balance equations for fundamental sub‐models, permeability, cure kinetics, resin viscosity and void formation for constitutive sub‐models. At the end, numerical methods widely used to simulate the filling process are presented and published simulation results of mold filling and process cycle are reviewed.     

Modeling nonisothermal impregnation of fibrous media with reactive polymer resin

The manufacture of polymer composites through resin transfer molding (RTM) or structural reaction injection molding (SRIM) involves the impregnation of a fibrous reinforcement in a mold cavity with a reactive polymer resin. The design of RTM and SRIM operations requires an understanding of the various parameters, such as materials properties, mold geometry, and mold filling conditions, that affect the resin impregnation process. Modeling provides a potential tool for analyzing the relationships among the important parameters. The present work provides the physical model and finite element formulations for simulating the mold filling stage. Resin flow through the fibers is modeled using two-dimensional Darcian flow. Simultaneous resin reaction and heat transfer among resin, mold walls, and fibers are considered in the model. The proposed technique emphasizes the use of the least squares finite element method to solve the convection dominated mass and energy equations for the resin. Excellent numerical stability of the proposed technique provides a powerful numerical method for the modeling of polymer processing systems characterized by convection dominated transport equations. Results from example numerical studies for SRIM of polyurethane/glass fiber composites were presented to illustrate the application of the proposed model and numerical scheme.     

The effect of the packing parameters,gate geometry,and mold elasticity on the final dimensions of a molded part

Despite a significant number of publications and the increasing use of numerical simulation, there is still a debate about the optimum gate design and packing conditions in the molding industry. Shrinkage uniformity for unfilled polymers is dominated by the time dependent pressure distribution in the cavity and the resulting volumetric shrinkage; gate freeze-off is obviously important and difficult to predict; and pressure gradients during the packing phase, depend on process and design parameters and are also affected by the mold elasticity. Molding trials have been conducted on an instrumented mold (fan gated rectangular slab, 2 mm thick) under a variety of processing conditions and with different gate thicknesses using HDPE (Solvay Eltex A1050). Pressure decay during the molding cycle at different locations along the flow path have been correlated with sample thickness distribution. Overpacking at moderate packing pressure is shown to be a direct consequence of mold elasticity and to be related to both filling flow rate and gate thickness. The decay to a finite residual pressure can be computed by coupling the mold elasticity with the PVT behavior of the polymer. The results highlight the importance of gate design and processing parameters on the dimensional accuracy of the part and low internal stress level. When dealing with thick gates, packing pressure profiling appears to be the best way to avoid gate area overpacking. Mold elastic deformation can play a significant role in the cavity pressure-time history, even for a seemingly stiff mold construction.     

Physical and numerical modeling of mold filling in resin transfer molding

Finite element modeling and experimental investigation of mold filling in resin transfer molding (RTM) have been performed. Flow experiments in the molds were performed to investigate resin flow behavior into molds of rectangular and irregular shapes. Silicone fluids with viscosity of 50 and 100 centistoke as well as EPON 826 epoxy resin were used in the mold filling experiments. The reinforcements consisted of several layers of woven fiberglass and carbon fiber mats. The effects of injection pressure, fluid viscosity, type of reinforcement, and mold geometry on mold filling times were investigated. Fiber mat permeability was determined experimentally for the five-harness and eight-harness woven mats. Resin flow through fiber mats was modeled as flow through porous media. Pressure distributions inside both types of molds were also determined numerically. In the case of resin flow into rectangular molds, numerical results agreed well with experimental measurements. Comparison between the experimental and numerical results of the resin front position indicated the importance of edge effects in resin flow behavior in small cavities with larger boundary areas. Reducing the resistance to resin flow at the edge region in the numerical model allowed for good agreement between the numerical simulation and the physical observations of the resin front position and mold filling time.     

Flow front advancement during composite processing: predictions from numerical filling simulation tools in comparison with real‐world experiments

Liquid composite molding (LCM) techniques are innovative manufacturing processes for processing fiber reinforced polymer parts used e.g. for aerospace structures. Thereby the reinforcing material is placed in a mold and infiltrated with a low viscosity polymer matrix. Increasing production rates as well as part complexity lead to high production risks such as air inclusions or incomplete mold filling. Numerical mold filling simulations are promising tools enabling the composite manufacturing engineer to detect dry spots in the mold and find the optimal positions of the resin entry and ventilation system at an early process development stage. Today, different numerical models and software packages are available for modeling the flow through the reinforcing structure for visualization of the flow behavior. The goal of this study is the systematic comparison of two different software packages, namely PAM‐RTM^® and OpenFOAM. Both software tools are operated as they are commonly foreseen. Real world experiments under real process conditions are the basis for the assessment of the numerical predictions. The resin transfer molding (RTM) experiments are executed in a tool with a transparent upper mold half in order to see the flow front advancement. POLYM. COMPOS., 37:2782–2793, 2016. © 2015 Society of Plastics Engineers     

注塑成型工艺参数对汽车保险杠翘曲变形的影响研究

结合Moldflow模拟分析软件和正交实验设计,通过对汽车保险杠的注射成型过程的数值模拟,系统分析了熔体温度、模具温度、注射时间、保压压力和保压时间等工艺参数对制件翘曲变形的影响规律.研究得到了最佳工艺参数组合方案,导人Moldflow软件分析后发现保险杠的翘曲变形得到明显改善;并通过实际的注塑成型实验验证了Moldflow分析结果.     

Modeling the chemorheological behavior of epoxy/liquid aromatic diamine for resin transfer molding applications

The analysis of the chemorheological behavior of an epoxy prepolymer based on a diglycidylether of bisphenol‐A (DGEBA) with a liquid aromatic diamine (DETDA 80) as a hardener was performed by combining the data obtained from Differential Scanning Calorimetry (DSC) with rheological measurements. The kinetics of the crosslinking reaction was analyzed at conventional injection temperatures varying from 100 to 150°C as experienced during a Resin Transfer Molding (RTM) process. A phenomenological kinetic model able to describe the cure behavior of the DGEBA/DETDA 80 system during processing is proposed. Rheological properties of this low reactive epoxy system were also measured to follow the cure evolution at the same temperatures as the mold‐filling process. An empirical model correlating the resin viscosity with temperature and the extent of reaction was obtained to carry out later a simulation of the RTM process and to prepare advanced composites. Predictions of the viscosity changes were found to be in good agreement with the experimental data at low extents of cure, i.e., in the period of time required for the mold‐filling stage in RTM process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4228–4237, 2006     

正弦波形梁构件的RTM工艺模拟研究

本文采用PAM-RTM软件对航空用正弦波形梁典型构件进行了模拟分析,对构件进行了几何建模及有限元划分,选择构件不同位置采用线注胶或点注胶的注射方式对构件进行了常压力注射下RTM工艺模拟研究,由此确定了最佳注射方式以及注胶口、出胶口位置,根据干斑缺陷可能出现的位置优化了出胶口的设置,得到了无缺陷的构件制品并对预成型体铺放过程中可能出现的边缘效应对树脂流动及干斑缺陷的影响进行了研究。研究表明：合理设置出胶口是一种较好的消除干斑缺陷的方法,计算机RTM模拟为复合材料模具设计及构件制造提供了重要依据。     

Thermal dispersion in resin transfer molding

This investigation focuses on the effects of thermal dispersion in resin transfer molding (RTM). A set of volume-average balance equations suitable for modeling mold filling in RTM is described and implemented in a numerical mold filling simulation. The energy equation is based on the assumption of local thermal equilibrium and includes a dispersion term. Thermal dispersion is an enhanced transport of heat due to local fluctuations in the fluid velocity and temperature away from their average values. Nonisothermal mold filling experiments are performed on a center-gated disk mold to investigate and quantify dispersion effects. Good agreement is found between the experimentally measured and numerically predicted temperatures, and a function for the transverse dispersion coefficient in a random glass fiber mat is determined. The results indicate that thermal dispersion is important in RTM processes and must be included in simulations to obtain accurate predictions.     

Analysis of resin injection molding in molds with preplaced fiber mats. II: Numerical simulation and experiments of mold filling

This work presents the results of numerical simulation and experimental visualization of the mold filling process in resin injection molding with preplaced fiber mats. The mold filling experiments were conducted with various mat stacks consisting of continuous random glass fiber mats and bidirectional stitched glass fiber mats. The use of two different mat types in the mat stack created porosity and permeability variations. The effect of these permeability variations was studied by taking flow pressure measurements and observing the progress of the flow front of a non-reactive fluid filling a clear acrylic mold that contained the reinforcement mat stack. Numerical simulation corresponding to each experiment was also carried out. The numerical results were compared to the experimental measurements.     

注射模浇口数目和位置的优化设计

给出一种注塑模具浇口位置和数目的优化设计方法.为达到减少塑件翘曲变形和熔接线的目的,以平衡充填和浇口数目最少为优化目标,以最大注射压力为约束条件,将浇口位置坐标作为设计变量,并根据浇口位置在充填数值模拟中对浇口数目和注射流率进行处理,从而可以同时优化浇口数目及其位置,优化求解采用遗传算法.算例表明,提出的优化模型和算法是有效的.     

Sensitivity analysis on resin transfer molding processes with edge effect and curing reaction characteristics

The mold filling time and resin flow front shape are of fundamental importance during resin transfer molding (RTM) processes, because the former influences productivity and the latter affects composites quality. In this article, considering both edge effect and curing reaction characteristics of the resin flow process, the sensitivity analysis method is introduced to investigate the sensitive degree of mold filling time and resin flow front shape to the key material and processing parameters. The function employed to describe the resin flow front shape is defined, and the mathematical relationships of the key physical parameters, such as fluid pressure sensitivity, flow velocity sensitivity, mold filling time sensitivity, and resin flow front shape sensitivity, are established simultaneously. In addition, then the resin infiltration process is simulated by means of a semi‐implicit iterative calculation method and the finite volume method. The simulated results are in agreement with the analytical ones. The results show that under constant injection velocity conditions, both the change in the resin temperature and the alteration of the inlet velocity hardly affect the resin flow front shape, whereas the influence of edge permeability on the resin flow front shape is the greatest. This study is helpful for designing and optimizing RTM processes. POLYM. COMPOS., 36:2008–2016, 2015. © 2014 Society of Plastics Engineer     

Development of resin transfer molding process using scaling down strategy

The virtually developed resin transfer molding (RTM) manufacturing process for the large and complex composite part can be validated easily with the trial experiments on the scaled down mold. The scaling down strategy was developed using Darcy's law from the comparisons of mold fill time and mold fill pattern between full‐scale product and scaled down prototype. From the analysis, it was found that the injection pressure used in the scaled down mold should be the full‐scale injection pressure by the times of square of geometrical scale down factor, provided the identical injection strategy and raw material parameters were applied on both the scales. In this work, the RTM process was developed using process simulations for a large and complex high‐speed train cab front and it was validated by conducting experiments using a geometrically scaled down mold. The injection pressure as per the scaling down strategy was imposed on the scale downed high‐speed train cab front mold and a very close agreement was observed between the flow fronts of experimental and simulated results, which validates the scaling down strategy and the virtually developed RTM process for the full‐scale product. POLYM. COMPOS., 35:1683–1689, 2014. © 2013 Society of Plastics Engineers     

树脂传递模塑充填过程的数值模拟

树脂传递模塑成型（RTM）工艺是在一定温度及压力下把低黏度的树脂注入预先置有增强纤维的模具中,然后固化成型的一种复合材料液体成型方法。本文建立了RTM工艺充模过程的数学模型,并采用有限元/控制体积法实现了对复杂薄壁构件的充填模式、压力场和速度场的模拟。     

A process performance index and its application to optimization of the rtm process

Resin transfer molding (RTM) is a promising manufacturing process for hig formance composite materials. However, the fact that RTM process design has traditionally been an expensive, time‐consuming trial‐and‐error procedure has p ited its wide application base. This paper proposes a solution to that problem—a simulation‐based optimum process design scheme for RTM. This scheme ei engineers to determine the optimum locations of injection gates and vents so both process efficiency and high part quality can be ensured. Essential to this mum process design scheme is a process performance index, which is defined respect to the major factors influencing RTM process efficiency and part quality This index is then used as the objective function for the RTM process design optimization model. Gate and vent locations are the process design parameters optimized. All data is obtained by running an RTM simulation program, and th netic algorithm (GA) is employed to carry out the optimization procedure for design parameters. It is found that constant pressure optimization will yi process with a short flow path, whereas constant flow optimization will yield process with smooth and vent‐oriented flow pattern. Although there is no dry factor in the objective function, it is interesting to note that both constant pres and constant flow optimization procedures result in process designs with a mil mum probability of dry spot formation. This study finds that, in general, cons flow optimization should be employed if injection pressure is not a major cone otherwise, constant pressure optimization should be used. Two case studies presented to illustrate the efficacy of this approach.     

Resin transfer molding (RTM) process of a high performance epoxy resin. II: Effects of process variables on the physical,static and dynamic mechanical behavior

The effects of processing variables on the mechanical behavior and the void content of one‐part epoxy based glass fabric composites produced by resin transfer molding (RTM) were investigated. The variables studied included injection pressure, injection temperature, and fabric structure. Image analysis was used to measure the void content in the composites. Variations in injection pressure and temperature were found to have a significant effect on the quality and the mechanical performance of composites. The optimized physical and mechanical performance of the composites was obtained by processing the resin at 160°C under 392 kPa pressure. Molding of highly permeable EF420 fabric required a shorter mold filling time, but resulted in reduced flexural strength and storage modulus in the resulting composites as compared with that of the composites containing 1581 fabric.     

Analysis of the vacuum infusion molding process

The vacuum infusion molding process is becoming increasingly popular for the production of large composite parts. A comprehensive model of the process has not been proposed yet, making its optimization difficult. The flexible nature of the vacuum bag coupled to the varying pressure inside the mold cavity results in a variation of the cavity thickness during the impregnation. A complete simulation model must incorporate this phenomenon. In this paper, a complete analysis of the vacuum infusion molding process is presented. The analysis is not restricted to the theoretical aspects but also reviews the effect of the main processing parameters. The parameters investigated in this paper are thought to be those of most interest for the process, i.e. the compaction of the reinforcement, the permeability, the infusion strategy and the presence of flow enhancement layers. Following the characterization experiments, a 1‐D model for the vacuum infusion molding process is presented. This model is derived assuming that an elastic equlibrium holds in the mold cavity during mold filling. Even though good agreement was found between simulation results and experiments, it is concluded that additional work is needed on the numerical model to integrate interesting findings from the experimental part.