Resin Velocity Research Articles

Application of capacitive sensors and controlled injection pressure to minimize void formation in resin transfer molding

AbstractVoid formation as a result of irregular resin flow at the flow front is discussed and a practical method for reducing void formation during resin transfer molding (RTM) is introduced. In this study, a sensor system is developed for in situ measurement of resin velocity inside a closed cavity. Assisted by the acquired data, a resin injection system is augmented to automatically adjust the injection pressure and achieve a uniform flow front velocity. It is proven, that the developed system is suited to monitor the resin flow front and is able to sufficiently control flow velocity of a linear flow front. Test specimen produced by this method show significantly reduced void contents in comparison to a common resin transfer molding process.

Vacuum assisted resin transfer Moulding process review and variability analysis using Taguchi optimization technique

A process variability analysis is carried out to find the most influencing input parameter and corresponding output parameter variation using the L9 approach. The common factors, levels, parameters, and responses are mentioned in the following section. The mean response curve for the output parameters is also presented. Empirical relations are obtained for finding the responses in terms of the common factors. EBX936 (Non-Crimp bidirectional, Glass Reinforcement Manufactured by-Tech. Textile, USA) with 3, 6, 12 number of layer (NOL) is the material system used in the analysis. The infusion pressure is kept in the workable range of 60 to 70 kPa as normally used in the VARTM process. Very high vacuum at inlet increases the resin velocity through the preform and hence the time of infusion will reduce drastically, giving very little time for proper saturation of fibers in the preform. Therefore, to keep the velocity in the middle range of velocities during the infusion low injection pressures are selected. The viscosity of the resin is selected in the range 0.2 to 0.3 Pa.s.

Experimental and Numerical Investigation of Resin Flow Within Different Shapes in the Process of Composite Construction by Using of the Resin Transfer Method

The main objective of this paper is to analyze the injection cycle in manufacturing of rectangular, rhombus, triangular, trapezoidal parts by using of the resin transfer method. To this end, the resin flow of the injection cycle in rectangular, rhombus, triangular, trapezoidal molds is studied using both experimental method and numerical simulation. Injection cycle is modeled for two composite parts with glass resin epoxy fibers. The injection device is used for experimental measurements. The available resin in the injection mold and its movement toward forward and permeability in rectangular, rhombus, triangular, trapezoidal molds are measured by using this system. Different tests were conducted for woven glass fibers. Then, the finite volume method was used to model the flow of resin in four molds. Finally, the injection time for glass fiber was determined by experimental and numerical methods, and numerical simulation results were compared with experimental measurements. In this research, resin velocity graphs for woven glass fibers are plotted, which show a decrease in the velocity of the resin from the injection site. It was observed in a 90 layout with a woven vertical glass fiber with a porosity of 0.6607, the rate of resin advance compared to porosity is 0.623, and also porosity permeability graphs are presented in a layout for glass fibers. The porosity in the glass fibers in the 9-layer mode was 0.6607, and in the 10-layer mode, it was equal to 0.623.

Smoothed particle hydrodynamics simulation of dual-scale flow during resin transfer molding

Smoothed particle hydrodynamics is a Lagrangian meshless particle method, which can be applied to the modelling of complex flow in molding simulation. In the present work, firstly, by comparing the results of smoothed particle hydrodynamics and volume-of-fluid simulation for micro-scale flow within the fiber tow, the feasibility of smoothed particle hydrodynamics to simulate the flow in porous media was demonstrated. Secondly, the dual-scale flow in the dual-scale fiber preform during resin transfer molding was investigated using smoothed particle hydrodynamics simulation. The resin melt was modeled as fluid particles, and the fiber preform was regarded as dual-scale porous media depicted by fixed boundary particles. The smoothed particle hydrodynamics simulation described the evolution of the flow and the formation of the void. The effects of several factors on the size of the void were also studied. The results showed that the void size increased with the increase of vertical inter-tow dimension while decreased with the increasing resin velocity and viscosity.

Applying CFD in Manufacturing of Polymer Composite Reinforced with Shape Memory Alloy via Resin Transfer Molding Process

This paper aims to study the manufacturing process of polymer composite reinforced with shape memory metal alloys by RTM process using ANSYS CFX ® software. The mathematical modeling consists of mass and momentum conservation equations applied to a metal mold with dimensions 0.3 × 0.3 × 0.002 m³ containing ten NiTi alloy wires 0.0005 m diameter. Results of the flow front position of the resin (polyester resin mixed with calcium carbonate particles), pressure, streamlines and resin velocity fields during the process are presented and discussed. We conclude that the addition of calcium carbonate resulted in increased resin viscosity and greater inlet pressure obtained at the entrance of the mold which resulted in short time to full fill the mold and the highest pressures at the NiTi alloy wire surface were obtained in the central region and near the mold entrance.

Multi-scale computational fluid dynamics of impregnation die for thermoplastic carbon fiber prepreg production

A multi-scale computational fluid dynamics (CFD) model of a pultrusion process was proposed for unidirectional carbon fiber (UD-CF) prepreg production. Polyamide 6 (PA6) and polyacrylonitrile-based CF were used as the thermoplastic polymer matrix and reinforcement, respectively. The non-Newtonian viscosity of PA6 was expressed by Carreau's model. A micro-scale CFD model was constructed to obtain a proper resin permeability to CF filaments, while the tow domain was treated as sliding porous media in the macro-scale CFD. The resin velocity profile showed a similar shape to the relative resin amount experimentally measured in the UD-CF prepreg. The uniformity index of the resin velocity (UIv) on the outlet surface was calculated for 45 case studies with several tow speeds and resin flow rates. The tow speed showing a maximum UIv was remarkably well expressed as a linear function of the slip velocity, which is the difference between the tow speed and resin velocity.

PS0011-227 VaRTM樹脂含浸時の平織繊維材におけるボイド形成のモデル化

During resin impregnation into fiber bundles in vacuum-assisted resin transfer molding (VaRTM), entrapped air in resin may remain as voids in the products. Since the presence of the voids deteriorates the composites mechanical properties, prediction of the void generation is required. The purpose of this study was to evaluate the effect of the resin impregnation angle in an anisotropic fabric on the relationship between the amount of voids formed and the resin velocity. We performed experiments on 2D radial-injection VaRTM using laminated anisotropic plain-woven fabrics, and determined the void distribution and the formation of the void. Based on the experimental results, we developed a mathematical model for predicting the void formation for an arbitrary impregnation angle and velocity. Comparison of the model predictions with experimental results revealed good agreement.

The investigation of bubble mobility in channel flow with wavy porous media walls

During composites processing, thermoset polymer resin is injected into network of densely packed continuous fibers with the goal of complete saturation. The formation and entrapment of gas bubbles, due to the presence of air or volatiles during processing, will create voids in the cured composite. Voids can degrade the mechanical properties and increase design risks and costs. Thus, there is a need to understand the two phase flow of resin and bubbles through channels within fibrous porous media. A two-phase flow model of a channel containing resin and gas bubbles is presented. The boundaries of the channel are porous media with sinusoidal wavy or corrugated walls, which represents the wavy nature of the porous media. This causes the change in bubble movement dynamics, due to the non-uniform pressure gradient induced by non-rectilinear walls. Parameters such as porous media permeability, channel waviness, and channel width are studied to investigate the influence of wavy porous wall effects on the two-phase flow and how these parameters may influence the likelihood of bubble entrapment. By maximizing the bubble mobility, which is the ratio of average bubble velocity to average resin velocity, one can remove the bubbles from the system before the resin cures.

Resin transfer molding process: a numerical and experimental investigation

Resin Transfer Molding (RTM) is one of the composite manufacturing technique that consists in injecting a resin pre-catalysed thermosetting in a closed mold containing a dry fiber preform, where the resin is impregnated. In this sense, the aim of this research is to study theoretically and experimentally the RTM process. Experimental and simulations of the rectilinear infiltration of polyester resin (filled and non filled with CaCO 3 ) in mold with glass fiber preform were performed in cavity with dimensions 320 · 150 · 3.6 mm. Numerical results of the filling time and fluid front position over time were assessed by comparison with experimental data and good accuracy was obtained. It was verified that, the CaCO 3 content affect resin velocity during filling, the permeability of the reinforcement and resin viscosity, thus the filling time is affected strongly.

Analytic Study of Non-Newtonian Double Layer Coating Liquid Flows in Optical Fiber Manufacturing

In mass manufacturing of optical fibers, the wet-on-wet polymer resin coating is an efficient process for applying double layer coatings on the glass fiber. This paper presents an analytic study on the behavior of non-Newtonian polymer resins in the double layer coating liquid flow inside a secondary coating die of the optical fiber coating applicator. Based the approximations of fully developed laminar flow and the power law model of non-Newtonian fluid, the coating liquid flow of two immiscible resin layers is modeled for the simplified geometry of capillary annulus, where the surface of glass fiber moves at high fiber drawing speed. The effects of important parameters such as non-Newtonian fluid properties, the coating die size, and fiber drawing speed are investigated on the resin velocity profiles and secondary coating layer thickness.

A Computational Investigation of Thermal Effects on Resin Coating Flows in an Optical Fiber Drawing System

In manufacturing optical fibers, there has been intense research efforts of continually increasing fiber drawing speed to improve productivity. However, higher speed fiber drawing poses new challenge in many areas of optical fiber manufacturing. In this paper, thermal effects on coating resin flow in an unpressurized coating applicator are studied numerically. Present simulation results found that higher fiber drawing speed leads to severe viscous heating in coating resin flow and significant increase of resin temperature, which in turn leads to substantial viscosity decrease. These thermal effects profoundly alter the resin flow patterns and velocity profiles in the coating die and they should be considered in controlling the final coating thickness.

Control of resin flow/temperature using multifunctional interdigital electrode array film during a VaRTM process

Most conventional methods for flow control during resin transfer molding have varied the applied pressure using pressure regulators. However, with this method it is difficult to control the flow far from the inlet or outlet points. The present study proposes a flow control scheme by monitoring and actuating flow/temperature using a thin multifunctional interdigital electrode array film. The film is used for estimation of resin impregnation and temperature distribution, and increases the resin temperature by dielectric heating at arbitrary positions on the film, thereby increasing the resin velocity at the required positions. Foam cored GFRP structures were impregnated with resin by VaRTM, and the effectiveness of the flow control scheme assessed. The occurrence of dry spots was effectively prevented.

Glass Fiber Permeability Using the VARTM Process

This study investigated a flow rate control system for the vacuum-assisted resin transfer molding (VARTM) process. Using Darcy’s equation, the permeability of multiaxial glass fiber composites is predicted and experimentally confirmed. The resin velocity vector is inversely proportional to the fiber mat length and resin viscosity, but proportional to the fiber mat permeability. In this study, the permeability of the preform and viscosity of the epoxy resin were measured using multiaxial glass fiber by VARTM. The permeability and time for impregnation differed according to the fiber direction in the VARTM process. The results indicated the need for further study of reinforcement fiber permeability in VARTM processing design.

Similarity Relations of Resin Flow in Resin Transfer Molding Process

Liquid molding processes, such as resin transfer molding, involve resin flow through a porous medium inside a mold cavity. Numerical analysis of resin flow and mold filling is a very useful means for optimization of the manufacturing process. However, the numerical analysis is quite time consuming and requires a great deal of effort, since a separate numerical calculation is needed for every set of material properties, part size and injection conditions. The efforts can be appreciably reduced if similarity solutions are used instead of repeated numerical calculations. In this study, the similarity relations for pressure, resin velocity and flow front propagation are proposed to correlate another desired case from the already obtained numerical result. In other words, the model gives a correlation of flow induced variables between two different cases. The model was verified by comparing results obtained by the similarity relation and by independent numerical simulation.

Resin Velocity and Temperature in Screw Processing

To analyze the effects of forces that affect the resin and its movement while it is processed in a screw, a simulation method is proposed based on finite element. The method includes mainly two series of equations and their numerical calculations. The movement equation of the resin in a screw represents the stress, the strain, and the relationship between velocity and stress of the cells. A discretized differential equation is used to express the exchange of shearing heat. Combined with the displacement and temperature boundary, the equations are solved by the numerical calculation procedure, and velocity and temperature distribution are worked out. The computation sample has illustrated the validity of the proposed method. And the results have shown its importance in an industrial application with aspects such as redesigning a screw or improving the quality of the plastic products.

Unified saturation and micro-macro voids method in Liquid Composite Molding

The topic of this paper concerns void defects. We introduce a model to describe the macroscopic resin flow considering the compression of residual air in the preform. A microscopic flow model is also developed to account for the microvoid formation due to the variation of resin velocity at the flow front. According to these mathematical models, a numerical simulation code was developed to perform a combined macro and micro flow analysis with the saturation of the medium. The results of these simulations are compared with experimental results obtained by the laboratory device. We present the real-time measurement of the void content evolutions during the injection, using an original sensor. Our technique is based on the electrical conductivity of the injected liquid. After the material and method presentation, some results obtained during injection are shown. The developed analysis technique and the numerical simulation code can be used for obtaining the optimal processing conditions and design parameters in manufacturing of composites by Liquid Composite Molding (LCM) processes.

Numerical Modelling of Design Parameters for Manufacturing Polyester/Glass Composites by Resin Injection Pultrusion

Resin Injection Pultrusion (RIP) is an automated, continuous process and is one of the most cost-effective methods for manufacturing composite materials with constant cross sections (such as rod stock, beams, channels and tubing). In the present work, a 3-D finite volume technique was developed to advance the liquid resin flow front through the fibre reinforcement in the injection pultrusion process. The objective of this study was to improve fibre reinforcement wet-out and thus the quality of the pultruded part in an injection pultrusion process. The complete wet-out of the dry reinforcement by the liquid resin depends on various design and process parameters. The design parameters explored in this study were the aspect ratio of the final composite, injection slot width, injection slot location from inlet of injection chamber, and location of the multiple injection ports. The numerical model simulates the flow of polyester resin through glass rovings and predicts the impact of the design (geometric) parameters on wet-out, resin pressure field, and resin velocity field. The location of the liquid resin flow front has been predicted for an injection slot, as well as for five discrete injection ports.

Manufacturing Modeling of Three-Dimensional Resin Injection Pultrusion Process Control Parameters for Polyester/Glass Rovings Composites

Pultrusion, sometimes referred to as continuous resin transfer molding process, is a continuous, cost-effective method for manufacturing composite materials with constant cross sections (such as rod stock, beams, channels, and tubing). The objective of this study is to improve the fiber reinforcement wetout and thus the quality of the pultruded part in the injection pultrusion process. The complete wetout of the dry reinforcement by the liquid resin depends on various design and process parameters. The process parameters modeled in this study are fiber pull speed, fiber volume fraction, and viscosity of the resin. In the present work, a three-dimensional finite volume technique is employed to simulate the liquid resin flow through the fiber reinforcement in the injection pultrusion process. The numerical model simulates the flow of polyester resin through the glass rovings and predicts the impact of the process parameters on wetout, resin pressure field, and resin velocity field. The location of the liquid resin flow front has been predicted for an injection slot as well as for five discrete injection ports.

Multiple Injection Port Simulation for Resin Injection Pultrusion

Resin injection pultrusion is a continuous process for manufacturing composite materials. Complete wet-out of the reinforcement fibres in the resin injection chamber is essential for producing good quality pultruded parts. The magnitude of the injection pressure is extremely important to achieve good wet-out of the reinforcement fibres. At high pull speeds, high viscosity, or high fibre volume fractions, the injection pressures required to achieve complete wet-out are very high and are practically very difficult to achieve. This work focuses on reducing the injection pressure needed to achieve complete wet-out by using a multiple injection port system for epoxy/glass rovings and polyester/glass rovings composites. The recommended injection pressures for complete wet-out are predicted for a variety of processing parameters. Darcy's law for flow through porous media is employed for modelling the fibre/resin system of injection pultrusion. The governing equations are solved via the finite volume method to predict the resin pressure field, the resin velocity field, and the location and shape of the resin flow front. Different permeability models1,2 are used to determine the transverse permeability and the longitudinal permeability.

Injection Pultrusion Simulation for Polyester/Glass Mat/Rovings/Mat Composites

Producing quality pultruded parts requires that complete wet out of the reinforcement fibers is achieved in the injection chamber. The magnitude of the injection pressure is extremely important for achieving good wet out of the fibers. This work focused on the impact of pull speed, resin viscosity, and product thickness on resin fiber wet out in the injection chamber for a polyester resin (mat/roving/mat) composite. Recommended injection pressures for complete wet out are predicted for given sets of processing parameters for polyester/glass fiber (mat/rovings/mat) composites. Flow through porous media (Darcy’s law) is employed to model the fiber/resin system of injection pultrusion. The governing equations are solved, by using the finite volume method, to predict the resin pressure, resin velocity field, and resin moving flow front location. The Gutowski (Gutowski, T.G., Morigaki, T. and Cai, Z. (1987). The Consolidation of Laminate Composites, Journal of Composite Materials. 21(7): 172-187) permeability model is used to determine the permeability in the roving layer and the Kozeny-Carman (Carman, P.C. (1939). Flow through Granular Beds, Trans. Int. Chem. Eng., 15: 150-166) model is used to predict the permeability in the mat layers.