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2022-08-25
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The application of Moldflow software in the design of injection molding mold

the acquisition of high-quality injection molding products is based on excellent product design, mold design and injection molding process. Many defects of injection molded products (such as weld marks, short shots, product deformation, etc.) are related to the flow mode of melt in the mold, so the control of melt flow mode has become the key to optimize the injection molding process. With the rapid development of CAE technology, especially the introduction of Moldflow software, computer simulation and analysis of injection molding process can be realized; Predict the possible defects of the melt in the process of filling, pressure maintaining, cooling, etc. before the mold test, so as to help the process personnel analyze and improve, improve the success rate of the first mold test, so as to reduce the manufacturing cost and shorten the development cycle. In this study, Moldflow software is used to dynamically simulate the filling, cooling, warping and other behaviors of a thin-walled injection molding product, which provides a theoretical basis for the mold design of the product and the determination of injection molding process parameters, so as to improve the molding quality of the product

1 injection molding CAE

injection molding CAE technology is mainly composed of three parts: (1) establish the mathematical model of melt flow and heat transfer in the mold cavity according to the basic theories of continuum mechanics, plastic processing rheology and heat transfer; (2) According to the distribution of pressure field, temperature field and velocity field in the forming process, the quantitative solution method is established by using numerical calculation theory. (3) according to the above model and calculation method, the dynamic filling and cooling process of the melt in the actual forming is visually displayed on the computer screen by using computer graphics. The core of this technology is to establish a reliable mathematical model and the corresponding numerical calculation method

for thin-walled plastic parts, hele Shaw flow model based on unsteady and non isothermal conditions can be used, combined with continuity equation, motion equation and energy equation based on continuum mechanics theory to describe the injection process, as well as constitutive relations and boundary conditions to describe material properties, Accurately describe the injection filling process (generally, the above equations need to be reasonably simplified and assumed in combination with the characteristics of injection molding, so as to obtain the control equation that can best reflect the process and is convenient for numerical calculation). The model thus established is the midplane model, which is solved by using the mixed finite element/finite difference numerical method combined with the flow analysis network method, so as to obtain the pressure field in different time periods in the actual injection process Simulation results of temperature field and other changes (the solution method adopts finite element approximation in the flow plane, and the thickness direction and time derivative adopt finite difference approximation, which integrates the advantages of the two and is suitable for the simulation of arbitrary shape cavities in the plane). Through the above methods, the following governing equations of rectangular coordinate system can be obtained

2 example analysis

2.1 molding process

the plastic part is a plastic connector, the material is ABS, the external surface quality requirements are high, and the mold design is the first mock examination with four cavities. Moldflow's MPI module [] is used to simulate the melt flow process of the plastic part, determine the gate position, analyze the filling, cooling, warping and accumulation of pneumatic force, predict the filling time, cavity pressure distribution, temperature industry is the carrier distribution to solve employment, and provide process parameters for the actual injection molding

2.2 modeling

create a solid model in Pro/engineer software, convert and save it into STL model, import it into Moldflow software through STL file format, and generate a finite element lattice model for numerical calculation in the preprocessor of MPI. Figure L shows the divided lattice model of plastic parts, which contains 14956 triangular elements

2.3 process parameter setting

according to the process requirements of the selected material, the process parameters are set as follows: injection pressure 130Mpa, mold surface temperature 40 ° C, melt temperature 240 ° C

2.4 optimal gate location

the design of the gate mainly includes the gate. Lu Changqing, the director of China Zhongwang, said that Zhongwang attaches importance to industrial cooperation and the development of new energy vehicles, has prepared sufficient resources for this purpose, and will make the necessary investment and capacity construction number, location, shape and size in due course. The shape and size of the gate determine the flow direction and equilibrium state of the polymer. When the flow is unbalanced, it is easy to cause uneven shrinkage and warpage deformation, and affect the location and internal stress orientation of bubbles and weld lines; The number and location of gates affect the filling mode of pouring 1:1

no matter what form of gate is used, the opening position has a great impact on the molding performance and molding quality of plastic parts. Improper gate position often makes the gas in the molding cavity unable to escape during the injection molding process, resulting in injection defects such as short shots, cavitation, scorch marks, etc. Therefore, reasonable selection of gate position before mold design is an important link to improve the molding quality of plastic parts

Figure 2 optimal gate location

in this study, Moldflow software is used to analyze the optimal gate, and the gate location is set according to the analysis results, which can avoid plastic defects caused by improper gate location. The specific processing process is: grid division, reasonable adjustment, cavity layout, analysis content and parameter setting, material selection, injection parameter setting, etc. Figure 2 shows the best gate position obtained by moldflow. software. According to the analysis results, the position indicated by the arrow in the figure is the best gate position, and the designed gating system is shown in Figure 3

Figure 3 layout of gating system

2.5 analysis of simulation results

2.5.1 filling

the design of gating system directly affects the filling behavior of melt, and the ultimate purpose of filling analysis is to obtain the best design of gating system. Figure 4 shows the analysis results of mold filling time. Different colors reflect the change of melt flow state and mold filling process, from which we can know whether the cavity is full and whether the mold filling process is balanced. It can be seen from Figure 4 that the filling time is 1.272s, and the color transition is relatively soft, indicating that the filling process is relatively gentle, and the mold condition is also reasonable. This proves that the gating system shown in Figure 3 is feasible

Figure 4 mold filling time

2.5.2 cooling

Moldflow software can also be used to analyze the cooling effect of the mold cooling system, calculate the cooling time and forming cycle. On the premise of uniform cooling of plastic parts, optimize the layout of cooling pipes, shorten the cooling time and forming cycle, and improve production efficiency

the cooling scheme and temperature distribution of plastic parts are shown in Figure 5. According to the analysis results in Figure 5, most positions of plastic parts have reached the predetermined ejection temperature (60 ° C), indicating that the setting of cooling water channel is reasonable and the cooling scheme is feasible

Figure 5 cooling scheme and temperature distribution of plastic parts

2.5.3 warpage analysis

through warpage analysis, we can understand the deformation of plastic parts, which helps designers predict the shrinkage of materials and optimize the design of cooling system in mold design, so as to control the deformation of plastic parts. Figure 6 is the warpage analysis diagram of plastic parts. It can be seen from Figure 6 that the minimum warpage deformation is 0.0037mm and the maximum is 0.7273mm; The maximum warpage is located at the free end of the plastic part (as shown by the arrow), which is mainly caused by the shrinkage of the plastic part. Through CAE analysis, the design scheme meets the quality requirements of plastic parts

Figure 6 warpage analysis of plastic parts

3 conclusion

the Moldflow software is used to determine the optimal gate position of the mold, and the melt filling, cooling and other processes are simulated, which optimizes the injection molding process parameters, reduces the product development cost, and helps the process personnel understand the causes of defects from the essence and find out the elimination methods

analyzing the melt flow in the cavity in advance through CAE can guide the mold design and evaluate the rationality of the design scheme; Before mold processing, using CAE software to test and repair the mold can improve the success rate of one-time mold test

numerical simulation provides a fast, accurate and practical analysis and evaluation method for mold design, which is of great significance to reduce the scrap rate of mold repair, reduce costs and improve product quality. (end)

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