Application of the hottest injection CAE Technolog

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Application of injection molding CAE Technology in mold design and development

in order to enhance the reliability of mold design, Hisense mold company introduced American moldflow/mpi material flow analysis software for injection molding process simulation analysis (CAE), including filling, pressure maintaining, gas assisted, warping and other stages. By combining the injection molding CAE technology with the rich practical experience accumulated by the company in mold development for many years, it has played a very significant role in determining the mold pouring system and gas assisted process plan, helping customers improve product design, predicting and improving injection molding defects, greatly improving the reliability coefficient of mold development, and achieving significant economic benefits

I. Introduction to injection molding CAE technology

cae (Computer Aided Engineering) technology is literally understood as computer-aided engineering, which is exactly the analysis, calculation and Simulation in engineering design. Injection molding CAE technology is an important part of CAE technology. It is based on the basic theories of plastic processing rheology and heat transfer, establishes the physical and mathematical models of plastic melt flow and heat transfer in the mold cavity, uses the numerical calculation theory to construct its solution method, and uses the computer graphics technology to visually simulate the dynamic filling, cooling and other processes of the melt in the actual molding on the computer screen, The state parameters (such as pressure, temperature, speed, etc.) in the forming process are given quantitatively. Injection molding CAE technology can analyze and simulate the mold design scheme on the computer before mold manufacturing, predict the potential defects in the design, and provide a scientific basis for designers to modify the design. The direct benefit of applying injection CAE technology is to save time and effort, reduce the times of mold testing and repair, shorten the mold design and manufacturing cycle, reduce costs, and improve product quality

the general process of CAE analysis of injection molding is shown in Figure 1

Figure 1 general process of injection molding CAE analysis

II. Application of injection molding CAE Technology in mold design and development

most articles on injection molding CAE technology introduce the functions and applications of each module of the software from the perspective of software. Based on the experience of CAE analysis of injection molding in recent years, the author introduces several main application fields of injection molding CAE Technology in mold design and development from the perspective of enterprise demand and use

1. determine the mold gating system scheme

the gating system of the mold has a decisive impact on the final injection molding quality of the mold. A reasonable gating system can make the plastic melt filling balanced and uniform, avoid many injection molding defects, obtain satisfactory plastic quality, and extend the service life of the mold. Determining a reasonable gating system scheme is the most basic work of injection molding CAE analysis, and it is also a very important aspect of mold design. Especially for hot runner mold, one is to be fast. In the early stage of design work, gate layout must be provided for designers to design relevant structures and order hot runner; Another requirement is to be accurate. Because the hot runner is expensive and cannot be changed after it is made, the scheme of the gating system must be accurate. This puts forward higher requirements for material flow analysis. At present, mature injection molding CAE analysis software takes flow analysis as the most basic module, and the accuracy of analysis is relatively high

the most basic requirement for determining a reasonable gating system is flow balance, so that the melt can be evenly and synchronously filled into all parts of the workpiece. At the same time, some key quality areas should be taken into account, so that the weld lines can be produced in places that do not affect the appearance requirements. The following is an example of the layout of the gating system for the back shell of a 29 inch TV. The gating system is a four point hot runner with gate diameter φ 4.5mm, sprue diameter φ 10mm, the layout is shown in Figure 2

Figure 2. The simulation analysis results of the pouring system layout of the 29 inch TV rear shell

part filling are shown in Figure 3

Fig. 3 Simulation Analysis of part filling

from the analysis result, it can be seen that the flow is relatively balanced, and the melt can basically fill all parts of the part evenly and synchronously, so as to achieve a relatively satisfactory injection effect

2. determine the gas assisted molding scheme and predict the gas penetration effect

gas assisted injection molding technology is a new plastic injection molding technology. Its principle is to use high-pressure gas to produce hollow sections in the plastic parts, and use gas to maintain pressure instead of plastic injection to complete the injection molding process. Compared with the ordinary injection molding process, it can eliminate the shrinkage marks on the surface of the parts, reduce the internal stress of the products, save raw materials, prolong the service life of the mold, and shorten the production cycle. It is known as a revolution in the injection molding process whose import volume is affected by the massive import of precious non-metallic minerals such as diamonds. It is widely used in almost all plastic parts fields, such as household appliances, automobiles, furniture, daily necessities, etc

gas assisted injection molding process involves the gas-liquid two-phase flow and interaction of polymer melt and high-pressure gas, so the design parameters and control parameters of gas assisted injection molding process are greatly increased. The difficulties of gas assisted molding scheme mainly include two aspects: one is the layout of air duct, including the determination of air inlet mode, air duct configuration and section size; The second is the process parameters of gas assisted injection molding, including the determination of shortage volume, delay time and gas pressure curve

mature CAE gas assisted analysis can solve these two problems. By completing the simulation process of gas assisted injection molding on the computer, predicting the flow and penetration of melt and gas in the mold cavity, optimizing the product and mold design, improving the layout and size of the airway, and optimizing the molding process parameters, the reliability of gas assisted mold development can be greatly improved. For example, Xiangxi laodi biological Co., Ltd., Hubei laolongdong Eucommia ulmoides development company, Henan hengruiyuan Industrial Co., Ltd., Gansu runlin Eucommia ulmoides development company, etc.

the following is an example of CAE simulation analysis of 29 inch TV front shell gas assisted mold: analysis material: BASF 466i; Air inlet mode: nozzle air inlet; The cross-section form of the airway is shown in the figure below

process parameters: mold temperature: 50 ℃; Melt temperature: 230 ℃; Injection time: 3 s; Cooling time: 20 s; Injected melt volume: 98%; Air intake delay time: 0.5 s; The gas pressure control curve is shown in the figure below

the gas penetration effect is shown in Figure 4 and figure 5

Figure 4 gas penetration (1)

Figure 5 gas penetration (2)

from the above analysis results, it can be seen that after scientific CAE simulation analysis, the reasonable airway layout and gas assisted process parameters are determined. The airway is evenly configured on the whole workpiece along the direction of material flow, and the gas can effectively penetrate to the end of the airway, fully playing the role of pressure maintaining, which is helpful to solve the problem of shrinkage marks on the surface of the workpiece, Improving the surface quality of parts plays a significant role. This result is also fully verified by the later model test

3. the product adjustment meets the flow balance or design needs

for some molds, the gate position can only be limited to a certain area. For example, for the rear shell of TV set with straight gate, the gate can only be placed in the box with label in the middle of the back of the workpiece, not in other positions. The material flow balance may not be guaranteed when the sample of the accelerating gear is cooled. In order to solve this problem, it is usually necessary to adjust the local shape and wall thickness of the product. For example, the ultimate goal is to achieve balanced filling by reducing the wall thickness or setting a choke in the direction of faster filling, and increasing the wall thickness or reducing some heat dissipation holes in the direction of slower filling. The following is an example of the rear shell of a LCD TV. With a fixed straight gate, there is a large difference in the flow balance on both sides. The flow balance is achieved by adjusting the local wall thickness

Fig. 6 filling condition of the preliminary test scheme

the filling condition of the preliminary test scheme is shown in Fig. 6. It can be seen that there is a large difference in the flow balance on both sides, and the filling on the right side is slow. According to the slow filling on the right side, increase the wall thickness of the internal area of the black line shown in the figure below by 0.3mm to play a drainage role. The flow after wall thickness adjustment is shown in Figure 8. It can be seen that the flow balance of the whole workpiece is significantly improved, and both sides are basically filled synchronously

4. predict and improve injection molding defects

there are many defects that may appear in the injection molding process, and those that have a great relationship with the layout of the gating system are weld marks, trapped gas, shrinkage and warpage, etc. these defects can be improved through CAE analysis

Figure 7 partial adjustment and drainage of wall thickness

figure 8 filling after wall thickness adjustment

weld marks are thin linear marks formed on the surface of the workpiece after the melt flow front meets, which not only affects the appearance of the plastic part, but also reduces the strength of the workpiece. However, because most molds have multiple gates, and there will be holes of various shapes on the parts, the generation of weld lines is inevitable. Only by modifying the gating system or adjusting the wall thickness can the weld lines be reduced, reduced or located in relatively unimportant areas, so as to reduce the impact on the appearance or strength of plastic parts. For example, the welding line of the front shell of the TV cannot be located at the four corners, because that is the place where the fixed picture tube is under the greatest stress. You can try to make it located in the horn window hole area on both sides, while the rear shell of the TV can try to make it located in the heat dissipation hole or decorative stripe area

trapped gas is formed because the air surrounded in the middle cannot be discharged after the front of melt flow converges, which will cause defects such as scorch, short shot or surface speckle. For trapped air, the air can be driven to the parting surface or other places easy to be discharged by adjusting the pouring system, the local wall thickness of the workpiece and other measures, and it can be discharged out of the mold through the exhaust slot. If this cannot be achieved, the position of trapped gas can be accurately predicted through analysis, and exhaust inserts can be added at the corresponding parts to achieve the exhaust effect

concavity is also a common surface defect, which is mainly caused by insufficient pressure holding. It usually occurs in thick walls or places with reinforcement, columns and other structures on the back. Although dimpling generally does not affect the strength and function of the workpiece, it has a fatal impact on the appearance of the workpiece. Through the pressure maintaining analysis of injection CAE software, we can predict the area where shrinkage may occur, and take corresponding measures, such as reducing the thickness of thin wall, adjusting the position and size of gate, and taking shrinkage prevention measures at the root of rib or column. For those that cannot meet the requirements, gas assisted injection molding can be considered

warping deformation is relatively easy to occur on flat parts, long conditions and box parts, which is mainly caused by the residual internal stress inside the plastic parts. The causes of warping deformation are complex, mainly including the orientation difference of polymer chains in plastic, the uneven volume shrinkage in flow direction and vertical direction, and the bending stress caused by uneven cooling of parts. Through the warpage analysis of injection CAE software, the deformation trend and the proportion of various factors can be predicted, so as to take corresponding measures. However, because the factors leading to warping deformation are very complex and sensitive, it is difficult to accurately predict the size of deformation quantitatively, and can only qualitatively predict the trend and relative amount of warping deformation, so as to provide reference for taking corresponding measures

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