Application of the most fiery gas assisted injecti

2022-10-20
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Application of gas assisted injection molding CAE in the design of automobile bumper mold

Abstract: using CAE technology, the structure design and molding process conditions of automobile bumper mold are simulated and analyzed, and the bumper mold structure that meets the actual production needs is successfully designed; The gas filling molding process and filling effect were optimized, the surface quality and mechanical properties of the products were improved, and the success rate of the first trial was increased

key words: gas assisted injection molding; CAE; Optimized design; Automobile bumper

in order to solve the molding difficulties and narrow process range caused by injection molding due to its large size, although China's polyurethane industry has a considerable range of problems, large automobile molds often adopt the design form of increasing the number of hot runner and gate [1]. Results the mold cavity filling was difficult to balance, and the number of weld lines increased, which seriously affected the appearance quality and mechanical properties of the products. As an innovative injection molding process, gas assisted injection molding breaks through the limitations of traditional injection molding and is gradually applied to a variety of plastic products [2]. It is of great practical significance to apply gas assisted injection molding technology to the design process of large automobile molds and use CAE technology to simulate and analyze the gas assisted molding process in the structural design stage. Taking the structural design of gas assisted injection mold for automobile bumper as an example, this paper deeply discusses the application of CAE Technology in the design of gas assisted injection mold

1 CAE simulation analysis conditions for gas assisted injection molding

1.1 raw materials for analysis

the injection molding raw materials used for analysis are pp/epdm produced by DSM company, and the main molding parameters are shown in Table 1

1.2 injection molding machine for analysis

see Table 2 for the main parameters of the injection molding machine used for analysis

2 CAE simulation analysis process of gas assisted injection molding

2.1 introduction to analysis

plastic filling morphology depends on the form of mold gating system, such as gate, runner size, gate position, etc; The design of the air passage includes the intake form, the position of the intake point, the distribution of the air passage and the size of the air passage. There are two types of air intake commonly used in bumpers, one is from the mold cavity, and the other is from the inlet of the main flow channel. This paper adopts the form of air intake from the cavity. The gas mainly passes through the larger part of the local wall thickness of the product, so this part must be equivalent to an airway in the modeling process, and the shape factor must be set; The automobile bumper mold generally adopts the short shot or full shot gas assisted molding process. The key to a good gas assisted molding process is to deal with the relationship between several factors, which are inlet time, injection time and inlet pressure

the analysis of this set of automobile bumper mold started from these three elements, and successively adjusted the gate position, gate number and the setting of gas assisted molding process, and finally achieved good results. This set of automobile bumper parts belongs to thin-walled narrow and long parts, with a wall thickness of 1.2 ~ 2mm and a total length of about 1200mm. The lead screw and nut are used as performing elements

2.2 analysis of the original scheme

Figure 1 shows the original design model. As shown in Figure 1, parts are fed at three points (a, B, c); The runner is a hot runner with a diameter of 12mm; The gate is a side gate with a width of 8mm and a length of 2mm. The wall thickness at the edge of the workpiece is large, so it can be used as an airway. In the modeling process, it is equivalent to a one-dimensional cylinder, with a diameter of 7.2mm and a shape factor of 1.13. D is the air inlet point. The analysis conditions are shown in Table 3

Figure 2 shows the gas hollowing rate of the original scheme. It can be seen from Figure 2 that there is uneven gas seepage near the airway; And part of the gas enters the hot runner through Gate C, making it difficult to adjust the molding process. The reasons for the above defects may be as follows: first, three gates cause uneven filling, which affects gas penetration; Second, the pressure is too high and the delay time is too short; Third, the inlet point is too close to the gate

Figure 3 shows the weld line analysis of the original scheme. It can be seen from Figure 3 that there are a large number of welding lines with large size on the surface of the product, which greatly affects the surface quality and mechanical properties of the product

2.3 analysis of optimization scheme

the following adjustments are made according to the problems found in the analysis of the original scheme: the number of gates is reduced from the original 3 to 1; Reduce the maximum air pressure to 25MPa and increase the delay time; Design the feeding point to the opposite side of the air inlet point. The analysis conditions are shown in Table 4. Figure 4 shows the gas tunneling rate. It can be seen from Figure 4 that the gas penetrates the airway evenly, the seepage area is small, and no gas enters the hot runner

Figure 5 shows the change curve of gas assisted process analyzed by the optimization scheme. It can be seen from Figure 5 that the pressure at the inlet of the main runner is only 29.11mpa, so the product is easy to form. The delay time of air assisted intake is 0.9 ~ 1.1s

the optimization analysis of the original scheme makes the gas filling more uniform, reduces the number of weld lines, improves the apparent quality of the workpiece, improves the mechanical properties of the workpiece, reduces the cost of the mold, and optimizes the forming process

3 conclusion

1) taking the automobile bumper mold as an example, the gas assisted injection molding technology is applied in the mold design; At the same time, gas assisted CAE simulation technology is supplemented in the design process to simulate and optimize the forming of the design scheme, which greatly improves the quality of products, saves mold design and manufacturing costs, and optimizes the forming process conditions. Therefore, it has very important practical significance

2) the best design scheme of this set of automobile bumper mold is: adopt a hot runner and feed from the middle of the product at a single point; The thicker part of the edge of the product can be used as the air passage, and the rest of the air passage design does not need to be added. The air can be introduced from the middle part of the product in the form of cavity

3) gas assisted injection molding process of bumper mold: molding temperature 225 ℃; The maximum air pressure is 25MPa. The delay time of air assisted intake is 9 ~ 11S

references

1 Li Wei, Li Rongxun, China plastics, 2001, 15 (1):48

2 Shen Changyu plastic mold computer aided engineering Henan: Henan science and Technology Press

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