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Research on Lightweight Injection Molding (CAE) and Numerical Simulation Calculate of New Energy Vehicle

Pubblicato online: 15 Jul 2022
Volume & Edizione: AHEAD OF PRINT
Pagine: -
Ricevuto: 13 Feb 2022
Accettato: 10 Apr 2022
Dettagli della rivista
License
Formato
Rivista
eISSN
2444-8656
Prima pubblicazione
01 Jan 2016
Frequenza di pubblicazione
2 volte all'anno
Lingue
Inglese
Introduction

The rapid development of the new energy industry reflects the importance of green and low-carbon transportation. However, short battery life and limited range limit its development. For new-energy vehicles, weight loss means more mileage. Research shows that when the total vehicle weight of a pure electric vehicle decreases by 10KG, the range can increase by 5%–6%. The lightweight of the automobile becomes the direction that more automobile manufacturers pay attention to. The technology of plastic instead of steel is one of the important means of vehicle lightweight. The weight of the automobile can be greatly reduced by replacing the original steel parts with plastics under the condition that the service performance of the product is invariable. The proportion of plastic parts in the whole car parts is increasing, including the whole car interior and exterior trim parts and even functional parts and structural parts.

An important role in improving the quality of plastic parts. However, many times of traditional model tests, not only will reduce the production efficiency, but also lack of scientific basis. With the emergence of injection molding CAE technology and CAE simulation of the molding process, the influence of processing conditions, molding conditions, mold design, and runner design was analyzed and predicted, thus, the possible defects in the molding process can be simulated. It is of great significance to obtain high-quality plastic products.

In this paper, the new energy automobile front-end frame of a factory is studied, and the traditional sheet metal is replaced by polypropylene plastic. Then the mechanical performance is proved by hyper mesh, and the injection molding process is simulated by Moldflow. In this paper, through the design of the orthogonal test, selection of test factors and evaluation indicators, the simulation results of variance analysis, and range analysis to find out the impact of test factors on the experimental objectives, to reduce the defects of the optimal parameter combination.

Structural design of automobile front-end frame
Establishment of model and mesh generation

According to the requirements of manufacturers, the automobile front-end frame is modeled by UG software. The original sheet metal quality is 10.5 kg, if plastic instead of steel for polypropylene PPLGF30, the quality is 6.8 kg, weight loss of 3.7 kg. Its structure must meet certain mechanical performance before production, and mechanical analysis is done in the hyper mesh. Therefore, we need to carry out a finite element analysis. The original data model is imported into Hyper Mesh to preprocess the 3D model, and the Mesh is divided. Then we apply a load to add a rigid connection element Reb 2 near the force point frame engine lock grid. As shown in Figure 1, using the mid-level technique, the mid-level is automatically extracted and manually repaired. It uses 5mm as the edge length of the global grid to divide the product grid and automatically sets the thickness as shown in Figure 2.

Figure 1

Added location of Reb2

Figure 2

Thickness setting results

Analysis of mechanical properties

The Opti struct solver in the hyper mesh is used to analyze the six main stress points of the front-end frame. They are, respectively, the limit tension of the latch, the cushioning impact, the pedestrian impact, the condenser support strength, the radiator support strength, and the oil cooler support strength. The results of the static analysis are shown in Table 1.

Information table of statics analysis

Load Size/(N) Mounting point displacement/mm Maximum stress / (Mpa) Design requirements/(mm) Whether it meets the design requirements
Lock limit pull 5200 15 139 15 Yes
Cushion impact 1000 0.8 20 4 No
Pedestrian impact 4900 15 208 20 Yes
Condenser support strength 390 0.6 6.8 3 No
Radiator support strength 360 0.6 5.6 3 Yes
Oil cooler installation strength 180 0.3 3.6 2 Yes

The speed of a car on the road is not always the same. As a result, the force on the engine lock changes alternately. To prevent fatigue failure under alternating stress, we also need to carry on the fatigue analysis to the plastic part. According to the data provided by the manufacturer, the stress sub-value is 1000N, using N-code solver in hyper mesh, the total time of load spectrum is set to 200s, the sampling frequency is 1000, and the material is PP-LGF30. Then get front-end frame damage cloud figure 3 and Life Cloud Figure 4. Both figures show that the longitudinal beam mounting hole and the engine latch mounting hole are the most vulnerable parts. Moreover, the life in 6122s, which is much longer than the required 1200s. Therefore, the front-end frame material itself meets the design requirements and meets the requirements. No modification of the material is required.

Figure 3

Damage cloud chart

Figure 4

Lifespan cloud diagram

Establishment of injection molding system
Grid division

To reduce the mesh quantity and improve the mesh quality, we first triangulate the mesh in Hyper mesh, whose size is 15mm. And then import it into Moldflow. To guarantee the quality of the grid and the accuracy of die flow analysis, the aspect ratio should be modified. The maximum aspect ratio was 6.79, and the average aspect ratio was 1.78. It meets the analysis requirements, the matching percentage value of the mesh partition is 90%, the partition result is as shown in Figure 5.

Figure 5

Grid model

Design of the gating system

To reduce pressure and heat loss and control costs, we choose to use a hot runner in the main channel. In this paper, the gating system combined with customer requirements, the use of balanced runner. We choose to use “Point gate” at the gate. There are eight of them, and they each have three gates on the top beam. We set them symmetrically at the engine lock and set one gate on each side of the beam. The lower beam is provided with three gates, and the positions of gates and runner are arranged as shown in Figure 6.

Figure 6

Gate and runner position

Preliminary simulation of the forming scheme

The front-end frame is made of SABIC Innovative Plastics US, LLC. As requested by the manufacturer. PP-LGF30, aka polypropylene. Its advantages are low density, lightweight, high crystallinity, regular structure, and excellent mechanical properties. It is suitable for making mechanical parts and corrosion-resistant parts. In combination with Moldflow software, the recommended processing parameters for this material are mold temperature 70 °C ∼ 90 °C, melt temperature 200 °C ∼ 360 °C, holding pressure 40 ∼ 44Mpa, injection time 2s ∼ 4s, holding time 40S ∼ 60s respectively. The forming window analysis determined that the initial forming process parameters were mold temperature 70 °C, melt temperature 200 °C, holding pressure 40 Mpa, injection time 2 s, holding time 40 s, as shown in Table 2.

Preliminary molding process parameters

Mold temperature (°C) Melt temperature (°C) Holding pressure (Mpa) Injection time (s) compress time (s)
70 200 40 2 40

After cooling, filling, compression, and warpage analysis, it is found that the main defect is warpage. From Fig. 7, it can be concluded that the maximum warpage is 1.023 mm, and the warpage is controlled to 0.5–0.8 mm according to the requirement of the enterprise.

Figure 7

Warpage deformation

Optimization of process parameters

The standardized orthogonal test table can not only reduce the number of blind tests but also make the factors be more comprehensive tests in fewer test times. Through the data processing, we can also find out the influence degree of each test factor on the test index.

Orthogonal test factors

According to the above analysis, this paper takes y 2 warpage as the optimization target, and marks it as a, B, C, D, E with mold temperature, melt temperature, holding pressure, injection time, and holding time as the experimental factors. For each process parameter, a test range is selected based on previous experience as shown in table 3. Based on the number of test factors and levels, 25 sets of orthogonal tables with 5 Factor 5 levels are used as shown in table 4. Based on the number of test factors and levels, using 25 sets of orthogonal tables with 5 factors and 5 levels, the different process parameters and their corresponding plastic warpage values are as shown in table 4: RA = 0.080, RB = 0.208, RC = 0.096, RD = 0.198, Re = 0.163, it can be seen that the factors that influence the amount of warpage are the melt temperature B > the injection time d > The holding time e > the holding pressure c > the die temperature a, that is, the melt temperature has the greatest influence on the amount of warpage, die temperature has the least effect on warpage.

Factor range table

Horizontal range A Mold temperature (°C) B Melt temperature (°C) C Holding pressure (Mpa) D Injection time (s) E compress time (s)
1 70 200 40 2.0 40
2 75 240 41 2.5 45
3 80 280 42 3.0 50
4 85 320 43 3.5 55
5 90 360 44 4.0 60

Orthogonal test table and test results

N0. A B C D E Y2/mm
1 1 1 1 1 1 0.812
2 1 2 2 2 2 1.201
3 1 3 3 3 3 0.794
4 1 4 4 4 4 1.221
5 1 5 5 5 5 0.964
6 2 1 2 3 4 1.102
7 2 2 3 4 5 0.881
8 2 3 4 5 1 1.093
9 2 4 5 1 2 0.812
10 2 5 1 2 3 1.048
11 3 1 3 5 2 0.870
12 3 2 4 1 3 0.939
13 3 3 5 2 4 0.989
14 3 4 1 3 5 1.102
15 3 5 2 4 1 0.712
16 4 1 4 2 5 0.904
17 4 2 5 3 1 0.971
18 4 3 1 4 2 0.632
19 4 4 2 5 3 1.102
20 4 5 3 1 4 0.924
21 5 1 5 4 3 0.791
22 5 2 1 5 4 0.888
23 5 3 2 1 5 0.901
24 5 4 3 2 1 1.211
25 5 5 4 3 2 0.801
k1 0.962 0.896 0.897 0.960 0.917
k2 0.987 0.940 0.968 0.827 1.002
k3 0.922 0.882 0.936 0.935 0.839
k4 0.907 1.090 0.992 1.025 1.002
k5 0.918 0.890 0.905 0.950 0.970
R 0.080 0.208 0.096 0.198 0.163

The effect of each factor level on the warpage is shown in Figure 8. The value of the ordinate represents the warpage under different factors. With the increase of the horizontal value of the die temperature, the warpage of the product decreases at first and then increases and reaches the lowest value at A4. The melt temperature and holding pressure increase with the horizontal value, the amount of warpage first increased, then decreased, then increased, then decreased, and reached the lowest value at B3 and C1. With the increase of injection time, the amount of warpage first increased and then decreased, then the trend increased and reached the minimum value at d4, and the warpage deformation decreased first, then increased and finally decreased as the holding time increased with the level value and reached the minimum value at E2. The optimum parameters are A4B3C1D2E4, the die temperature a level 4(85 °C), melt temperature B level 3(280 °C), holding pressure C Level 1(40 MPA), injection time D Level 4(3.5 s), and holding pressure time E level 2(45 s), as the combination is in group 18 of the orthogonal test table, Moldflow carries out die flow analysis and the result is shown in Fig. 9. The warp deformation is 0.632 mm.

Figure 8

The influence of various factors on the mean value of warpage deformation trend graph

Figure 9

Warpage deformation

Analysis of variance

The analysis of variance can correctly reflect the degree of influence of each test factor on the target and distinguish whether the difference in test results corresponding to each level of a certain factor is caused by a change in a certain level. As shown in Table 5, the melt temperature F value is 6.565, the melt temperature is a significant factor affecting the warpage deformation of the product, and the mold temperature has the least influence. The degree of influence of each test factor on the warpage deformation from high to low is melt Temperature B>Injection time D>Holding time E>Holding pressure C>Mold temperature A, that is, the melt temperature has the greatest influence on the warpage deformation, and the mold temperature has the least influence on the warpage deformation. This conclusion is consistent with the results of the range analysis.

Analysis of variance of warpage deformation

factor Deviation sum of squares Degree of freedom Mean square error variance F Compare F (a=0.05) Critical value
A 0.023 4 0.03656 0.009141 1.000 6.390
B 0.151 4 0.15660 0.039149 6.565 6.390
C 0.033 4 0.04802 0.012005 1.435 6.390
D 0.117 4 0.15693 0.039233 5.087 6.390
E 0.102 4 0.06699 0.016748 4.435 6.390
error 0.02 4 0.12869 0.032171
total 0.59379 24
Production verification

We install the mold on the injection machine and set the best injection process parameters combination of A4B3C1D4E2 corresponding value, after confirmation, injection molding production. Fig. 10 is a sample from the trial mold. The sample has no obvious appearance defect, and the warpage deformation is within the tolerance. It meets production requirements.

Figure 10

The actual production mold

Conclusion

In this paper, the automobile front-end frame is taken as the research object, the whole plastic front-end frame is designed with Hyper mesh software, and the mechanical performance is verified.

The results of Moldflow were analyzed by the method of orthogonal test, the optimal configuration of injection molding process parameters, and the influence of each factor on the warp deformation of evaluation index under the test conditions are as follows: melt temperature B > injection time D > holding time E > holding pressure C > Die temperature A.

CAE analysis of optimized configuration process parameter combination A4B3C1D4E2. We compared the optimized analysis results with the analysis results of the system's recommended process parameters, and the simulation results showed that the warpage was 0.632 mm. It is 38% less than the initial warpage (1.023 mm). It achieves the optimization goal.

Put into actual production. In the premise of satisfying mechanical properties, plastic instead of steel, to achieve a lightweight design. It provides correct theoretical guidance for setting the actual injection molding process parameters. The weight of the automobile can be greatly reduced by replacing the original steel parts with plastics under the condition that the service performance of the product is invariable.

Figure 1

Added location of Reb2
Added location of Reb2

Figure 2

Thickness setting results
Thickness setting results

Figure 3

Damage cloud chart
Damage cloud chart

Figure 4

Lifespan cloud diagram
Lifespan cloud diagram

Figure 5

Grid model
Grid model

Figure 6

Gate and runner position
Gate and runner position

Figure 7

Warpage deformation
Warpage deformation

Figure 8

The influence of various factors on the mean value of warpage deformation trend graph
The influence of various factors on the mean value of warpage deformation trend graph

Figure 9

Warpage deformation
Warpage deformation

Figure 10

The actual production mold
The actual production mold

Factor range table

Horizontal range A Mold temperature (°C) B Melt temperature (°C) C Holding pressure (Mpa) D Injection time (s) E compress time (s)
1 70 200 40 2.0 40
2 75 240 41 2.5 45
3 80 280 42 3.0 50
4 85 320 43 3.5 55
5 90 360 44 4.0 60

Analysis of variance of warpage deformation

factor Deviation sum of squares Degree of freedom Mean square error variance F Compare F (a=0.05) Critical value
A 0.023 4 0.03656 0.009141 1.000 6.390
B 0.151 4 0.15660 0.039149 6.565 6.390
C 0.033 4 0.04802 0.012005 1.435 6.390
D 0.117 4 0.15693 0.039233 5.087 6.390
E 0.102 4 0.06699 0.016748 4.435 6.390
error 0.02 4 0.12869 0.032171
total 0.59379 24

Preliminary molding process parameters

Mold temperature (°C) Melt temperature (°C) Holding pressure (Mpa) Injection time (s) compress time (s)
70 200 40 2 40

Information table of statics analysis

Load Size/(N) Mounting point displacement/mm Maximum stress / (Mpa) Design requirements/(mm) Whether it meets the design requirements
Lock limit pull 5200 15 139 15 Yes
Cushion impact 1000 0.8 20 4 No
Pedestrian impact 4900 15 208 20 Yes
Condenser support strength 390 0.6 6.8 3 No
Radiator support strength 360 0.6 5.6 3 Yes
Oil cooler installation strength 180 0.3 3.6 2 Yes

Orthogonal test table and test results

N0. A B C D E Y2/mm
1 1 1 1 1 1 0.812
2 1 2 2 2 2 1.201
3 1 3 3 3 3 0.794
4 1 4 4 4 4 1.221
5 1 5 5 5 5 0.964
6 2 1 2 3 4 1.102
7 2 2 3 4 5 0.881
8 2 3 4 5 1 1.093
9 2 4 5 1 2 0.812
10 2 5 1 2 3 1.048
11 3 1 3 5 2 0.870
12 3 2 4 1 3 0.939
13 3 3 5 2 4 0.989
14 3 4 1 3 5 1.102
15 3 5 2 4 1 0.712
16 4 1 4 2 5 0.904
17 4 2 5 3 1 0.971
18 4 3 1 4 2 0.632
19 4 4 2 5 3 1.102
20 4 5 3 1 4 0.924
21 5 1 5 4 3 0.791
22 5 2 1 5 4 0.888
23 5 3 2 1 5 0.901
24 5 4 3 2 1 1.211
25 5 5 4 3 2 0.801
k1 0.962 0.896 0.897 0.960 0.917
k2 0.987 0.940 0.968 0.827 1.002
k3 0.922 0.882 0.936 0.935 0.839
k4 0.907 1.090 0.992 1.025 1.002
k5 0.918 0.890 0.905 0.950 0.970
R 0.080 0.208 0.096 0.198 0.163

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