Optimization of Automobile Body Structure Based on Topology Method

Topology is an important branch of mathematics, which mainly studies the related characteristics that geometric figures can remain unchanged when they change shape continuously, that is, the invariance and invariance of topological space under topological transformation. Optimization is a 1 branch of applied mathematics, and it is a 1 method to select the scheme to achieve the optimal goal under certain constraints. It has been widely used in many fields such as engineering design and project management. At present, Japanese automobile researchers are perfectly combining topology method, optimization and computer aided engineering (CAE) and successfully applying them to the optimization process of engine cylinder block and control arm under suspension. This paper introduces the basic principle and optimization results of applying topological method to optimize automobile parts, and gives an example of applying topological optimization analysis program to optimize spot welding position and blank holder position.

0? order

Due to the need of environmental protection and improving fuel consumption, major car companies are rapidly promoting the lightweight of car bodies. In order to realize light weight, high strength steel plate is the first choice for automobile white body. With the application of high-strength steel plate, the thickness of the plate decreases correspondingly, and the stiffness of the whole car body also decreases. As a related countermeasure, it is very important to use the lightest material to make up for the reduced stiffness. At present, it can be improved by topology optimization. Topology optimization method is to keep the necessary units under the premise of giving a certain design space. Through topology optimization design, complex and unique shapes can be applied to parts. At present, this method has been applied to the optimization of engine cylinder block and control arm under suspension. For the car body composed of thin plates, it is difficult to design a specific part shape by topology optimization method because the unit size and calculation load must be considered emphatically in the process of topology optimization, and the unit size cannot be excessively reduced. Based on the preliminary design guide, the researchers realized the topology optimization of thin shell elements for the sensitive parts of the current car body structure.

In this paper, the design space composed of solid elements is introduced into the automobile body structure composed of thin shell elements, and the shape of parts is improved by topological optimization method. In addition, the application of topology optimization analysis program in spot welding and an example of gluing position optimization process are also introduced.

1? Shape optimization of parts based on BIW static stiffness

1. 1? Analysis

Figure 1 shows the vehicle model used in the optimization process of BIW. The whole vehicle model is published by NCAC, and the body is composed of thin shell units. Fig. 2 shows four constraints of the vehicle body carrying load. Restraining the front suspension mount and the rear coil spring mount * * * accounts for three of the four conditions, and the remaining 1 load condition is loading above the vehicle 1. 000? n？ Load. At the same time, the researchers set four conditions to change the load position, and verified the rationality of the spatial design method of the body composed of thin shell units by using the body-in-white shown in figure 1. The target part is set as the joint part of the side beam and the cross beam that constitute the rear floor in the sensitivity analysis. Fig. 3 shows the optimized target component. In the process of introducing the design space, the researchers removed the end parts of the transverse members, thus arranging the design space composed of solid units. Considering the load transfer requirements, the design space composed of solid units is connected with the ends of the cross beam, rear side beam and floor composed of thin shell units. The objective condition of optimization is to minimize the sum of ride comfort under the four load conditions shown in Figure 2. Constraints should also consider the shape of parts generated by thin plates in the design space, and set its volume percentage to 20%. In addition, researchers make full use of the reserved results based on topology optimization method to optimize the shape of parts and ensure their stiffness.

1.2? Optimization result

Fig. 4 shows the rest of the car body after topology optimization. The reserved part is composed of the rear side beam and the cross beam, which mainly reserves the floor side plane of the design space. It is generally believed that the load should be transferred from the loading point to the floor through side beams and cross beams.

1.3? Shape research based on optimization results

Fig. 5 shows the shape comparison between the new part and the original part generated by the topology-based optimization method. The optimized parts, like the original parts, are connected with side beams, cross beams and floors by spot welding. On the basis of the original parts, the torsional stiffness of the optimized parts is increased by about 4.3%, and the mass is increased by 0. 1kg. In general, it is difficult to improve the torsional stiffness of the car body. From the point of view of quality efficiency, researchers believe that torsional stiffness can be optimized by this method (that is, the stiffness of parts can be strengthened at the expense of minimum mass increase).

Fig. 6 shows the effect of part optimization by comparing the distribution of strain energy. In this optimization example, the sum of ride comfort of components can be minimized. In the original part, the edge of the cross member and the corner position of the floor have produced great strain energy. Therefore, it is proved that the strain energy of the edge line and corner position of the transverse member is greatly reduced after optimization.

2? Shape Optimization of Eigenvalue Parts of Body in White

2. 1? Analysis

Fig. 7 shows the state of bending deformation of the front part of the vehicle body obtained by eigenvalue analysis of computer aided engineering (CAE). As the object of this study, the forward bending mode which only moves in the width direction of the car body is selected. The total length of the car body is 4? 178? Mm, its deformation is expressed by 25 times. As can be seen from Figure 7, the car body will only face the state of forward bending. Judging from the eigenvalue of this bending mode, the original body bending eigenvalue is 3 1? Hz, the characteristic value of body forward bending with better handling safety will be 40? Above Hz, therefore, researchers will exceed 40? The research is aimed at the higher value of Hz.

For the body-in-white shown in figure 1, the space design method is introduced into the body composed of thin shell units, and the optimization model is established. The target part of the optimization process is set from the radiator bracket to the front of the upper part of the engine in the front bending area. Fig. 8(a) shows the state of the original vehicle body; Fig. 8(b) shows the state after the parts are detached from the original car body; Fig. 8(c) shows the state after the design space composed of solid units is introduced into the vehicle model. For the car body with the radiator fixing frame and fender bracket removed and the front member retained, the design space composed of solid units is configured. In addition, considering the load transfer requirements, the design space is connected with the car body, the optimization target conditions are set to maximize the front bending eigenvalue, and the volume percentage of the front bending eigenvalue is set below 20%. As a performance verification, models with different cross-section shapes are generated by using the results retained after topology optimization, and their shapes and plate thickness are adjusted at the same time, thus verifying the eigenvalues. In addition, as a technical comparison, the tower-shaped support rod used to fix the bumper is verified, and taking the parts designed based on sensitivity analysis as the optimization goal, it is verified that the characteristic value is improved by increasing the plate thickness.

2.2? Optimization result

Fig. 9 shows the state after topology optimization using the car body model. The result of retaining the features is that the front part presents an X-shape. Firstly, the radiator fixing frame is contracted once, then connected with the left and right mounting parts of the bumper, and then contracted again at the lower part of the car body, so as to obtain the predetermined state result. It can be seen from the results that in order to improve the characteristic value of front bending, the scheme of supporting the front suspension and bumper through connectors is effective.

2.3? Research on Part Shape Based on Optimization Process

The optimized parts are assembled on the car body. As a comparison with the optimized parts, tower-shaped support rods connecting the left and right suspensions are adopted. Figure 10 shows the parts with increased thickness after sensitivity analysis. The thickness of these parts is also set according to 1.2 times, 1.4 times and 2.0 times respectively, and the eigenvalue analysis is carried out. The figure 1 1 also shows the forward bending characteristic values of the parts after using the tower-shaped support bar, increasing the plate thickness and optimizing the shape. After optimization, the forward bending characteristic value of the part is 55? Hz, this value is greatly improved. The characteristic value of tower-shaped support rod is increased by 0.2? Hz, for the forward bending part, the increase of eigenvalue can not play a significant role. In addition, even if only the thickness of the high-sensitivity part is increased, for example, by 25? For example, Kg, the eigenvalue can only be increased to 35? Hz, its effect is incomparable in the optimization process.

3? Optimization of spot welding position of white body spot welding

3. 1? Analysis

Figure 12 is the schematic diagram of spot welding optimization program. The figure simulates the flange part of the part, press 20? Hmm? Example of adding welding points through interval setting. Original welding point 40? Hmm? Spacing arrangement, after optimization, according to the minimum of 20? Hmm? This spacing is set as the target welding point of the optimization process. According to the topology optimization method, only the welding points that have a great effect on improving stiffness are reserved.

On the vehicle model, according to 10? Um, 20? Well, 30 years old? Hmm? Adjust the minimum solder joint spacing respectively to study its influence on stiffness. The vehicle model adopts the car body shown in Figure 1, the load condition adopts the torsional stiffness load constraint condition shown in Figure 2, and the welding point is described by solid elements. Compared with the original setting of 3 on the car body? 906 solder joint, press at least 20? Hmm? Solder joint spacing; Set the optimization target number of welding points to 3? 168; Press the lowest 10? Hmm? The optimized target number of welding points is set to 10? 932; Press the lowest 30? Hmm? Set the optimization target number of solder joints to 1? 679. Set the above welding points as the target conditions in the subsequent topology optimization process, so as to minimize the sum of the ride comfort of the four load conditions and make them the constraint conditions with the maximum stiffness, thus retaining the ratio of the number of welding points to the number of optimized welding points. The number of solder joints retained after optimization is set to 200, 400 and 600 respectively according to the minimum solder joint spacing. In addition, the reserved results based on the topology optimization process are used to generate the vehicle model, and its stiffness is verified by CAE.

In addition, other welding points are added near the welding point with high strain characteristics, and the results are compared with the optimized results. Fig. 13 is a schematic diagram of welding points supplemented by traditional methods. The method adopted is that the distance between the two sides of the welding point with large strain energy is 20? Hmm? Two welding points have been added at the position of. According to the sum of strain energy, the welding points under the above four load conditions are sorted, and the target number of welding points is set to 100. On both sides of 100 target welding point, press a minimum of 20? Hmm? The distance between joints has increased by 200 welding points.

3.2? Optimal analysis results of solder joint position

Figure 14 shows the remaining solder joints after topology optimization under the condition of minimum solder joint spacing of the whole vehicle model. This is the result of adding 200 solder joints under various solder joint spacing conditions. The reserved welding points are mainly distributed in the rear cross member (rear cross member), the upper and lower parts of the B-pillar of the car body, and A? Perimeter of shock absorber column and tower support. In addition, when the solder joint spacing is small, it can be seen that the reserved solder joints are densely distributed; When the solder joint spacing is large, it can be seen that the reserved solder joints are scattered.

Figure 15 shows the effect of using topology optimization process to supplement welding points to improve car body stiffness. In the case of all minimum solder joint spacing (solder joint spacing is divided into 10? Um, 20? Well, 30 years old? Mm), with the continuous supplement of welding points, the stiffness is improved. But when the solder joint spacing is 30? Hmm? With the increase of welding points, the effect of stiffness improvement gradually tends to saturation. In addition, under the condition of the same supplementary solder joints, the smaller the solder joint spacing, the more obvious the effect of stiffness improvement. This phenomenon is due to 10? Hmm? The distance between solder joints is small, which is beneficial to improve the stiffness of solder joints. Solder joint spacing 30? Hmm? However, due to the limitation of solder joint spacing, it is usually impossible to directly improve the stiffness of components.

Figure 16 shows the comparison of the traditional method and the topology optimization method after adding 200 welding points respectively. The solder joints supplemented by the traditional method are concentrated in the upper and lower parts of the rear cross member and B-pillar, while the solder joints supplemented by the topology optimization method are basically distributed in the whole body. Figure 17 shows the effect of improving stiffness by using traditional methods and topology optimization methods to supplement spot welds. The stiffness improvement effect of topological method is 3 times higher than that of traditional method. It can be considered that the position of subsequent solder joints was determined by traditional methods in the early stage, but it could not adapt to the strain state in the process of repairing solder joints. On the other hand, in the application of topological method, it is considered that the position of supplementary welding points has been optimized in order to maximize the stiffness when 200 welding points are supplemented.

4? Optimization of gluing position of body-in-white structure

4. 1? Analysis

Regarding the optimization of gluing position, the figure 1 BIW model is adopted, and the load condition is the same as the optimization process of solder joint position. In the whole vehicle model, according to the gluing state of flange surface, the retention force is adjusted by topological optimization method, and its influence on stiffness is studied. The adhesive is usually set as a solid unit, and the total length of the coating is set to 103? m？ Structural adhesives. Because the front and rear bumper parts, the roof, the sub-frame and other parts are not the main application parts of the adhesive, they are usually not within the research target.

In order to minimize the sum of ride comfort under four load conditions, the researchers set the location where the adhesive is applied as the target condition in the process of topology optimization. In order to maximize the stiffness, the ratio parameter of the amount of adhesive retained/the amount of adhesive to be optimized is used as the constraint condition. After the optimization process, the binder retention ratio was set to 80%, 60%, 40% and 20% * * * respectively. In addition, using the reserved results based on topology optimization process, the whole vehicle model is built, the coating length of adhesive in the flange length direction is measured, and the stiffness is verified. According to the characteristics of the binder, the elastic modulus used in the research process is 3.0? GPa, Poisson's ratio 0.45, specific gravity 1.0, and its stiffness is verified by CAE.

Researchers use CAE to accurately build structural models. However, in the case of using adhesive, the process is highly dependent on manual operation, so it consumes more man-hours. Therefore, aiming at the optimization process of solder joint position, the method of improving stiffness by adjusting the gluing position is emphatically studied. Due to the automatic replenishment of welding points, the working hours can be reduced to less than 50%. Use the welding point optimization program shown in Figure 12, and the welding point optimization program and 10? Hmm? The welding points are separated, and the bonding unit is configured to form a state of near continuous bonding. In addition, it is required that the optimization process of bonding unit and adhesive should be consistent, and the original welding points should be retained. As for the whole vehicle model, compared with the original factory 3? 906 solder joints, the researchers set the optimization target number of solder joints as 10? 932. In order to minimize the sum of ride comfort under four load conditions, 3? 600 joints. Through the result of this reservation, the coating position of adhesive was studied.

4.2? Optimization analysis results of gluing position

Figure 18 shows the binder retention position after using the topology optimization method on the vehicle model. The main reserved painting positions are the rear cross member (rear cross member), the upper and lower parts of the B-pillar of the car body, and the A? Column, periphery of shock absorber tower bracket and front apron.

Using the optimization method based on solder joint position, in order to focus on the gluing position which is beneficial to improve the stiffness, the 600 solder joints added by topology optimization method are compared with the gluing position. Figure 19 shows the best position of these welding points after coating adhesive. The reserved welding points are mainly the rear cross member, the upper and lower parts of the B-pillar of the car body, and the A? Peripheral areas of columns and shock absorber tower supports. Compared with the position of adhesive residue, the distribution positions of the two are almost the same. For example, the front panel and the upper part of the rear panel of the car body are the parts with fewer reserved solder joints.

On the other hand, it is generally believed that adhesive can give full play to its role in areas with dense solder joints. Figure 20 shows that the spacing between welding points is less than 20? Hmm? Parts, and the solder joint spacing is greater than 20? Hmm? Suitable for parts coated with adhesive. Due to the application of this method, compared with the position with larger spacing in Figure 19, it also shows the retention result of discrete solder joints, which can be regarded as the application position of continuous adhesive (that is, the gluing position is clearly pointed out).

Fig. 2 1 gives an example of applying this method to mass production of automobile body. The body is a plug-in hybrid electric vehicle (PHEV) version. The rear door opening position, tailgate opening position and wheel cover opening position are optimized by topological method and coated with glue.

5? label

This paper introduces the application of topology optimization method in automobile body. For the body composed of thin plates, the design space and topology optimization method composed of solid units can be used to optimize the shape of parts and strengthen the optimal configuration of parts. This method can design high-quality parts in the field of automobile model with complex load transfer path. In addition, the topology optimization method also has a good effect on the optimization of solder joint position and gluing position. At the same time, the solder joint position and gluing position can be effectively optimized through the whole vehicle model. In the future, the application fields of topology optimization methods can be gradually expanded.

Note: This article was published in the third issue of Automobile and New Power magazine in 2020.

Author: [day]? Kento Takanobu et al.

Finishing: Peng Huimin

Editor: Worcester

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.